Vulcan and Hammer Leaders

Leaders is the generic term for the guide which allows the pile hammer to be positioned on top of the pile and then started to drive the pile to its desired head elevation. Although not a prominent part of Vulcan product line, the company did produce leaders of many kinds. This page is also intended to give an overview of pile hammer leaders in general.

Additional Sources:

Leaders can be broadly categorised in two ways: the method by which they interface with the hammer and the way by which they are connected to (and guided by) the crane.

Hammer Interface

Pile hammer leaders basically guide the hammer in one of two ways: from the side or from the back.

Vulcan hammers–in common with most American pile hammers–were guided from both sides of the hammer, with both hammer and pile between the guides. Leaders such as this are referred to as “U-type” leaders. Most of the Vulcan hammers shown on this site are riding in U-type leaders, both onshore and offshore.

Onshore-Leaders-Jul-73
Onshore, “U-type” leaders, at the West Palm Beach yard in July, 1973. The hammer (and driving accessory) rode between the two large pieces of square tubing at the bottom of the leaders. Structurally sound, the leader system suffered the disadvantages of a)bolted connections (most contractors preferred pinned ones for easy assembly and disassembly, and b) the protruding triangular gussets on the back caught the air hose.

European practice prefers to guide the hammer from the back. This is generally referred to as a “spud” type leader. The spuds have both a structure for stiffness and rails to interface with the hammer. These rails can be of several types, including round rails (Delmag, Nilens) or two channels back to back (Russian.)

 

 

Crane Interface

There are several methods of interfacing the leaders with the crane, depending upon the nature of the job and the preference of the contractor:

  • Swinging Leaders
  • Underhung Leaders
  • Fixed Leaders and Spotters
  • Offshore Leaders, Stub-Type Leaders or Flying Extensions

Swinging Leaders

The most common type of leaders, these are simply suspended from the crane (at some distance.) For most plumb pile applications, they are suitable.

 

 

Underhung Leaders

Underhung leaders are attached to the boom point, either rigidly or through a cable.  Underhung leaders at one time were popular, but have been largely displaced by fixed leaders.

 

 

Fixed (Extended) Leaders

Fixed leaders are connected to the crane at two points: the boom point, generally using a swivelling connector, and at the base of a crane using a spotter.  This setup allows the maximum manoeverability of the pile hammer, which is especially important for complex batter piles.  It is also generally more efficient in moving from one pile to the other.  The concepts and examples of the various features of fixed leaders are shown in the photographs below.

 

 

Stub (Offshore) Type Leaders

These leaders are a shortened version of swinging leaders. They are intended for use with a template, which both holds the pile in place and sets the batter angle of the pile as well. Virtually all of Vulcan hammers used offshore were run in these leaders.

Vulcan-560-Daelim-1991
A Vulcan 560 in Vulcan manufactured offshore leaders driving pile for the Korean contractor Daelim in 1991. Although Vulcan would have considered this an “onshore” job, it is a classic example of an offshore style hammer used to install a steel jacket. Note that the jacket is acting as the template, which in turn aligns and positions the piles. The leader and hammer assembly is lowered through the conical, adjustable stabbing bell and than the pile is threaded onto the pile cap, the assembly assuming the batter of the piles. The assembly is suspended from the hinged lifting bale at the top of the leaders. As the hammer drives the pile, the leaders are lowered to keep up with the hammer’s progress.
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Vulcan Expanding Mandrel, and Mandrel Driven Shell Piles

mandrelFrom a corporate standpoint, the Vulcan Expanding Mandrel (right) was one of its more forgettable products. But the application of mandrel-driven shell piles is an important one in deep foundations, as it represents, from a design standpoint, an interesting combination of driven and drilled piles.

Pile Shells and Mandrels

Driven piles can be divided into two types: low displacement piles (such as H-beams and to some extent open-ended pipe piles) and high displacement piles (wood piles, concrete piles and closed-ended pipe piles.) Which one you use depends upon the application and the geotechinical environment you’re working in.

Advocates of drilled piles, such as drilled shafts and auger-cast piles, note that, once you’ve drilled the hole into the ground (or while you’re drilling,) you can fill the hole with reinforcing steel and concrete and have a deep foundation. The main weakness to that approach is that, in many soils, the soil will either completely collapse into the hole or contaminate the concrete during the pour, thus compromising the integrity of the foundation.

Closed-ended pipe piles eliminate this by providing a barrier between the concrete (which the pile is filled with after driving) and the soil, both along the shaft and at the toe of the pile. They also provide whatever advantage there is in displacing the soil during driving. However, to prevent collapse during driving, a minimum wall thickness is required for driving which is beyond what is necessary for the structural integrity of the foundation.

closedendpipepile
Closed ended pipe piles, waiting to be driven.

So what if the wall thickness could be reduced, saving the expense of steel unnecessary to the foundation? The answer to that “what if” is mandrel-driven piles. By using a heavy mandrel which is inserted into the pile before installation and driving the mandrel, the impact force is transmitted along the pile shaft, thus reducing the driving stresses the pile experiences (as opposed to transmitted all of them through the pile head.) Getting a mandrel that can survive the rigours of driving has been one of the greatest challenges of driven piles.

The most elaborate system of shell piles (as opposed to regular pipe piles) and mandrels developed was the Raymond Step-Taper system, with its matched system of pile configurations and mandrel cores. This was used successfully for many years, but is a very specialised operation. (Another solution to driving Step-Taper Piles was a hammer which actually was inserted into the pile, as described in the Vulcanhammer.info Guide to Pile Driving Equipment.)

A more generic solution was to use corrugated steel pile, similar to the corrugated pipe used in storm water drainage. Thin walled, reasonably rugged in handing and economical, corrugated shell pile is probably the most common type of mandrel-driven pile in use. The shell is lifted into place in the leaders, the mandrel is inserted into the pile and locked into place, the mandrel and pile are driven into the ground, the mandrel is removed and the shell pile filled with concrete. To prevent soil from plugging the shell, a boot is frequently used at the pile toe. Shell piles can also be installed on a batter (as shown above,) something that drilled piles have serious difficulty with.

An interesting side note is that it is necessary in many cases to cut off portions of the shell for proper pile length. In Third World countries, the cut-offs find their way into use as culverts in poor sections where the authorities have not seen fit to provide proper drainage.

VIWI-Bulletin-90-Page-1More details on this can be found in Vulcan Bulletin 90, which you can download by clicking on the cover image to the right. This also shows a cross-section of Vulcan’s mandrel as well.

