Wooden Trimaran

This last weekend I took my new design, the A18
canoe/trimaran down to Lake Powell for its first sailing session. The
occasion was the Second Annual Lake Powell Messabout and I am
overjoyed with the results of the boat's first time on the water.

For one of the first sailing sessions, I took along Chuck Leinweber,
owner and publisher of the Duckworks Magazine for Boatbuilders. Chuck
brought his Garmin GPS and we clocked several of the runs we made.

In winds that varied from 13 to 18 mph, the A18 punched in at 13.1 mph
while sailing upwind. We didn't get a reaching leg clocked as we were
having too much fun to pay any attention after the first set of times
were recorded.

The cool part about all this is that the boat is still not setup with
its full trampolines from ama to main hull. This meant that the boat
could only be sailed from the main hull. I'm more than certain that
when the tramps are installed and I can move out to the amas for
counter-balancing, the speeds will easily reach 15+ mph in the same
conditions.

The boat is very nicely balanced from the tiller with only the
slightest hint of weather helm. She turns smartly through the wind on
a tack and gives very good feedback when the leeward ama starts to
press fully under hard sailing loads.

The demountable feature of the aka beams allows the boat to be taken
apart on the beach and reconfigured for a 6' beam trailering mode.
Standard sailing beam is 15'. Setup for the entire boat is right around 40 minutes without rushing.

The boat weighs somewhere in the 350-375 lb. range I can't give an
exact number yet as i haven't had it to the scales and gone through
the weigh/unload/weigh-again procedure. Very specific numbers as soon
as I get off my butt and do that.

There are two very informative articles at both Duckworks and
Watertribe that deal with all the specific info on the boat along with
a nice collection of photos showing the boat under construction.

The hulls are built in a multichine design from 6mm Okuome in the vaka hull and 3mm Okuome in the amas. All the decks are stripped with 1/4" x 3/4" red cedar. The boat is glassed inside and out in 6 oz. set in PTM&W epoxy. I fabricated all the metal fittings in 316 stainless steel. The rig is right off a Hobie 16 cat as are all the sheet trimmers and hardware for sail control.

Comments anyone?

Chris

 

Tri

The boat looks real good and congratulations on getting sailing! It's a great feeling!
You're not planing on flying the main hull are you? Looks to me like the main hull and amas are designed for planing-is that right?
Could you give more details like the overall beam and the beam/length ratio of the amas?
Is that a Hobie 16 main?
I built a 14 and a 20' tri years ago and they were a lot of fun. Best of luck to you!

 

Kudos..

Hello...

Its a great feeling isn't it - thing is - don't stop - don't get bored - keep tweaking...

Good job - I am envious of your joy - just now I am a bit bored...

Nice end of day photo too...

CHEERS...

SH.

 

Moving Forward

Thanks for the comments, guys. It's always great to hear from fellow enthusiasts.

Doug:

I am not planning on flying the main hull. That process brings all sorts of other structural issues to the table and this main hull is built to accomodate a couple of people and their gear for a decent coastal cruise. I would like to build a small, flying center hull boat someday, but it will be decidedly more narrow in vaka beam and likely built in foam/carbon laminate.

As for planing of the main hull. Geez, that's a loaded question, isn't it? Just what is a planing multihull, anyway? I think the potential for actually planing the main hull with both amas clear of the surface is so wildly infrequent and so seriously limited as to duration as to be a conversationally moot point.

I hear lots of trimaran owners talk about planing their boats and I do see the main hull on the surface allright, but the leeward ama is fully depressed. I don't consider that to be planing. More, a seriously unweighted main hull which provides for very reduced wetted surface and the attendant speed increases that would go with that process. I do see this boat achieving that potential on a regular basis.

Yes, it is a rig directly from an H16. I wanted the boat to be doable as a project for anyone in the world without having to fund an exotic rig and pay for shipping of a trick spar.

The BOA is 15' The B/L for the main hull is 6.75 That's rather chubby for a fast trimaran, but the main hull is not purpose designed to be an all out trimaran. More a seriously modified canoe hull than can sail quite fast and still carry a lot of stuff for cruising.

The ama B/L is 13.7 which is ideal for fast sailing. Yes, the amas are flattened-out towards the sterns to provide added lift when sailed hard. The amas are more lke 125% displacement forms as the boat is intended to be a beach tri in nature and thus, actively sailed by the crew as moveable ballast. Larger amas would have necessitated that the boat be taller in freeboard as well as having the weight increase through added materials in the amas.

I settled for this design as I wanted a reasonably light boat that could be easily trailered by a mid sized car.

Sean:

Yeah, that post-trial boredom thing. I know exactly of what you speak. I was sort of thrashed after I put in such a hard push to complete the boat. Now, I really want to see it concluded correctly, painted and detailed with all the original concept stuff.

