Good Intentions is a William Akin Ingrid 38.. Double ender, full keel with
outboard rudder. (Colin Archer to some) The design displacement was to be
27,000. I've only been in the water a little over a year and at the time of
launch I was already down to the design waterline before loading the
cruising gear and provisions. So, my point, she probably displaces at least
14 ton now with 70% of the gear onboard and about 10% provisions.

Her calculated hull spd is ~ 7.5 knots and I can achieve about 6.5 with the
25 hp Volvo @ 2000 rpm and a clean bottom.

As can be seen in the picture http://hood.hctc.com/~esteve/launch15.jpg the
rudder is deep and has a lot of area. My estimate is 10 sq/ft. With the full
keel and at 4-5knots the rudder requires very little effort to steer a
straight course, however to make a hard over turn, it takes the full
strength of the helmsman on a 6 ft tiller. Part of this is due to the 37.5
deg. angle of the rudder and the fact that the prop aperture is in the
rudder.

Under sail the steering characteristics are different. Much easier on the
helmsman.

Thanks for the input Jim and everyone else. I really appreciate the
technical info.

Steve
s/v Good Intentions

The 1/4 HP motor on my WH only runs when moving the rudder.
It is current limited to 22 amps max. But that would only
happen in pretty rough seas.

Doug
s/v Callista

"Jim Woodward" wrote in message
om...
How big is Good Intentions, Steve? 1/4 horse is bigger than the
autopilot pump on Swee****er (Swan 57, actual weight about 60,000
pounds in round-the-world trim). I don't remember how strong it was,
but both physical size and power consumption suggest around 1/10hp.

As an extremely rough check on the sensibility of your numbers from
Glenn's formulas, the motor driving Fintry's hydraulic steering was a
2hp 220VDC. She was designed to be bulletproof -- Lloyds 100A1
Maltese, for navigation on the North Sea -- so I suspect that half
that would have done fine. Since rudder area varies as displacement
to the 2/3 power and speeds are probably similar (under 10 knots), 1/4
horse should be good up to around 1/4 of Fintry's displacement, say 37
tons.

1/4 horse is 186 watts, so a perfect motor would draw 15 amps at
12VDC. Your results will vary with reality, maybe double -- small DC
motors aren't very efficient.


Jim Woodward
www.mvFintry.com


"Steve" wrote in message
...
Thanks for the formulas Glenn.

I ran the numbers to get some idea of what I might be looking for.

Seems I should be using about a 2"X20"X1.5" cylinder, 318psi @ .186gpm.

Using a slightly oversize pump at a lower RPM, I would need a 1/4hp
motor to
achieve the 15 sec. hard over time.

Seems do-able on paper. I just don't know what the max current draw
might be
for this motor. I'm sure someone has a formula for this as well.

Steve
s/v Good Intentions

I gotta say that this is one of the better discussions I have read on this group
in a long, long time. I am enjoying this immensely. Steve, you have a neat boat,
and I hope you can do some decent traveling in her. Glen, you have a great
head..good to have you around.

Cheers,

Larry DeMers


Glenn Ashmore wrote:

oh,oh,oh, I forgot you have an outboard rudder. 15 seconds is probably
a pretty good rate. That ol' girl should keep her head pretty well with
no help and probably will not want to turn any faster than that anyway.

Don't ask me about the control box. The electronic side of my brain
overheated on that remote control light switch and blew out completely
after figuring out the automatic flush/backwash circuit for the
watermaker. :-)

Steve wrote:

Thanks again Glenn.. Makes sense, however (as always), as you can see in
this picture http://hood.hctc.com/~esteve/launch15.jpg
the rudder pintle line extends up and behind the head of the rudder. So this
would require a tiller arm of at least 20" and even that is awkward due to
the rudder angle of 37.5 degrees. The cylinder could be rail mounted and
reach over the tiller head but that wouldn't be very elegant.

Looking at this problem and the picture, I am thinking of a cylinder mount
on the boomkin and a tiller arm lower down and perpendicular to the rudder.

I could resolve this by installing the tiller arm though the stern post into
the lazarette, but I really hate to give up all that storage. And then there
is the engage/disengage problem and sealing up the opening for the tiller
arm

Just about anything that is behind the stern rail would require a method to
remotely engage, disengage from the helm position.

Strange how a serious cruiser would call it a problem while DIYer will see
this as a mental challenge.

The (mental) wheels are turning. I'll start a new topic in
Rec.boats.cruising when I get some ideas.

Oh Yah! before we abandon this Elex topic, I still need a 12vdc controller
design. Haven't actually found anything here that I could get my head
around.

Thanks again.

Steve
s/v Good Intentions



--
Glenn Ashmore

I'm building a 45' cutter in strip/composite. Watch my progress (or lack
there of) at: http://www.rutuonline.com
Shameless Commercial Division: http://www.spade-anchor-us.com

Bruce in Alaska wrote:

You missed the point entirely with the above. The PWM for the rudder
position is set in the controller design and does not care what mechanism
is moving the rudder, andlong as it has postive control over that
mechanism. (ie move right, oir move left) The rest is already designed
into the controller feedback loop, and a nonissue for the user. It
could be an issue if you were designing an AP controller from scratch,
but that is not the case in this thread.

Unfortunately that IS the case. He wants to control the drive from a
simple tiller pilot output. That is just forward and reverse. No PWM,
no braking, no rudder angle input, no fancy logic. I don't see a way to
do it in the first place but a balanced double ended cylinder will make
what ever solution he comes up with a whole lot simpler.

-
Glenn Ashmore

I'm building a 45' cutter in strip/composite. Watch my progress (or lack
there of) at: http://www.rutuonline.com
Shameless Commercial Division: http://www.spade-anchor-us.com