60' Moth-A Preliminary Detailed Design Exploration

Doug, I'm impressed.

I'll be the first to say when my knee jerk reaction is in error.

I still feel that SA/WSA is too simple to be of much value. Although Doug is correct that a boat with a higher SA/WSA ratio should be faster.

I took the liberty of generating some drag and power curves for Doug's 60' CKSDBMF and an ORMA 60' Trimaran. I considered both wetted surface (skin friction) drag and induced drag fom the foils on both boats. I did not consider wavemaking drag, spray drag, or foil profile drag. Both boats will probably have similar additional drag in these areas.

Bottom Line:

Doug is absolutely right. The 60'MF is potentially faster than a displacement multi-hull.

I used Doug's Figures for foil sizes and weights. The 60'MF rig ends up being about 100' tall, which just happens to be the limit for an ORMA 60.

The ORMA 60 has only a 151% advantage in Sail Carrying Power over the 60'MF

My calcs show that the 60MF should be able to lift and foil just over 10 knots of boat speed. The drag polar peaks at lift off, then goes down until the boat speed is 25 knots or so. The negative slope of the drag curve (pink) is due to fact that the CL required of the foils goes down faster than the drag due to skin friction goes up. I used an AR of 7.5:1 (15x2) for both the main foil and the rudder foil and a max CL of 1.3.

The drag curve for the Tri (blue) has a flat area from about 10 knots to 20 knots for the same reason. The foil produces the needed lift at lower CL values as speed increases.

Somewhere between 20 and 25 knots the MF has lower drag than the Tri and the MF enjoys a drag advantage at all speeds above 25.

I added a line (yellow) to show the relative drag of the two boats.

The violet line shows the 151% power advantage for the Tri.

Right about 35 knots boat speed the Power Advantage curve meets the Drag Penalty Curve and above that point the MF should be faster.

I did some basic rig efficiency calculations to get a feel for the total drag vs power available for the two boats. These curves are purple for the MF and brown for the Tri. It is interesting to note that below about 15 knots boat speed the MF has very little power to spare. From 15 to 30 knots the percentage of available power required to equal drag is almost the same, and above 35 knots the Tri has more spare power than the MF.

These very basic calculations show that at 50 knots both boats have power to spare. This cannot be true, since ORMA Tri's have not hit 50 knots. I made no attempt to estimate parasite drag for either of the boats. At boat speeds over 15 knots or so, the aerodynamic drag of the hull and rig start eating into that extra available power and in practice all the extra power seems to be used somewhere in the 40-45 knot range.

I still don't think that a 60'CKSDBMF can be built that will foil reliably if at all. However, if it could be built it has the potential to compete with ORMA 60's.

 

60 monofoiler

Very interesting ,Mr. Hough. At this point SA/wetted surface used in the way I did(just hulls + both sides of foils) SEEMS like a good comparator/indicator of performance when used to compare displacement hulled & foil assist boats to a full flying foiler. No other comparative ratio I've come across yet predicts that the Moth would be faster than an A class cat.So I think it may have some relevance in this specific kind of comparison.In comparing two foilers(around the same length) I look at Lb.'s per sq.ft. SA("wing loading"), SA per sq. ft. mainfoil area, and mainfoil loading at 80% of displacement.
I'd be interested in learning about any other comparative ratio that would perform similarly to SA/ws in predicting the results of Moth foiler vs. an A class cat.
+++++++++++++++++++++++++++++++++++++++++
Just out of curiosity ,why don't you think it can be built to "foil reliably if at all"?

 

Just for grins I did three runs.
Same weight (80% of 18000 = 14400)
Main Foil Areas of 20, 30, & 40 ft^2 thus WSA of 70, 90, & 110 ft^2
Same AR of 7.50:1
Same Sail Area of 2500 ft^2
So we have 35.7, 27.7, 22,7 for values of SA/WSA
This represents foil loading of 360, 480, & 720 lbs/ft^2

As SA/WSA predicts the drag is lower at higher ratios.

