# 60' Moth-A Preliminary Detailed Design Exploration

Discussion in 'Sailboats' started by Doug Lord, Sep 6, 2006.

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1. ### Doug LordGuest

+++++++++++++++++++++
SEE POST #16(or #30) for a very rudimentary analysis by an individual who doesn't think this boat can be built but that if it could it would be at least as fast as a 60' displacement hulled multihull and potentially faster than an ORMA 60.
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Please read the whole thing if you're interested. I consulted with a naval architect on this and tried to be as detailed a possible. Questions and comments from those interested are encouraged.
****==================================
60' MOTH-A Preliminary Detailed Design Exploration
==================================
I've long been convinced that the bi-foil revolution in dinghy design sparked by the Moth Foiler has potential for larger boats as well. The Out 95 guys in the UK and Sean Langman are also exploring this idea-among others. I decided to look at the numbers for a scaled up Moth just for the hell of it. I was surprised by the results.
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I) The base boat: LOA- 12.75', SA- 86 sq.ft.;weight: 60lb.hull + 150 lb. crew =210lb.s all up.
II) Scaling up:
*A) Sail Area-Since sail area varies as the square of length I squared 12.75(162.5) and squared 60(3600). Then I divided 3600 by 162.5 and multiplied the result by 86(Moth SA) . So the scaled up SA=1905sq.ft.----------------------- ****
B) Weight- Weight/displacement varies as the cube of the length. So I cubed 12.75 (2072.67) and cubed 60(216000).Then I divided 216000 by 2072.67 and multiplied the result by 210(Moth sailing weight). So the weight of the scaled up boat is 21,884 lb.'s.----------

