floatation foam

Most boat manufacturers use two part spray (or pour) polyurethane foam that is mixed automatically and injected into the compartment. It has it's advantages: Convenient, because you can build in compartments and fill them through a small hole. It will fill any shaped compartment. It is impervious to oil, gas, bilge cleaners and so on.

Disadvantages: The injection process is sensitive to temperature, humidity, dirt in the gun, mixing ratios, and the exotherm of the foam as it expands. If it gets to hot you get broken glass. If it doesn't get hot enough you get bread dough.

Get it right and it's great stuff. Get it wrong (which happens frequently) and it absorbs water like a sponge.

Some manufacturers (usually small aluminum boats) use polystyrene block foam. They build compartments under seats and put in the foam before the box is fastened under the seat. The foam is not in the bilge and completely enclosed so it is never exposed to gas, oil or cleaners that would dissolve it. But styrofoam is also friable, that is goes to little pieces (we have all seen them) as it ages, and is susceptible to shock and vibration. Polyester resins will dissolve it so if you coat it with fiberglass you must use and poxy resin.

Others use extruded polystyrene which is readily available as sheets, almost any hardware store carries it, and is cheap. But like the regular styrofoam it needs to be protected or placed where it won't be exposed to gas, oli, etc. I bag it in polyvinyl plastic sheets, seal it in. Water can't touch it and neither can gas and oil. It doesn't go to pieces when subject to shock and vibration like regular styrofoam. You can also seal it in fiberglass using epoxy resin. Do not use polyester resin, it dissolves polystyrene.

On small boats, usually dinghies or rowboats, air chambers are the flotation of choice. They are easy to build in, provide stability for a swamped boat, and don't flood because these little boats are usually too slow to be easily holed by rocks, logs and other debris.

There are other solutions as well but those three are the most popular.

 

That is certainly a good option, next time I'm looking for foam I'll price it. The weight seems comparable.

 

I've cut enough floors and fuel tanks out of stink boats to have learn't that two part polyurethane foams have a limited life before it all becomes a sodden sponge, not in my boat !

 

That would be the 2lb/cuft mix, 4lb/cuft seems to be a different story. But the extra weight is a deterrent.

 

I did extensive tests with the 2-part foam because it seems like a very attractive option. I decided never to use it, firstly because the stuff is extremely dangerous when exposed to open flame - and the non-flammable ingredients are even worse. One only needs to read up on the Japanese PU bank robbery and the Bali PU disco disasters to mention two examples to realize how poisonous the gasses are even of the foam doesn't burn itself.

Consider that you are never going to get a fire aboard, and apart from that the foam actually does absorb moisture over time, the next thing I very much disliked about it is that if a piece cracks off or comes loose it acts like sandpaper to the next piece. Boats does flex and this foam does not like flex.

I got the impression that they only use the foam since most people goes to water so few and far between that by the time they have a complaint about the water absorption the defense is the boat is "old".... 3 to 5 years, which imo is brand new, boats last many many years. I even had the distributor here in SA take me on on a public forum and when I started publishing the truth about the foam he wanted to continue the argument offline and then he wanted to end the argument quietly. They are fully aware of the problems.

The two part foam is not a marine foam, it is an insulation foam. And for insulation is is good if you never get a fire. It is easy to apply and yes it does make the form more rigid when poured. I however absolutely dislike that they lie about the dangers and shortcomings just to make the few extra bucks. They even got the foam to be classified as "green" - it is not.

 

Maybe Mr Fanie, would be so kind as to be more specific about this very good foam he knows, like mentioning the technical name of the product or the brand or commercial name so if anyone is interested at least have a clue to try to find it ...

 

Check out this link: http://www.sondor.co.za/pg.php?pid=10

This taken from the Sondor Industries webpage re their buoyancy foam and I quote:

" Sondor's foam is a fully cross-linked closed cell expanded polyethylene. It has excellent buoyancy characteristics - able to support approx. 1000 Kg/m³. Our SPX is fully closed-cell, and will not absorb water even if the material is cut open.

It has superior tensile strength, elongation and weathering capabilities, and is resistant to chemicals, oils and fuels. Sondor SPX complies with SAMSA regulations section 9 & 9.1 regarding floatation requirements. [Category A-E: (Off-shore) as well as category R: (Inland waters)] "

Hope it helped you.

Here is a picture of a piece of the foam turned on a lathe I have made by Sondor Industries Fanie mentioned.
It indeed has all the advantages Fanie mentioned and more - just a bit expensive though.

