Building an Autopilot Base

[AJ_n_Audrey]

Thanks Noelex for the input on 7075 corrosion. I can also get 6 or 5 series plate, so I'll go that route instead.

[AJ_n_Audrey]

I now have the 3/8 inch 5052 backing plate (6x6 inch) drilled for mounting bolts, and platform is glassed on with triaxial cloth.

Question for DeepFrz - you suggested using annuli in the bolt holes, and I looked online to see about how to go about that, but found very little. The platform is 1.5 inches thick (doubled 3/4 inch marine plywood). Would you make the annuli slightly shorter, like 1.4"? And do you know of any sources for SS annuli? I'll have to measure diameter, but I'm guessing it will not be a standard size. I'm thinking you want the ID of the annuli to be just as small as possible such that the bolt can still be inserted, right?

Also, is the 1/8 inch (or slightly less) SS plate on the top of the platform really necessary? Before I get one, I just want to be sure I'm not really over doing it.

Thanks again to the advice I have received from all - it made a big difference to the design and execution of the base.

[antoha]

I would avoid dissimilar metals if you have no reason for that. Why do you want a stainless plate on top instead of another aluminum, like the backing plate? Yes, bolts are stainless I realize, but autopilot foot is aluminum.

[AJ_n_Audrey]

Originally Posted by antoha

I would avoid dissimilar metals if you have no reason for that. Why do you want a stainless plate on top instead of another aluminum, like the backing plate? Yes, bolts are stainless I realize, but autopilot foot is aluminum.

Good point; galvanic action is a consideration. I'll check the clearance height again between the top of the drive and the bottom of the propane tank well, and maybe go with 0.1" alum. Probably good enough.

[DeepFrz]

The inserts should be a close tolerance fit to the bolts and if possible the exact length so that the pressure is on the insert as well as the plywood. Epoxy the inserts in. Actually, if the inserts are slightly shorter you should be okay with the base plate on top and the backing plate on the bottom.

You shouldn't need a top plate as you have the base of the drive unit.

[AJ_n_Audrey]

Pic attached of nearly finished base, completely glassed in, painted with BilgeKote, and annuli (bolt sleeves) installed and epoxied in place. I'm debating whether to add another vertical support on the outboard (to port) side of the propane well, and the other possible addition is a stainless L bracket, again on the outboard side, connecting rib to platform.

It may not be obvious, but the base is attached via bolts and glass to the rear bulkhead, the stringer, and it is bolted to the large mahogany lumber which the quadrant base is constructed from. I'm close to saying, "good enough".

Thanks again to all who have offered help and advice!