Movable Ballast Multihull Design and Construction

system · May 5, 2004, 7:48am

Movable ballast in multihulls has great potential but is generally more expensive than other means of increasing righting moment substantially.
The two major system types include:
A) A carbon rack designed with a module located on the centerline containing the winches. The winches move the whole PBS(Power Ballast System) system fore and aft and a cart or rack +cart side to side.A rack plus cart that moves side to side together can allow more righting moment within the F48/min40 rules so look carefully at this design option. This system requires that the boat is designed for it and it requires room at the center of the boat for a module to recess into the hull. The whole PBS is mounted on a carbon tube that allows the unit to move fore and aft; this also allows the unit to be easily removed. Guyatt 280 winches are ideal for weight up to three pounds because of their power and speed.The battery is located in the cart that moves and is part of the ballast.Disadvantages of this system(aside from weight) are that the boat can still capsize/pitchpole and will likely turn turtle when it does so. Therefore the PBS module that you build must be absoluely watertite. If the design is done properly the module should float above the turtled waterline but it will be close enough to be soaked by waves.
This kind of system can be a lot of fun to sail because you have just about the same freedom of movement with the PBS as you do with the crew on a beach cat.It is expensive and requires two Guyatt 280’s ,two(+ one short ) carbon tubes ,the center module, the cart and two end pieces to hold the carbon tube together.You can support the ends of the rack by trapeze wires to the mast as long as they are clear of the main.The cart needs to be designed to slide on the carbon rack(you can build in guides or recesses for the track) and can use a wire or small carbon tube as a backup guide.
The boat needs to be designed with the extra displacement required by the total amount of weight of the system; if it is not the system will NOT work.
Just as an aside: a tri can be set up so that the CB of the AMA is just slightly forward of the CG of the whole boat: this creates a natural pitch resistance. Too much separtion can result in a pitch up as the boat tacks.This is important in the system described below.
B) Canting keel applied to a multihull-cat or tri: this system is just now in the design stage unlike the previous system which has been built and tested. I’ve done a lot of work recently incorporating a canting keel in a small very narrow hull.It dawned on me that since I was able to make that work the same thing could be done on a model tri. On a cat the system is easy with the canting keel pivoted above the waterline on a carbon tube mounted on a module centered on the forward cross arm. The beauty of either application-cat or tri -is that the system MAY also right the boat! This has not been tested yet but there is no reason someone can’t try the idea on their own.But again, the boat must be designed for it. The tri version using a canting keel -so far- has no way to move the weight fore and aft-a real disadvantage! The cat version moves in both directions. I can send a small hand sketch of both if you’re interested in exploring this further. Keep in mind that you can just use a fixed keel but it offers far less speed potential because the weight can’t be moved significantly far to windward. Any system using a bulb is going to be slower than one that doesn’t but if you design your system to be able to right the boat then that may be worth it.

You don’t have to be a rocket scientist to determine how great the potential is for this kind of system-just two pounds extra weight can DOUBLE power to carry sail-a HUGE increase in potential speed. With the systems removable light air performance in steady conditions is improved and in fluky conditions it might pay to leave the weight on the boat or just remove part of the ballast.
An on-deck “Trapeze Power Ballast System” can be a lot of fun to sail with but you have to make sure that you design your boat for the extra displacement required or you’ll be wasting your time. I can help you think it out with sketches ect.

edt:sp
Doug Lord
–High Technology Sailing/Racing

Tranth · May 5, 2004, 4:33pm

INFOMERCIAL…
P.S. I think I’ve heard this before somewhere…

19 out of 7 people have trouble with statistics

system · May 5, 2004, 4:52pm

Any Class of RC boat “sailing at the moment” will benefit greatly by adding TWO POUNDS of ballast onto its Keel!.
On the Keel is exactly the best place to have extra ballast, NOT above the LWL, on the DECK.
Most boats “sailing at the moment” have a keel that is removeable, or the extra ballast could be fastened to the existing one and be detatched for light airs.
Pick any boats specs and work out the RM for an “on deck” 2lbs ballast, then do the same for a “on keel” 2lbs ballast, or are you so sold on this idea that you didnt want to try?.
edit,
A couple of weeks ago you asked a question about " water-proof connectors" you needed to connect a “small battery” and didnt know how to keep the water out.
Well, now it seems this “small battery” has grown in size and is now a 2lbs weight.
I gave you the answer to your problem, but I will make Damn sure I dont give you any more!!!.
You say "I can help you think it out with sketches ETC I bet you can, because thats all you have!.
YOU want feedback from the forum, to help you to make a Commercial Product, well, no more from ME!!.
John.

