Tiller and rudder servo arm?

What is the general theory behind rudder set up? Is the arm on the servo short and the arm on the rudder long, or are they the same on each? Do people adjust them for different conditions. The IOM i am building will have the rudder servo below deck midships exiting behind the main sheet post.

Hey AB,

Your rudder servo arm will most likely turn 90 deg stop to stop.
You probably don’t want the rudder deflection more than 30 deg each side of center so the tiller arm (on the rudder post) should be longer than the servo arm. Leave them both long until you have test sailed and are happy.

Bear in mind that, within reason, longer arms on both ends helps minimize slop due to imperfect clevis/connector attachment, i.e., a 1/32" clevis pin inside a 1/16" tiller arm hole will allow more radial slop on a 1/2" arm than a 1" arm.

If you have a computer radio you can adjust the endpoints of the servo travel to fine tune your rudder travel. Try not to go below 100% travel as you are basically leaving torque (and resolution) on the table.

I use exponential on my rudder channel to soften the response around center.

You probably won’t change your hardware set-up once you’re happy with it.

Hope this helps,

The top competition sailors in the UK set rudder throw to around 55 degrees either side of neutral on an IOM.


Could it be that “brakes” are useful at the starting line?

Why not? Exceptional maneouverability, the ability to do lightning penalty turns (smile).

Sort of related…
My boat will “jump” or pop the bow out of the water if I throw in a hard tack in the right conditions. While it’s certainly fun to watch, is this fast?

Mine too, any ideas what causes it?

The top competition sailors in the UK set rudder throw to around 55 degrees either side of neutral on an IOM.
Today 07:04 AM

Maybe the top sailors can control their thumbs well enough to put in 35 when they want it and 55 when they need it. Unlike me who thinks tack and full rudder are synonymous.:smiley:


If you just kinda bang the stick hard over, well, I guess not.

Watching Ken Binks make a lightning tack, however, is another matter. Ken is a 9-times UK champion RC flyer (free aerobatics, I think), and he knows how to feed the sticks in, and then out, in the ‘right’ way. He can make the fastest tacks, and the quickest penalty turns, of any RC sailor on the planet. I don’t just mean the turn is executed quickly; I mean the boat barely loses any speed because (1) he is feeding the sheets exactly in tune with the changing apparent wind angle during the turn, and (2) his rudder throw progresses as the hull swings. (If you just bang the rudder over, it stalls. If you feed the rudder in so it matches the swing of the transom such that you keep its angle to oncoming flow at no more than an instantaneous 15 degrees, it won’t stall and hey presto you have just gained a boat length on me…)

Is this fast?

No. It brings the boat almost to a dead stop. Under normal conditions, a gentle rudder pressure to bring the bow up into the wind…maybe a little more rudder as the bow passes head to wind and an ease of the rudder as the boat falls off onto the new tack. However under extreme conditions of wind and waves, a full rudder ‘crash tack’ may be all that gets you around.

When the boat is heeling, application of the rudder to tack has a downward component, pulling the stern down, and so the bow pops up.

Thanks guys.
One more thing to work on…

I suspect the guys running 55 deg rudder throw are using expo?

Just when I think I’m approaching mediocre something knocks me back down again.:confused:

Hi Don

I know the feeling. Over some years of watching the planet’s best, I have a short list of stunning, jaw-dropping skills:

I’ve mentioned Ken Binks for the planet’s most efficient penalty turns.

Craig Smith I rate as having the greatest boat control. I saw him reverse his IOM into his preferred starting position on the line with 15 seconds to go in a world championship ‘A’ fleet.

Graham Bantock can calculate a lay-line better than anyone I’ve seen. With 20 boat lengths to go to the windward mark, he’ll tack onto the line that clears the mark by 25 mm. No more, no less. He’ll then sail that line perfectly straight while everyone else is weaving, luffing and footing and fighting to do it…

Martin Roberts knows what the wind is going to do before it does it better than anyone I’ve seen. He’ll change tack when you immediately think, ‘He’s lost it, what the hell has he done?’, and then 4 seconds later the shift comes in that immediately positions him in complete command…

I use a DX6 computer radio and by using the Dual Rate switch and End Point Adjustment it allows me to set my rudder throw at two different settings. I have a prestart setting with ±60° of travel and then an upwind setting with ±40° of travel. It allows me to be very maneuverable in pre-start, but not over turn the boat during tacks on the beat. Works for me anyways…


Too true Lester !! I have sailed against Ken, Graham and Martin at different times, and seen these exact skills in action. Truely amazing and humbling at the same time!

As regards expo and computer radios - Martin Roberts tends to use the cheapest non-computer radios. It’s all in the thumbs…

Has anyone seen or tried using gears and belts instead of rudder arms and rod connections with the rudder servo? I was at the hobby shop a couple of days ago and saw the belts to drive the small heli’s and started to think maybe that could work? push and pull?

I regard it as a form of self-handicapping (smile). If Martin ever decided to take technology seriously, his winning gaps would mean no one would want to sail against him again. Similarly, if Peter Stollery ever decided to sail a competitive IOM or Marblehead, he’d be a multiple world champion.

Not that my skills are terrific but I find that using the exponential settings on the better radios is a big help when you start out as it helps to reduce overcontrolling the boat when you are trying to go mostly in a straight line. It cuts down on the amount of weaving you do but still allows you to have full control/full travel when you do need it. I also find that as you improve you/I tend to start to reduce the exponential effect until you have learned to keep your finger from moving so much and/or learned to use the trim switch for minor setting changes.

Most servos don’t actually deliver the advertised 90 degrees anyway so travel with a standard kind of radio is something less than 45 degrees each side to start with. Another place the better radios are good because they can allow you to drive the servo to full travel or even slightly past depending on the servo.


I have seen boats where there are two rods connecting the servo to the rudder, one from each side of the servo arm to each side of the rudder arm. This gives a pull/pull and eliminates any loss caused by the rod deflecting as it is pushed (in compression)