MPX-11 Very Small High Power Trimaran

Discussion in 'Multihulls' started by Doug Lord, Jul 13, 2010.

  1. Doug Lord
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    Doug Lord Flight Ready

    MPX-11 Very Small High Power Trimaran/ Foils for Righting Moment

    I've broken this out of the other thread because I believe it has the potential to be considered on its own. I think there is a lot of room for major developments in small trimaran design in terms of maximising the trimaran configuration while using the latest technology to make it all feasible.In this thread I'm going to look at how this potential design can be refined for cost effectiveness, comfort, portability ect.

    I know this is a lot of detail-but-unfortunately, the detail is required to understand the concept and to explore its feasibility. Besides, it can be fun to learn new stuff! Have fun!.... NOTE: as the design progresses this thread will be frequently updated.
    I've got to tell you this has been eye-opening--something like walking down a deserted beach and finding a treasure chest. As I've had time the last few days I've looked at what could be realistically possible for an 11' trimaran. First, I threw out every preconceived notion I had. For instance, at this size displacement hulls don't work for maximum power. At this size, well, don't laugh-it's remarkable what is possible-I'm astonished and excited about these preliminary results. I'll post a rough sketch or two when I can and I'm building a model that will probably be weeks off. The model will give both me and you a real 3D view of the boat-and will help me in the design and "styling" critical to this sailing machine. But first the numbers: without these first I would have no idea what was possible-these are essential at this stage of the development of the concept and represent realistic and achievable weight ,SA ect. And what a picture they paint-if you take the time to look!
    Preliminary numbers

    Note #1: the MPX-11 uses planing hulls because at this size displacement hulls carrying this kind of weight can't be "skinny" enough to take advantage of the low resistance characteristics of a high L/B hull-particularly with the main hull. It may be possible to use a skinny (L/B 14/1 or higher) ama hull coupled with a hydrofoil.
    Note#2: The MPX-11 uses two lifting hydrofoils-one on the rudder and one on the main foil. These foils are critical to the function of the boat. The system they comprise will be called the Flight Control System(FCS) and its derivation and application is detailed in subsequent posts.

    --Main hull beam-4.75'
    --Main hull beam at the waterline 3.5'
    --L/B-mainhull at waterline-3.14/1(planing hull/planing threshold: 6.6knots.
    --Overall beam- 14'(12' cl ama to cl ama)
    --LOA- ama-9' (updated 7/3/10)
    -- Ama LWL-6'
    --Ama beam- 2'(max and max at waterline)
    --Ama L/B- 3/1(planing hull/planing threshold-4.89 knots
    --Weight-120.61lb all up( 16 lb. heavier than a scaled down WETA) (NOTE: as mentioned numerous times weight is a realistic target. However, boat weight could increase 53 lbs and still allow a max crew weight of 190lb with NO adjustment to any of the ratio's below!
    --Max crew weight-243lb ( note this gives a little wiggle room for hull weight) updated 7/7/10
    --Minimum crew weight(at max power)-120lb (boat can sail in same windstrength with minimum or maximum crew weight(!)
    --Wand- altitude control system used in combination with the lifting hydrofoils on the daggerboard and rudder. Can be used to control sailing angle and compensate for different crew weights. Allows the boat to fly the main hull much earlier than it otherwise would.
    --Sail Area- 130 sq.ft /19' mast length AND mast tip above water(about same mast/LOA proportion as an A Class Cat)
    -- Max Pressure/w/o reefing 2.00 lb/sq.ft( 1.8 for F18 and 18 tri)Note: at this pressure there is no lift either up or down on the main foil-except in regard to pitch control and gust control-except when sailed by a minimum weight crew.Then the main foil would develop a 124lb down force maintaining maximum RM even with the lighter crew-automatically. A.5lb per sq.ft gust would add 108lb of downforce at the main foil. The boat should be reefed(or the sail twisted off) in these conditions to prevent potential structural damage. After testing a warning label similar to the one installed in the Rave cockpit would probably refer to max speed or max apparent wind.(update 7/11/10)
    -- SA/WS:
    a. not flying main hull-5/1
    b. flying main hull-17/1(moth on foils=16.1/1)
    -- SA/D= 41/1
    -- W/SA= 2.8 (same as Moth w/gulari) (Weight/ Sail Area="sail loading"-quick and dirty comparative ratio for low resistance boats-particularly foilers. 26' Mirabaud and 11' Moth about the same)
    -- SCP/total weight=70%+ -(NOTE:Bethwaite says a planing hull with a ratio above 30% will plane upwind-see note below)
    --MAX RM-2664 max pressure above
    update: 7/11/10
    ---The crew will sit on a very comfortable sliding seat with a backrest.
    ---The seat will slide a maximum of 2' .
    ---The boat will have a simple robust folding system-nothing to take apart-ready to go in 5 min.
    --- See Wand above: this boat uses just two lifting hydrofoils which are critical to its operation.
    ---Ideas under consideration:
    a. gybing daggerboard like some dinghies and the Capricorn F18 Catamaran
    b. canting mast

