TOPIC: foam under the floor ?

I have seen on several restoration videos on youtube ,that many people are using a two part foam filler in the space under the floor. It seems to me that all it will do is trap water,and eventually become water logged . So, am I missing somthing? what are the pros and cons of using these products? what are the right and wrong ways to using them?

I'm no chemist, nor an expert on boat building / restoration. There are several schools of thought on the under-floor foam, it's an opinion thing much like many other topics found here. At the end of the day it's a judgement call only you can make. We do the best we can with what we have to work with, right!? A couple of points I learned from my research;

The two part foam today is made of much more advanced materials, I don't think there is an issue with absorbing water if you use a reputable product. US Composites, Express Composites, West Marine, and numerous other suppliers sell tried and proven products that are designed for the marine environment. Ole Red has found some stuff out in OKLA they use to set telephone/power poles and the like with, said to be very sturdy and of the "closed cell" design.

Many advise the under floor foam ads hull rigidity and sound deadening qualities to their rebuild, not to even mention the "floatation" aspect of reasoning. Should the boat ever get swamped or take on water, the thought of it NOT going straight to the bottom could gain merit in a big way. Will the under floor foam itself keep the boat afloat - maybe (probably?) not but it's a start, right?

If your hull is watertight, the floor (sole) is properly glassed in, how is water going to get into the cavity to start with? (Some have mentioned condensation from temperature changes, I store my boat in the garage when not in use.) Some sort of drainage and/or ventilation points have been suggested, there are good arguments both pro and con IMHO.

Just my two cents worth, hopefully others will be glad to give their opinions as well.

All New boats under 22 ft must have flotation foam added to the hull with enough capacity to enable level flotation of the hull by regulation of the USCG. But this does NOT apply to Back Yard Boat Builders. So as Mark states it's totally up to you if you want to use it. The 2 Part pourable foam of today is almost but not totally impervious to water penetration and it does add a lot to the strength of your hull. It's very easy to use but adds about 5-6 hundred dollars to the price of your build. A lot of guys use the Pink or Blue SLAP foam from the Big Box stores and cut and shape it to conform to the areas below the deck. Problem with it is gasoline with EAT it. Bottom line...Your Boat...Your Choice!!!

Happy New Year!!!

I put in my boat. We had a pretty lengthy discussion about here www.fiberglassics.com/fiberglassics-forums/home/main-forum/advice-needed-on-venting-sealed-bilge

Bottom line for me is that I would do it again, but I would make sure there was a way for any water that did get in to get out.

Hope the discussion helps,
Bill

A way for water to get out is also a way for water to get in. I fill the area beneath the flooring with foam to above the height of the stringers and then shave it off level. After the marine plywood is in, I totally seal everything with fiberglass mat to a point about 4" up sides of the hull. The result is a rock solid floor under foot, substantial hull stiffening and maximum floatation. If my system fails when the boat is another 50 years older, I won't be involved with the repairs.

I'm totally in support of the foam. When I put it under the floor of my Johnson Deluxe it became rock solid and deadened that hollow sound. I put my deck down first, fileted, and tabbed it in. Then I bored holes in the deck to pour the foam under the deck. I made sure there were extra holes to let air escape. PB'ed the wood plugs back in and laid 2 layers of chopped strand mat over the entire deck and up the sides several inches to create a type of bathtub to keep water out. The trick is to not ever screw into that part of the deck, but glass in an extra layer where needed to fasten everything down without penetrating the bathtub.


I bored 27 holes total.

Keep the wood plugs to glue back in.

Ready to mix and pour. I had about 30 seconds to mix it up and pour it in.

You can see it expanding in the cavity and you will feel the deck and hull get warm everywhere it touches. That helped me know it expanded nearly everywhere.

After the foam had hardened.

Remember that plug?

Glued back in with peanut butter.

After sanding and the 2 layers of CSM. You have to look hard to see the 27 holes I bored into the deck.

Andrew had better luck than we did the first time. We bored 2" holes and poured in foam...what we "thought" was the right amount. The foam came up out of the holes and then hardened...but the foam beneath wasn't finished doing it's thing. The result was that we stood there and watched the expanding foam make the decking convex...a lot! So...we tore all the decking up...not much choice. That was when we found that there were a LOT of voids beneath the floor where no foam had spread. We shaved the foam to the level of the framework, added more foam to fill the voids, shaved again and then installed another floor. From then on, we have used the "overfill and shave" method. The decking goes on after all the foam is level with the framework. No problems. (See the "after" photo in my post above.) I like no problems.

