Retro fitting positive bouyancy

PabloPicasso

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Jim Schofield asked about how much positive bouyancy is needed to keep a yacht afloat ( over on the jester forum). I asserted there that retro fitting positive bouyancy was impracticle , and like not to be effective and if this was a priority that getting an Etap was the answer. etap yachts can continue sailing whilst swamped I've read, it seems unlikely fitting bouyancy bags or foam blocks would allow a yacht to do this if it wasn't designed in at the pre build stage.

But perhaps this is not the case? Is retro fitting bouyancy for ocean sailing a good idea?

What's the best way yo go about it?

Has anyone tested a retro fit successfully?
 

Tranona

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Well trod subject. Yes, it is possible to retrofit bouyancy - if you don't want to live in the boat as the amount required takes up serious space, particularly if it is fixed rather than inflatable. Risk of sinking is vastly overrated which is why so few boats have ever been sold as "unsinkable" - the Etaps and some Sadlers being the exceptions.
 

prv

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Has anyone tested a retro fit successfully?

Roger Taylor's MingMing has retro-fitted positive buoyancy, but it only works because of her highly specialised purpose - she's not so much a yacht as a kind of one-man ocean survival/travel capsule. I believe Roger has walled off the forepeak and all the space aft of the companionway and filled them with foam, and lives in a small carpet-lined space in the middle, controlling the sails through a tiny hatch and not even leaving the cabin while at sea.

So it might well be feasible for the Jester, the purpose is quite similar. But it's not usually practical for coastal cruising with more people wanting more comfort on board.

Pete
 

lw395

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It seems a bit like planning to survive a particular accident, the likely outcome being 'having a different accident'.
sinkings are really very rare, going to great lengths to make it impossible seems a bit like not believing in heavier-than-air flight.
How many yachts actually sink in a year?
Discounting wrecks sinking on the mooring and racing collisions inshore?

One option might be to have a light keel plus water ballast tanks, which could double as buoyancy tanks?
Plus a few watertight bulkheads a la Titanic....
Or approach the problem from the other end and jettison the keel before sinking....
If you have say a 12m boat weighing 8 tons, you could guess the hull and deck area at say 12m * (4m + 2m)=72sq m.
Which suggests making the hull and deck of the order of 11cm thick foam sandwich would do the trick?
Or just get a trimaran.
 

Seajet

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Years ago there was a system one could retrofit to any boat, called ' Unsink '.

It consisted of buoyancy bags stowed deflated under the bunk cushions etc, and compressed air bottle/s.

I can see various snags, like you couldn't really test it before the real moment of need, and the bags may well suffer chafe in the daily use of the bunks.

It never caught on; while I wouldn't want to rely on it, I wouldn't mind it as a Plan Z up my sleeve !
 

elton

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Years ago there was a system one could retrofit to any boat, called ' Unsink '.

It consisted of buoyancy bags stowed deflated under the bunk cushions etc, and compressed air bottle/s.

I can see various snags, like you couldn't really test it before the real moment of need, and the bags may well suffer chafe in the daily use of the bunks.

It never caught on; while I wouldn't want to rely on it, I wouldn't mind it as a Plan Z up my sleeve !

That sounds as mental as driverless cars, nuclear fusion, and Snowden's encryption keys. It could only work by displacing water that had entered the cabin. Any space not occupied by the inflated "buoyancy bags" would remain occupied by water, unless at that state of inflation, it allowed the boat to float in the water to a level at which water could be drained or pumped from the boat.
 

prv

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That sounds as mental as driverless cars, nuclear fusion, and Snowden's encryption keys. It could only work by displacing water that had entered the cabin.

Well, of course. That's what any form of internal buoyancy does.

All sorts of reasons why these bags (there were several systems available for a while, one of the Pardey books has a chapter on them) weren't practical for real world use. But they did fundamentally do what they claimed, and keep the boat afloat. Of course it would be in a swamped condition, exactly how low depending on how many bags and where you'd mounted them; what you were supposed to do at that point varied between the promoters. Some suggested that you would repair the damage, pump out the water, deflate the bags and go on your way - rather optimistic, although in mid-ocean in the days before EPIRBs and suchlike, people have made some heroic repairs for lack of any alternative. Others more realistically suggested that you'd be waiting for rescue, but that a swamped yacht with all its gear and supplies is still a more viable proposition than a hastily-launched rubber raft.

The problems with these systems weren't when you fired them, it was the weight and space and inconvenience of tanks and hoses and big rubber bags (imagine stowing several additional dinghies around your boat!) and blocking access into under-bunk lockers. Also the fact that they had to be custom made for the boat or at least come in a wide range of shapes and sizes, so chandlers would prefer to stock a pile of one-size-fits-all liferafts instead (and there was no online ordering, so if it wasn't on your local chandler's shelf you didn't buy it). And finally, the fact that just not that many boats suddenly spring a leak in the middle of the sea, so making major and costly preparations for it isn't really worth it.

Pete
 
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