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

High Performance Self-Righting Trimaran: The Test Model

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Thanks, Gary. I made some progress over a short time but now its back to Real Life for a while. Wish I could just stay at it!

PS- I changed the bow from the original small model and it exceeded my expectations-you'll see it better when I turn it over and finish the forward deck/bow.

 

High Performance Self-Righting Trimaran: The Test Model

Here is the revised preliminary sailplan-moved forward:


rough sketches: left, original-right, modified version(rake may increase a bit)-click on image-

 

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

Here are the first round building sketches for the ama, curved piece, curved foil and cross arm. Background is another plan and it makes it a bit hard to see. Ama is a 10' "sliver" and is not designed to sail on-it is designed to impact the waves and release easily.
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--The "curved piece" basically connects the ama to the cross arms by raising the cross arms above the hull. But its main purpose is to provide substantial extra buoyancy since it is 6' long ,4" thick and 2.125' around the curve for a total buoyancy of 268lb. It is thin to reduce drag in inadvertent immersion-it is not designed to be used normally when sailing-it is emergency buoyancy.
-- The ama is 10' LOA and attached to the "curved piece" in a staggered manner such that the bow of the ama is 1' aft of the bow of the main hull. It's designed to be flying from light air on up and has a thin forward section spreading out to a hard chine for the aft third or so. The theory is that the hull will not be "sticky" during momentary encounters with waves above its planing speed. In encounters with waves before the main hull is flying the ama is at an angle that should reduce drag somewhat in momentary encounters. Total buoyancy of the ama is 198lb. Total buoyancy of the ama and the "curved piece" is 466 lb. or
62% of the total weight including keel ballast.
-- The 4" OD cross arms do not go straight across the boat-they are angled forward. This is beneficial in creating the optimum range for crew movement in the cockpit between ballasted and unballasted configurations. Also, since the beam is so great(a bit over 22') folding won't work so the beam will be reduced by unplugging the tubes from each other for trailering.
--(very tentative dimensions)-The curved foil is essential for the MPX system to function well-keeping the boat relatively level until the main foil is unloaded 100%(other than pitch and heave induced loading) and unloading the vertical fin. As of now the foil will stick out under the ama 5' with a 2.25' radius and an aspect ratio of 7/1. Chord will be about .71'(8.5"), section 63412 (maybe). It will be capable of supporting the entire weight of the boat at 13 knots( 15mph) within the drag bucket of the foil. Of course , being a curved foil it will be completely adjustable-variable angle of incidence( +1 to + 2.5 degrees) of the vertical lift section without interfering with the lateral resistance developed by the board. The vertical section of the curved foil will be designed to unload the daggerboard that supports the main foil and the leading edge will be adjustably toed in between 1 and 3 degrees. You can get the model dimensions by multiplying the above by 3.375,so under boat: 16.875 " with a 7.59" radius, and a 2.39" chord. An interesting thing I'm going to test is to extend the end of the foil 6-8" tangent to the curve which will help to maximize vertical lift. It will also mean that 6-8" of the foil will always stick down....
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Note: Updated overall beam is 22.5' max. Because of the fact that max lift on the curved foil occurs inboard of max beam and ama is not used in "normal" sailing the max wind pressure(before depowering/reefing) quoted in post 54 has dropped from 2.2 lb. per sq.ft. to 1.98 lb. per sq.ft. which is still higher than the maximum for a double trapeze F18 with the windward hull just flying and both crew on trapezes(no depowering or reefing). As testing and design go forward this may be increased again because of the ability of the main foil to pull down(as well as lift up). We will decide, in engineering the boat, whether an increase here is worth the structural cost and weight cost. My guess is that we have more than enough power and will probably depower and/or reef above this point.

click on image:

L to R-1) ama, 2) ama section at transom +curved piece, 3) curved foil, 4) cross dihedral, curved foil, red waterline= mod/heavy air, blue waterline=light air, pencil waterline(thru main hull)=static, pre-takeoff.

