[C320-list] Linear autohelm

[Stephen Cox]

>From the relevant Mechanical Linear Drive manual the Type 1 Linear Drive is rated at 18-36 W and the Type 2 Linear Drive is rated at 48-72w.  Note the minimum of the Type 2 is greater than the maximum of the Type 1.  What makes you think the ACU-200 will happily drive this without letting the magic smoke out that powers all electronics?  Even assuming it manages for a while what happens when you get into strong sea and wind conditions?  The power consumption will go up and again, the magic smoke will escape the ACU-200 and it will stop working.

Why would you go to the trouble of installing an under deck drive and not use a hydraulic system that will take the punishment of rough seas and strong winds?  Have you ever thought what is inside the Raymarine Mechanical Linear Drives?  Have a look at https://forum.raymarine.com/showthread.php?tid=1943  There is a belt drive in there and the gears even on the Type 2 are plastic.  Lot of money to fit an autopilot that still relies on these components.  After having to rebuild my Wheelpilot more than once due to stripped plastic gears I went to a hydraulic under deck system on my C320.  In my case I kept my SPX-30 controller but fitted an Octopus hydraulic linear drive as found in https://octopusdrives.com/download/linear-drive-brochure/# and used a Jefa tiller arm rather than the Edson.  I mounted the hydraulic ram back to the transom rather than the bulkhead.  I personally don't think the plywood bulkhead to be a structural element sufficient for the potential forces involved. 

Stephen Cox
Tegwen #1141


> -----Original Message-----
> From: C320-list 
> [mailto:c320-list-bounces at lists.catalina320.com] On Behalf Of 
> Greg Arnold
> Sent: Sunday, 21 August 2022 14:49
> To: C320-List at Catalina320.com
> Subject: Re: [C320-list] Linear autohelm
> 
>    I also am thinking about making the upgrade to a Raymarine 
> below-deck
>    linear drive.  There is quite a lot of info on this topic 
> on both the
>    320 Association site (including pictures) and in the 
> Google archives of
>    the 320 discussion group.
>    The most popular mounting location for the Raymarine 
> linear drive seems
>    to be above the little door on the athwartship bulkhead 
> that separates
>    the aft cabin from the lazarette area.  Has anyone had any problems
>    with this location?  On my boat, this bulkhead has a 
> thickness of only
>    1/4", and does not appear to be designed to carry any structural
>    loads.  Also, this location restricts the length of the 
> tiller arm due
>    to lack of space between the bulkhead and the rudder post.  The
>    shorter-than-recommended tiller arm adds stress to both 
> the autopilot
>    and the bulkhead.
>    Other Catalinas such as the 380 and 400 mount the drive beneath the
>    swim step.  This doesn't work on the 320 because it puts 
> the drive too
>    low.  However, around serial number 380, Catalina shifted 
> to a new 320
>    deck mold that put a seat on both sides of the swim step.  I would
>    think the drive could be mounted beneath that seat on the starboard
>    side, with the drive extending forward to the tiller arm on the
>    starboard side of the rudder post.  A local 320 owner who 
> drilled this
>    seat for a stern anchor roller says the seat is balsa-cored, which
>    means it should be quite robust.
>    The problem with this below-seat location is that the 
> Raymarine Type 1
>    drive is not long enough to extend from there to the 
> tiller arm.  That
>    is fixable at a price of several hundred dollars by using 
> the Raymarine
>    Type 2 Long drive, which appears to fit perfectly.
>    One advantage of the below-seat location with the Type 2 
> Long is that
>    you would be able to use a full length tiller arm.   Also, 
> the Type 2L
>    has a 16" rather than 12" stroke, which will eliminate any steering
>    restrictions of the shorter Type 1 drive.
>    Raymarine says the electronics of the ACU-200 are not 
> robust enough for
>    the Type 2, instead you must use the (very expensive) 
> ACU-400.  This
>    makes sense if you have a big boat that requires the Type 
> 2.  However,
>    the Cat 320 should not place any more load on the Type 2 
> than on a Type
>    1, so I don't think you would need to upgrade from the 
> ACU-200 to the
>    ACU-400.
>    Interesting facts learned by looking at the autopilot posts on
>    forum.raymarine.com:  The Type 2 Short is identical to the Type 1
>    except for motor size (so, depending on how you look at 
> it, the Type 2
>    does not have a more robust construction than the Type 1, 
> or the Type 1
>    shares the robust construction of the Type 2).  And the 
> Type 2 Long is
>    identical to the Type 2 Short except for stroke length.  
> So the Type 1
>    and Type 2L are identical except for the 2L's larger motor size and
>    longer stroke.
>    One final point: under-deck pilots are really expensive.  
> The Type 1 is
>    $3700, plus you need a $600 tiller arm.  Add sales tax, and you are
>    around $4500.  That doesn't include installation, which a 
> local boat
>    guy says will be more than 20 hours and may be 30 hours 
> (at $100 per
>    hour).  You are looking at a price of around $7000, so a 
> few hundred
>    dollars more for the upgrade to the Type 2L drive is just pocket
>    change.
>    Greg Arnold
>    Santa Barbara, CA
>    2005 C-320 #1054
> 
>    On 8/20/2022 4:59 PM, surprise thompson87.com wrote:
> 
> I think my boat was one of the first to convert to a below 
> decks linear drive fr om Raymarine. Pictures of the install 
> are in my owners gallery folder. (“Surpris e” #653). This was 
> the best upgrade I’ve made to the boat. Highly recommended.
> 
> Scott Thompson
> 
> 
> 
> On Aug 20, 2022, at 5:50 PM, John Meyers 
> [1]<jcmeyers7 at gmail.com> wrote:
> 
> I am thinking about putting in a linear autohelm. Haven't 
> been on a boat with it. Not finding much written about this 
> especially on the 320 unless I am looking in the wrong place.
> 
> Any advice? Go for it? Avoid it? Which brand/model is good?
> 
> Thanks
> 
> John Meyers
> Muskegon, MI
> WInd Chime
> 1997 #406
> 
> References
> 
>    1. mailto:jcmeyers7 at gmail.com