There's the tramps to sew, there's a sculptural dashboard visor unit, some hatch fittings for being able to secure the covers properly, trapeze wires to install, etc. and then it's truly done.

Chris

 

Planing

Chris, thanks for the info. My 20' tri had a planing main hull and narrow displacement ama's. My 14 footer was more similar to Bethwaites HSP series and sailed the majority of the time with the main hull planing and the "ama's" in the air....

 

Planing claims

I take it, then, that you classify the HSP design stratagem as of the trimaran category?

I don't see that as clearly as you do, perhaps.

I, instead, see the HSP as a narrow, monohull dinghy form with augmented flotation at the ends of arms to prevent capsize. From that form, I would expect the main hull to have claims of being planed.

Here's the technical rub for me with regards to more traditionally accepted trimarans (or cats for that matter) offering-up claims of being planing hulls. If the boat uses one of the other hulls, or amas, at all during the sailing exercise of what is called planing, then the claim is hyperbole for the after-sailing bar talk session. You can't have it both ways in my book. If the boat uses two hulls or more and one is partially immersed for support, then the planing claim is out the window.

The critical balance issues of holding a trimaran on plane during sailing and not once touching an ama to the surface are where the discussion gets its power. If you are going to make claims of that sort, then why all the extra weight, complication and expense of havng a trimaran in the first place?

The claims of these behaviors are so infrequently supported by anything more than brief moments of reality, as to make them highly specious. As one dude told me some time ago, "You can make bowling ball plane if you put enough power to it"

I guess it comes down to this... and I apply this argument to power boats as well when they claim to plane.

Can the vessel in question elevate its principal hull with... power sources coming only from the boat itself, beyond its bow wave, keep it there and have no added appendages in the water at any time to provide additional assistance? Can it do it effortlessly and repeatedly in a wide variety of conditions?

If you can make those claims, have substantiation through witnessed accounts as well as video proof, you'll have my attention and respect.

I would like to hear more about the boats you had that could perform the planing feat, though. That type of boat must have been a blast to sail. I'm guessing it's more like this boat, http://www.billoch.com/arq/disenios/d72.html than one more like a trad tri.

Chris

 

Planing multi's

Well, at the time I built my 14 I had never even heard of Frank Bethwaites HSP's nor, of course, had I seen Julian's Pteradactyl. In retrospect and in light of those development's and my own foiler designs I would call the 14 a monohull with buoyancy pods today.
The 20, on the other hand did use the amas to augment stability after about 12 mph of wind(in addition to the crew max out) but the main hull was designed as a planing hull and would begin to plane way before the amas had any role in stability(at about 9-10mph wind). As the wind increased the ama played a greater role in stability unloading the main hull which almost but not quite flew while continuing to plane. There is nothing contradictory at all about having a tri designed to perform this way but as cool as it was I would do it entirely differently now.
A new boat I'm looking at in the future sometime is a square 18'-20' tri with planing, stepped amas that utilizes a way to eliminate the negative effects of a step at low speeds. It would have one altitude controlled hydrofoil on the main hull daggerboard and a rudder t-foil for pitch stability. The main hydrofoil would primarily pull down and would work with the rudder t-foil to control pitch stability while adding RM to the whole boat.It would be designed specifically to be a beach cat killer...
By the way, you are familiar with Yves Parlier's ORMA 60 planing cat aren't you? If not I'll try to find a link for you.

 

Foil Assisting

Hi Doug,

I did see the Parlier cat when it first rolled-out and followed the development for awhile. I believe the boat experienced some teething issues at first (don't they all) and then I sort of lost track of the reports with only sketchy info after that.

I am intrigued by the stepped hulls and have occasionally wondered if the boat proved-out as conceptualized or the roughness of the ocean waters had a serious negative effect on the potential.

Your approach with foil borne assist is also intriguing. You say the foils are designated to solve the low speed issues surrounding the stepped variation. I'd like to hear more on that approach.

Here is a foil assisted trimaran I drew recently (not built yet) that incorporates foil assist in the amas and also with the previously mentioned T-foil rudder. I didn't see the boat as a foiler per se, but more a foil assisted craft that reduces wetted surface drag and therefore achieves greater speeds under sail. The vaka hull is derived from a 21' sea kayak form intially. The sail area of 180 sq. ft. comes from two sprit rigs in schooner style setup.

The ama foils are canted inward at 45 degrees and centerboard structured so they can be retracted into the amas when the boat is not sailing.

Human power is derived from dual, Hobie Mirage drives. The boat can also be propelled conventionally with either single or double bladed paddles. Outboard hiking benches help to provide crew assisted righting moment. The benches are removable and quickly stowable.

I see it as a reasonably fast, very light weight boat, primarily for coastal adventure racing in events such as the Watertribe Everglades Challenge and just plain fun day sailing for guys who have interests in kayaking as well as sailing.

