adding boyancy with plastic bottles? - SailNet Community

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Go Back   SailNet Community > On Board > Boat Review and Purchase Forum > Sailboat Design and Construction
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Old 07-05-2010
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adding boyancy with plastic bottles?

my boat has a wooden deck but the hull is fiberglass, under the cockpit thers a large empty space. I am tempted to fix styrofaom but dont want a permanent fix, so I was thinking wy not fill the space with empty bottles?

if this is silly let me know, I just want my boat not to sink.

rgds
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Old 07-05-2010
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Jobi
Each cubic foot of air will give you 64 lbs of buoyancy in salt water. If your boat weighs 6000 lbs that means you will need 94 cubic feet to keep it afloat. A space that equals 4' x4' x 6'. Also for a boat to be livable, much less sailable when kept afloat this way the flotation would have to be evenly distributed throughout the length of the boat. I wouldn't bother, instead concentrate of making sure the seacocks are solid, hoses double clamped and in good condition, hatches leakproof and solid, and so on.
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yes all this makes more sens.

I want to permanently seal one side of my cockpit, half of it is a berth anyway, and the rest is easy access.

I also want to change the cabine hatche for a good seawrthy door with seals and lock, probably top opening?

the seacocks ar solid from exterior but flimsy inside out. shold the boat take water the cabine top is the only air pocket that mai keep the floating, if the seacokcs blow out the boat will sink faster then I can bail.

cheers

Last edited by jobi; 07-05-2010 at 11:04 AM.
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Old 07-05-2010
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is it just me or this thread is posted in 2 forums?
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Old 07-05-2010
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Bilge pumps.
I remember reading of a small vessel sailor who brought his water for voyaging along in plastic bottles, then tossed the re-capped empties into spaces such as you describe. The intent was a little added floatation insurance.
But as was suggested, you're far better off making certain your boat is seaworthy to begin with, having wooden bungs alongside the seacocks as emergency stoppers, etc. Watertight bulkheads and other compartments help isolate against any flooding too.
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If you hit something it will be forward. The best solution I have seen is to isolate the area under the V-berth with a watertight bulkhead to the berth top. Not perfect but that is where the damage is likely to be. On Atom James Baldwin built a water tank under the V-berth effectively creating a watertight compartment. See this link Atom Voyages | About the Sailboat Atom
There is also a lot of good ideas on his site. His boat is a 28' Pearson Triton so the sizes are comparable.
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what an amasing link, this guy is doing exactly what I intend.
many thanks
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Old 07-05-2010
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You really want to make the boat seaworthy before adh ding bottles for flotation.

Also, distributing the flotation and making sure that it can not move is a good idea. If you get holed and all the plastic bottles float out the hole, they're probably not going to help you much, are they??? Glassing in closed-cell foam is probably a much better idea.

This is how it is done on ETAPs, Boston Whalers and most multihulls. Of course a multihull has an advantage of not having to support a keel or ballast.
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You might note that one doesn't need to add enough floatation to compensate for the entire displacement of the boat. A 6000# boat will likely have 2000# to 3000# of metal (ballast, fittings, etc.); the rest is going to be pretty much neutrally buoyant (fiberglass, wood, etc.). One only has to worry about the negatively buoyant metal. So, to keep a 6000# boat from sinking, one really only has to provide about 2000# to 3000# of positive buoyancy (plus a bit to keep it from being too close to neutrally buoyant). However, using 2500# as an example, one would still need more than 550 2-liter bottles to keep it afloat. Given that no matter how careful one is about packing such bottles there will still be quite a bit of unsealed space between them, bundles of closed-cell foam might be a better (if somewhat more expensive) way to go about such a project.
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sins my boat has a wooden deck, I can easaly fit 2in styrofoam inbetween structural beems across the entier boat with the only exeption being centre cabine as it would afect head room. when I look at it this is enough flaotation to keep this boat afloat.
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