Formula 100 Technical Development

This topic has been started at the specific request of Gappy(Blair Gerard)-- the proud owner and developer of the first F100 canting keel model in the world…
Anybody anywhere working on F100’s is more than welcome to contribute to this topic!

Doug Lord
–High Technology Sailing/Racing

Doug thanks for starting the new thread.

I work in the marine industry in New Zealand suppling most deck gear and hardware, hydraulics and ecltronics and so forth you we have a number of major brands which include Lewmar, Navtec and Brooks and gatehouse to a varity of boat builder and boats and when the AC teams were around these also. I do all of the hands on work for the our company along with specing the boats out as well and comissioning a number of boats. I recently did the Navtec comissioning on the New Pyewacket which a is leading quite a discussion here.

I have done quite a bit of sailing mainly in dinghys but in the last few years have done a lot of big boat work including a coupel of Hamilton island race weeks and The Sydney to Hobart which was on a boat built here for a US owner the boat was called ICON and was a Bob Perry 66 and based in Seattle now. At the moment I am sport boating on a 6.5m boat and we are doing very well having won all of the trophys last season and doing pretty well so far this season.

Any way thats enough about me.

My F100 just started out as myself wanting to build a canting keel 1metre as I did not want to sail one metres and deal with their politics so I started to build a boat and made a mould and a lot of friends have since taken hulls and decks off this although they are opting for fixed keels at the moment.

The basic boat is as below:

Length 1000mm
Beam 250mm
Draft 450mm
Bulb weight 1.9kgs
Fore and aft foil 200m deep
Rig 1.75 from waterline.
Sail area unsure as I have not worked it out.

I have not gotten to technical with it as I have just wanted to get out sailiong but it is finshed properly and I am trying to refine things slowly. The hull shape seems good I did modify the bow slightly and this has imporved things. One thing to watch out for is the boat may seem balanced when you set the bulb up on the keel and float correctly fore and aft but once you start powering up the bow seems to dig in a bit and I know that Grunta found this with his boats initially and I am working on correcting it with a new fin and bulb.

The workings of the RC gear are quite simple I have a Futaba 4 channel set and I did not want to spend to much on this until I new that the kel and so forth would work so this was about all I had to buy as I had some servos and I had a couple of the hitec winch drum winch which I have used for teh sails and keel. I thought initially that these might struggle but they have proved me wrong so far. I use the normal right hand stick for rudder which controls both the aft rudder and fore rudder but they have different amounts of movement on them. The up and down on this stick controls the back stay more on this later and the left hand stick has keel control on the side to side stick so move the stick to the left and keel cants to port the up down on this stick is the sail control and fully down is sails in as this makes it easier oin the hands to control the keel up as this is mainly when you use it.

The sails I am using are a custom made main sail with enough roach not to get caught in the backstay but I am looking at a new main and I using a 1metre A rig jib and I can carry this up into 15knots at the moment and up wind is fine in a bit more breeze it is just when you turn the corner you have the problem but reaching seems best rather than trying to run dead down wind as you can use the keel on the reach. The reason for having a backstay control and this has only been added in the last week was to depower the main in the gust and drive off the jib which works pretty well and then you can power up again by letting it off slightly but also it helps put more jib luff tension on in the gust so it helps in two ways.

The keel control is just with the Hitec winch as discribe earlier but it is done with a 2:1 purchase and has wires instead of rope as I had some vectran but it chaffed badly as the pulleys moved on the angle change with the keel from side to side so I use 1mm flexi wire and I am very happy with it. I am also working on a new keel sealing system as my present one although it works is not the best and is like a boot system around the keel. The new one is going to have needle rollers and shaft seals and i will put it into a new boat which I hope to start building in the next few weeks.

Any way enough for now hope everyone finds what I have to say usefull and I keep on posting.

Any questiosn fire them back.

Time for a cold beer it sure is warm here at the moment.

