Gunnels too thin and weak? Is space an issue? I came up with this:
http://i1191.photobucket.com/albums/z474/ned14/001.jpg
http://i1191.photobucket.com/albums/z474/ned14/003.jpg
http://i1191.photobucket.com/albums/z474/ned14/005.jpg

Materials are 3/8" threaded rod, nuts bolts and washers, treated 2x12 and 2x2 painted with rubberized spray paint (home depot), drill with bits to countersink, and a 7" seat mount ($12 instead of $65 for the Scotty product) used for a riser so the arm clears the gunnel.
The seats are filled with foam, so you can't mount the base to them and I didn't want to drill into the seats. This system lets you sandwich the seat. Downriggers don't pull downward so much as laterally when underway, and so torque was a issue. The 2x2's extend a few inches past the 2x12 to help distribute the torque load along the front of the top and bottom length of the seat. Note how the 2x2's extend past only one side of the 2/12 (the side with the torque). Another issue is that you have to countersink the bottom of the lower 2x12 (under the seat), and make sure the bolts don't come in contact with the hull. When the boat is in the water, the hull will flex up a bit, and the bolts will wear through the hull if there is not enough clearance.

Strong enough to lift the boat from the 2 mounts.

The threaded shafts that connect the 2-2x12's just need to be snug-tight, or you'll crush the boat seat.
Any of you want to try this, PM or I can send more pics on request.

That is slick.

Duraboat makes downrigger mounts that work great and only require 4 bolts, neoprene washers and nylon lock nuts all stainless steel to match your boats hardware. Around $16-20. I've had mine since 1990 on my 14' duraboat, they take up no seating space.

Here are your pics.




Good job.

Thanks for the Pics Dogfish.
TYDY: I found the gunnels to be too flexible and thin for 10-12 lb downrigger lead with mounts similar to the Duroboat mounts (tried 'em). If I snagged at good speed, it seemed the gunnel might buckle. How much lead do you use?

Wouldn't work for me, don't have space beneath bench. I'm going with the Scotty clamp for downrigger mount with a 2x4 instead, and another clamp on for the rod holder.

I use 10&12# balls. Location, location, location. Mount one bracket left rear directly behind seat. mount one bracket right btwn. back bench & center bench. The seats are bolted to the gunnel which gives them rigidity. Aluminum is some damn tough material, even though it flexes. i.e., airplanes,jets,etc. I've snagged downrigger before. just be prepared to loosen drag if this occurs. If you're worried about it, make a small backer plate with some aluminum from home depot and be sure to use quality stainless steel 1/4" neoprene washers on outside(water side) available from duraboat or west marine.