How do I build an autopilot shelf?

[Joe500]

I would like to install a below deck autopilot on my Beneteau to replace the wheelpilot, which seems to only work well in very light conditions. The hardest part of the project to me seems to be building a mounting pad which can resist the heavy loads exerted by the linear drive. I am attaching some pictures of the area around the steering quadrant. Where should I put the autopilot shelf and what should I build it out of? Can I attach it to the existing plywood bulkheads shown in the photos? Can I build something out of steel rather than doing fiberglass work? Where could I get steel parts for a project like this? Do I need to reinforce the shelf by bracing it against the fiberglass hull? Any recommendations on designs and parts required would be much appreciated. Also, I'd love to see any photos of how others have done this. Thanks, Joe

[atoll]

hopefully someone will come up with some photos of an existing installation on a 375.

generally the first thing you need to do is to offer up the linear ram to the quadrant and work out where the drive pin is going on the quadrant,then you need to work out the lenth of travel.

the obvious place for the linear drive mounting pad is on the transverse bulkhead.
this may have to have a "U" slot to be cut away for horizontal alighnment,then a pad mounted,then braced for stiffness.

my choice would be plywood,epoxy and cloth,as this can all be done in-situ with the minimum of tools.

[donradcliffe]

Originally Posted by Joe500

I would like to install a below deck autopilot on my Beneteau to replace the wheelpilot, which seems to only work well in very light conditions. The hardest part of the project to me seems to be building a mounting pad which can resist the heavy loads exerted by the linear drive. I am attaching some pictures of the area around the steering quadrant. Where should I put the autopilot shelf and what should I build it out of? Can I attach it to the existing plywood bulkheads shown in the photos? Can I build something out of steel rather than doing fiberglass work? Where could I get steel parts for a project like this? Do I need to reinforce the shelf by bracing it against the fiberglass hull? Any recommendations on designs and parts required would be much appreciated. Also, I'd love to see any photos of how others have done this. Thanks, Joe

You will need to engineer a mount AND a quadrant connection which will repeatedly take 1000 lbs of thrust.

For the quadrant, I would take one of the two almost quarter-round sections, and cut a 1/8" SS sheet to go top and bottom, then thru-bolt them through to the horizontal webs on the quadrant with at least 8 bolts. Then drill and tap a hole through the SS sheets for your autopilot drive pin.

For the shelf, you don't seem to have a lot of useful existing structure, and you need to mount the fixed end of the ram about 20" from the quadrant. You may also have interference issues with the cockpit drain tubes. I would mount the drive to a 3/8 aluminum sheet, which is bolted onto 3/4" plywood with angle brackets, and the plywood is glassed to the hull and tied into whatever existing structure you can use.

[gjordan]

Whatever you do , make the mount bullet proof. I once delivered a 1/3 million doller, brand new boat from Berkley Cal. to Oregon. We didnt get 10 miles out of the Golden Gate before the shelf holding the drive ripped right off of the bulhead. Make it much stronger than you think you need and maybe it will hold up.___Good Luck_____Grant.

[minaret]

Originally Posted by atoll

hopefully someone will come up with some photos of an existing installation on a 375.

generally the first thing you need to do is to offer up the linear ram to the quadrant and work out where the drive pin is going on the quadrant,then you need to work out the lenth of travel.

the obvious place for the linear drive mounting pad is on the transverse bulkhead.
this may have to have a "U" slot to be cut away for horizontal alighnment,then a pad mounted,then braced for stiffness.

my choice would be plywood,epoxy and cloth,as this can all be done in-situ with the minimum of tools.

+1. Or built onto the stringer. Only other thing I would add is that I have done this job (the shelf) many times with a synthetic ply substitute like Coosa board. It is easy to fit and bond in place, takes laminate very well with no prep, and will never delaminate or rot.
I always make sure to have the ram all attached and set up, with the arm in the center of it's range of travel, when fitting a pattern for the shelf. You also want to make sure the rudder is amidships when fitting the shelf, I have seen that one go awry. I prefer to make sure the shelf is tied in to the hull as well as a bulkhead or stringer...

