Building an Autopilot Base

[AJ_n_Audrey]

Hopefully this is the correct forum for this. The previous base for my Raymarine 12V Type 1 Linear Drive unit ripped off in the Bahamas in April. When I got to looking at the installation (done for PO by a major boatyard), I'm surprised it didn't come apart sooner. I built a jury-rigged base using lumber and fasteners I had aboard while in Marsh Harbor, and it got me all the way home, but it is not a long term solution (it moved more and more the further I got from Marsh Harbor). I believe I need to epoxy-glass the attachment points to the hull, probably using marine plywood doubled or tripled, and tied into the existing stringers. And based on the observed tendency of the unit to move up and down, I think I need stainless or more plywood to stabilize the mount vertically, with the vertical support butted up into the bottom of the cockpit seat.

So that's a lot of words and no pictures. Does anyone have pictures or plans for a truly solid autopilot base? This is a project I'd like to do only once more. Thanks in advance!

[fallingeggs]

I recently completed this project. The AP base fit directly along the hull, so perhaps this won't help you much. I just needed a thick base for the bolts to bite into.

I first used 1 inch wide strips of 1/2 plywood along the hull to form the initial base. Secured these with a lot of thickened epoxy.

I sanded this base to get it a bit flatter before apply the second base of 1/2 inch plywood using strips more like 3 inches wide. Again, using a lot of thickened epoxy.

Last were 4 layers of bi-axial cloth (I think 9 oz), with lots of thickened epoxy. The cloth covered all the plywood base and about 3 inches onto the hull.

This formed a nice square along the hull for me to lag bolt the drive into place. Used 1 1/2 inch bolts, probably 3/8 inch thick.

[Paperbird]

I fabricated (and probably over-engineered) a platform for our WH autopilot, but I suspect it is very installation-specific. We have a center cockpit Pearson 422 so the autopilot ram is under the aft bunk. My guess is that you'll have to study your own situation and design to fit. But maybe some of the things I did will help, so I'll try to describe ours a bit.

There is a vertical bulkhead adjacent to where the ram mounts, so I built about a 4"x6" platform out of 3/8" marine ply throughbolted to 1/4" aluminum plate. That was then supported on each end by 3"x4" side plates which were attached to the platform base with 1/4" aluminum angle stock. Then the platform and both side plates were attached to the vertical bulkhead by aluminum angle stock through bolted with a substantial backing plate covering the entire area. I then glassed (bi-ax cloth and resin) the bottom of the platform sides (inside and out) to the hull.

Like I said, probably overkill, but I've read about too many installations coming apart under the stress of the ram working back and forth in heavy seas, which is exactly when I figured we would need it most. Several years of use now with several offshore passages and no movement yet detected. I still check it occasionally during routine maintenance of the steering quadrant or other bits under the bunk.

I have some sketches I can scan and can snap a pic or 2 if you think it might give you some ideas on how to fab yours. Let me know.

[AJ_n_Audrey]

Thanks Stephen and Greg. My boat is a Pearson 367, and there is no real solid vertical surface to attach to. I'll probably have to do something more like what Stephen described, and I like the idea of lots of glass cloth and epoxy which basically are thickening the hull significantly. The stringer I tied into for my 2x4 temporary base runs lengthwise and I think ultimately is tied to the rails the engine is mounted on. But still, the stringer is only 1/2 or 3/4 inch plywood glassed to the hull. If I cut two ribs from 3/4 inch marine plywood and mounted them perpendicular to the stringer, about a 12 to 16 inches apart, and then glassed-epoxied the whole thing, I think I'd have a massively over-engineered base that I would never have to worry about again. And even with all that, I'll probably install vertical 3/4 inch plywood pieces to double as the support for my propane tank locker and a failsafe vertical support to keep the unit from rising. Before I worked on the linear drive I did not really appreciate the amount of force that thing can generate, so I'm taking no chances.

[DeepFrz]

I would not recommend lag bolting the drive to the mount platform. It really should be through bolted. Any movement in the drive unit or the drive platform will result in failure sooner or later. When you are glassing to the hull/stringers make sure you grind off any gel coat down to bare glass.

Make it strong as there are tremendous forces transmitted through the drive to the hull and install it according to Raymarine installation specifications which can be found on their web site.

[DeepFrz]

Check out this article.

Installation of Raymarine 6001 Linear Drive Autopilot

[AJ_n_Audrey]

Originally Posted by DeepFrz

Check out this article.

Installation of Raymarine 6001 Linear Drive Autopilot

Thanks for the reference! I really respect Garner's work on his 367, and how well he has documented it. I should have looked there first, but I am not sure I can follow his approach exactly. It appears that his aft bulkhead is set up differently than mine; mine is removable with a hinge in the middle, whereas his appears to be fixed. The issue with converting the removable bulkhead to fixed is that it makes access to the rudder post packing gland nuts extremely difficult, and it's not easy as it is.

Also, the attachment of the linear drive to the quadrant in my case is via a plate bolted onto the underside of the radial. Unless I want to completely re-do that (and I'll consult the Raymarime guidance docs on installation to see if the current attachment meets their standards), I need a different solution. It is possible that the original attachment to the bottom of the radial is flat wrong by Raymarine standards, so I'll investigate - after all, the base that was built for it by PO's boatyard was definitely substandard.