    These are all targets albeit very realistic targets and the potential is just flat wild.

    More Power, Much more Comfortable, Much easier to sail than ANY similarly powered up boat!

    More later.....
    --See link to Design Ratio's below

    --SCP(sail carrying power)= the RM in ft.lbs divided by the distance in feet between the CE and CLR. To get Bethwaites ratio this number is then divided into the total weight in pounds.SCP/Total Weight- A ratio of 30% or better permits upwind planing.
    MXP-11 projected weight based on actual hull and ama areas using a very high tech laminate to achieve extraordinary light weight.
    It must be emphasized that this is just ONE of a number of building paths that can be taken. Because of the very wide weight range of this little boat other more cost effective ways to build will be looked at down the line-stay tuned!

    Laminate=.47lb/sq.ft./ carbon+foam+paint(2layers 5.7oz carbon+ 1/4" 6lb density foam)(Imron or similar in the mold)
    weight=laminate X 1.2(structural reinforcement)

    Main Hull=27.48lb ( 1.6-1.8 times the weight of the same length Moth hull)
    Ama = 12.69lb ( 72-82% of the weight of a Moth hull and MUCH smaller)
    Ama = 12.69lb
    Cross arms-3.32" OD carbon,24' @8.5oz. per ft.= 12.75lb (compared to an OD of 2.625" for the WETA cross arm-measured on weta,dl,7/10/10)
    Folding system= 12lb
    Seat system= 6lb
    Daggerboard,and lifting foils= 12lb
    Mast=12lb ( 1.3 times the weight of the WETA mast)
    Sail=10lb(based on existing sail weight)
    Total Preliminary weight estimate: 120.61 lb. includes rigging, line, ext. tiller, and rudder stock-everything required to sail. Note: again, these are target weights. There is a great deal of latitude in weight where weight can increase(and max crew weight decrease) substantially without affecting the ratios shown.
    updated 7/9/10

    L/B updated 7/11/10
    post updated 7/15/10


    Gino Morrelli(famed multihull designer with Morrelli and Melvin):
    "Foils are definitely the way to go: it's an instant turbo".
  2. Doug Lord
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    Doug Lord Flight Ready

    The System / Foils for Righting Moment: Flight Control System(FCS)

