multiONE Stability

Ever since I helped found this class many moons ago I’ve mentioned the characteristics of stability that work against this class-anf the F48/mini 40 as well.
Too many people think it’s ok to scale down an F48 to multiONE size or to scale down an Open 60 to F48 size. Doesn’t work well!
And if you’re trying to build a class like the multiONE I wouldn’t worry so much about how cheap it can be built I’d worry about designing/building it to a high standard that will allow people to enjoy racing the boat in winds over 5mph! This is a serious design problem in these boats -and in F48’s. If people buy these boats and try to sail them in any wind and they capsize/pitchpole on a regular basis they aren’t going to stay happy.
You simply can’t ignore this problem in the multiONE class especially because without the use of foils(and maybe fixed keels in the Sport end of the class) these boats will simply be too difficult to sail in stronger winds. Movable ballast WITH hydrofoils is possible but movable ballast by itself will not cut it.
I suggest that the real challenge in the multiONE class is not COST but is making a multiONE that can be sailed faster than a one meter monohull in the SAME conditions as a one meter monohull.
This should be the priority because if the boat can’t do that then it will not gain any following. Boats that pitchpole/capsize when the wind blows will just turn people off…

Doug Lord
High Technology Sailing/Racing

What makes the Open 60 inherently more stable than an F48 or multione?

Is it that the inertias and timescales involved gives the skipper more time to react?

Is it that the wind is (on a scale basis) stronger as the boats get smaller?

Is it the speed of the servos?

Are there any advantages to the smaller multihulls over their bigger cousins? If cost isn’t it and stability isn’t it then the only thing left is the ability to throw it in your car. And that is not much of an advantage…

Anyone who is serious about promoting these classes should try to figure out what the issues are and look for inexpensive ways to solve them. If servo speed is the issue, then you should look into faster servos. If reaction time of the skipper is the issue, maybe gyros should be considered to automatically ease the sheets if the boat heels up to far or too quickly. Or maybe people should look into more flexible masts that would produce dynamic sail twist…

And whatever happened to that company that offered self righting catamarans? Maybe the smaller multihulls should have the extra added excitement of capsizing. If you could recover from a capsize, it might make for a fun aspect to the sport…

Just some food for thought…

  • Will

Will Gorgen

Multihulls whether large or small benefit from high beam to length ratios but when scaling a large multi to a small one the pitch resistance of the small one is proportionately much less than the large one.In other words the proportion of resistance to pitchpole as compared to the force acting to cause pitchpole is much lower on a model than on the full size boat. But even with less beam to length ratio small multi’s still have a large pitch instability in winds over 8mph with full rigs.
The solution, in my opinion, is hydrofoils since they will 100% eliminate pitch or roll instability and allow the boat to just go fast(in most conditions). I submitted a lot of info about hydrofoils to the multiONE site and it is easy to access for anyone interested.
The PoP UP system was pretty expensive; they’re out of business.(sold to a guy down here that has no interest in the multihulls)
I think movable ballast combined with a rudder T-foil and anti-diving planes would also work to an extent(requiring more skill) but a boat must be designed for movable balast or it will not work at all.
I think a small cat with a canting keel slung from between the crossarms and capable of moving fore and aft and side to side could produce a fun beginners boat but moving the weight costs money.
Hydrofoils are the least expensive option to prevent pitchpole or capsize in most conditions even if they are made retractable–and well within the capability of some intermediate and expert builder/designers.
The priority in the multiONE class(&F48) should be stable ,fast boats first and cost second…
Example: If you scale an Open 60 down to F48 size the changes at the same beam to length ratio are truly incredible: The full size boat in 17k of apparent wind with a 20/1 beam to length ratio has the RP (resitance to pitch moment) exceed the PM(pitch moment) by 1.79 times. Scaling that same boat down to 48"and sailing in the same wind shows that the now the PM(pitch moment) exceeds the RP(resistance to pitch moment) by 8.3 times!!!
Factors that help the model a little(very little) are that typically model ama’s are around 14/1 beam to length instead of 20/1. Factors that make no difference include wind speed; a lighter wind will still show the much greater lack of resistance to pitch of the model.And a multiONE is much more pitch sensitive than an F48!

Doug Lord
High Technology Sailing/Racing

I don’t have any experience in rc multihull sailing but I can see that flipping them could not only be anyoing…it could be cold and wet too. A while back I was looking at some video of rc iceboats and what they did to stop the iceboats from tipping over was they used very stretchy sidestays that stretch in the gusts and they never tipped…could this be done on a multihull? I have no idea. but maybe it’s worth a look

David, well worth an experiment!

