Ballast/Displacement Ratio-minimum for self-righting

[Doug Lord]

I've edited this question to more specifically explain what I am trying to achieve-instead of a new post. The reformulated question ignores the Ballast/Displacement Ratio.
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So I'll try again:
Assume the boat is lying with the mast more or less horizontal-maybe just the tip touching water.It is flat calm and the sails are dry(not touching the water):
1) the CG of the rig,incl. sails is 35' from the heeled CB of the hull and it all weighs 1250 lb.
2) 35X 1250=43750ft. lb.
3) the CG of the bulb is 12' from the heeled CB of the hull
4) to balance the boat in this position, the bulb would have to weigh 3646lb
(3645.834 X 12= 43750ft.lb.)
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My question is about judgement hence the desire to have an experienced designer/engineer answer:
We know it takes 3645.834Lb. to balance the boat in this position with no net RM or tendency to come upright. My question is: what multiple of this bulb weight would you use to bring the boat upright in flat water and no wind? Forget about sailing RM-it does not matter for the purposes of my
question. Forget about anything to do with the hull-it is largely* irrelevant for the purposes of this question.
* Assume the hull form contributes little to nothing to stability at any angle.
__________________

[Paul B]

What do experienced monohull designers think would be the minimum ballast displacement ratio for a fairly narrow 60' monohull with the CG of the bulb 10' below the waterline in order to self-right after the wind that knocked it down quits.You can assume very light displacement and a carbon rig. This is not the minimum ballast/displacement ratio to meet any standard or sail well : just simply the minimum to cause the boat to come back up with no wind to hold it down.
I know this is an odd request-I'm just trying to back up some research I'm doing. Thanks!


This is an idiotic question.

First, without any details of the hull shape no one can answer this. "Assume a carbon rig"? How tall, what's it weigh, etc? A 10' draft on a 60 footer?

Second, if you were doing "research" on something that has some preliminary design work done you would be able to calculate this yourself. Well, not you, but someone who knows how to design a sailboat.

Third, who wants to to stay knocked down until the wind stops?

[fng]

Or have to pull down wet sails to get upright.

[Paul Kotzebue]

Ballast / displacement ratio is not considered when evaluating stability. It's one of those ratios that are used to compare similar boats without drawing any kind of meaningful conclusion.

Every hull form has its own unique stability charactersitics. While there is no minimum ballast / displacement ratio for any given boat, there is a maximum vertical center of gravity (VCG). It is not uncommon for naval architects to calculate the maximum VCG at various drafts or displacements to meet a certain stability criteria.

Ballast does not work independently from the rest of the boat. As far as static stability goes ballast, boat, rig, etc. is all one object with a fixed center of gravity.

[sorenfdk]

This is an idiotic question.

There is no such thing as an idiotic question - only idiotic answers!

Paul B; it is clear that you know something about some things, but why do you so often have to act as an annoying know-it-all?

It is evident that we need some more information to answer the question. Please just ask for that information and leave it at that!

[Doug Lord]

Please re-check the first post-I edited it to make the question reflect the judgement I am interested in more clearly.

[fng]

At 60ft is this something that intends to go offshore ? If so you have catogory 0, 1, and 2 to comply with, and then you have to be built to iso 12215. In little old NZ vessels wanting to go offshore had to have a positive righting moment through to 115 degrees ( prior to the isaf/ iso changes )
this could be a good place to start

[Doug Lord]

At 60ft is this something that intends to go offshore ? If so you have catogory 0, 1, and 2 to comply with, and then you have to be built to iso 12215. In little old NZ vessels wanting to go offshore had to have a positive righting moment through to 115 degrees ( prior to the isaf/ iso changes )
this could be a good place to start
======================================

Thanks fng but this is not part of any design-it is a question of judgement on one specific issue and not related to any other issue.

[Paul B]

There is no such thing as an idiotic question - only idiotic answers!

You are clearly wrong. Just last week I was involved in a discussion with some business colleagues regarding the sheer idiocy of the often quoted, "There are no stupid questions."

Every person in the group was able to quickly tell an anecdote showing this quote to be, well, stupid.


Paul B; it is clear that you know something about some things, but why do you so often have to act as an annoying know-it-all?

It is evident that we need some more information to answer the question. Please just ask for that information and leave it at that!

I'll simply note here you have not answered the question either.

You have been here long enough to realize this is simply a fishing expedition where The Lord of Non-Foiling is trying to get someone, anyone, to commit in writing a number that he can use in another argument about how adding lead ballast to his proposed 60 foot foiler is a bad idea.