Chris

 

Foiling tri's

Chris, great rendering! I would assume that the boat wih it's relatively narrow beam isdesigned to sail on both forward foils at the same time?
My concept uses a varible geometry to solve the step problem in light air; the foils are primarily to stabilize the boat in pitch and to let it sail at an angle of heel on one planing ama with the main hull substantially clear of the water so it can handle rough water better than ,say, a Rave type foiler.
Parliers boat did very poorly between something like 8-20kts of boat speed but over 20 drag dropped substantially. Unfortunately, he recently capsized the thing while trying to set a record. From what I read it did real well in a seaway ...
The idea of a very low wetted surface main hull(for light air) with planing amas for strong winds flying the main hull has a lot of appeal to me. I'll build a model before long. See http://www.microsail.com for pix of my radio controlled F3(andvideo) .It's a Bradfield type foiler which has a wave height limit before bottoming out. I think the heeled(foil assisted) tri sailing on a planing ama could beat it in waves-maybe.

 

I think a lot of people have a problem with the idea that the main hull planes but the amas do not -- they're still in semi-displacement mode (not planing but being driven faster than their hull speed). Farrier trimarans do this a lot. They do indeed plane, and it has nothing to do with the main hull being unweighted by the load shifting to the leeward ama. The main hull planes naturally as it exceeds its own hull speed, just like a skiff hull. It's still carrying most of the boat's weight. The ama is just keeping it from tipping over. Whether the ama planes or not is immaterial.

An ORMA tri is different, in that the leeward ama actually carries the whole boat's weight -- like a lightweight beach catamaran.

Anyway, congrats on your new boat. I've always been intruigued by the Tremolino, and the Farrier Tramp/Eagle may be the best family daysailor ever. There's a lot of unexplored potential in this kind of boat.

 

That Planing Thing

Hi Matt,

From your description, then, you'd be able to say a catamaran planes the exact moment that the windward hull is riding right on the surface? Or that any normal displacement hulled boat with any planing appendage such as a water skier is, in fact, planing as well? I think you can see where this is going.

As soon as you allow for the description of the main hull of a multihull as planing, I want to know what is really the main hull. For example, which of the hulls of a Harryproa are the main hull? www.harryproa.com

Beyond that, there's the question of which hull is actually supporting the weight of the vessel under these conditions of planing. When the weight shifts on a trimaran to the leeward ama and the main hull leaves the water, is the main hull anything more than an appendage to the supporting hull? Does that not, for design purposes, now also shift the obligations of the newly weighted hull to perform many of the tasks previously assigned to the job of the "other" main hull? If not, why do so many racing tris have rudders on all three hulls?

Is the main hull of a tri called that because the mast and central storage reside within that hull? On the catamarans of the Lake Geneva racing fleet; the ones with the hefty central pod that helps to stiffen the mast structure and provide storage during the race, which hull is the main hull? I think that, from the previous claims in this thread, that possibly the argument could be made that it's really a trimaran that is constantly flying it's middle hull.

In the process of desiring to get to that magic place that sailors crave; the planing hull capacity, we have bought ourselves into simplistic solutions for already settled arguments.

Personally, I feel it's the sailors lust to have their boats get free of the displacement mode, like the fast motor driven craft which seem to go on a plane at will due to power and hull shape.

One can describe it any way they like, of course, but it doesn't change the fact that it ain't happenin' except in the rarest of situations. To borrow one of Ian Farrier's oft quoted idioms... "If it walks like a duck and quacks like a duck, it must be a duck".

When the boat can plane regularly under the power of its sail, the descriptive group name for the boat will have left behind one of the key identifiers of what is a trimaran and it becomes something else. Perhaps a float assisted skiff like those already discussed.

I just love this argument because the claims in this direction are clearly pushing the boats into the territory of nomenclature no man's land. I can just see the sign at the edge of the accepted descriptor territory now, "Caution you are now leaving the world of trimarans and entering the world of... well, you're entering another world, that's what you're doing. Wild claims of planing are accepted beyond this point"

Chris

 

Very nice boat

 

Hyper-Planing Trimaran

Evolution of the species. I give you the hyper-planer. Various combinations of sail/engine power ensure that this sailing trimaran will get up on and remain on plane as long as the crew desires. No after session haggling, No scientific quibbling, no descriptive conflicts... just pure planing.

 

Mtri

Hmmm..ah,26'?! Chris, you've convinced me: you really believe what you wrote about planing multihulls....

 

Yes, it's two ways of looking at planing (at least),
1) If speed/length ratio is larger than 2 or 3, then we are planing,
2) if more than x% of the total weight is supported by dynamic pressure, then we
are planing.

Maybe both conditions should apply?

Do you have any drawings of your trimaran?