High performance small tri project [Archive]

frosh

05-13-2007, 06:35 AM

I would like to now transfer the sub-thread that has developed for some time into this new thread which is inspired by Frank Bethwaite's HSP that commenced in the 1960's and continued for 20 years with him building and testing 19 different human powered versions. We now continue his contribution with my own tri project, which although more of a a true tri than those of FB, which were more accurately monohulls with side bouyancy pods, is truly in the same spirit as his HSP work.
I am going to try and transfer the postings that relate to this topic specifically, to this new thread, if I can work out how to do it.

Please bear in mind when talking about low drag hulls that there is no such thing as a low drag hull per se. For instance when comparing displacement hulls to planing hulls, for hulls of the same LWL and displacement, the narrower, deeper, small transomed displacement hull will give lower drag at speeds below 'hull speed'. The broad transomed flatter planing hull will giver lower drag at speeds above 'hull speed'. At some point the resitance curves of each hull wil cross over, and maybe more than once. The point is to look realistically at the available thrust and pick the hullform which gives the lowest resistance at the most likely operating speed. If cost is no option and there are no size restrictions, make the hull as long and narrow and as light as possible. If you can always guarantee high thrust, then maybe a small flat planing hull is the way to go, but it wil not give you good all round performance.

Mal.

This is a huge coincidence to talk about two types of optimum hull shapes when I am about 90% complete in my experimental tri project.
The Vaka is as long and narrow and light as I could make it given that the main constraint was for a 2 person high perfomance off the beach style craft, that was light enough for 2 average sized adults to be able to pick up the fully rigged tri and carry it a short distance without too much effort.
Vaka is 5.6m x 0.4m with a semi planing/planing bottom shape. The transom is half the width of max. beam and a fairly flat arc section compared to the rest which is an arc section of steadily decreasing radius as one moves closer to the bow.
Amas are fully planing designs based on on the US lake scows shapes but built to optimum strength to weight ratios.
The tri is designed to be balanced by crew weight rather than ama bouyancy, and will incorporate a trapeze for the crew.
In lighter winds almost no water contact is expected for the leeward ama.
In stronger winds, which is the common situation in the Perth WA summer season, the total displacement will be shared between the vaka and leeward ama which I expect will be planing in such a fashion that ama immersion will be very slight. In addition I have already tested the vaka in a proa configuration and it goes from displacement to planing mode with no noticable hump at the transition. I will be testing the completed tri around August this year. I will post more later with some pics.
Regards-

Chris Ostlind

05-13-2007, 09:01 AM

Well, the coincidence continues, Frosh, as I was just cycling through the list of interesting projects with which I was trying to maintain some measure of connection. Then, you posted the update on your project boat.

I really like the whole range of potential multihulls in the off-the-beach envelope of possible craft. I'm especially drawn to those trimarans that require considerable crew activity to maintain their footing. Getting the amas down in size a bit and reducing the overall weight of the boat is a big help in almost all areas.

I'm really looking forward to seeing your pictures and hearing of your trials.

I can't remember which rig configuration you are planning on running. Can you give me a refresh on that part of the design? And how about the choice of boards (rudder and keelform)?

Chris

frosh

05-13-2007, 10:53 AM

Hi all, this is mainly in response to Chris' last posting. I weighed my 7'6" by 1'11" amas at 22 lb. each complete. I normally work in metric but I can think in the Imperial scale also. Vaka around 90lb. Carbon crossbeams maybe 12lb. for the whole set. Overall beam 10ft. Skinny 21 and a half ft. carbon mast with adjustable tension triple diamonds stays. Carbon boom, soft mainsail 110 sq. ft. ala James Wharram Tiki wingsail (with luff sleeve, and fairly high aspect), with small carbon gaff. Jib about 50 sq. ft. Should weigh in all up around half of an F18 catamaran, I hope. F18 is 385lb.
2 assy kites, tiny one about 85 sq ft. for Perth (20 -25 knot Fremantle Doctor) For the "medical" definition see:
http://mediatheek.thinkquest.nl/~ll118/en/development/types.list.fremantledoctor.html
Also a 190 sq ft assy kite if we find we want push the limits a bit.
You asked about under water foils. Carefully selected timber hand foiled WRC, with 2 layers of epoxy glass, around the size of that on a 29er. Very light, and daggerboard close to a NACA 0010 and rudder blade close to a NACA 0012, and quite high aspect. Only fitted to vaka; no foils on amas. I expect to keep the daggerboard fully down all the time.
I will get myself into gear in a few days and get the digital camera out and start posting photos of the various bits, as everything is separate at the moment.
Really happy to hear of your continuing interest.
Other interesting development is that Rob Denney who lives a couple of miles from me spoke with me on the weekend and he has agreed to crew with me when he is available. His feedback and suggestions will surely be very valuable, in the ongoing evolution of this project. I expect the tri to go extremely quickly on some points of sail, but have no clue how fast it might be expected to get around a triangular course. I can't wait to find out though! :?: :) :)

Phil Stevo

05-17-2007, 06:50 PM

Replies:
I have never seen an Itzacat. Must have been a WA boat.

The first Kitty was built as a NZ Q class 12 and won the second Interdominion 12ft championship in Aukland. The Q class and Aust 12 assoc replied by banning cats. It was certainly faster in 1958, but the skiffs are much different now. It would be very interesting to see a 21st century 12ft cat against the 12s.

In the 60s and 70s I went to a lot of cat regattas, The planing XY and other similar hulls could not match the narrower quickcats etc. Similarly at 20ft the Attunga was no match for the austral and later the tornados. Narrower always semed better. Maybe todays build weights will change things, good luck. (My first own design and build was a 12ft cat with narrow hullls which normally beat the Kittys)

Maybe I got lucky last year with the development canoe, but it is not out on a limb in design, just a development in known directions, known to work well on other classes: Basically straight, narrow and light seem to be universal tickets to success.

Anyway you are having a go, so no critism. Try not to make it too complicated, make it easy to test, not too many inovations or you will never know which ones are working and which are not. Do not go the path of Doug L and create something so out of left field that it has just lead to ridicule. Maybe a more standard rig initially will be a better test of your platform.

You need everything else proven to be right before the wing mast. I have one down on my ultimite list of Moth develpments, but no point if everything else is not perfect. There is lots of design info published by Steve Clark's Cogito team to start with but building it strong and light is the real challenge.

Doug Lord

05-17-2007, 08:06 PM

Do not go the path of Doug L and create something so out of left field that it has just lead to ridicule. Maybe a more standard rig initially...