Cheers Blair

Blair, glad you posted! Sounds like your boat is using twin foils like CBTF but they aren’t set up with collective(both rudders able to turn SAME direction)-is that right? on my new boat ,thanks to the radio I’m able to have one servo for each rudder(foil) and program the radio for collective that, as of now, will operate off a three position switch( to change or shut off when tacking) and a dial to change the amount of colective from that preset on the switch.
I did a test boat along time ago -a 36"- that had mechanical mixing of the twin foils but that had the disadvantage of linkages between each rudder and the mixing “slider”. Collective is definitely more complicated but is critical to reducing drag on a CBTF boat–what are your thoughts?
I’ve got plenty of questions so excuse me please: 1) what cant angle from the cl are you using? Mine is set up for 55 degrees. 2) How fast does the keel move from center line to max cant angle? My target is one second-not achieved on the first prototype.What are your thoughts regarding keel movement speed?
3)Have you raced the boat at all?
Looking forward to more info and ,again, congratulations on having the first canting keel F100!!
PS- Like your radio setup-it’s exactly the same one I use-seems the most logical and intuitive for keel control…

Doug Lord
–High Technology Sailing/Racing



I have played around with the foils and having them on a collective but I was using a mixer out of my rc glider and found it a bit hard to work with as I had to use the up down control on the right hand stick which I now use for back stay. I would like to go further with it but I need a new radio set for this and would like to work on a few other things first.

My keel is canting to 45 degrees as I am limited by intravell by the pulleys but I hope to work on this to get closer to the 55 mark.

With regards to the speed mine is not overly quick it takes about 4 seconds from hard over to hard over and I find this fine it dumps alot quicker and if it canst to quickly I think you would find that the boat is real jerky to sail I don’t think that speed is off the essense I think be able to control it suitably with out jerking the boat around to much.

I have not raced yet as I have wanted to work a few systems out and I am slowly getting there I am sailing it about 4 times a week and learning heaps. One thing that I have found really important is the rig and I am only using an alloy tube on my prototype as the next one will be carbon but when you are generating so much righting moment from the keel the rig needs to be pretty solid as there is not point in haveing all of the moment and a rig the goes out of colum and then loss sail shape and power. Thus the need for a backstay set up as you need to depower in some larger gusts.

I hope all of this is of interest to both Doug and other.

Cheers Blair

Blair, in sailing with twin foils have you noticed any"quirkiness" to steering the boat" Does see have weather helm?
When you tack with a twin foil boat I’ve heard that, at least in fullsize boats, you lose less speed than a conventional fixed keel-is that borne out in your experience?
Also that as a result of more speed thru the tack you tack quicker in a smaller turning radius–can you comment on your observations?
Keep us posted on new developments! Do you know of any others besides John Beavis building canting keel F100’s or? down there?

Doug Lord
–High Technology Sailing/Racing

Just thinking- - - - - - - -
The drag of the Keel and ballast bulb on a standard sailboat, which is counteracted by the buoyancy of the Hull, is in equilibrium when the boat is sailing, so the boat sails normally.
Drag is pulling to the rear and buoyancy is resisting it by holding up the Bow.

The same factors are present in a Canting Keel system.
When the Keel is displaced by 55 degrees from vertical, the drag of the Keel is now to one side of the boat.
Will this offset drag not cause the boat to turn to that side?.
The amount of speed and performance, which is lost on any model sailboat by a very small amount of weed or grass which is picked up while sailing is considerable.
When the keel is displaced there will be a lot of normally unseen drag acting on the boat, without a force to stabilize it, other than the Rudder, if that is used to correct the boats heading, even more drag is produced.
The gains of having an upright Rig with a Canting Keel, should be diminished by the sum of the extra drag produced.
Or, the gains from the rig will be greater than the drag and the boat will be faster.

John, the canting keel boat is actually substantially better off than a fixed keel boat.
If you consider the conditions in which a cantng keel boat would have the keel at 55 degrees to weather a similar sized fixed keel boat would be heeled 35 to 40 degrees.The canting keel boat would have little or no heel to the rig or hull.
So if you viewed the fixed keel boat from above there are three tings you would be able to immediately see: 1) the keel of the fixed keel boat is probably generating an turningmoment to weather,2) the rig being displaced to leeward of the boats centerline is definitely creating aturning moment to weather ;3) And finaly the keel/bulb drag is creating a turning moment to weather.
On the canting keel boat viewed from above the hull is not heeled so generates no turning moment, the rig is not heeled and it generates no turning moment; only the keel displaced to weather creates a slight turning couple.
All in all the effect on a canting keel boat of the displaced forces found on a normal keel boat are probably somewhere between 50 and 60% less in the same conditions.
It is even better on a CBTF boat where the collective facility dials out leeway so the canting keel strut is not producing induced drag…

Doug Lord
–High Technology Sailing/Racing

Well, we?ve got a foot of snow here and I?m killing some time, so I figured I?d stop in here and see what?s up. I had intended to stay away, but boredom led me here.

