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  1. #36
    Senior Member
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    Quote Originally Posted by lostboy View Post
    A particularly intriguing theory and of absolutely no relevance to what I posted. Perhaps that's why Bill and Grumpf are so short? They haven't got as good in-built suspension as some of us
    They must have had a lower spring rate as children.

  2. #37
    Quote Originally Posted by phil_in_poole View Post

    I think the MFP force are 2 different things at planing and non planing.
    I definitely agree with what happens when a UJ breaks at speed, the mastfoot doesn't ram itself into the deck it flies up/downwind. Then at none planing speed the force acts downwards and gouges a hole in your deck.

    Once you are planing along, the rig force has already been applied and the sailor, board and rig are all moving forwards with the rig drive still acting against friction and drag, but with less load on the mast foot than at the 'getting going' stage because the great initial resistance and drag has been overcome. So the external forces are in some sort of equilibrium.
    But the internal forces come into play if the mast foot breaks, and the momentum of the board etc will keep you moving forwards temporarily whilst the internal force here the sail leverage on the boom will mean the mast foot will probably jump to windward when it breaks, because at that point the sideways load on the mast foot is greater than 'mast foot pressure' in a forwards or downwards direction.

    I'd add, the relative sideways load on the mast foot will also depend on what size rig your are on and on chosen boom height because of the leverage issue. With a waveboard or freestyle board under a 5m rig, the broken mast foot might well head downwards towards the deck of the board. I scratched the deck of my board when it happened to me.

    It's important to separate internal and external forces. It's like when you are on a plane to France your hand luggage is travelling toward Paris at the same speed as you, but it can still fall out of the overhead locker. The bag falling out of the locker does not prove it can't be travelling to France. This is a great debate for a night in the pub.
    Now back in the UK.

  3. #38
    Senior Member Radialhead's Avatar
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    If only it was that simple. You can't just ignore the substantial forces acting on the sail.

  4. #39
    Senior Member Radialhead's Avatar
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    I don't think I've seen anyone say it doesn't exist; obviously it does. But not all the time, & not necessarily to any measurable amount in many cases. It depends on the size & type of sail (i.e. the height of the CE, which appears to be extremely high in your setup), and how far raked over it is.

    E.g. I don't think there's any vertically downwards MFP in this photo: http://www.minorcasailing.co.uk/site...dsurf_jump.jpg

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