Dinghy Design: Ideas for High Performance Disabled/Physically Limited Sailing

[Doug Lord]

Just to round out the various possibilities here are the preliminary specifications of an 18' trimaran designed to be self-righting-that is: automatically self-righting like a keelboat. It is highly experimental and a model is being built to test the concept. Should the model tests go well the full size boat would be built on the same hull as the Trapwing in the previous post. Should the tests pan out then this will be the highest performance singlehanded boat under 20' I know of suitable for disabled sailing.

Thread that provides details of the model being built now to test this concept: http://www.boatdesign.net/forums/mu...-self-righting-trimaran-test-model-36058.html

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The first preliminary design numbers are based on work I did for a two person 18' tri in another thread in the multihulls forum.. They have been "massaged" 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.
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 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.
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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

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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(and even that may not be necessary).

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.
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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.

 

[Doug Lord]

1) A sail can certainly cause a bit of suction but usually slacking the sheet prevents it from being a problem. Problems with sock luffs holding water and any design that allows the sail or mast to fill are important to prevent. A disabled design should be automatically self-righting with no crew action required other than slacking the sheet(s).

Even that may be too much. . .

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You're probably right but when you look at the boats being used now for disabled sailing few if any meet the criteria of self-righting( from a 90 degree or so knock-down). So I think there is work to do to determine what characteristics are essential for a high performance boat that is suitable for disabled/physically limited sailing.
Thanks for your posts....

 

[Doug Lord]

Here are a few rough illustrations of different versions of the Trapwing concept(sliding trapeze wire supported wing with sliding ballast inside the sealed wing) :


Pictures:
-- Left to right, 1st row: sketch by "sailing kid"(AU) of turbo version, original rough sketch of turbo(foiling) version, rough sketch of 12' "sport" version.
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--Left to right, 2nd row: final preliminary sketch of production prototype 15' version, 15' transom, sailplan of 15' production prototype version-note harness for shroud to stay clear of sliding wing.
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--3rd row: jib system for high aspect ,square top jib with jib boom and sliding pivot point: pivot point slides to leeward(adjustably) while leading edge stays on centerline; boat would have a single sheet for both main and jib(borrowed from the Swift Solo system), original rough sketch showing sliding wing on 15' version.

(click on image)

 

[Doug Lord]

Here are some models that I designed built and sailed over the last ten years using a "Power Ballast System" which was the forerunner of the Trapwing system:

--Left to right, row 1: This is the 36" "Super Scow" with the PBS-the rack slides athwartship and fore and aft and the weight slides on the sliding rack. In addition when viewed from behind(or in front) the whole rack will pivot on a fore and aft axis. When the weight and rack are centered miniature shockcord holds the rack level and when the weight begins to move the rack tilts down on the windward side. This works to keep the wight low and the lee side of the rack clear of the water( a responsibility of the skipper,too). The degree that the rack can pivot is fully adjustable for the conditions before the model is launched.
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--Left to right, row 2: The first picture is a schematic of the PBS(Power Ballast System). Pictures 2 & 3 show the system on the microMOTH.
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--Row 3- This is the Melges 24RC a model I built with Melges' approval and whose section spacing I altered forward of midship with John Reichels' (Reichel Pugh Yacht Design) approval. The model used a larger version of a PBS and also flew an asymmetrical spinnaker with retracting bow pole. The lines had to be altered to allow room for the spinnaker trough forward of the forestay.
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Each of these boats(except the microMoth) also had a small fixed keel to guarantee that it would not permanently capsize when sailing under radio control.


You can see more detail if you click on the images:

 

[Doug Lord]

I would sure like to see suggestions, comments and ideas by others that could be incorporated into a high performance dinghy design for disabled/physically limited sailing. Don't be bashful-if you don't think the idea I've proposed is or is not viable say so-but say why with as much technical information as possible. No idea is too radical to, at least, post here. Put some thought and effort into your ideas and lend a hand in in this effort!
There are many people that have a "need for speed" under sail but for one reason or another aren't up to sailing a "normal" skiff. That's where ingenuity comes in and where you can make a difference.
There is huge room for development here and your help in thinking more about this could help me and many others who are considering designs along this line. The more detail the better.

