creative buoyancy

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creative buoyancy

Post by chris » Mon Mar 10, 2014 11:23 am

The old buoyancy for my 1946 Int 14 consisted of layers of 30mm thick sheets of builder's foam insulation all cut and fitted to shape. The boards have some stiff covering. It probably is non absorbent but it does look like the sort of tight foam that would take up some water anyway. What you see in the photo weighs in at a total of 12kg! so its effectiveness is not great anyway.
The 'tanks' in the boat are not designed to be watertight at all. They form seats either side about 6-7ft long and there should be a bow tank (old marks visible) all these are fitted on top of the ribs with no attempt to fill in the gaps to the hull skin. Good flow of air and water which I think is desirable.
My problem is what sort of buoyancy to use? There's no access for inflating bags and anyway round bags would either have to be small in diameter or squash out the shape formed by the tank boards (which are all solid timber not slats by the way.) I don't want to fix bags elsewhere on the hull either.
Although I have reservations about polystyrene it is an old fashioned idea that ticks nearly all the right boxes. Large blocks shaped and fitted rather than thin pieces. Obviously it must be a type that will not absorb moisture. But I expect there is a decent acrylic paint or sealer that could be used over it too and stop it coming apart.

I'm thinking about this now as it might affect how I fix the tank pieces back in soon.

Any thoughts or alternative ideas welcome please
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Re: creative buoyancy

Post by Obscured by clouds » Mon Mar 10, 2014 11:41 am

polystyrene/styrofoam, shaped would be my choice. painted/coated with something to encase it - a latex based floor paint maybe.

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Re: creative buoyancy

Post by Ed » Mon Mar 10, 2014 1:02 pm

Polystyrene would seam like the best bet...

but do you have any photos of where the buoyancy will fit? that would help with possible better ideas.

I think that shaping expanded polystyrene sheets would be easiest. You don't have to coat it, if you don't want as it won't absorb much water. You can carve them to fit as you go.

Another idea would be to cast them in place using epoxy foam. Epoxy foam is still hard to use, but has nowhere near the explosive and high-pressure action of polyurethane foam. I can't confirm I havn't used it, but have been told that it is much easier to use than poly foam. ... foams.html

Of course you would have to work out how to stop the foam from attaching itself to the boat.

All in all, maybe not such a good idea.....but you never know, and you did say 'creative'.

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Re: creative buoyancy

Post by Bill-Conner » Mon Mar 10, 2014 1:26 pm

An old Firefly bow bag may fit?

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Re: creative buoyancy

Post by chris » Mon Mar 10, 2014 1:41 pm

Photos of the two side tanks/seats
I will be able to get to the inside by removing the thwart and seat tops (only 110 screws!)
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Re: creative buoyancy

Post by roger » Mon Mar 10, 2014 2:00 pm

Looking good Chris
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Re: creative buoyancy

Post by JimC » Mon Mar 10, 2014 2:29 pm

Blue styrofoam, eg Dow Floormate, has much lower absorbtion than ordinary foam

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Re: creative buoyancy

Post by davidh » Mon Mar 10, 2014 4:27 pm


There IS a solution..... let me tell you the story!

Way, way back in the very early days of Contenders, the boats came from imported Australian 'MarinePak' kits. The late, great Mel Moncur (who went on to do some clever things in FDs and Tempests) had built his boat the story gets tricky! Had he forgotten the buoyancy or always planned to do something else! Whatever, he filled the buoyant tanks with ping pong balls, loose (I've no idea where they all came from....)

Now the thing about buoyancy is that this is a bit like insurance - you need it when something goes wrong. In Mel's case it was a major Tee-boning by another boat that opened up the hull - letting all the ping pong balls spread everywhere over the water. With his reserve buoyancy lost, Mel's boat was waterlogged and needed rescue.

It was a long time before he lived the episode down.....but in principle, it worked well¬!

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Re: creative buoyancy

Post by chris » Mon Mar 10, 2014 4:32 pm

Love it!
Very creative lateral thinking but ultimately nothing but a load of .....s.

