[C320-list] steering geometry question

[Jeff Hare]

Hi Graeme,

I just completed this project last weekend. Special thanks go to Allan Field
and Scott Thompson who were great resources (and Jon Vez for sending
pictures of the Rudder travel limiter configuration used on his C355)

Rudder post is 2.860" in diameter according to Edson.  The factory rudder
travel seems to be around or slightly over 40 degrees each direction.

On our hull (#809) from the wheel amidships,  I used to get exactly 1 and
1/2 turns of the wheel each direction.  With the AP installed I now get
exactly 1 and 1/4 turns each direction with my installation.  After studying
it a bit and experimenting with mounting angles etc, there are several
aspects of the geometry here that really does prevent a linear drive unit
from doing the full lock to lock you get from the factory on the C320.  But
with the mounting/drilling dimensions/angles I used, I give up very little
turning radius and I suspect the final turning angle I get is a little over
75 degrees total.

Much of this is limited by the 12" maximum travel of the Linear drive's RAM.
RayMarine wants the RAM connected out 10" from the center of the post which
results in a max angle of 70 degrees.    

I attached the ram at about 8" out from center to increase the turning angle
a little beyond the RayMarine max of 70 degrees.  If I went less than that,
I might get more throw, but the RayMarine said the wear rate on the RAM
would increase dramatically, not to mention that the average stresses on the
aft cabin wall where the RAM attaches would be much higher and could cause
the tabbing to weaken or break over time or in rough conditions.  The aft
cabin wall is very thin and not great structurally.  It's weakened by access
panel.  Hence the large backing plates to spread the load.

I've been documenting the process pretty carefully with lots of pictures.  I
made a CAD drawing file for the Linear drive backing plate that I sent to a
machine shop.  The backing Plates I used to sandwich the aft cabin wall
where the RAM is mounted are larger than those used by Scott or Allan.  I
didn't use a mirror polished plate like they did but would recommend it.
Mine is brushed finish because it was cheaper and would be ready quicker.
But I can have it polished later if I want.

The unit I installed is the RayMarine ACU-200 Sail Pack (p/n T70155) with
Type 1 Linear drive and Rudder Position Sensor to allow software control
over the Linear drive's turning limits.  

Edson sells a Tiller arm to attach to the rudder stock that is specially
milled for the C320 rudder post.  It's a nice piece but needs to be
shortened slightly to give enough clearance on the C320.  Also, you'll need
to drill the rudder post.  I used a high quality Dewalt bit dipped in ALUMET
872 cutting oil before I started and with my cordless drill, I was done in 2
minutes with a few 6" long coils of SS cuttings.  Rather than drilling all
the way through the post and thru-bolting it, I drilled a 5/16 hole and
tapped it for a 3/8 coarse thread high strength stainless bolt.  I believe
this is sufficient. 

Edson also sells a Rudder Stop kit that (P/N: 862-WIRE) (mentioned earlier)
that replaces the bump stop system used by the C320 in favor of a cable stop
with rubber shock dampener used in newer installations and larger boats.

For mounting the Rudder Position Sensor, I made a simple wooden unit that
clamps around the rudder support tube, therefore is already angled the same
as the rudder post and is height adjustable for perfect alignment with the
tiller arm.  I'll be working up an illustrated article for the website that
others can also use for a reference but will be happy to discuss it with
anyone starting the project before the write-up is done.

-Jeff Hare

-----Original Message-----
From: C320-list [mailto:c320-list-bounces at lists.catalina320.com] On Behalf
Of Graeme Clark
Sent: Wednesday, September 16, 2015 11:58 AM
To: C320-List at Catalina320.com
Subject: [C320-list] steering geometry question

I'm 250 miles from my boat and planning a below deck autopilot installation
so would like to know approximately what is the angle or travel for the
rudder (degrees either side of central) and the approx diameter or the
rudder quadrant, so I can calculate the actuator throw I will need and where
to connect it to the quadrant (or possibly make up a new radius arm

Anybody have those figures to hand by any chance? Doesnt have to  be that
accurate at this stage

Thanks

Graeme

#366, Mk 1, Jaskar.=