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

High Performance Self-Righting Trimaran: The Test Model

About two more weeks and I should be back on the model full out.....



From Gino Morrelli(famed multihull designer with Morelli and Melvin):

"Foils are definitely the way to go: it's an instant turbo".

 

High Performance Self-Righting Trimaran: The Test Model

In the very little time I've spent on this project in the last few weeks I have completed the "lofting" . I drew the dihedral, ama+ curved piece full size to allow the jig to be built very accurately. And laid out the curved ama foil full size(see post 163 ). Next step is to remove the poster paper from the table and put a 4 X 8 sheet of plywood down to serve as the base for , first, two jigs to allow assembly of the curved piece and ama and then the full assembly jig. Hope to get to it in the next week or two.
click on image:

 

High Performance Self-Righting Trimaran: The Test Model

This was inspired by this thread: http://www.boatdesign.net/forums/multihulls/trimaran-tornado-cat-40413.html I had no need to do it for this design since the model is based on a hull I have that specifically suits the self-righting concept with enourmous extra volume in the deck area of the bow.
Further, I have designed and built two trimarans with planing hulls as this one has. And everybody is probably familiar with the Weta tri. It has an L/B ratio of 5.3/1 and this boat has an L/B ratio(level) of 6.26/1. My 20' tri many moons ago was similar to this one in L/B ratio.
The sections in the sketch below show the midship section of the SRT-"A"- and two other sections- "B"= lowest wetted surface with a 12/1 L/B ratio and "C"
-16/1 L/B ratio with just a touch more wetted surface than "B" but a significantly skinnier hull. That's approximately the same L/B ratio as a Tornado with one hull flying . All three sections have the same area that reflects a displacement of 750lb.

If I wasn't trying to make a self-righting tri work and I could start with a blank sheet of paper I might choose "B" or "C"-probably "C" because the skininess might help more in heavy air tacking even when flying the main hull because there will be two hulls in the water during a tack even if you're using ama foils. If the MPX foil system(bi-foil arrangement on main hull) works there is a good chance that the SRT could complete a tack-and especially a gybe w/o the main hull touching down. Also, because of the high dihedral of the SRT the main hull can pitch nose down slightly and heel reducing wetted surface about 20% in very light air-bringing it down to about what "C" is. The L/B ratio would go up(hull gets skinnier) as well but I don't know how much.
click on image:

 

High Performance Self-Righting Trimaran: The Test Model

The jig table is up. It's just a piece of plywood not quite as wide as the boat is long(48" vs 60.75") but long enough(8') to set the whole boat up.
Have decided to do the assembly in two stages:
1) the amas will be ground and assembled to the curved pieces using two small jigs. Then the curved pieces will be carbonated and the ama+ curved piece assembly filled and sanded. The curved foils and trunks will be built.
2) the jig will be set up on the plywood such that the curved piece+ama assembly can be bonded to the cross arms and the cross arms bonded to the main hull. That will be done by laying up a tube over the main hull verticals so
the whole crossarm/curved piece+ama assembly can be removed.
3) I hate sanding especially on a project like this where I have to be extremely carefull not to add too much weight so I may do the cosmetization
of all these parts first(after the curved piece+ama assembly) and before anything else. Just for psycological reasons to get it mostly behind me.
Back on it after Thanksgiving-so have a good holiday. We still have an awful lot to be thankful for amid all the trouble, sickness etc.......

click on image: 1) drawing/lofting table, 2) jig table just set up on top of the other table---

 

High Performance Self-Righting Trimaran: The Test Model

I'm considering an idea that would allow the curved piece/ama assembly to pivot a few degrees to change the ama orientation depending on the boats angle of heel(which can be fairly precisely set and maintained). The thing that bothered me is that to make the cross arms hinge along a parallel axis is a real pain and more complication than I want to get into. The max pivot would be about 8 degrees corresponding to the ama bottom being flat on the water from an angle of heel of 10 to 18 degrees.
So I decided to do an experiment with 11 degree off-axis hinges(see pictures). I used model airplane flap hinges and used scrap balsa(and cyano and baking soda) to set up the arrangement exactly( well ,similar in princible with the exact angles) how it would be on the model.
It surprised me that it worked perfectly with no binding or twisting as best I could tell. Now, what am I going to do with this info? Still up in the air....