So if you, Soren, give an answer then The Lord will be posting all over the internet that you, Soren F. on Boatdesign.net, have calculated the need for only X and that is insignificant in the whole scheme of his self-righting 60 foot monohull foiler.

He has done this before, citing other people by taking their answers out of context, even when they ask him repeatedly to stop quoting them.


So to make things easy, and to make you happy, I will answer The Lord's initial question: 37.

[jehardiman]

I've edited this question to more specifically explain what I am trying to achieve-instead of a new post. ....snip...
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* Assume the hull form contributes little to nothing to stability at any angle.
__________________

[My emphasis in the above quote]

As pointed out, this is a contrived question. The real crux of the matter is that the hull is designed poorly, as has been stated.

Anyway, since we venture into the absurd, as long as the bulb weight is 1 mcg greater than the weight required to balance the rig on the fulcrum point as proposed, the vessel will always attemp to right. Of course the randomness of the environment will make it more or less successful, but in a perfectly benign environment as proposed it would always come to upright, it is just a matter of time. If you wanted it to come up in a given time you could calculate the mass moment of gyration and then work the additional weight needed (including resiting moments due to roll velocity on the laterial plane and the rig). Of course it may roll to the other side and then oscillate for a long time depending on damping, but it will eventually reach upright equlibrium. What is an acceptable length of time to reach upright stability is the question you are really asking.

Of course just having a microscopicly small righting moment will not give this vessel any abilty to carry sail. But that does not seem to be the issue here.

[sharpii2]

Hi, Doug.

There are two kinds of stability.
1.) is form stability, based on the sectional shape of the hull, and
2.) is pendular stability based on the weight distribution of the craft as a whole.

Pendular stability is the type you describe. It is like a buoy or a fishing bobber, where the Center of Buoyancy (CB) is above the Center of Gravity (CG) when the craft is upright.

Form stability is usually when the CG is above the CB and, as the craft heels, the CB shifts to leeward faster than the CG. Obviously, there is a limit to how long this can go on. This is generally governed by the Beam of the craft. Eventually the CG shifts to leeward past the CB and then the craft has negative stability and capsizes.

Most seagoing monohulls use a combination of the two types of stability. The form stability is for sail carrying ability, because it is usually near its greatest while the craft is upright enough to make sail carrying practical, say 45 deg. heel or less (the pendular stability is helping here too, but to a lesser extent). Once the heel gets much beyond this point, say 60 deg.,the form stability starts to run out. At this point the pendular stability starts to kick in. But in all but the most extreme types, that starts to run out too. This is because the CG in these craft is still above the CB, but to a lesser extent.
Once that happens, the craft continues to capsize until completely upside down. But this condition doesn't usually last. Usually it was a wave that capsized the craft in the first place. That being so, it is all but certain other waves will hit the craft while upside down. This is where the magic comes in. If the wave that capsized it had to knock it down to 120 deg. heel, the wave that hits it while capsized has to only knock it past 60 deg to put it in a position to right itself. The righting process can start very slowly (assuming the wave that hit the craft had just enough energy to push it past 60 deg.), but as the boat becomes more and more righted, the righting moment increases until the craft reaches its maximum righting moment at about 60 deg. heel from upright. Then it starts to diminish until the craft is upright.

There are two extreme types of hulls where this is not true. The first are multihulls, which have only form stability, but an extreme amount of it. The second are plank-on-edge monohulls which have almost exclusively pendular stability.

The plank-on-edge monhulls had very narrow beam, comparable to hulls on a multhull. Their draft was often greater than their beam. The problem with these boats was their maximum righting moment was at 90 deg heel and diminished progressively after that. At about 60 deg heel from upright, they had already lost half their righting moment. And this was with the masts canted up only 30 deg from the waterline. The solution, of course, was to add more ballast (my guess would be at least 100% more). Then reasonable righting moment could be had to carry sail at a reasonable amount of heel, say 45 deg or less.

I only bring this up to give you an idea of what you're up against.

To answer your question, I propose the following formula:

((Righting Moment - Capsize Moment)/(Capsize moment))*((2pii*Capsize Arm)/32.2)

This will give you an approximation of how long it will take for your craft to right itself in seconds, under the following assumptions:

1.) Once righted, craft has no momentum left to heel it over to the opposite side, and
2.) There is no appendage friction of any kind.

Both of these assumptions are obviously false, but I think this formula could still be useful to help you get to where you want to go.

