Many boats have built-in buoyancy tanks. Our 1999 Gemini catamaran has one in the bow and stern of each hull. Theoretically, they contain enough air to keep the boat at least awash if the hull was holed.
There are two possible problems, though:
- the manufacturer won’t guarantee that they’re 100% airtight (that is, water could seep in)
- what if the hole or crack extends into the buoyancy tank area (or if the deck-to-hull joint is compromised in the tank area)
We decided that we wanted our tanks to be positively buoyant so that the amount of water that could get into each tank was limited. I don’t think that this is a frivolous quest, as we know of two Geminis that have sunk when water entered the boat. Of course, no one knows that water filled the buoyancy tanks but it’s definite that the tanks didn’t keep either of those boats afloat; one is known to have gone down by the bow and the owner thinks that the tank was breached. Another friend credits watertight bulkheads on his larger catamaran to keeping his boat afloat (and letting them reach safety) when they crashed into an unlit weather buoy off the East Coast of the US.
Basically, creating positive floatation means filling the tank with something that is lighter than water and which can’t be infiltrated by water.
Some people have used plastic water and soda bottles. The disadvantage is that they are hard to pack tightly enough to keep them from making noise underway. But what to use instead?
One hot day as we readied ourselves to jump in the water to lounge and cool off, it hit us that we were holding the solution to the buoyancy problem in our hands. Swim noodles!
Most swim noodles that you find have a hole in the center, but you can buy ones with a solid core that are much better for this purpose. I did a lot of looking online and found the best deal on eBay. I started with 4 cases of 20 each, which exhausted their supply. I then found smaller quantities on Amazon that were slightly more expensive per each but still better than anything else I could find. (Note: I could find cheaper noodles with holes in the center, but since they have about 15% less flotation as a result, didn’t want to use those.) Links to both of these below.
When we started, we really didn’t know how many noodles it would take to fill the four tanks. Measurements were guesstimates at best as the tank shapes were higher irregular. Just because of shipping, we ended up with each of the four original cases coming on consecutive days (and the extras from Amazon being ordered when we saw we still needed more) — and I’m glad they did! Getting them into the dinghy, aboard Barefoot Gal, unboxed and then into position took more time than we had realized. And, because of the strangely shaped tanks, we had to cut over half the noodles (pro tip: a serrated bread knife does this easily). It certainly didn’t qualify as a difficult job, it was just more time-consuming than expected. And, of course, required some boat yoga.
I hope we never find out how well this works to keep the boat afloat. My calculations say that a single 2-5/8″ by 60″ solid core noodle has about 11.5 pounds of floatation. We used a total of 108 noodles, adding over 1,200 pounds of flotation.
Sources:
- Cases of solid core pool noodles on eBay (supplies are very erratic)
- 6-packs of solid core pool noodles on Amazon (best price I can find)
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Carolyn Shearlock has lived aboard full-time for 17 years, splitting her time between a Tayana 37 monohull and a Gemini 105 catamaran. She’s cruised over 14,000 miles, from Pacific Mexico and Central America to Florida and the Bahamas, gaining firsthand experience with the joys and challenges of life on the water.
Through The Boat Galley, Carolyn has helped thousands of people explore, prepare for, and enjoy life afloat. She shares her expertise as an instructor at Cruisers University, in leading boating publications, and through her bestselling book, The Boat Galley Cookbook. She is passionate about helping others embark on their liveaboard journey—making life on the water simpler, safer, and more enjoyable.
Anonymous says
that’s using your noodle!
Vivienne says
Hi Caroline
In the name of science, I think it would be a good idea (and only fair to us) if you would test this out properly! haha
Kind regards
Vivienne
Gary says
How about used tennis balls? Mary tennis clubs give the used balls away. Thousands in a years time. Maybe lightly spray them with a mold control agent.
Carolyn Shearlock says
They do not all float — our dog loves to play with tennis balls but we’ve learned that they’re not a good toy on a boat.
Chris Wick says
Carolyn, what have you heard about spray foam on boats?
Is it something that can be used the same as the noodles for flotation?
Or does it get waterlogged over time?
Thanks
Carolyn Shearlock says
For it to not pick up water, it has to be closed cell foam. I’m only seeing a few sources online and they don’t actually mention using it in a wet environment — you’d need to call and confirm. The other thing is if you think you’d EVER need to get into that compartment, say to run a wire, you wouldn’t want it filled with foam. However, foam would fill it more completely than the noodles do.
Ron says
If closed foam is found a 1/4 to 1/2″ ABS conduit laid in advance would give you a cable pass-thru. Be sure to cap both ends. Cheers
Anonymous says
Seems like you get a two for one benefit. Not only do you get the lift of the foam, you get the space filled by something other than water, and water is so heavy.
Wayne says
A fellow Gemini owner used USCG approved 2lb expanding waterproof foam from U.S. Composites. It seems like a cheaper alternative
http://www.shopmaninc.com/foam.html
Yvonne says
We used empty water and soda bottle in our Gemini.
Mark Pearce says
For anyone,
I just bought a 1999 Gemini 105M. I opened up the stern buoyancy tanks to inspect them. I found both tanks have about a one inch hole drilled into the bow side of the tank wall right along flush with the bottom of the tank. This is my question: seeing how they are identical, I have to think it was intentional. since they are at the bottom of the tanks then the tanks can still hold air, though it would be less displacement since the air will be under pressure. I did find standing water in both tanks. So bottom line, ARE THE HOLE IN THE TANKS BY DESIGN? ARE THE HOLES SO I CAN SEE IF WATER HAS LEAKED THROUGH INTO THE FRESH WATER HOLDING TANK SPACES?
Also, looking for ideas for routing bilge hoses, was thinking of routing them up through the floor of the fresh water holding tank spaces and then through hule in the stern berth mini “closests”. Ideas?
Thanks Guys!
Over thinking new cat owner, A.K.A. Mark