====================================
Nobody should be afraid of ridicule and let that stop them from trying any experiment or experiments. For the most part ridicule emanates from those who don't understand what you are trying to achieve or the degree to which somethng that appears not to have worked did work. There is an element of criticism that is well founded ,well reasoned and very constructive; there is another element of criticism-ridicule- that emanates from uninformed small minded people whose opinion is not worth the cyber space it
uses. No one should be afraid of a cyber MOB and hold back on ideas they think are worthwhile-that goes for discussing them and doing them and showing others what you've done. One bit of constructive criticism is worth a hundred
bits of trash from useless jackases.
I made many mistakes on my first full size foiler design/construction but I also did a lot right including the weight, learning about manual foil altitude control systems, a square topped jib, the Swift solo(Bram Daly)sheeting system and many other things. I'm glad I did it and a damn proud I had the guts to try. The next one will be much,much better.
aeroskiff_trial001.jpg
http://www.monofoiler.com/images/aeroskiff_trial001.jpg

frosh

05-18-2007, 12:09 AM

Good responses from both Stevo and Doug. And that is really saying something, as I am normally the person most guilty of saying that Doug has a one track mind and is usually coming up with ideas out of fairyland. Doug, from what you said in the last posting, I have to be man enough to take back some of my past criticisms of you.
Phil, I am very familiar with the Quickcat having been a member at Elwood Sailing club in the 60's where Quickcats were probably the biggest racing class. BTW I raced a Sailfish at Elwood in those days, my second ever boat. The Sailfish had a lot in common with the Aussie Moth apart from the fact that it had a beam of only 3 ft. I had a huge amount of fun with it. The Quickcat was certainly extremely fast for it's era.
As far as making it simple goes.-- I already have the mainsail, jib and two assy kites that were custom made by a professional sailmaking firm to my overall specifications. I have never used either kite as yet and they are brand new, sitting in their sail bags. The main and jib have been used about 5 times when the boat was in a "tacking proa configuration" It went better downwind than upwind but we were on a big learning curve, very similar to you when you sailed your DC the first few times. Furthermore my crew was my son who although being a very accomplished windsurfer, knows almost zip about regular yachts, so I had to try and teach him the basics, like sheeting a jib correctly, how to perform a tack etc. This was very difficult for me because I was sailing a lightweight powered up boat that was quite radical anyway. The biggest problem was that on one tack it was a "Pacific proa" and on the other tack it became an "Atlantic proa". This just became too much to cope with and although it showed promising bursts of speed, with the vaka clearly planing, there is no way we could have sailed it around a triangular course without a lot of swimming.
Therefore the decision was made to give back the ama which I had borrowed from my 23ft. home designed and built OC2, and start with new amas. Origiinally the amas were going to be close copies of a Hungry Tiger Moth, but stretched out to 12ft. and with a broader transom.
I had a mistake happen while vacuum molding the first hull in my female mold that I built with great effort. There were large areas where the outer skin of 200 gsm woven carbon which was nicely in place in the mold did not fully join up with the 5mm klegecell foam core. Unfortunately I did not know this yet and spent a lot more money and time bonding a second layer of carbon onto the inner surface of the foam. Finally after removing the hull from the mold I discovered the weakness. After a lot of soul searching and anguish, I decided to put the carbon foam hull and female mold out for the next rubbish collection, as I couldn't stand looking at them anymore.
I then went off at a tangent and decided to build 2 amas without a full mold, only a bottom surface mold, in a shape close to that of an American Inland lake scow. Anway it is almost finished and I will post some photos on this site very soon.
Bye for now, and regards.

Paul Scott

05-20-2007, 06:09 PM

frosh, glad you are messing about with a gaff rig. A few years back, while in the design stage of my 40' uldb cruising sled, which was 30' at that stage (I know, I know...), I was talking to Paul Bieker about a gaff rig, which I didn't wind up doing ($$$$$), and I wound up going with Bob Perry, but it looks like the idea reappeared a year or so ago at the Wooden Boat Institute at Port Townsend, Washington State, USA, on a 15' footer that Bieker designed for them. I'm sorry, I've lost the web site for it (arrghghghgh), but I think the article was in Woodenboat. You might find it interesting, esp. how they are using the gaff/mast for twist control.

Doug, keep on it. You're having what I call Intense Fun. Like we all are. That's ok in my book.

Paul

Doug Lord

05-20-2007, 06:50 PM

Thanks Frosh and Paul. You guys may find this interesting. It is a blurb I wrote about my "wing tip rig" about 10 years ago. Probably the most significant( if anything is) thing is the upper outhaul. Don't have very much info from full size testing since its only been used on one 16 footer; the results in model testing are encouraging though:

===================
The Wing Tip Rig represents a powerful planform for a sail that unlike most modern fully roached or square top rigs does not require full battens (which don't work too well on models).** Further it features a drag dissipating tip design and an upper outhaul resulting in a capacity to shape the sail better than any existing sail. The essence of the Wing Tip Rig™ is better sail shape, drag reduction, and light weight (compared to fully roached sails).
=================
Wing Tip Rig background
------------------
The first Wing Tip Rig was used on a on a 16 footer I designed in 1975.
The top of the sail has a short adjustable gaff. It is a modern version of the gaff rig. Using vang tension allows very precise control of sail twist-it adjusts the range of gust response.
The newest version of Wing Tip Rig(F³-see below) has been refined to provide performance closer to a solid wing than any existing soft sail planform.
The Wing Tip Rig in its primary embodiment on the Spinnaker 50, F3 and America One mains(and on the aeroSKIFF jib) does a number of things:
It provides an aerodynamically superior planform without requiring full battens.
The tip shape reduces induced drag for more power upwind.
The outboard top corner (peak in gaff terms) is adjustable using an upper outhaul which works to control the camber at the top of the sail.This works wth the mormal outhaul on the foot to give unparalled sail shape control.
The lack of full battens allows superior performance in lite air as compared to fully battened sails-particularly in models.
Twist, over the whole sail planform, is easier to induce and to remove than in virtually any other sail type allowing perfect matching of the sail to prevailing conditions.
Depowering is easy and is automatic, when the rig is set up properly, providing excellent gust response.
The benefits of the Wing Tip Rig™ are less drag, more power and more effective depowering.
There is a measurable difference in model performance with the Wing Tip Rig™ when compared to an identical model without it!
-----------------
The only time it was used on a full sized boat the upper outhaul had a spring that pulled the "peak" forward and a line that ran down the mast to pull the peak aft. It was a bit of a problem to hoist. On models no such problem but then again it can only be adjusted on shore unless rigged to a servo.The model version and maybe a future full size version uses a "gaff"(extruded carbon on models) that fits into a bushing in the top of the mast and is free to rotate completely independently. Might still have some potential....
------------------
mfoilerf3_14a.jpg
http://www.microsail.com/images/mfoilerf3_14a.jpg
-----------------------
Back to the topic a bit:
I think the greatest drag reduction on sailboats
(seahugger or foiler) will come from rig improvement.

Paul Scott

05-20-2007, 08:03 PM

frosh, I think the LARGE windsurfer-ish hulled Bootiful (the smaller one) might prove your point. Hope it isn't moldering in a field somewhere.

