Best Mounting for Hydraulic Autopilot Arm

[deblen]

Originally Posted by PhilDuhs

After noticing a slight "clonking" noise when using the autopilot in a following sea on my Beneteau 54 I traced the cause to small movement of the hydraulic arm where it's attached via 4 bolts to the boat inside the lazarette (see attached image "Autopilot Hydraulic Arm Mounting.jpg").

When installed 4 years ago the installer simply drilled through the wooden platform and bolted it through (see "Current Autopilot Mounting - Above.jpg" and "Current Autopilot Mounting - Below.jpg"). With the high loads on the arm and with it only being fixed through wood the holes are now slightly larger and consequently I'm getting some movement - and I'm guessing it'll now get worse fast.

Asking another B54 boat owner to check their installation there should have been a metal plate added to the underside of the wood (see "Proper Autopilot Mounting - Below.jpg") to prevent movement.

I have 4 questions that'd it'd be great to get the opinions on before I effect a repair in the next few weeks:

1. Should I put stainless steel plates above and below the wooden platofrm to better prevent future movement, especially now that 1 or more of the holes though the wood are slightly too large?
2. Should I use much larger stainless steel plates than what's show in the photo to better fix them to the wooden platform (ie. larger surface area for bonding)?
3. What's the best way to fix the metal plate(s) to the wood - just Sikaflex or should I use additional bolts on the corners of the larger metal plates as well?
4. Are there any tricks to better prepare the stainless steel plates for the application of Sikaflex to ensure good adhesion to the wooden platform?

All thoughts and advice much appreciated.

Phil
S/Y 37 Rocks

Looking at pics 1,2,3-I see what appears to me to be a solenoid operated bypass valve assy thru bolted to a horizontal(parallel to waterline) " deck".
If I am correct,I can't see why this BP valve would ever move.It is not mechanically connected to ram or steering gear & there should be no strain on it.

I can't see a ram or rudderstock in these pics.

The 4th pic shows a metal plate with 4 screws/bolts holding it to a vertical? bulkhead.
Again,if I am correct,I suspect this plate may be the mounting backing plate for the ram(the end that is fastened to hull as opposed to the other end which would be attd to the quadrant/tiller arm on rudderstock.

Again,if I'm correct,this is where any slack/clunk would appear,as it takes all the push/pull from rudder.

If I'm totally off track,I will bow out of this thread with apologies.
Cheers/Len

[DeepFrz]

deblen, look more closely. Hydraulic ram is off to the top right in first picture. Looks white and is attached to the motor pump mechanism that you think is bypass solenoid.

The 4th pic shows a metal plate with 4 screws/bolts holding it to a vertical? bulkhead.

Bottom of horizontal bulkhead or shelf.

[deblen]

Originally Posted by DeepFrz

deblen, look more closely. Hydraulic ram is off to the top right in first picture. Looks white and is attached to the motor pump mechanism that you think is bypass solenoid.


Bottom of horizontal bulkhead or shelf.

Ok-I see it now-thanks DF.

My experienced opinion is that it will be very difficult to hold the mounting bracket on back end of the ram from moving, over time, in this setup.
Would have been better design if it had been bolted to a vertical bulkhead instead,but....
In the existing setup,the bolts thru f/glass deck are in sheer.
If that deck is cored,then it will need the bolt holes drilled to perhaps an inch at least diameter,& another 1/2" of core dug out. Then masking tape over bottom of enlarged holes,fill with epoxy resin & fibre mixture.This will tie upper & lower glass facing of deck together in this area.Re-drill for a tight fit of original bolts.Use nylock nuts & flat washers & really tighten.
My opinion is that just putting bushings(metal,whatever) in holes will just result in the holes wearing by bushings moving. Fiberglass,especially thin layers as in a cored deck will not stand sheer forces of thru bolts very well without gradually enlarging holes.
I learned this the hard way.Just passing my lesson along.
Cheers/Len

[DeepFrz]

In the existing setup,the bolts thru f/glass deck are in sheer.
If that deck is cored,then it will need the bolt holes drilled to perhaps an inch at least diameter,& another 1/2" of core dug out. Then masking tape over bottom of enlarged holes,fill with epoxy resin & fibre mixture.This will tie upper & lower glass facing of deck together in this area.Re-drill for a tight fit of original bolts.Use nylock nuts & flat washers & really tighten.
My opinion is that just putting bushings(metal,whatever) in holes will just result in the holes wearing by bushings moving. Fiberglass,especially thin layers as in a cored deck will not stand sheer forces of thru bolts very well without gradually enlarging holes.
I learned this the hard way.Just passing my lesson along.
Cheers/Len

I agree although the backing plates will make a big difference. On an autopilot drive there are huge forces at work against those 4 bolts so the whole mounting structure is of vital importance.

Phil, on your boat I would suggest that you inspect the shelf that the hydraulic system is mounted on and how it is mounted to the rest of the boats structure. Ensure that the whole structure is very sound and has been reinforced. You might check with Beneteau to see if there have been any service bulletins released on the steering system of your boat.

[antoha]

Can you drill a bunch more holes in that shelf? Then you could sandwich it with two aluminum plated (below and above the shelf), thus distributing the load. The existing holes would then just accept bolts, but the actual mounting would be to the aluminum rather than to the shelf.

Another suggestion: these are M12 bolts, right? (It being an LS 50 ram, from the looks of it). 12mm is just under 1/2" - so if the holes are just big enough for those (and if the ram's mounting plate accepts them), maybe that's the ticket? Plus an aluminum backing plate.


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[PhilDuhs]

Thanks for all the additional comments!

The holes in the mounting plate are 11mm - and currently I am using 4 x 10mm bolts so I guess I could look for 7/16" bolts which are closer to 11mm although there doesn't seem to be any movement between the bolts and the mounting plate - just between the mounting plate and the wooden platform it sits on due to the holes in the platform enlarging over time. Of course looking for 7/16" bolts over here in Turkey won't be the easiest - it's strange a French company makes the holes an odd size...

I have discovered another complication - there is very little clearance between the holes (especially the ones furthest from view) and the underside of the cockpit floor above - certainly not enough for an electric drill to be held vertically above. Fortunately there is space below so I'll just have to do things upside down .

I could definitely bolt larger mounting plates (above and below the wooden platform) as you suggest antoha. I was initially steering away from using stainless steel in case it reacts with the mounting plate but the bolts that have been used for the last 4 years are stainless steel and haven't caused any problems so I think SS plates will be ok.

Should 4mm thick plates should be enough?

I'm keen to recess the top plate into the wooden platform 2-3mm so that I can bed it in epoxy resin to ensure it's level as well as to reduce the additional height the plate will add. It looks like the top of the plywood platform is already coasted in a layer of fibreglass (see the initial photos) so this should be relatively easy with the Dremel tool I hope...

I've checked the overall structure of the shelf the mounting plate is bolted through DeepFrz and everything seems ok there - no signs of movement of cracking anywhere.

Any other thoughts?

[antoha]

How are you going to recess the platform to accommodate the slight sinking of the metal plate? I mean: to make that surface straight, flat, and level? I would not be able to even if I tried really really hard. Another consideration is to avoid sanding with power tools in tight spaces if you like to keep your lungs the way they are.

Is 4mm going to really change the geometry that much?

Drilling in tight spots: 90 degree drill?


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