[Doug Lord]

Thanks very much, Sharpii2! I'll work with this a bit and see what I find. I appreciate your effort.

[Paul Kotzebue]

To answer your question, I propose the following formula:

((Righting Moment - Capsize Moment)/(Capsize moment))*((2pii*Capsize Arm)/32.2)

This will give you an approximation of how long it will take for your craft to right itself in seconds, under the following assumptions:

1.) Once righted, craft has no momentum left to heel it over to the opposite side, and
2.) There is no appendage friction of any kind.

Both of these assumptions are obviously false, but I think this formula could still be useful to help you get to where you want to go.

How did you derive your proposed formula? You did not specify units, but I'm assuming the moments are ft*lb, capsize arm is ft, and 32.2 is the acceleration of gravity in ft/sec^2. That being the case, the answer to your formula will be in seconds squared, not seconds.

[booster]

Hi!
Kotzebue and shapii2. Seems that the formula by sharpil2 needs a = to be a real formula. Perhaps something on the left side of the = helps it to be in seconds? For once I feel for the canting-keel-man who must be struggeling with the equation...
Regards,
Booster

[Manie B]

sharpii2

thanks for a civil answer, nice to see gentlemen on the forum

a good read - and a good answer to what was intended as a relatively modest straight forward question, its nice to have an answer that can take one back to basics

[tspeer]

...Assume the boat is lying with the mast more or less horizontal-maybe just the tip touching water.It is flat calm and the sails are dry(not touching the water):...My question is: what multiple of this bulb weight would you use to bring the boat upright in flat water and no wind? ...

I'm not sure you're asking the right question. The condition you cite is for maximum righting moment. But there are two other cases that are equally important, if not more so.

The first is the slope of the righting moment curve at zero heel angle - the initial stability. Alternatively, you may use the righting moment at some modest heel angle, say, 15 - 20 deg. This area is important because it determines how much sail area you can carry under the modest conditions when the boat will be most efficient.

Then there's the maximum righting moment, which largely determines how much energy is required to capsize the boat for wind-induced capsize. It also determines how much heeling moment can be tolerated for a wind-driven capsize, of course.

But I think the point you're really looking for is the heel angle at which the righting moment vanishes. The larger the heel angle, the smaller the region of upside-down stability and the more likely the boat will flip right-side up when placed upside-down in a wave-induced capsize. A wide boat, even with a heavy bulb keel, can have almost as large a range of stability upside down as right-side up - much like a multihull in that regard. Hence the Open 60's that have capsized in the Southern Ocean and stayed upside down. I think a lot of designers shoot for something like 140 degrees as the point of vanishing stability.

So if you've calculated the maximum heeling moment that can be applied, it's not so much a matter of making the bulb some multiple of that moment, but rather one of looking at the range of positive stability. That could be achieved with a heavier bulb for a given hull form, or it may be achieved by the shape of the hull, freeboard and deck house.

[Doug Lord]

Thanks Tom and Jehardiman-and everybody who has tried to help!

[BeauVrolyk]

Doug,

My Father used to answer questions like the one you asked, when I was very young, by saying: "How long is a piece of string?" His point being, you haven't provided enough information in the question to elicit a useful answer.

I think you need to decide how quickly you want this mythic boat to right herself, how much she'll resist heeling to begin with (so she can actually sail), and what sorts of seas your boat will be sailing in.

In the process of answering these additional pieces of your question, you'll solve your initial query. This is because I believe (I don't know, but I'm pretty confident) that whatever righting moment you'd want from the keel, for any reasonable boat that a normal sailor would actually want to sail on, would completely swamp the forces you're discussing.

For what it's worth, most folks start with a certain desired stability, either for speed or comfort, and then work backwards to get the ballast needed to provide that stability. Also, as others have said, the designer includes the form stability as well as the stability from ballast. While it may be intellectually interesting to you to know the balance point, and you might be tempted to just add a little extra weight to get a boat that is quite light and will eventually self-right, almost no one actually wants a boat like that.

I am reminded of the time my friends took a picture of me and two of my friends standing on the side of the keel of a Santana-20 in the San Francisco Bay. It had broached badly and wasn't coming back up again (with its chute flogging sails full of water) even with nearly 450 extra pounds standing upon the keel. A great example of not enough ballast stability.

[Paul B]

Also, as others have said, the designer includes the form stability as well as the stability from ballast.


What you and other like Tom are missing is Doug's mythical boat has the hull flying above the water. He is thinking "giant foiling Moth". So he is not concerned about form stability, there is virtually none.