Vulcan Expanding Mandrel

Vulcan’s Expanding Mandrel was designed by Clemens Hoppe of Hercules Concrete Pile, patented under U.S. Patent 2,977,770, and licensed to Vulcan. It was produced in two sizes, 12″ and 14″, which corresponded to the two sizes of shells it was intended to mate with. The driving head at the top of the mandrel was configured to mate with either a Vulcan #1 or Vulcan #0 series of hammers.

The mandrel used a system of cams to expand the mating surface of the mandrel to the corrugations of the shell. A manual cam lever at the top of the mandrel is used to expand the mandrel once it has been inserted into the shell. Once the pile is driven, in theory the lever could be used to radially collapse the mandrel and permit its extraction from the driven shell.

“In theory” is important because the Vulcan mandrel, in common with just about every other mandrel in use, was prone to become jammed due to the impact of driving. This brings up one aspect of mandrel use that is well known amongst those who do it: mandrel driving is some of the most difficult driving a pile driver can experience (offshore pile driving is probably the most difficult of all.) To start with, the mandrel is by definition a “high impedance” transmitter of force, which means that it presents a high apparent resistance to the hammer.

Beyond that, when the mandrel jams, the most common method of freeing it up is a delightful procedure called “bumping out,” where a sling is wound around the mandrel head to a beam above the ram. The ram is sent upward to impact the beam; like a pile extractor, the sling transmits the upward impact to the mandrel head and (hopefully) loosens the mandrel to allow its extraction. Raymond superintendents were especially adept at this, which helped earn them a reputation as hard on the equipment. It also inspired Raymond to develop the full-length column rods and later cables to hold its hammers together, something which Vulcan belatedly adopted.

The Vulcan Expanding Mandrel, manufactured primarily at the West Palm Beach facility, was mildly successful, but never dominant in the shell pile market. Although Vulcan’s distribution system was part of the problem, the Vulcan mandrel lacked the durability of the more popular Rusché and Guild Mandrels (something that the latter’s inventor, Charlie Guild, wasn’t shy about reiterating!) Both Guild and Fred Rusché were serious Christians; perhaps their experience in the shell pile installation business was an impetus for that!

The 1970’s saw the end of the production of the Vulcan Expanding Mandrel.

Vulcanaire Supertherm, and the Airmizer Hammers

Energy conservation is an important consideration today in a world where the competition for energy sources is intensified by rising demand. But making best use of fuel isn’t new, and both the Vulcanaire Supertherm and the Airmizer hammers were Vulcan’s contribution to energy savings.

Both of these products were the original idea of Moses Hornstein, the owner of Horn Construction in Merrick, NY.  He was evidently focused on saving fuel and energy in the operation of his hammers.

Vulcanaire Supertherm

The Supertherm was first demonstrated in late 1964. The Supertherm was simple in concept. As described in the unit’s field service manual (which has more information on the unit:)

The installation of the VULCANAIRE SUPERTHERM is intended to raise the volume of air produced by compressor through the expansion of air by the use of heat. To achieve this; exhaust gases, which are normally wasted, are diverted through the use of a diverter valve and transferred through a heat exchanger through which also passes air from the receiver on the compressor. The temperature of the air is maintained within certain limits by the use of an automatic control device to produce the greater volume of air to be used on equipment at an elevated temperature.

The objective for the contractor was to use a smaller compressor to power the same size of pile hammer.

Supertherm-1200-Horn-Constr
Vulcanaire Supertherm mounted on top of a LeRoi 1200 CFM compressor at the time of its original demonstration.

Production of the unit was performed at the Special Products Division in West Palm Beach, as the Chattanooga facility lacked the fabrication capabilities necessary to produce the unit.

Supertherm-Gardner-Denver
A Supertherm (yellow) being installed on top of a Gardner-Denver compressor in the mid-1970’s.

Although the unit worked as intended and performed well, the simple concept didn’t translate into a simple design. With numerous parts and complex fabrication and assembly, the unit was uneconomical to produce and difficult to install. Air compressor manufacturers learned how to use hot exhaust gases in other ways to improve the energy efficiency of their products.

By the late 1970’s, even with the elevated energy prices of the era, production of the Vulcanaire Supertherm had gone cold.

Airmizer Hammer

Hornstein was not content with increasing the efficiency of his compressors: he and Vulcan commissioned the Austrian engineer John J. Kupka to develop the “Airmizer” hammers.  These were compound hammers similar to MKT’s “C” hammers, and used a similar cycle that James N. Warrington used with the California hammers.  Some photos of this hammer are shown below.

Expensive to build and complex in construction, the Airmizer hammers were less successful than the Supertherm, and the remaining inventory was scrapped in the late 1970’s.

Vulcan 106: the “Switch-Hitter”

Note: the field service manual for the 106 can be found in the vulcanhammer.info Guide Volume 1.

Bulletin-106-Cover
The cover for Bulletin 106 for the hammer of the same size designation.

Creating excitement in a “need-driven” type of equipment like pile driving equipment isn’t easy, especially one with as long of a history as Vulcan’s. Vulcan tried to do just that with the 106 hammer, a hammer which both technically and from a marketing standpoint came in with a great deal of promise but never quite lived up to it.

The introduction of the Vari-Cycle in the late 1960’s made it possible to change the energy of a Vulcan hammer without having to change the operating pressure.  Installing the Vari-Cycle in the #1 and #0 series hammers was problematic due to leader clearance issues, but another issue was that many specifications required a certain ram weight. Additionally, the desire was there to make some improvements to the design which, although successful, was certainly not perfect.

The result of this was the 106 hammer, the “Switch-Hitter,” complete with the baseball theme as shown in the literature cover at the right. Although it was certainly possible to change the ram in a #1 hammer to an 06, the idea here was to allow this to be done without disassembling the hammer.

106-Features
A diagram of the features of the 106 hammer.

Other than the removable weights, the biggest objective for this hammer was to remove the keys, which are the most persistent maintenance item on a Vulcan hammer.  That included the ram keys (the “Octo-Conic” system worked, but not the way it was designed,) the slide bar key, and the upper column keys, which were replaced with the column nuts.  The lower column keys were left on the hammer.  The 106 saw the introduction of the valve detent, designed to reduce valve flutter and the use of the ubiquitous door springs on the valve.

The 106 was introduced in 1971.  Vulcan was issued a patent on these innovations (U.S. Patent 3,566,977) but, as was all too often case with pile driving equipment, the innovations didn’t pan out as expected.

