Rolling a cone shape to match transom contours...

[Revisionist]

Howdy gang... Hope all's well...

I'm hoping someone here can help me with a problem. I'm currently building an aluminum swim grid on a seventy foot fiberglass yacht. So, basically I'm bolting a plate onto the transom that wraps around the curves of the stern to weld the platform itself to.

Obviously, both the transom and the sides of the vessel have sweep toward the waterline so the corners of the transom themselves need to be rolled to shape before I can mount them to the hull and continue on.

My question is this: How do I roll these corners on a machine to match the curvature of the transom?

Simply powering the aluminum around the corner with porta powers and bolting it on isn't an option since I can't bolt through that section sufficiently to hold it due to inaccessability on the inside of the hull. It must be screwed or lag bolted at this junction. So it must be rolled to shape first.

Are there measurements and calculations I can transfer from the corners of the transom to the shop that I can use to roll this tapered cone shape to match? Or is there something even more simple I'm missing here.

Any help that could be given would be greatly appreciated. Thank you.

Dan

[DGreenwood]

A potential dammit' here is you must remember (if I am visualizing this correctly) that your flat bar bent to match the transom curvature will no longer be a straight line (looking from straight astern). Now you have to start with a piece that is over sized and cut that to a straight line.

My approach would be to strike a straight line on the transom at either the top or bottom of the proposed mounting plate (laser works good). Make a doorskin pattern of the plate as it will lie arond the curve. Lay that pattern on your plate and cut it out. Then make a doorskin pattern of the transom curvature in the horizontal plane. Take the whole shootin' match to your freindly neighborhood smart guy with a press and have him push it into shape.

Lastly...I don't like the sound of that baby not being through bolted???

[Revisionist]

Thanks for the response. Basically what I did is what you envisioned. I made a doorskin template using a laser level to determine the top and bottom of the one foot wide stripe. I cut it out oversize by two inches on an aluminum plate so the curvature is already compensated for on the pattern. What I had planned on doing was taking three patterns of the corner, top, middle and bottom and taking it to the rolling machine and starting the curve and slowly adjusting the radius to produce a cone shape. Unfortunately, this is more trial and error than getting a good fit the first time. I was just wondering if someone had a way of taking radius measurements and laying our tapered increments to get the corner rolled perfectly off the machine...

Tis my hope, but I may have to do it as I first thought. On the through bolting... It's only the corners themselves I can't get at. Fifteen feet of the back of the transome is water tank so I can get inside and put backing plates and through bolts in that area. It should be sufficient with enough 3/4" stainless bolts and lots of adhesive. It's the fit I'm worried about.

Thanks again.

Dan

[DGreenwood]

Good deal on the through bolts!

The only other thing I can think of is maybe slightly over bending the curve out toward the end and pulling it flat with the bolts.

Good luck