Planing Trimarans II-the real thing?

[Doug Lord]

Originally Posted by cavalier mk2

I just refreshed my memory from Yves website. I remember looking at those hulls on the catamaran thinking they would be great offwind but would suffer a penalty in certain conditions to windward with the fuller bow punching into wave tops. Perhaps a longer wavetop piercing nose ? I do like the idea though I wonder about light air speed comparisons.

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The significance of the model in the pictures above is the geometry. It was created with a lot of calculation and a preliminary lines plan and then was carved from balsa based on the previous info. What is shown by the model is that, in fact, a hull like this is possible-which I had my doubts about when I first conceived it. The fact that a stepped planing hull and a high L/B displacement hull as top and bottom of the same hull could be achieved for the proper numbers is flat remarkable. It still blows me away. It could "easily" have been patented but I chose not to. It offers a lot of potential with the remaining problems nothing compared to the geometrical solution the concept is based on. For those with no clue the inception of "planing" on the stepped hull is at a very slow speed so the imagined tacking problem is a non-starter as proved, incidently, by Parlier's work on an RC model, a small prototype and L'hydraplaneur.
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Click on image and then again on resulting image to increase or decrease size:

[Chris Ostlind]

Doug,

Aside from the rubber arm back slapping of oneself so evident in your own write-up, you have managed to create a non-event duck looking for a place to land.

You have broken the continuity of the external skin of the ama at a place where it needs to have maximum strength as a cantilevered form. This will necessitate a seriously robust internal beam that can carry the loading and will drive the complexity and cost of the build into the stratosphere... not to mention the added weight for a boat that thrives on light, responsive hulls.

A component of the submerged hull will be further hampered with poorly designed flow optimization by placing the needed groove for the rotating mechanism precisely where best flow is supposed to happen. This flow breakdown will happen for either surface of the ama that is presented. Installing a flap on the leading edge of the slot will not solve the problem anymore than the same type of application solves the issues surrounding the use of a typical centerboard, You can "maybe" reduce the damage to the smooth flow a tiny bit, but you'll never make it go away completely. This fact, alone, is a killer for this design's effectiveness.

I would think that you would want to look for better performing shapes for existing hulls, simpler, less fussy control sets on deck, better aerodynamics for the overall boat and a design that could either be built easily by the average dude, or manufactured easily and affordably as a production example. None of those hit list items are in evidence here.

"For those with no clue the inception of "planing" on the stepped hull is at a very slow speed so the imagined tacking problem is a non-starter as proved, incidently (sic), by Parlier's work..."

If the above statement is true, then how come Parlier, himself, said that his cat would not plane until it was hitting 20+ knots and all sailing done below that speed was sluggish when compared to standard hull forms not dedicated to a planing function? Those comments are all over the place at both this site and at Sailing Anarchy's forums and are easy to obtain, should it be necessary to squash a bug.

We get the feeling, Doug, that you are afraid of dealing with the potential drawbacks of a design such as you propose and only wish to hear comments that don't ruffle your feathers.

You have been told many times on these pages that there's no free lunch in design. That to get something you desire, you have to give something up to get there. That the further you press your desire to drop everything in the name of what you see as Holy; that being your search for speed as the most important thing for sailors... the further you travel from having an all-around tractability within the same design.

[Doug Lord]

Originally Posted by Chris Ostlind

Doug,


You have broken the continuity of the external skin of the ama at a place where it needs to have maximum strength as a cantilevered form. .

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You should read more about stuff before you ostlindize it! The refined version,
not shown in the model, uses a one piece hull with the forward attachment point a flush(where it has to be) collar that allows rotation and robust strength. The model simply illustrates the geometry and the concept-not the details of construction but some of those details are covered in a previous post.

post #8:

Originally Posted by Doug Lord

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There is hardly any load on the rotation system on the updated version that uses a collar around the hull just aft of the step. Allows the hull to be made in one piece....
You're right about the shock loading-it would have to be addressed...

