Lake waves, and the origin of a new powerboat

Waves, despite their well-understood mathematical and physical properties, remain a rather subjective point of discussion among cruisers. There's the tendency to exaggerate, of course- we've all heard a story that goes something like "I was beating into a force 6, there were 14-foot waves coming over the bow....". (Force 6, of course, brings an average wave height of closer to 9 feet given unlimited fetch.)

Even accounting for the exaggeration factor, though, lake and coastal cruisers seem to have a dramatically different perspective than offshore types. Smaller boats might be a part of that, but the waves themselves are also different. Give a system deep water and a long distance over which to develop, and you get ocean swells- tall, but gentle. Add a bit of land, some shallows, some conflicting currents, and things can get pretty messy even if the waves aren't all that big.

My cruising, for the foreseeable future, isn't going to be open ocean. It'll be on inland lakes and canals, coastal areas, and perhaps a few short open-water passages: Florida to Cuba or the Bahamas, that sort of thing. Whatever the next boat is, it will have to be comfortable for my wife and I in all of these conditions, and for us plus guests on all but the open-water passages. I'm not willing to give up trailering, though, and I'm not particularly interested in buying a three-tonne pickup to haul the boat around. So what will this boat look like?

Let's start with the waves. About one-third of the available boating time, Lake Ontario looks like this:

Lake Ontario

This is not a big deal by offshore standards: force 5 winds, waves a bit over a metre high (perhaps a metre and a half out in the open). But boats don't scale the same way waves do. Look at Steve Dashew's recent report on the FPB 64 sea trials, then think about how things scale. When we move from the FPB 64 to the design I'm working on now, we have reduced the boat's length by a factor of 2.3 and its mass by a factor of 20. The waves scale differently: in my case, they're half as high and about one-third as long as those which Steve's boat must contend with in the above-linked article. (It is worth noting that an FPB 64 can remain safe, albeit not necessarily luxury-liner comfortable, in waves many times higher than these.)

The result of this hand-waving scale argument is that, for the kind of use I'm interested in, the boat will have to contend with waves that- although of relatively comparable height to those in the ocean- are shorter, steeper, and acting on a much lighter boat.

Speed is a Big Deal for many powerboaters, including me, so can we plane in these conditions? Well, yes- Coast Guard RIBs and motor lifeboats do, some speedboats do, and there are plenty of cruisers that try to. But it's hard to do so comfortably, or with a significant payload. In a boat around the one to two tonne mark, planing in a force 5 is likely to result in some combination of mutiny and desertion among the crew- especially if those seas are attacking from abeam. So we need something that can knife into these waves without getting tossed around like a cork, and- because of particular preferences and sensibilities among the crew- should remain close to level, rather than heeling or rolling excessively.

Undoubtedly, a sailor reading this would think "now, why would you drive a stinkpot and pass up such great sailing weather?" Because, for much of the remaining two-thirds of the boating season, the lake looks like this:

Lake Ontario

That's perfect powerboat weather, and it causes the sailboats to either luff around at half a knot, or fire up the motor. Oh, and there's also this thing called a "bridge" that blocks a lot of the canals we want to cruise. We can always get a sailing fix from dinghies and from crewing with friends and family.

There's also the issue of cargo. Whatever I build as my next boat, it will almost certainly be pressed into duty as a work boat for a few weeks of the summer. Lumber, propane tanks, concrete, furniture, shingles and all sorts of other heavy, bulky stuff need to be moved in and out of the cottage up north. After doing six trips in the rain a couple of years ago to replace old mattresses with new, I'm very much in favour of a boat that can move this sort of stuff, in the dry, in one trip.

I should also mention the "pontoon boat factor", at the risk of offending any offshore-cruiser types who might still be reading this. Several years ago, when my grandfather's runabout was in the shop, he borrowed a ten-horsepower, 18-foot pontoon boat. It was ugly, it was slow, and you could open a ranch-style gate and step onto- not into- its cockpit, which was surrounded by comfortable couches. Everyone loved it. So this sort of easy, walk-on, side gate access has to be a part of the new boat: no rolling at the dock, no clambering down into a low cockpit. Since the cockpit can't be dropped low, the centre of gravity will be a bit high; couple this with the need for very high initial stability, and a multihull is the obvious choice.

We want to knife through those short, steep waves without too much spray, fuss or pitching. A rapid motion is OK; we're used to that from our time in Sunset Chaser, but excessive roll angles make the crew nervous and would not be welcome. We also want to carry a lot of cargo- about one tonne, minimum. We want high initial stability, the capability to cross a hundred miles or so of open water, and a one-level layout that won't force older crew into awkward contortions while boarding. Add to the list trailerability and good fuel economy, set no limit on build complexity, and a folding trimaran emerges as the solution that is- for us- the appropriate answer.

Starwind 800 power trimaran

More details on this design will be brought to light in future blog posts.



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