    The Flight Control System(FCS) that allows the MPX-11 to be able to function over a wide weight range with extensive latitiude in crew weight and boat weight is worth some detailed discussion.
    Some may be familiar with the Hobie Trifoiler and Rave hydrofoils-both used fully submerged foils with dual independent altitude control systems. What that means is that each boat had two main lifting foils, one on each side of the boat that supported a large portion of the weight. I know the Rave very well having sailed it many times and having designed a production RC foiler based on the Rave technology. The Rave has virtually unlimited righting moment because the lee foil lifts up and the windward foil pulls down. The foils each have a flap that is controlled by a "surface sensor" or wand that provides instant feedback to the foil when "altitude" or distance above the water changes even slightly.
    The system is so effective that the Rave crew sits in the center of the boat regardless of the windspeed. But there is a small drawback: the boat has a fairly specific limit on speed/apparent wind/ wind pressure. This was so critical in the Rave that there was a warning in the cockpit of some boats
    not to exceed 30 knots. Doing so could be hazardous to the structural integrity of the boat.
    So back to the MPX-11: the Flight Control System(FCS) on the boat uses a foil on the rudder and a foil on the daggerboard with these advantages:
    1) the foils greatly aid pitch stability which is critical in such a small boat with so much sail area,
    2) the foils allow the boat to fly the main hull in much lighter wind than would otherwise be possible,
    3) the foils allow the boat to sail with maximum righting moment regardless of crew weight in the range of 120lb to 243lb. So the boat can be sailed at max power by almost any weight crew!
    4) the foils are controlled by a wand, as above, that sets the "altitude" of the main hull and, effectively, the angle of heel of the whole boat. The wand can be adjusted so that this angle can be changed. What is cool about this is that the foil system does all this automatically!
    In this application the foil lifts vertically from the lowest speed to approximately 15 knots wind speed where it gradually neutralizes. In the course of normal sailing with the maximum crew the foil never pulls down. With the lightest crew the foil will pull down automatically to allow the boat to develop the maximum righting moment(same as with the heavy crew) regardless of the crews weight.
    The downside is that in the strongest winds-probably over 25 knots the sail will have to be reefed to prevent structural damage. The exact point will be determined by testing. On a fully developed version of the boat this point be determined by a speedometer included with the boat with a never exceed speed for the full rig. A small price to pay for the fantastic benefits The System provides-and well proven in the Rave.
    While the Flight Control System(FCS) is unique in its conception for use on a trimaran ,the designer of the cat "Happy Feet" has utilized a system capable of offering similar benefits-though it has other operational benefits unique to a catamaran. Happy Feet helped to inspire the MPX-11 Flight Control System(FCS) along with the Rave and to a lesser extent the Trifoiler. I've looked at three small tri's potentially using this system and have done the numbers that assure me that it is certainly worth trying experimentally and holds a great deal of promise.
    In fact, there is no way under the sun that a powered up 11' trimaran like the MPX-11 could work without it.
    from Gino Morrelli(famed multihull designer with Morelli and Melvin):

    "Foils are definitely the way to go: it's an instant turbo".
    Last edited: Jul 15, 2010
  3. Munter
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    Munter Amateur

    new thread, same topic.

    Hi Doug,
    This looks to be the same boat we were discussing in this thread before you went back and re-edited your old posts.

    Never mind - we can cover the same ground here if you like. I'm going to quote you now because I don't think its fair for you to go back an change your old posts without acknowledging it. Its like re-writing history and doesn't give a fair view.

    Doug said:
    Doug - there are a few problems with this proposed design. Primarily, I think your nominated mass is extremely optimistic. Can you show how you arrived at the target mass? I'm concerned that if you build it expecting the target mass it will float well below its lines (nowithstanding the "wiggle room" you refer to). Also, given that the mass looks light I'm also concerned that the boat won't have the structural integrity to handle the loads from the downward pulling foil. When a gust hits, most boats lean or fly up on one hull. With a downward pulling foil on the center hull, this boat won't be able to resolve the gust pressure in that way. The downward pulling foil can't change altitude straight away so it will put an enormous stress on the cross beams going out to the lee float. I see you have some calcs on sail loading - what wind strength do you expect to achieve the max sail loading of 2 lb/sqft? I suspect that even when depowering the rig in stronger breezes it will be all to easy to exceed that value. As you have acknowledged above - this will result in structural damage to the boat.
    Also - as a planing surface the lee float will not contribute to resisting leeway so that portion of the foils left in the water will be the only elements resisting leeway. I understand you have based your calcs on moth foils for convenience. Will these be big enough? A moth has only 8m of sail, I believe you propose 12 - won't that overpower the moth foils? As you well know, the moths use windward heel so that the horizontal is loaded up and the vertical is loaded in compression only. Your tri appears to lean to leeward so when the foil is producing lift it will also be contributing to excessive leeway. I'm concerned that the vertical foils will ventilate in this state as they are running at the free surface and air could easily be sucked down them. As you now note, when the foils are pulling down then will also partially pull to windward but at the minimal heel angles you will need to keep those foils in the water this will only be a fraction of their total area. I think leeway will be a problem.

    I'm sorry if this all sounds a bit negative. I want to encourage you to explore the idea further but I think these are real issues that could compromise the execution of this boat. There are probably solutions out there to these problems it will just take good design (an perhaps a slight scaling back of the rhetoric) to get there. I think it's too early to be popping the champagne corks to toast the success of your latest venture.
  4. Doug Lord
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    Doug Lord Flight Ready

    DLA-Dynamic Leveling/ Foils for Righting Moment

    As mentioned earlier the MPX-11 utilizes a system that is a derivation of systems used on the Rave and Hobie trifoiler. Both boats used systems where the hydrofoils developed all the RM for the boat so the crew was able to sit in the center. That means the foil system on each boat was able to lift up and pull down simultaneously. Here is a short excerpt from an article by Greg Ketterman who describes the result of the system as "DLA":