III) Analysis/judgement calls- The most surprising thing when I was first doodling with these figures is the weight. At almost 22,000 pounds the scaled up Moth was way heavy by comparison to an ORMA 60 trimaran(12,000lb.'s) and to L'hydroptere(11,975lb.'s). But the defining characteristic of the Moth above all else is that it is a MONOHULL. So to preserve that characteristic at this length I decided that it would be important that the boat was selfrighting like any other(hopefully) 60'monohull. The "weight budget" certainly would allow that.
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So this is what I came up with after playing with the numbers for some time and running the whole thing by a friend who is a naval architect:
60' MONOFOILER-----------------------------
1)LOA-60'-------------------------------------
2) Target Beam 50'-increase from scaled up Moth; about same proportion as aeroSKIFF 14(see post#15 Peoples Foiler Thread)
3)Target SA: 2500 sq.ft.-increase from scaled up
Moth.------------------------------
4)Target Minimum all up sailing weight including 5231 lb.s on an 18' 60° canting strut: 14,731lb.'s.--------------------------------
5) Target boat weight w/o canting keel ballast:
9500lb.'s--------------------
6) Maximum additional ballast: 3771 lb.'s water ballast in a sliding tank-perhaps sliding within forward cross beam or just aft of beam. Tank is filled while over hull to limit weight of plumbing requirements. approx. dimensions: 1.5' X 6' X 6.4'. Possible fore and aft ballast sliding system .----------------------------------------
7) Weight with maximum ballast:18502lb.'s(plus 2-4 crew)
==================================
Summary:
-LOA*60'---------------------------------------
-Beam-50'--------------------------------------
-SA 2500sq.ft.----------------------------------- -Displacement:
14,731lb.'s ; Max: 18502---
-Draft(off foils) max
18'-------------------------
30 sq.ft. main foil; 15 sq.ft rudder
foil-------*
===============================================
COMPARISONS--------------------------------
----------------------------------------------
D/L ratio- 60' Monofoiler: 30.4--------------- D/L ratio- Orma 60/L'hydroptere: 24.8------
Bruce Number-60' Monofoiler: 2.03---------
Bruce Number-ORMA Tri: 2.39--------------
Bruce Number-L'hydroptere:2.65------------
(Bruce number is the sq.rt .of SA divided by the cube root of displacement)----------- --------- For what it's worth, the following comparison is between the 60'Monofoiler and the 60'ORMA trimaran.And I consider it one of the most important comparisons of all. The ORMA trimaran is presumed to have 60% of it's displacement supported by a "banana foil", with 30% of it's weight supported by the ama while flying the main hull. For this comparison the 60'Monofoiler is presumed to be flying on just two foils. The vertical fins of neither boat are included and both sides of the foils are included:
1)Orma 60-estimated ama wetted surface 124 sq.ft; estimated foil wetted surface 32 sq.ft.(both sides) Total 156 sq.ft. Now this figure is divided into SA(3000sq.ft.) giving 19 sq.ft. of SA per sq.ft.of wetted surface.
2) 60'Monofoiler Mainfoil area(both sides): 60sq.ft..Rudder foil area(both sides) 30sq.ft.. Total is 90 sq.ft . Dividing SA(2500sq.ft.) by this figure gives 27.7 sq.ft. of SA per sq.ft. of wetted surface.
==================================
**Notes and Design Considerations
( see below for "More notes..." including lift calculations, foil
==================================
A) The number one design consideration for this boat was that it was self righting and that it would qualify as a monohull under any rule. Therefore it does not have buoyancy pods that in any way resemble or that could function like a hull-simple rectangular spaces at the maximum beam supported by carbon cross tubes. These buoyancy tanks in combination with the 18' 5000+lb. 60° canting bulb would prevent capsize and or right the boat from a knockdown. The weight in the bulb was specifically chosen to be 1.5 times what would be required to right the boat from a pitchpole. The canting keel could be explored a lot since it is relatively light for a 60 footer(5200+lb.'s). It would be ideal for it to be clear of the water when the boat is foiling-at least above 20 knots.
B) When an Orma tri fly's the main hull it does so with about 2lb. per sq.ft. of windpressure on 3000 sq.ft. of sail. The 60'Monofoiler with max ballast can sail with it's maximum SA in about the same pressure. And in lighter conditions it can ditch up to 3700+ lb.'s of water ballast facilitating relatively light air take off in an 9-12 knot wind.------------------------------
(see Righting Moment below)
==================================
Preliminary conclusions:
It appears to me that the 60' monofoiler could be built but right at the top end of available technology.It would be likely to equal a multi of it's own size that did not use foils and appears to have more SA per sq.ft. of wetted surface than even an ORMA tri though especially in light air the ORMA would be faster since it can retract it's hydrofoil . The concept of an extremely fast selfrighting hydrofoil holds a lot of promise.
===================================
--------------------------------
More notes and references:
1) Righting Moment---------------------------
When off the foils the heeling arm (CE-CLR) is 43'. When on foils it is 51.75' . Hull bottom clearance to water is 10.75'. On foils max draft ,level,is 5'.
This boat is a monofoiler and as such will be sailed heeled to weather 15° at maximum righting moment.
Elements of Righting Moment:
A) rig CG is approximately at the
CE; 1460lb. @ 14.5' to weather= 21,170ft.lb.
B)canting bulb- 5,231lb.'s at 60°( 15.6') +
3' weather heel =5231 X 18.6'= 97,296 ft. lb.'s.
C)Hull 8040 X 5'to weather= 40,200ft.lb.
D)rack(deck) ballast 23' = 6' to weather
=29 X 3771= 109,359 ft. pounds
================================================
MAXIMUM RIGHTING MOMENT= 268,025 ft. lb.'s (A+B+C+D above)
MAXIMUM PRESSURE WITH 2500sq.ft.(268,025 divided by 51.75=5179. Divide 5179 by 2500(SA) = 2.07 lb.
================================================

