Movable Ballast for Small Multihulls / Self-Righting?

Discussion in 'Multihulls' started by Doug Lord, Nov 27, 2010.

  1. cavalier mk2
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    cavalier mk2 Senior Member

    Doug anything that floats and has a sail is higher performance than Platinum Dumbo because it works and exists.
    Speaking of righting folding tris, a system that would work without the mast has water pumped into the folded ama after the flooded extended ama brings the boat to 90 degrees. Just enough is added to bring the boat past 90 then the immersed ama is pumped out. This avoids the mast levering of the Farrier system. It would work (pun) really well on tris like the old Telstar and Searunner 25 where the ama folded is lower than the main hull.
  2. Doug Lord
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    Doug Lord Flight Ready

    SRT-Preliminary Design Numbers--Summary

    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.


    Bruce Number: 1.83 F18=1.66

    -- 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 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
    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.
    Last edited: Dec 13, 2010
  3. Doug Lord
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    Doug Lord Flight Ready

    Response to Dynamic Affect(s) of Pitchpole/capsize on Multihull Foiler Crew

    Update on foiler sailor response to pitchpole/capsize enquiry:
    A) There is not one valid reason why a mast can't be an integral part of a selfrighting system on a smallmultihull-if it is designed for it! With a carbon mast and fiber shrouds the mast can be built to be strong enough in the event of a pitchpole/capsize.

    B) It occured to me the other day that the boat I propose would be very similar to a Rave(in crew seating/speed in strong wind)-only with a bit more SA and lighter. So I thought I'd ask experienced Rave sailors and the designer of the Hobie trifoiler what the dynamic consequences of a pitchpole would be.
    1) In the Hobie trifoiler there has never been a capsize or pitchpole except once during testing where an ama broke off-the result was a very slow settling with NO consequences to the crew-the crew was not thrown and did not/does not require any form of restraint.
    2) I talked to the designer of the manual control system for the Rave who has thousands of hours in the boat: in all those years the boat has only capsized/pitchpoled twice-once in heavy conditions with the boat going very fast with two crew. The crew sits in the Rave with their legs under the deck-there was NO dynamic affect on the crew whatsoever-the boat seems to go into slow motion and reaches a vertical position with the mast holding it upright and the crew simply climbs out. No danger to the crew , no dynamic effects as a result of the speed and no restraints required.
    3) added 12/12/10-heard from the third of four hydrofoil sailors I wrote to about the dynamic affect of a pitchpole or capsize. He sits on a trampoline to sail his boat and has only had a couple of pitchpole incidents with this boat. He was thrown off the boat but said that if he had been sitting in a cockpit like a Rave he doesn't believe he would have been thrown out.
    So for the design of the SRT(self-righting trimaran) this is good news. No restraint will be needed in the extremely unlikely event of a capsize/pitchpole. Of course, testing would tell the complete story but these actual experiences in similar(though not self-righting) high speed boats show that a disabled person would be highly likely to be able to sail an SRT safely WITHOUT RESTRAINT/MINIMAL RESTRAINT(depending on the disability) and with NO dynamic consequences due to a capsize or pitchpole. Good news and an important design milestone.
  4. Doug Lord
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    Doug Lord Flight Ready

    Small SRT (Self-Righting Trimaran)

    I'm going to take a look at this concept(singlehanded self-righting trimaran) in a much smaller version-probably about 14' LOA(changed to 15' 12/19/10) and see if it is workable. Not going to do a design just some preliminary numbers and see if its possible to approach the W/SA and SA/WS of the 18 and make a direct comparison to a Weta with two people aboard and to a 16' cat like the Falcon(with two crew). And maybe some others.
    To make it work the boat will have to have ballast in the same way the 18 does-on the t-foil daggerboard. And that will probably make it difficult to achieve the numbers I want-for "relatively" high performance-not the "ultimate" in potential performance like the MPX-12.

    Preliminary numbers 15' SRT(self-righting trimaran) :


    Beam- 15.6' (foldable)

    SA- (upwind)-190 sq.ft.

    SA (downwind)-332 sq.ft.