    "Hydrofoil boats can be categorized into two categories; 1) Incidence controlled hydrofoils* and 2) surface piercing hydrofoils. The difference lies in the way the boat maintains the proper altitude above the water surface. A surface piercing hydrofoil boat maintains proper height by varying the amount of foil submerged. The boat raises up as the speed increases and reduces the amount of foil submerged and therefore the lift. The boat finds equilibrium at the proper altitude. An incidence controlled hydrofoil sailboat has a mechanism that controls the angle of attack of the foil to maintain the proper altitude. It is generally believed that surface piercing is simpler, but incidence control is more efficient. In reality, it is the method that works with fewer problems that is simpler.
    From the beginning it was felt that incidence control was better suited for a sailboat even though most of the existing hydrofoil sailboats were of the surface piercing type. There are many advantages of the incidence controlled foils; however, the most important is what I call the DLA (dynamic leveling affect). This is the increase in righting moment or stability due to the ability of the windward foil to pull down. The DLA has little affect on the low wind performance, but it essentially makes the top speed of the boat limited to the strength of the boat. Conventional boats with a finite amount of righting moment can only extract so much power from the wind, but with the DLA, the righting moment is virtually unlimited.
    Intuitively many people think that the added drag of the windward foil plus the increased induced drag of the leeward foil would offset the gain in righting moment, but calculations show and practice proves otherwise. The dynamic leveling affect not only produces a dramatic increase in top speed, but is also responsible for all the other key features that this stability provides.
    The other major advantage of the incidence controlled foils is they are less affected by the waves and other surface affects. Drag and losses associated with the surface are the major reason incidence controlled foils are more efficient.
    All hydrofoil sailboats have problems with ventilation; however, surface piercing foils have larger problems, because the foils are piercing the surface at a smaller dihedral angle which makes it easier to ventilate."

    * On the Trifoiler the entire foil was moved to control RM, lift and negative lift hence the term "incidence controlled foils". On the Rave the incidence was generally fixed at +2.5 degrees for the main foils though some owners found a way to decrease the incidence on the windward foil. Lift and negative lift on a Rave foiler is generated by the wand (designed by Dr. Sam Bradfield), a surface sensor(dragging in the water) and attached directly via linkage to a flap on each main foil. The wands are independent just like the trifoiler "incidence controlled" foil sensors. History Original/Magazine Articles/Multihulls 1990.htm
    from Gino Morrelli(famed multihull designer with Morelli and Melvin):

    "Foils are definitely the way to go: it's an instant turbo".
  5. Doug Lord
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    Doug Lord Flight Ready

    The "Happy Feet" System/ Foils for Righting Moment

    Arnie Duckworth in Thailand has got a boat that has made a unique contribution to the application of hydrofoils to multihulls. The system he uses
    is remarkable for a cat because it uses just two foils-like the incredible Moth monofoiler. Both foils are fully submerged except when anchored when they fully retract clear of the water. The main foil uses a wand connected to a flap like the Rave and Moth(and Mirabaud, the R class and the RS600FF) to control altitude.
    But there is a difference: The foils are mounted to a module that slides athwartship! This allows the foil module to slide to leeward, and according to Duckworth that allows the whole boat to fly.
    In my opinion what may be the larger contribution of this out of the box thinking is that with the foil module centered the wand system can be adjusted to fly the windward hull and keep the boat at any desired angle within a small range. That means the system can be configured to lift the windward hull earlier than it would otherwise lift and that as the wind picks up the system begins to pull down adding to the righting moment. Brilliant idea!
    This is part of the inspiration for the system used in the MPX-11. (see post # 2)


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

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


    click on image-(note retracted foils clear of the water) :

    Attached Files:

  6. Chris Ostlind

    Chris Ostlind Previous Member

    Uhhh, so sorry to tell you, Doug, but that boat of Arnie's is a catamaran. In your haste to keep this thread alive, it looks like you posted this last information to the wrong thread.
  7. Doug Lord
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    Doug Lord Flight Ready

    MPX-11 Summary-Flight Control System(FCS)