[colemj]

Someone must have added an autopilot to a 375 - that will be your best source.

Then I would try to fit a tiller arm to that nice square head on the rudder post and fit the autopilot directly to that instead of messing with the quadrant.

Don't underestimate the forces these pilots put on their mounts. Make sure you have a very beefy mounting place.

Mark

[Joe500]

Thanks Atoll, Don, and Jordan. I was thinking of buying an Edson tiller arm that will hopefully fit onto the rudder shaft sticking out above the quadrant. Suppose that tiller arm goes off to the port side of the boat when the rudder is centered. I think the arm will be short enough so as to stay inside of the cockpit drain tubes. Then, suppose I attached a shelf to the vertical piece of plywood located behind the quadrant as shown in two of the three photos (The transverse bulkhead that Atoll mentions.) Couldn't I just attach the shelf to the plywood with some bolts going through the plywood to a backing plate on the other side? I've never built anything out of fiberglass so bolts seem easier to me.

Is that transverse bulkhead strong enough? How do I tell? Would it make sense to add supports running from that bulkhead going forward towards the structure supporting the rudder shaft? There's empty space under the back part of the quadrant between the bulkhead and the structure encasing the rudder shaft. If I need supports, what do I make them out of? Wood blocks fiberglassed in on both sides? Steel tubes?

And where should I buy the brackets and backing plate for the shelf? Should I just go to the hardware store? Joe

[atoll]

if you dont want to use glass,10mm aluminium plate and 5mm right angle alu are going to be the easiest to work with,if you can bolt through the bulkhead behind the fwd transvers bulkhead this will give a strong "H" section to mount your drive plate on .

any steel/metal stock holder will be able to supply lenths of bar and plate.

can be cut with a fine ssteel grinder disc or the correct jig saw blade.


edit
the bulk head behind the transverse looks like the stern!
epoxying a piece of ply in for and aft to the stern/transom may be the best option then use rt angle and plate

[onestepcsy37]

before you go ahead with this major project i'd like to recommend a wheel pilot that works with large heavy boats. it's the cpt autopilot. i've used mine for several years now and am pretty satisfied with it - on a 37 foot 20000 lb cutter. their website is

www.cptautopilot.com

i think a properly installed below decks ap is best but i'm not doing a round-the-world, just florida/bahamas, and this one does what i need without a complex below decks installation and at maybe half the price.

[Matt Johnson]

Does your emergency tiller attach to the top of the rudder tube? If so, make sure whatever tiller arm you use for the autopilot still allows use of the emergency tiller. The autopilot can be used for steering if a cable breaks, but I would want to still leave the emergency tiller as an option.

Also, it really helped me to have the tiller arm for the linear drive installed and dry fit of the drive before I made my shelf. The area I thought would work perfect in fact couldn't once I fit everything in place.... It just looked like it could before with the measurements, but no linear drive in hand.

I also had a tiller arm made from a machine shop for $200. It looks just like the Edson, but is thicker and aluminum.

Fiberglassing in a shelf is a really easy way to do it. If you haven't glassed before, it really isn't anything to worry about. Just use more fabric than you think (thicker) and you'll be fine.

[witzgall]

I built a shelf last year. I was lucky - the Pretorien has a very easy to adapt space for a drive. Running across the back of the boat is a heavy timber brace. Forward of that, about 18 inches in front, is the bulkhead for the rear of the propane locker.

My first attempt failed miserably - I knew as soon as we got her out on the water that it was not going to cut it. So I enlisted the help of my good friend Tipper David in Beufort, NC for a re-design. Tipper is a master woodworker, and has the "Ultimate set of tools" in his shop. He has built some of the beautiful mahogany doors you see in front of many of the fine homes in Beufort. He took two, 1 inch think pieces of scrap from a door and laminated them together. Then we enlisted a friend of him that is a machinist to cut us a couple of pieces of aluminum angle for the braces. This was all bolted to the boats cross brace, and to the propane locker as well, with a small sheet of aluminum as a backing plate.