Paul

gggGuest

05-21-2007, 02:39 PM

frosh, I think the LARGE windsurfer-ish hulled Bootiful (the smaller one) might prove your point. Hope it isn't moldering in a field somewhere.
I'm pretty sure it is, it having failed to achieve anything of worth...

Paul Scott

05-21-2007, 07:16 PM

ggg- I know this is off topic, but judging from the press on it, the smaller one was ok (was it around 30'??), and it was the 60' that was the problem. ??

Paul

gggGuest

05-22-2007, 02:08 AM

I don't know enough to really comment. But I wonder why a 60ft version would be expected to be much faster than a thirty foot one?

CT 249

05-22-2007, 02:31 AM

Frosh, thanks to you and Phil for hte FW info, but you brought up some bad memories with the ItzaCat.

I'm fairly sure it was one of those I was asked to test many years ago for the Design Council of Australia. In anything but the moderately breezy reach in flat water in the vid, it was a wet, slow, evil-handling nose-diving wave-smacking helm-tugging platform-flexing sail-distorting heap.

It still got the design award, despite the fact that the only person who sailed it (me) said it had distinct problems and that the planing cat idea was around long before Noah. As one of the guys from the award panel said to me, the idea was pretty much to find reasons to bestow the award, not to withhold it.

Isn't there a basic physical problem? Cats have thin hulls. Thin hulls mean that the stagnation point is very small in area, so the boat will not develop much dynamic lift and won't plane well most of the time.

frosh

05-22-2007, 07:31 PM

Sorry, but I would have liked to respond earlier, but have been flat out at work.
Anyway CT, Doug, and Stevo and any other interested parties, here goes.
Starting with the Itza Cat. I would say it is a crude design, probably would go well on certain points of sail in moderate to stronger winds, in fairly smooth water only. I don't really know. My only info is from studying the video, and there is a much longer one out there on the net, than the short video in my earlier link. As far as racing it around a triangular course it would be awful IMHO.
It was put up be me solely to illustrate that a multihull is not forced necessarily to always have every hull as a narrow displacement style.
I am hoping that my tri will have the best of both worlds, (and not the worst of all worlds). Most of the displacement will be borne on the vaka which IMO is about as good as you can get to a small boat hull that has high performance capability, as either a displacement hull, or a planing hull. In stronger winds, my expectation is that more weight will transfer to the leeward ama which should strongly resist immersion by producing lots of hydrodynamic lift at speed. The Vaka has certainly not shown a perceptible transition hump when moving say though the 10 knot barrier while accelerating, in their previous trials. The planing amas are rather small, something along the scale shown in Hydroptere, but without the lifting foils. I have posted Freeship pictures of both the main hull and amas before. Here is another image of the whole thing assembled. Remember that the vaka is 40cm in beam with an arced bottom. The amas are 59 cm in beam at max point. and mostly flat bottomed, except for a slight V in the tail area. Chines are a little radiused over the entire length. The Vaka has very sharp chines in the rear half.
Now a bit about the gaff rigged mainsail. Aspect ratio is roughly similar to an International Moth, but with only four short leach battens, a luff pocket sleeve, and sail area of 10 sq. m. The gaff is very interesting and I have manufactured two very different ones. One is a simple carbon tube which fits inside a pocket sleeve at the head of the sail. It has an adustable outhaul, but no control lines leading down to the deck. It has a spectra line leading from the mid point of the gaff to the very top of the mast, and this line can be adjusted for tension. It's tension setting makes a huge difference to the fullness and general shape of the upper half of the mainsail.
The second gaff is more exciting IMO but not yet tried. It it like a short fully carbon sail batten with a lot of width for its short length. It is carefullly varied in thickness so that when under compression takes up a true aerofoil shape, just like a properly manufactured full length sail batten. The gaff batten slides inside the pocket sleeve also, as did the tube version. (not at the same time of course), it is one or the other. The adjustment lines fitted at strategic points, and when tensioned can create a fairly low cambered mainsail shape at the very head of the sail, or a more deep shape. Either way there should be some auto gust response as the adustment lines would not restrict the aft end of the aerofoil batten from falling away slightly under high wind pressure.
I will be testing both gaff versions in a few months time.

tspeer

05-26-2007, 10:41 PM

Here are some papers that describe different design philosophies for determining the shape of trimaran hulls. Note that design of the topsides can be almost as important to performance as design of the underwater shape. Antrim selected wide, elliptical sections for the aft end of his ama, not so much for planing, but for reducing windage of the windward hull. Both Shuttleworth and Antrim cover the change in total wetted area with righting moment for trimarans compared to catamarans.

Shuttleworth and Antrim both talk about the fore-aft shift in buoyancy as the righting moment changes. Shuttleworth's stability indices can be converted to a footprint plot (http://www.tspeer.com/temp/stabilityindex.gif) that shows the importance of providing reserve buoyancy forward in the ama to prevent diagonal capsize/pitchpole. From the looks of the drawing above, I'd say the amas are way too far back - their center of buoyancy needs to be ahead of the center of gravity by an amount that depends on the L/D of the rig (http://www.tspeer.com/temp/hullbalance.gif).

Shuttleworth, John, "Reflections on the Design of Brittany Ferries GB (http://www.john-shuttleworth.com/Articles/BritFertalk.html)", Jan. 1982.

Shuttleworth, John, "Multihull Design For Heavy Weather (http://www.john-shuttleworth.com/Articles/NESTalk.html)", Heavy Weather Sailing 4th Edition, International Marine, Camden, Maine, 1992.

Shuttleworth, John, "Beyond the Tektron 50 - the design of the new Dogstar 50 (http://www.john-shuttleworth.com/Dogstar50-article.html)", Mar. 2002.

Antrim, James K., "Design of a 40 ft Multihull for Offshore Racing," Marine Technology, Vol 27, No. 5, Sept. 1990, pp 285-299. (Available on SNAME Small Craft CD (http://www.sname.org/newsletter/news0204.htm))

frosh

05-27-2007, 05:20 PM

From the looks of the drawing above, I'd say the amas are way too far back - their center of buoyancy needs to be ahead of the center of gravity by an amount that depends on the L/D of the rig -QUOTE- Tom Speer.

The whole key as to whether my design will work successfully, as I expect it will, even with the amas NOT moved from the position shown in the diagram I posted; or whether your opinion is correct depends mainly on the following provisos.

Are the trimaran heeling forces generated by the sails on any point of sailing forward of a broad reach going to be counteracted primarily by:
EITHER (1) The buoyancy and leverage arm of the leeward ama, or
(2) The weight of the crew sitting far enough to windward to signicantly reduce the load of the leeward ama so that it is not hard pressed into deeper and deeper immersion as the wind strength increases. Even more important, the crew will control with agility and weight transfer to windward, the amount of pressure fairly precisely, and consequently how much downforce will be transferred to the leeward ama.

Conventional trimarans follow the principle described in (1) above. Your references and own arguments are completeley valid if this is the case.
In the case of my experimental tri, I am relying hardly at all on principle (1) and almost entirely on principle (2).