system · May 5, 2004, 5:55pm

Thanks JD. On a multihull if you use a Power Ballast System it is important, for best performance, to have no bulb underwater. Further, it is important to have the ballast be able to move quickly fore and aft as well as the maximum distance possible side to side.
If you compare the righting moment generated by 2 lbs. placed on a fixed keel fin to 2lb.s placed on a Power Ballast System at max extension the righting moment of the latter is exactly DOUBLE the fixed keel righting moment.
Fixed keel or more likely canting keel ideas may have some merit in training but I rather doubt the value compared to a full max PBS or foil system.

Doug Lord
–High Technology Sailing/Racing

system · May 5, 2004, 6:06pm

My dear friend[:-banghead]
who cares???[^][:-boring][:-boring][:-censored]

We’ve heard enough of this crap…blah blah blah blah-------->ENOUGH[:-boring][:-boring]

[:-captain]-----------[:-pirate]

[:-captain] @----[:-pirate]

[xx(] [B)]

[:-pirate]

Yours

ADLA

Keep your friend close…but keep your ennemies even closer…to the one—>wanna live with me?

system · May 5, 2004, 6:10pm

So now you are saying that a Canting Keel is NOT the best thing on the Planet for all RC boats?.
after boring us half to death about the merits of them,YOU are finally admitting, that YOU have found a gap in YOUR market!!!.
I am really looking forward to you getting your “SUPER COMPUTER”,unquote, then you will run out of excuses for no photos etc, but we will not see anything sailing will we?.
You are nothing but an information Leech, bad enough, but you never do anything with it.
END of conversation; no more EVER!! IF you answer, it will be a waste, I will NOT be reading it, or any more of your pathetic drivel.
John.

system · May 5, 2004, 6:15pm

go JD[:D], go JD[:D], go[:D][:D]

ADLA[^]

Keep your friend close…but keep your ennemies even closer…to the one—>wanna live with me?

Dick_Lemke · May 5, 2004, 6:57pm

<blockquote id=“quote”>quote:<hr height=“1” noshade id=“quote”>Originally posted by lorsail

Fixed keel or more likely canting keel ideas may have some merit in training but I rather doubt the value compared to a full max PBS or foil system.
<hr height=“1” noshade id=“quote”></blockquote id=“quote”>

Hmmmm - a strange and unexpected departure from your “in-your-face-don’t-know-what-you’re-talking-about” comments regarding the suggestion to Cougar about smaller IOM rigs/sail area and a trainer keel with lead.

Since I made that comment, and you said how ignorant I was to make such a post, we seem to be hearing the sound of “tap-dancing and soft shoe” as your position, like the weather and wind, changes on a daily - perhaps hourly basis.

In posts following my suggestion, you (and Matthew) have NOT responded to my question why a 300-400 square inch sail area wouldn’t work for training. You since then, have posted that a canting keel with lead might be the best solution for a trainer, and now it seems you might be admitting that perhaps even a fixed,(but changeable foil with a lead bulb) might have some merit in training.

Unfortunately, you spoil your opinion, and you still feel the best answer is PBS and/or foils - both of which are
…currently not available,
…are for only experienced builders,
…must have the proper hull design, and
…even if they were available, you admit to their significantly higher (perhaps as much as $800 more - depending on number of winches and radio channels required) costs.

Exactly which music are you currently “dancing to” if I may ask… what happened to the “postively, the fastest, most fun, nothing can touch this” … statements were heard only a few months ago. You recall the ones where some suggestions were made and questions asked and you felt they were personal attacks? Surely you don’t forget that quickly?

