Current flotation foam best practices

[jbo_c]

What are the current thoughts on best practices for flotation foam/compartments?

Airtight or vented? If vented, how?(My boat will be outside, so don’t want mice taking up residence in my foam compartments.)

Pour foam directly onto epoxy-primed wood or line compartment?

Condensation concerns inside? How to minimize?

Drain and/or inspection holes needed for every one?

Do any of these answers change if the compartments are above the water line? (I’m planning to have almost, if not all, of mine above the water line.)

Finally, seems like I’ve seen advice to warm the components prior to mixing to maximize expansion(?). Necessary/good idea?

Thanks.

Jbo

[Fuzz]

My thoughts,some will agree and some not, for what it is worth. Foam poured into places will deaden sound and stiffen up things. Plus if holed you have a much better chance of being able to deal with the problem.
The downsides of foam is it is a pain to remove so you can do repairs in the area, cost and weight. Also tests have shown even closed cell foam will absorb water. One way or another even well sealed compartments have water find its way in. I am in the middle of repairing a well built boat and sure enough I found water in its foam. Not much but it was there.
As for me if I ever build another boat I would prefer to have foam but I want it above the water line. And I would like weep holes in the low spots so if/when water gets in it has a path out.

[Jaysen]

What fuzz said. Only had to poke on Boston Whaler two years after a high grade refurb to see how much water closed cell foam hold.

If you really feel you must use it, I think the idea of using some other, larger encased item, say plastic balls, that you pour the foam around, is the best idea. Also line the compartment with something to make removal easier. Say 2mil plastic sheet.

[cape man]

Under the sole of my Dory are 13 separate "compartments " defined by the stringers and bulkheads. Each was meticulously sealed in epoxy , and taped along the edges, including where chase tubes penetrated, before pouring the foam. The foam was then shaved off to the level of the compartments. The top of the stringers and bulkheads were covered with a solid bead of thickened epoxy before placing the epoxy sealed deck on top. The deck was then sealed along all the edges, filets built, and then two layers of overlayed glass tape used to secure it to the sides and rear deck. The deck was then covered with another layer of glass.

To get water in the foam you would need a penetration of the deck, the bottom of the boat, or along the sides (none of which has ever occurred), and then the water would be isolated to the single compartment where this happens, and the amount would be restricted to the very small spaces where the foam did not completely fill the compartment, or what little the closed cells would allow in. The foam is extremely adhesive and somewhat structural which assists in securing the stringers and bulkheads in a tight chop or pounding waves, as well as dampening noise. The former attribute would be lost if you line the spaces with plastic.

To me it's not the foam's ability to absorb and hold water, but how you build and seal the compartments to assure water never gets there.

12 years later I notice no increase in draft or weight of the boat and am confident everything under the sole is still solid and dry. I hope I'm right!

With all that said, the one issue I have never tested, nor want to ever test, is the location of the foam leading to the boat flipping over if ever totally swamped due to its location. However, moving the foam up along the sides would have consumed a LOT of space in a small boat like my Dory.

My 2 cents...

[fallguy1000]

What are the current thoughts on best practices for flotation foam/compartments?


Install limbers like a wet bilge and create a peek hole/dry sump area. Line with 4-6mil plastic and foam. Any leak should manifest itself at your peek. Seal the peak well; it cannot leak or it'll fool you.

Airtight or vented? If vented, how?(My boat will be outside, so don’t want mice taking up residence in my foam compartments.)

Vents are sources of ingress. Vent it if you want, use a pipe and a screen to raise the vent up. You can buy submersible vents and seat them in pvc. Epoxy won't work; seal the pvc with black mamba fhg (credits to Aripeka Angler).

Pour foam directly onto epoxy-primed wood or line compartment?

Line it.

Condensation concerns inside? How to minimize?

Condensation occurs when air is inside. To minimize condensation; you would fully seal the sole; it is hard to do well. This means no vents.

Drain and/or inspection holes needed for every one?

Limbers mean one inspection port and sump in the back.

Do any of these answers change if the compartments are above the water line? (I’m planning to have almost, if not all, of mine above the water line.)

Foam in the back should be above the waterline. In case the vessel takes on water; you put enough foam in place to offset engine and batteries above dwl.

Finally, seems like I’ve seen advice to warm the components prior to mixing to maximize expansion(?). Necessary/good idea?

Nope. You need all the time you can get.

Thanks.

Jbo

[fallguy1000]

ps

Capeman's post describes the other way to fly. Seal it well.

6 ounce glass is not enough to close the sole!

It might be good to ask him how he glassed the sole and tabbed it.

[cape man]

12 oz biax tape (2 over lapped layers) and 16 oz cloth on top (it was free).

[Jaysen]

The plastic idea was to make the foam easier to remove. I’ve seen it done two ways. One was as a “bag” taped into the compartment that allowed the foam to just be pulled out while. The other was as a kind of central “no stick” with the edges all exposed to get a seal. Again the idea was to make it easier to remove.

In my opinion, which isn’t worth much, neither method reduced stiffness or noise reduction as both methods still result in the foam pressing into the enclosed area with “crap it bulged!” levels of force.

[Dougster]

I went the Cape Man route on the LB22. Seems fine to me.

Dougster

[jbo_c]

Thanks for the replies. Only got about 3-4 more weeks before cold weather stops me, so I guess I’ll have time to decide.

Jbo