UPDATE: 11-25-11 In studying this thing last night I could see a very small amount of twisting in the plastic hinge at deflections of 45 degrees or slightly more. No misalignment of the movable surface occurred at any time/deflection. Doesn't matter, in my possible application, because max total deflection would be 8 degrees. And it will move and be set-not move continuously. But I find it very interesting that it works at all.....

Sorry for the slight blurriness in picture 1. Still don't get that.

 

High Performance Self-Righting Trimaran: The Test Model

My Styrofoam Lady finally got back from vacation and I took her the pattern for the curved foil one-off "molds". Basically, the styrofoam is being precisely cut to the radius of the curved foil with the outside surface exposed. This will allow me to make one off foils with either a symmetric or asymmetric section.
So, I'm probably going to go with a 63412 section with the "flatish" part outboard. Each board will be made with 20 pieces of 2X2 twill, .007" ,5.9 oz carbon fabric and 12 pieces of .012" uni carbon. Final thickness will be about .284" for a T/C(thichness/chord) ratio of 9.5% for a 3" chord. This foil has the heaviest loading of any foil on this boat at max. speed.
The daggerboard and mainfoil, are being built one off with .125" plywood core(main and rudder foil=2 .065" pieces wth flap material bonded between them) with 5 pieces of 5.9oz carbon each side and 3 pieces of.012" uni each side.
The rudder and rudder foil will use the same core with 4 pieces of 5.9oz carbon cloth each side and 2 pieces of .012" uni carbon each side.
All will have T/C ratio's of about 9%. All(except the curved foil) will have symmetric sections.
The main and rudder lifting foils will use short flaps similar to the ones shown below from the F3, with sealed mylar flap hinges built into the foil. The main reason for this is the "thinness" of the foil which increases the propensity of the flap to bind under load. And, considering everything, the best thing these foils have going for them in this model application is that their design is proven to work on the F3 /MicroMoth.
Should have the one off styro molds late next week.

 

High Performance Self-Righting Trimaran: The Test Model

These pictures are before and after grinding-prep for filling and sanding. The worst of it is on the amas where I missed the trim window and now have excess grinding to do.


Pictures, L to R : 1) bow will be slightly changed-grinding part of the bottom off, 2) view from top, 3) view from bottom,
4) bow-changed, 5) & 6) as above but grinding done.

click on image-

 

High Performance Self-Righting Trimaran: The Test Model

Picked up my two curved foil molds from Sharon Dixon of Architectural Foam and Art in Rockledge ,FL. today. Perfect-I think they'll work very well. The molds are 180 degrees but the foils are around 160 degrees tentatively which gives some latitude. Molds are significantly wider than the foil is.

click on image--

 

High Performance Self-Righting Trimaran: the Test Model

Merry Christmas and Happy New Year to everyone following this thread! I'm caught up with my Real Life obligations and should be back on the project almost full time starting Tuesday.
----
See the stryrofoam molds in the last post? Well a guy on another forum sparked an idea I should have thought of a while ago: use the cut outs(or similar) from the semi-circular section to make a matching quickie mold for those "molds"! My plan had been to hand finish the inside of those foils but I didn't like the way the lamination would work out doing that and this way each half will be laid up perfectly and bonded as a single unit with almost no
hand work and the lamination will be in the correct order and place. It is a quick way to build a set of curved foils and would work at almost any size.
I'll see Sharon Tuesday and get the matching halves then or soon after.
The top and bottom halves of the section have to be hand sanded out of the styro but thats no big deal.

 

Merry Christmas Doug!

Looks great so far! I'm looking forward to seeing how the lifting foils develop.

 

High Performance Self-Righting Trimaran: The Test Model

Thanks, Raps! Should be making a lot of progress over the next few weeks.

 

Models

Merry Christmas too you also ...

Working on a model also at this end but curved lifting foils are not an option for me right now

I'm trying to figure out how you post your pictures such that we can see them right away ... Do you have all your pictures online somewhere first ?

 

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Hi, ADG- I have them in a saved file on my computer. I use the "Manage Attachments" just below where you add a message. Click on that and click on "browse" and select "pictures" and then "upload".

 

model cat

Giving it a try ... Hmmm, looks like it's gonna work Thanx for the info

 

model cat

Now THAT'S fun !
I suppose the hulls are much like your "B" hulls from above. L/B ~ 14:1