 

High Performance Self-Righting Trimaran:Full Size Comparisons

Now that we have calculated all foil areas for the model and full size ,time for some interesting ,updated ,comparisons:

SA/ws(sail area to wetted surface)
--immersed daggerboard area when flying= 3.5sq.ft.
--mainfoil area= 7.56 sq.ft.
--rudder area(immersed when flying)= 2.4 sq.ft.
--rudder foil=3 sq.ft
--curved foil(one down)=5 sq.ft.
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TOTAL=21.46
SA/ws--SRT---SA=284/21.46=13.23

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for reference:

--F18, one hull flying, one board ,one rudder= 6.03/1
--Moth,flying=13.65/1

 

I'm impressed that you can build to an accuracy of 1/1000 of a pound.

 

High Performance Self-Righting Trimaran: The Test Model

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Well, thanks -but it's not built yet so the accuracy to which it is built is unknown. Nice to have a target, though.....

 

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

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There is an error in the F3 calculations shown above. The Coeficient of lift was figured without taking into consideration the heeling moment created by the rig at or near takeoff. Because the F3 has dual independent altitude control systems on the main foils the foils provide 100% of the righting moment required by the boat. Therefore, the approximate Cl of the F3 foils near takeoff was .82 as opposed to the .519 referenced above.

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More info on the SRT foils-model and full size......

SRT Foils:
a) Full size:
--mainfoil=3.78 sq.ft. with a CI of .9 (approx 30 degree down flap) at takeoff
dropping quickly to .6(approx. 15 degree down flap-and within the 63412 drag bucket) and then lower still.
SAper sq.ft. mainfoil=75sq.ft.
Mainfoil loading-158.7lb. per sq.ft.
--rudder foil= 3sq.ft and under .6 at takeoff.
--curved foil= 2 to 3.55 sq.ft, .6 or less at takeoff on up(one used at a time)
b) Model foils:
-- mainfoil(all tentative)=41 sq.in., 2.25" chord, 18.22" span, 8/1 aspect ratio
operates at the same CI as the full size foils but takes off in lighter wind.
SA per sq. in. mainfoil: about 75 sq.in.(variable)
Mainfoil loading-.326 lb.per sq.in.(48.6lb. per sq.ft.)
--rudder foil(all tentative)= 20sq.in, 1.5625" chord, 8.2/1 aspect ratio.same as full size rudder CI.
--curved foil: Max length under ama= 15.72", 2.25" chord, 7.6" radius 35.37 sq.in.-only part of which is nominally in use at any one time.
Note: for experimental purposes all model foils may be symmetrical because they may lift either up or pull down(tentative).
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Picture: the actual main foil to be used on the fullsize boat, except that the flap size will be increased and the "dihedral tips" will be flattened.

 

Right side up-at least the picture is. Just wanted to be able to study it without hurting my neck. Hope to get back to it shortly.
click on image:

 

High Performance Self-Righting Trimaran: The Test Model

I've found a new epoxy resin-to me,at least. I previously used a 4/1 resin that took a long time to set up and needed to be post-cured in production to be able to turn over a mold in 8 hours. I recently discovered Resin Research whose eastern US headquarters is just down the road from me. I got a chance today to meet one of the guys associated with the company-Sam Barker- and he was first class-extremely knowledgeable about the product. This stuff has some unique characteristics that will fit right into to my work on the model and into the mods on the full size hull. I'm real excited about this stuff and I'm damn lucky to find a company like this so close.
Heres some details of the resin(Kwick Kick) that I'm going to use: http://www.resinresearch.net/id22.html
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The fastest setting hand lay up epoxy yet. As fast or faster than polyester resins in many production scenerios. Mimicks polyester resin in curing by thickening in a similar way but without the hard gel time. This system has only one speed, FAST. Also compatible with our other systems so this can be dropped into production when speed is nessesary.


Some examples:
Ambient Temperature 70F (21C) 80F (27C) 90F (32C)

Pot Life
Kwik Kick 18 min. 14 min. 11 min.

RR 2000/2100F 22 min. 17 min. 13 min.
RR 2000/2100S 40 min. 30 min. 22 min.

Set Time - Tack Free
Kwik Kick 1.5 hrs. 45 min. 30 min.

RR 2000/2100F 3 hrs. 2 hrs. 60 min.
RR 2000/2100S 6 hrs. 4.5 hrs. 3 hrs.


Some typical working aspects and tips:

1. The low viscosity wets out fast and a fast lock time virtually eliminates resin drain but doesn't preculde the continued ability to move the resin and continue work for the entire pot life and beyond. This system stays where it's put better than any other, even on vertical and curved surfaces.

