Lightweight hull material - Folding boat

[suwarrow]

I'm hoping to build an ultra lightweight folding dinghy and would welcome some advice.

I'm thinking of something designed along the lines of a Seahopper, Stowaway, Instabote, Portabote or Banana Boot (inspired by... not a copy).

These last two utilise polypropylene / polyethylene in their hulls. It seems to make some sense as its a durable and affordable material but can anyone outline the drawbacks or suggest a better hull material?

Cheers,

Tim

[Petros]

the polypropylene/polyethylene are low maintenace materials but they are not very strong, so the boat ends up being heavy.

Light weight of course means carbon or kevlar composite sandwich, which is costly. You can actually make a fairly light weight folding boat with careful design in wood. A lightweight wood frame (like cedar or sitka) with a polyester fabric cover would make a light folding boat, similar to a folding kayak, but an open dingy instead.

I have been thinking about the same thing for several years. If folding kayaks are so common, why not folding dingys too?

[rasorinc]

How about a rubber like or plastic material and a foot pump and blow it up.

[suwarrow]

Originally Posted by rasorinc

How about a rubber like or plastic material and a foot pump and blow it up.

Problem is I don't want to re-invent the wheel. There are plenty of cleverly designed inflatable boats / RIB's out there.

I am hoping that this concept folding boat will primarily be used as a sailing dinghy and no-one (with the possible exception of the Henshaw Tinker Tramp) has yet produced an efficient inflatable hull shape for sailing.

There is some potential to use drop stitch inflatable panels, which are still relatively new, and are extremely rigid when inflated (see the inflatable SUP made by the red paddle company). They can definitely produce strong flat panels but I'm not sure if its possible to produce the curved panels that would be needed to form the hull.

The main issue aside from cost of production and design is the time it takes to inflate. The particular joy of a folding boat is, if designed properly, it can only take seconds to unfold.

[suwarrow]

Originally Posted by Petros

the polypropylene/polyethylene are low maintenace materials but they are not very strong, so the boat ends up being heavy.

Light weight of course means carbon or kevlar composite sandwich, which is costly. You can actually make a fairly light weight folding boat with careful design in wood. A lightweight wood frame (like cedar or sitka) with a polyester fabric cover would make a light folding boat, similar to a folding kayak, but an open dingy instead.

I have been thinking about the same thing for several years. If folding kayaks are so common, why not folding dingys too?

I know what you mean about polypropylene/polyethylene not being very strong (rigid). I suppose this could be combated by welding or bonding a light frame onto each panel however, as I understand it, welding or bonding polypropylene is a difficult process...

Carbon or Kevlar composite is a great idea but as you say probably too expensive for a folding boat.

There have been some really interesting skin on frame type canoes. I believe Klepper (Klepper Master) made a number of sailing dinghies in this style a couple of decades ago. With the advances in skin membranes (maybe Hypalon or something similar) this could work well.

It doesn't suit me personally however as I believe the skin could get punctured and once again it will probably take a little while to unfold / construct the boat each time you want to use it.

Other thoughts:
- Stowaway Folding Boats make a great boat out of GRP but its too heavy.
- Instaboat make another great boat out of aluminium, but to my mind this isn't an attractive hull material and once again is probably a bit too heavy.

Maybe plywood sheathed in a light GRP or something similar is the only answer???

[Claudg1950]

Suwarrow:

I am also planning to build something along those lines, and I am also concerned about the long-term strength of hinges.
For what I could see, in addition to polypropylene and polyethylene, PVC fabric and neoprene seem to be in use for hinges.
If you navigate youtube, you will find several instances of home made folding boats, among them a gentleman that made the hinges with #50 fishing line (later covered with PVC) and another that installed several traditional cabinet hinges (and then he covered them accordingly with a tape).
If you go to youtube, you will also find something completely different: a series of square boats built in one piece of 1/4" corrugated plastic. Enter "no parts boat" at youtube and see what comes out. Food for thought.
All the best.

[suwarrow]

Claud

Interesting stuff on YouT ube - thanks.

If you're interested in folding boat hinges I can recommend this forum:

http://groups.yahoo.com/group/flapdoodle_dinghy

Search on 'hinges' in the forum.

It was started by a guy called Bill who designs and sells plans for a folding boat he calls a Flapdoodle. He and his fellow builders are a fountain of knowledge...

Hope it helps in you're design.

[Claudg1950]

(Re: Flapdoodle) Great link!!! Thanks a lot!!

By the way: I assume that by now you have heard of the classic Jess Rathburn folding kayak design. If not: Plans were originally published at PM magazine June 1963, and from then on, there have been many versions and many sets of drawings. Among others, this: http://www.instructables.com/id/8-Folding-Kayak/

The corrugated plastic used in the "no parts boat" is also known as Coroplast. A gentleman by the name of Pax Rolfe built, some ten years ago, a version of the Rathburn kayak out of two pieces of Coroplast: http://www.foldingkayaks.org/build.shtml

But you probably knew about this as well; you seem to know everything there is about the subject, and then some. All the best.

[gonzo]

For lightweight, you can't beat plywood.