MODERATOR: your don’t have to lock this topic… I have saved Doug’s post and above quote, should it become necessary for Doug to do an “edit for sp/gr” as he is fond of doing, and just happeneing to change the quoted post during the same time.

system · May 6, 2004, 3:24pm

I think movable ballast has some potential especially the rack systems described in the first post but it must be clear that they require additional weight to function. An F48 or 2 Meter designed from the get go as a retractable foiler will be equally as light as a “normal” multihull yet have unlimited stability-completely automatic.
A movable ballast system which I have sailed many hours is a lot of fun-in some respects more fun than a foiler because it takes skipper skill to keep the ballast in the right place-but is not as fast.
I think it is something to consider because it is legal under all the multihull rules and down the line there may be separate foiler and “normal” multihull classes.
Any multihull that uses movable ballast must have hulls designed for the weight; a foiler can be built using a combination of hulls that meet the criteria under “Foiler Design”; in other words some existing tri designs can be converted to a foiler if the CB is in the correct place on the main hull and if the ama is made smaller than called for. Cross arm position has to be determined by the requirements of the foiler not necessarily what is called for in the original design.
So basically, for a movable ballast boat you need the hulls to have been designed for the extra weight and most available plans that I’ve heard of aren’t. But for a foiler if you follow the critical guidelines under “Foiler Design” you can ADAPT some current tri designs but they will be substantially modified with a single cross and a rig further forward than on the original plans: the key is that the main hull CB be in the vicinity of 53% aft…

I don’t think it is wise to train a beginner on a multi with less than max sail area FOR THE CONDITIONS: the ideal situation is light air with a full rig.If you use smaller rigs in light air the handling of the boat is adversely affected.

Doug Lord
–High Technology Sailing/Racing

Dick_Lemke · May 7, 2004, 7:14pm

<blockquote id=“quote”>quote:<hr height=“1” noshade id=“quote”>Originally posted by lorsail

(1) Any multihull that uses movable ballast must have hulls designed for the weight

(2) If you use smaller rigs in light air the handling of the boat is adversely affected.
<hr height=“1” noshade id=“quote”></blockquote id=“quote”>

(1) So what you have been saying - and are saying - is that a multihull hull/displacement design MUST be correct and designed for the weight being used/carried. Yet … You also indicate that the weight of a PBS system must be removed for adequate/acceptable performance in light air.

MY QUESTION: To which weight are you designing the boat to carry - the weight WITH the power ballast system, or the weight WITHOUT the power ballast system. This follows previous questions to you (yet unanswered) as to how one can design a rig placement for boats WITH foils, but needing to move the rig (significantly as I recall, you said) when NOT using the foils? You see, we seem to get two different answers for the same questions, depending on which theory is the “theory du jur”. No where have you mentioned the need to reposition the rig with the soon (perhaps) to be released X3. In the interests of educating beginners - which theories/instructions are correct?

(2) The only thing affected by a smaller rig on a multi is the issue of top speed! Handling will remain exactly the same because the rig is a balanced rig, designed for that sail area.

The last time I drove (earlier today) I noticed NO DIFFERENCE in the handling of my car - whether at 5 mph or 70 mph. I will admit I did notice things happened sooner and faster at 70, which is precisely my point… are we teaching new multihull sailors boat handling and sailing skills - or putting them into situations where the boat can quickly become over-powered? Heck, even motorcyle driving lessons are conducted on small displacement motocycles, and in confined areas until the operator feels comfortable. I fail to find logic in your position of using something that is overpowered and that they aren’t experienced yet to handle.

After all, with all your years of multihull sailing experiences, and your admonition as well as agreement that experience is needed to sail a multihull differently than a monohull, it seems once again you are suggesting full power and “learn-by- capsizing”. This only offers the new multihull sailor two things …

a) Capsizing due to an overpowered boat which will force them to come to you to purchase one of your foiler products, … or

b) Disappointment in the multihull performance and potential loss of a new multihull sailor - which has no impact on you one way or another.