Doug, please show us your data on the above test results. You have certainly tested you CBTF boat to state what you have, yes?

Everything you state above is unfounded and most importantly, incorrect! John brings up an interesting point that you have defended with no factual information what so ever.

I would think a more appropriate answer would be something like.

<font color=“blue”> ?Interesting point John. I might disagree but being that I have yet to sail CBTF RC boat I can not say you are wrong. When my CBTF F100 is on the water and I can collect the data, I will let you know if in fact you have a valid point. Thanks.?</font id=“blue”>

Rather, you make up some defensive scenario in you head and try to prove John wrong.

Hmmmm -

I’m still trying to come to grips with that “magic” (and as yet unfounded/proven) 55 degrees!

Why is it 55 degrees - and not 45, 30, 56 or maybe even 59 1/2 degrees?

Why is everything so black and white, and the boat has yet to sail?

Why are others using different degrees of cant to their keel?

<blockquote id=“quote”><font size=“1” face=“Verdana, Arial, Helvetica” id=“quote”>quote:<hr height=“1” noshade id=“quote”>All in all the effect on a canting keel boat of the displaced forces found on a normal keel boat are probably somewhere between 50 and 60% less in the same conditions.<hr height=“1” noshade id=“quote”></blockquote id=“quote”></font id=“quote”>

How was this measured? Against which fixed keel boat and in which r/c class? If the F-100 has yet to be built and delivered - on what - or how - are you basing these claims?

Inquiring minds want to know!

Greg, I think you should be carefull about making such pronouncements about something you obviously don’t understand! You haven’t ever-to my knowledge --sailed a canting keel boat whereas I have many,many hours experience sailing and racing several different canting keel prototypes.
Further, I just received an award(a carbon plaque identical to the one placed in any CBTF boat) from CBTFco for my technical mastery of the CBTF concept and the defense of CBTF I have provided on several forums.
My attempt was not to prove John wrong just to try to illustrate how the physics of both types work.
The two types of boat sailed in the same conditions sail completely differently-one is more or less upright the other is laid down-that is if your test condition is the one that would have the canting keel extended to nearly its max. In those conditions a fixed keel boat would most certainly be heeled way over and the canting keel boat nearly upright.
Comparing the forces acting on the heeled boat vs the upright boat is not rocket science and should be easily understood by most sailors.
If you can specifically discuss exactly what I said that was incorrect I’ll do my best to explain it better.

Doug Lord
–High Technology Sailing/Racing


Doug did not make up that scenario. It was probably explained to him by the guys at CBTF inc. and it is based on solid physics. In fact, the phenomenon Doug describes was described to me (in slightly different terms) by the technical guru at W.D. Schock Boats (the manufacturer of the Schock 40) when I took my ride on the Schock 40. He indicated that the rig on the Schock 40 ended up being placed significantly aft of a “normal” position on a similar sized fixed keel boat in order to offset the lee helm. A normal boat cancels out that lee helm when it heels and the drive of the sails generates a turning moment to weather.

So the theory has been proven out on full sized boats.

Now the question is how much different will model boats be? Given the much lower Reynolds numbers, the keel generates substantially more drag (proportionally) than full sized boat keels do. Given that model boats have longer keels (proportionally) than full sized boats, the relative moment arm is greater as well. So will that extra drag and longer moment arm change the equation and cause the boat to generate more windward helm than a full sized canting keel boat? Probably. But will it be more than a fixed keel boat? I doubt it, but only once we have had a chance to sail the boats will we know the answer.

