Tony. I have never bothered, BUT, but I should imagine that ordinary expanded polystyrene (ceiling tiles) would fit the bill, and would be best fitted as the boat is being built. This means that the pieces could be trimmed to fit exactly in all the unused spaces of the hull and thus alleviate that sinking feeling. Builders yards sell 1" thick sheets, only costs a few quid, and get a hot wire cutter (from "hobbies, for instance) to cut the stuff as using a knife is incredibly messy. Your radio compartment could be used, and holes cut to accomodate the radio gear would be tidy and fill even more hull space. An alternative for the boat thats been built might be the packing stuff that looks like cheesy wotsits, this can be inserted via hatches or holes cut in appropriate place, bulkheads etc etc. I have often wondered about using builders foam, as this can be squirted through smaller openings and fill the voids to perfection, however it expands ferociously and might just as well split the hull apart if you wernt careful. Ashley.

Hi Tony,

As Ashley mentions polystyrene foam is probably the best stuff to use, but don’t bother buying it, you will find all you need in a skip ! – they are full of it (its where I usually get mine from).  Putting in into the spare space of, say the bow, just break of small pieces and rub in your hands until its reduced to small balls, prop the boat up and pour them into the bow, now just dribble a little PVA glue to lightly cover and leave till set.

Don’t for get to add pieces of tile under any hatches

You can actually buy bags of beads in craft shops, look out for old bean bags and kiddies toys.

Cheers – Ken

Gerald, good job I only wondered about builders foam !!!!! I will wonder no more. Ashley

      At the start of this thread, Tony suggested putting expanded polystyrene into a model to make it un sinkable, Tony take a leaf out of the RNLI’s book, they designed this feature into a modern lifeboat which might have been an Arun, but I’m not sure. to their grief, the 2 pounds to the cubic foot foam chosen went mouldy, and the boats had to be taken off station to go away to be cleaned out. I have a couple of tupperware containers to house the electronics. when the water gets in,they provide buoyancy which is good , but you have a few respondants suggesting polystyrene beads which must be good just think about draining any water out, just don’t trap it in. Salt water is very very corrosive

     Tony, Shrek    Take a leaf from the Royal Navy’s book, All their helicopters are fitted with emergency flotation gear which comprises a sea cell battery which generates electricity when immersed in salt water. These are connected to cool gas generators that blow up baloons fitted to the hubs of the main landing gear wheels. Because the main wheels are for’d of the centre of gravity, they have to stuff an enormous baloon up the tail cone.  The combined positive buoyancy of the three baloons is enough to keep the helicopters afloat. You may have noticed that Sea Kings have a boat hull, and it has been known for a Sea King to taxi on the water to land, and even more amazing, it has been known for the pilot of a ditched Sea King to keep the engines running and engage rotors and take off again from the water’s surface Take note Ashley. I have noticed that RNLI RIB’s appear to have flotation gear fitted to the mast, but to reproduce the function in a model must be nigh impossible.. I suppose the best solution would be to give the hull a massive amount of positive buoyancy  by inserting containers of air like varnished smartie tubesor ping pong ballsMike D