Ok, bear with me on this one - it may get long... 'cause we are talking about the boat for this posting.
Here is the back-end of our boat - a 22' North River. Great for fishing, but only okay for towing kids on tubes or waterski'ing. So... all during fishing season we've been trying to figure out how to put a tow tower or pylon in. I've also gotten some good input from the ifish.net forum, from guys who have towers on their fishing boat and some websites for tower mfg'ers.
After all the inputs, here is a basic design my friend and I came up with. I wanted the tower to be easy-in, easy-out. Also, didn't want to make drastic changes to the flooring or boat. Another major requirement was the ability to tow 3 tubes at a time if necessary. Oh yeah, it has to be out-of-the-way, too.
Here is a side-view of the design. Under the flooring of the boat there in the corner are solid bulwark beams, so we have a good point-of-contact for the base of the pylon to keep it from rotating upward. If we could bend the tubing to make contact with the transom, the pylon itself should take most of the stress from the moment forces created by piles of kids screaming "go faster!".
So... my friend came over and brought his tools - a true friend indeed! We are using two 10-foot long 2" Aluminum tubing (T4). Here you can see the first bend coming out of the floor from the frame, bending inward above the battery box, and up along the motor. This bend keeps the pylon away from the ski-step on the back of the boat. Good so far!It took a couple hours of bending, checking, bending a little more... but it went smoothly.
Here is the bent tubing... (now lets hope they meet in the middle!)
...and here is the bender. We used a 12-ton tube bender. Here we are putting the 90* bend in the tube to come across the top of the outboard and join up to the other side. This photo shows the ski-step on the back of the boat, too.
With the tubes bent and lined up, we made the cuts.Good friends are rare enough... but it takes great tools to make a good friend great ;-) Thanks Brent!
Here is a diagram of the frame and bulwark features the base of the pylon will be resting in.
There is about 7.5" from the top of the flooring to the bottom of the boat hull, so our plan is to 'insert' the pylon bases through holes in the flooring down 6 inches or so to rest against the bulwark.
Here is a photo showing how the legs of the pylon will insert through the flooring. We removed the original flooring, and cut plywood with mount-holes as a template. Eventually this will have covering over marine-plywood for a permanent fixture.Also, I'm working on a design for a hole-screen. These holes will work great when the pylon is out for washing down all the blood and fish-slime during fall chinook...
Anywho... after bending the tubing, my friend has taken them back to the shop for welding. Here is the update photo showing the tubes welded together and the flat cross-beam we added for strenght / stability - the perfect place for rod holders!I'm thinking we will polish the pylon and coat it with Sharkhide rather than powder-coating... any suggestions out there?
And here is the finished tow bar! My friend brought it over last night... Note the three attachment hooks at the top of the bar, for the tow ropes to wrap across the top with the loop coming down and around each peg.Also, the bases of the tubes have 'feet', to add stability and keep the pylon up off the bottom of the boat and engaged with the bulwark.
It fit on the first try! I was afraid after the welding and cross-bar we would have more bending to do. Not so! The tower dropped right in, is steady and stable, and just as we hoped.
It looks great! This pylon turned out so nice we may never take it out of the boat... just keep it in as a rod-holder / boat role-bar.
Now for field testing it... stay tuned for the field trials. I've done some bending-stress analysis (Bernoulli-Euler Equations, etc) and also some bend testing in the Barn... stay tuned for the results!
The costs so far are minimal - $84 for the aluminum tubing, and about 4 hours or so of 'work'. I owe my friend a couple fishing trips for this one, or better yet, I'll pull him on a waterski ;-)