My suggestion at least allows a new multihull sailor to learn, gain experience, and sail SLOWLY until he is ready to move up tolareger sail area, mores speed and trickier handling. At that time it is HIS choosing, but until then, we have yet one more boat on the water and sailing - albeit perhaps slower than the others.

system · May 8, 2004, 3:56pm

Answers:

A movable ballast boat is designed for the max weight it will carry. In steady light air the PBS can be entirely removed to reduce wetted surface;wl length in these conditions doesn’t matter since wave making drag is insignificant. In FLUKY light air conditions the PBS may be beneficial with part of the ballast removed.
a)DESIGNING A FOILER: when designing a foiler as compared to a “normal” rc multihull the rig will generally be further forward than a boat that is designed w/o foils. There is an exact physical determinant of where the rig should go on a foiler(SEE Foiler Design); in my experience it tends to be further forward than on normal rc multihulls.It does not move except as described below.
b)SAILING A FOILER: the rig does not move on a foiler between light and heavy air unless you use a reefing system that removes the jib as part of the reefing procedure. Then the mast moves forward a bit to compensate in heavier air.
Beginners: My point is to let the beginner sail with the maximum sail FOR THE CONDITIONS. “For the conditions” means the maximum sail area the boat can handle in a specific set of conditions w/o being overpowered.
In my experience sailing a multi that is underpowered FOR THE CONDITIONS results in a sluggish, poorly performing boat.

Doug Lord
–High Technology Sailing/Racing

Dick_Lemke · May 8, 2004, 4:22pm

<blockquote id=“quote”>quote:<hr height=“1” noshade id=“quote”>Originally posted by lorsail

Answers:
2)
a)DESIGNING A FOILER: when designing a foiler as compared to a “normal” rc multihull the rig will generally be further forward than a boat that is designed w/o foils. There is an exact physical determinant of where the rig should go on a foiler; in my experience it tends to be further forward than on normal rc multihulls.It does not move except as described below.
b)SAILING A FOILER: the rig does not move on a foiler between light and heavy air unless you use a reefing system that removes the jib as part of the reefing procedure. Then the mast moves forward a bit to compensate in heavier air.
<hr height=“1” noshade id=“quote”></blockquote id=“quote”>

If the rig is designed further forward on a foiler and (as you propose to do on your X3 when it arrives) you retract the foils during a race for non-foiling condions - why would you NOT move the rig aft to the position it would be on a “normal” multihull?

Not moving the rig to compensate for using or not using foils seems to indicate the location of the mast really can’t be that critical - otherwise it too would have to be constantly adjusted to meet your posted criteria … Slightly forward for wind and foiling conditions, and slightly aft for light air, with foils retracted and sailing like a “normal” multihull.

Yet we all know that rig position relative to center of lateral resistance plays a big part on the handling and trim of a sailboat. Right?

system · May 8, 2004, 8:44pm

The rig on a foiler is further forward because the Center of Lateral Resitance(CLR) is further forward due to the load carrying requirements of the hydrofoil supported by the dual fins that make up up the lateral resistance for the boat.
The CLR does not move whether the foils are retracted or not: when retracted the same job is done by a different foil(the hydrofoil) in the same place-no change of position of the Center of Lateral Resistance.Viewed from the front the vertical fin+ hydrofoil assembly pivots(hydrofoil moves in an arc toward the mainhull) at the cross arm and the vertical fin becomes horizontal with the hydrofoil becoming vertical and ,in lite air, does the job of the vertical fin.
Also , on a retractable foiler design , the balance does not change appreciably between light and heavy air hence no rig movement is required unless you use a reefing system that requires removal of the jib.

Doug Lord
–High Technology Sailing/Racing

Dick_Lemke · May 9, 2004, 10:50am

Huh ?

<blockquote id=“quote”>quote:<hr height=“1” noshade id=“quote”>2) a)DESIGNING A FOILER: when designing a foiler as compared to a “normal” rc multihull the rig will generally be further forward than a boat that is designed w/o foils. There is an exact physical determinant of where the rig should go on a foiler(SEE Foiler Design); in my experience it tends to be further forward than on normal rc multihulls. It does not move except as described below. This makes sense and seems logical. <hr height=“1” noshade id=“quote”></blockquote id=“quote”>

<blockquote id=“quote”>quote:<hr height=“1” noshade id=“quote”>The rig on a foiler is further forward because the Center of Lateral Resitance(CLR) is further forward due to the load carrying requirements of the hydrofoil supported by the dual fins that make up up the lateral resistance for the boat. And with the rig forward, the Center of effort of the sails are also further forward<hr height=“1” noshade id=“quote”></blockquote id=“quote”>

<blockquote id=“quote”>quote:<hr height=“1” noshade id=“quote”>The CLR does not move whether the foils are retracted or not.<hr height=“1” noshade id=“quote”></blockquote id=“quote”> Sorry - but this does not compute! When on foils, the CLR location is based on the area of ONLY the forward foil and the rudder. When NOT on foils, the area making up the CLR location is spread along the entire leeward float (including what small portion of the hydrofoil is still in the water). Based on the entire area of the leeward hull AND the remaining portion of the foil in the water, the CLR location HAS to move back since the entire length of the floats must now be added to the original CLR location furnished only by the deployed foil.

