Dinghy buoyancy-bags...are they really any better than large blocks of polystyrene?

[DJE]

I've seen a few dinghies with watertight bouancy tanks and blocks of foam glassed in inside them. I've always assumed that with the tanks full of air they will support the boat and crew sufficiently to allow bailing or sailing out the water through self bailers. But if the tanks are damaged or the bungs left out the foam will keep the hull afloat so that it can be recovered.

 

[Kelpie]

That's about right. Certainly in the Wayfarer class (other dinghies are available!) you must have, IIRC, 40l of permanent buoyancy in each tank. The large hatches into the buoyancy chambers make for easy access and poor sealing. I can confirm that with the tanks flooded the boat will be awash and un-bailable- but the permanent buoyancy will stop it from sinking completely.

 

[Greenheart]

I'm sure you're all right, the blocks of foam visible in the Osprey chambers aren't there except to prevent actual foundering, if the seat-tanks flood.

I'm still thinking of boxing-in the aft-compartment, whether as buoyancy or dry stowage...but I'd leave a tunnel to the transom flaps. The similar boat in the Diefenbaker Youtube vid, doesn't seem to have any rapid cockpit draining system...(my awful photo, sorry):

View attachment 30169

I daresay she floats so high that there's no danger of the cockpit filling during capsize...but that doesn't prevent lots of spray coming aboard too...

...I've got port and starboard self-bailers (in good working order, I pray) but when it's really breezing-up, I'd sooner see sixty litres of water slide out through the back in a few seconds.

I even wondered if I could hijack SWMBO's "exercise ball"...heaven knows it doesn't get any use at home. It's rated for...ahem...hefty persons to bounce on it, so it should be tough enough to fit into the bow cavity, then inflate. I should think it's 50 litres...what's that, 500N of buoyancy?

P'raps I can fit one in a sock at the masthead too, to prevent inversion...