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

I'm bogged down in the Real World so have not been able to work much on the model-that should change before long. Here is a summary of the model so far and my thoughts about it:
A while back, I designed and built unique production RC sailboats-which I designed and built the tooling for. I'm damn good at building and finishing plugs to a high standard so that an extremely high quality mold can be built. But this is different-and I'm not good at building one offs-or should I say they have been a real pain in the past to finish cosmetically to a level I'm satisfied with while at the same time maintaining a one-off weight budget.
I played around with the numbers on this one so that I'd get a model that would give good results in testing while allowing me a weight budget that I hope I can live with while having an excellent finish by the time I'm ready for RC testing. Again, the main hull for this model is scaled down from a full size boat that is to be the Trapwing prototype(Design Challenge thread in "Sailboats") with some mods.
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Self-Righting Trimaran-Model Specifications
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The model is scaled down to the following dimensions(reference the full size dimensions in post #1 of this thread) / weight will be carefully and precisely scaled down. Scale 1'= 3.375" :
1) LOA-5' (60.75")
2) Beam- 6'
3) SA 3077sq.in( 21.4 sq.ft.)(tested sail area will vary a lot)


Target Weights :

1) Main hull = 3.858lb
2) Amas(for both)=1.25lb
3) Mast and Sails =1.05lb
4) 2 "curved pieces"(ama extension)=1.25lb
5) 2 cross arms = .74lb 1.1" OD CST carbon
6) 2 foilsets = .74lb
7) "crew" = 3.9lb
8) Ballast = 3.9lb

All up---16.688lb

Note:
a. leeway in these targets is given by the "crew" weight which can be made up of RC equipment, battery etc as long as CG is in the right place for the "crew".

b. For both model and full size pitchpole* RM ,keel alone, is 1.6 times HM for rig,incl sail. RM including buoyancy due to dihedral at capsize is 5.87 times HM for rig including sail. Keel will not ever act alone.......Cross arm dihedral will be adjustable for testing on model.

c. The mast weight based on the Fiberform Tornado section multiplied by 1.27 to account for greater RM of the 18 tri and then scaled accordingly.

d. Main on model will not use full battens since they are very difficult to make work right in small scale. On the other hand, if my sailmaker thinks he can do it since this is, after all, a 20sq.ft. sail I'm open to change. In either case the main planform will be nearly rectangular....

updated 1/10/11---Corrected for new length of 60.75" which allows one foot to equal 3.375"

e. The ama reflects a full size ama+ curved piece* with a total buoyancy of 657lb. Boat all up=750lb.
f.** curved piece is integral to the ama and critical for the self-righting capability of the boat. The ama for the model will be a "normal" high L/B hull with the exception of the "curved piece". A planing ama may also be tested.
g. The model will be sailed using foils for foil assist and flying.
-- "self-righting" in the context of this concept means that the boat will right itself automatically with no intervention from the crew except to ease the sheets.
h. model designed to take off(lift main hull) in about a 5mph wind(as is fullsize) and will use the performance info from the F3 model I designed and built in the mid nineties-it became the worlds first production RC foiler,so:
--SRT model mainfoil area= 68 sq.in.
-- rudder foil= 34 sq.in
-- ama foil/ full flying= 11 sq.in----Foil assist approx 8 sq.in.
-- For full size reference: this foil area is about 10% more than a Rave foiler but the system is entirely different and takes off MUCH earlier than a Rave. In addition, the main foils of the Rave continue to load up as the wind increases while the mainfoil of the MPX concept unloads the faster it goes(with standard crew and ballast) The model will takeoff in about the same wind as the F3(5mph). On the MPX concept the ama foil will eventually support the max weight of the boat with main and rudder foils mostly unloaded.

*pitchpole=boat floating bow down with tip of mast touching water. It is unstable like this(theoretically) and will likely roll to one side accelerating automatic righting process.
** see last picture below for "curved piece" that connects ama for the MPX to the cross arms. Same thing will be used on this boat though the ama is entirely different.
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Self-Righting Trimaran (SRT)Full Size Specifications

Length: 18' / 5.49m

Beam: 22' / 6.7m (foldable for trailering)

Ama LOA: 10'

100% ama buoyancy: 337lb.