Despite the differences, the Seadragon approach has made me reconsider the vertical elevation of the base, and I think I need to raise the unit closer to horizontal with the quadrant to eliminate or reduce vertical forces. My linear drive would be addressing the attachment to the quadrant from the port side, so about 90 degrees different than Garner's mounting position which is more or less directly aft of the quadrant. I'm thinking I will create a platform on top of ribs attached to the stringer. Ribs will be epoxied and tabbed to the hull, and I think I'll join the two stringers with a rib (or two) between them. Anyway, I will take measurements tomorrow and draw some plans.

Thanks to all on this great forum for sharing their insight and experience.

[deblen]

You may find some helpful info in these old CF posts.

http://www.cruisersforum.com/forums/...nt-140087.html

If your rudder stock is tilted off vertical,then you must tilt the plane of the ram at the same angle. Otherwise,the ram will be pushing up or down on the tiller arm & this will cause leaking or breaking.

The best way to mount a ram is to use a 4"x 4" x 3/8" length of marine aluminum angle. A self aligning bearing is slid over the rudder stock & bolted to one end of the angle. The back end of the ram is bolted to the other end of the angle. Then the whole assembly is bolted to the hull stringers using thru bolts. Now,all the pushing/pulling is contained within the angle assembly & the hull bolts serve only to stop rotation.
Sadly,many rudder stocks are not long enough to allow the installation of a steady bearing.Perhaps,a short extension could be welded to the stock.

Cheers/Len

[DeepFrz]

The only requirements on positioning the ram are that when in the center position the ram and the quadrant arm form a 90 deg. angle and the ram is within (I think) 3 deg. of horizontal with the ram taking into consideration the angle of the rudder shaft. So if the rudder shaft is vertical then the drive will be horizontal. If you cant attach to the hull and to a bulkhead then you can build in a small bulkhead or two along the hull, extending along the bottom of the hull as much as you feel is required, with a top mounting base. The backing plate is also very important, IMO.

[deblen]

Originally Posted by DeepFrz

The only requirements on positioning the ram are that when in the center position the ram and the quadrant arm form a 90 deg. angle and the ram is within (I think) 3 deg. of horizontal with the ram taking into consideration the angle of the rudder shaft. So if the rudder shaft is vertical then the drive will be horizontal. If you cant attach to the hull and to a bulkhead then you can build in a small bulkhead or two along the hull, extending along the bottom of the hull as much as you feel is required, with a top mounting base. The backing plate is also very important, IMO.

Yes. The plane of the ram operation must take into consideration any rudder stock tilt.

From my old CF post

[Halien]

I installed a linear drive in my Tartan 33. It was a PITA; I'm a big guy, and there's not much room to work around the rudder post. The drive mount required several compound curves and angles to fit properly against the inside of the hull and produce all the right angles between the drive, the radial, and the rudder position sensor. The installation had to go on the port side because the propane locker was in the way to starboard. I made the mount from 3/4 inch Baltic Birch plywood sealed in epoxy. I chose this material because it's higher quality than the Fir marine ply I can get locally.

I'm no engineer, and I can barely draw a circle backwards, so I took the measurements in the instructions seriously. I tried the "measure twice" method for patterning the mount, but the shape was just too complicated for me to figure out. I ended up using cardboard and balsa wood to make a pattern. It took me about a dozen tries with tape measures, levels, and a framing square for right angles to get a pattern that fit perfectly. No kidding, that was the worst part of the project. Glassing it in was a PITA too, because it had to sit in a very precise orientation for everything to work right. I epoxied 1/8 inch Balsa strips on the mounting edges to act as a standoff so I don't get hard spots on the hull from the ram's loads (you can also use foam strips). Then I tacked it to the hull with thickened epoxy and literally held it in place with a level until the epoxy kicked. When it seemed solid I taped it down hard so it wouldn't move and filleted all the joints. The next day I used biaxial cloth tape backed with mat to tab it to the hull. Then I added another layer of the same tape.

I've logged a full season and a few hundred miles of autopilot use now, and nothing has budged.

The drive is attached to the radial. On my boat there isn't room for a tiller arm. I had a 1/2 inch thick aluminum drive mount tab fabricated to go on the forward bottom of the radial, right under the rudder stop mounting plate. I had a piece welded to the top plate (that contains the rudder stop) so the the two pieces together create a mounting tab of the correct length. The machinist installed a bushing the thickness of the radial between the top and bottom pieces. The drive pin is mounted in there at the recommended distance from the rudder post, and it's supported bottom and top by these two plates. I've had some autopilot failures at sea. If this one fails, it won't be because of the mount on the radial.

The rudder position sensor was kind of a job to get right. You can see in the pics that it's mounted at the end of a narrow extension bolted to the main mount. That took a lot of measuring to get right, but when I commissioned the autopilot the RPS needed no compensation. I'm kind of proud of that, because I can barely draw a straight line either, lol.

