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Author Topic:   Foam Construction Techniques
jimh posted 10-08-2000 10:01 PM ET (US)   Profile for jimh   Send Email to jimh  
In BOATING MAGAZINE for OCT 2000, an article on THE WORLD'S TOUGHEST BOAT wanders into some comments about construction techniques using foam injection.

"A potential problem with conventional fiberglass grids is that foam--used for strength and sound deadening--is often injected into them after they are bonded in place. The expanding foam creates a great deal of internal pressure that strains against the bond."

(They make this point to contrast with the use of pre-formed foam stringers and grids.)

I was reading this and thinking about the Whaler construction technique, where the still uncured hull and liner sections are clamped together, then the foam is introduced. Sprue holes allow the foam to fill and escape.

So does the Whaler technique suffer from this problem of the foam exerting pressure against the bonds of the hull and liner?


bigz posted 10-09-2000 08:43 AM ET (US)     Profile for bigz    
In a word yes --- and I have seen the results with rippled hull sides to various degrees.

Speaking of this side effect if "over" filled and then capped before all excess escapes --- just yesterday speaking with the fellows at our marina working on a gas tank pick up problem in a ? forget the boat manufacture but right on the forward deck area was a "big" crack bulging up and it was certainly caused by the foam expanding after plugging --- first time I have ever seen an actual crack from this problem ---

One surveyor said this rippling on the topsides of glass boats can also be caused by a poor lay-up procedure --- in the case of Whalers the foam in many cases will expand out into the ripples still maintaining a sound hull, aside from cosmetics really not a problem


PS Whaler QC is aware of this and are extremely careful since it does fall under the 10 year warranty for defects ---

lhg posted 10-09-2000 02:17 PM ET (US)     Profile for lhg    
Regarding use of the word "liner", I think we should be careful here, since BW has, until recently, never used this component. The Classic Whalers were always made from what they called inner and outer hull molds, forming the one-piece boats that we all know so well. The inner mold was always clearly in evidence, whether it be blue or desert tan, and it formed almost all of the interior detail of the hull. In the Outrages, only gas tank and well covers were needed to round out the boat, plus the teak gunnels. On the Revenge models, a liner was used to form the cabin, and on the Whaler Drive models, one formed the full transom stern deck.

Now again, since 1991, the company is using a more traditional "liner" as a major third component to form most of the interior of the Outrages & Conquests, which is resulting in the much heavier hulls. The inner hull mold,
essential to form the foamed hull, is greatly simplified, from what I can actually see of it, and the "liner" forms the majority of the visible interior detail - gunnels, fish wells, storage areas, splash wells, etc.

The original and continuing use of "liners"
developed from the traditional construction of non-whaler boats. The "raw" interior of the outer hull had to have an interior "liner" to complete the boat. BW's never needed this, and that was the beauty of the design concept - no trapped inner bilges and dead space between the hull molds. But as the company has migrated into the hands of conventional style boatbuilders, their familiarity with the "liner" panel design process has resulted in the larger Whalers now being made this way.

bigz posted 10-09-2000 02:41 PM ET (US)     Profile for bigz    
Thanks Larry, that was the word I was trying to remember "liner" --- for the cabins and stern sections ---

Liner verbage for the original hull sections is incorrect right?

dfmcintyre posted 10-09-2000 05:03 PM ET (US)     Profile for dfmcintyre  Send Email to dfmcintyre     
When I took the tour in 1977, they were bonding still somewhat wet hulls togeather. I didn't ask and don't know if that was always the case... i.e. what if the line shut down for the night with the inner and outer waiting for mating and foaming. They would be dry by the next day.

I'll bet that they went through a few hulls trying to dial in the right amount of liquid foam to pour in the hull!. I do remember they would tilt the whole setup a few degrees bow up, prior to the pour so the liquid foam would run down the keel.


Ed Stone posted 10-09-2000 08:27 PM ET (US)     Profile for Ed Stone  Send Email to Ed Stone     
I had a 1976 Boston Whaler bass boat model
with a third liner and never once thought of
it as a inferior Whaler.

I still believe Whalers Uni-bond const.
is superior to competitors style of
building hulls.

jimh posted 10-09-2000 09:02 PM ET (US)     Profile for jimh  Send Email to jimh     
Let me get back to the original question:

The article asserts that the pressure of foam expanding pushes _against_ the hull bonds of many conventionally built boats.