    So far in this thread I have addressed the application of hydrofoils to the boat. The boat is very small with lots of sail area so the number one function of the foils is to help control the pitch of the boat.This is augmented by manual adjustments of the relative angle of incidence of the two foils but is basically an automatic function such that as the boat tries to pitch down the altitude control system prevents the main foil from going lower while any slight change in pitch attitude, say pitch nose down, automatically and instantly creates a stern down force from the rudder hydrofoil. The two foils working together allow tremendous pitch stability.
    The next major benefit is derived from technology proven beyond a shadow of a doubt on the Hobie Trifoiler, Rave and the incredible "Happy Feet" cat. Lest you have any doubts as to the boats ability to overcome the drag created by using the foil to pull down or lift up read Greg Kettermans comments in post # 4. The concept of using hydrofoils in this manner-just two of them on the main hull- with either a planing ama or a foil assisted ama stands a good chance of revolutionizing small trimaran design. It is an application of "foil assist" to small trimarans( or large for that matter!) that helps them to transcend the normal limitations that still continue to constrain most designers. Using this Flight Control System(FCS) offers the potential of small trimarans performing better than they ever have in the past-a major leap in performance. The system also has potential applications on less high performance boats helping them to be more stable.


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

    "Foils are definitely the way to go: it's an instant turbo".
  8. Doug Lord
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    Doug Lord Flight Ready

    New ideas

    There are a number of small race boats with unique systems that might be of interest on this little boat if for no other reason than because it is so small and the forces relatively light that they could be fairly easy to implement.
    1) The F18 Capricorn cat is the only small cat I know of to use gybing boards-like the 505 and some other boats. Theoretically, it helps vmg upwind. It would be as simple to implement on this boat as on any monohull with the exception of the fact that the daggerboard will be loaded at times due to lift or negative lift from the main foil. It gets a little more complicated with that in mind-not sure its worth it.
    2) Canting masts are used on many large tri's and a few small boats to keep the mast(at least) vertical so that the projected SA isn't reduced due to heel.
    This could probably be done by hand with a block and tackle on a small boat like this.
    3) Anyone who has looked at the LAC thread may have noticed the pictures of Steve Clarks canting daggerboards. They are there to allow him to vary the lift from the board and the installation is obviously lightweight or he wouldn't have used it. It might be possible(and advantageous) on this boat to cant the board+ foil as well so that when the main foil is lifting up it does not also have a small vector of lift pointing to leeward. If the board+ foil was canted to (at least) vertical then that negative side effect would be reduced a great deal.
    It might even be possible to link the board and mast so that they cant together though this would be counter productive with a light weight crew aboard because the hydrofoil might be pulling down.
    These are just some considerations as the design of this boat progresses...
  9. Doug Lord
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    Doug Lord Flight Ready

    MPX-11 Rig

    I've decided to explore the feasibility of using a square top main +square top jib(masthead) similar to the one I used on my 16' foiler and that will be used on the Trapwing. This rig is experimental but has potential advantages that are hard to ignore. The mast would have a endplate/buoyancy pod similar to ones I 've used on other boats I've built over the last 30 years. The rig becomes easy to depower by just dropping the jib and there would only be one sheet a-la the Swift Solo arrangement(slightly modified).
    The rig would easily adapt to a canted mast if I decide to incorporate that.
    Most importantly, though, I think this rig will develop more power than most conventional rigs and probably be easier to sail. It will certainly have a lower CE than most triangular rigs or rigs using a square top main and triangular jib for the same amount of sail.

    pix: aeroSKIFF and Trapwing rig:

    (click on image and then on image again(left picture))

    Attached Files:

