Zip 20" Transom with Modified Tumblehome

Questions about modifying a design

Moderators: ttownshaw, billy c

Post Reply
User avatar
Shelboss
Posts: 12
Joined: Tue Dec 19, 2017 6:14 am
Location: Hopkinton, MA

Zip 20" Transom with Modified Tumblehome

Post by Shelboss » Tue Jun 26, 2018 5:44 pm

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 :)
Attachments
Long shaft transom with Modified Tumblehome
Long shaft transom with Modified Tumblehome
Frames on BF Rear web.jpg (29.77 KiB) Viewed 4281 times
Dimensions for the modification
Dimensions for the modification

PeterG
Posts: 701
Joined: Mon Dec 03, 2007 7:08 am
Location: Connecticut

Re: Zip 20" Transom with Modified Tumblehome

Post by PeterG » Tue Jun 26, 2018 6:34 pm

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.
Murphy's Law: Anything that can go wrong, will go wrong.
Griffin's Law: Murphy was an optimist.

User avatar
sproggy
Posts: 233
Joined: Sun Jan 01, 2017 12:04 pm
Location: Welwyn Garden City, UK

Re: Zip 20" Transom with Modified Tumblehome

Post by sproggy » Wed Jun 27, 2018 1:17 am

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.

User avatar
Shelboss
Posts: 12
Joined: Tue Dec 19, 2017 6:14 am
Location: Hopkinton, MA

Re: Zip 20" Transom with Modified Tumblehome

Post by Shelboss » Wed Jun 27, 2018 5:39 am

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

PeterG
Posts: 701
Joined: Mon Dec 03, 2007 7:08 am
Location: Connecticut

Re: Zip 20" Transom with Modified Tumblehome

Post by PeterG » Wed Jun 27, 2018 7:11 am

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!
Murphy's Law: Anything that can go wrong, will go wrong.
Griffin's Law: Murphy was an optimist.

Hercdrvr
Posts: 977
Joined: Mon May 11, 2015 12:52 pm
Location: McKinney TX

Re: Zip 20" Transom with Modified Tumblehome

Post by Hercdrvr » Wed Jun 27, 2018 7:35 am

I hope the 1/4” plywood will make the decreased radius bend. Good luck,
Matt B

hoodman
Posts: 2246
Joined: Thu Nov 10, 2011 8:48 am
Location: Lafayette, IN

Re: Zip 20" Transom with Modified Tumblehome

Post by hoodman » Wed Jun 27, 2018 9:10 am

Yeah, you might need to do the boiling water/wife's bath towels trick.
Matt

Building a Geronimo......!
viewtopic.php?f=2&t=25139

User avatar
Shelboss
Posts: 12
Joined: Tue Dec 19, 2017 6:14 am
Location: Hopkinton, MA

Re: Zip 20" Transom with Modified Tumblehome

Post by Shelboss » Thu Jun 28, 2018 5:43 am

Increased radius bend, I went from 16"" to 17" so it should be easier.

Stevel
Posts: 22
Joined: Sat Jul 28, 2018 2:13 pm
Location: Tulsa oklahoma

Re: Zip 20" Transom with Modified Tumblehome

Post by Stevel » Tue Aug 07, 2018 8:17 pm

Did you have to modify the other two frames?

User avatar
Shelboss
Posts: 12
Joined: Tue Dec 19, 2017 6:14 am
Location: Hopkinton, MA

Re: Zip 20" Transom with Modified Tumblehome

Post by Shelboss » Fri Aug 10, 2018 9:54 am

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).

Post Reply

Return to “Design Modifications”