Recently I got a job designing a batch of ferries to be 85′ long. They have to be ready for the America’s Cup next year. The builder had some 75′ molds which were based on an earlier 65′ design. They asked if it was possible to use the existing molds.
I 3D modeled the two hull designs, superimposing them in each other, in transparent mode. To my surprise the existing molds will work, with some inserts, and a foot more freeboard..
One of the guys from Steamradio just had a 40’ performance trimaran designed by Shuttleworth. I was surprised how much it resembled a study that I did for Phil Steggall a few years ago. It didn’t get built and I forgot about it. It is almost the same sailor use program. And it was based on improvements to my 40’ tri, the Geko. The Geko was optimized for singlehanding and light weather. The two trimarans above are for more wind than Geko usually found.
The beams are not swept forward on Phil’s boat. I asked multihull engineer and composites god Ronnal Reichard about that. He declared it an inefficient idea as it introduces an added twisting moment to the main beams. He dismissed the advantages of helping the ama bow as the ama has much more section property to work with, to ease that stress. The tri had square L/B design of course.
It has been suggested that swept forward beams keep the weight of the beams forward. The vast majority of the bending load, and thus the laminate, is near the middle and aft.
The biggest improvement to the Geko would have been adding the flare to the main hull. Any crew or guests need to toss their bags and foulies somewhere, out of the middle. I forgot about that. I thought everything else worked pretty well, for a shorthanding fast 40’ tri.
Boards in the amas solves the board intrusion in the main hull, but if short tacking, one needs a crew or it is more difficult to tack smartly. I wanted smart tacks on the Geko. Not everybody has to short tack all day in light weather.
Where to helm from is an interesting exercise. And I found that it is most dependant on the crew or lack of. Reflexively, everybody should be up on the high side. These boats typically have almost deck sweeping mains, and are doing twice the speed of anything else out there. Anything could be happening behind that main. I always ended up in the cockpit, down low, so that I could see traffic approaching from the low side, helm in one hand, and mainsheet in the other.
With a crew, that is not a problem, but where to steer from depends on how much the helm (owner usually?) trusts the mainsheet trimmer. I pretty much only trust myself when it’s gusty, unless Dave Calvert is crewing….
Is that a pair of main winches I see on the top view on the back beam? That suggests it’s optimized for at least double handing or a crew then. Double handing I was told.
the Shuttleworth tri
It’s all very interesting, imagining how design affects life blasting upwind. And the interesting ways that a design can be fitted to the owner’s individual needs.
This picture from 5 years ago came up on Face. “Yesterday I got to visit the next KHSD 65′ catamaran ferry for Lake Victoria in Uganda. CM developed plywood and epoxy once more. It is being built in Everett, WA and again by Thain Boats. http://www.thainboats.com/
With some of the crew yesterday.” After posting it, I got some updated pictures of Bluebird, now in Uganda. First, from 5 years ago.
One hull is winched toward the other on the water. The beams slide through one of the hulls, on teflon cleats in the glass tube.
This is a two couples arrangement. One couple would probably have shower in the other hull, ond only one berth.
It is finally moving along again. One new drawing here today, and the rest tomorrow, barring somebody’s emergency. I recall the 3D modeling was done 2 years ago?
Recall it was this rendering.
and below is the sail plan.
This just showed up. The design has been updated since this was done. And I am doing a version with a more protected cockpit next.
http://themarineinstallersrant.blogspot.com/2015/11/local-boats-i-like-eco-trekker.html?m=1
Notice how the tension members on the A frames are treated. These two wire systems each have have roughly double the forestay load on each of them. Stainless does not like to be cold-worked. A thick continuous wire making a sharp turn is a classic failure mode. It is less costly. I am a bitch about details like this. Mine cost more to do, but are more reliable. This is a mission critical part of the catamaran.
Now the cheaper way. And look how planning for the furler down low helps. Get it done right.
I’m catching up enough to take the time to post things I saw early this summer. Here is an interesting comparison again on the 65 charter cats. Side by side my 65 daycharter Alii Nui and a Trilogy 65 by Marples. Both were built by Schooner Creek only a few years apart. The Constant Camber 65 was interesting because it had almost everything that CM had 30 years ago (and still does) and almost nothing that CC had back then; except having to build a surfaced mold.
Here are two ways to do the bow tube ends. First, Alii Nui. Notice how the tramp extrusions on the hull are at the same plane as the slide groove in the mast section. The tramp can be flat and secure. Notice also that the hull brackets are on the inboard side, not the top. That allows a shorter bow tube, which is stronger. And no chance to trip over the bracket on deck.
Now the other cat. And notice how the vertical tabs can bend back under load. I imagine they will have to keep after the caulk joints at the hull. Notice above how the bracket is bolted to the hull. No delta at all.
I just got a quick shot of the 55′ Moondance Cat daycharter cat in Buffalo, NY. CM construction in developed plywood/epoxy. The builders made the hull from the two panels wired together in something like 4 hours elapsed time when I was there.
