Foam under sole?

I am replacing the rear section of the sole in my 1987 Sylvan - VERY rotten and disgusting! - and I see the factory filled the void under the sole with expanding foam - great idea for manufacturing - extra support, no floor squeaks, and some condensation resistance. On the other hand, it traps moisture against the hull and the under-side of the sole sheeting, prevents drainage, and inhibits air circulation.

I am tempted to replace the sole and provide ribs to improve the strength.

What is the experience of them what's done sole replacements? Which is best - air space or foam?

 

Air space absolutely. You want to allow drainage and promote air circulation.
Framing new with wood, you can use plywood or solid wood for frames, or a combination of the two.
Describe the size of the boat, and the depth of the bilge. Have you worked with epoxy and glass before? As you have discovered, factory builds don't seem to anticipate a hull life exceeding 10-20 years, while a proper construction can last far longer.
Two issues: support of a live load above and maintaining hull shape below. No two hulls are shaped alike, so it would help if you showed us some photos of the hull inside after the foam is removed. Include the depth from keel to sole at its deepest.

 

Alan knows of what he speaks. I've found ventilation to be so important that I did an experiment this winter. I installed two small AC fans in my boat while it's in storage. The boat is in a yard, adjacent to a river about 120 miles north of New York City. Of course it's damp and cold and rainy and I've always noticed most of the boats in the yard come out of storage smelly, moldy and in need of a good clean up. Well, I've been restoring my old Silverton over the past few years and got the cabin fabricated in the fall. Not wanting a moldy, smelly cabin after all my hard work I decided to connect these fans to a timer and run them for three hours in the morning and three hours in the evening. I was down there yesterday checking on my boat. Guess what? That small amount of forced ventilation (one fan in the main cabin and the other ventilating the engine compartment) provided enough airflow to keep the boat bone dry and looking and smelling clean as a whistle. No condensation whatsoever. I've decided that I'm going to continue this while the boat is docked this summer. Assuming I get the rest of the restoration done in time!

Go for as much ventilation as you can.

MIA

 

Okay, air space it will be - that was my preference anyway.

It is a 21 foot aluminum hull, about 6" drop from the bilge to the chine and only about 20" to span (with 1/2" marine ply) between the stringer and the chine so it wont take much for ribs.

I have experience with glassing (mostly aircraft) and many decades in engineering so I think I will be fine.

I LIKE the idea of fans! When I re-do the rest of the sole (next winter), I will include a couple of 115V muffin fans to push a little air down the outboard sections and down the bilge (they're cheap).

Thanks guys!

 

The foam is there to provide the required emergency floatation.

 

I figured it was there for flotation ..... I can swim!



Got the foam ripped out along the port side. Looks like I can get by with one wood stringer half way between the metal stringer and the chine.

This boat had sort of a "manhole" in the centre of the sole with a wood grate over it. Under the floor there is a second sheet of aluminium, sort of like a trough, that would have drained to the bilge through a grate. I presume this had something to do with being a fishing boat.

I intend NOT to create the same "manhole" in the new sole, just a solid floor, but the dirty so-and-sos riveted that extra sheet of aluminium directly to the hull so I can't remove it.

I can't believe how much WATER is in the foam! Every place I squeeze the foam, it oozes water and this boat hasn't been in the water for more than 2 years. It is going to be a few hundred pounds lighter than when it last came out of the water

VENTILATION VENTILATION VENTILATION!

 

I had an old Glastron years back. When I went to replace the fuel tank, same thing. I don't think that they knew (or cared) about the differences between closed and open cell foam back then. Well, at least you'll get it fixed!

MIA

 

You might want to check with your local authorities & insurance company. In some places floatation foam is a legal requirement. If you do have to replace it you can get closed cell foam in sheets that is semi rigid so you can put some in sitting of the stringers which will still allow some ventilation and drainage.

 

Gonzo has a point. However, there are a lot of places aboard to hide flotation. If you can get the flotation up high, do it. The bilge is no place for foam. Use your imagination.

 

Well now that would complicate things!

As a fishing boat (very open design) they pretty much had foam in every enclosed space - expanded foam under the floor and sheets of rigid foam behind the side panels - and I doubt if they achieved neutral buoyancy even with that but they must have had enough buoyancy to get certified. So I guess I better look into the regulations.

 

I can see the point about the foam as floation but here's my question.

If the foam was open cell and just soaked up water, would it make any difference if the boat were to actually go down? Seem's to me that water filled foam would weigh about as much as plain old water.....

 

I would put it down the centre and any extra that is required under the seats (assuming you have pressed bench seats) or under the gunwales.

 

Dianne, you're in Manitoba so the Canadian rules apply, which require flotation in NEW boats under 6 meters (19 ft 8 inches) in length. Look here http://www.tc.gc.ca/eng/marinesafety/tp-tp1332-section4-1346.htm#monohull. Since your boat is over that length it was not required to have flotation, but that is what the flotation under the sole was for. Plus that the boat is over 20 years old so the rules most likely no longer apply. But check with the Canadian Boating Safety Office.

Everyone is right that ventilation is a good thing, but they are wrong in that flotation is not. Flotation does not require foam. It can be sealed air compartments, sealed plastic bottles, ping pong balls or anything that traps air or excludes water and provides the right amount of flotation to float the boat, the machinery and the people. On the web site link I gave you it shows the formulas for calculating that. It's also at my web site http://newboatbuilders.com/pages/flot.html You didn't say if this is an outboard or inboard. Either way, at that legnth they were probably just providing basic flotation, not level flotation. Basic means the boat just doesn't sink. So if you want to replace the foam you can put it anywhere in the boat there is space.

Foam soaking up water is a huge problem with pour or spray foam (actually the same stuff, 2 part foam) It is better to use pre made block foam, preferably closed cell polyurethane foam. However, polystyrene, styrofoam, will work fine if it is placed where oils, gas, and other strong solvents can't get to it, or it is encased in glass or plastic. Polystyrene insulation foam from Home Depot provides the flotation in my 12 foot rowboat and works just fine.

Swimming is not the issue here, survival is. The water in Canada is really cold year round. Without a survival suit you wouldn't last long.

 

Interesting stuff Ike. What I read on the two links you posted pertains to fairly small craft (20 feet LOA). I'm guessing on larger boats these requirements are considered impractical? My 27' Silverton (1973 build year) had no foam in it whatsoever when I disassembled her.

Thank you for the links,

MIA

 

Wow! Great post Ike - just the information I was going to search for.

The boat is an I/O, guestimated all-up weight of 2500 pounds.

I considered using SM foam sheet under the floor but don't want it to squeak. It would also be a pain to cut to the required wedge shape. My boyfriend suggested plastic pop bottles LOL!