However, when I add the induced drag from the foils a different picture emerges. At lower speeds the 40 ft^2 foil gets the boat up at a lower speed and continues to have lower drag until the speed reaches about 23 knots. From 23 to 28 knots the 30 ft^2 foil has the lowest drag, and over 29 knots the 20 ft^2 foil has the lowest drag.

So the outcome is:

Below some speed, larger area (lower foil loading) has lower drag even though the SA/WSA ratio is lower. This speed range is High CL / Low L/D.

Above some speed, smaller are (higher foil loading) has lower drag as predicted by a higher SA/WSA ratio. This speed range is Low CL / High L/D.

So it is not safe to say that High SA/WSA ratios (forcing high foil loading) is always faster. It is faster at very high speeds, but the low speed range would be very slow and the lift off speed high compared to the big foil boat.

There may be a relationship between SCP/Weight and optimum SA/WSA or Foil loading. At first glance it would seem that since a more powerful boat (High SCP/Weight) should be able to operate at higher average speeds, it would have better performance at a higher SA/WSA or Foil loading. The design goal would be to have the lowest area under the total (skin friction + induced drag) curve for the speed range the boat is capable of.

The 20ft^2 (720 lb/ft^2) foil is in Blue
The 30ft^2 (480 lb/ft^2) foil is in Pink (Magenta?)
The 40ft^2 (360 lb/ft^2) foil is in Yellow

 

SA/ws

So far SA/ws does accurately predict the performance of the Moth on foils and the A cat just not how much better the Moth is. And it seems to accurately predict the performance(faster/slower) of the 60' monofoiler vs the ORMA theoretically, according to your figures. I think SA/ws can be used as an indicator of potential when comparing a boat on foils to one that is not or that is using foil assist.
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Interesting foil comparisons.The biggest advance with 60' monofoiler mainfoil would be if there could be a way to hydraulically vary the span maybe 4-5 sq.ft each end.On the aeroSKIFF 14 and on my new boat the idea will be tested with removable foil extensions that you plugin/unplug before leaving the beach.

 

I did quite a bit of this sort of thing when I was optimising RC Glider Designs. At the edges of flight envelopes you find some counterintuitive things. i.e. Higher A:R is not always better. Low wing loading is not always better.

Looking closer at the last graph I tossed together. Having either different foils (like 18's have different rigs) or variable foil geometry would make it easier to fine tune a boat for conditions.

For more data, I set limits for CL Max of 1.6, 1.3, & 1.0 for the 30 ft^2 foil (480 lb/ft^2 loading 90 ft^2 total area). Very interesting! While the High CL got the boat out of the water sooner it pays a big induced drag penalty to do so. The drag penalty for max CL = 1.0 was much smaller than for higher values.

If the foil(s) were trimmed to 0 CL below S/L of about 1:1 (7.7 knots) the only extra drag is from wetted surface. At those lower speeds the extra drag is on the order of 25 pounds. It does not appear to make sense to try to get the boat up on foils until wave making resistance starts to change the slope of the drag curve.

In this figure, I've altered the foil curves for the Max CL and added the skin friction component of hull drag (Cyan Line).

To design the optimum foil configuration, the foils should be just big enough to lift the boat at around S/L = 1.2 or so. This should be the point where the hull's skin friction + wave drag = skin friction + foil induced drag.

I think this would minimize the light air performance hit for dragging the foils around in displacement mode. More answers = more questions.

 

And the exercise becomes fairly moot in real terms the moment the big multihulls install foils of their own. Then the big foiling mono goes right to the back of the pack once again.

A desperate exercise in order to justify a foiling device as competitive with a conventional multihull.

What's next... a nuclear powered turbine, a warp drive, or perhaps a hyperspace particle emitter?

At least Howard Hughes actually got the Goose off the Water. Of course, he had real money, which is more than I can say for the perp of the dream scheme in this thread.

Like a teenager who always has the time to try to balance four pop bottles on top of one another, but never enough to get his homework done, you are still wasting time, Dougster. Time that could be spent in the shop building a non-existent prototype. Time that could be spent fulfilling a proof of concept effort instead of hypothesizing about off the wall, giant skiffs to go head hunting.

Did your Momma ever teach you about hard work?

 

Of course, that is exactly the point. All other things being equal, the boat with the best power to weight and power to drag ratios will win.