Ama attachment(curved piece ) buoyancy: 320lb

Total Buoyancy for ama + curved piece attachment: 657lb

Draft w/boards Up: 6.4"

Draft, daggerkeel down: 4' 8"

Mast Length: 28' / 8.3mm

Sail Area:
--284 sq.ft. upwind SA
--575 ft2 / 53.4 m2 downwind SA

Total Boat Weight incl. ballast and crew : 750 lbs

Crew weight: wide range-for these numbers 175lb.

Ballast: (at the juncture of the daggerboard and main foil)- 175lb.

Boat weight minus crew and ballast: 400lb

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COMPARITIVE RATIOS:

Bruce Number: SRT=1.86 F18=1.66

SA/WS:
-- not flying-SRT=5.73/1 F18=4.77/1

-- flying main hull-SRT=11.14/1 F18(flying one hull)=6.03/1

SA/D: SRT=55 F18=44.16

W/SA-smaller better): SRT=2.64 F18=3.29
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Click on image/ patterns for model hull sections are right side up(!). Because of the hull shape it is convenient to build the model right side up and then remove it from the station extensions. See modified sections below:
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High Performance Self-Righting Trimaran: The Test Model-- CHANGE--

I've had a lot of time off this project due to demands of my "real" job and that has actually turned out to be a good thing. I came up with some problem areas that I hadn't checked in detail until yesterday and today:
1) The boat is being built on an existing hull. The intention was to modify that hull to raise the freeboard and change the bow by extending the length 2'. What I ignored in this plan was the attachment of the cross arms and how that would affect sitting in the cockpit. It won't work! Too cramped and the whole installation would be heavier than I anticipated. I use the word "anticipated" loosely-it's hard to anticipate something that didn't occur to you-I just ASSumed it was ok.....
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2) Because of some technical issues that have to be resolved with the MPX system and the extension that is required of the daggerboard- trunk leg room is further impacted and so is weight more so that I had originally allowed for.
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3) Same potential issue with the mast step-the raised freeboard could require an extension that would be heavy and a real drag to do.
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Conclusion: I am not going to go with the Trapwing hull shape which will simplify both the model and full size modifications. All the specifications above remain the same just the shape of the resulting hull may not be as "pretty" as the Trapwing hull. It's a good thing I've been spending too much time at my "real" work because I'd have had the other shape built by now-and I think this simplification is the best way to go. I have a few more weeks of intense "real" work before I can get back to this project.

Pictures: L to R-the Trapwing hull was based on the hull in the bottom picture with the modification of higher freeboard and more length and was going to also serve as the SRT. The actual boat will now resemble the bottom picture with a similar bow (but about half the vertical height) as the top photo. The racks on the lower picture are in the same position as the crossarms will be but they will look a lot different. Same mast step, same daggerboard trunk. Maybe the same rudder position initially just to save time-with a 2' retractable gantry added later if it is warranted after testing. Same sail plan as in previous post-after testing with less area. Pictures 2), 3) and 4) are of the hull now as it sits in the shop.

 

Yawn

 

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Hey, great comment tabman! Thanks....

 

I'm just teasing I really want to see physical progress! I've seen the pictures a hundred times, like most folks I want to see something new, forward movement, concrete progress.

 

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me too

 

High Performance Self-Righting Trimaran: The Test Model-TESTING

Test Summary-Updated 4/17/11


Because of the expense of this model and because it is based on an existing full size hull that I want to use to test multiple ideas I've decided to do the same thing with this model which will be an excellent test platform even if the self-righting concept doesn't work. The boat will be made radio control-I used to build rc boats for a living so this thing will be done in a very professional manner and will be built from the get go to facilitate multiple tests. Here is the test "program" in order:
1) test the ability of the SRT version to automatically self-right from a pitchpole or capsize,
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2) test the SRT version under sail in tough conditions,
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3) test the MPX foil system( main hull foils that control pitch and automatically control sailing angle. Foils unload as boat goes faster)
#3 & #4 & #5: http://www.boatdesign.net/forums/multihulls/mpx-11-very-small-high-power-trimaran-33686-15.html--particularly the last page.
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4) test-to the extent possible- a scaled down planing ama,
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5) test curved lifting foils with a planing ama and a small "normal" ama. As of this update the MPX system will use a retractable, adjustable, curved lifting foil in the ama to eliminate the force component to leeward generated by the mainfoil between take off and main foil unloading at about 10-12 knots true wind,
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6) possibly test "power foils": very small foils that pull down the windward hull allowing the whole trimaran to heel to windward while the main hull is supported by a bi-foiler arrangement. "Veal Heel " for trimarans.....
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High Performance Self-Righting Trimaran: The Test Model-- CHANGE--

See modified sections below. Note they are upside down and right side up as compared with original sections above. They are ready to be cut from balsa:


Pictures: L to R- 1) bow sections right side up, 2) stern sections, right side up, 3) bow sections upside down and bow piece right side up, 4) stern sections upside down. All are ready to be cut out of balsa and glued to board......Sections 1-5 have additional pieces to be glued to them after bottom half of boat is planked and removed from board.

