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From: David (no email)
Date: Wed Dec 31 2003 - 10:44:48 EST
>Bill Kimley wrote:
>I installed a #2 pump on Diesel Duck 44 that had a 13" cylinder (BA-175)
>and it failed on the first four day cruise. The locking pin broke on the
motor
>shaft. Installed the smaller #1 pump and it has worked fine for a 9000
>mile cruise from Hong Kong around the Pacific finally landing in San
Francisco.
>
>According to a company rep (AutoNav) the high volume of the #2 pump
>instantly moves the small piston so far that the computer causes the pump
>to operate back and forth in multiple very short spurts. This can stress the
>shaft. Note: AutoNav, like me, uses the same computer for #1 and #2.
>Bill Kimley
Then Arild Jensen wrote:
Looking at the Diesel Duck 44 and a Hatteras LRC 42 there seem to be a
considerable difference in rudder size not to mention big differences in prop
size and speed. <snip> Knowing how a particular brand of autopilot
responds to a given boat hull is not
easy to predict ahead of time without having a past use database.
Going back to the original question; if Skooch is fairly responsive to the
helm
then a type 1 pump will likely work.>If Skooch requires a fair amount of
wheel to get the boat turning at the normal cruising speed then upgrading
to the type 2 pump may be required. If a Type 1 is too slow and a type 2
is too fast flow rate adjusters can be inserted <snip> to get the correct
rate of turn.
cheers
Arild
There have been many thoughtful responses to my inquiry. Thanks to all.
So far nearly everyone suggested "bigger is better" when it comes to
designing auto pilots. I will follow this route, with reservations. The
discussion above shows that on some installations the larger pumps may over
power the system and cause problems. Skooch has a greatly different
steering system than the center barn door type rudder on the Diesel Duck.
Skooch has twin engines and twin rudders and a smaller keel, less ballast.
Skooch moves fairly to the rudder and is not what I would call sensitive,
but I have only driven a dozen or so boats over a lot of years.
I will get the bigger pump system. As Arild pointed out one can adjust the
flow downward and Raymarine has additional expensive software called a
"Rate Gyro" which attends to this exact problem while it "learns" the boat
movements and adjusts the rate of turn based on the gyro-compass and sends
this info to control how far to turn the rudder.
Now all I have to do is put it in. Thanks for all the help, and I will
report back to the list after the first cruise this spring.
Skooch - Hatteras LRC 42
Worton Creek, MD
David Stahl
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