I'm positive there are some small voids that didn't get filled as the foam expanded. The only way to ensure you get everything is to apply the foam like Jan did. I poured 7 mixed gallons under my deck, enough to float more than 4000 pounds, I figured that was enough to do the job and I couldn't find any big areas that didn't get warm to the touch. I was happy with how it turned out.

Actually there IS one other way. Use a piece of 3/4" Malamine with plastic stapled to it that's cut to fit over the area to be filled with foam. Do your calculations for the amount of foam needed, mix it up and do the pour. Place the panel on top Plastic side down and then get a Fat Guy, ( I Qualify !!!) to stand on the board for about 5 minutes. If you do your calculations just right it should expand and Maybe lift the board (and the Fat Guy) just a bit and fill the cavity just right, Your waste, trimming, and fill-in will be very minimal. That's my story an I'm stickin to it!!!

Wow! thanks for all the input.I really did not expect this much response. I was planning to use foam to fill under the floor,but I did not know all the benefits.I can't make up my mind to do somthing with out knowing why. even if everyone is doing it. the Performer does not look to have a very large cavity under the floor,so I don't think I will gain much in the extra floatation department.The extra hull rigidity and sound deadining seems like a good enough reason to include foam in my plans.

How about some thoughts about adding foam in a boat that did not originally have it. I am thinking about my 59 Glastron. It would be easy to seal up the spaces between the stringers and pour foam. However, the stringers themselves are inverted fiberglass channels and could probably not be properly filled. Sealing off the "drains" (see photo) would itself be easy, but would this create a potential problem elsewhere? Would I still need to have a drain for inside the stringers?

You asked for thoughts so here goes. I have never tried this, but I think it would work. Basically you want to provide a drain path for any water that might get in. How could it get into a sealed bilge you say? Well, how about a situation where you have just beached the boat on a nice sandy shoreline but there were stones that you didn't see that rubbed off the gelcoat on a spot on your keel. Now you have water getting into the bilge but no way for it to get out if it is completely foamed and sealed. So, what if prior to foaming the area you lay down some plastic sheeting (maybe just some trash bags) in the bilge. You would not want o cover every area as you want the foam to adhere to the bottom in some spots for rigidity. You also leave the drains open by covering over with the plastic. Then you add the foam. Now, if any water gets in it can drain under the plastic (which is under the foam) to the rear where you would have a small well area with a conventional drain trough the transom.

I think this method would allow the original intent of the design to function so far a draining water out; while giving the advantages of floatation safety, and hull dampening that foam provides. However, as someone pointed out, this method could also allow water to get into the bilge through the well under some conditions, so it is not without concerns. The attached photo of my Saber Craft shows the well area that I am talking about. I just foamed and sealed this boat and then provided a small vent. I only thought about the plastic idea after it was all done. I think I will always wonder if the boat is really perfectly sealed and whether the foam is getting soaked. No way to know unless the boat starts to get real heavy.

Just some thoughts,
Bill

No photo sent - Too large to attach so I have to learn this new computer ( a Mac).

But, I'm sure you get the idea.

I would think that if you put a hole in your boat, all bets would be off anyway. I could alway epxoy a layer of Kevlar to help prevent puncture, but not sure if that is really necessary.

The boat does have a "well" at the transom where the stern plug is located. There is a drain hole on each side into the stringers and one (I believe similar to what is shown) to drain the center sections. My thought wa to seal off the center sections, including the center hole in the well and fill with compatrments with foam. Keep the holes in the side or install a couple of dinghy drain plugs to keep water from getting in through the back.

An ounce of prevention is worth a pound of cure. Ben Franklin

There is a remote chance that water could get into my basement, do I dig a ditch to give the water a place to go or take every precaution to keep it out?

I would say 95% of the waterlogged foam we find in these classic boats is caused be shear neglect (sitting for many years in the weather with standing water, leaves, and debris) during the years they were considered old junk boats. Seal that deck up as tight as you can, put in all the foam it can hold and take care of it. The occasional water from normal use isn't going to do the damage that 20 plus years of neglect did.

i'm sure glad i don't have to adress this problem as i don't have a floor in the mantaray. the hull is the floor. but theres also a downside to that design. it will probably sink like a hunk of lead if capsized since theres also no foam. adding about 10 foam noodles under the deck hopefully will keep the bow barely afloat for rescue if ever it should fill with water. ron

Mark S said it better than i could have but general thought if you can afford it and plan to use your boat than definatly do it! i love us composites great prices,delivery, and support. Best of luck with your build and the foam is easy to use. I prefer foam,trim, deck, glass over method myself.

