It's a rare boat indeed that is tasked with one and only one mission. The degree of flexibility that's expected, though, varies greatly from boat to boat. My requirements for my next boat fall in the "does everything reasonably well" category, which necessitates a lot of head-scratching and balancing of trade-offs during the design phase.
How do you combine multiple sets of requirements in one vessel? One common approach is to throw size (and money) at the problem. Can you have a 30-knot offshore fishing machine and a dockside luxury palace in the same package? Of course you can. It might be 18 metres long, cost three million bucks and have engines capable of powering a small town, but it can be done- and is indeed done on a regular basis.
For the Starwind 860, the more size / more money approach won't work. Our budget isn't that big, for one thing, and we have to keep the overall dimensions below the Highway Traffic Act limits for towing over land.
What are these multiple missions?
Hauling furniture and building materials around in a lightweight runabout is not fun. The high sides and deep cockpit of a sport boat make it hard to load propane tanks, bags of cement, stacks of lumber, mattresses and other heavy and bulky cargo. I've done that many times, and it gets tiring pretty quickly. One tonne of cargo at a time would be a nice minimum to aim for, in our case. Pontoon barges excel at this kind of work, but they're fundamentally incompatible with our next mission...
Lake and Coastal Cruising
In our case, this could mean 4 to 6 people for up to a week (with camping on shore), or two people for about a month. The Great Lakes can brew up some nasty chop that renders pontoon barges and other low-riding vessels helpless, and causes low-deadrise planing hulls to pound like crazy. Some of the best cruising grounds around here are blocked off by bridges, or require a trip over land, so we want to be able to tow this cruiser inland- and a sailing rig is hard to justify if it's constantly being folded down for bridges. At the same time, we'd like the ability to cross to the Bahamas in good weather, or to handle the Northumberland Strait without making anyone nervous.
A fair bit of this boat's working life will be one-day jaunts to the beach, or to nearby islands. This means carrying six or more crew, plus some fishing gear, water toys, and maybe a couple of kayaks. Unless we want to be telling friends "sorry, too windy, can't take you out today", the boat has to be able to handle 1 to 2 metre waves and force 4 winds without getting too uncomfortable, and be able to keep on going in force 6 if something nasty comes up while we're out. For day trips, you also want enough speed to spend most of the day at interesting places and still be home for dinner. An efficient, quiet 10 knot cruise, with the ability to crank it to 20 if needed, would be ideal.
At this point, the trade-offs aren't looking too bad. There are quite a few boats already out there that are decent day-trippers, can handle moderately bad weather, will fit on a trailer, and can carry a tonne or so of cargo.
But now we add more constraints:
We'd like to be able to take older friends and family out for trips in this boat. When you factor in arthritis and the other perils of aging, a lot of common design features have to go out the window. Clambering over gunwales becomes impossible. Large steps up or down from the dock are a no-go. Significant heeling when people step on board or move around is also unacceptable. And we don't want to rule out the youngest generation either, which means we can't rely on lifelines, handrails or sailor sense to keep everyone safely on board. The cockpit will have to have high, solid bulwarks to keep everyone contained and dry, and should be over the boat's centre of motion to minimize the physiological effects of pitching and rolling.
Fuel is expensive, and isn't going to get cheaper. Using hundreds of horsepower to drive this boat is simply out of the question for us. That doesn't completely rule out a planing hull; there are several existing designs in the mid-20' range that will plane with 50 hp or so. But the hull shapes needed to achieve this are low-deadrise, shallow-draught shapes that aren't compatible with our requirement for running in force 5-6 conditions.
If we stick to a displacement or semi-displacement hull, the efficiency and speed requirements force us towards a long, slender shape. But it's hard to combine long and slender with the high initial stability that we need so that we can work on board and bring older, less nimble crew. The solution is to add outriggers for stability, while concentrating the crew around the centre of gravity to mimimize the effect of the boat's motion on them.
With the people concentrated in one area, the boat's extremeties can be relatively simple. The Starwind 860's forepeak, lazarette and outriggers are basically just bare structural shell, which is very cheap to build. This makes it easy to stretch her overall length out to 8.59 m (28'2"), improving efficiency and comfort without adding to the cost of the project. The usable space in the main hull is about what you'd expect from a typical 7 m (23') power cruiser, but in a slimmer and more efficient package.
The central cockpit and its wings can now be enclosed by high, solid bulwarks without looking too weird. And since the outrigger tops are nearly level with an average floating dock, there's no clambering over gunwales to get on board- just walk on, open a gate and sit down. Underway, this cockpit will be dry, protected and comfortable. At anchor, the outrigger decks come into play. These offer a large, stable platform for fishing, swimming and other activities.
The outriggers are rather widely spaced by power trimaran standards, to maximize initial stability and to minimize the drag-inducing interference between their wakes and that of the main hull. They'll have to fold to fit on a trailer, and this marks the biggest headache in the design: Folding linkages are complex and hard to build. Folding trimarans are nothing new, and there are many possible ways to arrange the linkage; for this boat, I've chosen a six-bar linkage that simultaneously retracts both outriggers to their resting spots under the wings.
We're still debating whether to have a low windshield with a full canvas enclosure, or a hard pilothouse with canvas aft. Canvas is easier to build and can be folded down when you don't need it, but a hard pilothouse might let us coax an extra month or two out of the Canadian boating season.