Welcome to the UKWA Home Page Forums Technical CB location Re: Re: CB location

#9177
Swiebertje
Participant

@Colin Parkstone wrote:

If you move the bolt hole in the boat upwards with the leading edge vertical, it does not move the leading edge forward.
It must stay in the same postion ?
So I dont see the logic that you have a total of 40mm movment ? Or have I read your post wrong?

It does, if you also move the hole in the CB up (up with the CB in its up position). As I wrote before: Assume we keep the leading edge of the CB level with the keel, with the CB in the up position. Then the distance between the bolt and the leading edge changes when the bolt is moved up. When the CB is then turned to its down position this vertical distance translates to a horizontal distance. I know the CB is not allowed to be turned beyond 83 degrees, but the difference with 90 degrees is small. In other words the vertical tolerances of the holes in the hull translate to horizontal movement of the leading edge when the board is down. Hence the total tolerance we have in the position of the leading edge is the sum of the horizontal and vertical tolerances of the bolt holes in the hull.

Actually we have more options: The bolt hole in the CB is not defined by the rules. Obviously we don’t want the CB to stick out of the hull in the up position, that could be a practical limit on the forward position. But a hole could be drilled just behind the leading edge, that would move the CB aft almost 90 mm, the vertical distance between the bolt and the keel. In this case the CB may not fit the CB case anymore. I suppose the shape of the CB case dictates the minimum distance between the leading edge of the CB and the hole through the CB.

So, for a board maximal aft:
– Drill the hole in the hull as low as allowed and as far back as allowed.
– Drill the hole in the CB right behind the leading edge. This may cause the CB not to fit the CB case in the up position.

For the board maximal to the front:
– Drill the hole in the hull max up and max forward.
– Drill the hole in the CB as far aft so that it just does not touch the front of the CB case in the full down position. This may cause the board to stick out under keel when it is up.

But the question is: What position is best and why? Aft or front?

Maybe the rules need a change and include the position of the CB’s leading edge at keel level in lieu of the bolt position?
I mean, 130 mm is way too much play for a one design class.