Design Challenge: Trapwing-"on-deck" ballast-12'-22'

interesting concept, doug...

have you thought of shaping the trapwing in an wide arc curving towards the watersurface with some small floating devices at either end... so that it looks like a trimaran with 2 small outriggers...
then when heeling over move the whole trapwing some distance to windward, the moveable ballast on it of course as well...

the leeward floating device at the trapwings tip will follow the curve of the trapwing and thus coming up a bit, while the windward floating device goes down and with it the ballast at ist end... lowering the CG and increasing RM because you 'extend' its righting arm, whereas in a flat configuration the righting arm is decreased the more it heels... (this increase in righting arm will only work to a certain heel angle of course)

the leeward outrigger might still be on the surface adding to bouancy and form stability...

and now consider mounting the shrouds via some linkage on the trapwing to the side of the hull...
if you move the trapwing to windward the shrouds will be 'shortened' on the windward side and 'lengthened' at the leeward side and thus shifting the whole mast to windward, let it stand upright instead of heeled to leeward with the hull...

i do not have a scanner at hand right now otherwise i would try and draw some explenatory scetches...
there are some serious technical issues to overcome of course but as an idea it is sound - i think...

 

Thanks capt vimes, appreciate the input! One minor thing to consider when racing(against different boats) is that the Trapwing boats are supposed to be monohulls-so the more they work like a trimaran the harder it will be to make the case for a monohull.
There will definitely be buoyancy at the ends of the wing but my theory is that the system will move fast enough that ,after some practice, the skipper may be able to mostly keep the wing out of the water. That's the idea,anyway.

 

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Here is a neat sketch(by "sailingkid") that's a bit shy of detail but captures the essence of the planing version of this concept:

 

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capt vimes, I missed this first time around-sorry. My initial reaction is that adding shroud loading to the wing would drastically affect the power required to move the wing which, right now, is very little. The skinny hull turbo version of the boat would be designed to sail on hydrofoils and would also sail upwind with veal heel which would angle the whole boat to weather up to 20 degrees.
The Trapwing 15 is designed to be sailed flat- very little if any heel(except in very light air). It seems to me-at this point- that keeping the wing independent of rig loading would probably be the best way to go. As of now the shrouds are attached to the boat with a bridle so that they don't interfere with the fore and aft movement of the wing.
Thanks again for your comments!

 

These are the final rough sketches of this boat-next step are a sail plan sketch, building plans and probably a model. 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. Depending on the results of some experiments the hull may also feature a stepped planing hull or midship interceptor. The Trapwing slides athwhartship 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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The boat will be built "one-off" out of thin(.125") Okume from Boulter and carbon. She will be built upsidedown from the inside out, with the bottom* the last to be done. Since I insist on an excellent finish and I hate to sand I'm trying a new technique(to me) this time. Once the wood is completed and faired to the degree necessary, sheets of very thin carbon ,laid up on sheet glass with a vacuum(no gel coat or primer this time), will be bonded to the wood to (hopefully) 100% eliminate sanding with virtually no weight gain. Many of my models that were to be painted had primer sprayed into the mold instead of gel coat. Worked well with the right primer and was much lighter. In this case, no primer since I want to see how good this system will turn out with the carbon weave exposed. This system may produce a spectacular finish comparable to a molded finish with almost no sanding and be pretty quick as well.
* Note:The plywood skin is attached to frames on the outside of the boat; the deck and cockpit are done first,then the sides. The inside is then carboned and the frames,spin trough and tube added and carboned in. The bottom is fitted ,carboned on the inside and immediately bonded in place. Finally, the sides and deck are removed from the frame and the (minor!)fairing and sheet carbon "skining" is done. The chine and deck edge are carboned in the old fashioned way-so a bit of sanding there. The extruded "bent" carbon rod for the bow handle(see rough sketch) is added when the sides are and dressed up at this point.--------
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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Trapwing 15 Preliminary Sail Plan / Jib System

Here is a rough sketch of the sailplan @ 147 sq.ft. and the jib system. The main is a reefable luff sock type with camber inducers. This same system was used on my 16' foiler and worked well with shrouds as shown. As mentioned previously, the shrouds terminate in a bridle to allow fore and aft movement of the wing. The top of the mast is 21.25' off the water; the top of the rig is 22.8' above the water. Both sails will have full battens.
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The jib system uses a molded carbon boom/endplate with the forestay and clew attached directly to it. The tack(luff tension) is adjustable as is the clew attachment. This is similar to the system used on model boats except that the pivot point of the jib boom/endplate is attached to a sliding car on a track that slides athwhartship. This is done so that the luff of the jib stays on the cl. A non structural extension of the forestay fits into a recess in the deck to prevent fouling the spinnaker. An external "leech line" is sometimes used on model boats but probably won't be necessary. The pivot point will be movable on the boom about 6" fore and aft. This system is being used to add to the control of the square top jib.

