There has been some mention of sinking on other threads. A simple prevention method is to insert 13 ping-pong balls into the hull. This will provide 16 oz of flotation, and they are easily inserted and removed thru the battery hatch. This works best if all moving parts are above deck, otherwise you would have to worry about interference. The balls will add about 1 oz to the overall weight. An equivalent amount of cut-up foam could also be used, which would weigh about half as much.

Hi Walt, if you are going for foam there is always the expanding foam that can be bought in cans - carefully injected this can be a fullfilling experience

As I’ve mentioned this before, the simplest and lightest solution for positive internal flotation is to put a partially inflated zip-lock sandwich bag(s) into the forward part of the hull. I’ve also used almost fully inflated zip-lock "snack " bags, they’re a bit smaller and might be more appropriate for those skinnier hulls. Sealed and partially inflated, the bags can easily be snaked around any internal bracing to be stowed forward and out of the way.

Bags will give as much or more bouyancy in a flooding than pig pong balls, and they won’t roll around. And expanded foam is not all that light and it is unpredictable to apply. Guessing the right amount to use is tricky, and unless you plan to contain it in a capped soda bottle it has the potential to deform your boat or blow its sides off. I know this from personal experience!

My inspiration for using “air bags” comes from kayaking and whitewater canoeing. Flotation bags are used in these other water sports (that need internal bouyancy more than we do) because they are the most adaptable means of supplying insurance against losing the boat and possibly the paddler’s life.

13—thats alot of balls…:slight_smile:

some one had to say it…

I might be able to get a couple into my v-12 or my 507…

Id sooner go with foam as it can be cut/sanded to fit…ping pong balls are not exactly “space saving”

I like thebag Idea too. but I see those sandwich bags leaking air over time…

I agree if I were starting again with either a V12 or 507 I would foam the hull to start with before doing any thing else.

I have seen three sinking’s in a year two were easy Lawrence Hartley was lucky to get his 507 back from 5+ meters deep at Cotswold!

As a minimum now always use bubble wrap to fill empty spaces


The expanding foam is not a good idea to use in a model boat because it absorbs a lot of water and doesn’t let it go easily either.

With the size of the Footy, it’s better to make the effort to make the hull water-tight than add foam or any kind of floatation, but you are welcome to put your boat to the test.

What about those sealed bags that you find used for padding when you get something mail order that’s packed in a box? If they fit, seems like one would be ideal. Or maybe iron a bag to seal it.

Or perhaps just use several bulkheads?

You might think those shipping ‘pillows’ are good, but I’ve done some time observation experiments with them already, and they didn’t hold their air for any length of time. After only 1 week, they were flat. Light weight, closed-cell foam is still the best thing.

I too, agree if I were starting again with my V-12A I would shape a piece of foam to fill the forward part of the hull.

And bubble-wrap appears to a good way to fill empty spaces after-the-fact.

Here’s what I will be experimenting with. I found small mylar balloons, 4" across by about 1 1/2" thick in the shape of a heart.:love:
Actually they are party favors. And best of all, they are self-inflating. Just a little squeeze of a small container sealed inside the balloon and it inflates. Some online buyer comments state that they last a month or more. Others state that a little shaking regenerates whatever gas is chemically produced and they reinflate.

With the careful placement heart’s pointy end forward, I’m hoping I’ll get a pretty good filling of the open space in the bow. I also want to determine how much weight this little balloon keep at the water surface.

I’ll post my results here.

Howard Maculsay

It’s easy to figure out the displacement of flotation, and it’s just that.

Get a pail or a tray, and a smaller container that will fit the flotation object, like a big margarine tub in this case. Fill the smaller container with water exactly to the rim. Press the flotation object completely into the water so it spills over into the large tub, and either weigh this water or measure the volume and convert to weight.

No need to convert to weight, Archimedes ;-). At least if you have a reasonably big bucket. Just do the same to your boat and make sure that the flotation displaces more water than the boat does.

If you only have one large container, you can drill a hole in the side and put in a tube or spout so all the overflow goes to the small container. Or don’t do overflow and just measure the rise. Helps to use a container just large enough to contain the boat.

I hope you didn’t jump out of the tub and run around town naked saying “I’ve got it” or something.

Of course if you have a scale, and you’ve already weighed your boat, you could hang a string off the edge into a bucket with a big weight, and then add the flotation. This way the weight of the flotation is subtracted from the measured displacement. Possibly less fiddly this way, and surface tension won’t be a problem. Come to think of it, if you do the Archimedes thing, add a tiny bit of detergent to the water to cut surface tension.

Or just figure water weighs about 16.3 grams per cubic inch.

Thanks TomoHawk:)

So, as long as the weight of the displaced water is greater than the weight of the boat I want to keep afloat, I’m good to go.


My understanding is that Archimedes had a towel wrapped strategically around himself. If he had no towel, I am sure Miss Lodge, my Latin teacher, would have mentioned it.

Was she THAT old? :stuck_out_tongue:

Visualize Queen Elizabeth the First in her later years, red haired and strict, an MA in Latin, Head Mistress of a boy’s boarding school----Yes, now you’ve got it!
That was M.A. (Oxon.)


You mentioned the heart shaped float, so my method would be good to measure the displacement of that one item, or to figure out the water displacement of any kind of odd flotation item. You can drill a hole for the water to flow out, or any other fancier way, but it is still the same thing.

Remember that good flotation has the ability to displace water while being itself very light, to not absorb water itself (like spray-foam does) or to fail and take on water or to be otherwise useless. And the purpose of the internal flotation is to keep the hull floating, in case the hull gets a leak so you can recover the boat, not to keep on sailing! Please repair the hull before you continue sailing.


Measuring the displacement of the entire boat isn’t a good idea if the keel is attached, as the (lead bulb) throws things off. Does your boat have a waterline at the deck? I think not. A scale is the best thing for determining the weight, or displacement requirement, and displacement up to the water line is the final measure if the boat will float correctly.


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I don’t get the bit about leaving off the keel. If the keel is on, the boat will sit lower in the water, so you need it. Or is the keel jettisoned when there’s a leak??? The flotation from the displacement of the keel bulb will be nil. The flotation from wood in the hull is another matter, though, of course. But the conservative course is probably not to count that. I was once in a boat that capsized whose flotation was calculated carefully according to these principles, counting on the displacement of the hull’s materials. Every time I got back in to bail, it would sink until the gunwhales were two feet under the surface. I couldn’t bail that fast.

TMaculsays comment was about the measure of floatation of objects placed inside the hull, not the displacement of the boat itself, with all ballast attached. To measure the displacement of the boat, you’ll need the keel, rig, radio, battery and everything else attached. That is a different thing from measuring the capability or displacement of flotation itemsplaced inside the hull.

Even if the hull itself floats, like one made from wood, you’ll need floataion to guarantee the boat will float with all ballasting elements attached. We don’t usually do that because sailboats are relatively slow and you can more readily avoid a collision with another boat or obstacle, but for powerboats, especially with gasoline engines, you add enough floatation to counteract the 8 LB. engine, and a lttle more for the hull; and so there is a formula to figure what length (when using standard pool noodles) to use.

I guess I’m still missing something, because a quick review of the first post makes a reference to sinking. You don’t know if you have enough flotation to keep it from sinking if you don’t know what your boat displaces. So IMHO it’s necessary to measure both.