 

I had a piece lie in the sun for about 5 years, it changed color from an almost black to a slightly more dark charcoal, and that was all. You can squeeze a piece flat as hard as you can, dunk it under water and release. Take it out, dab it off with absorbent paper like toilet paper to dry off excess water, then squeeze to see if any water comes out. Nothing, not one single drop.

In thin sheets it feels soft, but thick it becomes quite rigid, I jumped off the workshop table on about 200mm thick and thought I was going to break my legs...

Had the idea for a long time to make big blocks, then mill a boat shape, glass it over and cut the cavities like seating, cupboards etc. out Permanent flotation.

The cat I am still going to build before I'm 309 1/2 years old will be fiberglass and the interior lined with a 20 to 30mm sheet. It will offer sound proofing, heat insulation and be soft if you fall or bump into something.

 

Production boats are constructed to get them off the floor and out the door. $$$$$. Foam is put in to cover their insurance butts and government regulations, and since it's required to be put in, they can use it's initial stiffness to put in thinner and cheaper laminates. That it will eventually absorb water is not their problem, the same as built in equipment is sometimes impossible to get at to repair without major deconstruction. Aftermarket problems are not their problem.

I think the Titanic sunk not because hollow "sealed" chambers were breached, but because their flotation system was just a series of watertight bulkheads that didn't go all the way to a deck to create a sealed chamber. If it would have had sealed chambers it wouldn't have sunk. As it was it reached a critical point where water reached a high enough level in a few breached "chambers" that it just went over the top of the bulkhead and filled the next unbreached "chamber" and then the next etc. until it sunk.

 

Simple trick we use for sunfish- empty 2 liter and 1 liter plastic soda bottles with the caps siliconed on. Jam them in and they won't rattle around.

They will eventually break down- in about 50,000 years

 

The Titanic sunk because of a number of decisions made about the ship, during the design phase, building phase, fitting out phase and of course it's last voyage. Little about the design was wrong, in fact it was about as good as they could get. She was built to a high standard and operated at a high standard. In retrospect, is easy for us to think she was mishandled, but she really wasn't. It was very common practice in the era to run hell bent on a new record - they where setting them all the time. Major large ship disasters where considered a thing of the past, with modern 20th century engineering and rightly so, as a major "event" such as Titanic's sinking, just hadn't happened in a long time. It was assumed that engineering had over come the vulgarities of the sea. This particular skipper had a full career at sea and never experienced a hiccup, so was rightly overconfident. Most of the era where.

If you examine any major catastrophe like this or a plane crash or a ferry capsize, etc. one commonality constantly reappears; a spiral of errors, which when compounded, have a cumulative effect that leads to disaster. No single big thing goes wrong, rather unrelated events occurring in sequence, spiral out of control and are usually worsened by human factors that have an escalating effect.

All too often catastrophic exogenous shock is the blame for Titanic, but this couldn't be further from the truth, is extremely rare and with retrospect we can see this quite clearly now, though the idea of bulkheads or skipper's actions, etc. keep attempting make a difficult set of circumstances more simply defined.

I too take exception to simple qualifiers for failed engineering or disasters, such as Titanic being just a bonehead at the helm or the lack of futuristic bulkhead approaches. I can list several decisions that all contributed to the set of problems she was burdened with. None caused it, but all contributed to it.

 

Alternate Flotation

rturbett, I also have read/heard about using plastic bottles. I was heading in the direction of using those pool noodles, I believe it was on here somewhere I first read about them being oil/fuel resistant and didn't absorb water (2nd most important consideration after fuel). Tucked and glued in under the sole/deck and up the sides under the gunwale it should never sink completely. Since I have to completely rebuild from the bare hull up I can fit them from bow to stern

 

Off Topic Question

Anyone can reply, how do I up load pics here (CRS sufferer here lol) I have a few pics of a cuddy cabin I want to put on my boat while I'm working on it

 

Thanks Paul, nice overview of the titanic. I have heard also that it is mostly a series of events that lead to serious problems, I remember one story that started with a small fire, and that caused the next unforeseen problem which lead to the next which eventually resulted in... cant remember

The problem with bottles are that there are quite a bit of open spaces between them and hence flotation lost. Coke bottles are made from PET and are tough, you have to put them in a freezer then seal them before they go in a boat.

 

Titanic

Yes Fanie, I saw a documentary on Titanic and they said a smouldering fire in one of the coal bins may have weakened the keel area under the bin. They also said the riveted hull and the type of steel used (brittle and wouldn't pass muster now) were two more factors in her sinking. Perhaps if they had hit head on instead of the glancing blow she might not have sank