Best Mounting for Hydraulic Autopilot Arm

[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

[roland stockham]

My thinking would be that you dont need a plate above as you aready seem to have a metal plate as part of the ram. Looks like this is alloy so adding a stainless plate couldcause corrosion. If you are worried about the amount of play then fill the holes with rein and re-drill. In anycase some sealer under the top plate and around the bolts will keep water from getting into the wood

[motaman9]

You could put stainless steel sleeves inside the existing holes since they are enlarged due to the prior loads and to prevent further enlargement. Use a strong resin to secure the sleeves in place. It wouldn't hurt to have a plate above and below to spread the stresses out. I'd also separately thru bolt the plates to each other with similar sleeves. Our ram is bolted to a piece of angle iron that is in turn bolted to a longitudinal stringer and was then resined over and gel coated. Admittedly, I prefer to deal with issues like this once so I tend to err on the side of overkill so I hopefully won't have to deal with it again.

18-8 Stainless steel has no reaction with aluminum. Make sure that your bolts are 18-8 type material. Also 300 series stainless will work. Just don't use any 400 series stainless steel as it is magnetic (has higher carbon content) which is the reaction problem.


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[PhilDuhs]

Thanks for the comments - I guess I could also just move it 20-35mm further forwards (towards the silver a/c pipe) and just drill new holes - the current bolts are 75mm apart.

Are the stainless steel sleeves generally available in various sizes? Sounds like a good idea although I guess all it's really doing in effect is acting as a larger bolt size passing through the wood - which of course is a positive.

It's a good point re the possibility of corrosion if I have a top plate of stainless steel against the aluminium (I can't remember specifically, it may also be steel) of the arm mounting. That said, the current bolts are also stainless steel and there's no sign of corrosion. Perhaps a thin layer of Sikaflex between the top plate and the mounting block??

Any recommendations on the thickness of the stainless plates? Something like 6mm (1/4")?

I also like the idea of doing something well and then being able to forget about it so keen to get this right!

Thanks again,
Phil

[motaman9]

Maybe something like this would work ?

http://www.amazon.com/Round-Spacer-S...838720&sr=1-10

That's just a sample...the I.D. is probably too small for the size of the bolt you'd be using but that's the last one I had in my history that I used for a project....

Or maybe a "shoulder spacer" that has a lip on one end?

I should have said "I've always heard that 18-8 doesn't react to aluminum" in that prior post....I've used that combination in a few marine applications with no adverse condition developing so far.....

It is also my understanding that Anodized aluminum won't react to stainless unless you accidentally damage the coating. It's possible that the base for the ram is steel and there is a nylon sleeve or a bushing of some sort between the two metals. In our case, the rod inside the ram is stainless but is not in contact with the aluminum casing of the ram due to the bushings and seals. Our mounting plate appears to be steel but again there is a beveled bushing that prevents the two metals from making direct contact and the base has a heavy coating on it.

As for how far apart to make the mounting holes for the plates, I'm no engineer, but it seems you could get into a rabbit hole of calculations for the amount of force the ram could potentially exert and strength of the supporting materials. I'd think that you'd run into a limitation of space before you reached the optimal distance between the bolts and plate thickness so I'd go with as much distance as you can get and still be practical with access and available flat surface area. I'm assuming the fiberglass area is cored since you mentioned having wood involved so you could remove the wood or coring in the area of the holes and fill the area with resin to reinforce it and remove the worries about water intrusion through the bolt openings.

Hope that helps....

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[DeepFrz]

You definitely want an annulus in the wood, be it reinforced resin or stainless steel. I don't think you need a top plate though and I wouldn't bed it in. Be careful about moving the mounting as it should have been put in the optimal position. You could check that but if you do move it make sure you adhere to all the mounting guidelines for the ram.

I personally would overbore the holes, coat the edges of the ply with epoxy resin, put plastic on the bottom of the holes and fill with reinforced epoxy resin, then drill the holes in the same place leaving the epoxy annulus. Then add the plate on the bottom of the ply. There would be no harm in bedding the plate in epoxy but not necessary IMO.

