backpack dinghy design idea

hello, i'm new to the forums and boat making. i saw the origami folding boat web site ( http://www.woodenwidget.com/TheRange.html ) and it made me think about even more portable boat designs. i was wondering if you guys had any advice about even lighter contruction materials and folding design ideas to create a similar dinghy that could comfortably transport (under lightweight collapseable oar power) 2 adults and a load of groceries from land to an offshore anchoring that would be light enough and small enough to fold into a backpack sized bundle.

the intended use of this would be in fair weather. what is a reasonable size boat for that capacity? also, i would prefer the boat be designed with maximum dryness of passengers in mind, preferably so with weather permitting they didn't have to get wet at all getting in and out of the boat.

my first thought on design was to make it slightly longer with a center hinge to cut the carrying size down, and make the sides a bit higher and the beam wider. sitting low in the boat seems to be a good design decision that the origmami made for stability.

please let me know your thoughts, especially on contruction materials for the rigid parts that are both light, sturdy, and can have joints made stiff.

-grift

 

If you were silly enough, you could vacuum down some 300csm onto thin foam on a sheet of glass, those sheets then could be cut out and joined using two part contact cement, same as they use on inflatables. Use a 420 denier neoprene or hypalon piece as a flexible joint. It would be strong, flexible seamed, yet quite rigid in the topsides and bottom if you do it right.

It would certainly be light. Make the mess about 8 feet long, snub nosed pram style, and you would then have a nice backpack dinghy.

 

is that similar to how surf boards are made? last night when i was falling asleep i had a thought that surf boards were both very light and rigid.

i'm still not sure how to make a hinge in the center that works for folding and is stable when in use. the whole frame could alternately be made with some sort of tubing in X patterns instead of boards to expand out and lock in place. i need to do some drawings and find a good way to make models to explore that though.


-grift

 

surf boards are often made with glass both sides of a thin foam core (often this is built over a superlight foam blank filling the board inside space). Usually not Chopped Strand Mat (except sometimes in the outer layer) because woven/knitted/unidirectional fabric is stronger.
If you use 400gsm outside, 200gsm inside (I have seen such a layup on a foam sailing dinghy), and a 4mm 100kg/m3 foam core, with epoxy it can weigh under 2.5kg per sqm. 3mm ply boats can be built even lighter, it can be very roughly about 1.5kg/sqm without epoxy I think. I have a chopped-up race kayak from 3mm cold molded wood - stiff enough due to the curvature and unbelievably light.

There is also the soft fabric over frames sort of boatbuilding.

Personally I favor slender hulls for almost anything, if there is need for stability use a smaller second hull. Long slender hulls can be built in sections that can be bolted together, if a proper gasket is used in place of a full bulkhead at the join, or the deck is minimal, the sections can be stuck inside each other to save space.

 

The hinged seam is simply two pieces of hypalon material, one glued on one side, the other glued on the other side. That way they are very flexible, yet totally waterproof.

 

If you really want it to be light and small enough to carry in a backpack then a skin on frame boat is the way to go. The frame could be constructed of alum tubes with shock cords inside like a modern tent frame. Snap the frame together and stretch a vinyl coated fabric skin over it. When collapsed it shouldn't be much bigger or heavier than a tent.
C.O.