Doug Lord
High Technology Sailing/Racing

Doug, i think you may be wrong on this one. In my experience with the two cats i have built(multione and mini40)i think it is actualy quite easy to design a stable multi at this size. Ok ive flipped both boats numerous times but think ive now got sailing the multione boat pretty much sorted. Firstly the width and the low aspect rigs make it damn near imposible to fly a hull let alone capsize, and ive sailed this boat now in winds over 25 knots with full rig. Secondly yes it does pitchpole if pushed downwind but quick reaction on the rudder will often pull it out of nosedives if gusts are anticipated, as on a full size cat. I am going to fit T foils on the skegs to slow this pitchpoleing action down, but in a cheap boat some weight in the back would work i am sure. Ill agree with you that conventional thinking/fullsize scaled down is hard to get to work, my mini40 uses IOM rigs and is very hard to control in high winds. Very wide boats (46" is allowed in multione i think!) with low aspect rigs, lots of bow volume and somthing to keep the sterns down is the way to go.

If its not blowing it sucks!

I have to say I strongly disagree with some of what you said. There is not any correlation between price and stability or price and speed. And yes, bigger boats are more stable. However, they are also exponentially more expensive. Even a “cheap” boat like the Victor wildcat is very sailable. With a few mods its pretty stable, only capsizing in high winds(15kts) when the skipper is not paying attention. This is an issue for ANY size and ANY design multihull. The flexible stays is a great idea, I will work it into the WilderCat experiment.

Multihulls, reguardless of size, will always require more skill to sail that a keel boat. Thats just life. The only thing in this world that will make a boat capsize proof is a chunk of lead. No one wants that, so we live with the risks!


Help me out here guys: I’m not sure what you disagree with. Are you saying that hydrofoils are not the solution and/or that no “solution” is needed?

Doug Lord
High Technology Sailing/Racing

There’s one of stopping you get wet & cold (grin)
Put a bit of carbon fibre vertically down from the center hull with a bit of lead, remove the 2 outside hull if a tri for cost savings purposes, and want do you have a proper yacht!!!
If you want more fun change the vertical down piece of carbon to a swinging bit. Take the rudder of one of the redundant hulls and put it in front of the swinging bit and you have CKTF, now you’re talking!!!

Sorry I couldn’t resist the chance, from a lead belly from way back

I have built several different catamarans and now obviously have moved over to the trimarans. Instability in higher winds is definately a problem with boats this size. I agree with Doug Hydrofoils is the way to go. The only problem? To do it right takes alot of time,energy,building,money,studying…etc.etc. Moveable ballast has worked well on the cats I have and I am now working on a gyro controlled moveable ballast system. This unit will move forward and aft, and outboard automatically depending on the heel of the boat. I am hoping this works well. We’ll see shortly!!!

You can not scale the open 60 multihull directly down for several reasons:

  1. If you build it relatively as lightweight asa open 60 boat with the same amount of rig, you sailing conditions will be under 4 knots.

  2. Water is relatively thinner, so the hydrodynamics work differently around the boat

  3. The gust force is higher compared to the larger sisters.

However I dont believe the foils to be the ultimate solution. Show me at least 1 modern boat wich has been successfull against modern multihull designs. On modern race course theres at least 50% upwind as a distances and because of the higher speeds on downwindleg the time spent on the legs are like 25% downwind and 75% upwind… No foiler this far has been able to beat Hobie tiger on race track, never mention about a tornado.

My concept for a killer boat will still focus on the upwind capacity. When the boat goes well upwind you just need to survive downwind. And i jhavent still seen a foiler going well upwind. Rave goes upwind as well as 49’er, and downwind a bit slower. As long as the foiler dont beat a monohuller on upwind, they have practically no chance against multihulls on a race course.

Ofcourse this is trollfood if you read it to the letter, but thats my opinion coming from my experience.

Hannu J

Luck runs out, But skill
Doesn’t - A tornado sailor in Round Texcel

Who cares if they flip somtimes, just means you need more skill to keep them up and racing! Im sure Hydrofoils is a way of solving the stability problem but if they prove slower then Ill go for a non foiler everytime, ok you’r gonna lose it somtimes but so will any Multi, weather its a hobie 16 or a Open 60, you just gotta find out how far you can push it and know when to back off. How many high performance boats dont wipeout from time to time? If you want total stability go sail somthing slow with lead on the bottom!

If its not blowing it sucks!

“Who cares if they flip somtimes, just means you need more skill to keep them up and racing!”

Right to the nail my friend, right to the nail!!

Ofcourse, this “having the chance to flip over”- concept must be faster, making the boat hard to handle is not a goal, making it as fast as possible is. If the fastest boat is also hard to drive then so be it. When handled properly, fastest boat will win. Its the same thing is every racing system there is.