 

Doug ,the rig looks great. I have a couple of questions. How do you reef the main ? If the luff pocket is to be effective the battens are presumably under tension holding the pocket against the mast. Even if the battens have cars and are on a track some how they must be shortened (telescoping?)to lower sail, or a separate out haul might be fitted to each batten. Seems complicated. I know that on my wrap around sails it is imperative that I let go the out haul and any reefs when lowering sail or the luff will bind. The problem is amplified with a tapered mast with a suitable leading edge. Does the jib pivot point slide to leeward or is it hauled to windward ?

 

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Thanks ,Timothy! On the original rig the battens didn't initially have camber inducers and it was just a matter of lowering the sail-the battens really didn't cause any problem but they were not ideal either. Then we(my sailmaker and I) tried a couple of camber inducers. They were a problem until we came up with a "guide wire" that ran thru the camber inducer. It worked ok but on the new rig a method (adding delron to the back side of the mast) will be used to reduce friction. The luff of the sail had a zipper so it could be opened up as the sail came down. The first system wasn't ideal but proved that the concept would work. I'm not 100% convinced that we need a reefable sail on this boat but the proto will have one. The mast section is a constant diameter round section. By the way, the main would be reefed only after removing the jib....
Also, there is no reason to shorten or remove battens-they can be just rolled up with the bottom part of the sail.
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The jib pivot slide slides to leeward and the limits are adjustable. The only part of this that hasn't been tested is the non-structural "forestay extension"
which is necessary because of the spinnaker-(I think).

pix-orig rig:

 

Numbers

Inspired by Pi and because I'm ready to check the prelim numbers, heres what I have so far. This is the non turbo version w/o the keel:
--SCP=133.6 (RM divided by distance from CE to CLR)
--Total weight(displ.)=439lb
--SCP/Total Weight= .3
--SA/ws= 4.2/1
--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 Gulari) relevant only to boat with foils which it probably won't have.
--SA/D(SA in sq.ft divided by volume of displ. raised to the .667 power)=40.69
--DLR(Disp. in long tons divided by(lwl/100)cubed= 57.86
--S#=9.59 (see following post for details)

 

S Number

The S number is presented here by Eric Sponberg: http://www.boatdesign.net/forums/bo...ulation-implications-30857-14.html#post344904

And it is defined as:

"The equation for S# is an exponential and logarithmic function using DLR and SA/D as the primary variables. We already know how to calculate DLR and SA/D, and I am going to remove the slash “/” from SA/D so that it is less confusing in the S# equation— we’ll use the term “SAD.” Although the S# equation looks complex, it can be easily programmed into a calculator or a spreadsheet. Here it is:


S# = 3.972 x 10^[-DLR/526 + 0.691 x (log(SAD)-1)^0.8]
Brooks collected a list of boat designs and their particulars from various published sources and calculated their S#s. Then he classified the boats according to the following categories:

· Lead Sled: S# = 1 to 2
· Cruiser: S# = 2 to 3
· Racer-Cruiser: S# = 3 to 5
· Racing Machine: S# = 5 to 10
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For the Trapwing 15 :
S#= 9.59

 

Doug. Would you remind the infidels why you are putting the jib "tack" on a track? Are you planning on needing any rig tension to keep that supremely high aspect jib luff taught? What happens when that load is applied at the gunnel instead of on the centerline? It looks like unnecessary complexity.

 

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First, the jib "tack" is not on a track-it is attached to the jib boom adjustably just aft of where the forestay is attached to the same boom. The clew is also attached adjustably to the aft end of the boom.
Then the pivot point of the jib boom is attached to a car on a traveler. The pivot point is adjustable fore and aft on the boom. This gives tension on the jib leach better than you can get any other way as best I can tell.
On the original incarnation of this type of jib I had a jib traveller but no boom
and could have used more tension. Then I used a back stay but I think there was an untoward amount of tension on the forestay. This way I think I'll have more control and less total tension required.
The original jib traveler on a bigger version of this sail was attached only at the gunnel-this will be pretty much the same. I'm fairly well convinced that a masthead skinny jib like this could be better all round on this type of boat. It actually uses a shorter traveller than it would if it was carrying the jib sheet, which on this rig is led from center on the deck with very little load. Its actually simpler and more effective than version 1- I think, and both appear more effective than a "normal" jib of the same area.
see the sketch above....

 

Yes, I understand the layout but why is the rotation point on a track?

 

Well, the jib wouldn't set unless the point of pivot moved to leeward. It would not function well at or near center(or at all with the restraint we are using at the front end of the boom). It moves to leeward until the angle between the CL of the boom and the CL of the boat is around 8 degrees-though it is fully adjustable.
On some "normal" model boats, the forward end of the jib boom is actually to weather when the pivot is on the centerline. Through experiments I know this system points better than that arrangement.

 

Do you mean that if the rotation point were fixed it would have a tendency to backwind the main?
I think your design ideas need to be tempered by some practical experience and time on the water. There is more to design than optimization of a single variable. For example, the high aspect jib will likely prove twitchy and difficult to set, particularly if you try to run some rig tension down the leech and have a floating tack. The high aspect might be theoretically more efficient but I think in practice you would find handling issues reduce it's effectiveness to below that of one of more normal proportions. I'm not going to comment further. I think you've made up your mind already and discovery of these issues will have to wait until the boat hits the water. When will that be?