Buoyancy – a little guidance to keep you afloat

Let us embark on the debate between buoyancy bags and buoyancy tanks for open boats. I’m not sure how this will be affected by current EU legislation for small craft, if only because no-one seems clear about what that legislation means in practice.

Buoyancy bags have the following advantages:

  • they are lighter
  • it is easy to see if they are leaking
  • it is easier to maintain the hull structure
  • depending on the design, they are cheaper
  • the amount of buoyancy is easily adjusted.

On the other hand…..

  • you can’t stow anything in them
  • they are fiddly to install
  • they don’t fill all the space available for buoyancy because of their rounded corners

I think that is the major points covered. I prefer to see at least some bags because it allows you to adjust the amount of buoyancy. If you have a boat where a capsize is, if not commonplace, at least a foreseeable event, too much buoyancy can have undesirable consequences should the worst happen, for example:

  • if the wind is blowing on the bottom surface of the hull, it is driven onto the rig, itself angled downwards because the hull is floating too high. This increases your chances of turning turtle. As you watch the plate disappear back into its trunk, you can muse on the vicissitudes of life. Or decide who is to go under the boat to push the plate out again.
  • if the boat doesn’t turn turtle, then it tends to twiddle round such that the hull drifts to leeward. Right the boat and it could re-capsize onto you when the wind catches the sails.
  • at best, the centreplate will be high off the water. You are cold and tired and have the job of heaving yourself up to the plate before you start. Bad news.

At a first approximation, there should be buoyancy equal to about 2.5 times the weight of the boat and gear (not crew). Then select a nice warm, reasonably calm day to do some controlled tests to get your buoyancy right. Apart from the fact that you’ll probably be surprised how difficult it is to capsize the boat in the first place, you will confirm that you are able to right the craft, and be able to check that the plate is at or just above the water-line. When righted, it is helpful if the boat does not continue to fill through the centreplate case. Perhaps the most important benefit from this sort of experiment – and/or its ensuing adjustments – will be that you will be less worried about a real capsize. After all, you can’t love a boat you fear.

If you have or require tanks, then proprietary hatch covers are good for sealing them as long as the holes are big enough for the passage of articles for storage. If not, you’ll have to devise your own with bits of rubber and lips and catches and so on. Strive for simplicity here.