beautiful skeleton

Have you considered wrapping the skin onto a prefit frame and gluing that into place after it is wrapped?

1. Build frame to fit.
2. Wrap fabric onto frame.
3. Position wrapped frame into bow or stern and glue into place.
4. Seal fabric and frame edges.

 

I've now added decks fore and aft to my boat and reckon a SOF bouyancy chamber would be possible, but probably not by using fabric. The easiest way to do this would be to either use buoyancy bags, or make up some foam blocks to fit in the ends. The fabric only needs an inch or two to bond well enough using the proper adhesive, so it might be possible to make entirely fabric chambers, but I suspect that it'd be trickier to do than its worth.

I'm just going to use some glued together foam in the ends of my boat for buoyancy.

Jeremy

 

I'm not at all keen on either foam blocks or bouyancy bags. I regard both as being fairly nasty substitutes, and really I'd prefer to ditch the SOF method and use something else if it became a question of using bags or foam blocks instead of a "real" bouyancy tank.

I wasn't thinking of using fabric to bulkhead off the ends. I was assuming plywood bulkheads, with a shaped edging about 30mm or so wide for bonding area. Plywood makes sense since it will be used for the web frames anyway. Just make a really wide web frame and it becomes a bulkhead.

I've been thinking about the loads on the bond. Normal hydrostatic/hydrodynamic loads shouldn't be a problem as they are basically pressing the cloth against the bond. Seems to me that the critical load case would be when you have a large force inside the boat pushing outwards. Two obvious examples would be someone kicking the inside of the boat by mistake (easy enough to do) or if it was sitting outside and got a lot of rain dumped in it (could happen).

 

Bonding isn't a problem at all, but getting a bulkhead to fit neatly against a fabric hull, without creating a nasty hardpoint, is. In my boat, the frames don't touch the skin, only the stringers do. It would be possible to create a buoyancy chamber using a totally skinned sub-section, consisting of a couple of ply frames with effectively a double skin. These would be easy to build before the boat was skinned, in fact before the stringers are attached, or they could be made up as removable components, fitted after the boat's built and skinned.

 

IMHO, separate plywood boxes would be too much weight and complication for no structural benefit. Might as well build a plywood boat instead.

Double skinning is a possibility. I can see how that might work, as long as the webframes were wrapped before the stringers were attached, and as long as the attachment points for the stringers were sealed.

I am assuming that tensioned cloth is going to take a straight line between the stringers. Make the bulkhead follow that. The only problem would be underwater, if there is significant deflection of the cloth under normal loads. That could create a hard line across the flow, but I'm not sure much of a problem it would be. The boat I am thinking of would only have tranverse spans of unsupported cloth around 100 mm wide.

 

I doubt fabric deflection would be a problem. Once heat-shrunk this stuff goes really tight. My stringers are only 1/2" diameter, so the gap between the fabric and the frames is only 1/2". The stringers are around 150mm apart of so on average and it's hard to push the fabric in enough to tough the frames.

I wasn't thinking of ply boxes, BTW, I was thinking you could make fabric covered buoyancy chambers using either the frames as end members or else some additional frames, with their own stringers. It'd be easy to fabric wrap a "basket" frame buoyancy chamber and then fit it, either between frames or maybe as an intrinsic part of the structure.

 

Hmm. Methinks that if deflection is not likely to create a serious problem, it would be better to go with the simplest and most elegant solution.

Just a note: the tanks I am thinking of are around six feet long each. The idea is to deck over and bulkhead off all parts that aren't required to hold a rower and a passenger. I rough terms this is nine feet of cockpit with a six foot bouyancy compartment each end.

 

Jeremy, is this your boat at Beale Park? http://i4.photobucket.com/albums/y139/Clayhithe/101_2275.jpg

I came across the photo is a thread in the WoodenBoat Forum. http://forum.woodenboat.com/showthread.php?132054-Beale-Park-2011

 

Yes it is, taken before some "kind" member of the public decided it would be fun to see if my prop would plough up the turf and powered it up with the prop resting on the ground..............

The result was a broken gearbox which led to my retirement from the challenge before I'd had a chance to try the boat out - months of work wasted by a few seconds of thoughtlessness. Some people are so moronic they shouldn't be allowed to breed, IMHO

Jeremy

 

Very sorry to hear about your misfortune.

 

Bad luck.

I saw your boat on Saturday, and must say it is very well made.

Will there be an electric drill race next year at Beale Park ?

Just bought a new drill

H-A

 

Jeremy,

I've lost track, what did the boat weight when you finished?

Any concerns with the aluminum construction?

Marc

 

great thread, i'll be starting my own SOF boat shortly.

 

Thanks for the reassuring words, folks, they are much appreciated. As you can imagine I was a little annoyed at the time, but I'm already thinking ahead to fitting my home-brew front rowing system and getting out on the water in the boat.

I am pretty sure that there will be another race next year, judging from the positive response from both the sponsor (Makita) and the organiser (Watercraft magazine). It may be more than just a race, as a large part of the attraction for the public this year was the wide variety of propulsion systems and Heath Robinson contraptions that were entered.

The finished weight of the boat is much greater than I was aiming for, primarily because the paint that I used added around 3kg - it has ended up weighing just under 15kg (~33lbs). With hindsight I should have taken the time to clean the fabric properly and just give it a couple of coats of clear varnish. I painted it with a water-based flexible hard coat finish, made by Plastidip, that was a complete pain to use. I'm sure this paint is OK for some applications, but I wouldn't recommend it for a SOF boat. I wish that I'd stuck to my original plan to use the aircraft fabric paints I'm familiar with, although expensive it would have given a better finish with far less work and would have been lighter, too.

Overall the aluminium construction worked very well. It was quick and easy to build the frame, with no waiting for adhesives to cure in the main. If I'd not opted to avoid using wood anywhere then it would have been easier, as plywood for the transom and stem would simplify the build a fair bit, plus the floor boards would be nicer and easier to make from plywood. The boat attracted a fair bit of attention at Beale Park, and seemed to be a bit of a camera magnet at times, so I suspect there will be a few more photos that may appear on the web and maybe in one or two of the boating magazines before long.

Jeremy

 

build quality

looking at your finished project, I have to admit to envy. the fit and finish, not to mention all the details that you incoporate are great. The dolly for the boat and the drive unit are two noticeable examples. keep us up to date and let us know how the boat preformed with the drill motor. In your build, how did you shape the ribs, and were the stringers pre-bent or just wrapped around the ribs? I'd love to try the technique if I ever finish my other projects. I like my SOF boat, but I made it way too overbuilt and consequently way too heavy. It is fun to row, but in a head wind and chop, it is a challange to keep moving. In ocean rowing, weight isn't always a bad thing.