View Full Version : Sheer trimming question

06-02-2014, 07:50 PM
So I've flipped my glued-lap boat over, and it definitely needs the sheer trimmed a fair amount. My question is: how to shave bits off with cross-spalls, or, in my case a couple of molds still in. I think I'll make a spall or two to hold the shape, but do I remove this stuff to trim the sheer?

Seems like another silly question, but i just gotta know.

Thanks in advance,



A nice pic that doesn't really show the problem.

And two that do.



Gib Etheridge
06-02-2014, 08:24 PM
Install the rail and a couple of temporary spreaders then remove the forms and trim to the rail. Looks good, nice job.

06-02-2014, 08:57 PM
I would put new cross stalls in (level to the waterline) below the projected sheer and cut of what is above. Then sharpen up a plane and go to work...

Binnacle Bat
06-03-2014, 09:21 AM
From the photos it looks like it is less of a sheer problem than a kink in the planking. Before trimming the planking I would clamp temporary battens in the way of the gunwale and see if they lay fair in three dimensions. You may find that things even out if you release the shear strake from the molds.


Tom Lathrop
06-03-2014, 09:34 AM
From the photos it looks like it is less of a sheer problem than a kink in the planking. Before trimming the planking I would clamp temporary battens in the way of the gunwale and see if they lay fair in three dimensions. You may find that things even out if you release the shear strake from the molds.


Mostly agree but I would call it a sheer problem.

This is usually caused by having a too wide bulkhead just forward of the area where the dip in the sheer occurs. Its a bit ugly and should be fixed if practical. Nothing beats the eyeball in preventing an unfair sheer. You have to back off now and again and just eye things, regardless of what the designer calls for.

06-03-2014, 09:51 AM
Look like the boat did a banana. The bow rose. Did you use a bow form mold ? Can you push the bow forward ?

06-03-2014, 12:07 PM
That is a weird looking knuckle, it looks to me like that plank got forced into place instead of falling gracefully along the mold (or the mold was way off). Put another way, it appears to me that the overall length of the sheerline is too long and the plywood was forced out wards to accommodate the extra length. I'd be inclined to pull the two remaining molds and see what happens when the hull is allowed to 'relax" a bit.

Gib Etheridge
06-03-2014, 12:19 PM
I'm thinking that if you dry fit the rail it may pull that low spot right up into place. If it doesn't you could apply a rabbetted inner rail at the same level as the outer rail and cover up the gap. If you do that you should fill the gap between the rails with something to avoid moisture pooling in there.

06-03-2014, 12:34 PM
The sheer plank seems to have puckered in as is contrasted in these two shots. The stern shot shows little or no such pucker.
Maybe just spread the hollow and run a batten on the sheer to check.
Set the saw blade shallow to only 'nick' the cross spalls.
My 2 cents.


06-03-2014, 12:47 PM
Really hard to understand from a picture.

it you cut the sheer plank too long, then forced it into shape you would generate a bulge in the sheer. If you started fastening aft and moved forward , this bulge Would accumulate forward of the last bulkhead.

if it were a mechanically fastened boat I would break the forward fasteners free , shorten the strake and refasten.

with glue its not so Easy..

is the measurement from the inside face of the stern post to the inside face of the stem as to plans ?

if it were an inch short a bulge would develope in the sheer plank.

Is the boat still Limber Enough for you to force the head , top, of the stem forward ?

06-03-2014, 01:26 PM
I think the photos made it look worse than it is. I think what appears to be a warp in the plank is an optical thing. I went back to the full-size patterns and found that I had left the sheer plank about 1/4 inch proud everywhere, but at the stem, it was more like 3/4! So there's a bit of a "hump" in the plank profile from about two feet back, to the stem, which I'll trim.

Talk about over-compensating! Sorry for the confusion, but I really appreciate the replies.

Here's a batten showing the hump, a close-up of the same, and the actual gunwale dry-fit.




06-03-2014, 03:15 PM
Same on both sides?

06-03-2014, 03:47 PM
It is. I cut the planks out as a pair. Just left way too much extra as a way to make sure I could get a nice sheer line.

The rail seems to make a fair line, now. I did manage to space out and cut a 10 inch scarph in my half inch rail stock. So instead of 10:1, I've got 20:1

Anybody know if a really long scarph will tend to leave a flat spot more so than a normal length scarph? 1st-time builder here in case you can't tell!


The King of Dopey Questions

06-03-2014, 05:59 PM
First time? Beautiful boat, not ssure what to say about the long scarph vs a flat spot, probably not.

06-03-2014, 06:28 PM
I'm glad it was a lining off issue and not a more difficult fix. The pictures made it look a lot worse than it is. I will be turning my boat over soon so I am starting to wonder what she'll look like too.

06-03-2014, 06:34 PM
The longer the scarf the less likely it is to form a flat spot.
HOWEVER, much steeper than 12:1, and the thin end of the wedge will begin to disintegrate and tend to curl.
Not worth the trade-off IMHO.

Binnacle Bat
06-03-2014, 08:04 PM
Time to get out your biggest step ladder and look down at things. If the curve of the gunwale is eyesweet, you are there. If in doubt, try a thicker batten, and see if everything still looks fair from every direction.

Perfect is the enemy of good. Press on, and enjoy!


Tom Lathrop
06-03-2014, 09:26 PM
Falcon, you misled us. There is apparently no true unfairness in the sheer or local bend in the sheer plank. Just trim to your eye and go. Luckily, for whatever foresight, you left material there to make the needed correction. It will be fine. In our defense, I will say that such a dip at that location in the sheer is all too common unless molds are faired with a true batten before planking. Usually it is not possible to completely correct without major surgery if the local unfair bend is really in the plank. It can often be faked to look sort of OK to the eye in the same way you are doing although that does to apply to your sheer.

06-04-2014, 01:36 AM
Have a good look while wearing a pair of these..they're wireless...bluetooth jobs...kinda like Google glass, but cheaper.

. I use them all the time when I must fair a line.

Stand back so you get a good view.

http://s29.postimg.org/rdiacw2qf/image.jpg (http://postimage.org/)
image sharing sites (http://postimage.org/)