The biggest problem was in the removable weights.  Once installed, these would “belly out” and freeze in the space provided, and the “Switch-Hitter” would no longer switch.  So the central purpose of the hammer was defeated.

Beyond that, the column nut/key combination was soon to be overshadowed by the installation of tie cables on Vulcan hammers.  Already standard on Vulcan offshore hammers and Raymond hammers, the “cable through the column” arrangement was superior to the set-up on the 106.

The only innovation to be propagated from the 106 to the other hammers was the valve detent, which, although helpful, did not overcome thing such as hammer icing and the use of motor oil.

Proposed Hammers During the 1960’s and 1970’s

We look at the hammers that began the change in Vulcan’s product direction during the late 1920’s and early 1930’s, and we also document the “last hammers” of the 1990’s. Here we look at those hammers which were proposed during the 1960’s and 1970’s that were never built.

Vulcan’s “Last Hammers”

As we noted elsewhere, Vulcan was an innovator from the beginning of the air/steam line in the 1880’s until the end of the Illinois corporation and beyond. Unfortunately, from the mid-1990’s on, Vulcan was unable to take its ideas and put them into reality. An example of this is the Sea Water Hammer. But there were other projects in the works; below are just a few of them.

Vulcan 6250

6250
After the 5150’s were produced in the late 1970’s, Vulcan did not produce a new offshore hammer larger than 500 ft-kips for more than fifteen years. This was for a number of reasons that we discuss elsewhere. One opportunity to break that dry spell at the high end came with the Jamuna River Bridge project in Bangladesh. The winning contractor was Hyundai, a long-time customer of Vulcan. Vulcan made a number of submissions to Hyundai for this, but the most innovative was the 6250. This 1500 ft-kip hammer (shown above, all dimensions in millimetres) incorporated a number of departures from Vulcan’s normal offshore design, some of which were from the experience with the 5150 and 6300 but others which came from its acquisition of the Raymond technology. The latter included the straight capblock shield with mandatory micarta and aluminium, slide bar guide block and cables through the column to the head (onshore hammers had this, but not offshore ones.) Unfortunately, Hyundai opted for a hydraulic impact hammer and the 6250 never saw production.

Click here for more information on the 6250.

Vulcan 513/515/517/525 Hammer Series

d35373Offshore wasn’t the only place where Vulcan was applying Raymond technology. When faced with hammers with ram weights larger than 10 kips, Raymond opted to use the #0 frame for hammers such as the 3/0, 4/0, 5/0 and 8/0, all with 3.25′ strokes and 12.5, 15, 17.5 and 25 kip rams respectively. This resulted in a lighter hammer than, say, the Vulcan 014, 016 or 020 hammers.

Vulcan had plans to directly incorporate cable versions of all of these hammers, but ultimately developed 5′ stroke versions of them, incorporating Raymond features both from existing Raymond hammers and from those which they were unable to bring to reality. The “flagship” of this line was the 525, featured at the right. It was a 5′ stroke version of the 8/0, albeit with a single piece ram. It would have incorporated a 125 ft-kip hammer into a 37 kip machine.

Below are links to the general assemblies and specifications of this series of hammers:

Interestingly enough, Vulcan’s last new production hammer model was the 5110, which “did a Raymond” by putting a 110 kip ram into a 560 frame. This hammer was delivered to Global in 1996 and has been successfully used offshore.


3DEXCITRVulcan 488 Vibratory Hammer

In 1994 Vulcan put together a design for a successor for the 4600 hammer. It was intended to compete in the larger vibratory market, especially for the driving and extraction of casings for drilled shafts. It was also suitable for driving larger sheet piling projects as well. The result of that effort was the 488 hammer; a view of the exciter is shown at the left. It included many of the features of the Foster vibratory hammers that Vulcan was producing at the time.


Vulcan 1400A Vibratory Hammer

The 400 and 1400 vibratory hammers, the first high frequency vibrators produced in North America, were introduced in 1987 and 1988, respectively, and both were successful models. Both, however, had their limitations. Both were long hammers, and although they could get into tight places, low centre-of-gravity vibros are easier to handle. Moreover neither hammer was really suited for excavator mounting and downcrowding.

The 400A addressed these concerns and became a successful hammer. In 1997 a preliminary design was drawn up for the 1400A, shown below. Unfortunately Vulcan abruptly discontinued all work on vibratory hammers after this. Click here for more information on this hammer. The design has since been completed by Pile Hammer Equipment for its excavator mast.

d35434

Vulcan: the Offshore Experience

Everyone has an experience in their life that they count the greatest. Corporations do, too. For Vulcan Iron Works, that experience was its involvement in offshore oil development.

PMW 5150 1979 Apr 23
Vulcan’s Executive Vice President, Pembroke M. Warrington, in front of a Vulcan 5150 for his customer, Brown and Root, April 1979. It arrived from Chicago on the rail car, waiting to be offloaded. Equipment of this size was almost commonplace in the offshore oil industry. Twelve years later Pem stated that Vulcan had been “the experience of a lifetime,” and equipment like this was a large reason why that was so.
5100
Vulcan 5100 hammer driving pipe pile in the Gulf of Mexico. This photo graced offshore literature in the late 1970’s and again in the 1990’s.

Come join us as we take a look at Vulcan’s involvement offshore, which follows a fascinating (and very profitable) saga of American commercial history. You can click here to start or pick one of the topics below:

About the Photos

mcdermott-dual-bargeWhen putting together this collection, we wanted to tell the story of both the construction of conventional platforms. It’s tempting just to surf the web and take “stock photos;” however, we chose to use something closer to home. Virtually all of the photos in this section were either taken by Vulcan employees or were commissioned by Vulcan and taken by professional photographers. Many of these photos were rescued from destruction when Vulcan sold its Chattanooga facility; they are a priceless legacy of a great endeavour.

For their part Vulcan’s employees were not photographers; they were service, sales, technical and management people. The photos weren’t always the best, but they told the story better than just about anything else we can think of, and modern digital processing has improved many of these shots. Most of them are named in the narrative.

Although there may be others, three professional photographers are known to have their work in this collection:

  • Sam R. Quincey of West Palm Beach, FL, who took the outside photos of Vulcan’s Florida executive office;
  • Bill Blakeney of Palm Beach Gardens, FL, who took some of the better photos offshore; and
  • Jim Wilson of Hixson, TN, who took those of the plant expansion dedication.