2) The 50' beam could be one "wing" but would probably work better as two beams supporting a fixed empty "tank" at each end for buoyancy. A small tank containing up to 3770 pounds of water will also slide across the forward beam or just behind it. For the sake of getting the boat defined as a monohull based on whatever rule the buoyancy would not look like or function like a hull while normally sailing. In the event of a knockdown it would help to right the boat. I've talked with Alex of the OUT 95 project and he says their solution(ultra narrow hull with very wide wings on a 32 footer) is legal under the rules. Exactly which rules he was referring to I'm not exacly sure.
********The hydrofoils on this 60' monofoiler are in the hull : one mounted on the daggerboard and one mounted on the rudder.They might be partially retractable in non foiling conditions. No foils on the end of the wings.The canting keel strut would be behind the daggerboard.(Like Maximus among others)
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3) The canting strut is right on the edge of feasibility. But it probably can work: its half the weight of a VO 70 bulb but half again as long.Based on the fact that the load is 81% of the load on a Vo70 the engine hp required is likely to be about 23hp(vs 29 for the Volvo).
The Volvo 70 has a max speed so far of 40.6 knots according to Sail mag-just 5 knots short of the top end(so far) of a G Class cat(100+')-same source. And ,as I understand it, they peg the keel max out in fast conditions.
The Farr design #550 Volvo 70 has a strut approximately 12-13' long with 9920 pounds in the bulb with a variable displacement from 27,558 to 30,865lb.'s. The monofoiler as stated above needs 5200+lb.'s at 18' to be self rightng.
******I don't think that the bulb/strut being offset will have too much negative effect when you consider that L'hydroptere maintains control at over 40 knots with most of the drag coming from a foil 20' to leeward using a centerline rudder. I think that it would be important on the monofoiler to figure out a way to get the canting strut and bulb out of the water over 20 knots-keeping in mind that it will probably be sailed upwind with windward heel like the Moth. The Volvo has a max cant angle of 40°, the Schock 40 and Max Z86's 55° and a 26 footer from Bethwaite 60°.
**This area would need plenty of research and testing. It is ripe for some sort of unique solution....
----------------------------------------------
4) Bruce numbers- I calculated the Bruce number for L'hydroptere from information on Sail Area given in Sail mag.. But looking at the head-on picture and using a scale ruler I'll bet they can't carry that area(3700sq.ft.) in the same pressure that an Orma tri can carry it's 3000sq. ft. The monofoiler can carry it's maximum sail area in the same pressure an Orma tri can carry it's maximum sail area. Regardless of it's actual SA for a given pressure a well designed multifoiler will be faster than the 60 monofoiler any day. But the monofoiler and ORMA even using "foil assist" will be closer.And a "conventional" multi sailing only on it's hulls(even flying the main hull with no foil assist) would be still closer in speed to the monofoiler-with the monofoiler probably having a significant edge.
**I 'm leaning toward believing that the Bruce Number or Bethwaites "SCP Divided By Total Weight Ratio" may not be good comparitive numbers when comparing an all out foiler to a "foil assist" boat like the Orma. **When you look at these Bruce Numbers you may see what I mean: Moth 1.56 ; A Class Cat 1.82 ; 49er 1.76 ; IC 1.58 . All the boats shown show a Bruce number indicating they should be faster than a Moth-and they are when it is not foiling. But when on foils the Moth beats every one of these boats. So I'm leaning toward SA/wetted surface as a possible way to compare the boats when at least one of them is a foiler. In my comparison of the 60' monofoiler to the ORMA I showed that even though the foiler was heavier it had more power applied to less wetted area than did the ORMA. Of course ,this is simplistic: it didn't take into account induced drag of the foils, the vertical fins or the wavemakng resistance of the partially submerged ORMA ama. Nonetheless, it seems like a good indicator....
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Additional Notes: Using this formula for lift: Area=Weight divided by(the factor 2.09 X speed in mph² X Cl(coeficient of lift) along with my copy of Theory of Wing Sections and the information there on the 63412 section(p522 &523) I came up with the following for the monofoiler:
Light displacement =14731 .8=11784------
Heavy Displacement=18502 X .8=
14802--
Mainfoil area 30 sq.ft.--------------------------
==================================
1) The boat will lift off at a boat speed of 12 mph(10.4 knots) with a CL of 1.3. This is outside the drag bucket(but way below stall) but ,of course ,as soon as the boat lifts off it will accelerate.Moths, using this foil, lift off at even higher CL's.--------------------------------
2) At a boat speed of 16mph(13.9 knots) the CL drops to .73-just inside the "drag bucket" for this foil.-----------------------------
3)At 23 mph(20 knots) after the additional ballast is added the CL is .44-well within the drag bucket. The additional ballast may not all be added at once but I checked it at the minimum speed for which some ballast would be added.
==========================
A personal note: I'm not at all convinced that sailing foilers are a good idea for ocean racing until the electronic systems are developed to spot partially submerged objects in time to avoid them. L'hydroptere was stopped by just this kind of thing. I think all high performance boats would benefit from this kind of equipment and I imagine it's not too far away or may be already available for all I know. Equipment like that would make a venture like this much more attractive to potential sponsors...

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### Dan SJunior Member

Ok, I’m going to apologize up front for quoting Doug’s 2311 word post, but I want to preserve it as posted.