Hannu J

Luck runs out, But skill
Doesn’t - A tornado sailor in Round Texcel

Bad mistake to use the Rave as a benchmark to knock hydrofoils: it is almost twice as heavy as a high performance hydrofoil it’s size needs to be. But I’ve never sailed one…
I have, however sailed the F3 hydrofoil in almost every condition as well as had years of experience sailing high performance non hydrofoil multihull platforms. The properly designed hydrofoil will beat any non hydrofoil multihull in almost any condition particularly if it has retractable foils for light air. Upwind performance of the F3 is SUPERB in addition to being virtually non capsizable or pitchpoleable!
Ignoring the real problems of the characteristics of small multihulls will backfire in any promotional effort as will having small multihulls that are slower that their monohull sisters.
I’m suggesting that all of us that are interested in these things work together to develop boats that solve the inherent weaknesses of these boats and capitalize on their speed potential to interest a much wider group of rc sailors in going fast. Going fast must be our priority so that we can clearly demonstrate the multi’s superiority over a leadbelly. AFTER we have boats from different people/manufacturers that are fast ,stable and capable of whuping the one meter mono’s THEN we can concentrate on reducing cost which won’t be that high anyway.
Performance MUST be the focus and a realistic understanding of the strengths and weaknesses of these boats is essential!

PS- Movable ballast has potential though it tends to be expensive. Using a movable ballast system on the D4Z F48 cat is among the most fun I’ve had rc sailing-it requires practice and skill and the D4Z is almost twice as expensive as a hydrofoil F48. But it is fun-really serious fun-you feel like you’re sailing a full size cat-almost…Ian’s experimentation with gyros is interesting but in my experience only a heading hold gyro would come close to working(expensive) and the Guyatt winches I use weren’t fast enough to match the gyro response. He may have a much better system so it will be great to hear about it.

Doug Lord
High Technology Sailing/Racing

Doug we’re thinking along different lines here. The boats i build cost as little as possible, the only reason I get to use carbon in my boats is because a guy i have done some part time work for who makes components for various cat classes including Tornados lets me mess around and experiment, using his materials and workshop. Otherwise I would be building boats in balsa still. I cannot afford Guyatt winches, gyro’s or any other smart gear like that, cos im racing fullsize boats at the same time. If you want to really get a fleet going you or someone else has got to produce a budget boat that will apeal to those who havent got the time or drive to build such a boat, and dont want to shell out megabucks on a boat you can’t race. Your a manufacturer, there is your market. Once youve got some competitive fleet action going on people will pay for your expensive toys, in the meantime lets keep to the pramble of the class rules; “At no point should features be allowed into the class that would exclude participation in competition based on the size of ones pocketbook.”

If its not blowing it sucks!

I’m not advocating expensive or cheap boats I’m advocating boats that are faster than comparable rc monohulls that tack and point well and that can get around an rc course in a good wind without capsize or pitchpole.
Price is not going to grow a multihull fleet for the long term---- performance will. You can put together expensive multihulls that don’t work well almost as easily as you can cheap ones that don’t work well.
As long as there is not a realistic assesment of the design quirks of these little speed boats keeping people interested will be very difficult.
Hydrofoils are not expensive; neither are retracting hydrofoils. And they are not difficult to understand but you have to spend a little time at it initially. Of all the solutions to small multi quirkiness the best answer I’ve seen so far is foils. And I’ve published just about all I know about it. It is not difficult to deal with and is a practical answer that can provide blistering speed with absolute control–something I feel is critical if the idea is to get more sailors interested in speed sailing…
By the way, Wenesday of this week if the creek don’t rise a friend and I will be test saiing the microMOTH with digital camera at the ready over on Merritt Island ,Fl. For a multiONE this thing has definite merit since with its large “sissy floats” it resembles a trimaran more than in the initial photos. But when it gets on foils the big difference between it and the F3(or X3) is that the F3 develops its own righting moment whereas the microMOTH uses a Trapeze Power Ballast System. From a sailing standpoint that means that the microMOTH foils are far less loaded than the F3 foils so that it has incredible speed potential in light to moderate air. It has no speed potential at all in lite non foiling air since the foils can’t be retracted–I’ll let you know what happens.
UPDATE: No microMoth sailing this week…10/23/03
Doug Lord
High Technology Sailing/Racing

This summer I participated in a race where there were 16 multihull boats–I was sailing a Nacra 5.2, there were Hobie 20’s, Hobie 16’s and 2 different types of Windrider trimarans. There were 3 16’ (I think they were 16) tris without foils and one Rave. The winds were light at 5-10 knots… I had never seen any of the Windrider boats in person, and expected the Rave to be extremely quick. In fact, many of the other multihull sailors were suprised at how slow they were. In all fairness, the 16 foot, non-foiled boats aren’t supposed to be serious racing boats, but day sailors. The Rave was the biggest suprise/dissappointment. I think that what Doug says about it’s weight makes sense because it was never able to get up on the foils, and without that it was a complete DOG. I’ve heard that either the crew weight has to be pretty light and/or the wind really has to be blowing to even approach hydroplane velocity. Has anyone heard anything about Hobie’s hydrofoil boat (called the trifoiler)? I wonder if it’s any better.


