Question about completely foam filled hulls

Do these manufacturers use stringers? or is the foam filled hull the stringer? Boston Whaler comes to mind here. when they put the deck and hull together and fill the area with foam do they first install stringers or does the foam become the stringer system as well?

 

Not sure about Boston whaler but most boat builders that are not using wood anymore are using fiberglass to make the stringet. There may be a foam mold but the strength is in the fiberglass not the foam . And of course that use different fiberglassing techniques and layering systems to create the strongest stringers possible. These foam Frameworks are made from a very dense foam and act like the steel frame in a car. These Framework skeletons many times are bought from specialized manufacturers that make them for the boat builders. it is amazing what they do now with computers and CNC

 

The foam may or may not be structural, it all depends on the manufacturer and the design of that exact boat. It can be done either way.

 

I can't see fill-foam being a stringer. If you make a foam sandwich that will give you a lot of stiffness, that fill foam doesn't give you much.

 

In most cases, production boats use the foam to add to the boat's overall stiffness, as well as address buoyancy requirements. Even 2 pound floatation foam offers some reinforcement to an enclosed space.

As to percentages of how much reinforcement they're looking to gain, well this would be applications specific, so individual boat designs have to be evaluated independently.

 

When I used to work on boats full time, repairing or just working with foam filled compartments was a nightmare.
I would be avoiding it if at all possible.

 

I was looking through blared's gallery and ran across this. There doesn't look to be anything but foam in there.

 

That would be more a structural type density, probably.

 

It doesn't take a high density foam to greatly increase the stiffness in a hull. Plus, the density of the foam increases when used in an enclosed space where it's not totally free to expand.

The other thing is while these low cost foams work very well for a while, they degrade over time, the rate of degradation can be affected by many things, so it's at sort of an unknown rate.

 

Countless shock loads will cause the PU foam to break down, especially low density stuff, it must be contained in such a way that water cannot infiltrate, or eventually you will be finishing up with soggy mush.

 

Which is/was the case with the pictured boat. I'm not sure what the density would be, but I'd guess much more than free-expanding 2lb/cu ft.

 

The foam shown above would be a fairly significant weight to the boat.
Stringers would "probably" be lighter.

 

You still need foam for flotation, so it's not like it's being totally eliminated by using stringers.

Add in marketing strategy and labor to put the stringers in and it may all balance out for the desired finished product.

I’m not saying it’s the best way to do it, only that Whaler has done well with the design.

 

Whaler's use 6 pound foam and it is considered part of the structure.

 

Stringers (weight) might be lighter than the foam IF only the panel/hull skin would be strong enough to support the structure. If you had to increase the thickness of the skin to gain rigidity in the area between the stringers, then there might not be any weight savings going to stringers