Ok,
1. “I consulted with a naval architect on this and tried to be as detailed a possible” – who did you consult with? Knowing who might lend some credibility to your post.
2. “Tank is filled while over hull to limit weight of plumbing requirements” – so we have a good chance of having to decrease the righting moment before we can increase it.
3. “18' 5000+lb. 60° canting bulb
·So to tack the hull has to either be 18’ above the calm water, or we have to slam a 5K lb bulb into the water at say 20+ knots. Please don’t tell me the bulb should be submerged
·Even at 60 degrees the hull has to be 9’ above the calm water, assuming the bulb will not be submerged, thus we just raised the CE 9 feet higher, thus we need more righting moment to counteract this.
·Just how much horsepower do you think you are going to need to hold this monster.
Please tell me this is a joke and not an attempt at a design brief.

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### RHoughRetro Dude

Nicely done Doug!

60' "Mono" foiler:

18 ft canted 60deg gives a 15.58 ft righting arm x 5200# = 81,016 lb/ft of RM

50 foot beam = 25 on each side

Assume that we can get 100% of the 3700# of water ballast (443 gallons or 8 55 gallon drums) all the way at the end of the arm: 25 x 3700 = 92,500 lb/ft of RM from the deck/beam ballast.

Total RM 81,016 + 92,500 = 173,516 lb/ft

(Just guessing here) The 60'MF rig will bee 100' tall, putting the CE about 40' up. This means about 2100-2200 sq/ft of sail at 2lb per sq/ft is about right until it starts foiling. (173,516 lb/ft / 40 ft = 4337.9# 4337.9# @ 2lb/ft^2 of pressure = 2168.9 sq/ft)

When it foils the sail arm increases from 40' to 50' ... so 173,516 lb/ft / 50 ft = 3470.3# 3470.3# @ 2lb/ft^2 = 1735.16 sq/ft

To carry 2500 sq/ft of sail in 2lb/ft^2 pressure the sail arm of the rig while foiling has to be 34.7 ft. That means 24.7ft when not foiling. What AR will a 2500 sq/ft rig have with the CE only 25 feet high?

60' Catamaran:

Total weight 18,500 (same as 60'MF)

50 ft beam (same as MF)

Total RM 50 x 9250 = 462,500 lb/ft

All other things being equal, the Cat has 2.66 times the available power.

Lets look at 2500 sq/ft of sail ...

The Cat has enough power to carry 2500 sq/ft of sail @ 2lb/ft^2 pressure with the CE 92.5 feet high!

The CE of the sail plan is about 40% of the semi-span, thus the 60'MF can only handle a semi-span of 25/.4 = 62.5 ft

The Cat could handle a semi-span of 92/.4 = 230 ft

AR = span^2 / area
AR 60'MF: 62.5^2/2500 = 1.5625
AR 60'Cat: 230^2/2500 = 21.16

Induced drag of the rig is CL^2/(pi x AR x e)

Assume CL=1

60'MF CDi = 1/(3.14 x 1.5625 x .8) = .254
60'Cat CDi = 1/(3.14 x 21.16 x .8) = .0188

Because the Cat can carry a higher AR rig it has 1/13th the induced drag.

As Tom Speer points out L/D is everything. For CL=1:

60'MF L/D = 3.937:1 (1/ .254)
60'Cat L/D = 53.15:1 (1/ .0188)

Let's ignore the huge advantage of potential rig AR and just use the same rig from the 60'MF on the cat (Doug was sleeping and I swiped it)

Rigs at 40+ knots are at least 50% of the total drag.
The exposed hull and appendages might be another 10%

That leaves 40% for Hydro drag (wetted surface, wavemaking, foil induced drag)

To keep it simple:

Cat: Areo 50 + Parasitic 10 + Hydro 40 = 100

MF: Aero 50 + Parasitic 10 + Hydro 0 = 60

Even if foiling reduced the hydro drag to ZERO the foiler has only gained 40%

The 60'Cat has 2.66 times the power, to get the same speed the 60'MF has to reduce TOTAL drag by 63%

Since hydro drag is not 63% of the total, it is not possible for the MF to reduce drag enough to beat the Cat.

Add the insult of the higher AR rig or more area at the same AR and the 60'MF does not stand a chance.