The Saga Continues

Global5100Aug96
The “last hurrah:” the final Vulcan 5100 produced goes to work for Global in August 1996. The 5100 and the hammers sold with it gave Vulcan a good finish when it was merged in November of the same year.

Much of what we have presented about Vulcan’s offshore adventure has been done in the past tense. This is a little misleading; Vulcan hammers are still used to install offshore platforms all over the world today, simple, reliable and economical as always. The sun still does not set on working Vulcan equipment.

However, it is a fact that Vulcan equipment is not as universal offshore as it was in the 1960’s and 1970’s. The reason for this is due to the nature of the offshore industry today. To use a trite phrase, the industry itself isn’t what it used to be.

The greatest motive force for offshore development–sustained elevated oil prices–was not in place from the collapse of the oil industry in the early 1980’s until the Iraq War in 2003. In the meanwhile, the nature of offshore construction has changed, conventional platforms giving way to all kinds of structures such as undersea completions, tension leg platforms, guyed towers, gravity platforms, and the like. Some of these do not require piling at all; others require underwater hammers such as the IHC Hydrohammer. Horizontal drilling technologies have reduced the sheer number of platforms needed for a given field. In 1977 a consulting group predicted that Vulcan would literally be “left on the shelf” if it did not develop an underwater hammer, which ultimately meant a hydraulic hammer. Vulcan lacked both the expertise and the financial resources to develop such a machine; the larger steam hammers were enough of a stretch. (Click here for Vulcan’s last foray into product development of an underwater hammer, the sea water hammer.) The Gulf was not the ideal venue to develop such a machine; the harsh conditions of the North Sea, along with the superior state of mobile hydraulics in Europe, were better incubators of underwater hydraulic technology than those which were available to Vulcan.

Any product line, however, that can span three centuries and two millenia in active use must have something going for it. Today Vulcan air/steam hammers continue to support one of the greatest expeditions the human race has ever undertaken.

Sea Water Pile Hammer

The concept of using sea water as the motive fluid for an underwater hydraulic hammer is an intriguing one. Doing so has two key advantages:

  • Eliminates the use of hydraulic fluid, which can be environmentally hazardous (depends on the type); and
  • Eliminates the need for a return line, irrespective of whether the pump/power pack is on the surface or underwater.

Vulcan initiated two efforts in the production of such a unit.

The first was a design set forth by John Lerch, Vulcan designer in the 1970’s. His concept for a sea water hammer is detailed here as a patent proposal. The proposal was not pursued.

The second was Vulcan’s effort with its Russian associates. This concept was developed in 1994-5; one of the developers was Dmitri A. Trifonov-Yakovlev, son of Alexandr Sergeivich Yakovlev, founder and designer for the Yak aircraft design bureau. Unfortunately, Vulcan’s difficulties prevented its commercialisation. However, a patent was obtained on it (U.S. Patent 5,662,175).

The rest of this page will concentrate on the latter concept.

Purpose of the unit

The use of underwater pile hammers for the installation of foundations for deep-water offshore oil platforms dates from the 1970’s. Most of the hammers used in this application are hydraulically powered. The hammer case (they are always of closed construction) is evacuated using compressed air and the hammer is lowered onto the pile for driving.

Although these hammers have been generally successful, there are two major drawbacks.

The first concerns the possibility of spillage of hydraulic oil by the breaking of the hose or couplings or simple leakage. This is environmentally unacceptable in many jurisdictions. One obvious solution to this problem is to use vegetable or other “environmentally safe” oils; this is common with vibratory hammers. However in some applications even this type of contamination is unacceptable (food preparation, for example) and others (such as ours) the governing authorities (such as the U.S. Coast Guard) have systematically refused to enforce the laws as written and require cleaning up “safe” fluids, even edible ones.

The second concerns the evacuation of the “diving bell” for the unit, which adds to the complexity of the hammer.

To address these concerns, the sea water hammer was developed. It is in reality a special type of hydraulic impact hammer and is primarily intended for driving into the soil steel tubular piles in onshore and offshore conditions. The main fundamental differences between a sea water hammer and more conventional hydraulic hammer are the working fluid and the open construction of the sea water hammer. Both of these features will be described below.

Overview of the design

The hydraulic hammer (Figures 1-10,12-13, see below) consists of the following components:

  • Ram 42 in the shape of a massive, thick walled cylindrical pipe with two circular sliders 84;
  • Tubular casing 30 which is used as a central guide along which ram 42 moves;
  • Pile cap 24 inside which damper 36 is located to decrease dynamic efforts acting on casing while pile driving;
  • Hydraulic cylinder 96 with the system of control valves and accumulators that are located inside casing 30 of the hammer;
  • Traverse 88 attached to the rod ear of the cylinder 96. The ends of traverse 88 are passing through longitudinal slots in walls of casing 30 and are attached to the ram 42 via dampening blocks 84;
  • Upper cap 66, which is attached to the casing 30 and cylinder 96 via a flange. There are guides provided to support the high-pressure hoses. There are provided ears 64 to hang hydraulic hammer to the hook of the crane;
  • At the bottom of the hammer there is a system of adjustable mechanical supports 58 to prevent hammer from rollover while driving of batter (inclined) piles.The hydraulic operating and control system (Figure 11) likewise is made up of the following:
    • Power pack comprising two parallel 3-plunger pumps 128 equipped with electric drive and thyristor control, coarse filters 126 and fine filters 132, safety valves 136 (which are included into pumps 128), back valve 130, valve unit 138, manometer 140 and drain valve unit 142;
    • Working cylinder 96 with rod 102 and control cylinder 188, the upper part of which is fixed to the working cylinder 96;
    • High-pressure hose 110 to supply working fluid from the power pack to the cylinder;
    • Hydro-pneumatic accumulator 116 to smooth pressure fluctuations in the pressure line.

    The control system (Figure 11) is constituted as follows:

    • Two-position main valve 180 with large nominal bores which provides either connection piston end or rod end of the cylinder motor or disconnection of these ends and connection piston end with drain line;
    • Two-position control valve (“pilot”) 176 with small nominal bores which controls main valve 180’s position;
    • Ram height adjuster made in the shape of a plunger 210 attached by its bottom end to the rod 94 and passing into the internal slot of control cylinder 188;
    • Hydro-pneumatic accumulator 120, which is connected via pipe lines with internal cavity of control cylinder 188 and via back valve 204 with pressure line of the power pack;
    • Mechanism of impact energy adjustment comprising of the adjustable reduction valve 146, valve unit 144, hydro-pneumatic accumulator 118 and manometer 148;
    • Differential hydraulic block 192 of pressure comparing in which values of fluid pressure from ram height adjuster and reduction valve 146 are compared. Block 192 is designed in the shape of piston-valve with a pusher. The area of the piston from the side of hydro-pneumatic accumulator 120 is half of the piston area on the side of hydro-pneumatic accumulator 118.

