Above can be seen very early designs for a 19ft tacking outrigger. Design still open to changes. Concept is an easy to build, cost effective, small cruising mulithull. Occupants will mostly be inside the cabin, but access to side deck (outrigger side) is possible as a means of stretching legs and gettng fresh air
Below can be found more recent sketches as I have settled on a few things. Firstly there is a single large sponson on the outrigger side, and the safety ama is to be retractable. I was unsure as to what width is required for a double berth, hearing that 42" can suffice, I settled on 48" for a little more comfort. Length is set at 19ft though it could be reduced to 18ft if desired. The outrigger folds inwards, the outrigger itself can overlap a little onto the cabin as it sits higher when folded as opposed to the beams themselves.
By reducing the distance between centerlines to 7ft 9" and increasing the trailering beam to 8ft, the outrigger can now sit on the sponson top as opposed to cabin top, resulting in a lower center of gravity when trailering. Beam overall when deployed is 11ft, which is quite a bit more than the jarcat. By having the cabin in one of the hulls as opposed to being on the bridgedeck the overall height of the craft is reduced, resulting in less windage. The main hull is still much beamier than the Jarcat so it will not be as fast
The board fits under the seat and is 45cm x 115cm, of which an area of 45cm x 70cm projects below the keel. This is an effective area of 3.5sqr feet, possibly a bit high but a slower speed craft often needs a slightly larger board. I based this board on the Scarab trimarans by Ray Kendrick
The design below has gone into software and I have calculated draught and other calcs based on a 700kg load. I decided on a heavier than normal load as it is anticipated that the boat will be laden with gear that will increase it's weight. Thus the hullform was optimised for a heavier load from the brginning as opposed to designing for a lighter weight and hoping for the best.
When compared to scow proa I have made some changes based on my trip to Port Phillip Bay. To overcome the issue of pounding I have tried to make the flat bottom as narrow as possible forward. I have given the bow a sharp entry and made it much more vertical than my present tacking-outrigger. I found the highly sloped stem on my boat did not work well going into steep closly spaced oncoming waves. The cabin is further aft when compared to scow-proa resulting is smoother motion for the occupants. By making a tacking craft and not a shunting craft, many things are simplified. Rudders and boards are much easier to do, and the rig is simpler too.
Influences on this design come from a few sources.
Farrier trailer tri
Davitri, a new 18ft italian trimaran
Flaquita tacking outrigger
The cross 18 trimaran, such a nicely shaped craft.
Arpex tacking Outrigger by Peter Mirow
Scarab trimarans by Ray Kendrick