  10. Doug Lord
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    Doug Lord Flight Ready

    Flying the main hull-MPX-11 and other sport trimarans

    The MPX-11 thread is a design excercise to see what is possible at this length in a small trimaran. I have been surprised and excited by the results that show that it is feasible to do a high performance trimaran design this small.
    One of the major criteria that I'm interesed in in small tri's this length and up to 20'(for now) is the design details required required to fly the main hull. The main reason is that such a concept allows a broader use of the trimaran concept than has been seen to date. If you compare a small cat, say with twin trapezes like the F18 to a square trimaran with twin trapezes the results are pretty startling . The tri could develop TWICE the RM of the cat. But I'm not interested in going that far yet-my interest lies in developing the systems that would:
    1) allow any sport tri,especially one designed for it, to fly the main hull. Not just fly the main hull but do so in the predominantly light winds found at the majority of sailing venues. I'd like to see a boat capable of flying the main hull in as light as 5-6 knots of wind and 7-8 knots of boat speed.
    2) I'd like to see the boat designed to use the same rig at least up to 1.8 lb. sq.ft. pressure-the max before depowering of an F18. So you can't just put a giant rig on the boat that would have to be reefed in a 10 knot wind. There is another solution-described earlier in this thread.
    3) And that leads me to a major consideration in doing this research and that is that the crew movement required would be very little-say just side to side in a 2' wide cockpit-not running 12' or more tack to tack, not having to move aft to prevent a pitchpole. No trapezes. In otherwords the boat(s) I'm looking to develop would all have the above in common and be very, very comfortable and safe to sail very fast. Comfort, speed and ease of sailing are the predominant criteria for the small trimarans that I'm interested in.
    4) Cost is always a consideration but the beauty of the systems I'm looking into-at least so far- is that they can probably be done successfully over a wide cost/weight range.
    5) Let me add this in regard to how the FCS system and flying a hull add to the performance potential of a small tri:
    a. It is NOT the greater RM that is the biggest gain from a performance standpoint it is the increase in the SA(sail area) to WS(wetted surface ratio) which can go from 2 to 5/1(not flying) up to 17 to 20/1(flying the main hull) or better-depending on the boat.
    b. coupled with that is the much greater resistance to pitchpole of a trimaran using this system.
    6) The Fun Factor: the boat that is the subject of this thread and the systems that make it possible seem to me to drastically increase the Fun it is possible to have with a small trimaran-more speed than most small trimaran designs with,at least, equal or greater comfort coupled with ease of handling and transport. I believe that these small boats can utilize a folding system that requires no heavy lifting and that can be accomplished in under 5 minutes. That's a target but I think it is essential if these kind of boats are to appeal to the public-which I surely think they will. Boats using the FCS(described earlier) offer more performance potential than any other small trimarans I know about coupled with extraordinary comfort and ease of sailing.
    This is all talk(albeit well researched talk) for now but based on a great deal of experience designing, sailing and experimenting with high performance sailboats. In this thread, the F18 thread and "High Power small tris" thread you have witnessed the birth of a sailing system-the Flight Control System(FCS) and in this thread, particularly, the details of how that system can be appiled to one small boat-the MPX-11. The applications possible go way beyond this boat as you will see over time. I am not interested in attempting to patent this system and will work with anyone that wants to give it a try. I'm going to be experimenting with it on a full size boat and may actually build a version of the MPX-11.
  11. Doug Lord
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    Doug Lord Flight Ready

    MPX-11: Planing Hulls

    A small tri like this with an all up weight including crew of 360lb has a problem if what you're after is speed. It is difficult at this size to get an ama or main hull with something close to 14/1 L/B ratio(or greater)-less is not ideal. So the other solution is to go with planing hulls on both the ama and the main hull.
    -One measure of a sailboats ability to plane I read a long time ago was that it needed 500sq.ft. per ton(long ton=2240lb)
    For the MPX-11 that equals: 2240/360=6.22, so SA/ton=6.22 X 130 or
    808 sq.ft. ton. About 1000sq.ft. per ton for a windsurfer with a 10m sail; A 7sq.m sail = 718 sq.ft per ton. Note that the MPX-11 can carry its sail in up to 2lb/sq.ft pressure.

    -Another consideration, particularly in larger boats is D/L ratio:
    Displ. in long tons/ [lwl in feet/100]^3=120.8, which is about half of a windsurfer.

    -SA/D=SA in sq.ft./ [displ. in cu.ft.]^.667= 41 just a bit less than a windsurfer with a 10m sail! And better than a windsurfer with a 7m sail.

    -SCP/total weight(see post #1 of this thread)=70% . Bethwaite reports that boats with a ratio above 30% will plane upwind. This ratio incorporates RM and seems like a valuable tool.

