Originally Posted by Rokraider
Are you suggesting leaving the existing tubes in place and inflating them up hard and then simply wrapping them with GRP?
I saw a tender like that once. It was hideous, but a good antitheft approach!
Actually he's talking about moulding a nice finished set of sponsons from GRP and then bolting the tube to the boat. I think its a bad idea for a number of reasons - and I say that as someone who has "hard" tubes:
- its a lot of work for little obvious benefit. By the time you've made and finished moulds, manufactured sponsons and bolted them all together in time and materials you'd be well on the way to a set of decent hypalon tubes! The ecconomic benefits of making moulds come from repeat production not one offs.
- GRP is fragile. Tubes come into contact with other objects alot (its one of their selling points!). If you want to make hard tubes don't make them from fragile GRP.
- bolting two solid objects together in a high load situation with continual flexing (which the joint will get every wave it encounters) sounds like a recipe for significant structural failure to me.
- ride quality is probably poorer with hard tubes (or overinflated ones) as the tube is unable to absorb any of the bounce.
- if the tubes are intended to be buoyant and have screw holes through them as well as the risk of other damage you need to consider the implications of 'free surface effect' on any water taken on board at such an extreme point away from the CoG.
If you really want to make hard tubes I would look at what other people have done. Almost without exception nobody uses GRP. There is one GRP "riblike" builder (linked above) but he is making a hull and tubes as one continuous mould not a bolt together. There are people making hard 'tubes' from polythene, or aluminium. Mostly these are part of a general RIB like shape that is built as one object rather than bolted together. There are a few builders supplying workboats who, for want of a better description, weld plastic natural gas pipe together to build hard, but slightly flexible, tubes together from very robust material. The "finish" is somewhat industrial and unlikely to appeal to leisure users -
Flugga Boats home page
Not specified multi-purpose work boat / in high density polyethylene / not specified / not specified - HDPE Crew Tender 9.00 9,00m - 29' 6 - DutchWorkBoats BV
although some people have tried:
The same material is used for a range of "RIBlike" Rigid-buoyant-boats from a number of manufacturers but typically moulded in one piece.