For sailing craft, that means High RM.

In the world of high speed on the water, no hydrofoil boat holds a water speed record that I know of. For a Hydrofoil to hold a World Water Speed Record they would have to create a special class: Hydrofoil Water Speed Record ... just the same as they do for Monohull Sailboats. Not the fastest boat, just the fastest hydrofoil.

The biggest budget on the planet once pursued hydrofoil speed ... AFAIK the US Navy has abandon hydrofoil technology ... there must be a reason.

The fastest boats on the water are planing hulls. Windsurfers, Yellow Pages, Miss Budweiser, Spirit of Australia (317.6 MPH in 1978), not one foiler of any kind. Please note that the only reason Miss Budweiser has a record is they have a special class for boats that still use propellers. It's kind of sad that Miss Budweiser and ABN AMRO ONE have to be in a special classes to hold records, but that is the fact.

The only use I can see for foils on sailboats is that they may be faster on boats that cannot plane or in conditions that are too rough for planning hulls and not rough enough to prohibit foiling. A pretty small performance envelope.

It would be far easier to engineer a foiling Catamaran or Trimaran than to get a 60' single track bi-foiler ... oops ... Monofoiler to work.

The nature of the wind and the loads involved will make the 60' foiler next to impossible.

The RM that Doug calculates for his 60' MF is at a 15deg heel to weather. That sounds reasonable enough, unless you have sailed a dinghy in a gusty breeze and waves.

Keeping the boat at a given angle of heel is tough enough when the boat's hull and rig are helping. The speed at which ballast must be shifted and sheets eased and trimmed on a 60'mf would be beyond the ability of mortals.

One of the problems the big MF faces is how to react to changes in apparent wind angle during gusts and lulls. The ability to steer with one hand, pump the sheet with the other, and move your torso to maintain balance is one of the reasons that foiling on a moth is possible. The crew outweighs the boat. To have a fighting chance, the 60'MF at 21,000# would need to have 15,000# of moving ballast on a 6,000# boat.

There is no way that a 60' boat with all the machinery to take on and exhaust water ballast, cant the keel 60deg, maintain foil trim, and trim sails is going to come in at anything close to 6,000#. Doug estimates 9500# for the boat and that cannot possibly include the hardware needed to sling the ballast around fast enough to keep the boat from crashing. It might include a 25-30hp donkey engine to cant the keel, but moving the deck ballast (8 55 gallon drums worth) back and forth on the 50 foot balance beam is going to take some serious power.

Another stumbling block (pitch-poling wave?) that prevents the 60'MF from working is that the Moth has intelligent ballast. The ballast looks ahead as is moving to counter the effects of wind and wave BEFORE the boat starts to react to them. 3700# of water sloshing around in a tank at the end of a 25 foot beam is no match for Rohan Veal on the racks of a Moth.

Since the end result is going to be a techno monstrosity that will only be somewhat faster than existing Multihulls, why would anyone invest time and money to develop the concept?

If the goal is to cross oceans quickly and safely, the effort is better spent on increasing the safety of multi's and trying to make them self right than on a Rube Goldberg 60' CKSDBMF.

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On a personal note: I respect Doug. I try to address the ideas he posts. Lately there have been some pretty lame attacks on Dough the person, not on Doug's lame idea (if you deem it so). When he finally posted some numbers to support his vision, they were accurate (as far as I can tell) and this thread shows that some pretty serious time was spent getting some ideas on paper. That deserves better than some of the comments posted.

 

The 1970/80's seems to have been the last 'boom time' for foilers. I remember the 'deluxe' ferry service from Macau to Hong Kong was by Boeing Jetfoiler. There were all sort of other routes that used them as well and not just the US Navy was building trial versions.

Now those, and hovercraft, have all been killed off by the ubiquitous catamaran. Same speed for less energy (fuel), better carrying capacity or less weather dependent ? I don't know, but something pissed on the foiler party last time around

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A quick google and I see that they haven't all been killed off by catamarans. Quite a few ferry services are still running, but with what appears to be a legacy fleet. Are there any ferry foilers in production?

