Jesper,

I agree with Mike that ½” could create big problems down the road. Something in the range of + or – 1/8”-1/16” is a good goal to shoot for.

First question is are you using an internal or external strong back? The alignment methods are slightly different. I have used internal strongback for both my kayaks but I can give you some general tips that apply to both.

You need to start with blocks you use to attach forms to the strongback that are square, plumb and precisely spaced by one foot. I find this the easiest part and relies lines drawn with a square to eliminates most of Mike’s out of alignment permutations.

Now you are left primarily getting the up/down and left/right alignments. The best tool for this is a string line across the top of the forms and along the waterline. If these are off your keel might have a side to side curve or the hull line might become unfair.

One trick that I used was coffee stirrers hot glued to the forms so that the string could align with the lines on the form. (see attached photo) I have also heard of people using the new low cost laser levels aimed through alignment holes.

One other trick I can share is that make sure you have a good clamping method as you screw them down. Most of my problems arose from the forms shifting as I was drilling/drilling into the forms