The 60' cat will be much faster than the 60' MF.

It was a good try Doug, but it still needs work.

Maybe a 150 foot beam? That would get the 443 gallons of water 75 ft to windward ... now the 60'MF is up to 358,516 lb/ft of RM and the Cat is only 1.29 times as powerful ...

Last edited: Sep 7, 2006
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### TaSSie_deVilResident Boataholic

Doug,

In all seriousness, I am all for foiling (about 1/2 way through converting my moth and building my foils as is)... but I really want to know what drugs you are on here.

The loads on the foils on a moth are sufficient to result in frequent failure of the hulls and foils as a result of foiling... the only moth foiler sailor that I know of that hasn't had a fairly cataclysmic failure of the foils or hull at any stage is Rohan, and most of that is due to the fact that he is physically quite light for a mothist (under 70kgs), but unbelievably fit in order to make up for his light body weight (easily the equal of a top laser, finn or 49er sailor). He also gets a new boat every year or 2 as a result of being sponsored, so that also reduces the chances of failure of the hull and foils through fatigue. His first foiler (now in the UK) has had some issues, as have some of the early HT foilers, mostly due to a lack of reinforcement of the transom and centreboard case. So, if you scale up the forces on a moth foiler alone (without adding lead or water ballast) by a factor of just short of 6, you are looking at one serious piece of engineering just to ensure that the hull doesn't snap in half.

So, scale that up to 60' and see how she goes, right? WRONG. It's not simply a matter of saying "well if I multiply it by the page number and divide by pi and the answer will be right".

Love the enthusiasm; but let's keep it simple, take this foiling thing one step at a time and make sure it works properly and reliably on the scale model first before we try to apply rules of static and dynamic similarity to a scaled-up version. Also, have you considered exactly what the span of the foils would be on your proposed 60' foiler?? My rough calcs have the main foil wing span at about 2/3rds the length of that on a cessna 182 light aircraft... try getting that in and out of a marina!

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### froshSenior Member

There is a way that Doug's idea is the best.

I have thought about the RM thing and not to detract from the thorough and well thought analysis of RHough but--- consider the following:
(1) We need a budget for this boat of the size of the GDP of a small country.
(2) We need to use an incredibly long pre-preg carbon tube to move the on deck ballast a very distance large distance after tacking, at high speed.
(3) Ballast should be the densest material that is possible to source on earth.
This obviously won't be water, and even lead can be improved on fairly easily if money is no object. I have researched that gold is denser than lead even though the periodic table shows that the atomic weight of lead is higher.
(The higher the atomic number the denser the material as a general rule)

From the Periodic Table of Elements http://www.school-for-champions.com/science/chemperiodic2.htm it is seen that Gold (Au) has the atomic number of 79 and atomic weight of 197. Lead (Pb) has the atomic number of 82 and atomic weight of 207. Thus the atom of lead is heavier.

But as you found, the specific gravity of gold is greater than that of lead. What that means is that more atoms of gold are packed within a cubic centimeter than atoms of lead. It is an unusual situation, but it is a property of gold that the atoms are packed closer together in normal conditions that are the atoms in lead.

For a 60 ft. monohull a tube 60 ft. long, well above deck (to avoid it digging in when the hull is heeled) should do it. The structural engineers can calculate the necessary diameter and wall thickness required to support around 5000lb of gold in a short solid rod made to fit as a precise sliding fit inside the carbon tube. Larger diameter tubing is better as it allows the gold ballast to be shorter in length increasing the efficiency of the system.
The cost of the gold at current price of US \$634 per oz. would be slightly in excess of US \$50 million.
Rapid movement from one end to the other of the gold ballast could be achieved by the use of compressed air stored in a titanium alloy tank on board. The air under very high pressure could readily be released to either end of the cross tube as required by activating a valve.
I am confident then with only a single hull in the water of an identical underwater shape to Rohan's Moth this would be the craft that could put any multihull well behind in it's wake!

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### Crag CaySenior Member

Argh....the perils of chatting to a NA in the pub. I hang a disclaimer round my neck when I start drinking:

" Whilst my enthusiasm for your project will certainly increase in direct proportion to the drinks with which you ply me, my competence is unfortuneately an inverse function. Anything I say between now and closing time must not be construed as contractural or even, after the first few pints, of being of any worth whatsoever'.