    Hydraulic system of hammer starting and stop (Figure 11):

    • Sliding valve 156, which is driven from mechanical device providing its switching directly after ram 42 impact upon the pile cap, valve unit 150, adjustable valve 152 and hydromechanical pusher 175 which controls pilot valve 176 position.
    • Two (2) small flexible high-pressure hoses 112 and 114 supply working fluid into the control system of the hammer. Hydraulic system of control provides to perform from the control panel, located at the base platform, hammer starting, impact energy adjustment, stop of the hammer and making single blows of the predetermined impact energy.

    Operation

    The control system is free of electrical or electronic control. To accomplish this there is a centre bore in the cylinder’s piston rod. A tube extends from the top of the cylinder which fits into this bore; in turn a rod from the bottom of the main piston rod fits into the centre bore of the tube. The accumulator connected direct to the control valve has its pressure set to a desired level before the hammer’s operation starts. As the ram rises, the fluid above the central rod and inside the tube is forced upward into the accumulator. When the accumulator’s pressure (and thus the pressure of this control fluid) is sufficiently high, the hydraulically operated control/pilot valve is shifted, which in turn shifts the main valve.

    Opposing this motion is the pressure on the other side of the pilot cylinder; as this pressure is varied, the point in the stroke at which the valve shifts is likewise varied. This opposing pressure is controlled by the needle valves on the power pack.

    To shift the valve back at the bottom of the stroke, a roller-actuated valve is mounted so that the ram releases it near impact. This admits pressure on the other side of the control valve and shifts the valve back to depressurizing the topside of the piston. It is noteworthy that the lower side of the piston is always pressurized and pressure is alternately applied to the upper side of the piston. This helps even out the flow and also always provides for some kind of downward assist.

    Prototype Unit

    Vulcan commissioned a set of drawing for a prototype unit. Specifications for it are shown below. The actual production hammers could of course range in sizes comparable to hydraulic hammers suitable for the large offshore pipe piling.

    SI Units English Units
    Rated Striking Energy, kJ 50 Rated Striking Energy, ft-lbs 23813
    Ram Mass, kg 3000 Ram Weight, lbs. 6615
    Stroke, mm 1500 Stroke, inches 38.10
    Energy with Free Drop, kJ 44.1 Energy with Free Drop, ft-lbs 21003
    Percentage of Energy w/Free Drop 88% Percentage of Energy w/Free Drop 88%
    Blows Per Minute 25 Blows Per Minute 25
    Power Output, kW 20.8 Power Output, HP 28
    Hydraulic Flow, l/min 132 Hydraulic Flow, gpm 35
    Maximum Pressure, MPa 20 Maximum Pressure, psi 2901
    Hydraulic Power Input, kW 44 Hydraulic Power Input, HP 59
    Percentage of Hyd. Energy over Theoretical Minimum 211% Percentage of Hyd. Energy over Theoretical Minimum 211%

    Drawing Nomenclature

    • 20 pile hammer
    • 21 lower end portion
    • 22 hollow piling
    • 24 annular pile cap
    • 25 inwardly directed lower end flange
    • 26 recess or shoulder
    • 27 central body recess
    • 28 bore
    • 30 elongated, upstanding, hollow tubular base
    • 32 annular, circular support ring
    • 34 radial pins
    • 36 shock absorbent material
    • 38 upper end portion
    • 40 annular, upper end face or anvil surface
    • 42 hollow, heavy, generally cylindrically shaped ram
    • 44 annular lower end surface
    • 45 finger
    • 46 plurality of radially oriented, upwardly and outwardly sloping vent passages
    • 48 plurality of openings
    • 50 lower end wall
    • 52 large central part
    • 54 guide assembly
    • 56 radially extending fingers
    • 58 enlarged head
    • 60 bracket or block
    • 62 lift ring assembly
    • 63 pins
    • 64 apertured lift eye
    • 66 top plate
    • 68 central bore
    • 70 matching size, upper end face
    • 72 upper annular groove
    • 74 lower annular groove
    • 76 upper resilient shock ring
    • 78 lower resilient shock ring
    • 80 wall ports
    • 82 diametrically opposed, radially oriented bores
    • 84 annular, resilient, shock element bearings
    • 86 opposite, axle ends
    • 88 transverse lift yoke
    • 90 longitudinally extending diametrically opposite guide slots
    • 92 clevis
    • 94 piston rod
    • 96 fluid operated lift cylinder
    • 98 removable cross pin
    • 100 annular lower end wall
    • 102 piston
    • 104 upper end wall
    • 106 hydraulic base element
    • 108 power pack
    • 110 large diameter, flexible, pressure line
    • 112 regulating control line
    • 114 small bore flexible line
    • 116 crank end hydraulic accumulator
    • 118 head end accumulator
    • 120 control accumulator
    • 122 fluid supply reservoir
    • 124 check valve
    • 126 filter
    • 128 hydraulic pump
    • 130 filter check valve
    • 132 pump filter
    • 134 high pressure manifold
    • 136 adjustable relief valve
    • 138 manual dump valve
    • 140 main pressure gauge
    • 142 depressurizing manual dump valve
    • 144 manual, two-way control valve
    • 146 manually adjustable pressure reducing valve
    • 148 control line pressure gauge
    • 150 manual operation valve
    • 152 pressure relief valve
    • 154 passage or line
    • 156 mechanically controlled valve
    • 158 mechanism
    • 160 cam follower roll
    • 162 axle
    • 164 pivot arms
    • 166 spaced apart brackets
    • 167 spring
    • 168 stem
    • 170 slot
    • 172 cam
    • 174 line
    • 175 pusher
    • 178 comparator valve
    • 180 main operating valve
    • 182 head end main operating valve connecting line
    • 184 crank end main operating valve connecting line
    • 186 crank end manifold
    • 188 small diameter inner control cylinder
    • 190 small diameter inner control cylinder line
    • 192 differential pressure block
    • 194 upper pusher
    • 196 main pilot valve
    • 198 top pilot line
    • 200 bottom pilot line
    • 202 interconnection line
    • 204 interconnection check valve
    • 206 piston check valve
    • 208 inner cylinder lower end portion
    • 210 control rod
    • 214 head end accumulator line
    • 215 alternate guide system
    • 216 heavy counterweight
    • 218 elongated hollow tubular outer shell
    • 220 upper annular end wall
    • 222 lower annular end wall
    • 224 hollow tubular ballast element
    • 226 elongated tubular inner side wall
    • 228 support ring
    • 230 second alternate guide system
    • 232 relatively light weight and short length tubular outside side wall
    • 234 annular, radial end wall
    • 236 plurality of ports
    • 238 inner side wall
    • 240 radial support pins

