My techie mates tend to dislike my approach to design and build but they’re not the ones doing it – they want it all designed, sealed and delivered before any building takes place.
Real life says that if you do not design in flexibility to change details even until the last moment, then you find yourself with some insurmountable practical problems at ground level, especially those due to local circumstances, and no flexibility in design costs time and money. My view has always been to build Plans B, C and escape routes into any project.
These cat hulls were simple, rectangular, some of the slamming* circumvented by a system of rails added after the initial joinery – that involved setting the base of the hull up near vertically against the current boat, slightly leaning in towards it, then once the base was glassed and coppered, it was lowered to the crossrails on the ground by three people using winches. Mass was around 750lbs.
It would still work using the winch idea but if I went to multichine construction:
… then turning the boat over becomes easier using a rolling motion, not a dropping.
Multichine is better in that it reduces slamming more but worse in that it requires more joints – expensive. But it rolls better than flat bottom or deep V.
The way it can be done is:
The boat is built upwards in this position, bottom facing the old boat which is still in its position, now supported by oak struts [I have 6] enabling the bottom to be finished from above, not underneath. This I was doing yesterday.
At the same time, a winch is used, the wire through the old boat along the beams, bolted the other side of the boat and the hook attached to the short side of the cat hull – that’s just a bit of extra support, not taking much strain yet.
Once the bottom is done, plus overlaps on the sides, the winch is tightened, the chocks are removed from the centre and then fore and aft, then we find out if the old boat will be pulled over. As it’s about 2 tonnes just now and the skeletal structure of the new hull is around 750 lbs, the winch method seems effective to me to lower the cat hull onto its short side.
The winch hook is now detached, then attached to the long side edge [reinforced by various 8 x 2 planks] and gradually cranked so that it lifts the long side vertically, the motion stopped by chocks now screwed to the ground crossrails, plus buffers sticking out from old boat.
This again is where multichines ease this motion – less sudden leaps. The remainder of the ‘inside’ of the hull now needs finishing, epoxying, painting etc.
Then it’s time for the second hull using a similar principle, again making sure the ‘inside’ is finished before making vertical. To keep the hulls separated, a series of stringers of one inch alternating on either hull do this, then the crossbeams for the canal go on to hold the two hulls in place for later hauling.