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### hansp77…

Hey Frosh,
You might want to think about Depleted Uranium
might be a little hard to buy, unless you have some close US military contacts, but dig around long enough in the tank battle fields of Iraq, and you might just find enough.

At 70% more dense than Lead it could be just the ticket.
Apparantly it is safe enough to fire at "our enemies" and leave lying around their countries, so it should be safe enough to strap to the bottom of your boat
If the coast guard or other authorities have any problems or disagreements with the safety of your 'ballast',
Don't worry about it.
Pull your sails up, and out-run the buggers!

8. ### Chris OstlindPrevious Member

Cyclic Matter

Way back when I first started college as a design student, my best buddy and I would post outlandish, for sale, specifications for a fictitious street hotrod on the student bulletin boards on campus. Because I was the illustrator in the effort, I would be tasked to draw said monster muscle car and then secretly post the notice. We hoped to draw a phone call or two on the posting and get a good laugh.

Some of the other design students caught-on that it was really an exercise in design fluffery and not really a substantive posting at all and soon the bulletin board was festooned with collections of outlandish mechanical enterprises, virtually impossible to actually bring to life as a driveable car... much less have the cash on hand to actually acquire all the parts as listed.

When I see this posting of Dougster's, I'm quickly swept back in time some thirty years ago to when I did this sort of enterprise for laughs. I knew I was being more than a bit naughty in tossing out the temptation of the century for those car nuts who were not in the know of the inside joke. I did it anyway, because I was young, exceedingly confident in my talent and just cynical enough to enjoy the responses from the guys who took it at face value.

Let's just get to the bottom of the issue here. The Dougster is a categorical dreamer. As such, he's never content to actually follow-through on anything that has a conclusion because that means the end of the Dream State. If one places enough objective blockades in one's path to the conclusion of this established dream cycle, one gets to opt-out, so to speak, at any time when the objective, real life issues begin to exceed the relative value of the dream's fulfillment.

Just look back through all the many hundreds of dreamy postings by The Dougster and you will begin to see the pattern that forms around each of these cyclic adventures he embarks upon.

It's something like this:

1. outrageous proposal
2. incessant hyperbole
4. crass defensiveness when challenged
5. ignore the substantive arguments of those who are making the most sense
6. anger with established proponents to the point of lashing-out at his previously "best buddies"
7. retreat to shadows and regroup
8. launch next outlandishness as if the whole previous enterprise had simply vanished

And here we are today, looking at yet another line of poorly supported, impossibly objectified and totally unrealistic reasoning with but the thinnest of threads of realistic potential. It's just so very much like the phony hotrods I used to draw as a 19-year-old design major that it brings a smile to my face.

When you can't finance even the smallest of techno-boats the next thing to do is turn to an outrageous design concept that even a Oil Sheik would gag over. Yep, that's the hallmark picture of a total dreamer.

We'd best give the boy a large field in which to run. Soon enough he'll shed his Megafoiler skin and be on to his next moment in the sun.

It's a Cyclic Matter... you wouldn't understand

9. ### Doug LordGuest

60'Monofoiler RM

Thanks for your time Mr. Hough; you pointed out a big deficiency in my doodling that I should have caught. I've just added RM to the original post and as you can see with the boat heeled to weather 15° while on foils there is more than enough MAX RM for 2lb.sq. ft. pressure( approx. the same wind pressure it takes to fly the mainhull on a ORMA 60)
==========================================
I'm afraid I don't agree about the comparative speed of your cat. I roughly calculated the wetted surface for a 60' cat flying one hull and displaceing 18,000 pounds and it leaves you with about 7sq.ft. of sail area per sq.ft. of wetted surface if you use the same sail area as the Monofoiler. The monofoiler ,on the other hand ,has 27.7 sq.ft. of SA per sq.ft. of wetted surface. The monofoiler also has substantially more power per sq.ft. wetted surface than the ORMA 60.
----------
Moth vs A Class cat-----
1)Moth RM=900ft.lb. and HM =946ft. lb. in 1lb. pressure.
2)A Class RM=2325ft. lb.; Max pressure 1.29 lb.sq.ft. very high aspect main
NOW THIS IS FAIRLY IMPORTANT:
This might help you to see that the sq.ft.SA to sq.ft. wetted surface is an accurate comparator of potential speed when comparing a foiler(on foils) to a "normal" multihull'. This is sort of like comparing test results from two large models and finding them in agreement with design predictions:
Moth: 27.56 sq.feet SA per sq.ft. wetted surface(see results for 60' monofoiler)
A Class cat: 7 sq.ft.SA per sq.ft wetted surface.
See results for RHOUGH's cat and for ORMA tri.
This is important because ,according to Rohan Veal the Moth is faster than an A Class cat in conditions over 10 knots!