This is not possible on even a Corsair (Farrier) Sprint 750, (a fairly small tri), although placing crew weight to windward as far as possible in a good breeze will undoubtedly add to performance. This is a small tri, and on anything larger, we can discount the effect of crew weight to windward in proportion to increasing hull and rig size more and more as the boat becomes larger. Whether this is in direct proportion or some sort of logarithmic proportion is not highly relevant to my design or this argument at all.

My Tri is expected to weigh in fully equiped to sail, without crew at around 85 to 90 Kg. This is less than 200lb. for you Americans. Crew weight depending on who is aboard will be around 160kg for two men fully clothed to sail.
Again this is in the region of 350lb.
Furthermore the heavier crewman will be fitted witha a trapeze so that he can extend another 1 meter further to windward when necessary.
The crew weight as a total fraction of sailing displacement is huge for any normal sort of tri, and so is the the proportion of crew weight leverage to sail heeling moment huge, in relation to any normal sort of tri. My tri is fitted with a fairly modest size rig with a reasonably low CE for the sails.
I don't want to go on with much more technical stuff in this post and turn it into a marathon, but this is the gist of it all.
There is also the fact that my vaka generates a lot of hydrodynamic lift in the region about 25 to 50% back from the bow. We already know this from real sail testing as a proa, and the forefoot tends to ride a bit above its designed lines already. This was exactly the same trim situation encountered by "Crossbow 2", in its proa incarnation. I will post a photo of Crossbow 2 sailing at speed in this trim situation next time.

frosh

05-27-2007, 05:36 PM

As promised in the previous posting here is the link to "Crossbow 2". It shows some superb, but old classic photos.
http://www.dcss.org/speedsl/crossbow.html

Also, Tom, I am not sure that you have got Jim Antrim's design philosophy correct about his broad flattened ama stern sections being for windage reduction and not for planing. I couln't find the article re Antrim in your links. Perhaps you can post the link more precisely so we can read Jim's words for ourselves.

CT 249

05-27-2007, 05:47 PM

Frosh, your boat looks to be similar in concept to the Bethwaite HSP. That had the floats even further back, and it was a stunning machine to sail.

tspeer

05-28-2007, 02:40 PM

...Also, Tom, I am not sure that you have got Jim Antrim's design philosophy correct about his broad flattened ama stern sections being for windage reduction and not for planing. I couln't find the article re Antrim in your links. Perhaps you can post the link more precisely so we can read Jim's words for ourselves.

"The weather ama is always completely exposed to the wind, and at least the top half of the leeward ama is exposed. Considering that 200 percent buoyancy was desired (exactly as much hull above the full load waterline as below), a section shape for minimum wetted surface, and a beam/depth ratio betwen 2 and 2.5, as well as a cross-sectional shape to minimize windage, a circular cross section for tha ama was an obvious choice. This cross section has a Cd of about 1.2 as compared to 1.5 to 1.6 for a more typical oval-shaped cross section (see reference [1]). The circular section is also ideal from a structural point of view both to resist torsion and for strength against hydrostatic pressure. In addition, hull surface area is minimized, and consequently hull weight."

"The ama bow sections need to be higher than they are wide for obvious reasons. I wanted the stern sections to be wider than they are high, both for dynamic buoyancy and to minimize windage. Consequently the ama cross sections shown in Fig. 8 are elliptical over the full length of the hull. Obviously waves will frequently be sloshing over the low or no-freeboard stern sections; however since the water will en effect be flowing downhill it will develop a slight forward force component that will at least partially compensate for the increased frictional resistance."

Antrim, James K, "Design of a 40-ft Multihull Sailboat for Offshore Racing," Marine Technology, Vol. 27, No. 5, Sept. 1990, pp. 285-299.

frosh

05-29-2007, 03:00 AM

Chris Ostlind

05-29-2007, 12:38 PM

Interesting that now, some time after the fact, that Tom Speer posts a suggestion that Antrim's amas were not of the planing type.

http://www.boatdesign.net/forums/showthread.php?t=14047&highlight=planing+trimarans

In fact, as Tom so purposefully demonstrates in his argument, Jim was going for a serious reduction in windage as opposed to his, so-called by others, suggestion that his amas would plane when pressed. He never made the "it will plane" claim. He only suggested that the forms were conducive to the potential. Big difference.

Thanks, Tom, for proving my point, even if you were some 8 months out of the loop.

Chris Ostlind

Doug Lord

05-29-2007, 01:07 PM

Jim Antrim most certainly does make the claim that his amas plane:
Under "Ama Shapes"-
1)-DIRECT QUOTE FROM JIM ANTRIM:" The high buoyancy planing geometry is highly resistant to burying the bow at any speed."
2) DIRECT QUOTE FROM JIM ANTRIM:"..dynamic lift from the ama hulls."
THE QUOTES ABOVE ARE FROM THE FOLLOWING WEBSITE:
Antrim 30+
Address:http://www.antrimdesign.com/trimarans/erin/ Changed:1:17 PM on Friday, September 30, 2005
==================
Chris, I think you seriously misunderstood Tom's quote of Jim Antrim-in that quote he refers to "dynamic buoyancy"- another way to describe planing.

Chris Ostlind

05-29-2007, 01:31 PM

I'm not going to do this dance with you, again, Doug. You're making words where there aren't any present.

Tom's comments support the argument I made and they come directly from Antrim's SNAME account.

Perhaps you can take on Tom's description of his take on Antrim's article from SNAME as a means to justify your position?

My position has been clear from the beginning and shall remain so until a serious set of proofs emerge. You have not provided that information and now, Tom has nicely supported my argument from Antrim's own posting.

It is rather convenient that Tom has provided this suggestion but when you take a long look at the amas on both Erin and the Antrim 40, "Zephyr", you will see that Jim has been consistent in his design application with regards to form and function.

Go ahead and argue otherwise, but you can't change what the designer, himself, has written on the topic. This suggestion comes after you have placed such great credence on the work of Farrier and his planing claims and design approach, so it seems only fitting that you would now graciously back away from the argument in light of this published position.

Or, are you suggesting that Jim Antrim has no idea as to his own design purpose?

I have merely made observations in the past that Antrim's amas were not of the planing variety and to support that observation, I directed you to Antrim's work on Erin. Now, Tom has further illuminated my position from a well documented paper published by SNAME, dealing with amas with design elements virtually the same... and you want to argue that point with impunity.

Go ahead... argue away.

Chris

frosh

05-29-2007, 04:10 PM

Brief Description

Easy handling and high performance sailing in this high quality and ocean rugged racer/cruiser. High buoyancy and dynamic lift from the unique ama design provide an unusual level of safety and control. -QUOTE- JIM ANTRIM

I think that this own quote from Antrim where the first paragraph emphasizes the design aim of his amas, as providing "High buoyancy and dynamic lift", pretty much settles what Antrim wants to achieve as his highest priority for the amas of his designs.
It does not seem about "Windage", although I accept that elsewhere he does discuss that keeping the windage down on both the leeward ama topsides, but more significantly the entire windward ama is an important part of his design brief.