 

Large monofoiler(s)

I think Sam Bradield held the record in the "B" class in speed sailing for some time with a hydrofoil. L'Hydroptere currenty holds the cross channel record, I believe.And the L'Hydroptere team has invested a fortune to gradually strip away problems and bring the boat up to a competitive level. Orma 60's are hydrofoil assisted and are without a doubt the fastest 60' multihulls-holding numerous records. Mediatis Region Aquitaine(Parliers 60' planing cat) uses rudder hydrofoils for pitch stability and holds the 24hr singlehanded record.
And the Moth is making history every day-already nearly the fastest dinghy under 20'-multi or mono.( watch the foiling 18)
You say a 60' monofoiler will be impossible to sail - I say you're dead wrong. Unfortunately, it will be a while before we find out for sure. However, there are numerous expert designers,engineers and sailors worldwide-some of whom I've talked to personally- that believe that this is possible-and that having the fastest monohull sailboat in the world is a worthwhile goal. If you can whip a few multihulls along the way all the better.And there is another point: the ORMA 60 tri or L'Hydroptere are, of course, multihulls and when raced the crews are on edge all the time fearing that the race, the boat and maybe their lives would be lost in the event of a pitchpole or capsize. The 60' monofoiler, on the other hand, being SELFRIGHTING would probably allow the crew the freedom to push the boat a lot harder. Could make a big difference.
A 60' SELFRIGHTING monofoiler that is as fast as an ORMA 60 trimaran would be a gigantic breakthru: multihull speeds on a selfrighting platform-you can't beat that.
As far as seaworthiness goes it seems to me that a monofoiler has a good chance of being able to handle much rougher conditions than ,say, L'Hydroptere. If you look at the picture in the September Sail L'Hydroptere is shown on just two foils-two surface piercing foils. That has got to be pretty hairy since the foil loading doubles in an instant on a foil system prone to ventilation in the first place. That simply would not happen on a two foil monofoiler . While maybe faster than an ORMA 60(according to Mr. Hough), the monofoiler would generally be slower than L'Hydroptere. Except if L'Hydroptere pitchpoles due to foil ventilation caused by wave action....
Some speculate that it can't be done because it hasn't been, others use facts to prove that if done it would be fast as hell. I guess the final chapter is yet to be written but one thing for sure: the reported death of the hydrofoil is a serious mis-interpretation of the facts-at least where sailboats are concerned.

 

Run its course

Just a couple of things as it looks to me like this thread is out of gas.

Self-righting is not self-crew rescuing, Doug. If the potential is to toss this boat out there where the big boys, such as the G-Cats live, then the Southern Ocean is not the place where self-righting anything is going to make one whit of difference to the crew on deck. If you go in the water and are not immediately back on board getting into dry clothing, you die... simple as that. The thrash of so-called self-righting is a wishful deceit in that regard. It will only apply to those who are below decks, behind a watertight entryway. If you biff it at speed in that water, it’s all over.

A multihull on foils is just as feasible as this pipe dream of a, BeheMOTH Skiff. (Trademarked name, by the way) More so, in fact, because at least folks have been doing them for some time now and there's a large file of accumulated knowledge to that end. The headstart, in fact, is phenomenal. Extrapolating Moth issues to a boat this size is out of your league... numbers on paper or not.

So, you still support the argument that stuff in the water does not represent a tremendous hardship for foilers? You, yourself, indicated that L'Hydroptere bit it hard in one of their speed attempts due to "something" in the water that tore-off one of the foils, so the boat had to be towed back. This is a remarkable admission from a guy who fumed so long and hard about the lack of reality in that argument.

Won’t that be a pretty site when the self righting, weighted bulb boat hits something at foiling speeds, taking out the forward foil and half the bottom of the hull with it? Do you still think self-righting is going to work as the hull volume is instantly filled with 38 degree water?

It would seem to me that being aboard a still floating multihull would, at least, afford a slender opportunity for a rescue. The long since sunken mono will offer no such protection and the boat will be lost with all the crew. You did say that the volumes present in the rack ends were only going to be sufficient to assist in self-righting, didn't you? That doesn't sound like enough flotation to hold up the full weight of the boat and its bulbed keel.