What he is looking for is a simple number or very simplistic (linear scaling) formula that he can use in his on-line arguments when people point out the need for lightness in a foiler and how the idea of ballast works against this.

He wants to be able to throw out a reply to anyone mentioning this fact by stating something like, "Tom Speer at Boatdesign.net calculated I only need a bulb weighing 37, so by my other formulas this PROVES my theory will be the greatest thing ever on the water!"

So any mention of form stability or other actual design considerations are meaningless to his quest.

[masalai]

On the original topic of the thread (for which I continually get "activity alerts") - - - - If you cannot keep the boat reasonably "upright" then you should not be operating it...
Competence is apparently not one of your things so be content to sail a dingy that you can get "upright" when you tip it over... AFTER you have successfully completed some training... and assessment... then, if your shrink and trainer will decline to go sailing, then find something else like flying piece of lead...

[jehardiman]

What you and other like Tom are missing is Doug's mythical boat has the hull flying above the water. He is thinking "giant foiling Moth". So he is not concerned about form stability, there is virtually none.


What he is looking for is a simple number or very simplistic (linear scaling) formula that he can use in his on-line arguments when people point out the need for lightness in a foiler and how the idea of ballast works against this.



Actualy, I think you don't him enough credit and have missed the thrust of his concept development.

Back in the late '60's there was concept put forward for high speed (100+ knots) sailing, a non-lifting pod foiler. This foiler used a lifting wingsail (some concepts had them Lighter Than Air) , a streamlined pod and a submerged foil as a depressor. Think of a kite sailer on a board with only a deeply immersed foil holding him down. He can get more speed because the foil can generate much more down force than the boarder, who only has his weight. And righting moment for sail carrying ability is not needed because instead of pushing the vehicle over, it is pulling the "boat" up.

However, when the pod is resting at zero speed in the water, there is the need for stability righting moment. I think Doug's question is how much weight is neccessary in the foil to return a cylinderical pod upright in a reasonable amout of time.

Here is a modern take on the concept using multiple hull instead of just one. From an aerodynamic, structural weight, and "crash and burn" impact point of view a single "hull" pod would be perferable.

http://www.gizmag.com/go/3272/

At least that is where I saw in the question going.

[Paul B]

Actualy, I think you don't him enough credit and have missed the thrust of his concept development.

Back in the late '60's there was concept put forward for high speed (100+ knots) sailing, a non-lifting pod foiler. This foiler used a lifting wingsail (some concepts had them Lighter Than Air) , a streamlined pod and a submerged foil as a depressor.

I think Doug's question is how much weight is neccessary in the foil to return a cylinderical pod upright in a reasonable amout of time.

At least that is where I saw in the question going.


While the concept you put forward could be interesting, it is not what Doug has been on about for the past 8 years or so, and currently.

You need to go read all the wackiness in his posts of the past few years before you start in on who has missed the thrust of his concept.

[Doug Lord]

Actualy, I think you don't him enough credit and have missed the thrust of his concept development.

Back in the late '60's there was concept put forward for high speed (100+ knots) sailing, a non-lifting pod foiler. This foiler used a lifting wingsail (some concepts had them Lighter Than Air) , a streamlined pod and a submerged foil as a depressor. Think of a kite sailer on a board with only a deeply immersed foil holding him down. He can get more speed because the foil can generate much more down force than the boarder, who only has his weight. And righting moment for sail carrying ability is not needed because instead of pushing the vehicle over, it is pulling the "boat" up.

However, when the pod is resting at zero speed in the water, there is the need for stability righting moment. I think Doug's question is how much weight is neccessary in the foil to return a cylinderical pod upright in a reasonable amout of time.

Here is a modern take on the concept using multiple hull instead of just one. From an aerodynamic, structural weight, and "crash and burn" impact point of view a single "hull" pod would be perferable.

http://www.gizmag.com/go/3272/

At least that is where I saw in the question going.
==============================
Jehardiman, "B" has no clue regarding the question I asked. Your suggestion is much closer. I wanted to look at this in a very limited way.

-----------------
Thanks, Masalai.

[sharpii2]

Thanks very much, Sharpii2! I'll work with this a bit and see what I find. I appreciate your effort.

Hi again, Doug.

With great embarrassment I have to admit a few mistakes I made on my post.

1.) The Plank-on-Edge heeled over 60 deg would still have about 86% of its righting moment left, not 50%. Heeled over 30 deg, then it would have 50% of its righting moment left

2.) The formula I gave you is not quite right. You need the square root of that formula to get your time to return to vertical.