    -SA/WS- Sail area in sq. ft. divided by wetted surface in square ft. Not really a planing ratio -more of a speed ratio(in my opinion). The MPX-11, flying the main hull, is equivalent to a Moth on foils! (MPX-11 flying the main hull =17/1 versus a Moth on foils: 16/1)
    So we know it will plane-and probably be quite fast with a 243lb crew on board!(or less)
  12. Doug Lord
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    Doug Lord Flight Ready


    So the MPX-11 is a summary of all these "systems":
    1) hydrofoils with a unique control system adaped specificaly for this boat-that allow increased pitch stability and control of angle of heel and RM automaticaly.
    2) planing hulls that allow the boat to use all the power available to it,
    3) a reefable and potentially unique rig with squaretop main and square top jib coupled with a buoyancy pod/endplate to prevent turtling.
    4) folding cross arms
  13. Doug Lord
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    Doug Lord Flight Ready

    MPX-11-design considerations/ new ideas

    I've started on a small model of the boat as part of the process that will eventually lead to a build-able design. In conceptualizing a boat -especially one as difficult as this one I've almost always built a model to help work out design and sometimes building issues. I almost always learn something that I had not considered before starting the model. You can bet I'll post pictures down the line. I have to work this in as a 4th or 5th priority for now so it will take some time. I'll tell you this: the more I get into this the more interesting it becomes.
    I found this the other day on the LAC thread-Steve was sort of chastising me for what he regarded as my assumption that his new boat was a foiler. That's because I published a picture of his new C Class cat where it appeared the lee hull was out of the water.This is most of what he said in the LAC thread, post 61:

    "The curved daggerboard and T foils modulate the frequency of how the boat pitches in waves. Which is what I was trying to achieve. When the boat launches out of a wave, it kind of glides back to the surface instead of free falling. This reduces the severity of wave encounters and also the need for volume forward. Only very short time on the boat yet. Much more to learn as we sail."SHC
    Beatings will continue until morale improves.
    Bear with me, here. The MPX-11 has small planing amas -sort of like(in function-not in appearance) mini jet ski's. I've watched these water rats in chop and they seem to pound a lot. So it occurred to me to consider a very small retractable hydrofoil just aft of the planing surface to help reduce any tendency to pound and to "smooth up" it's interaction with waves. Now my little tri controls the pitch angle of the planing surface with the combined action of the two main foils-you can actually change the running pitch angle of the ama from the cockpit.
    On Steves boat it is natural to "assume"(as I did) that his boat with curved lifting daggerboards and a rudder t-foil on each hull might be out to utilize the benefits of "foil assist" to lift the lee hull just a bit to reduce wetted surface. I had not considered Steves stated primary reason for using the foils but the more I think about it the more sense it makes. Of course, both things can also be true simultaneously....
    But Steves rationale hit the nail on the head and is just the impetus I needed to re-consider incorporating the small foil described above to work in concert with the planing hulls in moderate to heavy winds. So, I want to thank Steve for the push in a direction that could be very beneficial for the MPX-11...
  14. Petros
    Joined: Oct 2007
    Posts: 2,934
    Likes: 148, Points: 63, Legacy Rep: 1593
    Location: Arlington, WA-USA

    Petros Senior Member


    That is so small why don't you just go out and build a test bed along the lines you have in mind and try it out. You can build it cheap with 1/4" exterior plywood and lumber yard wood to build something to go out and test it. quick and dirty, and cheap and fast to build, and to alter. It will come in a bit heavy, but it will tell you if it behaves the way you want, try out Tyvek or blue tarp sails, etc. Once you get it the way you want you can than have some proper sails made, and perhaps some good profiled composite foils to add to the test bed. Than after you have refined the design further, you can than spend the money on good materials to build your final hull, with all the fancy finish and fittings.

    One of my engineer professors used to say "One simple test is worth 1000 expert opinions". Keep it cheap and simple, about $150 in materials (or less) and perhaps 40 to 60 hours to get something on the water and try it out.

    When you build something different than the normal "text book" designs, you can not always use text-book approach to developing and refining it. I find it a lot more fun, and satisfying, to build cheap proto-types to test concepts out rather than to spend a lot of time on plans and calculations. Otherwise you might spend all that time and money on quality materials and end up with something that does not perform as you expected.

  15. Doug Lord
    Joined: May 2009
    Posts: 16,679
    Likes: 349, Points: 93, Legacy Rep: 1362
    Location: Cocoa, Florida

    Doug Lord Flight Ready

    Thanks, Petros good thoughts! I appreciate your comments, unfortunately, I just don't have the time now. I'll be able to build a small conceptual model over the next few weeks but thats about it.
    As I said earlier the more I think about this thing the more interesting it gets. The "smallness" is surely a big plus from a development standpoint.
    I'll post the ideas that come out during the model build/preliminary design and then pull it all together in a presentation of pictures of the finished model.
    After that ,and depending on many things, it may be time to do just what you suggest.....
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