To foam or not to foam?

[ancient kayaker]

There seems to be several schools of though when it comes to buoyancy tanks:

Fill with foam so practically nothing can sink the boat

Leave them full of air so the space can be dried and checked for leaks and rot

Foam blocks have also been mentioned



What about partially filling the space with foam blocks or swimming pool noodles? That would provide reserve buoyancy in the event of a bad leak and also allow air to circulate and sniff testing to be performed. noodles would be less likely than blocks to congregate at one end, perhaps.

[Rick Willoughby]

Nothing beats solid buoyancy but it adds weight. If the boat is intended to be carried then the little extra weight reduces utility markedly.

Sold foam is certainly best in impact areas at bow and possibly stern.

Multiple sealed chambers are better than one or two.

It has been suggested to me that ping pong balls make for light weight fillers for buoyancy that achieves almost the same result as solid buoyancy providing there is no escape path. I have not found them supplied by anyone in suitable quantity.

Foam cored structure has the advantage of distributing the buoyancy. Typically considerably less dense than wood of the same strength.

Rick W

[Ad Hoc]

a.k.

It really depends what the "purpose" of adding buoyancy is for, since the solution will be dictated by the objective. Also, the hull material will also have an affect on which solution you decide to choose.

[PAR]

Air chambers can be ventilated, as you know Terry. Even with noodles or other loose fit blocks, there will be contact points where condensation can pool, collect or other wise find a place to live. Personally I don't think foam or other buoyancy device is necessary when you have an air chamber.

Now under decks, is a different story and a great place for foam. Also attached to the underside of thwarts is a good use for foam. I personally know that you're different Ancient Kayaker, but I wouldn't recommend it for the average owner, because they'd leave it unattended for a year or two. You on the other hand will keep it clean, dry and well stored. In this case it would be your call: "to foam or not to foam, that is the question". The pound or two the foam would add, will not affect the design you're building.

[apex1]

NOT


thats it.

Regards
Richard

[ancient kayaker]

Adding all the advice up, first the objective, which is to be able to right the boat easily after a blowdown and to survive an encounter with a rock or bigger, harder boat. No thwarts on this boat. The hull material is wood so prevention of rot is a factor.

All good advice, which seems to indicate I should have multiple sealed buoyancy chambers, capable of ventilation, and not foam filled. So be it.

Thank you!

[Ad Hoc]

what size is the boat...if not too big....fill it with foam, if you have the spare volume...just be careful with the type of foam and you'll need to protect the wood. Make sure it is not hygroscopic too.

[gonzo]

Many racing dinghies, where weight is a huge concern, use inflatable bags. They can be easily removed to clean and dry behind.

[ancient kayaker]

Many racing dinghies, where weight is a huge concern, use inflatable bags. They can be easily removed to clean and dry behind.

I'll look into that, not sure what sizes and shapes are available though.

[Ad Hoc]

a.k.
if you're concerned about a grounding, as one possible scenario, then air bags if inflated in the same 'compartment' may just burst or split when inflated on the object that has punctured the hull..

[Fanie]

Hi Ancient,

I believe that foam should be part of the design of a boat. I tell you it is a comforting thought to know your boat cannot sink, no matter what happens, hell or high water.

I agree with Par. The added weight is nothing compared to the advantages. Heat and noise insulation, permanent floatation, structural enhancemant etc etc. There is only one disadvantage, the little weight added. Anything elso is a plus.

If you look to add booyancy you will find lots of space for it. Any unused space can be turned into a feature - and added booyancy.

Personally I don't trust pour foams. I haven't seen one I would use on my boat.

I have mentioned before that I use PE foam. Now I agree it can be a pain to shape it to fit in some cavity, BUT, you need to do it only once. One big advantage of this foam is it can be formed to some extent. If you push the shaped piece into a cavity, you can force it in and it shapes itself in there.

Is this for a new build or floatation for an existing boat ?

[Landlubber]

On small craft with inspection ports in chambers, the very cheapest foam bouyancy is those foam squiggle noodles used in packaging for electronics, available for free from the local electronic store, they have to pay for them to be removed. You can change them ever few years so they are always fresh, and cost zilch.

[ancient kayaker]

Damage from grounding is unlikely as the boat is small and slow; it’s the guy with the twelve-pack under the thwart or the teen on the seadoo that concern me.

