I like the pvc canister from Customdivers (£78), though somewhat "floaty" because of its size.
Watertight to 180msw (590fsw).
Outside dim: 75mm (3'') dia by 125mm (5'') height, 250g (0.55lb/8.8oz) so positive buoyancy of 1.9kg (4.3lb). Belt mount is 36g (1.26oz)
Inside dim: 61mm (2.4'') dia by 115mm (4.5'') height, capacity 1.34 liter.
A PLB and/or Sat-phone inside this canister will still leave it +buoyant.
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Made me think... What else would you like to bring if there is no dive-boat there to pick you up.
- How about some fresh water! Your body (and you) can be quite dehydrated after a dive, especially if on OC.
You can get those small expensive 0.2 liter sachets of "emergency water"
Or you could make some yourself with small zip-lock bags. (With small bags you only loose a little water when it slips from your cold fingers)
- Stuffing these sachets in with you PLB etc. should weigh it down a bit.
Will probably not end up neutrally buoyant, but I guess you could put a bit of lead on the belt mount and make it part of your weight management.
- I believe in bringing water for longer dives, traditionally this would be in a squeeze-bag for use under and above water.
If you loose that squeeze-bag, you would still have some in your canister to save the day while you are bobbing on the surface waiting to be found.
- Maybe a lighter for when you end up drifting onto that deserted island...