 

High Performance Self-Righting Trimaran: The Test Model

SRT=Self-righting Trimaran
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I went thru a process in picking the model size based on the fact that displacement(weight) scales as the cube of length, sail area as the square of length. I picked a size that would allow enough weight(displacement) for the model to be effectively radio controlled and as large as I could practically(?) deal with. I imagine many are familiar with those rules of scaling-you can see the dimensions in the post above for the model and full size.
What may not be evident to most people-and a critical factor in testing-is that righting moment varies as the 4th power of length. Here are some interesting (updated)stats:
Upwind Sail area:
--full size=284 sq.ft.
--model=22.45 sq.ft.
Max RM:
--full size= 7500 ft lbs.
--model= 46.935 ft. lbs.
Max Windpressure per sq.ft. to fly the main hull without foil assist (based on Max RM)-
--full size= 2.2lb per sq.ft.
--model= .62lb. per sq.ft.
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Anyone that has ever fooled with models before probably already knows that you can't sail a model in the same wind pressure as the full size boat with max sail area. That means the model will have to reduce sail much sooner than the full size boat with them both sailing in the same wind. I'm not interested at this point in scale speed or scale wind speed-only max RM.
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If you've followed the theory behind the MPX system( two altitude controlled lifting foils on the main hull + one foil on the ama) you will realize that the reason for its use on this boat(or any other high performance small tri) is that the RM(Righting Moment) is so great on a small tri that it would not be physically able to fly the main hull until,in the case of the full size SRT, the windpressure on the sails was 2.2lb per sq.ft.. To put that in context ,the maximum righting moment of an F18 catamaran without depowering or reefing is reached in a windpressure of 1.8lb. per sq. ft.
The foils on the full size and model SRT allow the main hull to take off in very light air-around 5-6 mph reducing drag tremendously. As the boat accelerates and approaches the max wind pressure above, the main foils unload, allowing drag to be reduced even further virtually eliminating induced drag resulting from lift (on the main foils) with the ama foil now fully loaded(within its drag bucket at a CL of around .6 or less). The main foils' primary job then is to control pitch. The boats will both need to be depowered when their respective max windpressure is reached and the indicator will be speed-- determined thru testing. On the model and full size another indicator will be noticing that the flap on the main foil is staying above its zero deflection mark. The main foil uses an altitude control system similar to that used on a Rave and that will allow the foil to pull down increasing RM. That will be advantageous with a light crew but it will have to be monitored because of the huge force it is capable of generating.
Piece of cake-and a whole lotta fun-especially if the self-righting aspect of the concept works.
PS-if anybody is interested in the simple math used to calculate these values I'll be glad to spell it out....

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Easter Sunday pictures of some progress!
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Bulkheads up!

I had originally planned on building the model on a block of 1.5lb Styrofoam with the birch plywood glued to it so that it would be easy to move around. When it came time the damn stuff had warped. I've used 1lb styro for years to build plugs and have never seen this.
So I commandeered the dining room table...... Target weight for the completed bare hull(finished) 3.858lb.
Here are the pictures:


L to R--#2, center is the daggerboard trunk and mast step trunk. The little triangular cuts are weep holes so water will drain if it ever gets in. The other openings are access and lightening holes. Notches in the center of each bulkhead are for the keelson. Click on image for best detail:

 

SRT-half a hull+

More progress:

click on image---

 

SRT-hull planking complete-

Hull planking complete 4/27/11- minor fairing ,glassing and turn over next. Using cyano and baking soda is messy but very quick.....

click on image-

 

Nice work, are you using balsa for all wood in your model ?

Looking forward to more progress

Marc

 

High Performance Self-Righting Trimaran: The Test Model

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Thank you! Yes, all balsa.

 

Looking very good, Doug - hurry up and test it ... then build full size - we're all hyperventilating waiting.