However the fact that the very FIRST paragraph only discusses high buoyancy and dynamic lift is enormously revealing!

Why continue arguing about this then?

ALSO - Who is now prepared to stand up and be counted in the camp that
"Trimaran amas definitely dont plane!" So is anyone able to explain the meaning "providing dynamic lift", as it pertains to boat hulls, if the meaning is really something quite different to planing.

Remember if you make the statement supporting your contention that amas can never plane, please write your name underneath, so that the rest of us can later remember who you are.

Chris Ostlind

05-29-2007, 06:01 PM

Sam,

Don't all hulls provide some degree of dynamic lift as soon as they move forward under provided power?

Is that the same as planing?

My original contention which goes back to the hissy fit discussion back in November was: A trimaran does not plane if it is getting substantial weight shift support from the leeward ama under sail UNLESS... that body (the leeward ama) is also planing...In which case, the entire craft could be considered as being on plane.

Really simple.

I have never seen a vaka hull being fully supported on plane without the amas taking up substantial load in an immersed, non-planing, condition. The times when I have been shown photos and/or video clips to show a leveraged vaka skimming along the surface, it had substantial amounts of the leeward form fully depressed and not anywhere even close to planing. So, it remains that I take this position.

Tom Speer has indicated at least once in the past that he has, in fact, scooted across a body of water, on plane, with both amas fully clear of the water. This tiptoe balancing act would meet my description, but alas, Tom has not seen fit to provide anything other than his anecdotal commentary. He has not, apparently, repeated the exercise with decent documentation to provide a measure of support for his claim.

Now, Tom's a pretty aware guy and he doesn't seem to be the type to wander off the science reservation for rabid claims, so there could be real validity to his commentary. Likewise, because of his serious science bent on all things boaty, I'm entirely surprised that he has never come to the table with just a bit more of what he, himself, would expect from a colleague who put-forth this level of claiming position were it to be within the field of his profession. In short... where's the beef?

I get the yak-yak about planing trimarans for bar chatter after the sailing day. That part of it is just fine with me as one is supposed to extend one's story telling capacity for friends, especially when they are buying.

But, for a real scientific claim, I think everyone here would agree that there should be more than pub chat on the topic.

For the record, I'd love to see a trimaran flashing along on full plane with one, two or three hulls all doing the bad thing, as the case may be according to design application. It's just my position (shared by many others) that an immersed and fully weighted ama on the off side does not qualify the entire boat for the claim, dynamic lift to some degree in the ama design or not. Get that leeward ama up on the top, along with the vaka and you've signed me up as a proponent.

And this is no, "One Mississippi, Two Mississippi" kind of thing either... it's a substantial sailing rip of many hundreds of yards... let's just say five hundred to keep things clean.

Your new boat, Sam, just might be able to get the trick done and I hope it happens that way for you. I don't see it happening with any of the trimarans I design, nor do I see it from any Farrier boat, along with dozens of other speedy tris that are out there.

The slate is clean but we haven't gotten there yet.

Conventional style tri amas, whatever the source of the design, would have to have lighter hulls, really substantial rigs and amas shaped completely differently than the ones we typically see to provide a planing surface that could dynamically support a good portion of the boat weight, while the vaka supplies the rest.

So, go ahead and put my name on the list until the design idiom of the typical trimaran ama changes.

This isn't an emotional thing for me, so don't anyone go and get all mouth breathing snarly about the topic. Six months ago I asked for proofs in the form of a solidly shot video clip, an extended motor drive sequence, etc. and nothing that was shown came anywhere even close to showing a tri with its ama planing while the vaka hull was doing same. Plenty of cool shots of tris hauling ass, which I really got foamy about, but nothing that could stand the argument up with substance.

Six months and nobody can provide a single, good video clip to support the topic. Now, if you want something telling, that pretty much says it all.

My Name... Chris Ostlind

Phil Stevo

05-29-2007, 06:17 PM

It depends on what you call a trimaran, but this 3 hull boat certainly planes very fast:
http://www.macquarie.com.au/speedsailing/updates.htm

frosh

05-29-2007, 08:55 PM

Hi Chris and Stevo, and other interested people in this topic.
The entire purpose of my current tri, and there is no other purpose, is to prove once and for all, that a tri can be designed to fully plane on say two hulls simultaneously, the third hull being airborne. I am talking serious planing here, like an IC (International 10 sq. m Canoe) going flat strap on a reach in 20 knots of wind. No immersion of the leeward ama beyond an inch or two.
It might not work, but I have a very strong feeling that it will, and maybe even go quicker than an IC for a fairly similar overall length. (18ft. 6 inches, plus bowsprit). It will never be an open water travelling boat, but it is for blasting on our local bit of sailing paradise, The Swan River, in Perth, Western Australia.

frosh

05-29-2007, 09:01 PM

In my post. no 65 the link shows the boat that I refer to, top left photo. It is actually "Slingshot" not "Crossbow 2". Sorry about any confusion.

gggGuest

05-30-2007, 04:02 AM

I cannot imagine that anyone could have any serious doubt that a trimaran configuration could be made to plane on centre and lee hulls. Its just a question of having the appropriate shaped hulls. Surely the question is whether such a configuration would have useful performance or other characteristics when compared to a non planing boat.

The available evidence seems to suggest is that beyond a certain fineness ratio planing starts to lose its value, presumably because the efficiency of displacement sailing increases with the much lower wavedrag, and the efficiency of planing reduces with the decreasing aspect ratio of the hull.

So Bethwaites HSP was fat enough to plane, but couldn't operate successfully as a true trimaran (which, to be fair, was the idea). Successful trimarans in the past haven't planed. So surely the question is whether there's a sweet spot in the cross over area that will enable a *successful* planing trimaran. Actually making one plane should not be that big a deal. Three IC hulls (a Slurp in the middle, Nethercotts on each side maybe) would make a planing trimaran, but probably not a very good one...

PI Design

05-30-2007, 07:00 AM

Frosh - the boat must necessarily have some heel to get the leeward ama wet and the windward ama out of the water. Is the central hull optimised to plane at this angle? In my experience even small heel angles really kill the ability to plane on conventional hull shapes.
Off topic slightly, but somewhere on the net you'll find details of a pentamaran frigate which consists of two amas on each side - one slightly higher out the water than the other. At small roll (heel) angles only one ama touches the water. As the roll angle increases the second one does as well. This has the advantage of not putting more boat in the water than is needed, graduating the benefit of the amas. I've wondered whether this configuration could be applied to sailing tri's.

Paul Scott

05-30-2007, 10:18 AM

I think someone tried it with a catamaran (Quadramaran?) configuration using 4 hulls up in Vancouver BC. Harris? Can't remember if it was a planing concept or no. Many years ago. Was supposed to be interesting in waves.