2. UV stability is excellent with little or no discoloration in over 1000 hours.

3. This system contains UV absorber which allows it to be used in conjunction with sensitive substrates. I.E. Urethane foam, PVC foam, light colored woods, etc.

4. KK is significantly stronger than all other epoxies tested (numbers forthcoming)

5. Low viscosity also facilitates easier and more thorough mix. 2 to 1 ratio is easy.

6. Compatible with RR Additive F for easy sanding and finishing.

7. For surfboards KK is compatible with all modern fin box systems with no foam meltdown. Very low exotherm considering it's speed.

8. Excellent flex charateristics while still maintaining excellent dent resistance.

9. During initial tack free state KK can be hand molded using a hard roller. This saves significant sanding. Bubbles in laminates can be pushed or pinched out during this stage as well.

For further info contact us at gl10@aol.com Greg-Resin Research West
sambarker@cfl.rr.com 321-779-2369 Resin Research East
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High Performance Self-Righting Trimaran: The Test Model

Yee Ha! Back at it starting today. I'm moving the daggerboard trunk as mentioned earlier: the daggerboard is now in the trunk originally designed to be the mast step trunk on the full size original when it was 16'. The old trunk is being closed off. The new trunk is oversize making it easy to change if necessary.
Tomorrow or Sunday I will carbon the hull and should pull it the following day.
The hull will then be glued in an upright position on the board and the four vertical carbon tubes will be added, then the deck. The raised portion of the bow and gantry will be added next. Have the carbon cross tubes but not the ferrules to allow them to be unplugged for transport-will order this week.
Ama
Instead of using the foam I've already bought to carve the outside hulls I'm going to build them out of balsa-better control and easier to add the connectors for the "curved pieces" and the trunks for the curved foils. The trunks will be oversize and rectangular allowing easy insertion of the molded carbon trunks.
Upcoming fun
Before doing any cosmetic finishing I will do the vertical righting test where the boat has the ballast placed on a fascimile keel strut, the mast with proper rigging and sail weight, crossarms and amas in place. First test of many-can't wait! Then will come making the molds for the curved foils and trunks, mainfoil and rudder foil as well as cosmetisizezing the whole boat and preparing it for radio control. Like I said: yee ha!
Of course, they'll be pictures all along and it should go fairly quickly since I don't forsee a nasty intrusion by Real Life in the next month or so.

 

High Performance Self-Righting Trimaran: The Test Model

6-11-11--The bow was filled yesterday and last night to smooth out the strip planked balsa in prep for carboning, pix 1. Picture 2 shows the two original trunks-the forward one(bottom of picture) was actually a mast step trunk on the original 16-it will be extended approx 1" forward-the cut marks are there but don't show up well in the pix:
Note: the rough puuty work on the stb side of the hull was the result of the batch kicking too quickly. My solution was to refill by hand to get all the recesses created by the kicking. More sanding but another fill won't be necessary. The other side came out ready to glass.
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6-11-12-- just before carboning

click on image,L to right-1&2 6-11, 3&4 6-12:

 

High Performance Self-Righting Trimaran: The Test Model

Carbonated! Second brush on coat with "additive F" that aids flow and sandability to follow.
--Did the second coat with "additive F": one ml per oz. of hardener. Initially turns sort of milky then clears up.
Boat is in a makeshift "oven" for post cure.....

 

High Performance Self-Righting Trimaran: The Test Model

Pulled today. Best news is the weight check-1.7lb(target mainhull only complete 3.8lb) . Actual is closer to 1.5-1.6 because of balsa extensions and aft trunk still to be removed. She'll easily make the target with a lot of room to spare! Couldn't be happier!

click on image-

 

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Instead of the Kwick Kick resin I used resin/hardener similar to "2000/2100S" above. After considering it for some time and talking to a few people I thought I should have a bit more time for a relatively large object like the hull and deck. I'm still going to use the Kwick Set for the numerous small parts I have to build.
I've used epoxy resin on and off since about 1970 and produced a lot of rc models using a different epoxy. This is, without a doubt , the best stuff I've found. Virtually no odor. The test sample had perfect stiffness within 5 hours
and the post cure added to that. By "perfect stiffness" I mean stiff enough that if it was laid up in a mold as a small hull that it could be de-molded within 5 hours-6 hours.

 

Its an interesting shape for a multihull, it will be interesting to see how the testing goes