The problem with the original mounting is that the plywood will crush and the bolts will loosen thus you end up with all the force being put on the edges of the holes. That is why the holes get enlarged.

[PhilDuhs]

Thanks for the advice - much appreciated!

I assume the epoxy resin would just be same/similar to what's available from stores such as West Marine for normal fibreglass repair work, but what do you mean by "reinforced epoxy resin" - is there a specific product or type of product you can recommend?

In terms of the overbore, given the mounting bolts are centred 75mm apart and (I think) are 8mm bolts would a 20mm hole filled with the reinforced epoxy resin and re-drilled with 8mm holes sound about right or is that too large?

Lastly, any tips/tricks to ensure the holes I do end up re-drilling are exactly vertical/parallel with each other? I know space is a bit cramped under there so it'll be pretty hard to ensure the drill is 100% perpendicular to the plywood...

Phil

[Stumble]

Take a look at WEST SYSTEM | Use Guides

First step is to fill the current holes with thickened epoxy. Then mount two 1/4" G10 plates, on either side of where the current bracket is mounted. Do this following 'bonding' instructions. Drill thru the whole mess and rebolt it back together.

[deblen]

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

[DeepFrz]

WEST SYSTEM | Epoxy Fillers

There is a lot of information on this page. I would use a high density filler. There is a buying guide linked from this page that may say otherwise. Follow their directions.

As for drilling a vertical hole, two small squares or other square items stood 90 deg. from each other can help you eyeball the drill. If you don't have enough room for the drill to be held vertically then a 90 deg. adapter will help.

[PhilDuhs]

I've just got back to the boat and will do this job over the next week as time permits. One question, probably dumb, but worth asking - when you say:

"I personally would overbore the holes, coat the edges of the ply with epoxy resin, put plastic on the bottom of the holes and fill with reinforced epoxy resin"

Should I coat the inside edges of the hole with un-thickened expoy and then immediately fill with thickened epoxy (will use West Marine 404 to thicken) or should I allow the epoxy coating to harden around the edges of the holes before adding the thickened epoxy to fill them in?

I'd guess the former but happy to be corrected.

Thanks!
Phil

[Cheechako]

Distributing the load area with bigger plates is a good idea. Your ram is aluminum right? might as well use aluminum.
If your holes aren't rotted now I wouldn't worry too much about fancy epoxy hole fillers. just line the hole with some epoxy by brush if you want. It's inside the boat right?

[svlamorocha]

Originally Posted by PhilDuhs

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.

Phil

Have you asked Beneteau? When I was in a similar situation with a Beneteau USA boat they kindly provided detail drawings and instructions for the "right" way to install an autopilot drive on the boat in question.

In my experience the folks at Beneteau USA are great are providing that type of support. I cannot speak about France.

C

[Wulf]

[QUOTE=DeepFrz;1769888

As for drilling a vertical hole, two small squares or other square items stood 90 deg. from each other can help you eyeball the drill. If you don't have enough room for the drill to be held vertically then a 90 deg. adapter will help.[/QUOTE]

Easiest way that I know to ensure hole at 90 deg. if access restricted is to make a pilot to guide the drill bit. Just drill hole @ 90 deg or whatever angle you're looking for in a small block of wood using same bit as for the desired hole. This can be done on dock, table, cockpit etc, anywhere access to work is easy. Then align the block over where you want the finished hole & clamp/screw or just hold firmly while you drill a perfectly oriented hole.

[DeepFrz]

Should I coat the inside edges of the hole with un-thickened expoy and then immediately fill with thickened epoxy (will use West Marine 404 to thicken) or should I allow the epoxy coating to harden around the edges of the holes before adding the thickened epoxy to fill them in?

You only need to allow a short while for the epoxy to soak in. Apply the neat epoxy and then mix up your epoxy with cabosil or whatever you are using and fill in the hole. The plastic I referred to above I meant to say plastic tape, such as packing tape.