Radio Controlled Foiling America's Cup Catamaran: AC 50RC - Page 19 - RC Groups
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Nov 07, 2015, 09:20 PM
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Mini40 class

3 Mini40s in action on the estuary in a decent breeze. C rigs for most of the time though we did try B rigs for a while. Really good comparison of the conventional fixed V foil configuration versus the wand controlled T foil with flap. The latter is more docile and . . slow! The fixed v foil needs concentration upwind and exactly the right amount of lift, but can be fine. I think we need sets of foils of different lengths, as you can see that we have more than enough lift from the V foils. Number 59 especially demonstrates this by rearing its bows when heeled upwind.

The wand controlled foils may one day work but there is still so much to test, and I am not sure that I have the patience for the trial and error here - too many variables to sort out: size of fixed element of the foil; size of flap; angle of fixed element; depth of foil; wand length; gearing between wand and lever on top of foil, etc. This is my second set of T foils and, whilst better, and noticeably more docile upwind are still nowhere near as fast as the v foils. The T foils are also wider than the rules permit in the Mini40 class so this is purely an experiment right now.

.... And it is impossible to keep a boat up on its foils through a tack

A great day by the water!

Video is here:

3 Mini40 trimarans in a fresh breeze (10 min 17 sec)
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Nov 07, 2015, 09:55 PM
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DLord's Avatar

Ac 50rc

Ian, very interesting boats. The surface piercers really move-great work!
Next time would you post your mini 40 stuff in the RC Trimarans thread here: It's about half way down the same page this thread is on and already has some of your video.
This is the AC 50RC catamaran thread and you would be more than welcome to post video of your version of an AC 50 cat!
Nov 28, 2015, 06:12 PM
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DLord's Avatar

AC 50RC Design and Development

Jim(rcmm) is working now on a mini40 cat using outward pointing foils that are, coincidentally, very similar to the proven foil system on the Quant 23 monofoiler.
Seems to have great potential.......
His thread is here:
Apr 14, 2017, 02:47 AM
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Hi, I too am actively pursuing a foiling ACC cat. So far I have built a 1m AC72 replica. I have sailed this with limited foiling success. I am about to embark on a second version and I am keen to follow your standard as I had independently come to the conclusion that a bigger yacht around 1.5 m will make it much easier to get the necessary control elements installed while still being within the scale weights required. I have only recently discovered this RC site with all the great work you have done. Can you please confirm the latest spec for this new class.
Apr 14, 2017, 10:11 AM
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DLord's Avatar


I'm sorry to say that there is not much interest in an RC Americas Cup foiling cat so far. One major setback was the fullsize rule change from the AC 62 to the AC 49.2. Some people, especially in Germany think that a new dedicated AC class is not a good idea and should be limited to the existing mini 40 class-I disagree. My D4Z is sidelined temporarily.
The most important thing required to get a new AC foiling class going is to develop foil systems that allows light air takeoff , upwind foiling and tacking and gybing on foils. Ian Holts foilers are very good with great potential.
So I'd suggest you concentrate on developing a working foiler with a foil system that really works without regard to any rule. Check out John Xmans thread on his gigantic AC86 cat. Good Luck!

I still think the specs in the first post of this thread are the way to go. I think an AC boat should have its own class-not be a sub class of the mini 40. My D4Z is a few inches smaller than those specs and was intended as a test boat for a foil system. But the most important thing is to work on foil development-I'm changing the foils on my boat from the experimental surface piercing foils to wand controlled foils in the next few months. A wand controlled system with movable ballast is the way to go, in my opinion.
Last edited by DLord; Apr 14, 2017 at 10:35 AM.
Apr 16, 2017, 02:34 AM
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Thanks for the feedback. I like your ballast system. I had developed something similar for my boat but had to remove it to get the weight down. One of my biggest problems is keeping the electronics dry. Do you have any tips on how to achieve this? Also I was experimenting with using a gyro type pitch control. Do you think there is merit in this approach?
Apr 16, 2017, 04:00 PM
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DLord's Avatar

D4Z radio box

On the D4Z( see page 9 of this thread) I used a sort of triangular box just ahead of the forward crossarm to house the radio equipment. Mast step is on the hatch to this compartment. Works good. Had mainsheet(RMG280), F&A movable ballast(RMG280) and two rudder servos plus the receiver and battery inside. By using a more or less centered box you don't need openings in the hulls(except for waterproof vents).
On the new version of the D4Z I'm eliminating one rudder and mounting the single rudder on the center of the aft crossbeam and also changing the Trapeze Power Ballast System to a 100% independent system with its own receiver(same transmitter as the boat receiver) and battery. Allows it to be interchangeably used on two different boats. Also getting rid of the experimental surface piercing T foils and replacing them with wand surface sensor controlled T-foils. Foils will still be canted about 10 degrees.
It's important on a relatively narrow cat to use a movable ballast system instead of trying to let the foils develop all the righting moment like the F3 does because it's less drag.
In my experience, a gyro for pitch control is unnecessary IF your main foils carry about 80% of the load and your rudder foil is half the area of your total mainfoil area which works out to lower foil loading on the rudder hydrofoil which is ideal. The rudder foil or foils should carry no more than 20% of the total weight at takeoff.
Apr 16, 2017, 04:32 PM
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Dick L.'s Avatar
You may want to calculate the length of rudder and angle of heel and I think you will revise the idea of a center mounted rudder due to potential loss of steering in a gust when it is most needed. As you may recall, a lot of trimarans tried using a single, central hull and many switched to two rudders to assue the leeward hull could maintain steering control when the boat is heeled. Not sure I would trust foils to lift a hull up from being heeled, especially if the boat has no velocity to encourage a foiling situation.