[Doug Lord]

Originally Posted by Chris Ostlind

Doug,


If the above statement is true, then how come Parlier, himself, said that his cat would not plane until it was hitting 20+ knots and all sailing done below that speed was sluggish when compared to standard hull forms not dedicated to a planing function? Those comments are all over the place at both this site and at Sailing Anarchy's forums and are easy to obtain, should it be necessary to squash a bug.

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Parlier's boat would begin to plane at 12-14 knots but its drag would not drop below that of a high L/B displacement hull until around 20 knots where it had about half the drag of a skinny hull. At 40 knots L'hydraplanuer had only 25% of the drag of a skinny hull!
Parliers cat was very wide for its length(50'=.83LOA, L/B overall 1.2) and some would conclude that meant it tacked slowly-I wouldn't, necessarily, and have written Yves to ask him.

[Chris Ostlind]

Originally Posted by Doug Lord

You should read more about stuff before you ostlindize it! The refined version...

Well, to be bluntly honest about it all, Doug.... in my Ostlind-ized fashion. If you show images with a current discussion, then it is you who should hold off on the bombast until you get your act together enough to show your, "refined version".

You can do this with well executed 2D drawings that are clear and show the setup in three views to scale along with a well drawn perspective view... Or, you can provide a set of multiple view 3d rendered objects that correctly illustrate the so-called, refinements.... Or, you can make one of your hand-axe fashioned balsa models with crummy photography and buffalo your way through the presentation.

However you do it, the representations are totally in your area of responsibility and the old images should not be shown again unless they are germane to the discussion, which you so loudly admit in your own rant when you speak of the refined version.

Ya, wanna blab about your magical thingy, then get it together and build a model, or any of the above versions of your magical thingy, or quit talking about it as if it were presented in the here and now.

[Doug Lord]

Originally Posted by Doug Lord

This is more a question and is not specifically related to the "meat" of the other planing trimarans thread,which was: "can the main hull of a trimaran whose ama is partially immersed plane?" That is not the subject of this thread. Nor is this question part of this thread: " Can a trimaran ,flying the main hull, and designed with planing amas, plane?"
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This is the question I'm particularly interested in: IF a trimaran is designed to sail most of the time with the main hull flying AND IF such a boat was designed with planing amas that plane when the main hull flys-could it be faster than a tri that does the same thing(flys the main hull most of the time) with "foil assisted" non-planing, high L/B ratio amas?
---a. sub-question: could this boat be designed with planing amas whose wetted surface and total drag was less than the "foil assisted" ,non-planing, high L/B ratio amas when both are flying the main hull?
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The answers to the above questions may be able to be interpolated based on Parliers boat. The ama represented by the model is 13' LOA and is designed to work with an 18' LOA tri.
What is known based on the ama geometry is:
1) the displacement ama has a L/B ratio of 20/1,
2) the displacement ama will support the whole weight of the boat(though it shouldn't have to) at low wetted surface,
3) the planing ama should begin to plane at about 5-6 knots of boat speed,
4) the LCB of the displacement ama is designed to be slightly ahead of the static LCB of the main hull.
5) the center of lift of the planing surface is a bit further ahead of the static LCB of the main hull when the main hull is flying.
6) the rotational system is so simple that an 18 footer could easily(and advantageously) be sailed single handed particularly in light of the foils on the main hull(see below).
Note: the hull would be built as one piece-with a flush collar behind the step supporting the hull forward. The displacement ama and the planing ama can be set up with an angle relative to the main hull as viewd from forward. Both angles can be preset and would be different. Approximately 6 degrees for the displacement ama,bottom toed out. Approx. 13 degrees for the planing ama, bottom toed out.

Originally Posted by Doug Lord

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For the stepped hulls at speed some sort of pitch control is required. My solution is to use small lifting foils on a daggerboard in the main hull and on a rudder in the main hull which would:
1) be somewhat smaller than foils designed to fly the whole boat,
2) be set up to control the pitch of the ama in the water,
3) help the main hull to fly earlier than it would without the foils,
4) control the angle of heel of the whole trimaran automatically by using an altitude control system that would allow the mainfoil to lift up OR pull down as required.