Lots of good replies here. But I may be able to add some insights. I spent many years running the US Coast Guard's program testing boats for flotation.

Simply put, if flotation is installed correctly it works. It keeps the boat afloat and provides a much better platform to sit on and one that is easier for rescuers to see. It saves lives.

But then the question arises, how to install flotation? By the way, it doesn't have to be foam. I have seen everything from beer cans to ping pong balls used as flotation. If it displaces enough water then it works.

So, what did I do on my own boat?

I used polystyrene foam from Home depot. 2 inch thick planks, 2 feet by 8 feet. I cut the planks into pieces to fit into the voids. But first, I coated all exposed wood with clear penetrating epoxy sealer, and then several coats of regular epoxy over fiberglass. No water can get into that wood. I then bagged all the foam, that is, encased it in polyvinyl plastic sheeting and sealed it. So no water or any other liquids, like gasoline, can get to the foam.

see here: http://newboatbuilders.com/pages/SeaRay190.html

There a lots of ways to do this but this way ensures no wood rot, and no water in the foam, as well as no foam degradation due to things getting to it that shouldn't.

I could go on at great length about studies done on why some foam absorbs water and some doesn't, but if you search the posts here I think you will find other posts I have made on that subject. http://www.fiberglassics.com/fiberglassics-forums/home/main-forum/wet-foam-what-a-pain#66690

I think one way to know if you were having an unseen problem would be to weigh your boat first thing after the rebuild and keep track of any additional toys you ad later, then at the end of the season weigh it again. account for any weight you have added . then if there was a big difference you know you have got a problem. most gravel yards will weigh for a small fee. also most truck stops(not all) have scales.they are usually about ten bucks for each weigh. I will caution the use of these as they only weigh in 20 pound increments.

The recycling place near me will let me drive over their scale gratis if there's nobody in line. Just drive up til the tow vehicle tires are just off the scale, drop the tongue. She gives me a weight slip. 1 trip w/ boat & trailer, then later same day trip w/out boat. Gives me both trailer weight & boat weight.

It may help that I recycle there for both personal & work recycling, so they may recognize me. But it's usually pretty busy, so I doubt that has anything to do w/ it.

A question: I see old floating boat dock foam block a marine business quite often. Would this foam be good to use? Would it absorb water?


It seems putting all of most of the floatation under the floor would result in the boat flipping upside down if it were to take on water.

Wouldn't placing it higher make it more likely that though the boat may take on water, that at least it would stay upright?

It seems it would be a big plus to stay upright.

that is what i used, the rule is now the foam dock floats have to be the black capsulized kind that the animals cant eat and wont wreck the water, i called a local dock company and they had just removed about a 4x8 piece and replaced it with the new. he said come get it , i mainly used it to support the boat when i took it off the trailer i could mold it to fit the keel and stern . and i knew i was going to use it to fill the floor . i did and then i glassed the floor in and then there was the remarks of ventilation
under the floor. so i might have went overboard but i sealed the floor up tight and then drilled a three inch hole . i hope i can keep and water out but if i do seem to get any in i have the ability to circulate air through and eventually dry it out. so just another opinion ... but i like the idea to weigh the final product and keep tabs on it. another good idea. and i still have the below the deck drain hole too.

Do any of you seal the glass with resin or epoxy paint before pouring the foam? I think I will be using a combination pink or blue foam and then brace across the top. Then pour foam along edges and under block foam.

When I was wrestling with the foam issue (could I afford it, was it necessary, etc.) I decided the foam had to do 3 things if I put it back under floor.

1. Keep the boat from sinking if the worst ever happened.

2. Fill the hollow cavities and deaden the sound.

3. Add strength to the hull.

By using the mix and pour foam made specifically for this and pouring it under after the deck was tabbed in accomplished all three.

1. I added 7 gallons of floatation foam under the deck, enough to float more than 4000 pounds (my Deluxe will weigh 2500 tops).

2. The foam expands to fill the hollow cavities. I drilled extra vent holes around the perimeter and the foam came out all of them. That also let me know it expanded through out.