Vulcan, Underwater and Hydraulic Hammers

Vulcan never developed an underwater hammer of its own for offshore use. Although today use of these hammers for deep water projects is routine, the road to viable offshore hammers was a long one, even for companies better situated than Vulcan to get there.

The Ocean Pile Hammer

Vulcan’s first underwater hammer was the Mariner Pile Hammer, which was an adaptation and upgrade for its original closed differential-acting hammers. Vulcan made a few of these units, but the limitations of other aspects of underwater technology made onshore construction preferable “in the dry” for a long time.

For offshore platforms, however, working in the dry wasn’t an option. With conventional platforms, it was necessary to drive piles through the legs from the top. This had two disadvantages:

  • Piles had to have additional length to reach from the top of the jacket to the ocean floor, which both added to the pile weight and created a long transmission line for the stress wave, with the lossses to go with it.
  • The “add-on” length was limited both by the working distance under the barge crane and the weight of the hammer assembly, which (on batter piles) creates a bending moment .

As long as water depths and jacket heights were limited, these disadvantages were outweighed by the ease of construction that came from driving “from the top.” However, as the exploration for offshore oil progressed further from shore and projected water depths for platforms began to approach 300 metres, it became obvious that underwater driving–which would eliminate both of the problems described above–was the long-term solution.

Raymond and the “Air Gun” Hammer

US4138199-3
The “thin” concept of an underwater hammer, as embodied in a Raymond patent. The hammer 54 was threaded through the pile guides 38 to drive the pile 40.

Vulcan wasn’t the only entity thinking about air/steam hammers underwater. Raymond, which had produced its own steam hammers for more than half a century, financed an interesting experiment in underwater hammers which didn’t work out as expected.

Raymond recognised early on that one of the virtues of an underwater hammer would be that it would be thin, i.e., no larger than the diameter of the pile it was driving. This allowed the hammer to be threaded down through the pile guides on the sides of the platform. Also, by the early 1970’s Raymond had more experience than just about everyone else with hydraulic impact hammers with their 65CH and 80CH hammers. They understood that mobile hydraulics needed significant advances to be practical and reliable in an environment where both were crucial for economical platform installation.

Raymond turned to Bolt Associates to develop an air hammer suitable for underwater use. The Bolt Associates hammer was the invention of Stephen Chelminski. This hammer attempted to replicate the basic construction and principle of tubular diesel hammers by placing an air gun at the base of the hammer. As the ram struck the anvil, the air gun would release highly compressed air between the two, giving the ram upward momentum. The air gun also cushioned the ram impact to some degree, which was more important for onshore application than offshore. Raymond took the concept and modified it for the “thin” style hammer it desired.

US4098355-2
Operating cycle of the Bolt hammer, as modified by Raymond for underwater operation

Raymond was large enough of an organisation to finance extensive testing of the unit. Beginning in September 1974 they tested the RU-200 unit at Southwest Research Institute in San Antonio, TX. The 60,000 lb. ram hammer was placed in a 120′ deep cased hole which was filled with water. The hammer struck over 100,000 blows at refusal, performing well during the test.

Bouyed by these results, Raymond purchased an RU-300 for a job at the Maui field in New Zealand. It arrived on the jobsite in late 1975. A conventional platform, there were two types of piles to be driven:

  1. Pin piles, which were driven through the corner legs of the platform into the seafloor. Grouted to the platform after installation, these both provided geotechnical anchoring of the platform and structural reinforcement of the tower. They were to be driven from the surface, using a Vulcan 560.
  2. Skirt piles, driven around the pin piles (see diagram below.) Since they did not extend to the surface after installation, using an underwater hammer to drive them was advantageous as it eliminated long followers which dissipated driving energy.

OTC3270Figure1

Anyone who is involved in pile driving equipment development feels that new concepts and equipment always seem to get their first try on the most difficult jobs, and that was certainly the case with the Maui field.

To begin with, the sea and weather environment was poor, rivalling the North Sea. Throughout the first half of 1976, there were what seemed to be interminable delays due to weather, and the job was finally stopped in June. The hammer performed reasonably well when it had the occasion to operate. At the end of the year Brown and Root’s Atlas barge was replaced by Netherlands Offshore’s (NOC, the same company which bankrolled the HBM Hydroblok, shown below) Blue Whale.

The Raymond hammer worked its way through the first part of 1977 with several breakdowns due to dirt getting into the system (lack of sensitivity to this kind of thing was a strong point with Vulcan steam hammers, and Raymond ones for that matter.) The oil company consortium (made up of BP, Shell and Todd) felt that the Raymond wasn’t getting the energy to the pile, so they turned the job over to NOC’s Menck steam hammers. They didn’t do much better; what was happening is that the piles were experiencing severe plugging at the pile toe, a phenomenon poorly understood then. They resorted to jetting the plug with pressurised water (an unusual procedure offshore,) which helped some but not enough. NOC’s Blue Whale then was damaged during a severe storm in May 1977. The Raymond hammers, working off of a temporary work deck on the jacket, continued to perform, but in the meanwhile additional boiler capacity was installed on the Blue Whale during its repairs. The pile installation was completed in the last half of 1977 using the Menck steam hammers.

One major reason for laying down the RU-300 at the end was the hammer’s greatest weakness: its blow rate, which was only 8-10 blows/minute, as opposed to 45-60 BPM for the steam hammers. This made for slow pile installation. That blow rate was doubtless affected by the long hose that extended from the surface down through the ocean water to the hammer. The hose acted as sort of a “reverse Supertherm,” cooling the air and degrading the hammer’s performance

Raymond did not use the Bolt hammer again. Raymond was active in the offshore market for the remainder of the decade and into the early 1980’s, purchasing a number of Vulcan hammers for its offshore operation.