 

[Doug Lord]

One of the main themes of this design concept is that the resulting boat can be a planing, self-righting keelboat. I was intrigued by the K1 concept( http://www.boatdesign.net/forums/sailboats/neat-singlehanded-keelboat-uk-30059.html ) where the designer chose a narrow waterline semi-circular section hull that was designed to be sailed heeled instead of flat like most planing hull dinghies. The Bongo is an example of a small keelboat with a planing hull. I've never really thought that boat was a good way to go because in order to plane the Bongo must be sailed flat which means that the keel bulb is not developing any righting moment. And while I like the K1- and the designers thinking- I don't think it comes close to an easy to sail keelboat along the lines of a 2.4 meter. And no way are either the Bongo or the K1 "high performance".
--
The Trapwing system offers the opportunity to have the righting moment necessary to sail a planing hull flat with the power to carry sail that can offer upwind planing as well as off the wind planing.
The system offers high performance with a self-righting capability thanks to the design of the movable ballast wing and a bulb keel. Also, since the weight in the wing and the wing itself are moving to develop righting moment the crew is not taxed physically and can sail the boat with the ease of a 2.4 meter but with much more performance.
I don't think there is a small keelboat anywhere that offers all this and that makes it extremely attractive to me as a system that can fulfill the "need for speed" of a very wide range of people.
The Trapwing system can be applied to boats designed specifically for it from 12' on up. It is not a patented system and is a concept open for anyone to experiment with. A production version could be developed w/o any intellectual property hassles and with my full co-operation if deemed necessary. I am not "promoting" something that will benefit me in any way(except when I'm sailing one)-I'm trying to spark the imagination and to show that just because one is disabled or physically limited in some way it is NOT necessary to settle for low or moderate performance boats. High performance sailing is possible for just about everyone.

The advantages as I see them:
1) easy to sail by almost any weight sailor.
2) self-righting
3) high performance-planing upwind and downwind
4) variable wing ballast-moved manually or electrically
5) two seating options-
a.sit in and,
b. side to side
6) reefable rig
7) easily trailerable
8) beach launchable

 

[tabman]

Good Lord Doug,

Take this the right way please. . .

Just get on with building your model and skip the repetitive posts. You seem to be fixed on the idea, so as they say, "Build it and they will come".

 

[Doug Lord]

Good Lord Doug,

Take this the right way please. . .

Just get on with building your model and skip the repetitive posts. You seem to be fixed on the idea, so as they say, "Build it and they will come".

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Thanks Tabman-I'm doing exactly that. But I'm also trying to spark interest in other ideas for high performance design aimed at disabled sailors and people who aren't up to sailing "normal" skiffs. I've tried hard not to be repetititive but at the same time emphasize that their are other potential solutions and that suggestions
along those lines would be a great addition to this thread.
And there is lot of room for development.....

 

[Doug Lord]

ELECTRICAL SYSTEMS

In disabled sailing design a lot of innovative work has been done with electronics to allow reliable equipment for steering sheeting etc. On a movable ballast system-particularly the one on the 18' prototype the weight will be moved electrically with a "joy stick" control. In order for such a system to be viable it must move the weight quickly and be able to do that for at least 8 hours a day.
Thanks to Rick Willoughby for coming up with the tentative results here. The spreadsheet he did incorporates a 20% grade-uphill(which the ballast would see infrequently). Rick has been a very big help-incredibly generous with his expertise!

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Moving 70kg(154lb) 5.49m( 18')-full out on one side to full out on the other side/ times are 1/2 for CL to full out:

--1) in 4.5 seconds requires a 7.1 AH 24v battery for well over 8 hours of ballast movement equivalent to 5.49m(18') every 5 minutes.(1.83m in 1.5 seconds)
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--2) in 5.49 seconds requires a 5.8 AH 24v battery for the same(1.5m in 1.5 seconds)
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--3) 20AH Lithium= 16lb.(approx. 24lb for ni cad)

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This is a system that moves the wing and the weight inside the wing simultaneously. And for the purposes above we're talking the actual distance moved by the weight. So I'd probably go with a 20 AH 24 volt battery.
And it moves the weight faster than a crew on a trapeze could move their weight(CG) the same distance:


Full out to full out times for some trapeze equipped boats:

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Contender- http://www.youtube.com/watch?v=Pzrb-HYrxPM

