Thanks, Dick, I'll look into it.
P

I've removed the rudder and stock and measured up for the size of nylon block required (not easy, as it's quite awkward to get at) and ordered some nylon from a supplier.

When I had the rudder assembly on the bench, I lined it up as it should be according to the manual and it seems to have been almost 6 inches out of alignment, which I hope is the cause of the strange steering characteristics. I wasn't sure how to fix the block to the rudder stock, so I emailed a specialist adhesive supplier to ask what would be the best adhesive to use for nylon/aluminium and they said it was 'problematic' and they couldn't recommend any adhesive. So if anyone has any thoughts on this, I'd be happy to hear from them.

Meanwhile I'll carry on with cleaning and painting the rudder and when the boat goes back in the water I'll report on the changes to the steering characteristics, if any...

Best regards, Peter

Hello Peter,
I actually used a solid rubber block for my buffer and trapped it on the lowest bolt thro the channel section.A single bolt is sufficient as the block bears against the channel so can't rotate.You should find a major change as with that kind of misalignment the forward portion would make it switch abruptly.Rather as happens if you overdo the revs in reverse and the tiller slams across.
PeterL

Yes, that's exactly how it was, Peter. If I let go of the tiller for just two seconds, it would slam across and the boat would turn 180deg before I could react. It makes for a very exciting time when negotiating dozens of moored boats and you want to retrieve your woolly hat that's just out of reach...

I'll look into your idea of using one of the existing bolts, but as you say, there won't be any shear or turning forces on the block, so it shouldn't be difficult to fix.
P

Hi everyone,
can anyone say where the measurement of rudder rake is taken from/to?
Is it from the line along the front of the rudder stock or the line through the bolt hinges?
rgds
Chris

According to the handbook, it's the line along the front of the rudder stock. The projected line should intersect the rudder at a point just forward of the point where the bottom horizontal line of the rudder is tangential to the radiused bottom front corner of the rudder...

After removing the rudder from the stock, I found that the missing nylon block is not actually missing - it's just painted to look like aluminium, so it's a mystery as to why the rudder is so far out of position. I've fitted the new block on top of the old one, and sized it so as to ensure it stops the rudder in the correct position.

P

Actually if you look at the sketch by Bill Parker,now included in some of the handbook versions,and as I linked to above,the line extended down from the front of the stock seems to intersect the curve at something between a 1/3 and a 1/2 beyond the curve/horizontal intersection.In fact he described the line as ' intersecting the bottom round '
Slightly vague but in my case a block just slightly thicker than the depth of the channel did the job.That is the minm. spacer reqd.to halt the blade before it strikes the flanges of the channel.

Thanks for the responses re how to measure the rake - my current block sits inside the channel at the bottom front of the stock and is 35mm thick giving around 2.5in of rudder blade in front of the front of a line extended fron the front of the stock.

FWIW I made the block with sorbo rubber (as used to clean abrasive belts on sanding machines) along with some plastic soffit offcut, fixed with a single s/s screw through the front of the stock.
Under both sail and motor the boat tracks straight with the helm free but the moment something knocks her off course (wave or wind shift) she rounds up to the wind and can steer through a tack, so use of a tiller-mate has proved beneficial.
BW
Chris

Hi,

Adding a little more. Position of the tip of the rudder alters the amount of “balance” in the set up of the rudder. Area of blade in front of the pivot point v area behind. Some balance reduces the effort needed to push or pull the rudder. Raising rudder slightly reduces or removes the balance. The more it is raised the more weight you will get. When motoring the propwash changes the balance. Too much balance and the ruddder will flip to the end of its travel. (Faster water flow v sailing). The balance area pushes the rudder away from centre line once it is turned slightly. Boats with a vertical sliding rudder blade often have a wedge that controls the tilt forward. It seems from the thread you have a bush, that will slowly increase the balance effect as it wears ( or drops off )

Nick

Once again, thanks to everyone for your replies and suggestions, and here's an update:

To recap: I removed the rudder assembly over the winter and found the bottom tip of the rudder blade was almost 6" too far forward when fully down, so I assumed the nylon stopblock had come off. However, the block was still there, so I fixed another one to it, so as to increase the thickness by a couple of inches. I adjusted the thickness so that it put the rudder into exactly the same position as shown by the illustration in the manual.

I was uncertain what would happen when the boat was launched, but in fact it seems to have fixed the problem. There is now no longer a tendency for the tiller to whip across into full lock when left unattended. However, the boat now turns consistently to port under engine. At low revs there is just a gentle pull, but at high revs it pulls quite hard. I didn't get the chance to try it under sail, as there was no wind.

I'm assuming this is caused by the wash coming from the prop. Do other people have this?

All the best, Peter