TAll wingmast catamaran rig on a skiff?

would it work to put an "A" Class or formula style rig (only smaller, but still tall and wing looking) on a skiff or foil type of boat?

 

I don't see why not, Northbridge Seniors (14' skiff) often ran a rotating wing sytle mast... decades ago this was common.

http://www.ns14.org/

http://www.cstcomposites.com/MG14_and_NS14.htm

They where known as the Porsche of dinghies, for 100 sft of sail they where (are?) very efficient and quick around a course.

 

Wing

Have you seen these? A SOLID wing like the c class cats would be difficult though not impossibe(close to it though). The Moth has a highly efficient sail...

 

yes these are all very good, the ns14 came very close. but what I ment was a long wing mast and rectangle sail, you see these all the time on beach cats, but on monohulls the sail is always shorter and boxy, and the mast step is always way forward, is this because of righting moment? could you get away with a monohull that had a fairly tall mast, a rectangle wing sail (A class like) and a mast step further back then normal?

 

It's an interesting question. For the same stability index, the taller rig will have less sail area. So does the reduction in drag make up for the loss of power?

In rough terms, the height of the center of effort is going to be proportional to the length of the mast, so the lift will be inversely proportional to the length of the mast when limited by the stability of the hull. The aerodynamic drag is the sum of the parasite drag and the induced drag. The parasite drag is the sum of the skin friction on the sail, plus all the other windage - especially the hull and crew. The sail area will be less as the mast is made taller (sail area is proportional to the lift required), but most of the major windage sources will be the same, and the parasite drag/lift will increase. The induced drag is proportional to lift squared, and inversely proportional to the square of the length of the mast. So the induced drag for the same stability is going to drop by something like the length of the mast to the fourth power. That's a huge reduction. When you compute the drag/lift ratio (which is what counts in sailing performance), the increase in parasite drag/lift is going to be roughly proportional to mast height, while the induced drag/lift is going to be inversely proportional to mast height cubed. This simple analysis suggests the taller mast will be faster until the induced drag is roughly 25% of the total drag. I suspect the induced drag is considerably more than this for most boats.

Acceleration, however, is a different story. Acceleration is going to be roughly proportional to the lift over and above that which is required to maintain the current speed, so a shorter rig may accelerate better because of the greater sail area. And added drive may be needed to punch through a seaway.

It would take a VPP to examine the tradeoff for a particular design. Which is precisely why the first thing I'm doing with my boat is sailing to create a VPP. I, too, want to know if a taller rig with less sail area is going to be faster than the existing rig with conventional proportions.

 

But what if your going to have a taller mast and not reduce the sail area, because your going to offset the added instability by making the hiking wings wider and adding a trapeze instead of hiking? Reducing windage and drag, increasing lift, hull drag stays the same (in this case hydofoil drag will increase because I will make the foils wider to offset the taller rig a little) and righting moment is increased because of the wider wings and the trap. what do you think?

( I'm trying to design a monofoiler thats 4m loa, 45cm beam at waterline, has 10.5sm to 11sm sail area, trapeze, 2.4m wide wings, a tall wingmast beachcat rig, and comes in all up weight around 40-45kg, all so I can blow by the "A cat" guys at my local pond, they say it cant be done, I say it can. It's like a moth for guys that don't like hiking straps) definately not the peoples foiler, more like the "unlimited foiler"

 

Super Bi-foiler

Here are some basic ratios you can use to see where you're at. When you can why not start a thread about your boat?! Many people would enjoy hearing the details!
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Some info that might help-the W/SA ratio for the Monnard design is under Peoples Foiler II. You'll notice it is in exactly the same ballpark as are these boats:
New18 info and M4 added
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FOILER WEIGHT