Paul

PI Design

05-30-2007, 10:27 AM

Here's a link to the pentamaran.

http://www.usashipbuilding.com/panels/pdmt/downloads/pentamaran_hull_form.pdf

Nigel Gee (the designer) used to be president of RINA, so this is not some crackpot idea.

frosh

05-30-2007, 12:40 PM

Hi PI, A huge amount of thought, sketching and planning went to the idea that a central hull needed to be optimised to plane efficiently at low to moderate angle of heel, either towards port or starboard. I think that I have hit on something extremely close to optimum. Don't want to say too much at this stage for a whole number of reasons. I will let the forum know after real on the water testing. Remember it has sailed already as a tacking outrigger!
Any suggestion that 3 IC's joined together proves that a crude tri can plane might be true, but is entirely irrelevant to what I am attempting to achieve.

CT 249

06-03-2007, 08:52 PM

Hi CT, The Bethwaite HSP was exactly what I was trying to emulate, except I believed their floats were too small and became a liability every time one hit the water. Also the centre hull could easily be further optimised by going narrower . My aim was to turn these two negatives of the HSP into two positives.

Cheers. Sam

The only time I sailed the boat, I found that the floats worked as designed; that is, they would develop the planing lift to play a major part in keeping the boat upright. The flex in the alloy beams allowed them to skip without burying and they didn't slew the boat when they hit hard. The small size meant that they were training wheels; you couldn't cruise the boat along like a "regular" small tri such as the Supernova. However they did make the boat vastly more manageable than it would have been without them (increasing roll moment probably helped too).

The problem with increasing the float size, Frank believed, was that when you did capsize, a large float was impossible to sink and therefore the boat inverted and stayed there. That was part of the reason for the small floats. These had two parts; an outside shell that had ports so that it could flood (allowing you to sink the float when recovering from a capsize) and a small airtight section. When sailed normally the ports did not take up water.

The boat could be hard to recover, at times, and then it would pop up.

Frank said he modelled the hull on board design. IMHO, I thought that the concave stern sections were not the right way to go as boards with concave sterns were not as succesful; the concave was up the front where planing lift is generated. However, Frank does his homework and I may be wrong in applying windsurfer ideas so literally.

One thing that strikes me is that the IC actually works like the windward float of an HSP; the plank is a high-aspect planing surface and when you're going fast and drop in to windward, it normally just planes along.

In some ways the HSP was just a big Canoe, with a giant fixed plank. Damn fine boat.

Paul Scott

06-04-2007, 12:23 AM

CT, the HSP floats rotated like Gougeon's Adrenalin and Victor T floats?

Paul

CT 249

06-04-2007, 01:08 AM

Paul, they probably did rotate to some extent because the fore-and-aft separation of the light alloy tube crossbeams was quite small. The main flex, however, seemed to be up and down, which seemed to have a similar effect in allowing the float to give with the seas.

frosh

06-04-2007, 06:38 PM

Frank said he modelled the hull on board design. IMHO, I thought that the concave stern sections were not the right way to go as boards with concave sterns were not as succesful; the concave was up the front where planing lift is generated. However, Frank does his homework and I may be wrong in applying windsurfer ideas so literally. QUOTE - CT 249 - DISCUSSING FRANK BETHWAITE DESIGNING THE HSP.

I have done some sailboard design and construction myself for shortboards, apart from my tandem sailboard.
I built a bottom shape "form" or you might call it "mold".
I then built 2 boards from this mold, one for me and one for my son. Although over engineered (to last forever, which I expect they will), and about 10kg each, when state of the art would be closer to 6kg. they have performed above expectations, according to myself and son. (We have a huge number of sailboard sailing hours under our belts, and betwen us have owned around 20 different boards).
The description of the bottom would be as follows.
Bottom spring or rocker is long and gradual in the mid sections to bow. Small tail rocker in the final 30 cm.
Slight concave in the very first 40cm from bow. From there going towards stern, dead flat until around 75cm from stern. From this 75cm ahead of stern a slight V is introduced almost impercepible to the naked eye at first, then gradually becoming more pronounced and gradually increasing in size all the way to the very stern. Strictly speaking it is not a flat panel V at all, but has some convexity when you put a straight edge on the bottom, from side to the middle line.
It was almost certainly good instinct from extensive observation, and reading on my part, and good luck also, but I have been amazed how well this design performed, and handled. We both agreed that is was the most user friendly shortboard to foot steer and gybe that we had ever owned.

The real point of the discussion above, and I apologise for it's length, is that I used the same "mold" to build my trimaran amas also, before finally trashing the mold, as it was taking up space I desperately needed. What is interesting is that it seems very different to F. Bethwaite's concave tail design that he modelled after successful sailboard design.

Paul Scott

06-05-2007, 11:45 PM

frosh, did a 9.5' kind of close to what you are describing- more v in the tail for foot steering, and a bit more concave in front. Although it was spectra, and LEAKED. Good while it lasted, which was not for long! I would call this shape classic. Or epic.

Paul

frosh

06-06-2007, 04:32 PM

Hi Paul, our shortboard design was based somewhat on the STARBOARD carve model. About 2.6m long and 61cm wide, it was designed for early planing, and maximum manouverability, in the open sea in all wind conditions. It had bevelled rails which gradually disappeared towards the tail. Had 1.5mm marine ply incorporated into bottom and deck (like the wood STARBOARD), although they only use a very thin wood veneer. It also incorporated carbon, dynel, in strategic places, fibreglass and epoxy. These are probably the most indestructible short boards ever built. Probably 3-4 kg over optimum weight, but it doesnt feel that it slows them at all. Can hand them on to future grand kids in very likely perfect condition. Fins were hand made and slotted thru a casette like daggerboard case. Each fin cost a few $ each in materials, but many hours work. Could install and un-install a fin in 1-2 seconds, very handy.

Paul Scott

06-06-2007, 11:12 PM

frosh, my idea was to keep the water accelerating all the time at speed. Never give the water a break. Was that a concern with your board design?

Paul

frosh

06-07-2007, 08:02 AM

Hi Paul, I don't really understand your question. Please re-phrase, and I will try to answer re the design philosophy.
Sam

Paul Scott

06-08-2007, 12:17 AM

frosh

06-09-2007, 10:18 AM

frosh- when I did the board, it was in a series of boards that had the following idea; that at planing speeds, the flow was kept in constant acceleration, so that the flow didn't want to separate very much from the bottom. Or in other words, keeping the boundary layer thinnish. So the tactic was to shape the bottom so the flow was always being speeded up. At first we started out with a concave bow and added a gradual v, hoping that the flow would be accelerated from the middle (or top) of the concave, out from the v to two concaves which ran back to a flattish, or v'd stern, and let whatever de-acceleration happen in the wake. Then we went to what you are describing. (Although we usually went with tucked under rails to the edge of the concaves underneath. Held on to waves better.) My question was whether this was your theoretical approach? The constant acceleration idea that is. There was another idea that came from Sweden, that you wanted the middle cross sevtion totally turbulant, and the edges were where the weight was supported and the flow was smoother- looked kind of like this; __-------__ with square edges/sides. The square concave was usually about 1/4 to 1/2 inch deep. I tried one that looked like a cubist Hickman Sea sled- complete crap! It worked, but the envelope seemed kind of narrow. Well, really narrow. And the bow stayed down. Veeery entertaining. Hope this is a bit more coherent.