3. This foam sticks like glue to whatever it touches, so it created a mechanical bond between the deck and hull that added the extra strength.

If I had to do it again I would do it the same way.

I would not mix foam blocks with pour-in-place foam. The agents in the pour in place might react with the blocks and you could end up with a gooey mess. Gooey mess is not something that should be a part of boat construction.

I use the best marine products that exist for every facet of boat restoration. The time/cost of restoration labor is always the same. The only difference is the cost between the marine and non-marine materials, which really have no place in a boat. To me, that difference in price does not justify experimentation with materials created for other than marine applications. Stuffing a bilge full of "noodles" or cut-up blocks of styrofoam is simply a bad idea.

Nautilus, I like how your floors turn out and was wondering what you used to shave the foam to get it level on the floors. I think not only is it great for the floatation aspect, but also the sound deadening affect as well. I see that you are in South Carolina, I was just there over Christmas as I have a brother in Sullivans Island. He does a lot of boat projects down on the island. He is currently rebuilding an old Ashcraft into a flats boat for his son.

We experimented with a few ideas for shaving off the foam but the one that worked best is a 30" long piece of a 1" wide aggressive-tooth band saw blade. We wrapped the ends of it with duct tape and use it so that the blade cuts when you pull, not push. It works better with someone on the other end. The operation needs to be done twice. After the original giant globs are shaved level, more foam needs to be added here and there to fill the pockets that were below the framework. A palm sander with a 60 grit disc can be used to "fine tune" the top of the foam and clean off the framework.

A plain ole' carpenters coarse tooth rip saw works well too!!!

Yes, a rip saw (or back saw, crosscut saw, whatever) will cut the foam but the handle (and your hand) prevents getting level with the framing. Also, the blade is too short to span the distance between the frames.

I neglected to mention that we bent 4" of both ends of the band saw blade at a 90-degree angle so that the portion wrapped with duct tape sticks up to foam a handle. All cuts are level with the framing.

I was thinking one of those wire camp saws

I love all of the home-made tools and ideas that get done when working on a project. It never ceases to amaze me as to what we need to do to get the job done! I have been pretty creative with clamps, but the band saw blade is one that is pretty cool. I was looking at the flats boat that my brother is rebuilding and he glasses in PVC pipes in the forward bulk head on both hull sides for rod storage. He spends a lot of time working on ergonomics, placement, weight distribution etc, when designing his boat projects. Love to see everyones interpretation on what works for their specific needs an boats that they are working on. Pretty fun to see!

I always try to come up with new ways of getting a job done. Recently, I came up with an idea for a miniature marine propulsion unit for vintage fiberglass runabouts but I'm having a tough time finding weapons grade plutonium. The guy at Ace hardware looked at me like I was crazy. Duh! As if....! Obviously, he couldn't recognize a visionary when he saw one.

(Notice how I mounted the propeller in the bow...revolutionary concept!)

Hey this is an EAZY one...

All you got to say is..."Beam Me Up Scottie!""

Works Every Time!!!!

Search eBay for weapons grade plutonium. The feds will be knocking at your door soon enough.

Nautilus wrote:

A way for water to get out is also a way for water to get in. I fill the area beneath the flooring with foam to above the height of the stringers and then shave it off level. After the marine plywood is in, I totally seal everything with fiberglass mat to a point about 4" up sides of the hull. The result is a rock solid floor under foot, substantial hull stiffening and maximum floatation. If my system fails when the boat is another 50 years older, I won't be involved with the repairs.

This is how I plan to install the foam on the Custom Craft.

I'm pleased to see a restorer of Jan's pedigree agrees with me.

Any voids will allow moisture from condensation to accumulate. It's the same for houses, you either have to super insulate with no voids, or allow for ventilation.


Nautilus wrote:

I use the best marine products that exist for every facet of boat restoration. The time/cost of restoration labor is always the same. The only difference is the cost between the marine and non-marine materials, which really have no place in a boat. To me, that difference in price does not justify experimentation with materials created for other than marine applications.

Couldn't agree more!

Put hand holds on the bottom of your Classic if you put foam in the area between the hull and the cockpit floor. Foam, for safety's sake, needs to go as high as possible under the deck, with more going where the major weights are located.

I have been upside down in a boat floating with the bottom "turning turtle" and could not stay with the boat. No place to hold on!

Foam in that space for other reasons has been well covered in this thread.