The running theme of this thread has been my attempt to point out that the comparison of foilers of different weights WITHOUT considering POWER is ridiculous. Numerous experienced foilers(who should know better) tenaciously cling to "facts" that don't add up and hearsay about the role of weight in foiling. Few times if ever has anyone tried to explain why a boat like the RS600FF can be so similar to a Moth in performance yet weigh so much more. Most people are content with absurd explanations like that offerd by Phil S or Funk in previous posts. Thats too bad because foiler design and experimentation suffers when ignorance dominates the discussion.- as when anyone says that weight is the primary comparative measure between different foilers.WEIGHT IS CRITICAL WHEN COMPARING THE PERFORMANCE OF TWO IDENTICAL FOILERS but WEIGHT AND POWER must be considered together when comparing different boats.======================
Moth-
SA: 88.8sq.ft
Sailing Weight(includes crew): 220lb.
main foil area: 1.19 sq. ft.
Foil Loading(Lbs per sq. ft. at 80% max boat weight with crew):147.89
**W/SA: 2.47lb. per sq.ft.(sail loading)
***SA per sq.ft. of main foil area(a SA/ws ratio shortened to cover planform area of main foil only): 74.62
*SCP/TOTAL WEIGHT=43%
=======================
For ease of comparison foil areas for the next two boats were arrived at by using the same FOIL LOADING as a Moth.
Only upwind SA is considered. Moth crew=154lb.RS crew=160lb.; 18 crew =3X160lb.
=======================
RS600FF
SA: 131 sq. ft.
Sailing Weight(includes crew): 327lb.
Main foil area: 1.76 sq.ft.
Foil Loading: 147.89 lb. per sq.ft.
**W/SA: 2.49 lb. per sq.ft.
***SA per sq. ft. main foil area: 74.43
======================
M4
SA: 107 sq.ft.
Sailing Weight(includes crew): 259
Mainfoil area: 1.4 sq.ft.
Foil Loading: 147.89 lb.
W/SA: 2.42 lb. per sq.ft.
***SA per sq.ft.main foil area: 76.42
========================
New Foiling 18
SA: 354 sq.ft.
Sailing Weight(includes crew): 858lb
Mainfoil area: 4.64 sq.ft.
Foil Loading: 147.89lb. per sq. ft.
**W/SA: 2.41 lb. per sq.ft.
***SA per sq.ft. main foil area: 75.86
*SCP/Total Weight(Bethwaite ratio)
New boat=39%
Old boat= 33%
+++++++++++++++++++++++++++++++++++++++
+++++++++++++++++++++++++++++++++++++++
Note the different weights of the boats . Then note the Sa/per sq.ft. main foil area-this is a comparison of Sail area to wetted surface when the boat is flying using just the planform area of the main foil for comparison-THEY ARE NEARLY THE SAME FOR ALL THREE BOATS. Note the W/SA is almost identical for all three boats. This means that all three boats will foil at about the same time adjusted for differences in rig efficiency(Moth probably the best) and for hull L/B ratio as a measure of early takeoff potential(Moth by far the best). As I just said there are other factors and details that will marginally affect performance but this clearly shows how close all three boats are in their ability to fly despite the fact that the RS is 2.5 times heavier than a Moth andthe 18 is 5.6 times as heavy as a Moth.
What counts is power to weight ratio as a first look. A more detailed look showing a comparison of SA/ws ratios for all three boats reinforces the accuracy of the power to weight ratio.
More to come on ratio's......
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* For those that don't know Bethwaites ratio SCP/TOTAL WEIGHT is calculated as follows:
1) SCP= Righting Moment divided by the distance between the CE and the CLR
2) SCP is then divided by TOTAL WEIGHT(boat plus crew)
3) originally designed to see if a skiff had the power to plane upwind which,according to Bethwaite, it would do with an answer(in %) over 30.
4) Since the Moth is the baseline for all foiler comparisons comparing the Moth ratio with any other foiler is instructive.
5) One of the beauties of SCP/TOTAL WEIGHT is that it comes up with the SAME NUMBER whether calculated in English or Metric units.
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** W/SA= TOTAL WEIGHT(boat+crew)in pounds divided by SA in sq.ft. This is a comparison that is very relevant AS A FIRST LOOK at two different foilers. It has the drawback that it ASSUMES that the two boats have the RM to carry the sail they have. It basically describes the weight per sq.ft. of SA which is the sail loading(similar to wing loading). Compare to the Moth ratio.
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*** SA per sq.ft. of mainfoil area=The SA divided by the area of of one side of the mainfoil. It is a shortform of a SAIL AREA/WETTED SURFACE ratio which is most applicable to "airplane" foil configurations with the mainfoil carrying 80% of the load. Moth is the baseline.

Design For Flight


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thanks for the info, basicly thats what this Boat design is about, having the sail area (about) of a rs600, and the weight of the moth (about), that should be a good power to weight ratio, plus having the rig efficiancy and dynamics of an Acat, i think it should be fast, I'm willing to give up early foil performance for top end speed (to a point), and also stability for top end speed (to a point). Just trying to make a super fast mono foiler. There has been alot of interest in this idea in my area, so much that I have started coming up with a Formula.


SR 71 Foiler Formula:

LOA: 4.0m + 75cm max Gantry
BAW: 45cm min (Beam At waterline)
BAG: 75cm min (Beam At gunnel)
BOR: 2.4m max (Beam Of Rack)
SA: 10.5sm
Trapeze: Yes
MAX Mast Height: ?
MIN Weight: ?
*mono hull only (no windsurfers, no Multihulls)
*open foil plan (2 only, centerline mounted)

(would also like to do some testing for a reaching spinniker, to see if is faster, or if its even possible (at least worth messing with).

 

Speed

Keep in mind that over two years ago Rohan Veal raced a bunch of top Aussie A Class sailors and beat them around a course in five out of six races.
Good luck with your very interesting project!
As to the spinnaker you might contact Thomas Jundt the main behind one of the two foiling 18's. He is about to unveil the most innovative,radical 18 yet done. Though it is no longer within the current 18 rules it will pave the way for a new ,revolutionary foiling 18. His new boat has the main hull L/B similar to a Moth. See the "Foiling 18" thread for a way to contact Thomas-and watch the "sailboats" forum over the next few weeks for the unveiling.....
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I'd suggest you start a new thread under "Sailboats" regarding your project monofoiler and proposed specs.

