flotation tanks

[kokko]

Thanks to a tip I read here, I cut openings in the two cockpit seats and forward flotation tank and pulled out the old styrofoam. More than half of it was severely waterlogged and was tossed. I was able to salvage about 4 cubic feet. btw - a dremel tool makes short work of the cutting, but you will need a hook on a long pole to pull the foam bricks out.

Once the flotation tanks are dry - for the first time in decades - I will buy a few cases of swim noodles or some closed cell insulation and repack the space.

I also dropped the centerboard for inspection and refinishing. THe starboard side of the square hole was a bit rough, and there were some cracks. Dremel to the rescue again. I opened up the cracks and filled in in with marine epoxy filler.

Tomorrow I will pick up bottom paint.

[jpclowes]

Koko
If I remember correctly, my tanks took about 20 pool noodles. I think was able to save about the same amount of foam as you did.

Don't forget about the front tank too.

J.P.

[algonquin]

I will also be putting access ports on the seats and bow tank on my DS1. I have read about the noodles but am going a different route for the flotation. I will be using 2 liter pop bottles to fill the tanks. Even if they get wet they wont get soggy. Brad

[kokko]

Where do you get that many pop bottles? I think I will buy some 2" rigid insulation panels and cut them into long bricks. I calculated it will cost me $5/cubic foot.

[algonquin]

Where do you get that many pop bottles? I think I will buy some 2" rigid insulation panels and cut them into long bricks. I calculated it will cost me $5/cubic foot.

What ever floats your boat !!

I have been saving the 2 liter plastic bottles for a while and a few friends are also saving some for me. I asked the local returnable bottle redemption place and they have also offered to help me out for a nickle each.

What I like about the plastic bottles is that they will offer far more floatation energy than foam or noodles. They won’t mold or smell or need to be replaced. They are cheap like me. The bottles will fit easily through a 6 inch deck port.

I figure about $4.00 worth will be more than enough Brad

[GreenLake]

I'm following this discussion with interest because getting to my flotation tanks is high on my list, and reading about all the different approaches will be helpful.

What I like about the plastic bottles is that they will offer far more floatation energy than foam or noodles. They won’t mold or smell or need to be replaced. They are cheap like me. The bottles will fit easily through a 6 inch deck port.

Flotation energy is that a technical term?

My suspicion would be that the voids between the bottles would be larger, in total, than for the case of some other choices of material, mainly due to their necks. I also suspect that the weight of the bottles and caps is comparable to the weight of the same volume of foam (depends on the foam). As a result, if water fills the tanks, except for the volume of the bottles, the net buoyancy might not be better than for various types of closed cell foam.

Leaves the other advantages. If you can source them, it sounds like an attractive solution.

BTW, $4.00 would mean 80 bottles at 5¢, or 160 liters, or 350lbs total buoyancy - that seems low, so you must have a substanstial collection of free bottles. Just curious, what is the total volume of the tanks, in bottles?

[algonquin]

Hmmm ! Point taken about the voids.

I don’t have an actual lift in numbers available for the plastic bottles. Based on past experience as a meteorologist for the Air Force I would be willing to bet that the lifting force of a submerged plastic 2 liter bottle of air would easily exceed that of an equal volume of closed cell foam. Will have to try that with a given weight attached to each to verify that however.

Also I am only estimating that 80 2 liter plastic bottles will fill the seats and bow tanks. Will have more exact numbers later. “Feather” is still in tarps for now. Brad

[adam aunins]

I like the bottle idea, never thought of that. You could also use smaller water bottles in areas a two liter won't fit. The only down side I see is if you need to pull things back out, for any reason, the noodles would be easier than having to get bottles out of the far end of the tank.

[persephone]

So, I'm doing some work to my DS 1 this spring. I bought it last year from someone who seemed knowledgeable about sailing and boats. So I hadn't given much thought to the state of flotation material (I remember him saying he had replaced the foam a while back). The bow tank has a collection of bottles, they are about 6x6x12 inches, heavy plastic. All told there might be 15-20 of them. Today I opened the seat tanks and had a look inside.
They had in fact been emptied of foam, and partially filled with 2 litre bottles. One tank had 29.5, the other only 15!
How many bottles or foam depends on how much buoyancy you want. Fresh water weighs 62.4 pounds per cubic foot, sea water 64.3. I would think that you should plan to displace a minimum of 10 cubic feet to keep the hull, mast, sails and rigging afloat. One cubic foot is equal to 7.48052 gallons, or 28.32 litres. If I have figured this out correctly that's nearly 150 2 litre bottles! (I did figure this wrong initially, edited number after posting)
For informational purposes air weighs 0.07651 pounds per cubic foot, and a 2 litre bottle weighs about 2 ounces (I just weighed one on a digital scale accurate down to .01 ounces). All mathematical conversions and values taken from conversion table pg 4 of the Aviation Supplies & Academic's Aviation Mechanics Handbook.