Bob

[Doug Lord]

Hi again, Doug.

With great embarrassment I have to admit a few mistakes I made on my post.

1.) The Plank-on-Edge heeled over 60 deg would still have about 86% of its righting moment left, not 50%. Heeled over 30 deg, then it would have 50% of its righting moment left

2.) The formula I gave you is not quite right. You need the square root of that formula to get your time to return to vertical.

Bob
===================
Thanks, Bob-haven't had a chance to spend any time with it yet-but I will.

[sharpii2]

Hi, Doug.

I was just thinking.

Have you considered a 'V' foil?

What I was thinking of is a very narrow monohull which sat inside of a large 'V' foil which would have a 60 deg dihedral. This way, as the boat heels, the leeward arm of the 'V' would be providing most of the lift. The windward portion would be mostly out of the water. The keel bulb would, at this time, be about half its depth to windward, further enlarging the righting arm. The tips of this 'V' could be joined wing beam like structure which could double as a hiking board.

The beauty of this system is that most of the weight as well as most of buoyancy would be reasonably close to the water surface. The goal here would be to reduce the whetted surface of the hull (it would probably never be completely free of the surface) and to increase the righting arm of the system.

This system would be quite resistant to capsize due to the enormous dampening power of the arms of the 'V' foil as well as the long cross beam.

[Doug Lord]

Bob, interesting idea-can you draw a rough sketch?
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The type of problem I brought up earlier could occur on at least a couple of different types of boat that I'm interested in to one degree or another. The foiler concept Mr. "B" brought up doesn't fit the bill because it uses a very wide beam with buoyancy built in and would be self-righting with very little ballast because of the "assist" in righting from a pitchpole or capsize of that buoyancy.
The concept I'm working on that inspired this thread doesn't have that built in buoyancy so would sometimes only be wholly dependent on the ballast in the bulb to right from a knockdown to at least 45-50 degree angle of heel where the primary means of RM would become effective again. It would be 100% dependent on the bulb to right from a pitchpole.
The problem is that the sailing RM is not generated at all or very little by the bulb weight.
I was trying to find a way to think this out clearly by separating the functions intially but it seems I've just made it more complicated for some to envision. Oh, well...

[sharpii2]

Hi, Doug

You asked me for a sketch of my idea.

Here it is:

I know about as much about hydrofoils as you know about leprichans, so I have no idea if the proportions are anywhere near right. The all up displacement is around 1500 lbs.

[Doug Lord]

Bob, looks like it has potential. If it was me I might make the beam wider, foils shorter and consider a canting keel. I'm convinced a self-righting foiler is possible though I think I would lean toward just two foils. Thanks for the sketch and the effort!

[Perm Stress]

Calculating how much bulb (or any other ballast to that end) is necessary to counterbalance the rig is valid and fast way to get first approximation of ballast weight necessary for SAFETY, and have nothing to do with any PERFORMANCE.
For example, :
* For Micro class (5.5m long) sailboats there is a requirement to remain in equilibrium or right themselves from mast horizontal position, with sail set + 18 kg of additional weight on the spinnaker hallyard.
* There was similar requirement in old IOR rule: if certain stability parameter in formula is not satisfied, it was necessary to make actual stability test with mast horizontal, and additional weight on mast top; weight calculated according to dimensions of yacht
* There is something similar in most modern handicap or development class rules

This way, actual residual stability at 90 degrees of heel is measured (not, by the way, MAXIMUM righting moment, it could happen anywhere from ~15 degrees to 90 or even more depending on general architecture of boat).

Now down to actual question of "What multiple of bulb weight, which just balance the rig, is actually necessary?".
The real answer is "Nobody really know".

However, some starting information could be found in Kurt Reinke book "Yachtbau". I believe it is also published in English. in this book, he explain this kind of calculation and give a graph for required residual righting moment, depending on hull length and area of operation, for monohull yachts.
However, he also point out, that this calculation is only preliminary, and is not be compared with results of real detailed stability calcuation.

[sharpii2]

Bob, looks like it has potential. If it was me I might make the beam wider, foils shorter and consider a canting keel. I'm convinced a self-righting foiler is possible though I think I would lean toward just two foils. Thanks for the sketch and the effort!

Hi, Doug.

I don't think a canting keel would work well as the majority of the weight oh the boat would be high above the waterline, magifying the effects of any heeling.