 

Super Foiler

WA, you would want AT LEAST a 10/1(L/B) Length divided by Beam ratio(at the waterline) for your foiler. This is important for early takeoff.

 

The principle's the same. You've increased the stability, but that just shifts your starting point. After that, the question is, "What's the optimal rig for the new hull?"

If you're using inverted T foils, the span of the lifting foil has very little to do with the height of the rig. It has everything to do with reducing drag due to lift on the foil. You should make the foils as wide as you possibly can, subject to strength and stiffness limits. If you keep the same foil area, this means a higher aspect ratio foil, with less chord and less thickness.

Ideally, the lift would be the same on both sides of the foil, especially if you're heeling to windward, so all the righting moment comes from the crew, not the foils.

 

thank you so much, it's awesome that this place exists because its the only place i can seem to get alot of this input. class developement forums are so guarded. Thank you for being so helpful. Doug: does that 10:1 ratio include the gantry length as well? (thats cool that Rohan beat a-class in a moth, but I don't think I could, If I had to hike it down I'd be throwing up in the comity boat by the second mark) as far as Length to Beam, if the LOA is 4m wouldn't the 45cm waterline beam be good? and thank you Tom, I can take the foil width out of the stability equation.

 

L/b

I'd go with the highest(skinniest)L/B ratio you can manage(10/1 at the widest) especially since you're talking about using smaller foils for higher top end. That means that your hull will have to go faster in seahugging mode before takeoff-and the narrower the better at those speeds.
4m=13.12' . 10/1=1.312'=.4m=40cm .
It's the hull only for the purposes of L/B.
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Don't forget in your stability calcs to add in Veal Heel-about 15 degrees to weather. Should give you about 1' (.3m) longer Righting Arm(RA) for the boat(incl. rig) plus crew CG. To calculate it remember it is independent of the boats altitude as long as when heeled the wings don't touch. Draw the boat heeled and then draw a vertical line from the intersection of the vertical fin and mainfoil. Measure the RA from that vertical line; multiply the RA X the weight to give Righting Moment. It may make it simpler to find the CG of the Hull,Rig, and Crew separately and add the results. Good Luck!
====================
This guy has done a lot of experimental Moth work . He figures that with a Veal Heel of 20 degrees you get 19% more RM. Interesting reading. This is just part of his site-explore!
http://www.culnane.net/dc/moth/fram...ng/moth/wshpaper/index.html?nocache=265500648

 

so when you said "at least" you meant "at most"....... got it, thanks again

I've noticed everyone in the moth class going for super light foils ( hollow, vac mold, prepreg, autoclave) does that have any effect on the way the foils perform themselves, or is it just to keep the overall boat weight down? (if a class formula had a "min weight" and foil weight didn't have effect on foil performance, you could have solid core (ie "stronger") easier to produce foils and a lighter hull or sail rig..) :?:

 

Be aware that this is far, far from a new idea. Many good designers and sailors have added wingmasts to skiff types or boats similar (in some ways) to your concept.

Off the top of my head;

Canoe champion Sandy Douglass' mast fairings, 1930s (discarded)

Bee McKinnon's solid wing Canoe sail by the famous wingmast designer Clarence Farrar, 1940s? (discarded).

Some guy whose name escapes me's solid Moth sail of the '50s (discarded).

Hughes (?) wing mast on a Gwen 12 (light trap dinghy) in the '70s (discarded).

A succes sful US Canoe sailor and NA trialled an NS14 rig on a Canoe iin the '90s (discarded).

A 12' skiff /R Classs champ used a wing mast (discarded).

A Jutson 18 Foot Skiff used a wing mast (discarded)

A world champion 18 Foot Skiff used a wing mast (discarded).

A recent 12 Foot Skiff used a complete A Class mast and main (not yet proven but so far slow AFAIK).

Add in many wing-masts and solid wings on boards (discarded).

Gust response and weight seem to be the biggest problems. The gust response and handling requirements of something like a Formula cat or NS14 is orders of magnitude less than in a Skiff or a skinny Moth type. I'm not anti-0wing mast (one of mine is in my view as I write) but the evidence seems to indcate that they are not suited to all types of craft. In Skiffs, boards and Moths, gust response is one of the major aims.

The Capricorn/Taipan 4.9 wing mast may be more efficient than the smaller wing on the Hobie Tiger Formula 18, but the Tiger still wins more world titles. The stiff wide wing requires very high mainsheet tensions on the Taipan (the 8' wide 95kg Taipan sailed 1-up has higher mainsheet loads than the Tornado!) which also affects gust response; you'd die trying to work a T4.9 mainsheet as hard as you work an International Canoe mainsheet.

There's been a "giant Moth" with dimensions akin to yours around for years. It has never been faster (IIRC) the normal Moths, foils or no foils. Handling difficulties become acute. I wonder if the drag of a body on trap is a major factor in such a small low-drag boat and rig?