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Re: creative buoyancy

Post by jpa_wfsc » Mon Mar 10, 2014 5:59 pm

.. but all could have been saved if he had been wearing fish net tights arround his b___s!

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Re: creative buoyancy

Post by Rupert » Mon Mar 10, 2014 8:07 pm

Stockings would work better than tights - one leg in each tank...

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Re: creative buoyancy

Post by Michael Brigg » Mon Mar 10, 2014 8:21 pm

I believe the original buoyancy they used was solid cylindrical tanks, made from bronze!!

These would be tied into the boat with fine rope, wire or string, fine enough to thead through between the hull and the ribs, or perhaps tied down where other alternative anchor points could be found.

I had few of these when I put my clinker 14 into a boatyard for some preliminary work a few years ago, and unfortunately the silly b*****s put them in the corner where a new boatyard manager thought they were rubbish, and had them dumped :oops: :cry:

This shows the arrangement and detail...
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The buoyancy test was conducted by placing four x 56lb weights in the boat and filling her with water. The requirement was that the boat should float, though not very high. The main concern was that it should not go to the bottom. I think in those "good old days" the theory was that if you capsized that was pretty much the end of your race, so if it was likely to happen you would reef generously.

Things of course have changed.

When the tanks on my old firefly failed, I lined them with tubular buoyancy bags. Worked well enough!
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Re: creative buoyancy

Post by Garry R » Mon Mar 10, 2014 9:45 pm

Remember Chris when I got Gannet there were about 60 4-pint plastic milk bottles all roped together under the decks!! Get drinking. Of course you might be quicker with the internals of wine boxes - really tough those things and referred to by a post grad student of mine as a "handbag of happiness"!!!!

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Re: creative buoyancy

Post by chris » Mon Mar 10, 2014 11:54 pm

Michael, yes I am familiar with those. Iska Merlin 6 still has them swinging and rattling around. Those are welded aluminium tanks. Looks as if your 14 has a fore deck ...does it really?

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Re: creative buoyancy

Post by Michael Brigg » Wed Mar 12, 2014 3:43 pm

chris wrote:Michael, yes I am familiar with those....
Looks as if your 14 has a fore deck ...does it really?
Hi Chris. Well actually it is a bit of a hybrid. I've written a fair bit on "Blue Moon" already. If you look up "Blue Moon" in the Search facility its all there including a picture or two... I first found this forum while trawling the internet for any information.

THe decks were added to Blue Moon by my godfather in @ 1955, so he could use her on the sea at St Mawes where he used to take his Scout group. When I had prelimqary work done on her I had the decks removed and discovered some elegant half and quarter knees fashioned at the bow and stern, clearly showing her to have been originally open / undecked.

The pedigree remained uncertain. Alot of a "Whiff of the East" about her (Dougals words not mine!) and certainly alot of similarity to a Norfolk One Design, but one extra strake too many and twice as many ribs.

After looking up the design brief of 14ft boats about the time of her construction I find that she has all the features required for a "National Restricted Class, 14ft dinghy," (British Racing Assotiation.)

This pre dates the RYA and for that matter most of the International 14 class, and as such I think Blue Moon was build as a contemporary design alongside of rather tan as a fore runner of the i14, such as it was in the late 1920's or early 1930's. She is certainly a pre- WW II boat, and as such several i14's were built at that time in clinker construction,which prior to the Double skinned, tarred silk sandwich models (such as you are working on at present) was often the lightest construction technique. (For the same stiffness a single skin Carvel construction needs a much thicker, heavier planking.) However I am advised that the forward raked bow line would almost certainly rule out i14 pedigree.

There are no builders marks anywhere to be found, which might suggest she came out of the same stable as the NOD's which also have no makers markings. Unfirtunately that yard burnt doun several years ago along with all the records (if any) that might have identified her.

Here she is with her decks stripped of her. A much racier animal altogether! ... 630-14.jpg
Michael Brigg

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