Small trimarans under 20'

Doug, you've just made me take a trip down memory lane trying to find pictures of the speedsailor! I know I have a lot more on a backup disc somewhere, but it is a long time and many house moves ago. Here is one of it being assembled that shows the foil in the main hull to the left, and an image of the FE model without foils. They are low res images off our old web page, but I can't find any of the originals. I'll keep looking, though.

The boat is 6m long and 12m wide, but pivots to eliminate yaw and pitch torque, hence can be very spindly (everything in either compression or tension, other than foils and foil mounts). Sadly we never got to campaign it properly due to family issues, and Sailrocket has made it redundant, in terms of speedsailing, as the structure is only rated to 65kts. It is capable of sailing on both tacks, though, so is a bit more usable.

 

Very, very interesting! How did you tack the rig?

 

It's a proa, it shunts. The offset sheet for each tack gives a small turning moment, but that is all that is needed as the entire structure then pivots onto the new tack, bringing the wing onto the correct side. Sounds complicated but is actually very simple, just two strings.

 

I get it- very good! Do you think that's something Paul Larsen will do with his ocean going version of SailRocket?

 

You should be proud hump. I know it's thread divergent, but do you have any other images? I love how it looks. Like a big stick-bug.

 

I've no idea what the Sailrocket team will do next. From Pauls posts it isn't clear that they are certain at this stage, but it's bound to be entertaining!

Funnily enough, the original design of my speedsailor was always intended to be the precurser for an ocean-going version, hence the speedsailing compromises of both tack sailing and pivoting (the pivoting is only required for acceleration and manouvering phases, at max speed it is in a steady-ish state equilibrium).

Somewhere I have lots more photo's, if I can find the discs. My wife is away at the moment and is the most skilled at finding stuff (we've moved continents three times since then) so I'll get her to hunt when she gets back. We didn't take as many photo's as we should have, and all that my Mum took are on film, so that dates it. The boat hasn't touched the water for 12 years, and is sitting in the barn. I want to use bits of it for another project, so might get it out again before I butcher the bits, but it is very labour-intensive to operate.

Sorry for thread hijack, back to tri's.

 

Another great Ted Warren post on trimaran beam:

 

My UltraLight 20 is 75% square. As the boat gets lighter and the crew
becomes a higher percentage of total weight, the specific righting moment
increases. Any easy way to see this is that the CG moves to windward. With
two up on the UL20 the crew is ~66% of the weight. That simplifies the design.
At square you need pretty hefty beams.

So that really kills off the wider is better belief in the under 20ft then. At 20ft Ted is advocating just 75% beam due to the ability of the crew to become mobile ballast and having a greater effect on the the sail RM. Irens drawing up the SeaRail 19 went to only 4.5m, the Pulse is only 4.5m, all in that 75% slot.

Ted also raises the issue of the engineering loads on an over square boats, to justify over square you have to increase the weight of the boat which then means more volume in the hulls, its a vicous circle where gains are miniscule.

 

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No it doesn't* IF what you're looking for in a 20' tri is crew comfort and ease of sailing(and speed). On my boat the oversquare beam allows the crew to stay put or move a maximum of 4' side to side-instead of the 13' you'd have to move in Teds boat in a good breeze. No need to run from ama to ama every time you tack or gybe. Saying the gains are miniscule is just false, again IF you want the crew to be able to sit comfortably instead of running ama to ama. And if you want to maximise speed w/o crew movement. Teds 27 footer is square and his 23 is nearly square- he starts this post with " Square is Good"!

The engineering has been done on my boat and the beams are carbon 4" diameter(1.125" on the model). The whole boat should weigh no more than 350lb.
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* it's not a "belief" it's a fact.

 

Doug, if what your looking for is comfort and ease of sailing, there is no place for foils and a massive sail rig, so there is no need for large amas, and oversquare size. Foils are complicated, cost a ton, and require some attention to adjust and keep operating properly.

Not to mention, if someone is looking for comfortable and easy, they probably don't want to spend a ton on it either, they want something simple.

For racing, I could see foils being very useful, but on a small trimaran, crew positioning is much more effective, and those who care about racing are usually young and limber enough to run around and sit wherever.

If you are making a racer for the paraolympics for handicapped people, I could see it being incredibly useful, but if for some reason they flipped it, they might have serious issues depending on the person, so the 2.4 metre boats are much safer for them, even though they are a lot slower.

 

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That's just not true! I wouldn't call the rig particularly massive-it's designed specifically for the boat. People interested in this boat want comfortable, easy and very fast. The amas aren't large-they're quite small planing amas. They are attached to the boat with a "buoyant curved piece" and carbon tubes.
The concept of the Fire Arrow also allows for a 12'(+2 for gantry) X 17' wide high performance tri where the crew only has to move across a small cockpit. Again,comfortable, easy and very fast.
Concept model of the "MPX 12":

 

Ok, so these people are racers that aren't willing to move around? In that case, yes, there are all sorts of ways to deal with it, including the main hull foils. It seems like dual wand controlled foils, one on each ama, would be more effective, as the windward one has a longer lever arm in light wind. You would need a way to disable the leeward one in light wind, so it isn't sitting there trying to make the hull fly and just stalling out, causing lots of drag.

 

No, on the Fire Arrow, the wand controlled main foil is the best way to go,in my opinion. The Fire Arrow is not a "raceboat"-it is a 19.5' X 22' wide "sport trimaran". The ama UptiP foil is the best ama foil I've run into for a foiling tri, but the main wand controlled foil can be used on a tri without UptiP foils, using just foil assist with a planing ama or a "normal(long)" non-planing ama with no foil assist.
Beam is the key to eliminating the need for the crew to run ama to ama while still having a high speed tri.

 

Maybe for fire arrow, but this thread is not about fire arrow specifically, it's about all small trimarans, such as the weta, WR17, Strike 15, Ultralight 20, Sizzors, Mosquito, Akila 19, and many others.

What exactly is a "sport trimaran"? You mean a cross between a daysailer and a racer? I think you've just described the strike 15 when you say sport trimaran...

 

I don't think the Fire Arrow system is perfect for every small tri but any size tri could be designed to use the system. It's particularly advantageous on tri's from 12-20 feet because of the advantages of speed without being an athlete, dryness under sail and comfort. Variations could work well on larger racing tri's. It's a "Sport Tri" because it's designed for great comfort and great speed.
If the comfort element were removed the system could be turboed up by using the crew movement for extra RM-but I'm not interested in that. The efficiency of the curent system appears to work well w/o movable ballast.