Outrigger Touring Canoe

I have a stack of 13"x60"x 3mm Baltic Birch 3ply cutoffs. The grain runs long dimension in the center ply and short on the outside. I'd like to build a easily car-toppable touring outrigger canoe that's not too wide as an alternative to a kayak. I have 10' lengths of 2.5, 3, and 3.5" aluminum tubing on hand.

I'm 64, 200lbs, and have a reasonably fast 17' rowboat I built that I can hold at 5.3mph for a half hour or so but will cruise easily at 4. I don't need to go any faster than that and would rather not get wet either from instability or low freeboard.

Thanks in advance for your thoughts.

 

I assume you will do a search on the net to see what has already been done or is available as a design. I kept the FreeShip file I posted in the Fast Rowboat thread so that is available if you need it.

An outrigger canoe gets its stability from the ama rather than the hull shape so it's main hull can be designed for minimum wetted area, which should also minimize weight. The ama can be very narrow and does not require a lot of volume. Rick Willoughby's old pedal boat thread contains images of suitable designs you can adapt to your needs; I think they are hard chine designs but the beams and lengths will provide guidance.

You noted earlier in the Fast Rowboat thread that the ply will bend to a 19" diameter, that should suit a rowing shell type design built with the "vertical chine" construction method previously discussed. For new readers, it uses a fairly large number of short ply planks laid gunnel-to-gunnel and secured with ply butt blocks which would appear like ribs on the inside of the finished boat.

I have given the vertical chine concept some thought. The ribs needs a minimum glue joint width 3x the ply thickness on both sides of the join, for a total 18mm, but that should be increased, maybe to 1" to allow for small positioning errors since the rib will be underneath the planks during the build and difficult to locate precisely. The joints will have to be epoxied to ensure strength since it is likely that small gaps will be present in the joints unless a clamping method can be devised that is effective over the entire area of the joint.

Some experimenting will be necessary to see where the problems are with the method, but I think it can be tackled with a relatively small number of station molds and several fairly thick ribbands over the molds to define the cross-sectional shape and support the planking and ribs during assembly. Clamping the planks may be a problem, an alternative would be small temporary screws through the planks into the ribbands. Construction would probably start at the midships mold where the building form is stiffest and work outwards, so the completed planks and ribs add to its stiffness.

I see no need for longitudinal members such as stringers although gunnels will be required and a keel may be advisable, but in a rowboat an extra stringer may be useful for seat support. The gunnels can be simplified to inwales only if decks are used, which will suit heavier conditions, although an open boat will be lighter.

There are other similar construction methods you can research, such as Constant Bilge Radius style and the Radius Chine construction method. The Radius Chine method is for larger boats where just the curve of the bilge is done with ply panels laid crossways but is clearly related and may have lessons to offer. In the Constant Bilge Radius method the radius of the bilge and the radius of the gunnel viewed in plan are both constant which allows a partial length building form to be used; the partially complete hull is moved along the form as each section is completed. An advantage of the CBR method is, all the planks will have the same outline until they approach the stems, simplifying marking and cutting.

 

I built one outrigger canoe, very deep and narrow hull, had more drag than I expected, sure for higher speeds wave drag would be less, but at paddling speeds drag was more

Ideal underwater shape is semi-circle, though if you flatten it out a bit and end up with an elipse, the extra surface area is modest.

Outrigger, I would go with 8ft, because that is the lenght of a piece of plywood. I have tried shorter outriggers, around 5ft and they did not work well, an 8ft outrigger goes well.

look at easyrider kayak for inspiration

 

Rick Willoughby's human powered boat thread is here http://www.boatdesign.net/forums/boat-design/pedal-powered-boats-23345.html.

His main interest was pedal powered boats and there is a lot of emphasis on drive train and propeller design but there is some information on hull designs too. Long and narrow is the invariable rule for the main hull, same for amas.

Caveat: a long narrow hull has more wetted area than a shorter beamier one which increases the drag at low speeds during relaxed boating while allowing a greater hull speed; so if you’re interesting primarily in recreation rather than competition you may do better with a shorter hull than the designs shown in Rick’s thread. I have a 12' canoe which is faster than my 13+’ kayak with normal paddling. The longer boat wins in a race between the two boats regardless of who is paddling, but it’s harder to push along when simply cruising.

My own experience with using an ama on a sailing canoe suggested they can create a lot of drag and are best kept out of the water. Other people have also reported that extra drive available from a sail rig with the leeward ama in the water does not overcome the additional drag. It is easier to balance a narrow boat when paddling than when pedaling so the amas aren’t really needed all the time and there is less power available. I suggest mounting the amas high enough to keep them above the water most of the time. Of course, they need to be kept clear of the paddle blades . . .