Sorry, but I cannot buy into the two different scenarios of CLR location that you present. When you add in the area of a submersed leeward float as added CLR, to the previous CLR from ONLY the foils - there is a physical change in location of CLR! To use an easy to understand example, if one has a jib/main rig combination, and the boat is perfectly balanced upwind (neutral rudder) - IF you add on more sail area to the rear of the mainsail are you also saying the Center of Effort on the sails doesn’t change? Come on now !!

Again - I can’t buy into that theory. Sorry - that one you will have to prove. You have a contradiction between your quotes as you often do. If you do the math, you will see a shift of the CLR location backwards when the boat stops foiling and the entire underwater portion of the leeward hull becomes ADDED lateral resistance (as well as increased hull surface drag). And as the boat heels to leeward (remember, we aren’t on the foils any longer) the sumerged surface area (lateral resistance) of the leeward hull again increases proportionately as the leeward float goes deeper as the boat continues to heel more. This will continue until there is sufficient wind to again deploy the foils and be able to raise the hulls back out of the water. So if the rig remains forward, and the leeward hull goes deeper, the CLR location moves backward. This puts the Center of Effort (CE) location forward of the CLR resulting in increased lee helm and the boat will tend to want to fall off from it’s heading without rudder corrections. Rudder corrections = increased drag and drag = slow !

Matthew_Lingley · May 9, 2004, 3:02pm

Dick, From what I understand the normally vertical fin pivots inwards,so it is parelle to the water. This leaves one side of the T foil (or is it an L foil doug?) in the water as lateral risistance. As long as the foil area doesnt change too much and they also feather (ie dont start lifting sideways against each other!) I cant see there will be any change in the CLR.

Luff 'em & leave 'em.

Peter_Birch · May 9, 2004, 3:22pm

Personally I,m waiting to see this thing on the water working.

Let me get this straight. This system has a T-foil? that moves from the vertical to the horizontal and back. So this then means that it is pivoting/hinged in some way to the beam on each side.

Waiting to see the system that will be used to do this. There are so many physics theories that says that won’t work. It can’t be “pulled” down. It would require a solid lever system to push it down, so can someone please tell me how these foils get deployed?

I am sure that “The Master Craftsman” has some theoretical theory that says it can be done. Reality says it isn’t possible.

Peter

system · May 9, 2004, 5:29pm

Matt, you’ve got it exactly! The foils are semi “L” foils: a little sticking out on one side and alot on the other.
The CLR from deployed to retracted does not change at all; the effective area of lateral resistance stays the same and does not move forward or aft… The ama’s contribution to lateral resistance is negligible mainly because the geo CLR of the ama hull coincides exactly or close thereto to the actual CLR of the boat which is the same on or off foils.
Matt, you made an astute observation regarding angle of incidence: when the foil and vertical fin are deployed the main foil has a + 2.5 degree angle of incidence(related to the flight waterline) yet when the foil is retracted and acting as lateral resistance it has a 0 degree angle of incidence (parallel to the boat centerline)! This is accomplished by having the rotational mount angled up 2.5 degrees so that it is parallel to the foil when deployed; because of that angle and because the rotationl mount is always parallel to the centerline of the boat, as the foil is retracted it’s angle of incidence changes to 0 degrees.
The ability of the retractable foiler to eliminate the wands and hydrofoils in light air while having much smaller ama’s then normal and nearly equal weight makes her potentially very competitive.

Doug Lord
–High Technology Sailing/Racing

Dick_Lemke · May 9, 2004, 6:26pm

Matt - you are dismissing the entire surface area of the leeward float which is now in the water when it isn’t “flying”…This added surface area is "additional lateral resistance and is NOT there when the boat is “flying” and floats and main hull are out of the water. AND, it definitely is not in the same location when only the foils are supporting the boat!