Lets suppose that the drag of the keel does result in weather helm. So what? All boats develop weather helm as they heel and we have all learned to deal with that by tuning our rigs to keep the boat in balance. If a canting keel boat also generates helm, then the rake of the mast will be adjusted to compensate. The only problem would be if the canting keel at 55 degrees of cant generates more windward helm than the rig and keel of a fixed keel boat at 30 or 40 degrees of heel. I seriously doubt that will be the case. Full sized boats have certianly shown that the helm generating effect of the rig is reduced so the keel would need to be more than 60% of the helm generation for the two effects to equal out. I doubt the effect of the keel contributes to that much of the helm.

I am designing my canting mast US1M with a movable mast base bulkhead that will allow me to adjust the mast position. The forward most position for this will be the “normal” position for a Cobra hull. I will probably allow for about 2 inches of aft movement from there. So I consider this to be an unquantified effect that I need to be able to tune for, but I believe it will go in the direction of less windward helm rather than more.

  • Will

Will Gorgen

By the way, I am a rocket scientist and I understand it too…

  • Will

Will Gorgen

The estimate of turning couple reduction on a canting keel boat was based on the fact that roughly two thirds of the turning couple components present on a heeled fixed keel boat are not present on the canting keel boat. This was a very conservative estimate by the way.
On a canting keel boat you want the maximum throw(dis. side to side) with the keel possible; the limiting factor on models is the mechanism type and the room it takes up versus the beam of the boat. On my prototypes and on the new CK Trainer and F100CBTF 55 degrees IS the maximum throw I can achieve. More throw = more righting moment.

Doug Lord
–High Technology Sailing/Racing

I am Still thinking—thinking—thinking


You are right, the 55 degree number is fairly arbitrary. That is the number that CBTF used when they designed the prototype for the Schock 40 (the Red Hornet). Since that time, it has been a number that a lot of people have used as a starting point for their systems. Since many of those systems are licensed from CBTF, they tend to use the CBTF mechanism and simply scale it to suit their needs.

But there is a bit of science to it as well: The more cant you put into the keel, the more “unfavorable” the geometry gets at the end of the throw. The CBTF guys use hydraulics to actuate the keels on the full sized boats so the angle between the ram and the keel is the complementary angle to the cant angle. At 55 degrees of cant, the hydraulic ram is at 35 degrees to the axis of the keel. As that angle gets smaller, the force required to cant the keel gets larger.

Here’s the math if you are interested: The canting moment equals the sine of the cant angle times the bulb mass times the keel strut length times gravity. The hydraulic force required to cant the keel equals the canting moment divided by the cosine of the cant angle times the ram arm length. Combining those two you get that the Ram force equals the bulb mass times gravity times the tangent of the cant angle times the ratio of the keel strut length to the ram arm length.

The key lies in the tangent function. As you will note, the tangent function rises to infinity at an angle of 90 degrees and it is fairly flat near 0 degrees. So you can do a little bit of canting (near 0) with very little force, but as the cant angle increases the force required goes up dramatically (non linearly).

The flip side to that is the righting moment that you get for the additional cant which goes like the sin of the cant angle (plus the heel angle if we must be precse) so that actually levels off near 90. So you are not getting much bang for the buck as you get to higher and higher cant angles.

So someone in their engineering wisdom did a tradeoff study (along with a lot of packaging considerations and other strength concerns) and decided on a cant angle of 55 degrees.

For our systems the tradeoffs are slightly different. I have settled on a mast cant angle of 40 degrees for my US1M based on the torque of available servos. But I could do a mast cant of 55 degrees if I could find a servo big enough (and was willing to pay for it).

In general, the more cant you can put into the system, the better. But there are practical limits. Until you begin the detailed design work, you need to pick a starting number and Doug has (justifiably) chosen to use the same number that CBTF came up with (for many of the reasons he stated above).

  • Will

Will Gorgen

From Doug’s earlier post.

Shouldn’t the rig being to leeward turn the boat to leeward, not to weather. The effect of drag (wing force) on the rig from it being put to leeward of the boat should have the opposite turning moment of the drag force from the keel sticking out to windward under the water.

The centroid lift force created by the sails is rearward of the center of bouyancy of the boat then the force generated by the sails is turning the boat to weather but this is true no matter which way the boat is heeling.