What I tried to do with my sketch was to use the hull itself asshifting ballast.

I do sympathize with your critisism that the foils may be too large.

Perhaps the same size crossbeam could be used with smaller foils canted at some angle at each end of the beam.

Another possible critisism of my idea is that the boat would have to heel a lot (30 deg) before the Center of Lift moved to leeward. This was intended, as to use the ballast bulb itself as shifting ballast, with the added effect that it would be automatic.

This has the bad effect of creating a downward force conponent from the rig on the leeward side. Perhaps the angles of the foils could be reduced to 20 or even 15 deg.

Also, the rig could be designed to cant to windward. This should not be any more difficult to design than a canting the ballast keel.

Running my own formula with your question, I came up with about 3.35 seconds, with no friction and no dampening, do to foils and other appendages, with a 25% increase in the ballast bulb. With friction and dampening, it could take three to five times as long.

[Doug Lord]

Bob, thanks for your calculation and the configuration ideas.
Below are some very rough sketches showing a small and large buoyancy assisted self-righting foiler similar to the one "B" comented on-both with 110 degree canting keels. The third sketch is one of three versions of a boat I am building now-and the motivation for this thread. It is an experimental configuration where lead slides side to side inside a sealed "wing" supported by trapeze wires- and the wing slides as well. It is the "turbo" version of this concept specifically designed to be self-righting from a capsize or pitchpole. In either case the ballast bulb will be the prime mover in getting the boat back to a position where the sliding "on-deck" ballast would be effective again. It is possible that in the capsize case the buoyancy in the sealed wing could be brought into play. But the worst case capsize scenario is with the wing to windward so there would be little wing buoyancy in the water and the wing would be sticking straight up with the boat at 90 degrees. Again, I may find, experimentally, that in that situation the wing could be centered and the buoyancy in the wing would then add to RM. But in a pitchpole situation ballast is the only way it will right.

(red canting keel sketch NFlutter-60' Moth)

[Gary Baigent]

Doug, forget the bloody lead, go to beam for stability and power, and have spread foils off the floats, amas. Maybe I have an unhealthy fixation against carrying ballast (unless it is water and can be quickly dumped, or taken on for the rare occasions when it is needed) - and I still think Cheezilla is wrong in carrying heavy weight on an extremely wide and super stable platform - they don't need it IMO, do some calculations: 1 - to get equivalent power from sails on Alinghy type, weighted down with ballast to windward .... and then forced to carry extra sail to compensate for this weight, higher rig, much higher loads, more weight, more windage, more drag, heavier gear to operate big rig, motor weight in fixed position, this is keelboat mentality with resulting lower Bruce Number..... and 2 - a pared down Cheeze, still the super wide platform, no ballast, less gear, less weight, less rig height (but still pretty damned high of course) less sail area, less windage, less loads ..... and higher Bruce Number - as Uffa Fox said, "The only place where weight is good is in a steam roller."
Number 1 is for brute power and complexity ..... and 2 is for refinement and efficiency. Who is right, bludgeon or rapier?

[Doug Lord]

Doug, forget the bloody lead, go to beam for stability and power, and have spread foils off the floats, amas. Maybe I have an unhealthy fixation against carrying ballast (unless it is water and can be quickly dumped, or taken on for the rare occasions when it is needed) - and I still think Cheezilla is wrong in carrying heavy weight on an extremely wide and super stable platform - they don't need it IMO, do some calculations: 1 - to get equivalent power from sails on Alinghy type, weighted down with ballast to windward .... and then forced to carry extra sail to compensate for this weight, higher rig, much higher loads, more weight, more windage, more drag, heavier gear to operate big rig, motor weight in fixed position, this is keelboat mentality with resulting lower Bruce Number..... and 2 - a pared down Cheeze, still the super wide platform, no ballast, less gear, less weight, less rig height (but still pretty damned high of course) less sail area, less windage, less loads ..... and higher Bruce Number - as Uffa Fox said, "The only place where weight is good is in a steam roller."
Number 1 is for brute power and complexity ..... and 2 is for refinement and efficiency. Who is right, bludgeon or rapier?
===============
Hey,Gary-I think you're wrong about ballast-look at Hydroptere(fastest sailboat on the planet)-she carries a ton+ of ballast. Look at the Tornado-50% of its sailing weight in movable ballast. The 40' Aussie foiler Spitfire carries 30+% of her weight in ballast.
------
But all that is a different subject: what I'm working on are ideas to produce(for experimental purposes, initially) extremely fast boats/foilers that can also be self-righting and very easy(if terrifying) to sail. Ballast(traditional and on-deck; water and lead) can help achieve this if extremely carefully designed.
The boat with the sliding wing/inside sliding lead ballast creates more RM than a single man on a trapeze ,yet does it in a much more aerodynamically friendly enclosure that is bound to significantly reduce drag. It seems to me it is worth investigateing the potential of this application of movable ballast on a self-righting platform. One of my definitions of "having your cake and eating it too" is a monohull boat as fast or faster than a cat which is also self-righting. It is-to me- a worthwhile pursuit.

