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.

[Guest625101138]

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.

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]

Originally Posted by gonzo

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!