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Mark Aged 42 View Drop Down
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Post Options Post Options   Quote Mark Aged 42 Quote  Post ReplyReply Direct Link To This Post Posted: 06 May 21 at 8:23am
There was a story going around that back in the day, the top sailors went to the factory to pick a hull which gave better mast rake, due to variations in the mast pot installation. 
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JimC View Drop Down
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Post Options Post Options   Quote JimC Quote  Post ReplyReply Direct Link To This Post Posted: 06 May 21 at 10:35am
There are always a lot of rumours, but mast rake must be a nightmare on unstayed boats because a tiny variation in the step makes for a big variation at the mast tip.
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Post Options Post Options   Quote rich96 Quote  Post ReplyReply Direct Link To This Post Posted: 06 May 21 at 1:55pm
Originally posted by Mark Aged 42

There was a story going around that back in the day, the top sailors went to the factory to pick a hull which gave better mast rake, due to variations in the mast pot installation.†


It wasn't just the top sailors - it was quite common

Less rake = more potential leech tension
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Post Options Post Options   Quote tink Quote  Post ReplyReply Direct Link To This Post Posted: 06 May 21 at 4:50pm
Originally posted by rich96

Originally posted by Mark Aged 42

There was a story going around that back in the day, the top sailors went to the factory to pick a hull which gave better mast rake, due to variations in the mast pot installation. 


It wasn't just the top sailors - it was quite common

Less rake = more potential leech tension

I imagine the helm balance was also a major factor. 

It would be very fascinating to know if as rake tolerance was included in the original build manual, if it was added and then if it was changed over time. 

Interesting when they did the last Olympic single handed equipment trial they didnít like the D-zero because, and I paraphrase, Ďbeing able to adjust the mast rake makes the boat more technical to sail and distracts from the athleticism required by the sailorí
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Post Options Post Options   Quote KazRob Quote  Post ReplyReply Direct Link To This Post Posted: 07 May 21 at 9:36am
It's not just the tolerances on the rake that affect leech tension but also the relative stiffness's of the top and bottom sections which always varied a lot. In an ideal world you would probably want the mast pot to be as upright as possible but with a soft lower section F/A so that the rig is more upright downwind but still raked aft upwind and too section to suit your weight.
There was a nice video of Ovi's on FB which showed them controlling the mast pot rake during construction(within a few mm Chris T says)  https://fb.watch/5kMOyTTj9F/
OK 2139 & 2148
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Post Options Post Options   Quote tink Quote  Post ReplyReply Direct Link To This Post Posted: 07 May 21 at 7:04pm
Interesting about the mast stiffness, given relatively simple controls Iím sure itís easier to produce repeatable alloy masts vs composite but perhaps decades of windsurfer masts have improved composite mast repeatability 
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Post Options Post Options   Quote Oatsandbeans Quote  Post ReplyReply Direct Link To This Post Posted: 07 May 21 at 7:37pm
Not really-when you make Al spars they change shape as the extrusion die wears. If the die is new the mast will be significantly different to one made from a die on its last legs. Whereas with composites it is not like that and it is easy to get a consistent stiffness
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Post Options Post Options   Quote KazRob Quote  Post ReplyReply Direct Link To This Post Posted: 07 May 21 at 7:37pm
Originally posted by tink

......Iím sure itís easier to produce repeatable alloy masts vs composite but perhaps decades of windsurfer masts have improved composite mast repeatability 

One problem with the alloy masts is they were extruded and the extrusion dies wear over time so wall thickness will vary over time so that can have a big effect on stiffness. Even a +/-5% on wall thickness will give a big change in section stiffness.

Conversely, I know from boats like the OK and Finn where mast bend is critical that the carbon mast manufacturers now do really repeatable bend numbers (+/- a few mm).
OK 2139 & 2148
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Post Options Post Options   Quote tink Quote  Post ReplyReply Direct Link To This Post Posted: 07 May 21 at 8:04pm
So it comes down to quality control, as the die wears you replace it. An extension die is a few thousand  max and I imagine you get a significant number out of a die. Iím not convinced a simple die measurement is less  controlable than precision resin content, wetting out efficiency, fibre alignment, cure temperature and other variables 
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Daniel Holman View Drop Down
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Post Options Post Options   Quote Daniel Holman Quote  Post ReplyReply Direct Link To This Post Posted: 07 May 21 at 8:27pm
In my time laser sailing, I had top sections weighing between 2.6 and 3.1kgs. Thats the range of the 10 or 15 topmasts I had so the true population will be a bit broader. Thats all in the wall thickness - if you do the sums on inertia, that is a big, big difference which transcends going from a bendy to stiff mast in, say a Solo. So the extrusion tolerances are massive. I heard for the Atlanta games in 1996 the organisers bough 500 sets of spars and cherry picked the 500 closest of each spar to the mean.
My knowledeg of composites is that tensile performance of fibre can vary a bit within batches, but will probably even over a spar. Resn fraction can be controlled very precisely in almost all methods even wet lay, so I think that the 2.6 to 3.1kg range will be very, very easy to improve on in composite.
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