Menck, HBM and the “Thick” Hammers

As the 1970’s progressed, it became evident that underwater hammers were the “wave of the future” for at least some offshore oil development. Getting to that future, however, was not a straight line proposition, primarily for three reasons:

  1. Oil companies, sensibly, would develop their shallower water fields first. Steam hammers were by far the more economical way of installing piling for these platforms.
  2. Although elevated oil prices do encourage development of marginal and otherwise expensive to develop fields (and that includes deep water,) during the 1970’s and early 1980’s the imperative to bring oil onstream quickly discouraged the experimentation necessary to perfect new underwater technologies.
  3. The market for these hammers was a classic monopsony, with literally a handful of buyers to sell to. Changes in the status of these buyers could make or break an expensive development programme.

Combining the last two meant basically that, in order for a hammer manufacturer to put these hammers into the marketplace, it was necessary to find a “patron” who would finance the development of the equipment. An example of this on a much smaller scale was Vulcan’s IPH-16 with McDermott.

With Raymond’s problems with its air hammer, it was also evident that hydraulic impact hammers were the best way to achieve an underwater hammer. The fact that American hydraulic component manufacturers during this era had allowed their technological edge to be seriously dulled in the field of high pressure mobile hydraulics favoured development in Europe. Beyond that, the North Sea, with its limited construction season, encouraged development of more technologically sophisticated solutions for platform construction.


The company with the longest continuous history of underwater hydraulic hammers is Menck. Menck’s patron was the Dutch contractor Heerema, which was a technological leader in self-propelled, high-crane capacity barges for the demanding North Sea environment. Heerema largely financed Menck’s entry into the market and both tested and utilised their hammers (steam and hydraulic) extensively in their platform construction projects.  (More information on Menck steam hammers can be found here.)

Menck’s underwater hammer programme had its moments. The first underwater hammer Menck produced for Heerema was the “thick” MRBU 6000. By Heerema’s own admission the hammer was “maltreated offshore after having driven only a single pile.” The “thin” MHU 1700 saw its first job as a prototype on the Fulmar field in the North Sea in 1980, and a year later on the Magnus field. These confirmed the basic viability of the hammer, and Heerema used the hammer on 3-4 jobs per year during the early and mid-1980’s.

As is the case with most underwater hammers, it is necessary to feed compressed air to the unit to prevent the incursion of water, making the hammer a type of diving bell. As the MHU 1700 went deeper, the increased pressure and air density resulted in a signficant increase in the drag on the downwardly travelling ram. This occasioned the re-design of the interior of the hammer. On the Eider field, the hammer’s driving was so hard that the seals gave way and allowed ingress of water into the hammer itself.

Nevertheless, through all of the changes in the marketplace and in Menck itself, the company continues to produce working hydraulic impact hammers capable of underwater construction.


A successful underwater hammer which suffered an entirely different fate was the HBM (Hollandsche Beton Maatschappij) Hydroblok hammer. This hammer was developed by HBM for concrete piles onshore, and featured a gas cushion mounted into the ram. Adjustable, it lowered the peak force and extended the impact time of the hammer, which was a very favourable feature for concrete piles.

Hydroblok-Operation
The operation cycle of the Hydroblok hammer.

The Hydroblok first came to Vulcan’s attention in the late 1960’s, and so it asked its Belgian partner Nilens to investigate. In a 17 February 1969 letter to President H.G. Warrington, Nilens‘ H. Hellings described the hammer and its manufacturer as follows:

The “Hollandse Beton Maatschappij” is the biggest Construction Company in the Netherlands. Since 1966 this company is trying to build an hydraulic hammer. The a.m. (aforementioned) patent (U.S. Patent 3,417,828) is the theoretical background for their invention.

They built one prototype, a double acting hammer of 6000 Kg (+ 13.228 lbs) total weight, 100 blows per minute and with a rated striking energy of 5000 kgm (+ 36.150 ft.lbs) per blow. This hammer drives a pile four times faster than a Delmag D 22 hammer.

They have now a bigger hammer in construction based on the same principles with 14.000 kgm (+ 101.220 ft.lbs) energy per blow, 100 blows per minute and a total weight of 15.000 Kg (+ 33.070 lbs).

Mr. JANSZ of H.B.M. told me that they have the possibility to make a double acting hammer of 30.000 Kg (+ 66.138 lbs) total weight with a striking energy of 25.000 kgm (+ 180.750 ft.lbs). I suppose that the H.B.M. wants to sell this patent only to an American firm, building pile driving hammers, to build the hammer for the American market.

It is not clear whether there was any follow up by either Vulcan or HBM to this contact.

HBM’s main patron for offshore development was the Netherlands Offshore Company (NOC,) which financed the development of the larger hammers. These extended upward into such hammers as the HBM 3000, with an energy output of 1,580 kJ. Extensive information on these hammers is found here, along with details of the February 1979 test of the HBM 4000 and the “puppet weight” system to facilitate handling the hammer underwater.

HBM-1500-Amsterdam
An HBM 1500 on a test pile in Amsterdam. HBM’s access to onshore test sites for large hammers was a major advantage for HBM (and later IHC,) a fact which Vulcan found out the hard way when it attempted without success to have the 6300 tested in like fashion. That underscored the disadvantage of Vulcan’s inland location.

Although the centre of the hammer’s development was in the North Sea, a major incursion into “Vulcan territory” (the Gulf of Mexico) took place in 1977, when two HBM 3000’s was used on Shell’s Cognac platform. Performing at water depths of 300 metres, the hammers performed well, although, driving as they were into soft clay, the blow count generally did not exceed 20 blows/ft.

Although the Hydroblok hammers were doing well, there were storm clouds on the horizon.

The first was that, although well designed hammer, the Hydroblok was a complex one. With the high impact loads, pile driving equipment does not deal with complexity gracefully. One reason Vulcan’s line has survived for more than a century is its simplicity. The HBM hammers tended to be “high maintenance.”

Second, the principal designer for the hammers, Joost Werner Jansz, died suddenly 21 May 1979, just a few months after the successful test of the HBM 4000.

Third, the gas cushion that was the hammer’s most interesting feature was well suited for concrete piles. But for the high-impedance steel piles common offshore, a high peak impact force is the best. The Hydroblok hammers did well in easy to moderate driving, but against either steam or the Menck underwater hammers, in hard driving the Hydrobloks would reach refusal too soon.