[Gary Baigent]

Doug, I have nothing against water, (or movable and necessary human ballast) and with water you could perhaps take on or dump it with your mono tip truck, but have an aversion to lead, (and more so to wacko lethal chemicals of course) which you will be forced to carry all the time. Equals real slow in some conditions.
On the point of Hydroptere, yes, she cranks a tonne of water out to windward - but look at her low rig, (and can you feel those monstrous loads? - because they couldn't carry anymore sail with out the thing turning to confetti flotsam) and look at the fresh conditions she requires to achieve her (fantastic) speeds. She is purposely set up for high speed runs and I believe she is right on the ragged edge of top performance, sail carrying area ability and structural soundness - and congratulations to the team for succeeding on this dangerous tight rope. But what is she like in lighter conditions? Even dumped water, can't carry much more sail.

[Doug Lord]

Doug, I have nothing against water, (or movable and necessary human ballast) and with water you could perhaps take on or dump it with your mono tip truck, but have an aversion to lead, (and more so to wacko lethal chemicals of course) which you will be forced to carry all the time. Equals real slow in some conditions.
On the point of Hydroptere, yes, she cranks a tonne of water out to windward - but look at her low rig, (and can you feel those monstrous loads? - because they couldn't carry anymore sail with out the thing turning to confetti flotsam) and look at the fresh conditions she requires to achieve her (fantastic) speeds. She is purposely set up for high speed runs and I believe she is right on the ragged edge of top performance, sail carrying area ability and structural soundness - and congratulations to the team for succeeding on this dangerous tight rope. But what is she like in lighter conditions? Even dumped water, can't carry much more sail.
================
A couple weeks ago: 40 knots boat speed in 15 knots: 2.5 times windspeed!

[Gary Baigent]

Yes, definitely incredible performance - but she achieved that because the boat is so efficient, namely because she is light, super wide and has very clean air foil rig (but could still be better IMO) and creates an apparent wind that has to be .... say around 25 knots - plus I bet they didn't have their full load of water aboard.

[Doug Lord]

Yeah, I doubt they had any ballast on board that day. The bottom line is that while there are lots of ways to do high performance sailboats I think the use of ballast is pretty well required in a self-righting high performance boat-particularly if it is a monohull that one wants to sail at multihull speeds. The question is how little ballast can be used- and it seems to me you have to separate out the functions ballast is applied to:
1) sailing RM
2) righting from approx. 90 degrees to the point where #1 takes over again....

[Brent Swain]

The buoyancy in deck structures has a huge effect on ultimate stability. A beachball can be 100% self righting with a tiny ballast ratio, but a raft can remain inverted indefinitely with a 75% ballast ratio.

[sharpii2]

Bob, thanks for your calculation and the configuration ideas.
Below are some very rough sketches showing a small and large buoyancy assisted self-righting foiler similar to the one "B" comented on-both with 110 degree canting keels. The third sketch is one of three versions of a boat I am building now-and the motivation for this thread. It is an experimental configuration where lead slides side to side inside a sealed "wing" supported by trapeze wires- and the wing slides as well. It is the "turbo" version of this concept specifically designed to be self-righting from a capsize or pitchpole. In either case the ballast bulb will be the prime mover in getting the boat back to a position where the sliding "on-deck" ballast would be effective again. It is possible that in the capsize case the buoyancy in the sealed wing could be brought into play. But the worst case capsize scenario is with the wing to windward so there would be little wing buoyancy in the water and the wing would be sticking straight up with the boat at 90 degrees. Again, I may find, experimentally, that in that situation the wing could be centered and the buoyancy in the wing would then add to RM. But in a pitchpole situation ballast is the only way it will right.

(red canting keel sketch NFlutter-60' Moth)


Hi, Doug.

From your third sketch, I can see that your idea is probably workable. At least in theory.

The only problem I see is the slow reaction time.