The result is rock solid, but believe it or not, the bolts need re-tightening every 500 see miles or so. I need to put some thread locker on them.

Whatever you design, you need to account for the push pull of the ram, but also torsional stress, as the ram will attempt to twist the mount as well as push it.

Chris

[Tessellate]

Adding some personal experience to this thread.

I built a shelf using 3/4" birch plywood (outdoor-rated), epoxy coated it, and fiberglassed into a corner of the hull at two attachment points using 5-6 layers of fiberglass cloth, and a fillet of GFlex prior to that. This is with a Raymarine Type 1 mechanical drive.

I was alarmed to discover, after our first rough test last week (running down square waves in 30 kts against 1-2 kts current), that the plywood showed signs of starting to buckle at one point, along a line from the aft two thrubolts on the drive base.

This was amazing to me because 3/4" plywood should be quite strong. But I think the issue was due to two reasons: 1) I didn't use a backing plate for the thrubolts, just washers (washers the same size as the nuts and lock washers, not even fender washers!). 2) The wood grain is aligned with the direction of main push/pull force. It would've been stronger to align the grain the other way.

I've strengthened the shelf now by wrapping the mid-section in fiberglass cloth and adding large backing plates for all thrubolts.

It's pretty tough judging how strong is strong enough. I called Raymarine tech support and they said they don't advise on how to build a shelf sufficient for the forces of the Type 1 drive they sell. This thread is the only one I could find on the Internet about the subject. I also found a couple blogs, one where 18mm (~0.71") plywood was used, with a backing plate, and one where 1/2" G10 was used. I'll write a blog post on my install eventually as well.

[Oceansailor]

I would recommend avoiding wood for the autopilot shelf. Wood will work all the time due to humidity. This is the reason why your bolts come loose. I changed mine to a platform of aluminium. It is stiff and rigid. Autopilot steers much better as there is no play. Bolts never come loose.

[Joe500]

I was surprised to get a reply to this post seven years after I wrote it. From my end, I thought I'd provide an update to the community. We visited the Beneteau factory in South Carolina for a tour and talked to them about this project. While they did provide advice on the design after I insisted, they emphasized the difficulty of constructing the relevant parts properly, along the same lines of what many of you said as to how to make it strong enough to absorb the forces, and they did not recommend the project. We ultimately went with a Raymarine wheelpilot, which of course is much easier to install. For a 38 foot boat, it cannot handle sailing with winds above 20 knots; however, for the coastal cruising we do, which involves a lot of motoring, it works 95% of the time.

[Tessellate]

Originally Posted by Oceansailor

I would recommend avoiding wood for the autopilot shelf. Wood will work all the time due to humidity. This is the reason why your bolts come loose. I changed mine to a platform of aluminium. It is stiff and rigid. Autopilot steers much better as there is no play. Bolts never come loose.

I agree metal would be ideal, and I would've gone that route if there were any way. Unfortunately, it seems compromise is often synonymous with boats, and the ideal isn't always possible.

The linear drives dictate a very specific installation location - 27.5" from the tiller arm pin, within 5 degrees of plane with the rudder stock plane, and 90 degree angle to the tiller arm / pivot point. I think it's very rare that a convenient bulkhead is located in exactly that spot. So this is the reason wood of some sort often must be used.

Then the other factor when mounting to the hull is it's generally not a flat surface and some tricky angles must be carved into the mounting platform to get a good fit. Wood is much easier to work with than metal for contouring to an irregular surface.

Water is not a big concern because the wood is encased in epoxy. Also the linear drive should not be mounted in a location regularly subject to water, per the manufacturer's instructions.

I think Coosa board would've been worth looking at more closely. Fisheries Supply had it, but not in the thickness I would've required, and I was mostly unfamiliar with the material (ex, with regards to strength and what thickness would be sufficient).

G10 fiberglass board is also very nice, though very expensive and not as easy to carve / contour to the hull as wood is.