Full sze foilers currently on the market are blisteringly fast when on foils in 12-15k and above; they are dogs under that for sure.
I guess the thing that should catch most peoples attention for models is that a foiling model can take off in 5-6mph of wind-not 12-15 like a Rave or trifoiler.
And models can easily have retractable foils so that in light air (under 5) there is no drag from the main foils. There is still the rudder T-foil but if designed right it will add minimal extra drag since it will be set at 0 degrees. This low takeoff speed is not speculation -it is stantard performance on the F3; the new X3 has retractable foils so we’ll have to see if it performs as well as the F3 on foils.
Speed is one thing but for these small models, in addition to high speed in light wind or strong wind, foilers offer tremendous CONTROL: they require no input from the skipper to fly(other than to deploy the foils on the X3) and they are simply more stable as the wind picks up.
The ability to take off in 5-6mph and to be stable thruout the wind range is a big deal in small multihulls and is such an improvement over how these boats “normally” behave that it is worth spending some time understanding.

Doug Lord
High Technology Sailing/Racing

Hey Doug,

Correct me if I am wrong here, but it should be easier to get up on foils on a beam to broad reach than when beating or running DDW, right? So is the 5-6 mph wind speed for foiling on a reach? What wind speed can you expect to be foiling on a beat? What about the run? Do you ever sail DDW or is it better to sail hotter angles so as to stay on the foils? What sort of angle to the true wind can you sail to windward? 45? 50? 60?

Based on my own hydrofoiling experience (pedalling, not sailing) there is a lot less drag once you are up on the foils. So your speed increases dramatically once your hulls leave the water. So would you reach off until you foil and then be able to head up to a close hauled heading? Similar situation downwind - sail hotter angles until you are foiling and then bear away?

What about tacking? What windspeed can you expect to be able to execute a clean tack without dropping off the foils? What about gybing? If it is easy to stay on the foils through a gybe (much like staying on a plane through a gybe with a windsurfer) would you expect it to be faster (VMG-wise) to gybe instead of tack when sailing to windward?

I’m just curious as to what you saw on the F3. How soon will you be ready to play with the retracts on the X3?

  • Will

Will Gorgen

Will,I just got thru spending 25 minutes answering your questions in detail and posting the answer; something happened -I must have hit the wrong key-and it disappeared. Don’t have time to do it again now so:
I couldn’t tell much difference in speed between a close reach, beam reach and broad reach. The boat would pop up on foils at any one of those angles in 5-6mph wind which was accurately measured; sailing angles were never accuately measured. David Goebel and Dick Lemke have witnessed the F3 tack while on foils; I haven’t but it tacks very ,very quickly. Gybing downwind is required.
The F3 is painfully slow off the foils since the altitude control system wands keep the flap max down for takeoff. I and a few others are looking into “radar on a chip” to 100% replace the wand system. The F3 in lite air appeared to go at least twice the wind speed; in 16-22mph wind she appeard to go at or maybe slightly faster than windspeed(fully reefed).
I’m about to test the microMOTH that uses a manual(via radio) control of the single main foil flap-to facillitate jumping and to see if it can be done. A full size Rave can be flown by hand w/o wands and maybe the f3 could too after much practice and many crashes. The wand system is automatic and does not require radio control or skipper intervention and keeps the boat 100% stable.On the X3 the wand retracts with the foils.
Sorry about this-my other reply was more detailed but …
UPDATE/moreinfo: One thng Dick and I bought into on the F48 was the idea of limiting beam like in the mini40 class though the idea at the time we discussed this was to try and avoid as many purely artificial restritions as possible. That limit means that some design changes have been made to the X3 as compared to the F3 that if they have any negative effect at all will probably cause the new boat to take off in 1 or so mph more wind than the F3.If the beam were “correct” for a foiler it would be 60" for the F48. In the multiONE class we didn’t make the same mistake and the overall beam allowed is 48" which is perfect for a foiler.
One thing I learned in doing the F3 was that beam makes ZERO difference in tacking ability of a foiler; also that having to have a daggerboard or? on the centerline or at least lined up with the rudder is not true and lack of it means nothing in terms of pointing or tacking.
Doug Lord
High Technology Sailing/Racing