7 seconds full out to full out in good weather for the trapeze movable ballast system on the Contender
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Flying Dutchman- http://www.youtube.com/watch?v=dHsa0bUdFOM
6-8 seconds for the trapeze movable ballast system from full out to full out*

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505- http://www.youtube.com/watch?v=YqEhYl8X2Pc&feature=related
6-7 seconds for the trapeze movable ballast system from full out to full out

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12' skiff- http://www.youtube.com/watch?v=k2PvV820Qpk (toward end of video)
7-8 seconds for the trapeze movable ballast from full out to full out

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International Sailing Canoe-http://www.youtube.com/watch?v=Exb6i3E3r-4&feature=related
5 sec 50% out to 50% out;estimate 7 seconds full out to full out (very hard to find IC videos that show a boat tacking!)

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* full out to full out= max outboard movable ballast CG on one tack to the same position on the other tack.

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Trapwing Design Speed-4.5 sec for Trapwing in any weather full out to full out-(2.25 seconds from Center Line to full out)**...
**absolute minimum speed for wing +ballast movement. May be a bit faster but it will not, under any circumstances, be slower (within design framework with constant full out to full out tacking every few minutes for 8 hours+)

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[wheels]

Let me know when you're ready for a real live test cripple and I'll drive down from Sacramento

 

[tabman]

So what happens when a tack is missed and the boat is lying aback, and there is no input from the pilot?

 

[Doug Lord]

So what happens when a tack is missed and the boat is lying aback, and there is no input from the pilot?

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The boat sits ,listing a bit, into the wind and slowly drifting backwards then easing a bit forward until control is resumed. The boat won't sail itself but it will adopt a safe mode if the tiller(steering) is free.

 

[tabman]

Cool.

 

[Doug Lord]

Design Ideas: High Performance Self-Righting Trimaran

Let me know when you're ready for a real live test cripple and I'll drive down from Sacramento

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Hopefully, we'll get a boat out to CA one day-Dave Trude from SA is interested as are others. You would be most welcome! What is your sailing experience?

 

[Doug Lord]

I've worked on and researched this project for over 6 years while working my real job and dealing with bouts of Real Life. As time has gone by I have become convinced that this concept would be better in a smaller version -at least for any kind of production. It would be less expensive and easier to handle for disabled, physically limited and able-bodied individuals. I think a single hander is the way to go. I'm going with the larger version because I have the hull, foils and rig here that will be modified for both the Trapwing and SRT(should the model tests for the SRT warrant it. But the first pre-production prototype would be based on the following sketches and numbers. An even smaller version is possible but the consensus is that the 15 would be the best candidate for a production prototype ,should one ever be built.
So here is more info on the 15: (More sketches, row 2 & 3 of images in post 18 above.)

Trapwing 15 Proto

These are the final rough sketches of this boat( post 18 above). The boat allows "sit-inside" control(as well as a fixed side to side removable rail seat with seat back) and different rigs. The hull is likely to be foil assisted-with at least a rudder t-foil(with retractable gantryadded 3/11). Depending on the results of some experiments the hull may also feature a stepped planing hull or midship interceptor. The Trapwing slides athwartship and fore and aft (crew can slide F&A). The shrouds use a bridle to allow the wing to move F&A. The cockpit is self-bailing and the boat will be self-righting though a turbo version w/o the keel will be experimented with. The hull is wider at the waterline than it is on deck to keep weight down. For the "sit-in" version there is no need for hull flare.
--

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LOA 15'
Beam 4.5'
SA upwind-130-150 sit in(175 turbo)
SA downwind 230-325
Hull weight 110lb
All up sailing weight=521lb sit-in/439 w/o keel / turbo 475lb
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Comparative ratios: see Eric Sponbergs excellent reference below

This is the non turbo version w/o the keel:
--SCP=133.6 (RM divided by distance from CE to CLR)
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--Total weight(displ.)=439lb
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--SCP/Total Weight= .3
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--SA/ws= 4.2/1
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--W/SA= 2.98/1( Weight in pounds divided by SA in sq.ft./compares to 3.1 for R class and 2.8 Moth w 180lb crew)
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--SA/D(SA in sq.ft divided by volume of displ. raised to the .667 power)=40.69
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--DLR(Disp. in long tons divided by(lwl/100)cubed= 57.86
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--S#=9.59