High Performance MPX Foil/Self-righting Trimaran-The Test Model

High Performance Self-Righting Trimaran: The Test Model

I'm finishing up drawing the full size model bulkheads and will shortly be ready to cut them out. The bulkheads will be set up on a building platform consisting of a 10" X 12" block of EPS with a 12" X 60.75" piece of 1/4" birch plywood glued to it. Originally, I was going to use just a 6" thick block of EPS
but I thought better of that idea. You can't have too much stiffness in a building platform. I'm doing it this way to make moving the thing around easy.
The birch plywood gives me a good surface to cyano the bulkheads to. Because of the somewhat unusual hull shape I'm building this one off right side up-with the sides deck and cockpit done first. Then the bulk heads will be cut off the platform and most removed from inside the model hull.
As soon as the bulkheads are up I'll post the first picture and then on a regular basis(more or less as time permits) after that.

Pix-this is a 12" model of the hull(not the same deck on the new boat)-the new model is just over 5'. You can see the "tumblehome"(for lack of a better word) that makes building the model right side up advantageous:

 

High Performance Self-Righting Trimaran: The Test Model

I decided to start the pictorial record of this model/project with all the components of the hull(s) . Well, almost all-the carbon tubes for the mast and crossarms aren't here yet; neither is the thin carbon sheet to be glued to the balsa hull. The build will take place on this porch(overlooking the water) as much as possible and in my office. The shop is filled to capacity with the full size version of the hull the little red boat is based on and which will be used for the SRT full size tests if the model tests warrant it. Its a start:

(click on image)

 

It has been a little over two months since you indicated that materials for this model were ordered. Can you share with us the progress of the model building to this point? There seemed to be a large amount of excitement surrounding the announcement and now I'm getting anxious to see the work result from two months of building.

Certainly the photo from three days ago is just a teaser and the real boat is quite a bit more developed at this point? Please show us what you are doing on the exciting project as announced.

 

High Performance Self-Righting Trimaran: The Test Model

It has come to my attention that some people may add more to the term "self-righting" than I intend to be included for the boat that is the subject of this model test:
1) For the purposes of this model "self-righting" means that, if it works, the design will automatically right itself from a capsize or pitchpole with no action required by the crew except ,perhaps, to release the sheets.
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2) The boat will be tested to recover from a capsize or pitchpole that results in the mast being nearly horizontal-almost parallel to the water(approx-90-110 degrees). The rig will be designed and engineered to have the structural strength to withstand capsize or pitchpole at the maximum speed of the boat in, basically, inshore conditions. The system, at least for the boat that will be tested, would not be suitable for offshore conditions.
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3) Should the model pass the testing a full size version based on an already existing hull will be used to test the boat. Full size testing will determine not only the self-righting characteristics of the boat but will be used to set specific limits on the suitable wind and sea conditions for the system to remain viable. The purpose of the boat is to allow disabled sailors, physically restricted sailors and others to be able to sail very fast in a boat that will automatically recover from a capsize or pitchpole.
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4) While there are moderate performance trimarans now being used for disabled sailing that are not self-righting my goal is to try to develop a very high performance self-righting tri. I believe it is possible within the criteria mentioned above.

 

From the first post in a static situation the RM will be 3 times the HM will this be enough when you add in windage on the hulls? then it gets even worse when you add in the dynamic elements?

 

High Performance Self-Righting Trimaran: The Test Model

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I'm not 100% sure- that's why I'm doing the model-we'll see.
The ama is attached to the cross arms by a "curved piece" that is similar to the one in the picture below(for the MPX: curved piece at the top of the picture-different ama as well)-it adds about the same buoyancy as the ama itself. I doubt that this boat can capsize providing the rig holds-there is tremendous force preventing it as the boat goes over and significant RM if it went over 90 degrees with the mast more or less parallel to the water and the side of the main hull just touching the water. The tip of the mast, with its floatation, will rest on the water not under it.
Pitchpole is where it gets dicey and where the ama design and crossarm dihedral will play a big role.
The dynamic effects, how the boat lies vs a vs the wind direction post pitchpole and other elements are complex-the model will help me understand what is possible-and not possible.

 

High Performance Self-Righting Trimaran: The Test Model

Working Plan-Trapwing / SRT / model. ( Laying on top of original aeroSKIFF plan-1999) :

Click on image and then again on resulting image for best detail---

(Picture=12" model of hull in plan)

 

At last Doug, some art and not figures ... and the main hull looks very interesting. Still don't like your devil's tail floats though.

 

Do you think you could build an accurate hull from that "drawing"?

 

You talking to me, Paul - or Doug? If you mean me, sure, just check all the measurements and draw it up full size, then make your frames and strip plank it in light woods or foam. There are no tricky shapes really in a slim multihull - not like your beloved IOR classics.

 

Gary, I was asking you since you seem to actually build boats with shapes similar to this.

Other than scaling off the the sheerline, the chine, and the keel what info do you have to work from to "make your frames"?

Most people need a bit more info to define the shape. I suppose you could assume straight lines between the known points, but something tells me that would not be the intended shape.

 

The work is all there

Gday Paul,

There is actually enough in Doug's pic to build the hull with curves and all. Doug will probably increase the number of waterlines and buttocks later if needed but as the shape is pretty straight he may not.

If you look at station 1 you will see that there are intersections of the hull lines drawn from on top and from the side. If you get some graph paper and plot where the each line is at station 1 you can draw all of the station points for number 1. Repeat for all of the other stations.

This is easy if you have a hard chine boat. Curved stations require a few more waterlines unless you use a master pattern like Dick Newick to draw the frames or unless you know what you want.

cheers

Phil

 

Paul, yes, you can assume straight lines then draw in your curves; there is not a large distance to "curve" ... and the eye is very good at getting this right. Also, when you lay your gunwhales, stringers on, any unfair areas stand clear. Cheers, Gary.

 

Good day Catsketcher.

Considering there is not one waterline, buttock, or diagonal on that drawing an increase might be useful.

I do know how to read and fair a set of lines. Since Station 1 is not so interesting let's just consider the midship station.

The only defining points you have are the depth of the canoe body at CL (a fixed point), the height and breadth of the chine (a fixed point), and the height and breadth of the sheerline (a fixed point). If you want to include the deck you also have the height of the deck at CL, but let's disregard that for the moment.

So, is your assumption that the midship section is a V shape from the canoe body at CL upward and outward to the chine, and then another straight line from the chine upward and inward to the sheer?

If you are seeing something else I would like to see your interpretation, using only the information in the provided drawing of course.

 

If I recall correctly you used two or three bulkheads/frames (stations) in your current build. So you had to have had drawings of those stations prior to fastening your gunwhales, etc.