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From: Arild Jensen (no email)
Date: Tue Dec 30 2003 - 09:22:28 EST
----- Original Message -----
David wrote:
> The Raymarine folks told us to get the Type 2 hydraulic pump, which forces us
to
> buy the next higher course computer as well.
<snip>
Walt replied:
I ran into this dilemma when installing a Navico
Their tech support told me on a displacement or semi displacement boat with a
keel the smaller pump would work fine.
When I have looked at the installations, I have invariably seen too small of a
wire gauge from the
CPU to the pump with the resultant voltage drop.
Comment:
The above two conflicting bits of advice is a classic conundrum with all
autopilot installations.
It is also the main reason why this is perhaps the most error prone kind of
installation for DIY or even installers who only get to do a few units.
Walt correctly points out one common problem.
However this is only one aspect of the equation.
What is really a major issue is the rudder size and hull response to a
specific amount of rudder movement.
A small spade rudder and a fast turning prop will require "x" amount of
rudder angle to produce a given rate of turn but only a t some specific speed.
On that same boat with a slower turning prop you need a much larger rudder area
to get the same effect. ore else much more rudder angle
Autopilots which do not have a rudder angle sensor included must rely
entirely on the compass sensor to detect vessel movement.
This is not as effective as knowing how far the rudder turned to give a
certain amount of hull turn.
A larger pump can move the rudder ram faster than a smaller displacement pump
but the rudder angle sensor will provide feedback to prevent overshoot. No
rudder angle sensor can speed up a too slow rudder movement.
The reason Raymarine recommend the Type 2 pump is sound.
The more expensive controller has larger heat sinks and higher output current
capability FETS to switch the motor current.
For all my Raytheon installations I used type 2 pumps for this reason.
It gave me a greater range of response and eliminated expensive call backs
from customers who might need follow up field service.
It might be feasible to get by with the type ! pump but I would then
recommend you use the largest size hydraulic line possible as well as the
largest size wire to minimize voltage drop.
Since the controller may end up working harder when trying to drive a cylinder
near the maximum size range I would also recommend that you locate the
controller in a place where it can get adequate cooling.
I know this is exactly opposite to what you probably would like.
Most people prefer to bury the darn thing out of sight and out of mind in some
hidden corner with no ventilation etc.
When I worked at the Carver dealership, quite often the only place left to
mount it was in a closet. Poor ventilation etc.
All the more reason to use a Type 2 since it was designed to handle more heat
and dissipate it.
Down south a cooling fan might be required.
Selecting under size or marginal sized components will forever affect the
autopilot performance and possibly cause great dissatisfaction.
A perfectly performing autopilot will soon make you forget the higher initial
cost.
Good luck
Arild
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