On Feb 25, 7:36 pm, "muelec" wrote:
On 25 Feb., 10:45, "Bil" wrote:

snip

My new ST1000Plus accepts NMEA. The question arrises now. What should
I buy next, so that the internal compass of the ST1000Plus ist not
used anymore, or gives me good steering in waves (on a 5m boat).
Giro, Windsensor or even only GPS?

Urs:

1. The internal compass of the ST1000 is actually not too bad. It
averages your heading over a period of time, as a way of compensating
for the yawing of the boat due to waves or wind gusts. An electronic
compass with a higher frequency (ie one that outputs heading data very
quickly) would just make your ST1000 work very hard (making a lot of
tiny corrections).

So my first suggestion is for you to save your money (by not
purchasing anything) and to modify the calibration settings of your
ST1000 so it suits your boat. Read Chapters 5 and 6 of the ST1000
manual. In particular, do the test in section 5.3. This test checks
that the rudder gain setting of the ST1000 suits your boat (if you
don't have a manual, you can download one in *.pdf format from the
Raymarine website).

But be clear - no autopilot can anticipate the effect of a wave about
to hit your bow. You (or any attentive helmsperson) can. Recognise
that some conditions are beyond the design parameters of an autopilot.
And skilfull tiller work in a small boat is fun and admirable.

2. If you've checked and modified the rudder gain setting, the rudder
damping setting (if necessary) and the setting specifying your average
sailing speed and still find that you are not satisfied with the
performance of your ST1000, then:

a. read section 2.4 of your ST1000 manual about using Track mode. And
you would then equip yourself with a GPS receiver, plus the necessary
cabling (see Chapter 4 of your ST1000 manual), which outputs XTE
(cross track error) and Bearing to Waypoint (which can come in any of
several NMEA sentences, eg APB, BPI, BWR, BWC, BER, BEC, or RMB).

The ST1000 can work just on XTE, but if it is fed Bearing to Waypoint
data it does a better job. Section 2.4 of your manual gives good
guidance. Of course, using Bearing to Waypoint means that you have
first to mark waypoints.

b. I wouldn't suggest you equip a 5 m vessel with a gyro. And on a 5 m
vessel you are close enough to wind and wave not to need a masthead
wind instrument to get your ST1000 to steer to the wind. If you don't
agree, read section 2.5 of your manual.

c. If you wanted to pour more money into your particular hole in the
sea, feel free to consider installing an electronic charter and a
water speed instrument, and perhaps even a rudder angle detector, so
that you can let a small sophisticated computer calculate tidal set
for you too. But where's the fun in that on a 5 m sailing boat? You
would do better by getting all your surplus money, putting it a brown
envelope, and mailing it to me.

Cheers

Bil