I agree with Hough’s argument that the movement of that much water on deck represents the single biggest example of non-problem solving in this whole venture. I notice that you don’t answer the argument at all in your responses. That tells us all that you have no solution that can’t be picked to pieces with thoughtful analysis. Therefore, you have no answer. Unfortunately, its not a simple problem like, “what color to paint the hulls”. If this doesn’t work, the whole thing doesn’t work. Like a helicopter with crappy rotor blades, because the designer thought he could just toss a set of planks out there and it would work.

This boat, if anyone is loony enough to build it, will be obsolete the day it leaves the dock. Or didn't you follow the illustrious racing career of the huge mono-hull from New Zealand from the 1988 America's Cup squabble?

Here’s an interesting quote from that era, which holds enormous potential value to this enterprise.
"The development program has resulted in better boat speed. But even though it's the fastest monohull keelboat in the world, the chances of New Zealand beating the cat are close to zero."

"Computer studies show that it will not be a match, but at least it will be a contest on the water," said a slightly disenchanted Bruce Farr, the designer of the Big Boat (27.43 m LWL). Farr was summarizing the situation just before the most controversial challenge in the long history of the America's Cup.

Well, as it turned-out, it wasn’t even a contest as the cat drivers had to throttle back so that the TV cameramen could still keep both boats in the same frame from a helicopter at high altitude.

Overly technical boats are easy to design around, Doug. This is mostly because they are the biggest victims of their so-called technical superiority.

Really, Doug, do you not have anything better to do? I tell you what... I’m finishing up on an 18.5’ trimaran in my shop right now. Why don’t you get in your car and come out here and I’ll put you to work on a genuine boat, designed for real people.

 

The question remains: Why spend the time and energy to develop a Monohull boat that will not be as fast as a Multihull if both boats use the same technology?

If systems can be designed and built that would make a 60' Mono on foils stable, the same systems could be used on a Multi. The Multi will be faster, since it has the ability to carry more sail.

If the design budget for a foil-borne 60+ foot Monohulled boat was allocated to self rescueing designs for Multihulls. You would have your cake and eat it too. High speed and safety in one platform.

Is it your position that Multihulls cannot be made self-righting?

Is it your position that designing all the control systems that would allow a 60+ Mono to foil are more practical and have a greater chance of success than creating a self-righting Multihull?

For someone that is obviously well read and a supporter of new technology (to the point of allowing power assisted systems on sailing boats), can you not see that trying to make a silk purse out of a pig's ear Monohull is a windmill tilting exercise hardly worthy of your time and talent?

The only thing that keeps people sailing big Monohulls are rules that prohibit Multihulls.

The statement that crews of big multi's are "on edge all the time fearing that the race, the boat and maybe their lives would be lost..." is a very accurate description of the crews on a VO70. It reflects the mood of sailors I've talked to about VO70's ... and they are far from foiling.

If you are pursuing the big mono idea because it is your choice to try find a way to make it work (while knowing that the same solutions will also work on a Multi and be faster), great, more power to you. If you think that there is a magic solution that will make Monohulls faster than Multi's, you will have to find something that would apply only to Mono's (something that would not work on a Multi). I think you are going to be tilting at windmills for a very long time.

This is a good thread. I've enjoyed the mental exercise.

Randy

 

Randy, all the analysis you have done on the theoretical monofoiler is commendable. You almost proved Dougs case (which he scaled up from magazine articles and photos). However I notice that you have aircraft experience from some of your postings. If it is all about available power and drag forces when comparing multis and monohulls with length/beam ratios in excess of 10 on centreline foils (monofoil), then I put it to you that any powered aircraft that you might design will theoretically go faster if you cut the tailplane off. Power stays the same, but drag goes down perhaps as much as 20%.
Don't give me the case that such a plane will be so unstable that it will fall out of the sky, as you have given limited thought to stability and righting moments that need an amazing degree of very rapid intelligent adjustment.
Granted after several postings (18,20,22) saying that Doug is probably on a winner, you take a new tack in posting 24 now talking about the difficulty of sloshing that much water from side to side in an intelligent manner that foresees coming variations in wind strength.
I am almost dumbfounded that your argument cannot remain coherent from one posting to the next. It is disappointing, not because you give Doug a degree of credibility he has not yet earned, but because you seem to be wavering yourself, when I expected more from you.

