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

Discussion in 'Multihulls' started by Doug Lord, Dec 28, 2010.

  1. Doug Lord
    Joined: May 2009
    Posts: 13,891
    Likes: 118, Points: 73, Legacy Rep: 1362
    Location: Cocoa Beach, Florida

    Doug Lord Flight Ready

    This thread will detail the model I am building to test the self-righting capability of my concept. It is an outgrowth of this thread: http://www.boatdesign.net/forums/mu...ast-small-multihulls-self-righting-35654.html
    The model will be very precise and initially test the static performance from a pitchpole or capsize and then later on(if those results warrant it) test the scale model with radio control using foils in exactly the same manner as they will be used on the full size version should that be warranted at the end of model testing. The model will be based on the hull I intend to use for my Trapwing concept since it is already partially built and works perfectly in this application from a weight and sail carrying point of view.

    This is the post describing the tentative specs for the full size SRT(self-righting trimaran) from the thread above where I first conceived of it:

    The first preliminary design numbers are based on work I did for an 18' tri in another thread. They have been "massaged" in the last few days to meet the goals of an automatically self-righting small trimaran. No consideration of cost is given here since the boat is highly experimental. The numbers show that this boat will probably right itself from a capsize or a pitchpole-this must be confirmed by model and fullsize testing.
    The original numbers were for a two person boat using the MPX foil system(two lifting foils on the main hull with an altitude control system) with either foil assist, full flying foils or a planing ama. This boat is designed as a SINGLEHANDER. For this version the ama will be either full flying (preferably) or foil assist only. These dimensions are different than those posted earlier; they are preliminary and are bound to change as a result of testing and/or design refinement:


    Self-Righting Trimaran(SRT) / Preliminary Specifications:

    Length: 18' / 5.49m

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

    Ama LOA: 12'

    100% ama buoyancy: 375lb.

    Draft w/boards Up: 6.4"

    Draft, daggerkeel down: 4' 8"

    Mast Length: 28' / 8.3mm

    Sail Area:
    --277 sq.ft. upwind SA
    --575 ft2 / 53.4 m2 downwind SA

    Weight (with spinnaker): 400 lbs / 181.9 kg

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

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

    COMPARITIVE RATIOS:

    Bruce Number: 1.83 F18=1.66

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

    -- flying main hull-10.26/1 F18(flying one hull)=6.03/1

    SA/D: 53.89 F18=44.16

    W/SA-smaller better): 2.71 F18=3.29

    =====================
    How it works:

    1) the boat is designed to carry the weight of a crew in a wide weight range. For the numbers above the crew weight is 175lb..

    2) The mast is carbon and sealed. It has masthead flotation structurally integral to the mast. Shrouds are fiber and designed to support the mast in a capsize or pitchpole.

    3) The dihedral of the cross arms is 15 degrees.They must be carbon tube.(elliptical section if possible-NA)

    4) the sailing angle on foils is 13 degrees.

    5) the sailing angle with ama partially immersed is 19 degrees.(very tentative-boat is likely to be fully flying foiler)

    6) When the boat is capsized the RM exceeds the heeling moment(approx 500ft.lb. with sails uncleated) by about three times because:
    a. the center of buoyancy of the ama is 2' toward the mast tip from the CG of the boat giving a large righting moment(750ft. lb). This is due to the high cross arm dihedral and ama buoyancy of 375lb. The ballast in the keel is 5' from the hull CG giving an additional RM of 875ft.lb..
    b. Same is true when pitchpoled: the boat would be nearly vertical before starting to right. In this position each ama has about 180 lb. of buoyancy acting 2' from the CG of the boat. And the keel ballast acts as in a. above.

    7) No action is required of the crew to initiate righting except to uncleat the sails.

    8) From discussions with people who have sailed the Rave and Hobie Trifoiler it is clear that NO FORM OF RESTRAINT should be required to sail this boat. Testing is the only way to evaluate the suitability of this self-righting trimaran(SRT) for use in disabled sailing or for sailing by those with any kind of infirmity.
    ==================
    These preliminary numbers(and the sketches I've done to arrive at them) show me that the boat is very high performance and that it will automatically self-right. This means that at some point it will be worthwhile to build an RC model to test the righting performance-however, no decision has been made to proceed much further at this time.



