Gearbox Mounting Bracket

The Involute gearbox needs to be securely mounted on the torque box. The gearbox has four threaded holes in the bottom and four threaded holes on the top. The holes are fairly close to the corners so as to maximize leverage. It is possible to drill and tap additional holes, but four should be enough if the mount is done properly.

In this boat the mount has to also be adjustable in position fore and aft so as to accommodate the different leg lengths of different pilots. It is also useful in the event that I incorrectly measure my own preferred leg extension while pedaling.

So, the plan is to mount two 1/8 inch thick by 2 inch wide by 14 inch long aluminum plates on either side of the top of the torque box parallel with the top panel of the torque box. This panel is parallel to the stuffing box, so the gearbox can move fore and aft without affecting the angle of the propeller shaft. Two bolts through the torque box (and through the foam block inside the torque box) will secure these plates.

The gearbox will rest on two 7 inch long by 1.25 inch wide by 3/4 inch high aluminum 90 degree angle brackets, sort of like a sled. As the gearbox is narrower than the top panel, the mounting holes will be drilled in the angle brackets to center and align the drive shaft with the stuffing box.

Two bolts through holes along the top of the aluminum plates and through the raised sides of the angle brackets will secure the brackets and gearbox in place.

In addition, the side plates are not just flat pieces of metal. They, too, are angle brackets, with all but 1/4 inch removed from one side. This leaves 1/8 inch on the inside of the angle protruding, which captures the top edge of the gearbox sled and keeps it from being able to move in the upward direction. So, one can remove both sled securing bolts without fear of the gearbox somehow flopping out. This also spreads any upward load from the sled along the length of the aluminum plates, strengthens the plates, etc.

You might ask where one gets such strange sized angle brackets. I happened to have a bunch of 2 inch by 2 inch by 1/8 inch square aluminum tubing laying about from a previous project. A bit of quality time with a bandsaw to cut the pieces roughly to size, followed by some time with the bench belt sander was needed to convert these pieces to the proper size and shape.

Ok...this is cheating a little, blog-wise, but today (Saturday) I finished drilling the brackets with the exception of the holes to secure the mounting brackets to the torque box. I also removed the spider from the cranks I intend to use, and polished the gearbox.