 

I've made one change in my thoughts. I didn't think the theory supported even the possibility of a foiling mono being as fast or perhaps faster than a multi of equal length. I've always thought and still do, that the mechanics of making it work are beyond possibility. The obvious "solution" to a Monohull being faster than a multi would be to scale up a windsurfer. The pilot would control the beast from inside the machinery 60 feet off the deck.

Since I don't have a dog in this fight (I care not if the 60'MF lives or dies), I just crunched some numbers that did not appear reasonable at first, but at the level I looked at they are indeed possible ... if the control systems could be made to work.

I don't have enough knowledge to hazard more that a guess at the possibility of building a structure that will handle the loads at anywhere near a design target of 9500# plus lead. My guess is that even the 21,000# all up weight is optimistic at best.

When I'm wrong, I'm wrong. I was wrong when I thought that no combination of plausible numbers could be made that would support the limited claim that a foiling 60' "mono" could be as fast as a non-foiling multi. I said so, and provided some thought to support my change of mind (mark your calenders!).

I've never thought that the idea of a 60' MF was a practical answer to anything. I did find it an interesting problem to look at.

Mr. Lord has come up with quite few positions and ideas that I don't agree with ... the idea of a safety belt system to keep the skipper from injuring themselves on the shrouds when a jumping foiler crashes is a prime example of a flight of fancy ... That does not mean that all of his ideas are without merit. I admire his zeal and his willingness to expose himself to critique that often leads to ridicule (I am as guilty as any). One thing is certain, as long as there are people like Doug around to provide mental challenges, it keeps my brain active. Keeping the brain active seems to prevent or delay the onset of Alzheimer's, so I hope that those people are never ridiculed into submission.

As far as the tailless aircraft being faster, you are correct. The delta wing planform is a pretty good choice for high speed craft.

Randy

 

Randy, I admire the way you explained your position in your last posting. The reason I never bothered to crunch the numbers is that I know that from a theoretical viewpoint a long skinny monofoiler (like the one that Doug proposes) would be the quickest sail craft on the water if one ignored specialized triscaphs and such designed only for record attempts in perfect conditions.
However the obvious problem not even requiring engineering or hydrodynamic analysis is that an omnipotent being would have to be the skipper and ballast. Since God has not revealed himself for a few thousand years (if at all) then I must assume that such a skipper cannot possibly exist, therefore what is the point of analysis.
I was ready to ditch all future contributions to this forum if you had come out all gung ho and tried to defend the indefensible. Any way thanks for your humbleness, I might decide to stay on now.

 

60' Monofoiler

Mr. Hough,
Man, this was a great post(see below) but whats this about selfrighting multihulls? Why go to all the trouble of building one or two more hulls and the connecting structure to make it practical
when a simple monofoiler will do the trick? Seems like a lot of trouble. A selfrighting multihull has been tried and made to work in rc models. It used a system that allowed the mast to move.And there was a system for righting a tri just posted here or on one of the other forums. The problem is that you have to loosen something up or take something apart on every system I've seen.You have to have the system work from a capsize or a pitchpole and that's a really tough problem. My position, for now, is that a selfrighting monofoiler represents the best solution to multihull speeds (or faster) in ocean going boats with the caveat included at the bottom of the first post in this thread.
My previous post sums up my thoughts regarding your comments made since the incredibly well written(go Randy!) post below. With one added note: Julian Bethwaite in his Pterodactyl planned(plans) to use on-deck movable ballast on a 60 footer.Herreshoff used on-deck movable ballast on a boat of his. And I've used on-deck movable ballast on numerous rc models including the microMOTH for almost 10 years.Saying it won't work, is not fast enough or can't be controlled etc. is just plain ridiculous. But you're certainly entitled to be ridiculous until someone actually builds a 60 footer utilizing such a system. Just don't expect me to take that kind of comment seriously.

Now this is really gutsy( and very much appreciated!):
Post#16