Well, here are links to some pics. The angles are weird because I'm lying on my back in a a tiny space. Ask me anything. The storm door was made from the leftover plywood. I had a wave destroy a door at sea once, so I wanted one that was bomb-proof. Yes, you have to step up and climb out, but this only gets used offshore. When it's in and the hatches are shut, it's about 99% watertight.

I spent a few weeks at sea in my other boat with tiller pilots doing the steering. After a while, the noise gets to you. The sound deadening material I used is called Dynamat, and, at least in my installation, really works.

Pics (I can't find one of the radial mounting tab I had made):

[AJ_n_Audrey]

Just returned from the boat, and the attachment to the radial with bolted plate looks well-positioned and very secure, so I'll keep that. I have a minor issue with my thought about ribs extending up from the stringer - the SSB plate is right in the way - but I think I can do an arch to go over it, and I do think it will help from a structural integrity standpoint. Halien wrote a response (thanks very much!) in which he said he put 1/8 inch balsa between the edges of the plywood and the hull. I would not have thought of that, but doesn't it get crushed flat over time? And thanks for the pics - I feel your pain about what a tiny space it is to work in while doing all this. I spent beaucoup time in the port and stern lazarettes while in Marsh Harbor fabricating my temporary base. And the current angle of the linear drive to the attachment plate on the radial looks to be close to being within Raymarine's 5 degree tolerance, but I'm going to try to get it as close to zero (horizontal) as possible with the new base. Looks like a plan is coming together.

[Halien]

Greetings,

Foam, or in my case the balsa, is just there to keep the hard edge of the plywood base from direct contact with the hull. For tabbing I used 6 inch wide 17 ounce biaxial tape backed with 3/4 ounce mat. There are two layers, and the overlaps are staggered. It's tabbed inside and out. The highest force the ram is capable of is easily transferred over a large surface area to the side of the hull.

The only thing I can think of that might test the strength of this installation might be to get tossed around on some rocks and have the rudder beaten around mercilessly. I attached the ram with the anchor pin pointing downwards. In an emergency I can yank out the cotter pin and the ram will fall away from from the quadrant. I did this because I've had a tiller pilot drive belt fail, and when it does the actuator stays put. That's scary as hell when you're surfing down swells. With a tiller pilot, when the adrenaline abates you can just yank it off the tiller. It's a lot harder to deal with a seized linear drive.

I have a loop of amsteel attached to the cotter pin, and it's rigged so it can't snag on anything. That cotter pin gets inspected frequently, and I have spares in a baggie taped to the rudder post.

If any of this seems weird, it's all because I've had a variety of failures at sea. I'm trying to make things easier for myself and safer for the inevitable time it happens again.

[AJ_n_Audrey]

Originally Posted by Halien

Greetings,

Foam, or in my case the balsa, is just there to keep the hard edge of the plywood base from direct contact with the hull. For tabbing I used 6 inch wide 17 ounce biaxial tape backed with 3/4 ounce mat. There are two layers, and the overlaps are staggered. It's tabbed inside and out. The highest force the ram is capable of is easily transferred over a large surface area to the side of the hull.

The only thing I can think of that might test the strength of this installation might be to get tossed around on some rocks and have the rudder beaten around mercilessly. I attached the ram with the anchor pin pointing downwards. In an emergency I can yank out the cotter pin and the ram will fall away from from the quadrant. I did this because I've had a tiller pilot drive belt fail, and when it does the actuator stays put. That's scary as hell when you're surfing down swells. With a tiller pilot, when the adrenaline abates you can just yank it off the tiller. It's a lot harder to deal with a seized linear drive.

I have a loop of amsteel attached to the cotter pin, and it's rigged so it can't snag on anything. That cotter pin gets inspected frequently, and I have spares in a baggie taped to the rudder post.

If any of this seems weird, it's all because I've had a variety of failures at sea. I'm trying to make things easier for myself and safer for the inevitable time it happens again.

Thanks again for the input. Yesterday I ripped out most of the old temporary base made from bolted 2x4's along with some unneeded stuff that had been mounted to the hull by PO (a shelf for a watermaker pump) and a few odd bits that looked like the beginning of other projects that were not completed, perhaps also related to incomplete watermaker. After all that junk was gone, I realized there is a small, original bulkhead aft which I can attach to to stabilize the base in the forward-aft axis - good news. I just had not noticed it because of all the other stuff, and in fairness, I had not spent a lot of time in the port lazerette since May when I built the temp base. Now I'm ordering materials. I'll take pics for before-after and in process documentation.

[antoha]

Here are some photos from my installation (others show up in the link to an old thread above).
I ended up with many layers of triaxial cloth below and above the 3/4" marine ply, making a sandwich. Subsequent cloth layers cover more area, so that each layer grabs onto the hull also, and not just onto previous layers.
The holes for through bolts in both the wood/cloth base as well as the aluminum backing plate are just barely wide enough to force the bolts through, so there's no play.
After I was done, I painted it with gray bilge paint. Also, I made a cover so I don't have to worry about interfering with the drive when I fill up the sail locker. The cover is strong enough to stand on.
Anton