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Old 05-21-2013
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Making Your Boat Unsinkable

More than once I have seen posts saying it's easy to make your boat unsinkable, but after searching the forums, I don't see a comprehensive discussions about it. Best methods? Styrofoam added to bow and stern? Coring materials? Is there an equation for how much styrofoam I should use based on displacement/keel weight/etc.?

I recently was given a lot of 6" thick blue Styrofoam and wouldn't mind adding it to my boat so that if I ever screw up and fill it full of water, it won't go down! What are the recommendations for doing this properly?

I'm in a Starwind 22 with 2600 lbs of displacement and a 775 lb ballast. But I would like to know general suggestions that could be applied to any boat. (but ANY suggestions/advice would be appreciated!)

Thanks!
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Old 05-21-2013
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Re: Making Your Boat Unsinkable

The only way to keep it unsinkable is to keep it on land. Of course, Sandy disporved even that last year. Boats that are advertised as unsinkable never consider the consequences of a fire on board. Eventually all boats will sink.

Seriously though, you probably do not have enough volume to have it sink resisitent and a decent cabin space.
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Re: Making Your Boat Unsinkable

If you are out in rough weather or high winds and are concerned about being knocked down, put your hatch boards in and keep your companionway hatch dogged closed. Then the only way you'll sink is if you hit something hard really hard in the wrong spot, which seems unlikely on Lake Lemon.
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Re: Making Your Boat Unsinkable

Quote:
Originally Posted by CarpeAquam View Post
I'm in a Starwind 22 with 2600 lbs of displacement
Fresh water weighs about 62 lbs per cubic foot, so you'd need at least 42 cubic feet of foam. That would be a block 3.5' per side.
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Old 05-21-2013
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Re: Making Your Boat Unsinkable

Quote:
Originally Posted by Tim R. View Post
Seriously though, you probably do not have enough volume to have it sink resisitent and a decent cabin space.
That was my thought as well - not much room to create enclosed empty space in a boat this size.
If someone is really worried about sinking they should install a couple of heavy duty bilge pumps (one automatic, one manual), glass over all through hull openings, build a high bridge deck reducing cockpit volume, and enlarge cockpit drains. If one is really paranoid about it, get a big inflatable dinghy that can be filled with CO2 cartridges in emergency and keep it in the cabin.
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Re: Making Your Boat Unsinkable

Wasnt the Titanic unsinkable? No such thing as an unsinkable boat IMO
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Re: Making Your Boat Unsinkable

Quote:
Originally Posted by Rhys05 View Post
...put your hatch boards in and keep your companionway hatch dogged closed. Then the only way you'll sink is if you hit something hard really hard in the wrong spot, which seems unlikely on Lake Lemon.
Good advice... BUT, she has a trailer! I will be taking trips to the great lakes and the gulf someday (hopefully soon). I don't have ocean hatches and with a pop-top, thin companionway boards, and a large cockpit opening to the storage area, I wouldn't want to rely on that by itself.

Quote:
Originally Posted by Tim R. View Post
...you probably do not have enough volume to have it sink resisitent and a decent cabin space.
I would think that the a percent of the boat weight would be neutrally buoyant and the major factor would be the 775 lb keel. I've floated a 500lb boat lift with four 7"x2'x4' pieces of styrofoam. I would think that I could integrate enough in different spots to not lose considerable storage space but still keep it floating upright in an emergency. For instance, I would be fine with filling the front cubby under the v-berth, lining the bulkhead under the companionway, lining the storage area under the cockpit sole, and putting it in a few out of the way places.

But, how much is enough? Or am I wasting my time with the idea?
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Re: Making Your Boat Unsinkable

Alright, I've been crunching numbers:

The boat weight 2600 lbs with a 775 lb keel so there is 1825 of fiberglass/wood. I'm going to just assume that it's all fiberglass because I don't know how much wood is there, but fiberglass has a buoyancy factor of x0.33, so 1825x0.33 would be 602.25 lbs of buoyancy needed to float it alone. The boat plus the keel would weigh 1377 lbs in the water (IF there isn't any buoyancy already built into the boat). Styrofoam floats ~60lbs/cu.ft. so I would need about 23 cu. ft. of styrofoam built into it for me to be able to fill it full of water without it sinking.

I think I could put more than that in without filling any cabin space if I filled the front locker, lined the bottom of other lockers, and used the aft storage under the cockpit. Adding foam insulation to the walls would also add buoyancy (as well as sound/heat).

I'm probably not going to do that, but this doesn't seem unreasonable to me. Am I wrong?
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Re: Making Your Boat Unsinkable

Carpe,

I have a home built catamaran that has no lead keel but also no built in flotation. Not knowing/trusting the boat well enough for its initial week-long trip home, I stuffed both bows and sterns with large air bladders. My calculations were made so that the boat would float at least a bit above the water's surface (if both hulls were holed) and I suggest you do the same. Having the hull and deck completely awash just isn't an effective method of self-rescue. I admit secured foam is more durable than the air bladders I strapped into position, but I was only trying to give myself some extra time in the event of cat-astrophe (pun intended).
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Re: Making Your Boat Unsinkable

Quote:
Originally Posted by CarpeAquam View Post
I think I could put more than that in without filling any cabin space if I filled the front locker, lined the bottom of other lockers, and used the aft storage under the cockpit. Adding foam insulation to the walls would also add buoyancy (as well as sound/heat).

I'm probably not going to do that, but this doesn't seem unreasonable to me. Am I wrong?
Unless you glass that flotation space over, you can always easily remove the styrofoam or closed cell foam when you realize you need more space than you have left.
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