Paul

Hi Paul, I am struggling a little to fully follow exactly what you were trying for in your design but I will attempt to answer as follows:

The water flow being in "constant acceleration". Unlikely that this can actually be achieved, and if so why? Is it anything to do with Bernouli's principle?
"The pressure of moving air explains the upward lift on the wings of aircraft. When the air flows faster over the top on the wing then below, there is an upward push called lift".

When designing a shortboard it is always designed with planing as the only possible scenario. Apart from limitations of the rig and sailor, the main issue is wetted surface reduction, and control of the board via the feet. Any sort of concave bottom or the _------_ shape (also a form of concave) will increase hydrodynamic lift at marginal planing speeds but is actually slower at rapid planing speed.
Tucked under rails were the most common treatment for rail shape as it was a good compromise between a board that could be easily manouvered and had moderately sharp rails for clean water release to minimise water drag on the hull.
Starboard were the ones who introduced a variation of the tucked under rail with a sharp bevel ( instead of a well rounded arc), at around 45 degrees and about 15mm in width.
It was believed to allow good manouverability with the advantages of a hard sharp rail as used in the quickest slalom boards. I thought that the idea was probably going to work as they claimed. I would say our opinion of the performance of the finished product bore this out as a definite advance over the tacked under rail for most types of sailboards.
My aim was for the board to plane early, mainly due to some bow concavity and more than average width in the middle region. The flat bottom here was for the best compromise for max planing with minimum drag. At higher speeds there should be no bow nor mid sections ever in the water and only the last 60cm. of tail approx. This area needed to be slightly veed to avoid pounding in chop, to allow some small degree of softening the ride through rough water. It also aided rail to rail transitions when initiating a gybe, as the tail section was easily rocked over from one slightly vee'd panel to the other. As I stated in an earlier post these panels were vee'd but very slightly convex.
I believe that this facilitated slightly better control and ride as the bottom orientation to the water was always slightly changing. This explanation when read with my previous posting pretty much covers the whole design philosophy of my shortboard.
The fact that I have use the same bottom mold for the tri amas was partly a matter that it was convenient, and that I believed that for planing amas, many of the principles would be the same.

Doug Lord

06-09-2007, 11:21 AM

Frosh, from that perspective combined with your previous drawing I'd agree with Tom that the "ama's" are too far aft. Looks to me that the dynamic center of lift of the amas would be behind(or at best lined up with) the CG of the overall boat+ crew; is that right? And thats not even considering a desirable forward positioning of the lift to help counter rig induced pitching. Many tri's are designed so that the CB or center of dynamic lift or both of the ama's are ahead of the CB of the mainhull for this reason. I'm interested in your thinking here...
I'm curious about the overall beam: the load on the planing hulls would be reduced and their effectiveness would be greater with more overall beam. I'm fairly sure the HSP was proportionately wider. What is your rationale?
Just as a suggestion ,why don't you restart your topic under "multihulls" and add these sketches so everything will be in one place.And maybe you could post some pictures there too.

frosh

06-09-2007, 06:08 PM

Frosh, your boat looks to be similar in concept to the Bethwaite HSP. That had the floats even further back, and it was a stunning machine to sail.

Out of all the posters on this forum only one (to our knowledge) has actually sailed the Bethwaite HSP, and that is CT 249 (Chris Thompson). I am truly encouraged by his quote above. My concept is definitely not in the design style of the Farrier tris'. I have unashamedly based by boat in the HSP which was fascinating to see just sailing in a photo, which I have seen. I have contacted Bethwaite design to attempt to obtain such a photo. If I can, I will post it on the forum.
In the the 80's when the HSP was created in it's final incarnation, and was sailed by a journo with Julian Bethwaite, they claimed a top speed of 23 knots on the day; their first outing together on the HSP, remember no lifting foils. This was a phenomenal performance.
Doug, the main hull shape was heavily influenced by the recent Int. Moths prior to lifting foils such as the "Hungry Tiger". However I wanted a boat that had higher power to weight ratios, and less loading on each square foot of hull bottom. Further the HT Moth was very canoe like in design, emphasizing low drag in high speed dispacement sailing. I was determined to allow my design to break out easily from displacement to full on planing at moderate wind strength. I modified the bottom shape accordingly. It works, I have sailed in 15 knots plus of wind a few times, and there is no doubt to me as skipper that the main hull clearly lifted and very noticably increased in speed at the same time. Being a proa we got the best performance with the slim ama to windward and flying clear of the water.
Essentially what we had was a 5.6m x 40cm beam Moth for 2 crew with main sail and large jib. and it was for long periods sailing as a ultraslim monohull.
Problem was that the concentration levels demanded of 2 guys, each controlling one sail with high power to weight was too demanding and swims were fairly frequent. Frequent recoveries from capsizes meant early exhaustion for the crew. Hence the re-evaluation of the project to maintain or improve on the original performance and reduce dramatically the possibility of capsize. Also I realized that it needed to handle identically on either tack as under the mental pressure in strong winds, my brain did not fully adapt to the different configuration and sailing requirements needed on each tack. (Being completely different). Also I have 2 assymetric kites that I have never had the confidence to launch yet due to various instability issues. The new tri arrangement will pop a kite every time that we steer about 110 degrees off the wind. This is when we expect to see the spectacular performances I have been dreaming about. Obviously it is unknown quantity now!
You have to consider my boat as a giant planing Moth for two, rather than a conventional tri of any previous style out there.
Now about OVERALL BEAM:
The bigger the better for some designers, but loads on rigs and hulls increase hugely as the rigs become much more powerful which seems the logical way to go when one has increased the beam to around square. Remember that I had built essentially a 2mm thick marine ply main hull even with the arced bottom shape, and lightweight WRC framing. I didn't know how much force the whole boat could take without breaking up. My belief is that a small optimised rig on a low drag ULTRA LIGHTWEIGHT boat would perform as well as boat twice as heavy with a huge rig. The other factor was that unlike all typical tri's, righting moment would come from a very active crew hiking out to the max rather than the leeward ama providing buoyancy derived lift to resist sail heeling forces. My Overall beam is 10 ft. for a hull length of 18 ft. 6 inches. With one crew on a trapeze wire, structural loadings from the windward stay can dramatically reduced, and that is also an important part of the design philosophy. One more experiment is whether The James Wharram gaff rigged soft wing sail can function on a high performance boat. So far, testing has shown that it probably can, but much more work is to be done. Also we have recently stiffened the tiny section round section carbon mast with adjustable triple diamond stays. Without the diamonds the mast would be falling away far too much losing most of the rig power. No photos yet, but they will come! At that stage I will move the tri part of this thread to a new thread.