Just a couple of thoughts.
Apr 16, 2017, 06:41 PM
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DLord's Avatar


Thanks, Dick. I've noticed an oversquare cat in Germany that seems to be real fast and it has a center rudder. But what it doesn't have are wand controlled main foils supplanted with a ballast system. Not worried at all about the rudder coming loose.

#9 won the Flevo Cup in 2015......

Two cats from the Flevo Cup last year:

Last edited by DLord; Apr 17, 2017 at 09:29 AM.
Apr 19, 2017, 11:24 AM
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DLord's Avatar

Ac 50 / d4z

I had a major problem with the main on the first iteration of the D4Z: it used a luff pocket but the 2.2oz material didn't work for the pocket as it was built and actually prevented the pocket from pivoting from tack to tack-in fact it would drastically distort the main. So the redone version two will have a new main. It will temporarily use the D2 main .
The new foils will be wand controlled but I'm giving serious consideration to doing a wand system similar to the Whisper with wands integral to the foil as shown below. We'll see -I have to study this a bit because the Bradfield system used on the F3 worked well and allowed the use of bearings on the wand . I'm not sure that will work with a Whisper type set-up.

Whisper/ F101 foil with integral trailing wand. Wand is the black thing hanging parallel to the daggerboard trailing edge:

Whisper with trailing midship wands:

Apr 21, 2017, 05:10 AM
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I am a new member of this forum, but a frequent visitor I must admit.
These discussions are an inspiration to all of us tinkering with multihulls.
Jul 11, 2017, 08:28 AM
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Hi Guys,
First post, this thread has inspired me to get back into RC boats, being in 10-raters 20 years or so ago.
Are there any plans available for D4z ?

Has anyone done any work on balancing lift from windward to leeward foils ?

Keep it going

Jul 11, 2017, 12:34 PM
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DLord's Avatar


Originally Posted by PaulMason
Hi Guys,
First post, this thread has inspired me to get back into RC boats, being in 10-raters 20 years or so ago.
Are there any plans available for D4z ?

Has anyone done any work on balancing lift from windward to leeward foils ?

Keep it going
Paul, there are no plans currently available for the D4Z. Not sure what you mean by "balancing lift from the windward to leeward foils" but I'm thinking you may mean using the windward foil to develop downforce thereby increasing righting moment? If so, I've done a lot in that area starting about 17 years ago with the F3 which I designed with help from Dr. Bradfield. It used dual independent wands to control altitude . When the boat would heel slightly the leeward wand would increase lift on the lee foil and the windward wand would cause the windward foil to pull down. That system allowed the boat to automatically control its own stability. I've used a version of the same system on the Fire Arrow and am about to use a similar system on the D4Z along with a Trapeze Power Ballast System. I'll be glad to answer any further questions......
Jul 12, 2017, 05:38 AM
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Thanks for the reply, I'll have a look elsewhere to get a plan for the Hulls to get myself., or I'll have to call in a favour to get a can of an AC45.
And yes you were correct about foil lift. IIRC the real thing uses ultra-sonics to keep themselves level. I was thinking single foil for height and accelerometer for pitch control of the foils.

Jul 12, 2017, 11:14 AM
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John Xman's Avatar

AC-50 Class

I believe the only way to get this class going in the US is for someone to produce a "KIT" and make it basically like the 34 Americas Cup boats.
Hulls, Cross beams and Wing would be one design. Rudders and foils and controls by each skipper. Model the rule around the Americas cup.

I am considering shifting my focus to Producing the molds for this 60" cat, this Fall. (I will be doing a Prepeg Carbon hulls)
The design would include:
- Entire cat would disassemble for shipping.
- 12" long bows would come off for shipping.
- Wing would come apart into 3 Sections. (9'-0" height)
- Displacement target 14-15 lbs.
- Cross beams would be a standard "D" shape.
- Wing would be CF over foam.
- Internal foil box designed for pivoting and also serve as Radio board.

So I have a few questions before I jump on the Hull design:
1. Should the hull form have the bulge for the crew areas?
2. Match the Bow profile of the AC34 cats?
3. Any negative curvature in the bow area? Think GC32
4. "D" shape cross beams flush with top or set at centerline? I prefer centered.

So the big question here is how many AC fans do we have out there that would be willing to spend $500.00 to #700.00 on a CF cat KIT?
to get this Class started in the US?


John Xman

(PS I would prefer this class be 72" long)

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