P.S. I also forgot to mention that most of the bottles had collapsed to about half or less of their original full size. I would estimate they had been in there 20 years or so.

[persephone]

Oh, and for removing the bottles from the far end of the tanks I used the vacuum hose from my festool sander/dust collector. Snake the hose up to a bottle and the suction holds the bottle to the end of the hose while you withdraw it to the hole. A few times I was even able to pull the cap right into the end of the hose.

[jpclowes]

also forgot to mention that most of the bottles had collapsed to about half or less of their original full size

I always kind of wondered about that. I doubt it would be possible to regain the "factory seal" on the caps of the bottles. In areas where there is an extreme temperature variation (Like Ohio, where I live.) I wondered if the expansion and contraction of the air in the bottles would over time colapse the bottles. The air leaks slowly out under high pressure on really hot days, and doesn't get replaced when it gets cold. The pressure to replace the cooling air wouldn't be as high.

This could be bad too. Capsizing in the cold, when the bottles are less than full of air, your boat would be lower in the water, when you most want to be out of the water.

[persephone]

So now I'm thinking about the options myself. I like the pool noodle idea. Has anyone tried really packing them in under the seat? I was actually thinking about jamming and stuffing any unused area I could with flotation of some kind. I was thinking about inner tubes with steel valve stems (so the stems could be fixed to the outside of bulkheads etc...) allowing the pressure to be checked regularly without opening anything up. Obviously a tube has more weight to it that plastic bottles though.

[GreenLake]

In areas where there is an extreme temperature variation ... the expansion and contraction of the air in the bottles would over time colapse the bottles. The air leaks slowly out under high pressure on really hot days, and doesn't get replaced when it gets cold. The pressure to replace the cooling air wouldn't be as high.

Good point about the temperature cycling. The walls of the bottle need the overpressure to stay rigid, so they cave in when the pressure is low, instead of helping to draw the air in again - they're the weak link.

[algonquin]

I am following this discussion with great interest. I am not convinced that the 2 liter bottles are a bad idea as of yet. The collapsed bottles in persephone’s DS appear to have been there for several years. We also know what happens to foam that has been in these boats for several years.

I will be moving forward with the plastic bottles in my DS for this year and give it a try. I plan to use a sealer on the caps. I am not convinced that noodles or foam in a near air tight compartment are offering any flotation advantage. It’s the air in the compartment that will give you initial flotation. Once the compartment is flooded the noodles or foam may help. Once the noodles or foam have aged do to prolonged moisture exposure there is no longer any advantage. Does anyone know if the noodles will really float the weight of a DS and average crew ? I know that it takes an awful lot of noodles to get just myself to float.

Best solution is to make sure that the compartments are sealed to start with. It seems to me that once the seal has been breached and water enters the compartment you would be better off with bottled air.

I like the idea of inner tubes or air bladders. I plan to put an inner tube or two in the bow storage compartment and possibly one under the aft coaming.

Actually the best plan is not to turtle to begin with. Brad

[GreenLake]

The seats are (very approximately) 8" x 18" x 6' each. If they were square, they would hold 2/3' x 3/2' x 6' or six cubic feet. Only one seat should submerged (unless the boat is merely swamped rather than capsized) and then there's the contribution from the bow tank.

Geoff estimated in an earlier post that one would need 10 cubic feet of flotation, which he calculates provides about 660# of buoyance. That might not be enough float your boat sideways, esp. when you stepping on the centerboard. (There's a small contribution to the total displacement from the submerged part of the hull, coamings, etc. but I think that's less than the extra weight from wet sails).

So, all in all, it looks like the standard flotation tanks are a bit undersized. Based on these numbers, I'd predict that they're fine to prevent an upright boat from sinking, but there's not enough to allow righting.

Brad, your plan to add extra flotation and to practice turtle avoidance sounds pretty good.