I will have lots of buoyancy, about 500 lb on a 10 ft boat. There will be one tank per side, about 7' x 1' x 9", tapering at each end. They are that large because I want to try to see if I can right it after a knockdown with no need for bailing. They are also the seats and the side decks. This a a new build, by the way, haven't started yet but I'm cleaning up the workshop.

I thought a few long skinny noodles would stay put in the long narrow space and still permit drying through a single ventilation port. Par’s point about condensation at contact points is well taken, but a couple of years ago I saw some noodles with a spiral shape that might minimise that effect, if they are still available: I will take a trip to the local pool shop. I can also reach in and move them around occasionally.

I don’t like the idea of pour foams either, I would worry about rot due to an undetected leak and also excessive pressure since this boat is lightly built (it’s to be a car topper).

The foam squiggles is an idea although with a really serious hole they might float out; but I like the idea of being paid to take them away!

The air bags are probably the most expensive solution and could likewise be holed but they are pretty tough so it’s unlikely.

Dividing the spaces into several compartments complicates the build, not so much because of the partitions but because of the extra ventilation ports required. Interestingly, stability analysis suggests that the boat would remain afloat with an entire side tank flooded provided the inside wall of the tank did not also fail. It more or less becomes a narrower boat.

An impact capable of holing a sheer plank would most likely flip the boat and might even destroy it entirely, but it is likely that the remaining tank would survive. I made an ama for a sailing canoe a few years back that did not work too well; when it came time to trash it I was amazed at how much punishment it stood up to, and it was much lighter construction than I plan for the boat.

It would be easy to add solid foam under the foredeck, which will be roughly 5 sq ft. I can put at least 4 inches in and carve it to fit before gluing down the deck.

One idea would be an air-inflated dry-storage bag in each tank near the stern, they are removable and attached to hatches meant for kayaks, and will double for inspection. With the deck foam, even if the boat gets totally trashed that would provide enough buoyancy to keep the remains afloat.

[Ad Hoc]

To make the details easier to understand and give perhaps better advice etc, do you have a GA..otherwise we are all just talking about...well, talking!

[Zed]

FWIW I removed polyurethane foam from a 20 year old ply trailer sailor, it was still stuck fast with absolutely not sign of moisture or rot under it. In fact it was a pain to remove. I think that it weighs around 1kg per 25 cubic feet (?).

Edit: Just looked that up, they say 28 kg m3 that would make 25 ft3 19.6kg. I remember it making 25 cubic ft per litre mixed and it was no where near that heavy. I must have something wrong!

[keith66]

Over the years i have worked on a lot of boats with foamed hull parts, i hate the stuff! often the foam is waterlogged where it will cause problems. Buoyancy bags are good in small boats, available in many different sizes they are made by Holt Allen & Crewsaver in the UK, the latter are particularly durable.

[Wynand N]

With new compulsory buoyancy/flotation laws in my country, this is the buzz word in boating now.
My company install buoyancy and issue certificates according to our governing body SAAMSA and the only buoyancy aid approved by them is close cell expanded polyurethane foam - we use Resicon 44V20 type. Spaghetti noodles, polystyrene, bottles and other strange things are a taboo.

The difference this foam make to a boat is astounding in overall stiffness. We build a bass boat of 4.5meters (15 feet) in length and whilst the hull is still in the mold, we pour/spray the foam into the hull up to the floor level which amounts for about 310 liters of foam. It is then smoothed level, a 4mm plywood fitted over that and glassed over. Take note that NO longitudinal stringers or transverse frames/floor supports are fitted to the bare hull molding.
You can jump on this floor without denting it even a mm and the hull sounds solid from the outside.
One has to experience the stiffness and silence of these hulls through a chop on water compared with hulls without with foam fitted with floors/framing etc and the security that nothing can sink you even if you tear the hull open from bow to stern...
This bass boat only weighs 170kgs and she carries a beam of 1.95meter.

ZED, PU expanded foam weigh about 38kg per cubic meter (1000 liters)

[Zed]

OK...thks what's the expansion ratio? i.e. What does a litre of mixed material expand to? I had a friend that pumped it into the rails of his Datsun 1600 rally car, said that it stiffened the car a lot !

[Zed]

I remember now... it was 25/6 times volume mixed, 1l = 25l blown... that right?

