What's up with the Starwind?

Welcome back, folks. I hope you've had a merry Christmas. Or a merry last few Christmases, for that matter.
So, whatever happened to that weird, radical power trimaran we were working on? The one that filled these pages, oh, seven or eight years ago?

Well, life happened.

2015? We had a kid. Taking care of a kid for their first year, while working a full-time job, doesn't leave much bandwidth for anything else. I see some fathers who, once the kid is born, back away and go do their own thing, leaving the mom to do the child-rearing. I don't like that. "Success by Six" is a catchphrase for a reason; I'm of the opinion that if you're raising little ones, their needs need to take priority over pretty much everything else for those first few years, on both the mother's side and the father's. So, personal projects got set aside for.... someday.
2017? The startup company I was working for took off reasonably well, and got bought by a multinational, and they decided to keep all of us on and keep growing the team. In a way, the stability of being part of a larger company is nice; one doesn't have to worry, for example, if there'll be enough cash to make payroll when the corporate parent has fat bank balances in a dozen countries. But turning a company you helped build from scratch into a business unit of a global enterprise comes at a personal cost, in time and energy.
Then, with a rapidly growing daughter, the 1200 sq.ft. country home was starting to feel... well, just a little bit cramped. Our desks were in the dining room; kid stuff was spilling over everywhere. We didn't want to move, so enlarging the house seemed necessary. Contracting it all out wasn't in the budget. So, we start digging a hole, hiring concrete guys, and.....
2018, hello next kid! Construction and child-rearing in parallel. Not going to get much boat work done with all that on the list!
So, 2019 rolls around. A careful evaluation of the boat projects, our personal desires, our long-term goals, and the skills we need to learn to accomplish those goals leads us to the decision to buy a low-cost "classic plastic" yacht, a proper cruising boat, on which to explore and learn in ways that just aren't possible when day-sailing smaller craft. (This saga is detailed, behind a totally-worth-it paywall, at Attainable Adventure Cruising - https://www.morganscloud.com/2020/08/14/us30000-starter-cruiser-part1-ho... .) This turned out to be a good call. We've spent more time on the water, and on bigger water, than would have been possible had we kept the boatbuilding projects at the top of the list. And we've learned things about family cruising that will lead to meaningful design improvements in the things currently on my drawing board.
Oh, hi there, global pandemic. Welcome to staggered-shifts work, taking turns on school-at-home with work-at-home for 16 hours every day.
And that brings us to today, at the close of 2023. All of the house work is substantially complete. The additions, the renovations, the geothermal heat pump. A few details remain to be wrapped up here and there, but the essential to-do list is done. What's left on the list is all of the "when we get around to it" type.

What comes next?

Well, personal projects, of course. I'm an engineer; we don't idle well. I've spent the last year-and-a-half dusting off the Starwind plans and iterating on various ideas to improve this design. I'm not ready to disclose drawings yet. But, for the handful of you who are curious, here are a few points of interest.

For one, LiFePO4 batteries and laminated monocrystalline solar panels have got a lot better and cheaper since the boat was first drawn. She was originally envisioned to have a 60 hp gas outboard for speeds 6-18 knots, and a pair of 1 hp electric motors for speeds under 5 knots. As outboards got more expensive, and batteries got better, the calculus changed. The Starwind's mission is now best served by a purely electric drivetrain: LiFePO4 batteries in the bilge, a ~23 kW (30 hp) electric motor spinning a single big slow prop, a thruster for crosswind manoeuvres, solar PV on the top, and a sprint speed of about 12 knots (with the option to double or triple the range by slowing to 5-6 knots).
Ditching the gas engine saves a lot of money (which will be eaten up by the batteries), but also cuts the available propulsive power considerably. That means a longer, and differently shaped, hull is appropriate. The Starwind trimaran's main hull is now a full 10 metres on the waterline, and the boat spans 4.4 metres centreline-to-centreline between amas. That's a pretty substantial boat by area, but not by weight. We're targeting under two tonnes empty, for a D/L ratio of under 60 - absurdly light by any standard. She'll be able to carry about one tonne of people and stuff comfortably in any conditions at a minimal cost to range or speed, and I'm expecting her to be quite safe (albeit without the sprint-speed option) when carrying payload equal to her own two-tonne weight.
A ten-metre steel-framed trailer for a boat this size weighs one to two tonnes on its own. Boat, plus trailer, would be well over the 5,000 pound rating of most modern three-row SUVs. Our existing General Motors GMT 820 would handle it fine, as would most full-size (or, now, full-size-and-a-half) pickup trucks, but what cars might we want to own after that old GM dies? And who wants to fight for 40-foot parking spots at the ramp? Another factor became apparent while working through the drawings: the trailer would be an almost totally redundant duplication of longitudinal structure that already needs to exist in the main hull for the trimaran design to work. We can put something resembling aircraft landing gear on the boat itself, adding perhaps a third of a tonne to the boat. Yes, that brings a non-negligible cost in weight, speed, and range while on the water. But, in this case, it more than makes up for that penalty via the reduced weight of the complete road-worthy system. There's another benefit: a self-trailering boat can safely beach and refloat itself on any suitable surface. And it can be portaged by any truck or tractor that happens to be handy. You don't need to drive back to collect your own vehicle.
Optimizing around the trailering requirement leads to other interesting design decisions. For one, the biggest contributor to the trailering fuel cost (which is substantial) is aerodynamic drag from excessive frontal area. An F-250 pulling a four-ton 5th wheel camper, and a Freightliner Cascadia pulling a 19-ton cargo trailer, have a similar frontal CdA term and, surprise surprise, a remarkably similar fuel burn rate. Boats are inherently streamlined, except for the superstructure that sticks out above the truck's roofline. So, let's get rid of that superstructure. Our tent trailer RV folds down to minimize frontal area. Why can't the boat do the same? With the amas folded in (horizontally, now, to make room for the retractable wheels and to not leave crossbeams sticking up above the roof) and the cabin top folded down flat, I think we'll be able to keep the entire boat within the same 2.1 m nominal height as the truck that pulls it.
While we're at it, why should a trailer boat only be usable when on the water? What do we need to change in order to make it functional on land as well? In this case, not much. We got rid of raw-water cooling and winterization when we ditched the engine in favour of solar and batteries. The galley can work from the fresh-water tank, or be hooked up to a hose like any RV. The head isn't allowed to discharge overboard anyway, thanks to environmental laws, so we already need to make that water-independent. And... now we're at a trailerable boat that can serve as a decently passable fold-down RV during long over-the-road trips, or as a cozy guest cabin (at least during the warm season) when parked at home.

And that's where we are at now. An ultra-light, ultra-slippery electric trimaran, capable of proper coastal and inland cruising a few dozen miles at a time, and of serving as a mothership to a gaggle of kids and friends with their camping gear and water toys. Its flexible crossbeams fold out to party-barge size, with massive stability from the light but voluminous outriggers, when on the water. It tucks down to a clean, streamlined package for over-the-road travel behind any vehicle that happens to be handy, wherever you happen to be. And it can serve the "mobile living space" function passably well when parked at home, or on the road, extending its utility far beyond what a boat alone would normally be capable of in this situation.

Design detailing is underway now. Construction resumes as soon as the snow's gone and I can get the summer gear out of its winter-hibernation spot in my shop. Watch this space.



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