I used a "traditional", basic setup: a rope from the sheet through a block at the windward side of the cockpit to the tiller. And a bungee-style system to pull the tiller against this (ie to the lee).

I also might have used a 2-3 -part block arrangement for the sheet-tiller -rope, because I had one that I used with the BR. The point here was to reduce the force of the sheet pulling the tiller (or vice versa, if needed.). This also affects the scale of the movement. I'm not sure if I used this with JR, though.

The steering system worked well while going windward, but the suprising part was the stability downwind on a stud-keel + centerboard boat that weighs 500kg. I suppose everything just was perfectly balanced by sheer luck. The plump bow might have played a role, too, especially downwind.

So... with wind and sea up, we did the best approximation of Arne's idea without bungee -  bias the vane and servo off-centre to give the vane a constant force to act against, and not let it have to deal with a 'sign change'. That helped quite a bit. David's suggestion of gearing down the servo/tiller linkage helped, but there was quite a compromise between damping oscillations and getting sufficient tiller motion. I geared up the vane/servo linkage to compensate. I also shimmed the rudder stock, which had a little slop. Net result: oscillations of up to 25 degrees, in fair sized quartering seas and wind just shy of taking a first reef. 

I'll head into Whangarei tomorrow for sheaves/bearings/new blocks etc. and see if that helps...

Annie Hill wrote:

Bryan Tuffnell wrote:Fantail is one of those boats that I think a beginner would tend to oversteer on a run. The helm does load and she naturally yaws when running, and a steady grasp of the tiller resists this and holds her straight.

I'll take your word for that - I have to confess that I always found her easy to steer regardless of the point of sailing and hadn't noticed any tendency to yaw excessively.  But then, a dainty fin-and-spade boat, with junk rig is something of a contrast to a hulking great steel brute, with a long keel!  BTW, you do reef early, don't you?  So many people who haven't sailed junk before hang on to sail downwind because of the novelty of being able to go fast in the direction that they want without having to add extra sails.  But a reef or two often makes things easier without noticeably reducing speed.

Annie, has the vane ever operated successfully on a run?

Only in a flat sea and/or light conditions.  It was pretty good in Tasman Bay, but on this coast struggles a lot more.  I guess this would confirm the boat's tendency to yaw, with the then concomitant over-correction by the wind vane.  I did, once or twice, slack off the lines on the chain which sometimes helped and is a crude way of achieving what David suggests: moving the lines further forward.

Annie, I agree that Fantail is easy to steer on any point of sailing, with one proviso. I think you, and anyone with a bit of experience behind them, would know that when running you turn the tiller only to keep the heading constant. In my limited experience, with a flat sea and steady breeze, the helm can be left briefly even when running; there is no great tendency to yaw. However if either sea or wind fluctuates and the heading is maintained, a gentle but definite weather helm develops. I think (and have recently seen) that some people have a tendency to turn the tiller in response to rudder pressure, rather than heading change, and I feel that it's chasing the constant tiller pressure that causes oversteer. Pure speculation on my part, but I have a feeling that this is the key point that makes both a beginner and wind vane more challenged when running when conditions are anything other than very good (both need to ignore feedback from rudder pressure). I'm wondering if Fantail's short coupling and large rudder develops that little tiller pressure when she wants to yaw; the after edge of the rudder traveling in a greater arc than the leading edge. Maybe?

We've got strong, gusty, choppy conditions today and it's a bear to try Arne and David's suggestions... particularly as I can't find any bungee aboard. Hopefully things will steady and I'll have something meaningful to report soon.

Gak. The nearest automated weather station is report 38 knots. Perhaps tomorrow?

David Tyler wrote:

Bryan, you're 180 degrees wrong about the geometry. This servo worked on Tystie, too well. It is one of the cornerstones of servo pendulum design that when the servo tiller is pulled out one way, the servo blade follows it out the same way, thus putting in the necessary negative feedback. So, if the servo tiller is facing forwards, it must be below the power axis. 

Darn, that's twice now! David, I understand that the servo blade and its tiller must operate in the same sense to damp its response and limit it's actions. 

Where I'm confused is when the boat yaws. Say the stern yaws to port. The servo would sense this, swinging to starboard and correctly turning the tiller to starboard if left to itself. However, because the rudder isn't fully balanced it senses the yaw, and turns the tiller and by extension swings the servo. But, because the vane is doing its job it has also sensed the yaw to to port and has tumbled to starboard, holding the servo tiller, so the angle of attack on the servo is now acting against the desired starboard swing of the servo, trying to turn it to port instead, positively coupling to the original yaw to port. If this happens, this action would compete with the correct function of the unit as a whole. In other words, does feedback from the rudder moving due to yaw, which Fantail's does, damp the servo's yaw response (out of existence, possibly)? Does this make sense? This is what I really want to be wrong about, because the solution to that would be to put the servo tiller above the pendulum axis (or reverse its direction), which would compete with the servo's need for damping.

I'll try both shifting the tiller attachment point and the bungee - thanks guys.

Here's that photo:

http://www.junkrigassociation.org/Sys/PublicProfile/30361922/Photo/

61733681/61733710/0?dh=0&cppr=0

When reading about this, I understand that Fantail has the luxury problem of too powerful vindvane gear  -  quite the opposite of the problems I had when steering my 23’ Malena with a direct drive Belcher gear:

(see JRA Magazine 51 p.16 – 18.)

To get the straightest course upwind in uneven wind strength, Belcher ‘s advise was to set the counterweight low. In that case the weight itself would help to pull the tiller “up” to bear away in case a wind gust made the boat heel over (and increase weather helm).

When running before, Belcher’s advice was to move the counterweight up to make the vane top heavy. This was to help keeping a straight course with the boat rolling. The vane thus tried to make the boat turn to the side it rolled (..or at least to try to hinder the opposite from happening...), even before it had started to round up. This worked surprisingly well, as long as I kept the sailplan-to-hull balance right.

Another armchair idea for Fantail:
How would it be to use bungees on both sides of the tiller to make it want more to stay in centre?

Arne

PS: ..and yes, I repeat my suggestion of making artificial weather helm with a bungee. Nothing could be simpler than trying that...