============================================
Tassie, the foil areas and rudimentry lift calculations are shown in the original post for a 30 sq.ft. main foil -more or less 2' X 15'. Showing the boat taking off in as little as 10.4 knots boat speed-which would probably be 8-10 knots of wind.L'hydroptere(60') has TWO 22 ' long main foils plus the rudder t-foil.
The monofoiler has almost exactly the same sq.ft SA per sq.ft. foil area(mainfoil,one side) as does the foiler Moth but higher foil loading.

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### usa2Senior Member

Heres a thought. You could conceivably make a catamaran foil on the same type of "single" foil system the moth has now. What would you call the boat then?

I pose this question, because i think that comparing foilers to monohulls/multihulls, is a complete waste of time. These boats are not in the water, they are basically flying on it. therefore, what a dumb thing it is to compare the speeds.

11. ### Chris OstlindPrevious Member

Attempting What?

USA,

This is a desperate attempt to feel important and validate the busted process of the People's Foiler/AeroSkifferoo.

If you don't believe me, I have this \$30 million F1 project on the drawing boards that I'd like to compare to your \$13 million NASCAR rig. Do you really think your NASCAR can compete with my vaporous paper animal just waiting to snarl and spit.

Oh, did I mention that nobody is going to race these things against each other unless they have all the money in the world and they like to toss it about unceremoniously for pointless exercises. Oh, there is such a guy? But isn't he broke?

Then there's the drivers who have huge egos.

Our intrepid hero says, "Sign up now, Bruno, right here on the dotted line. Of course the boat is not yet ready, there are no sponsors and there is no funding... but I've got this really, really cool idea that pencils-out to be oh so bitchin"... No, really... I do."

"Bruno? Don't you just walk away from me like that, I'm somebody, darn it! .... uh, Mr, Peyron don't leave yet. You haven't seen my smoke and mirrors thing yet. I have a whole, retro slide show and a Power Point and a.... Please, Mr. Peyron?"

12. Joined: Jan 2005
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Location: AUSTRALIA

### froshSenior Member

This is too much to bear!

Dougster, I have been referred by a fellow MD to a shrink for marked clinical depression; and IT IS ALL YOUR FAULT!
You have the gall to make considered answers to everyone else in this thread but ME! Don't you see the damage you are doing?
I have probably come up with the one idea that could still make you look good, and become the super hero you deserve to be.
And you won't critique my proposal!
You obviously don't go to work judging by the amount of time you spend typing these long posts, and before I forget, the time required to use your scale ruler on the many sailing mags to scale up pics of foiling Moths, and come up with the outrageous stats.
How do you get hold of all the mags anyway? In my country they cost about \$7.70 each. Not a lot, I grant you, but prohibitive if you don't have a job.
By the way, do they have a disability pension in the US?

13. Joined: Nov 2005
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Location: BC Summers / Nayarit Winters

### RHoughRetro Dude

If we use SA/WSA to predict speed potential, the result of the prediction must close to observed results if the measure is to be considered valid.

27.56:1 compared to 7:1 predicts that the Moth would have 25% of the drag of the A-Class Cat. What speed result should we see?

Drag force = CD x Area x Density x Speed^2

If CD = .5
Wetted area per unit sail area:
A-Class = 1
Moth = .25
Density = 1 (water)
Speed = 10 FPS

A-Class Cat: Drag force per unit of sail area = .5 x 1 x 1 x 10^2 = 50
Moth: Drag force per unit of sail area = .5 x .25 x 1 x 10^2 = 12.5

Speed is limited by the ratio of power to drag. When Drag = Power the boat cannot go faster. Assuming that power per square foot of sail area is a linear function how much faster should the lower drag boat be?

In other words what value of Speed would make the drag per unit sail area of the Moth equal to the Cat?

