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Zip 20" Transom with Modified Tumblehome

Posted: Tue Jun 26, 2018 5:44 pm
by Shelboss
I had my transom all fabricated when I decided I wanted to increase the tumblehome. I settled on taking 1.7" off each side. I also had concerns with the original radius that the side planking needs to bend around, so I made this more subtle. The shear ends up higher on the transom and forms more of a barrelback look to the transom. You will have to use your imagination to see what the finished product will look like for now :)

Re: Zip 20" Transom with Modified Tumblehome

Posted: Tue Jun 26, 2018 6:34 pm
by PeterG
That looks really interesting, hope that works out for you. One thing to watch for, this transom mod changes the curve of the sheer and may look very different from the side. If you can, try modeling it on a CAD program or scale model in wood, to see if your changes look OK.

Re: Zip 20" Transom with Modified Tumblehome

Posted: Wed Jun 27, 2018 1:17 am
by sproggy
Raising the sheer at the transom means you’ll likely also need to raise it at frame 2 to keep the sheer fair in profile. In theory your change might need a change of profile at frame 2 between chine and sheer to keep the curves fair but as the change is minimal you’ll probably be OK.

Re: Zip 20" Transom with Modified Tumblehome

Posted: Wed Jun 27, 2018 5:39 am
by Shelboss
Thanks for your comments/concerns, sent me scurrying to the garage this morning to make sure I hadn't messed up :lol: . My sheer is cut to size, but needs to be planed to 5/8". Was able to bend it around frame 2 and 4 to get these shots. The sheer only rises about 1/2" so the change is very subtle and should be okay.
Rise from original is only about 1/2"
Rise from original is only about 1/2"
As seen from below
As seen from below

Re: Zip 20" Transom with Modified Tumblehome

Posted: Wed Jun 27, 2018 7:11 am
by PeterG
Oh I totally whiffed that you were that far along! You got the visual, if you like it the all is good! Make sure your sheers sit in the corners of the frames with the correct orientation, meaning vertical or parallel with the frame sides, whichever the plans require. Have fun!

Re: Zip 20" Transom with Modified Tumblehome

Posted: Wed Jun 27, 2018 7:35 am
by Hercdrvr
I hope the 1/4” plywood will make the decreased radius bend. Good luck,
Matt B

Re: Zip 20" Transom with Modified Tumblehome

Posted: Wed Jun 27, 2018 9:10 am
by hoodman
Yeah, you might need to do the boiling water/wife's bath towels trick.

Re: Zip 20" Transom with Modified Tumblehome

Posted: Thu Jun 28, 2018 5:43 am
by Shelboss
Increased radius bend, I went from 16"" to 17" so it should be easier.

Re: Zip 20" Transom with Modified Tumblehome

Posted: Tue Aug 07, 2018 8:17 pm
by Stevel
Did you have to modify the other two frames?

Re: Zip 20" Transom with Modified Tumblehome

Posted: Fri Aug 10, 2018 9:54 am
by Shelboss
No the distance between frame 2 and the transom is 4 feet so the sheer change to the transom is very subtle. I modified the top of the transom and frame 2 for a more integrated 20" transom look, but didn't change the sheer position of frame 2 (see modified Zip transom post).