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Ovington Laser |
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Mark Aged 42
Groupie Joined: 24 Aug 11 Online Status: Offline Posts: 98 |
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Topic: Ovington Laser Posted: 06 May 21 at 8:23am |
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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
Really should get out more Joined: 17 May 04 Location: United Kingdom Online Status: Online Posts: 6649 |
Post Options Quote Reply 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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rich96
Really should get out more Joined: 20 Jan 05 Online Status: Offline Posts: 596 |
Post Options Quote Reply Posted: 06 May 21 at 1:55pm | |
It wasn't just the top sailors - it was quite common Less rake = more potential leech tension |
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tink
Really should get out more Joined: 23 Jan 16 Location: North Hants Online Status: Offline Posts: 788 |
Post Options Quote Reply Posted: 06 May 21 at 4:50pm | |
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 didn’t like the D-zero because, and I paraphrase, ‘being able to adjust the mast rake makes the boat more technical to sail and distracts from the athleticism required by the sailor’
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Tink
https://tinkboats.com http://proasail.blogspot.com |
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KazRob
Far too distracted from work Joined: 22 Oct 16 Location: Scotland Online Status: Offline Posts: 245 |
Post Options Quote Reply 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/
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OK 2249
D-1 138 |
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tink
Really should get out more Joined: 23 Jan 16 Location: North Hants Online Status: Offline Posts: 788 |
Post Options Quote Reply Posted: 07 May 21 at 7:04pm | |
Interesting about the mast stiffness, given relatively simple controls I’m sure it’s easier to produce repeatable alloy masts vs composite but perhaps decades of windsurfer masts have improved composite mast repeatability
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Tink
https://tinkboats.com http://proasail.blogspot.com |
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Oatsandbeans
Far too distracted from work Joined: 19 Sep 05 Location: United Kingdom Online Status: Offline Posts: 382 |
Post Options Quote Reply 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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KazRob
Far too distracted from work Joined: 22 Oct 16 Location: Scotland Online Status: Offline Posts: 245 |
Post Options Quote Reply Posted: 07 May 21 at 7:37pm | |
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).
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OK 2249
D-1 138 |
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tink
Really should get out more Joined: 23 Jan 16 Location: North Hants Online Status: Offline Posts: 788 |
Post Options Quote Reply 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. I’m 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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Tink
https://tinkboats.com http://proasail.blogspot.com |
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Daniel Holman
Really should get out more Joined: 17 Nov 08 Online Status: Offline Posts: 997 |
Post Options Quote Reply 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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