    ---------------------------------
    High Performance Trimaran Test Model/ MPX Foil System// Design-Building pg 1-pg87
    [post="689441"]Testing and Development pg 88 on (link)[/post]
    ---------------------------------
     
    Last edited by a moderator: May 30, 2014
  2. Doug Lord
    Joined: May 2009
    Posts: 13,891
    Likes: 118, Points: 73, Legacy Rep: 1362
    Location: Cocoa Beach, Florida

    Doug Lord Flight Ready

    High Performance Self-Righting Trimaran: The Test Model

    The material for the model has been ordered yesterday and today. The boat will be built using a combination of styrofoam and balsa with a skin of carbon added later. The carbon skin is pre made in thin glossy sheets and should save a ton of finish work. 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.
    --------------------
    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:

    1) LOA-5'
    2) Beam- 6'
    3) Weight 16lb(all up)
    4) SA 3077sq.in( 21.4 sq.ft.)
    5) model "crew" weight 3.75lb
    6) model ballast 3.75lb
    7) Ama-L/B= 18/1
    8) Ama LOA= 2.8'
    Notes:
    --The ama reflects a full size ama+ curved piece* with a total buoyancy of 657lb. Boat all up=750lb.
    -- * 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.
    -- 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.
    -- 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:
    a. SRT model mainfoil area= 68 sq.in.
    b. rudder foil= 34 sq.in
    c. 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.
    -------------
    ---Picture on left shows what the main hull of the model (and full size boat) will look like. Some features of deck will be changed.
    ---Picture on the right shows the "curved piece" mentioned above that acts to support the planing ama in this picture but whose primary function on the new boat and model is buoyancy in addition to the ama buoyancy:
     

    Attached Files:

  3. creosote
    Joined: Dec 2010
    Posts: 30
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: USA

    creosote Junior Member

    When your boat tries to right itself, does one of the amas retract, or rather unlocks to change the center of gravity and all the other forces?
     
  4. Doug Lord
    Joined: May 2009
    Posts: 13,891
    Likes: 118, Points: 73, Legacy Rep: 1362
    Location: Cocoa Beach, Florida

    Doug Lord Flight Ready

    ==========================
    No. You could read post #1 above for a detailed explanation of how the system works-I'll be glad to answer any questions....
     
  5. Doug Lord
    Joined: May 2009
    Posts: 13,891
    Likes: 118, Points: 73, Legacy Rep: 1362
    Location: Cocoa Beach, Florida

    Doug Lord Flight Ready

    HPSRT: The Test Model----Foils

    The first full flying foiler I designed and built was the F3 RC model. It was the first of its kind in production RC models. This model will use foils based on the known Coeficient of Lift of the F3 foils at just after takeoff=.519.
    That gives a foil loading (in model terms) of slightly less than .188lbs per square inch for the main foil. The main foil carries 80% of the load=12.8lb; the rudder foil 20%=3.2lb. The foil section will be the same as the F3-symetrical 9% thick. Takeoff will be at approx. 5mph(4.35 knots).
    The mainfoil area will be 68 sq.in.with a 22" span and 3.125" chord. 7/1 aspect ratio. The rudder foil will be half the mainfoil area at the same aspect ratio. All this is based on what was proven with the F3.
    After preliminary RC testing I may experiment with a higher CL at takeoff for the model foils to be in line with what I know is achievable with a full size foil.
    ----
    There is a major difference between how the F3 foils were used and how the Test model foils will be used. The F3 used its foils to develop all the RM for the boat using dual independent wands(altitude control systems)-one side would lift up the other lift down-foil loading constantly increased. It was all 100% automatic.
    The SRT test model foils reach their nominal MAX lift right at takeoff and gradually unload up to the point where HM(heeling Moment) exceeds RM. Then the main foils begin to pull down(ama foil lifting up) automatically increasing righting moment( to twice takeoff lift on main foil) up to the maximum design windpressure(on full size 1.8lb sq.ft- on model .75lb sq.ft.). After this the boat must be depowered.

