rigid raft

[river runner]

I've been playing around with a design for a rigid raft. Kind of a cross between a Grand Canyon dory and a Grand Canyon raft. The photo of the rendering is as far as I've gotten and maybe as far as I will ever go. At the chine, there would be a floor with foam between the bottom and floor and the sides would be a box section filled with foam. There would be holes in the side, just above the chine, to make it self bailing. A framework would go over the top, just like if it were a raft, only out of laminated marine plywood instead of aluminum tubing.

[Land Lubber]

Rafts aren't rigid for a reason! Your dish would would fold up like a paper plate.

[river runner]

Wooden dories have been going down the Grand Canyon for years, not to mention Cataract Cayon, West Water and many others. You just have to build it strong and miss the rocks. I've owned an 18' cataraft and a duckie. I'm reluctant to ever buy another inflatable. They are a pain in the you-know-what. Rafts row like fat pigs, which is why people turn to dories.

[wayne nicol]

rafts made from hypalon remain flacid no matter how much you seem to pump them.
it is a tougher fabric, but more grippy on the rocks, and way tougher to pach riverside- and more costly.
boats made from pvc, are more rigid, faster, easier to control, greater loadability- slip over rocks better, are cheaper, easier to fix, puncture a bit easier , and generally the pvc boats are more "flippy".
personally i prefer pvc of the two.
rafts have their place, as do rigids. each to their own iu geuss.
rigids sure do row better- carry more, but not nice in a wrap situation.

[portacruise]

High quality inflatables like zodiac retain their high pressure pretty well but are not meant for rowing. There are some high pressure inflatable designs that are much faster than dories, but don't have as much room. http://www.youtube.com/watch?v=TYojUrSfreE Perhaps a fast pontoon version could be built around this concept which did win some races many years ago: http://www.cotuitcapital.com/mmarine...ltralight.html

Porta

[Submarine Tom]

I wouldn't call 3.5 PSIG high pressure but it certainly results in hard tubes on a Zodiac or Zodiac style inflatable.

-Tom

[portacruise]

Some go to 6.5 psi like these:
http://www.inflatablexperts.com/infl...ay_kayaks.aspx

P.

[Hussong]

Yes, you can build higher pressure inflatables with drop stitch fabric, but the cost of the boat is appropriately higher.

River runner, do you have some images that better show how the hard and soft materials would be incorporated in your proposed design? I read the description, but my take on that proposal may be different from that which you have in mind.

In general, I'd say that you may have an interesting craft in mind. It could give you the rowing responsiveness of a river dory, while also having a more forgiving form such as is seen with inflatables.

[river runner]

I owned a cataraft or pontoon raft. They row better than the oval shaped rafts. But I was surprised by how little it would carry. It was 18', which is a big one, and it wouldn't carry much more than a large canoe.
Keep in mind that I was lying in bed and thinking about boats for river adventures and came up with this idea. When I got up, I whipped up a design on the CAD program in about ten minutes.
One of my goals was to make something easy to build. Something any idiot, like me, could build in one summer. Something pretty much unsinkable. It would be pretty ridgid and very strong. A lot of floatation foam sandwiched between marine plywood and box sections. Superficially it would look a lot like a raft, but would row much better, won't leak, won't need pumping up, or putting together at the put in. Just pull it off the trailer, throw on the gear and strap it down, jump in and go. You have a solid floor to walk on and could even sleep on it.

[PAR]

Something flexible can tolerate a lot more abuse then something stiff, given the same weight. In short a stout, stiff raft/boat needs to be heavily built, but a structure designed to flex doesn't have to be, assuming the structure can rebound from localized distortions. A really good place for the Lindsay Lord method if you ask me, which is precisely what this method permits. You end up with a light, flexible but strong craft that can absorb twists, distortions and repeatedly rebound. Lastly, your image is difficult to workout, but it appears to have next to no freeboard, meaning you'll eat a lot of water.

[portacruise]

What about something like this with a rowing station instead of sail? http://www.youtube.com/watch?v=s0xTZH3nYAw
Compared to dory: Easy to build, lots of room, lower draft, faster hull length, collision resistant/unsinkable if using right polymers/supplementary floatation, recycle used kayaks/canoes for low cost, etc.

P.

[river runner]

Portacruiser: I still have dial-up, so youtube is a long wait, but I get the idea of it from the title. In a previous post I asked about the legality of using a canoe as a femaile mold, with the intention of making two canoes and joining them into a cataraft. This post was taken down because the subject had been addressed several times before. So, yes, I like the idea.
PAR: I'm not faimiliar with the method you mention. I'll do a search and see what I come up with but I think the idea/theory has merit. Yes, the freeboard is low, as it is on a raft, which was the point. Whether the flexibility of a raft would make it any drier is anyone's guess. But this brings up the real question here: if I want a rigid boat, why not just build a dory? I did build one, but not intended for something as extreme as the Grand Canyon, but I do have a draft for a Grand Canyon Dory. I'm not sure which would work better, some version of the raft idea or a dory.

[river runner]

I didn't find a whole lot on the Lindsay Lord method, but I take it to be a sheathed strip planked boat. Sounds a lot like the method for building canoes. I wouldn't want to go strip plank with this boat, but it might be possible to apply the principle to a plywood stitch-and-glue. I was thinking pretty heavy plywood with the bottom covered with multiple layers of glass. Maybe lighter plywood, smaller square "tubes" around the perimeter and the bottome covered with less layers, but of kevlar, would make it more flexible, and possible less likely to break-up.

[KJL38]

How about building the hull from foam covered in composite with everything up to floor level being a single block with scuppers along the bottom of the sides? Like a giant surfboard with sides.

Here in Western Australia a similar method is used to construct powerboats for racing in shallow rocky whitewater and they survive quite well. They use a lot more layers of kevlar than you would need due to their much higher impact speeds of up to 40 knots. Here is a link with a few pictures, obviously a completely different shape to a dory with an open transom instead of scuppers along the side but it gives an indication of the suitability of the construction for whitewater. http://au.news.yahoo.com/thewest/a/-...-descent-pace/

[river runner]

KJL38:
I think you Ausies are even more insane than us Yanks. Yikes! I've thought about building using that method. Plywood takes a fairer curve and needs less surface prep and finishing. I could combine the two by using a very light plywood over foam, then glassing the heck out of it.