Mounting downriggers?

[Milkdud]

What would you guys/gals out there suggest I use to mount downriggers to my boat? I have the cannon swivel bases already but the sides of my boat are just a thin aluminum sheet and I feel I need to put something under that to screw the swivel bases into....correct? It doesn't seem like the aluminum sides of my boat would be strong enough if the ball of the downrigger got caught on something. Any suggestions?

[stick]

Is this a flat gunwale or are you talking the aluminum sides of the boat with a rounded lip on top. I have mounted them on boats with a gunwale, and I have put marine grade plywood with a 1/8" aluminum plate with holes that match up with the swivel bases. Make the "underside" hardware as big as possible in order to distribute the torque of the downrigger itself and the extra torque if you get snagged up. We have snagged up the Cannon downriggers in the past and the boom bent before the gunwale gave out.

[Milkdud]

Yes my boat has the flat gunwale sides that you mentioned about 8-10 inches wide. Do most hardware stores carry aluminum plates and marine grade wood?

[stick]

They should carry the aluminium plates (needing to cut to size) and I'm not sure with the marine grade plywood. My dad had a chunk of it when I used it. That may be overkill since it should be out of the elements, and you ought to be more than fine with green treated plywood. I normally do everything to an overkill level. I also recommend stainless fasteners and locknuts for sure. I put locknuts on wherever possible due to the vibration.

[fivebucks]

Do not use green treated with aluminum. The old treated was fine but the new treated of the past couple of years reacts with alum and will corode it. I mounted my riggers with just a 1" piece of plywood under the aluminum (top inside of storage box and rod locker so no rain hits it). I then used silicone where the bolts come thru. I have had no problems at all.

[Sutty]

You might also want to look at a track system for your boat. Than you can slide the downriggers/rod holders out when not in use.

[Surface Tension]

Use a backer as suggested. A 1x8 pine board will work. You'll want to get this as wide as possible and into the corners of the gunwale. Use SS fender washers and locknuts & bolts.