    pix: F3 and F3 foils:
     

    Attached Files:

  6. Doug Lord
    Joined: May 2009
    Posts: 13,891
    Likes: 118, Points: 73, Legacy Rep: 1362
    Location: Cocoa Beach, Florida

    Doug Lord Flight Ready

    High Performance Self-Righting Trimaran: The Test Model

    Well, I have most of the stuff here except for the foam so I thought I'd go over how this thing will be built. Pictures to come later.
    I'm going to use a 6" X 12" X 64" block of styrofoam as a base on which to build the main hull*. At this point I'm going to glue thin plywood to the top of the foam so that I can use cyano to bond the bulkheads. Because of the shape of the boat I'm going to build it upright adding the bottom after the boat is pulled off the base. The main hull will be built out of 1/8th inch balsa to give me sanding room and because it is very easy to work with. The bulkheads will be sections off the original aeroSKIFF plans modified as per the small Trapwing model in the picture below. Once the balsa work is complete the whole boat will be "skinned" with very thin carbon fiber sheet that is glossy on one side. Haven't decided whether to paint the result or leave it just clear carbon. A problem with this is that the deck edges will be rounded exposing balsa. The mast step and daggerboard trunks will made of this same material. The most important thing is to maintain the weight so that the model will be suitable for use in testing.
    --
    The ama's will be built using one piece of 1.5lb/cu' EPS foam on each side of a balsa sheet cut into the designed shape of the hull and deck. The foam will be hand shaped to the appropriate section and the "curved piece" mentioned above will be joined structurally to the ama. A trunk will be included to allow testing experimental ama foils. I'm leery of the hand finishing of these two hulls and will experiment a bit with the thin carbon sheet. Because of the curvature of the hull surfaces it will be pretty easy to finish if I can maintain the weight budget.
    ---
    In case anyone is interested this is the source for the carbon sheets that I will use to skin the model: http://www.protechcomposite.com/servlet/the-Carbon-Fiber-Sheets--dsh--dsh--Glossy-Finish/Categories

    *this will make it much easier for me to move around during building.

    hull shape-deck will be different:
    (click on image)
     

    Attached Files:

    Last edited: Jan 7, 2011
  7. Alex.A
    Joined: Feb 2010
    Posts: 348
    Likes: 9, Points: 0, Legacy Rep: 108
    Location: South Africa

    Alex.A Senior Member

    Have you seen this - should fit the title.....
    Do away with the floats altogether!!!
     

    Attached Files:

  8. Doug Lord
    Joined: May 2009
    Posts: 13,891
    Likes: 118, Points: 73, Legacy Rep: 1362
    Location: Cocoa Beach, Florida

    Doug Lord Flight Ready

  9. Paul B

    Paul B Previous Member

    A "designer" who doesn't own a proper scale?

    You can buy a Pickett 235A for about ten bucks. That will give you six common scales to choose from.
     
  10. Doug Lord
    Joined: May 2009
    Posts: 13,891
    Likes: 118, Points: 73, Legacy Rep: 1362
    Location: Cocoa Beach, Florida

    Doug Lord Flight Ready

    ===============
    Another example of you not reading(or understanding): the scale I need is not available and wouldn't be required in "normal" design work.
    Not even the Pickett 235A has 3.33" =1' !

     
  11. Paul B

    Paul B Previous Member

    The 235A has everything you need to design to the scale you want.

    If you can't do simple math you can buy yourself an engineering scale with a 1:3 scale. But then you might have to learn the metric system.
     
    1 person likes this.
  12. Doug Lord
    Joined: May 2009
    Posts: 13,891
    Likes: 118, Points: 73, Legacy Rep: 1362
    Location: Cocoa Beach, Florida

    Doug Lord Flight Ready

    I'm doing the full size(model) sections so that I can just lay them on the balsa and cut them out. It would be convenient to use a scale ruler-the largest on my ruler is 3"=1'. So I checked to see what would happen if I shortened the model so I could have the convenience of using the scale ruler. Since displacement varies as the cube of length and if I used that scale the model would be 54" long(4.5'),the "new" model weight would be 11.7lb. From experience with these models I know that I probably could not build this model to that weight so it must stay at 5'.

