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 Raymarine ST1000 Tiller Pilot

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T O P I C    R E V I E W
Voyager Posted - 07/16/2021 : 08:39:23
Hello all,
Does anybody have experience with a Tiller Pilot from Raymarine? A friend has one and seems to be having some trouble with it.

It looks like a good, all-in-one unit with lots of smart features: stand-alone, connects to GPS and also uses NMEA connectivity for windvanes and the like.

Problem is that he has a small Wharram catamaran that has a dual tiller and rudder connected by a common rod between the two. The unit connects to the rod so there’s plenty of leverage, however, when the autopilot works hard in waves or gusts, the 12A fuse will blow out.

Now 12A is a healthy amount of current, so I wonder whether this is out of the ordinary for the unit, or if it occasionally blows the fuse.

A few suggestions included:
1. Use a slow-blow fuse
2. Add a large capacitor to absorb the transients downstream from the fuse. Perhaps a 2000uF cap at 25VDC.
3. Check all the mechanical connections for stickiness or friction and use a lubricant to ease the load.
4. Add a small value, high wattage “current limiting” resistor in line.

I think the slow-blow fuse may illustrate whether the problem is high current transients versus sustained high current draw. It could lead to over-working the motor so there’s a potential downside.
The capacitor approach would work if the current draw is indeed short transients. I believe the slow-blow fuse would be needed for the capacitor inrush current.
It’s always a good idea to grease the skids, so item 3 would be helpful regardless of what else is done.
The current limit approach might cut power for long enough to kill the microprocessor on the autopilot. That would be counterproductive…

Any thoughts or suggestions on this?
3   L A T E S T    R E P L I E S    (Newest First)
Voyager Posted - 07/16/2021 : 17:35:01
Steve, you’re probably right about too much mast rake because last week when we were out in 12+kt winds, we were reaching at 10kts and the tillers were pretty tough to adjust - so much so I found myself adjusting the tiller extension to sit against the gunwales to relieve the force. The “mast” is a 12ft tall 3” steel pipe with a forestay and two shrouds with turnbuckles. She’s gaff-rigged with a 110% jib sail.
Thanks for your viewpoint, I’ll make that suggestion.

Leon, my battery-power O’scope is in the shop, but I might still have my +/-20A analog ammeter somewhere. I also wondered about the lever-arm distance and how that affected the required force of the autopilot. What Ifound surprising is that the motor can draw more current than the fuse is designed to handle. I’d have thought that the maximum current draw would be substantially less than the rated fuse. I’m not sure if I agree with that design philosophy.

If it’s just an instantaneous peak, that’s a design compromise. If so, I wonder why a slow-blow fuse wasn’t in the original design? We’ll see how the fuse works out shortly.

Thanks!
Leon Sisson Posted - 07/16/2021 : 15:42:58
Although I don't have any personal experience to offer regarding a Raymarine ST1000 Tiller Pilot on a Wharram catamaran, here are my observations from using a ST2000+ on a Catalina 22 and 25.  (I also have an old Autohelm 1000 which I hope to some day get around to installing on the smaller boat.)

On my Catalina 25 with original unbalanced rudder, the Raymarine ST2000+ used to trip a 5.A circuit breaker in conditions which caused it to hit the limit of its travel.  After switching to a 10.A circuit breaker, I noticed that the ST2000+ would strain at the end of its stroke for a few seconds, then quit trying until the load was reduced (without tripping its breaker).
 
Also, under sailing conditions which called for rapid steering corrections, the ST2000+ seemed slow, requiring even larger tiller movements to make up for the sluggish response.
 
I spoke with Raymarine tech support about the specified 18" distance from pintle axis to autopilot tiller pin, which seemed cast in stone in the installation manual.  He said it's OK to treat that tiller pin position as more of a suggestion than a hard requirement.  So when setting up my Catalina 22 for a tiller pilot, I reduced that radius to 13", which seems to work fine, and steering response under tiller pilot seems much improved.
 
So along with Steve Milby's excellent advice regarding mast rake and sail plan balance, I'd suggest taking into consideration rudder blade shape (particularly balance) and tiller bar radius (from tiller bar pivot point perpendicular to rudder pivot axis).
 
I like the idea of a very large capacitor on the load side of the fuse or circuit breaker to dampen brief current spikes.  If you have a multimeter with a high enough amp range, or if the boat has a power monitor, it might shed some light on the max current surge issue.  For complete overkill instrumentation, how about a battery-powered oscilloscope across a fractional ohm resistor in series with the autopilot?
 
Steve Milby Posted - 07/16/2021 : 10:38:24
Obviously the load on the system is excessive, so reducing the load should be the first priority. Put either a bubble level or a plumb bob on the mast to determine how much the mast is rakeed aft. Then reduce the rake until the helm becomes nearly neutral. Consult the designer's recommendations for the degree of rake that is recommended, but I wouldn't hesitate to experiment with a little less of a rake. I don't think of those recommendations as "carved in stone." The designer put turnbuckles on each stay specifically so the owners could adjust them to their liking. My Cal 25 had a horrible weather helm when I bought it. It was so bad that I considered it dangerous. I adjusted the mast to very nearly perfectly erect, and it still had weather helm, but it was very light, and the boat became very fast.

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Notice: The advice given on this site is based upon individual or quoted experience, yours may differ.
The Officers, Staff and members of this site only provide information based upon the concept that anyone utilizing this information does so at their own risk and holds harmless all contributors to this site.