half hull modeller needs help expanding transom of Folkboat

[Shearwater]

>...hope that says it all. I have spent hours trying to understand that the radius for expansion waterlines equals ther halfbreadth radius plus R.

I'm trying to do a Folkboat, a picture is attached I hope. Can anyone here help me understand this ? I am quite intelligent but do have some failings with maths and perception.

 

[TernVI]

I think it may have been drawn for you?
In the top drawing, the shape beyond/above the rudder, as I understand it (and I could be wrong!!!!) is half the transom rotated about it's axis? Imagine ruling a crease parallel to the rudder shaft and folding that shape away from you?
So the top edge of that shape becomes a slightly cambered deck profile?

The buttock lines give the width of the transom at a few heights. That will give you an end-on stern view, but the shape of the transom needs to be stretched to account for it being angled towards you.

 

[Hacker]

Because the body plan view (top right on your lines drawing) is looking at an angled transom the overall size and shape is foreshortened. In order to be able to obtain a template you need to do the following.
On the profile view (top left) draw lines at 90 deg to the transom on each intersection of a waterline and a buttock line. Then (using the body view plan and the plan view) use dividers take the measurement from the centre line to where the transom shape intersects the relevant waterline and buttock line. Mark these points on the extended lines that you’ve drawn on the transom. Use a fairing batten to join these dots. This will give you a flat template for half the transom. It is easier to do on a full size set of lines drawings rather than a model sized one (less prone to measurement error and easier to run a fairing batten. I tried attaching a picture of one I did a few years ago but it won’t attach. If you want it, pm me.

 

[TernVI]

Looking at a few pix, I think the flat template for half the transom is in the top left, section, superimposed on the rudder.

 

[Hacker]

Looking closely, you are right. My explanation might serve to describe how it was done.

 

[Shearwater]

Brilliant people. Thanks so much for the eye -opener. I've already made Slocum's Spray without a separate transom (paint covers everything!) and the American R-Class 'Pirate' the stern of which is as sharp as a pencil..... but European classics need greater care and respect. If it works out I'll put up a pickie, but thanks once again.