foam in boats

Some boats have foam flotation, some do not. Why is this?
Also, it seems that it is the smaller boats that have the foam. Why do larger boats not have foam? Is there a point (weight) where the foam no longer adds any value?

[james_r]

I believe that we see flotation foam being used in small boats more often because, during their lifetime, they have a higher probability of being swamped than larger boats. The owner of a larger boat may find it harder to justify the added upfront expense when he is unlikely to ever need the added security.
From an engineering standpoint there's really no reason why all boats can't be made unsinkable. In fact, boats built by Etap of Belgium, the largest of which is 39' (11.88m), are all unsinkable (www.etap-usa.com). There are of course disadvantages: loss of space and higher costs (Etap claims a 30% higher cost for the hull and deck).

Having said that, many large custom cruising boats and all Open class boats have watertight bulkheads dividing up the interior, designed to keep the boat afloat if one of the compartments is holed. Many aluminum boats also integrate the fuel and water tanks into the hull, in effect creating a double-bottomed boat.

Etap appears to be the only builder that has bothered to have its yachts formally certified as being unsinkable. There doesn't appear to be much of a demand by the boat buyer for this feature, otherwise I'm sure builders would be more than happy to supply it. However, considering the amount of shipping containers floating around the oceans that may change in the future.

[Nomad]

Took the words from my keyboard James!

[Nomad]

Also, it quites the boat when running (by density) and is used as a space filler (ex. a boat with a grid system or side pads in an engine room this would be empty space)

You mention using foam as a space filler.

What's wrong with leaving the space empty? If it is properly drained and ventilated so it won't hold water, couldn't the empty space be better than foam which may absorb water over time and break down?

Yes you can leave the space empty…

In smaller boats the foam is used as an added reinforcement for the hull and the decks. Unfortunately foam (even closed cell) will eventually soak up water.

If your bulkheads are open and vented then I would not use foam If the bulkheads are completely enclosed it really doesn’t matter either way, if you have water leaks you have problems.

The flotation properties of foam are probably not very well tested in any boat. Overall workmanship and quality assembly are 100 times more important.

[james_r]

The person that started this thread asked why flotation foam wasn't used in larger boats. Foam used in sandwich construction to increase the physical strength of the hull and deck, and foam added to a boat to make it unsinkable are two different kettle of fish. In a large sailboat with a keel weighing several thousand pounds the 1/2" or so foam used in its construction would make no discernible difference if one were to hit a reef or a floating shipping container at 10 knots. It would go down like a rock. If you were to add several inches of foam to the inside bottom of the hull and, as Nomad suggested, to unused areas of the boat you could create enough buoyancy to keep the boat afloat.

Nomad was simply responding to my claim that there would be a loss of interior space by pointing out that not all the space was usable anyway. I suggest you look at www.etap-usa.com for one company's solution. If you don't want to use foam and unsinkability is important then the other option is to install watertight bulkheads which divides up the interior.

Incidentally, sandwich construction is used, to my knowledge, in vessels as large as 200+ feet in length and probably even longer. If you regard that as a smaller boat then you're way way out of my league.

[BrettM]

Nobody has mentioned that foam buoyancy is used to be a "save all" in the event of an accident. Larger vessels are normally fitted with a life raft which is an obviously more economical choice as size goes up. I do know of a newly built 37' boat with a dispensation for liferafts because it is fitted with sufficient foam buoyancy. Unfortunately that doesn't do much when the "accident" is a fire...

The Etap 37s looks like the boat to have. W/so much flotsam and jetsam floating around I would consider reinforcing the bow (or front thingy). What would improve the boating industry most however, is less economic blacklisting of various Americans. For instance, most new designs get lost after hitting the extreme corruption at the USpto.

[Limey]

Nobody has mentioned that it is the law in the USA for boats under 20' to have flotation (level flotation if an outboard) CE regulations also require flotation in boats under 6m and may require it in larger boats depending on the design category, stability and downflodding height

[pkoken]

The boat on the Etap-USA website has a funny looking rust stain on the genoa

To be of any use, the foam needs to be fire retardent, high density, closed cell, polyeurothane. In addition - it needs to be wrapped in heavey plastic and sealed closed with waterproof 100 mph gaffa type tape.

The ploy foam is a crumbly type stuff that no doubt you've al seen iin the thwart seat of various pressed alloy 12 ft dingys ised around the world as fishing tenders etc.

That foam - can crumble with the repeated poundings of comming off waves etc. In the event it's not plastic wrapped, the crumbs - once in the presence of water can float on down to your bilge pump - block it's screen and cause it to overheat / burn out - which is why survey authorities downunder require it to be plastic wrapped.

You need enough of it to displace enough water to float the boat when swamped. Whether theres sufficient ullage space to do that in some boats is debateable.

Its also prefferable to keep the plastic wrapped foam "up" off the bottom plates to help avoid corrosion in alloy plate boats...so some kind of 'chair' system is required to keep the foam away from floor plates of the hull.

Cheers!