Extra buoyance

Steve W, your experience I think the most illustrative and worthy of being taken into account.
I have seen placing polyurethane foam only in places impossible to access that, for whatever reason, had to be filled with something.

 

Hi Steve,
Although in my view table tennis balls are a certain solution, provided they are glued together, otherwise when a leak is sprung, they may just wander out. A round ball is very strong, no doubt about that and will form some resistance also. I have never heard of a table tennis ball having absorbed water.
Yes, water absorption, that is also my experience, concerning foam. That is the one reason why I am looking for other solutions than foam only. For those who are opposed to different idea's. I probably will not use tennis balls, as I have another different idea.
If one would like to save weight, empty wine bags are not a bad solution. They weigh 70 gram each for a 5 litre bag. For an 180 litre area, it means only 2,5 Kg versus 11 kg for foam. This foam most likely will indeed absorb too much water.
If a leak is sprung, one will probably only loose one 5 litre bag. The buoyancy is still basically intact.
The problem in life is that you first have to become an alcoholic to collect 36 bags , or alternative have a friend in the wine business. For the pessimists, wine bags are still after quite some years sealed, although I would glue them up, after having pumped air in them. (Use a glue which needs some time to seal)
We amateurs sometimes can come up with solutions.
Bert

 

Expensive is relative. If one has to replace the foam again or like to sell a boat and have suddenly collected weight versus the issued certificate (which we need before sailing on the sea and need a certain minimum buoyance), what would be then cheaper. You tell me. Bert

 

you could put your ping pong balls or pop bottles in some sort of mesh bag, something like what oranges or avocados come in, that way they wont escape if the tank is breached.

 

Some quick googling suggests it will cost $50 US for a cubic foot of ping pong balls, and that will only be 2/3 bouyancy and the rest air, seems like the wrong approach to me.

 

Good idea ! Most failures are cracks, but I have hit logs in glass boats, and know a guy who smashed up a glass hull by hitting one that left gaping holes. He had polystyrene block foam.

 

My mathematics are a little rusty, how do you get to 2/3, if I look at the ping pong balls in a liter jar, than its seems to me that they fill also the gaps. I think more likely to more than 80% buoyance. Can a mathematician help us out here? Bert

 

Yes, indeed a good idea. Thanks Bert

 

Steve, although I think it is a very good solution, one should get a better quality than those bags, which deteriorate too quickly, like oranges and avocado's bags. But the principle is very good. I also looked at those double sealing plastic Ziploc bags, but, I don't know whether we do not loose air over a period of time. Bert

 

That is not too bad, for 180 liter it would be $ 300 . That is not that much more than 18 tins of step 1 and step2 foam. Bert

 

https://en.m.wikipedia.org/wiki/Sphere_packing 74% max, you loose around the edges..

 

Those very thin plastic bottles they sell water in would work well and should be virtually free at any recycling place as they are so common, they are about as light in weight as any plastic bottle. I have been using a 1 gallon plastic gas can for extra buoyancy on my mooring. My mooring ball is 18" when it should be 24 to support the 1/2" top chain so I filled a new gas can with Styrofoam packaging peanuts and sealed the lids with silicone and shackled it half way down the top chain, works great and has been fully submerged for about 6 years now. Obviously it has not leaked so I didn't need the peanuts but wth.

 

Spheres will fill about 63% of an infinite volume. In a finite volume, they will fill less because of the boundaries. The percentage will depend on the shape and sizes. Also, the weight of the balls needs to be subtracted from the flotation.

 

In an infinite volume, that figure (63%) is not correct, the percentage is undefined. For a finite volume, in a worst case (see figure), the percentage is close to 53%. With reasonably small spheres, in relation to the volume to be measured, the percentage may be much higher.
None can know the number of ping pong balls, or % of total volume, without knowing the volume and shape (as Gonzo says very wisely) of the compartment to be measured.
I neither know how a weight can be subtracted from the "flotation" and what it is intended with that.

 

The only floatation medium where you don't need to subtract a weight is air, everything else has a weight that needs to be subtracted.