I can explain with a perfect example based on my big cat (and probably similar on your dinghy).

The cat is a uni-rig (main only) with circular underwater sections to the hull. The cross beam and mast is approximately 2-2.5 feet in front of the daggerbaord trunk. Mast is centered on the front cross beam.

“IF” I sheet in the main with rudders and boards up, the boat makes very little headway - but side slips to leeward (normally expected).

If I swing the rudder down but not the boards, I gain tremendous amount of weather helm and it increases until the rudder is vertical, at which time I get lee helm. I can sail this way, but the boat continually wants to foot off and effort must be made to push the tiller away from me in order to sail upwind.

I “can” sail upwind, … as the entire length of the leeward hull is adding to the lateral resistance from the rudder! As I pick up speed, and begin to push the leeward dagger board down, the helm begins to change from a lee helm to a neutral helm when the board is approximately 1/2 to 3/4 the way down. I could let go of tiller at this point and the boat would be sailing neutral. Finally, if I pust the board all the way down, I pick up nearly 15 degrees in pointing angle and the board just added even more lateral resistance. Only as the wind increases, does one have to reconsider how much lateral resistance is required/needed/wanted. Too much and the windward hull starts to lift and sail power is more than what can be transmitted to speed, so tipping moment begins. In really stong winds, an experienced cat sailor may raise his leeward boards, and keep the windward board down - allowing some side slip to the platform but without the tendency to tip sideways. If a boat has a crew of two, the cat skipper will leave both boards down and have the crew play the jib in strong gusts, or they may reverse sheets, and the crew will play the mainsail while the skipper concentrates on sailing his best possible angle for best VMG.

The same happens with a monohull… Just the smallest change in daggerboard or centerboard surface area for lateral resistance changes (dramatically) the entire handling of the boat. Raising or lowering the centerboard/daggerboard will certainly have an effect on overall boat steering, control and windward pointing! Basic Sailing 101!

So for Doug to dismiss the added leeward float hull area (now being imersed in the water when not “flying”) as being insignificant and saying added lateral resistance along the length of the hull does not change or impact the location of the center of lateral resistance is just plain 100% wrong!

For the sake of argument, assume the forward foil and the rudder are 2" in chord length (front to rear) when flying. You (and Doug) are now saying the when the leeward hull drops into the water, the added 48 inches in legnth of the float by 3/4 inch in submerged hull doesn’t affect the position of the CLR? … Heck, that much of the hull in the water just added 36 square inches of lateral surface area (additional CLR)! And that surface area contributing to CLR increases by 24 square inches for every additional half inch the leeward hull is depressed by the heeling of the boat!

This means if the center of lateral resistance changes to a new location, then the center of effort of the sail area also must change to retain the same handling and pointing features. Same thing happens when crew moves weight forward or rearward - there is a change in the trim of the boat so other changes must be made if moving the weight is a detriment.

system · May 9, 2004, 7:59pm

Dick,you probably posted your last post before my last one came up: just to reiterate: the geometric CLR of the ama on a retractable foiler is coincident with the CLR of the foil/fin combo whether retracted or deployed; therefore whether foiling or not the CLR of the boat does not move regardless of heel-and it heels very little in 0-4mph of wind.
Also the ama on an F48 retractable foiler would be a maximum of 36" LOA and as short as 30" or so. In addition, since it has no requirement to sail with the full weight of the boat the ama’s beam to length ratio is 18/1 which is MUCH narrower than a conventional rc tri’s ama…

Doug Lord
–High Technology Sailing/Racing

Dick_Lemke · May 9, 2004, 8:26pm

Gotta see it to convince me!

Even with a short ama of 30 inches, the heeling moment will submerge the ama - and if it goes down only 3/4 of an inch, it is still 22.5 additional square inches of lateral resistance spread along the entire length of the ama. Calcualtions usually assume a physical center average position for CLR. This would be well aft of the position of your forward foils. Perhaps by as much as 5-6 inches by my guess.

A heel angle of less than 5 degrees (depending on initial height of ama off the water in “static” condition) will result in the 3/4 inch of ama hull depth. With amas that thin and so little buoyancy, I would envison the ama to drop even deeper into the water adding yet even more underwater surface area.