Doug Lord

06-09-2007, 07:40 PM

Frosh, I got out my copy of High Performance Sailing and studied the pix of the HSP and based on that and what you've said I think I'm wrong about your ama's. The way you describe "using" the ama's and the way Bethwaite obviously did means they'll rarely if ever be in the water and therefore their position is largely irrelevant.
Yours look a lot larger than his as best I can tell.
Looking forward to pictures.

CT 249

06-09-2007, 08:45 PM

Okay, I've found the old HSP article I did in '88.

Dimensions - main hull 4.86m long, 0.46m wide. Main hull weight 27kg.
Floats 2m long.....longer than I recall them being, actually. Looking at a pic I'd estimate that float beam was about 0.20-0.25 wide but my visual estimate is at odds with the rough scaling of the pic. Frank modelled them on the wingtip stabilising floats used on the flying boats he captained, including the Catalinas he drove in WW2. Total weight 79.5kg. Sail are 16.3 sq m.

I was wrong about the floats having buoyancy tanks; the only positive buoyancy was their foam sandwich skin.

The HSP does have a lot of flare forward to stop nosediving. You could stick the deck 6" under water and it would pop out. Normally flare is accepted as a bad way to "cure" nosediving these days, but it may work okay in the HSP as the hull is so slender. The volume does seem to be further forward in the HSP. Frosh's boat could be closer to modern no-nosediving cats (ie A Class) where the deck shape is so low buoyancy but low drag that the boat drives along easily, without "tripping", until it pops up.

My rough estimate is that the bow of the floats are about half-way along the main hull, so Frosh's may actually be further forward.

Doug Lord

06-09-2007, 09:26 PM

The HSP MkXVII,p 187 of HPS, shows fairly long floats/amas but what is particularly interesting is the large amount of flare to both the main hull and ama/floats-definitely not 'wave piecing'-looks like the hulls might trip if pressed really hard.
HSP DUO MkXVIII,p319, shows almost no flare to either ama/float or to the main hull. Ama's appear to be proportionately smaller than on MkXVII.
I find it more and more of a stretch to call these boats (including my own 21 footer) trimarans since they are not designed to sail on the floats/amas. In fact, sailing on the "ama's" would be much slower on both Frosh's boat and the HSP's and on my foiler.
How about monohulls with buoyancy pods? They almost fit the definition some use disparagingly of "monohulls with training wheels" but that
is not accurate or meaningfull-these boats sail their fastest when sailed as monohulls with the 'pods" just there as backup(not training wheels). The configuration allows a high powered lightweight boat that is made easier to sail by having the pods and whose speed is not in any way dependent on them(other than for prevention of capsize to some extent both in light and heavy air).
This type of boat is a natural as a monofoiler using just two foils. But whether it has foils or not the type is much more monohull than it is trimaran in terms of how it actually works-in my opinion.

CT 249

06-11-2007, 01:14 AM

Training wheels (as in, the ones on kids bikes) normally are just used as back up in my experience.

I think there are problems with defining these boats as monos. Sure, they are designed to be sailed on one hull most of the time - but the very fact that you have the pods for capsize prevention changes the way you sail them, because the consequences of mistakes becomes much less.

Secondly, I think it's torturing the language to say that something that gives a degree of effective buoyancy because of its displacement is not a "hull". Therefore these boats have three hulls, not one. They may be small, they are still hulls.

Finally, there are other boats that have more than one hull, but are fastest when sailed on just one hull. The late F 40 and F28 tris sailed fastest on one hull, but they were trimarans.

A modern fast cat, well sailed, sails on one hull almost all of the time, upwind and down. In a typical day around our cat club course, I'd say a top A Class sailor may have two hulls effectively in the water little more than a HSP sailor would. The fact that the hulls are canted shows that the boats are designed to sail on one hull.

I think from memory, the top A guy (lightweight, ex world champ) was flying a hull from about 5 knots. The swiss lake cats fly them in less, I think. Does that make them monos too?

I agree that these are not the same as a normal tri, but in my opinion that doesn't make them a monohull.

frosh

06-11-2007, 10:58 AM

Hi all, I have also checked out the photos referred to by Doug of the singlehander and doublehander versions of the HSP in Frank Bethwaite's "High Performance Sailing". These much more than my tri concept are basically optomised monohulls with lateral hulls purely designed to prevent severe punishment by immediate capsize for mistakes or sudden changes in wind strength. I see both HSP's as a type of hybrid between a mono and a tri, probably with more emphasis on the fact that it is a planing central ultra slim skiff, of minimum drag that is the commmonly only immersed one, when trimmed for max speed. It is obvious that both leeward and windward hulls should be kept clear of the water when trimmed to perfection.

CT I think that your dimensions as in your posting where you recall the article you did in 88 must refer to the singlehander. The doublehander would be closer to 20ft long with quite short planing amas that are designed for emergency use to prevent frequent capsizing.

My tri has more substantial amas (particularly in width and bouyancy), that are canted outwards at approx. 15 degrees, and designed for the leeward one to always be in contact with the water. This has allowed me to contract the overall beam quite a lot. The overall beam is only 54% of main hull length, while the HSP appears to be closer to 65% in the photo.
My boat will be a true tri, and definitely not any version of a monohull at all, even though it sort of was, when it sailed previously as a Pacific Proa (starboard tack only). The ama will be pushed significantly into the water by heeling forces, I expect that possibly 100kg downforce might be acceptable at higher speeds. However I expect very minimal immersion of the ama when moving at speed. I also expect that this might be the quickest way to sail the craft rather than depower to attempt to keep the leeward ama clear of the water. An efficient sailboard shortboard does not produce much drag when moving rapidly as it is effectively optimised to plane with little wetted SA. I realise that there is a role from the de-weighting on the sailboard hull provided by the canted freesail rig which I cannot mimic in the tri.
F. Bethwaite had a total of nineteen prototypes over 20 years, this one is my version 2. It has a different design brief to all FB's 19 versions, and it was my choice not to copy any of his versions at all.
I believe that my main hull is possibly better than FB's best main hull from dimensions and shape, and also limited sailing experience already. The true unknown is the fully planing sailboard type amas (each with about 200kg total bouyancy). These are to allow the CB (dynamic) to be situated around 75cm to leeward of the main hull centreline, adding significantly to righting moment. I cannot determine from calculations, but hope that drag of the leeward ama, will be less speed robbing, than the reduction in drag on the centre hull combined with increased righting moment, will be significantly speed enhancing. Stability and resistance to further heeling should be fairly huge. This in turn will give us confidence to sail the craft really hard. BTW, I am still confident that the fairly aft ama position, will not lead to pitching forces tending to bury the bow of the main hull. Up till now there has been no indications that it will ever bury, but I could be wrong.