- Beam of around 2300mm, to allow the boat to be stored behind my house (the gap between the fence and my garage is 2400mm). This will also allow for trailering without wide load placards, being under 2400mm.
- Length of around 6000-6500mm. This is a bit more vague, as there's no specific constraint here, but the 6m length tends towards a 2300mm beam, so this is it.
- Maximum draft of around 800mm. More than this makes trailer launching at boat ramps really hard. Indeed even launching a boat with an 800mm draft will be hard. Stability and cabin room is however directly related to draft, so there is a strong push to maximise draft at the expense of trailerability.
- Maximum weight of around 1800kg unladen. The tow vehicle I am considering has a maximum towing weight of 2500kg. If we subtract 700kg for trailer, we end up with 1800kg for the boat. Stability constraints again push us upwards here, and trailerability constraints push us down. I think something around 1400-1500kg is probably reasonable. This implies a displacement of around 2000kg.
- As much sailing ability as I can get given those other constraints. Ideally I want something I can sail across the Great Australian Bight in, so some measure of blue water capability.
I'm working on the premise of a 6m LOD, 2.3m beam, 0.6-0.8m draft boat with centerboard mounted in a trunk below the cabin floor. Katie comes pretty close, but the draft is perhaps a little on the shallow side, at around 0.48m board up. Pretty-much everything that's designed without a board has a draft of over 0.9m, which I think is just a little deep.
To find a better compromise, I thought I might try developing my own hull shape. I started with the table of offsets for Buzzard's Bay by Herreshoff, as published in Sensible Cruising Designs. I found the table of offsets to be surprisingly lumpy, so abandoned any attempt to stick to the table of offsets and instead just started drafting lines in Sketchup. The process was first to draw a profile (face), and overall plan view, to constrain LOD, beam and draft. The shape is similar to Buzzard's bay but I brought the bow up more vertically above the waterline, and increased the radius of the turn of the bilge, giving the rabbet a hard inflection rather than a smooth curve.
Then I drew waterlines and stations, got them to line up, drew buttocks, found they were miles off fair, edited the waterlines, edited the stations, edited the buttocks, and went around the loop half a dozen times, until the waterlines, buttocks and stations all intersect with errors of <1mm or so. I think the shape is reasonably pleasing.
Here's the profile:
The plan view is below:
The rear view is also shown:
Finally the quarter-view. I haven't sheeted the hull in sketchup, so it's just a bunch of lines.