    Weight- hull+rig+foils-230lb(minus ballast) / 312lb incl ballast

    Crew-nominal 175lb-220lb Note: because of the foil system(lifts up AND down automatically) the boat can be sailed with a much smaller crew than this at the same power as max crew but the self-righting system might be compromised with a crew much less than 175. However, there may be solutions as yet unknown.

    Weight-all up-sailing w/crew=487lb-532lb

    Ballast- 82lb @4'

    W/SA-(weight divided by sail area)= 2.67-2.8(in the same range as a Moth)

    Max RM (any crew weight from 220 down with MPX foil system)

    Max pressure-2.1lb/sq.ft (approximately the same as an F18)

    Mast length-25'

    (more info to be added as I can)

    Weta numbers for reference:
    Weta Specs(most supplied by Weta Canada):

    Length - 14 Feet 5 Inches (4.4 m)
    Beam - Rigged 12 feet 2 inches (3.7 m)
    Beam - De-rigged 4 feet 11 inches (1.5 m)
    Main hull-beam at waterline- 2.71'
    Main Hull L/B at wl- 5.3/1 (planing hull)
    Ama length -11'(est)
    Ama beam - .625'(7.5")
    Ama L/B -17.6/1
    Sail Area - Main 8.3 sqm (89 Sq Ft)
    Sail Area - Jib 3.2 sqm (34 Sq Ft)
    Sail Area - Gennaker 8 sqm (86 Sq Ft)
    Total Sail Area-downwind- 209 sq.ft.
    Weight - Main Hull 123 lbs (56 kg)
    Weight - Float with Beam Frame 37 lbs (17 kg)
    Weight - Mast 9 lbs (4 kg)
    Weight - Rigged Total 220 lbs (100 kg)
    Mast - Length 21 feet 4 inches (5.6 m)
    Mast - Height above Water 24 feet (7.3m)??
    Design Ratios-"normal" boat:
    Normal boat is defined as boat with one 175lb crew

    --SA/WS=2.66/1(optimum immersion of ama for lowest wetted surface and max RM)
    --W/SA= 3.29
    --SCP/Total weight= 73%( Note since the normal Weta has a planing main hull this ratio is particularly interesting since boats with a ratio above 30% should be able to plane upwind)
    --Max RM-based on company reported capacity of 440lb and max buoyancy of ama-340lb.-(not a normal sailing configuration but one that must be used to engineer the boat or there could be product liability problems)-4815
    --Max "normal RM" -with one 175lb crew in hiking position and lowest wetted surface of ama for the best RM= 3048 ft. lb.

    cost approx. $12,000

    Falcon F-16 Specifications for reference:

    Length 16’-4” (5m)

    Width 8’-2” (2.5m)

    Mast 28’ (8.5m)

    Weight 240 lb

    --Total Upwind 201 sq.ft.

    --Total Downwind 389sq.ft.

    --Main 161 SF (15m2)

    --Jib 40 SF (3.7m2)

    --Spin 188 SF (17.5m2)

    --W/SA-@ single 175lb crew=2.06

    --W/SA-@ 2-175lb crew= 2.93

    cost approx $16,000

    Attached Files:

  5. Doug Lord
    Joined: May 2009
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    Doug Lord Flight Ready


    This will probably be my last post in this thread. I've gone over this enough that I'm convinced I should build a model now(start next week). The model will be 5' long and based on the trapwing hull that can easily be converted to this concept should the model prove out. The model will be scaled from the 18 numbers in the post above(post #77). Initially, it will be quick and dirty(ie unfinished cosmetically)- just done enough to allow the self-righting testing. Every component will be precisely weighed at my lab so that the scaling is precise. Dihedral and ama buoyancy(and location) will be adjustable. The model will also allow testing of the MPX foil system when radio control is added.
    I will start an SRT thread when the model is complete and tested.
    Brainstorm: 12/22/10 7pm-For the smaller version or for different requirements it may be possible to incorporate a "buoyancy Pod" which could be molded as part of the hull but connected to the hull only by a lever arm so that in a pitchpole the arm would pivot allowing the buoyancy to push the hull upright. This MIGHT be able to be accomplished w/o ballast.
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