[Wynand N]

right

[Fanie]

I will have lots of buoyancy, about 500 lb on a 10 ft boat.

500lb is going to be a bit heavy for a small boat, don't you think, and where will you put all that foam :D

[PAR]

Terry you only need about 4 cubic feet of foam. If it's a structural foam (lets say 8 pound density stuff) this will be about 215 pounds of buoyancy. If you use a light foam, like 2 pound density you'll get 240 pounds of lift. This is enough to permit your boat to swamp, completely filled with water, yet the rails will be above water, so you can pump or bail it out. There is such a thing as too much buoyancy, which shows up in a capsize. The boat floats on it side at about 95 degrees to upright, but causes it to float very high, making righting it more difficult. Ideally you'll want about 1/4 of the beam immersed in this situation, so you can grab the dagger board and leverage the boat back to her feet, maybe in concert with pressure on the halyard.

[Ike]

Terry

I have been involved with flotation in small boats for over 30 years, testing for flotation, repairing boats without enough or none, and all other aspects. There are many solutions, but foam is by far the simplest. But, it has it's down side.

As has been said here, pour foam, also called two part or spray foam, has it's problems. The major problem is water absorption. This is almost always due to improper installation, that is, not following the foam manufacturer's instructions to the letter, including such things a the right temperature and humidity. All of this can be eliminated simply by using pre-made foam blocks. They do not absorb water. We did a two year testing program on block foam and no water was absorbed in 2 years of immersion.

Polyurethane is the preffered type. It is solid, reliable, and is resistant to oils, gasoline and other solvents. PolyEthylene is also a good choice. That is what pool noodles are made of. It too is resistant to oils and gasoline.

As Par said, 4 cu feet of two pound density foam will give you about 240 lbs of buoyancy. This is far more than you need. I have about 2 cu feet of foam in my 12 foot rowboat, and it is rated for three people and a 2 hp outboard. Actually I ran all the calculations and I only need about 1 cubic foot but I added a little to make it float higher when swamped. As with you I want to be able to right the boat and get the water out. As for the weight of foam, 1 cubic foot of 2 lb density weighs 2 lbs. 4 cubic feet would weigh 8 lbs. This will hardly make a difference on the weight of the boat.

Some will say air chambers are fine. Well, they do work fine as long as they don't leak. Many builders use them on small dinghies and other small craft.

I think I was the one who suggested ping pong balls. Many years ago, back in the late 80's I actually tested a boat that had ping pong balls for flotation and they worked just fine. But as was said, where do you get them in large enough quantities? Actually most anything that traps air, and excludes water will work. I have seen air bags, plastic bottles, coke cans, and other stuff.

In my rowboat I used Polystryrene insulation foam. It is 2 pound density and comes in 2 by 8 foot sheets 2 inches thick at almost any harware or home improvement store, and it's cheap. I cut the sheet into convenient sizes and then encased the foam in fiberglass using epoxy resin. The glass was used just in case I do spill some gasoline from the O/B. If you don't have that problem then you don't need to protect the foam.

So my vote goes for foam, but not pour foam. Use pre-manufactured block foam.

[ancient kayaker]

As the design stand at present I have about 4 cu ft air per side tank, which will have smaller internal air bags at the stern, plus maybe 1 cu ft of foam under the foredeck.

I can get the air bags from a store that supplies small boat fittings fairly close to home. A friend of mine happens to have a couple of about the right size intended for a sailing canoe, which he has shelved for the time being; I'll make him an offer. They are very tough and hard to puncture, designed to be removed from the cavity and used for keeping camping supplies dry.

The polystyrene foam is available locally; I have used it before and it is very easy to work with, fairly cheap too. I will use it under the deck and either make it a loose fit in an unsealed cavity or make it removable.

If I have an outboard it will be an electric trolling motor as outboards are not permitted in some areas I visit, so fuel resistance is not an issue.

The tanks perform other functions as well as buoyancy, they serve as seats, side decks and structural stiffening. Capsizing will be prevented by the buoyant mast. I am hoping righting her can be done from inside the boat, but I can check all that in my pool before venturing into a lake, including righting using the daggerboard or other means.

I am surprised at how complicated this simple sounding question became; there were a lot of suggestions and information and I greatly appreciate you taking the time to answer in such depth. thank you.