Fourth, all of the Hydroblok hammers produced were “thick” hammers. Platform designers were increasingly drawn to configurations that required “thin” hammers.

HBM was working to address these problems, but time ran out rather suddenly when NOC was sold to McDermott. The latter decided that it had enough Hydroblok hammers for its requirements, and HBM’s entire underwater hammer programme collapsed. HBM’s parent sold the Hydroblok’s rights to Menck in 1981, and (except for some activity at BSP) the underwater hammer market seemed to be in the hands of one supplier.

The BSP Hydraulic Hammers

Another manufacturer to step into the offshore hydraulic hammer field was the UK’s BSP. One of their models was the “HA” type, which was basically a hydraulically actuated drop hammer; information on that can be found here. Another one was an open type hammer where the ram actually moved through the water (as opposed to the “diving bell” concept that HBM and Menck embodied in their hammers.) This was actually tested in Loch Linnhe, in Scotland, in 120 metres of water. This is the same concept that Vulcan developed in its Sea Water Hammer.

Although BSP had some success in the offshore hydraulic hammer market, it never achieved success to the degree that its Continental competitors–Menck and IHC–did.

The IHC Hydrohammer

Dik Arentsen, who had been head of Hydroblok’s R&D at the time of NOC’s sale, initiated the development of a new line of hydraulic impact hammers for offshore driving that addressed many of the weaknesses of the Hydroblok. It took some time finding a suitable corporate harbour to drop anchor in, but he and Ernst Mudde finally did so at IHC, where development of a new competitor to the Menck hammer took place.

IHC-S400-Test-Pile
The S-400. Mercifully IHC lost the orange colour early in its corporate life.

Vulcan first made contact with this group in 1982 and discussions went off and on throughout the 1980’s. The main stumbling block from Vulcan’s standpoint was that Vulcan was unwilling to invest in a large hammer (which were and are several times more expensive than their air/steam counterparts) give the market conditions it was facing. In the meanwhile IHC found a more receptive (and larger) customer in Heerema. Starting with an S-70, they proceeded to an S-400. Both of these hammers were successful, notably in the Gulf of Mexico, cutting into both Vulcan’s and McDermott’s territory. In 1988 Heerema ordered the S-2000. IHC was established and, with oil prices coming off of their mid-1980’s bottom, offshore came alive again with two major manufacturers of large underwater hammers.

IHC’s line was not only set up for offshore but also for onshore application. L.B. Foster was IHC’s first distributor in the U.S., but some dialogue with Vulcan continued. After Vulcan’s merger in 1996, those discussions intensified, but to no conclusion. Finally in 2001, Vulcan’s parent sold the air/steam line to IHC, which formed Vulcan Foundation Equipment, and from 2001 to 2009 the two organisations were united until the Vulcan line was sold to Pile Hammer Equipment.

Other Hydraulic Hammer Efforts by Vulcan

Although the IHC and Menck hammers were offshore underwater hammers subsequently adapted for land use, for most hydraulic hammers (such as the Hydroblok) the reverse is true. The first hydraulic impact hammers were developed for onshore use and those for offshore came afterward.

In the early 1990’s, aware that hydraulic hammers were advancing in both markets, Vulcan investigated three types of hydraulic hammers.

One was literally the first hydraulic impact hammer to be used in the U.S.: the Raymond. Vulcan acquired several of the 65CH and 80CH hammers, and eventually rebuilt an 80CH for yard testing. The initial tests showed promise but Vulcan’s difficulties in the mid-1990’s put an end to this effort. More information on the Raymond hydraulic hammers can be found in the Vulcanhammer.info Guide to Pile Driving Equipment.

Another was the Sermec hydraulic impact hammer, developed in the North of England. (The patent for this can be downloaded from here.) A video below, taken near Great Bircham, England in September 1991, shows the hammer in operation. (It also shows a BSP double acting air/steam hammer for comparison.)

Vulcan also took a serious look at marketing the Junttan hammers from Finland. Below is a video of this hammer being operated at Junttan’s facility in Kuopio, Finland, in January 1994.

Sea Water and Vibratory Hammers

Vulcan investigated the possibility of a sea water hammer twice, first in the late 1970’s and second in the 1990’s, in partnership with its Russian associates. Details on that effort and its results are here.

Vulcan also applied its vibratory line to offshore application, especially its largest model, the 4600. Vibratory hammers are fairly easy to adapt to underwater use, being generally hydraulic and with a closed case.


Published Sources

In addition to private correspondence and product literature, the following articles were very helpful in the development of this page:

  • “Raymond develops new underwater tool.” Offshore, 1974.
  • Gendron, G.J., Nelson Holland, H.A. and Ranft, E.V. “Underwater Pile Driving at the ‘Maui’ Field.” OTC 3270. Offshore Technology Conference, 1978.
  • Heerema, Edward. “Hydraulic v. steam pile hammers: contractor weighs the odds,” and “Which way for underwater use?” Offshore Engineer, February 1978, pp. 64-66.
  • Jansz, Joost W., Voitus van Hamme, G.E.J.S.L., Gerritse, A. and Bomer, H. “Controlled Pile Driving Above and Under Water With A Hydraulic Hammer.” OTC 2477. Offshore Technology Conference, 1976.
  • Jansz, Joost W. “North Sea Pile Driving Experience With a Hydraulic Hammer.” OTC 2840. Offshore Technology Conference, 1977.
  • Jansz, Joost W. “Subsea piledriving: a breakthrough.” Petroleum Engineer International, June 1978.
  • Jansz, Joost W., and Brockhoff, Henk S.T. “Unsupported underwater piledriving. Part 1: Theory and North Sea Experience.” Ocean Resources Engineering, December 1978, pp. 8-13.
  • Jansz, Joost W., and Reinold de Sitter, W. “How to rate piledriving hammers.” Ocean Industry, June 1979, pp. 88-96.
  • Jansz, Joost W. “Underwater Piledrivng: Today’s Experiences and What is About to Come.” Presented a the Second International Conference on Behaviour of Offshore Structures, 28-31 August 1979. (This may be Dr. Jansz’s last paper, as passed away three months before the conference.)
  • Heerema, Edward. “An evaluation of hydraulic versus steam pile driving hammers.” Offshore Engineer, June 1980, pp. 18-20.
  • “HBM Designs Slimmer Hammers.” Offshore Engineer, October 1980, pp. 92-3.
  • Knott, Terry. “Underwater hammers ready for a grander slam.” Offshore Engineer, August 1988, pp. 60-61.