You have to understand that drag is a small portion of the force developed by the sail; it is the sails force(LIFT) propelling the boat . Viewing a heeled keel boat from above with the rig substantially displaced to leeward the force from the sail(lets assume its acting thru the center of effort)is quite a ways from the centerline if the boat and acting in a direction to pull the boat forward creating a turning moment to weather.
Another way to visualize this may be to consider putting weight on the rig of a model sailboat(on a flat calm day) so that the boat is heeled 35- 40 degrees. Then attach a line to the mast at the approximate height of the CE; pull on the line and the boat will turn in the direction opposite the heel.

Doug Lord
–High Technology Sailing/Racing

Look at the forces involved. If the boat was heeled to windward the forces from the lift of the sails would still pull the boat into the wind/to windward. The force component due to the boat being heeled should be to weather since your sticking something out to leeward. If your driving down the highway and stick your arm out the window, it certianly doesn’t feel like your arm is being sucked forward by the drag force.

You can unbalance the sails by sheeting main or jib alone to create a turning moment in either direction. You can do that with the boat heeled either way.

In dingy sailing you normally heel the boat to windward to bear away, and to leward to head up. I’ve always understood it has somthing to do with the shape of the hull effectively changing as the boat is heeled. Its pretty dramatic in round bilge boats/scow type boats, less so in flatter and chined designs such as skiffs. I cant explain it but it works!

Luff 'em & leave 'em.


While the sails do produce some drag (much like your hand sticking out the window of a car), they also produce drive force (which your hand does not do). The drive force tries to move the boat forward. The drag force tries to move the boat backward. But since the boat does indeed move forward, it is clear that the forward drive force is stronger than the drag force. To state it another way, if the dominant force was drag, then the boat would not move forward.

If you move that drive force off to leeward (by heeling the boat), then the drive force is going to cause the boat to want to head up.

To relate this back to the original topic, if you keep the drive force centered above the boat (by canting the keel rather than heeling the boat to generate righting moment) then you have eliminated this moment trying to head the boat up. At the same time you have introduced a smaller force trying to head the boat up which is the keel drag offset to windward.

But this keel drag has to be less than the sail drive. Using the same logic we used above, if the keel drag was larger than the sail drive, the boat would not move forward. And since the keel strut is much shorter than the mast, the amount of lateral offset from a canting keel is going to be less than the amount of lateral offset of the sail drive due to heeling even though the strut cants more than a fixed keel boat would normally heel.

But as you point out, windward helm can be cancelled out by changing the balance of the sails. So if there is any adverse helm issues with a canting keel boat (which simple physics cannot predict) then you just tune the boat to deal with it…


I don’t know what kind of dinghies or scows you sail, but on all the dinghies (420, FJs Larks, Lasers, Tech Dinghies, Interclubs, 505s and more) and scows (M-20, E-Scow, C-Scow, A-Scow) I’ve sailed, when you heel the boat, it heads up. In fact, the first part of any good roll tack is to let the boat heel which causes the boat to want to turn into the tack. If you let go of the tiller during this phase of a roll tack (as my collegiate coaches used to make us do during practice sessions) the boat will head up. In fact, if you are good, you can execute the roll tack without touching the rudder at all by allowing the boat to heel at the beginning of the tack to get the boat turning.

Now, I’m sure you are going to say “well, yes, but the next thing you do in a roll tack is slam the boat back down with a massive hike to the old high side.” That is true, but if you do this while the sails are still full, it will bring the tack to a grinding halt. You need to wait until there is no more load in the sails before you roll it. When you do that, you are pushing the daggerboard against the water which pushes the boat further through the tack. And since the sails are luffing, there is no sail force to cancel out the turning.

When I was in sailing school, one of the teaching techniques that the instructors used was to remove the tillers and force us to sail without being able to steer with the rudder. We were taught that by using the balance of the sails, heel and fore/aft body weight, you could effectively steer the boat. As far as the heel was concerned, allowing the boat to heel up caused it to head up and flattening the heel caused it to head down.

I’m not sure if the water is frozen where you are, but since you are a dinghy sailor, the next time you go out for a sail try this - while you are sailing to windward, let go of the rudder and let the boat heel up. The boat will head up into the wind. Try it, you will see.

  • Will

Will Gorgen