Does floatation foam give structural support?

[sbklf]

I removed the floor and foam from the front half of my boat to repair the hull. A lot of the foam came out in sections (not a monolithic pour) and there were voids. How important is the foam from a structural standpoint ?

[lewisboats]

It depends on how it is used. When I make a tank seat, I use 1/4" ply. Were I to sit on just this, it would bend and sag. When I fill the chamber with sheets of foam, it adds additional support so the seat doesn't bend or sag. I would say it would depend on the thickness of the floor (actually the sole) and the number and spacing of the supporting structures (normally called the floor timbers or flooring timbers). The foam would not necessarily need to be monolithic to provide additional support. How much of the foam was in contact with the bottom of the sole?

Steve

[dereksireci]

Floatation foam does not, and should not be relied upon to provide any structural element to the boat. It is meant to provide displacement buoyancy in the event of swamping.

When fiberglass is deflected a small amount, it returns to its original shape. When 2 pound per cubic foot urethane foam is deflected it does not return to its original shape. So maybe the foam provides structure, but only once.

djs

[sbklf]

It looks like they poured foam before they installed the floor up to close then filled some of the low spots with resin and slapped the floor over it. I would say 75% was solid to the bottom of the sole.

I was considering a different flotation method that would offer no structural support at all to the hull and adding vertical support for the floor.

[JR-Shine]

most flotation foam is 2lb density - not very good. It might stiffen somethign up for a little while, but dont rely on it.

Joel

[jimslade]

One word, YES, ever heard of a boston whaler? If applied properly, it adds support to the sole.(floor).

[JR-Shine]

Yes, I know of boston whaler, they make big coolers in the shape of a boat:)

I have also been on a new BW when the bottom a large section of bottom ripped off due to a poor bond. It was less than 1 year old 21' happen 3 years ago while fishing of Savanah, GA.

[buckknekkid]

there is a goood article in Professional Boat builder about the gentleman who developed the Whaler system and then left to build his own boats. Google it and read about the trials and tribulations they experienced:idea:

[dereksireci]

One word, YES, ever heard of a boston whaler? If applied properly, it adds support to the sole.(floor).

Wrong!
Totally different animal.
The support for the sole of a BW is provided by what they call shear ties. They are fiberglass members that connect the hull to the the liner on the bigger boats or the deck of the smaller boats. The shear ties act as the web of the beam. The flanges being the surfaces tied together. Without the shear ties you have only foam and no strength.

The foam of the Whaler is not strictly free rise, therefore of higher than 2# density.

djs

[buckknekkid]

O K !!! I'll dig out the article and see if I can type enough to quote from it. The basic idea is that its a hit and miss thing if you just drop in a few pounds of two part and squeeze the guts out it. My last Whaler dinghy looked Sorta like a Martoony. Shaken not Stirred :P

[jimslade]

If you use no foam then you have two layers separated by air. It will break under load. So the foam is of structurall importance. Don't say I'm wrong without thinking your response through. Even air in a ballon adds structural integrity to the ballon. What I'm responding to is if He should replace the foam or leave it out. IT DOES HAVE A STRUCTURAL USE.

[Ike]

The foam in your boat is not structural foam. It is there to provide buoyancy in the event of a swamping. The foam used in Boaston Whalers is not the same stuff at all. It is a 4 lb density structural foam and does provide stiffness and strength to the boats as well as buoyancy. The standard pour foam used in boats for buoyancy will crush easily and compress if weight is placed on it. If you replace the pour foam with block foam it may provide some structural strenght, but not much. But as Lewis boats said if you fill the compartment completely with block foam it will give a small amount of rigidity to the floor. But that is not it's purpose. I haven't to date seen any pour foam that offers and great structural strength.

[seven up]

I have no experience with the 2 lb pourable foams. The 16 lb pourable foam that i am considering is described as: 2-part urethane, closed cell, need a hammer to dent it. the basic description.

Quite up there in price compared to the 2 lb.

The application would be for a small chamber in the bow, just for a block of reinforcement in a plywood cruiser. Important though is that i do not want to prevent any required flexing and cause a breach elsewhere.

Should this be posted as a new thread ??

[Ike]

You can certainly use 16 lb. It will provide structural strength and flotation (46 lb of buoyancy pe cu ft.) 2 part urethane is pour foam. Pour foam is just a generic name for foams that are made by mixing two components, and are done by the builde or user. Pour foam got it's name because originally people used to mix it in a bucket and then pour it into the space. Now days almost all of this is done with foam mixing guns. It's also called spray foam. Block foam is the generic name for foam made in blocks by the foam manufacturer.

[Toot]

Anybody know whether the higher density pour foams less susceptible to moisture and degradation?

[l_boyle]

No, foam does not give structural support. It save your boat from sinking to the bottom of deep water.

[l_boyle]

Wow, high density foam can blow your boat apart if you get too much of it in there... Just like that "Graet Stuff" uses around home.... I put a lot of it around my window one time, it expanded so much that I cannot get the damned window open... Hummmm, warped boat hull, will not plane well..

[Ike]

It depends on whether or not it is done right. Ifyou follow the manufacturer's instruction to the letter it should not absorb water. All foam degrades over time due to shock and vibration. The only thing you can do about that is not use your boat.

Again, if you do it right it will not blow your boat apart. And yes there is such a thing as structural foam. Foam is used in all kinds of structures to add stiffness and reduce weight. It is used extensively in boats in longitudinals on the bottom of boats in what are called Hat structures. It does not add to the sheer strength or compressive strength, but it does add stiffness.

If you read the instructions and figure out how much foam you need so you don't overfill the compartment it will not blow your boat apart, but just in case get a 1 or 1 1/2 inch hole saw and cut a hole in the top of the compartment so if it over foams, it has someplace to go. This is common practice in boat manufacturing.

[jimslade]

Thanks IKE.

[seven up]

yea, thank-you