Lulls in the wind can be just as deadly as gusts.
Racing dinghies have capsized to windward.

I have great skeptisism that you will be able to kant the ballast bulb the correct direction (windward for a gust, Leeward for a lull) quick enough to keep things under control. It will take an enormous amound of force to kant this keel (dozens of tons, by my reconing). Especially as far as you want to, 90 deg to either side.

I think it would be instructive to try to sketch the hydraulic system to do this as well as all the pumps and valves. Hydraulic systems trade force for time. The more force needed for a given power imput, the greater time that is needed to accomplish the job. This creates slow acting systems.

To speed things up, you need greater power imput. This applies to movable water ballast as well. And this greater power imput will inevitatably increase weight. And all this weight will be where it will be contributing little or no righting moment.

The big problem of trying to imitate a Moth foiler is that the huge movable ballast, the crew, which is as much as one and a half to two times the weight of the craft, can move about quite quickly.

The dinghy sailing people I have known are quite nimble and quick. This is almost impossible to imitate with robots.

[bistros]

Hi, Doug.
The big problem of trying to imitate a Moth foiler is that the huge movable ballast, the crew, which is as much as one and a half to two times the weight of the craft, can move about quite quickly.

The dinghy sailing people I have known are quite nimble and quick. This is almost impossible to imitate with robots.

I've been trying to get this point through to Doug for a long time, and you've missed a critical component.

Dinghy sailors, especially those of us who sail high performance boats have to be well AHEAD of ambient conditions - reacting to conditions results in capsizes - you have to ANTICIPATE and prepare in advance of problems to prevent trouble. This is where feedback loop based control systems fail. The Moth wand systems that function are placed as far ahead of the mainfoil as possible to reduce hysteresis as much as possible.

Part of the evolution of control systems for high speed boats is simplification where possible, reducing interaction required to allow the operator to keep his head out of the boat as much as possible. Cat rigs, wands, pitch adjustment by crew weight etc. all contribute to simplifying the potentially complex into a manageable amount of variables.

Optimizing the number of complex things that can be handled autonomically by crew weight is critical. By accumulating time in the boat, many control functions become automatic and unthought - someone like Bora Gulari does not have to consciously think about pitch plane adjustments while optimizing roll plane windward heel - it happens without conscious effort.

I know this discussion started as a poorly expressed desire to isolate roll axis self righting from righting moment, but in my opinion the whole topic is moot. Small boats handle both righting moment and capsize recovery by crew weight manipulation - and it is the most flexible and optimum use of that weight which enables the performance these boats are capable of.

Adding lead (or water, or batteries or whatever) is 180 degrees out of phase with optimizing performance in small boats where the crew makes up more than 60-70% of the sailing weight of the boat. As boats scale up in size, and crew's effect on these issues is moderated, these other methods of addressing the issues make more sense.

--
Bill

[Doug Lord]

Hi, Doug.

From your third sketch, I can see that your idea is probably workable. At least in theory.

The only problem I see is the slow reaction time.

.
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Thanks, Bob. Reaction time is interesting-as the boat gets bigger the time you have to react generally increases. I've used the on-deck movable ballast on numerous monohull models and boy that is tough(and fun). It's the RC helicopter of RC sailing and takes plenty of time to get the hang of. On both the versions in the 22' range(the two top photos) the weight is designed to move faster than a crew could move. That fact
and the model experience leads me to believe that on-deck movable ballast(coupled in some cases with a fixed or in one larger version,a canting keel) will work well in a range of dinghies from 12' to 22'. My new boat will experiment with this system and I'm going to convert a smaller two person dinghy and see what happens. Couple this with my firm conviction(backed up by lots of numbers) that a self-righting foiler is possible things get interesting.
The bottom illustration above (by NFlutter) is of a 60' Moth described in detail elsewhere in this forum. The 110 degree canting keel in that boat would
move at least as fast as a Volvo 70 keel since the loads are similar. The on-deck movable water ballast would move very fast. Both myself and a friend who is a well respected NA and ME( and has looked at the concept) believe it could work but that it is right on the edge of what is possible. Another individual looked at the concept and found that it had the potential to be at least as fast as an ORMA 60 tri flying a hull with 70% of the tri supported by a foil. So this technology could work but requires lots of experimental testing,re-testing and testing again.
Julian Bethwaite,no less, believes that an on-deck movable ballast boat in the 60' range could work as well.
As for me, I'm concentrating on small boats and will have results as soon as I can.
Bob, thanks again for your thoughtful and in-depth responses.