We need 20 FPS: .5 x .25 x 1 x 20^2 = 50

IF (THIS IS FAIRLY IMPORTANT) SA/WSA if a valid predictor the Moth should be TWICE as fast as the A-Class cat.

Observed data: Rohan Veal (a former World Champion) sailing HIS Moth is SOMETIMES a bit faster that SOME A-Class cat.

The flaws with using SA/WSA as a measure are two:

1. The premise is based on Rohan Veal being somewhat faster than some (insert class) boats. To be a valid premise it would have to be that foiling Moths (not just Rohan Veal) are faster than (insert class) boats.

2. The SA/WSA ratio predicts that all Moths (while foiling) should be twice as fast as an A-Class Cat. This is not the case. Not even the Rohan Veal case claims to be twice as fast. The SA/WSA formula logic is that if an A-Class cat can reach 25 knots (easy) a Moth should be sailing at 50 knots.

Since the 60'MF relies on the SA/WSA predictor to reach speeds equal to multi's, it is doomed to failure. The premise is flawed.

As I stated before top speed is drag limited.

Citing the Aero 50% Parasite 10% Hydro 40% SWAG I made and IF SA/WSA was valid; The 60'MF would have drag = Aero 50% Parasite 10% Hydro 10% (25% of 40%) for drag = 70% of the 60' Cat

Since the 60'Cat has 2.6 times the available power of the 60'MF it can easily overcome a 30% drag increase.

There are a host of issues that will prevent the 60'MF from sailing at all. Since the basic premise that it could possibly have higher speed is flawed, there is no point going into why the design could not be sailed. Foiling on a Moth works and foiling a 18,000# CKSDBMF won't work.

It was a good try Doug.

14. ### Doug LordGuest

60' cat / monofoiler

The estimated drag increase for the 60' cat just based on wetted surface and not including wavemaking resistance, vertical fins is 400% of the monofoiler.
Cat wetted surface flying one hull=349 sq.ft. Monofoiler wetted surface on foils 90sq.ft.
The SA/wetted surface ratio as I'm using it is an INDICATOR not necessarily a predicter of speed.In fact if the 60' monofoler had the SAME ratio as another more powerful boat I'd bet on that boat having an edge. So, far of all the commonly used ratios-D/L, SA/D, SCP/total weight and Bruce Number it is the ONLY comparison that predicts that the Moth would be faster than an A class. The story is twofold: the normal ratio's correctly predict that the A Class cat is faster than the Moth-in 10k or under(off foils) . And SA/wetted surface correctly predicts that the Moth would be faster when on foils.
SA/wetted surface does not predict total drag since the way I've used it the vertical fins of both boats are not considered, induced drag is not considered and wavemaking drag is not considered. Used the way I've used it, it is just an indicator that is proven in the Moth vs A Class cat case. Hopefully,as time goes by we'll get more examples to check out.
As it stands now the ratio, as I've used it, indicates that the monofoiler on foils might be equal to an ORMA and faster than an 18000lb(heavy) cat . At least that's a guess. What we know for a fact is that when there is a large discrepency in the ratio like between the A Class and Moth the foiler is faster when on foils. But we "know" it for this case only and it may prove to be invalid. I'm looking forward to finding out.
------------------------------------------
If the 60' cat had a 50' beam with 20/1 hulls the max righting arm would be about 23.5'. Which at 18000 lb. displacement gives it a RM of around 423,000ft.lb.'s . The RM of the monofoiler heeled to weather 15° is 268,000ft.lb.. So the power to carry sail of the cat is only 1.57 times that of the monofoiler(not 2.6).
If you multiplied the 2500 sq.rig that you borrowed from the monofoiler by 1.57 that would give a total SA at a low CE of 3925 sq. ft.
That would not do much for the cats SA/wetted surface changing it from 7sq.SA per sq.ft. wetted surface to 11 vs the 27 for the monofoiler.
========================
RHOUGH:" Foiling on a Moth works and foiling on a 18000# CKSDBMF won't work." That's the least thoughtful and most absurd comment you've made yet.

15. Joined: Jan 2005
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### froshSenior Member

Get this!

Dougster, I have taken my own Prozac (that was originally earmarked for you!) and made a miraculous recovery.
GET THIS! IT IS REALLY SIMPLE! THE F-----G 60' MONOFOILER WONT SAIL!
Now try to come up with something sensible to make yourself famous!

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