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TOPIC: What effect has the mast step position have ?

What effect has the mast step position have ? 2 years 10 months ago #6035

  • woham
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During the complete rebuild of an older boat 7XXX model, I started questioning the reasoning behind the positioning of the mast step. The conventional wisdom suggests you should place the mast step as far back as the rules allow (3048mm from transom rings a bell). Why is this? Is it a case of trying to get the space between the jib and main as big as possible to encourage the maximum airflow between Main and Jib, or is there another reason?
What about forestay tension? The further forward the mast the higher the possible forestay tension for a given rig tension, resulting in less forestay sag and therefore better pointing ability. As the angle of the forestay changes it is obvious that the jib car position has to be changed to get the same setting of the jib regarding leech tension.
The other aspect to consider is the rear edge of the mast gate, which on some boats gets in the way when the mast is being raked back to compensate for the aft movement of the centreboard center of pressure as the board is lifted. Usually when the wind is increasing, one is bending the mast anyway to depower the main so what looks wrong for the straight mast works better in practice as the mast bend increases.
If different boats are compared to each other the conventional wisdom appears to be that a Waterat, with the forestay located in front of the chute is able to point higher than a Rondar with the forestay behind the spinnaker chute. Is this true and if so why is this?
The other aspect to be considered is the centre of pressure of the combined sailplan, as this relative to the centreboard position will determine the weather helm and the "feel" of the boat.
I would be interested in any comments on the subject or any references to boat design or tuning literature on the subject.
:)
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What effect has the mast step position have ? 2 years 10 months ago #6036

  • mikeholt
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I think it is years of people testing and messing and that is where they all ended up. I have messed with moving forward for easier raking without hitting the back of the gate and really could tell no difference.
As to the pointing question... Not sure that is true, I think, foils, mast, weight and driver are the most relevant factors.
My advice would be to copy what is fast.
Mike
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