In the Whaler construction, isn't the foam allowed to expand and escape out of vent and sprue holes in strategic locations, thus relieving the pressure?

And also, this is curious:

In an advertisement (BOATING MAGAZINE OCT 2000) for the 28-Conquest, Whaler refers to its construction for that boat as "unsinkable Unibond-TM".

In another advertisement (BOATING MAGAZINE SEPT 2000) for the 34-Defiance, Whaler refers to its construction for that boat as "innovative Duobond-TM".


jimh posted 10-09-2000 09:09 PM ET (US)     Profile for jimh  Send Email to jimh     
Also, the premise that expanding foam exerts pressure is questionable.

After the foam dries to a solid, does it still exert pressure to expand? I don't think it does.

If you could suddenly remove the laminated hull from a Whaler, the foam wouldn't pop out another three inches, would it?


lhg posted 10-09-2000 09:11 PM ET (US)     Profile for lhg    
Yes, Ed is correct. The earlier 16/17's, in the Bass Boat and Newport configurations, had a gunnel liner that sat on top of the basic hull, widening the gunnels and forming a small bow deck. Also, the first generation Outrage/Revenge has a single thickness top liner hull bolted onto the very low sided "sled" foamed hulls.
In 1978, when the first of the V Outrages were introduced(20'), Dougherty went back to the conventional smaller Whaler hull configuration, where full height sides & gunnels were part of the foamed hull.
DIVE 1 posted 10-09-2000 10:05 PM ET (US)     Profile for DIVE 1    
Boston Whaler is the master for expanding foam techniques. When you put expanding foam in a confined area it exerts pressure on anything that it touches. The trick that BW learned long ago was how much foam to use for each hull, the proper method to fill the cavity, and how to provide proper venting so the foam does not distort or warp the hull. I have seen a lot of people drill holes in boats and pour in expanding foam to add flotation. If too much was added or venting was not sufficient, panels blew out, floors popped up, and sides of hulls have cracked.
DIVE 1 posted 10-09-2000 10:10 PM ET (US)     Profile for DIVE 1    
When expanding foam used in boats solidifies it does not exert pressure to expand. If you look at a severly damaged BW hull(fiberglass is missing) the foam that is not damaged is in its original shape.
Lil Whaler Lover posted 10-10-2000 07:45 AM ET (US)     Profile for Lil Whaler Lover  Send Email to Lil Whaler Lover     
Back to your original question: I have observed many Whalers, especially 13's since they were first made about 42 years ago. I have seen many that had been abused as "work" boats and had worn large holes right through the fiberglass and had foam open to the elements. Several of these were still in use even though some of the foam was below the water line. The foam is very stable after it sets up and it holds its shape, therefore logic tells me that once the foam has set up, it will not exert any additional pressure (or increasing pressure)on the fiberglass shells which contain it. As usual there is a caveat and that would be that the mixture of the foam is done correctly and therefore not subject to unexpected changes.
Just an observation pertinent to the question asked. Dave

triblet posted 10-10-2000 09:19 AM ET (US)     Profile for triblet  Send Email to triblet     
There's discussion of Unibond vs. Duobond
on the whaler web site. Basically, because
of the size of the Defiance, they had to
make some changes in the process (and the
size of the customer's checkbook ;-)

Chuck Tribolet

Reliant posted 10-20-2000 01:16 PM ET (US)     Profile for Reliant  Send Email to Reliant     
Jim - I asked your question to a friend of mine who has been a whaler dealer for 30 years. He had the opportunity of touring the Rockland, Mass. and then the Edgewater, FL manufacturing facilities for whaler while they were making boats. I asked him this, "isn't the foam injected into the cavity between the inner and outer hulls of whalers while the molds are clamped together, therefore the molds will take the pressure and not the inner and outer hulls while the foam expands." He agreed with me and said it is quite an experience as the molds creak like mad while the foam is expanding, escaping and drying. He also agreed with the other observations on this thread, that once the foam is dried, there is no more outward pressure on the hulls and the foam will maintain its shape even if a section of the hull were removed.

Hope I am answering your question,


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