I would use either a pneumatic cylinder or a hydraulic cylinder, gimbaled at both ends. Connected by a clevis pin fork and tang
arrangement at the tiller. I would connect a small accumulator tank in series with a simple ball valve where one end goes to one
end of the cylinder. The other connection of the cylinder connects in series at the accumulator tank so that all of these are in
series with each other in a loop. When the valve is open air or fluid simply moves freely around the system as the tiller is
moved. The closing of the valve solidly locks the tiller in that position. The key here is to use the largest internal diameter
plumbing as possible to reduce drag when the valve is open. These parts are available surplus everywhere and they are inexpensive.
Steve

"IanM" wrote in message ...
cavelamb wrote:
Hi Steve,

I'm trying to figure out how to make a toy, and need a bit of help
this time.

This is a Tiller Trim for my sailboat.l
The idea is to lock the tiller down so I can go do something else
for a few moments without the boat heading for the nearest land mass
or other obstruction.

There are products on the market that address this, and I've used all
of them at one time or another.

But THIS is what I want.
It's a screw device that drops onto my autopilot mounts and allows the
tiller to be moved slightly by means of a threaded rod.

This is for those times that I just need my hands free for a few minutes.
I don't expect it to steer the boat for miles on end (although it actually
could on certain points of sail, since the boat behaves beautifully then).

The autopilot (Otto) needs electrical power - and being a mechanical device
moving several pounds - constantly - it uses quite a bit of battery.
It also has to have the GPS system up and running for compass information.
In all it pulls peak of 5 amps(!!).
Here is a pic of Otto in place...
http://www.home.earthlink.net/~capri26/images/otto2.jpg

I have used it at times as a simple mechanical trimmer by powering up, setting
the trim via the steering buttons, and powering back down. It _can_ be done,but takes way too much time and attention.

My dream toy can be dropped in place and adjusted with a few twists of the handle - done. And if it needs tweaking, just twist
the handle a bit again.
No powering up or down, no bumping buttons back and forth trying to hit the
right spot. No power needed (yea!).

So anyway, this is what I'd like to have, but plainly, I'm an engineer - not
a machinist. Would you mind taking a few minutes and looking at the attached
to see if there is an obvious way to have it made - correctly, or at least
sensibly?

If you don't have time, I'd certainly understand, but I could use the help!

Thanks,

Richard

It looks fairly easily buildable out of on-board resources without access to a machine shop. There are a few small modifications
I would make though. Loose the pivot at the tiller end. The autopilot dowsn't use or need one there, why should your rod? Much
simpler to engage without.

Make it about 4" to 8" over length and equip it with either three or five sockets for the pin on the tiller, so it can be
centered or quickly biassed port ao starboard as required. It will vastly reduce the amount of twiddling required to adjust it.

Use an old bottle screw that's been retired from rigging use for the adjustment with a forked reverse threaded end. That's half
the coaming pivot done and most of the fiddly bits. The other half is a cut down rigging link, anchor connector or random block
of marine mystery metal to fit the jaws of the bottle screw end. Use the normal pin from the bottle screw end as the pivot.

The AP socket pin is then made from a bolt sized so the smooth shank is a nice fit in the socket, locktited into a tapped hole
drilled in the bottom of the previous part and then the head is cut off.

The normal thread end of the bottle screw is then either cut off and welded (if you farm it out), silver soldered or replaced
with a length of stainless all-thread long enough to give enough engagement to give a reliable bond with whatever high strength
polyurethane I have handy, into a piece of stainless (or possibly alloy if glueing - if thick wall, you may be able to tap it
for at least partial thread engagement for strength)

The other end has a durable hardwood plug glued in, lignum vitae if you have a bit, or some Tufnol rod or other engineering
plastic, nicely fitted to be a light driving fit, and sufficiently out of round to offer a decent glue line thickness on most of
it's circumference and the holes for the tiller pin carefully drilled using the one on the autopilot for a model.

Should be reasonably light, strong, professional looking and do-able for less than a drink out if I have scrounged enough parts
from the marina skip. I probably have enough materials on hand aboard to make one or two though I'd have to buy some all-thread
and the bolt to cut down for the coming socket pin.

Usage is fit to coming ( or un-park from stowage there) drop the closest socket over the tiller pin while helming with the other
hand and twiddle the bottle screw body for best course holding.

I wont be making one in a hurry though as I find a pair of lanyards and a couple of slipped hitches quite adequate or I can
always twiddle 'George's' push rod between my palms to adjust him with the power off.

--
Ian Malcolm. London, ENGLAND. (NEWSGROUP REPLY PREFERRED)
ianm[at]the[dash]malcolms[dot]freeserve[dot]co[dot]uk
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