Latest News: Forums Technical CB location

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  • #4149
    Swiebertje
    Participant

    Today I had a discussion with a Solo sailor about the best CB position. here is what we talked about:

    Assuming we want the leading edge of the CB level with the underside of the keel when it is full up, to avoid damage while on the trailer, the position of the leading edge, when it is full down, is solely defined by the position of the CB bolt. Also assume the bolt hole in the CB is re-drilled if the bolt holes in the hull are changed. This to keep the CB at maximum depth and level with the underside of the keel at all times. Under these assumptions, with the CB full down:

    • The leading edge is further forward when the bolt holes in the hull are maximal up compared to when the bolt holes are maximal down in the hull.
    • When the bolt holes position is moved forward in the hull, the CB’s leading edge moves forward too.

    Another way to describe what we were talking about was that we could move the leading edge of the CB forward or backward by changing the position of the bolt holes in the hull. Given the vertical (+/-7) and horizontal (+/-13) tolerances of the bolt hole positions in a Wayfarer, we could move our CB’s back and forward 40 mm and still stay within class rule limits.

    The question is: What would be the best choice, the CB maximal forward or maximal backward, and why?

    #9172
    bigal
    Member

    but in the W class don’t we want the CB set up to satisfy the max 83 degree angle of dangle rule ( 17.8 ) ??

    #9173
    Fantasia
    Member

    I do not pretend to know the answer, but I have been told that the optimum is to keep the distance between the centrboard bolt and the mast pin to the maximun; therefore if you in tend to move the centreboard, it should move aft (within the rules).

    #9174
    Colin Parkstone
    Participant

    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?

    CP 😕

    #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.

    #9179
    Colin Parkstone
    Participant

    As I have said many times, call us what you like (and they do at our club ) we are NOT a one design class.

    Point taken Bert, I get what your saying, Now! I took the point that I wanted the centreboard in the box!

    Yes, the leading edge should be the measuring point like the depth is. Maybe its why we dont have many measurment points on the Mk4 as to measure the centreboard the above way we would need to know where the transom starts???

    To leave the boat and moulds without any meaningfull measurements or way to keep the moulds for the builder in the same shape is foolhardy and never got my vote.

    We as a class will be almost a one design in a few years when all our old boats go cruising and we all sail a Mk4.

    No! I am not against the new boat, it is a ace boat and is the future of a dying class, Well Done Hartley.

    Now,Im going sailing as my soapbox is moaning about my weight. No I dont have lead correctors just pork pies!

    C P 😉

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