    The calculations:
    ---5' cubed = 125; 18'(the boat the model is based on) cubed= 5832
    The projected weight of the 18 is 750lb so: 125/5832= .0214. Multiply 750 by
    .0214 and the model weight is 16.05 lb.

    ---4.5' cubed= 91.125 ; 91.125/5832=.01563 ; 750 X .01563= 11.7 lb.-too light for a test model only 6" shorter........

    ---That means 1'= 3.33 in. which is very difficult so I'm changing to 1'= 3.375" . So 18 X 3.375= 60.75",

    ---60.75"= 5.0625' ; 5.0625 cubed = 129.75/ 5832 = .02225 ; 750 X .02225= 16.688lb all up weight

    UPDATE: going with 1'= 3.375" so length will go up by .75" to 60.75" but it will be easier to lay out and more accurate.

    update 1/10/11
     
  13. Doug Lord
    Joined: May 2009
    Posts: 13,891
    Likes: 118, Points: 73, Legacy Rep: 1362
    Location: Cocoa Beach, Florida

    Doug Lord Flight Ready

    High Performance Self-Righting Trimaran: The Test Model

    UPDATE:

    Target Weights(corrected for scale in previous post) :

    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.......

    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....

    *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.

    updated 1/10/11---Corrected for new length of 60.75" which allows one foot to equal 3.375"
     
  14. Doug Lord
    Joined: May 2009
    Posts: 13,891
    Likes: 118, Points: 73, Legacy Rep: 1362
    Location: Cocoa Beach, Florida

    Doug Lord Flight Ready

    High Performance Self-Righting Trimaran: The Test Model

    Found the place that took over the product line after Maclean Quality Composites ended their business: Rock West Composites and they have the tubes I need for the crossarms and mast. In case Rock West doesn't have the ferrules used to join the tubes for the mast another company has a wide variety: Carbon Fiber Tube Shop.com.
    Have all the materials except the tubes, sails and carbon skins. The thin carbon sheets to use in an experiment to see how they will work will have to wait for a while. Probably going to glass the balsa normally and make the static test and if that works and the boat self-rights automatically then I'll cosmeticize it and make it sail.
     
    1 person likes this.

  15. Doug Lord
    Joined: May 2009
    Posts: 13,891
    Likes: 118, Points: 73, Legacy Rep: 1362
    Location: Cocoa Beach, Florida

    Doug Lord Flight Ready

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

    Well, I was shocked when I went to get the styrofoam for the building base earlier this week. It was my first indication of the size of this model and ,boy, is it big! It was so big that I reconsidered my previous calculations for 54" or 48" but then decided to see if I could figure out how to lower the seat in my car. It's embarrassing to admit that I had to actually read the manual to figure out how to do it! But the good news is that I can build the big(60.75") version since there is more than enough room.
    ----
    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,
    --
    2) test the SRT version under sail in tough conditions,
    --
    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: http://www.boatdesign.net/forums/multihulls/mpx-11-very-small-high-power-trimaran-33686-15.html
    --
    4) test-to the extent possible- a scaled down planing ama,
    --
    5) test versions of reverse curve lifting foils as well as curved lifting foils with
    a planing ama and small "normal" ama( http://www.boatdesign.net/forums/sailboats/dinghy-design-open-60-influence-36401.html ),
    --
    6) test various versions of wand altitude control systems including a single wand controlling two athwartship foils,
    --
    7) test wand based and manual altitude control system with mainfoil/rudderfoil interconnect(Tom Speer idea),
    --
    8) 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.....
    --
    9) possibly test tilting main foil.
    =========
    PS- Thanks!
    =========


    Here are a few pictures of rc models I've designed and built:
     

    Attached Files:

    Manfred.pech likes this.
Loading...
Forum posts represent the experience, opinion, and view of individual users. Boat Design Net does not necessarily endorse nor share the view of each individual post.
When making potentially dangerous or financial decisions, always employ and consult appropriate professionals. Your circumstances or experience may be different.