Mast Position

[singlehander]

Hi All,

Advice please,,,,
I'm in the process of re-decking 813 and was wondering if there is a preferred position for the mast (Yep, I know; on the deck, upright, right way up, right way round, etc. etc.).
But more in terms of 'fore and aft-ness', if you will, within the measurement limits? I think this would be useful in deciding where to build in the strength features of the foredeck.
It would also be good if anyone has any ideas on how far aft of the mast, the shroud achorages should be (!) - (not too close, and not too far either, probably !)

Thanks, Bob

[scruff871]

Bob
I will do my best to try to help you but there may be others out there who will no doubt be able to help you more with the detail you require.
The rules have a wide tolerance for mast step positioning....457-762mm.
Rob Wilder- Superchamp 2006 and 2007 collated some dimensionsand I believe these may have been published in Chrysalis some time back.
Have checked one of our Boats this morning and suggest that a dimension of 585-600 mm from the forestay position may be about right to the front of the mast.
This is a starter suggestion as if you are going for the optimum or best positioning it will depend on your Centreboard shape[conventional or dog-leg].Arguably if you have a dog-leg centreboard the mast positioning could be moved back to get the balance right.
The shroud positions/chainplate positions are not so straight forward and may be detailed on the BMBA Plans.I can,t find any reference to their position in the written rules but I may have missed something.One of our Boatbuilders Godfrey Clark or Graham Pope may be able to assist on this or alternatively we can measure a couple this weekend for you.
Roger Witts

[tim757]

Don't be tempted to use someone else's data since every moth/helm combination is different! Hulls vary hugely from builder to builder.

My boat is a Plycraft and my mast is stepped in a different position with more rake than any of her sisters, but I'm short and use a dogleg board. At the 2005 Nationals I raced one of Brian's boats and changed all his 'standard' settings (mast rake/position, shroud tension and spreader length/angles) all with a significant improvement on speed and handling. Might have made an even greater impact had I had the boat a bit longer.

Ultimately, it's a process of trial and error, ideally only changing one thing each time. If it goes faster/ better; keep it. If it goes slower/worse; put it back and try something else!

If memory serves, 813 is one of Goff's, so he should be able to give some useful starting positions. (Although these'll all be wrong if yer 'doglegging'!)

[godfrey]

Hi, Bob
As a nominal position, I always stuck with 8 feet from the transom for the shrouds. Claridge went 2/3 cms further forward and Skinner a bit further aft (or was it the other way round???). As Scruff says;-600 from the bow which is 9 feet from the transom. Always measure everything from the transom (esp as you dont know where your bow will be yet,=beware the max/min length rule if you're doing much building up in that area). And no, 813 was not one of mine - it was the other lot!
Cheers
Goffo

[singlehander]

Hi,

Thanks Chaps,

That's most helpful, I always 'think' in feet, and the whole numbers you quote make the thing even easier!

Having seen it, (once) I like the idea of 'doglegging' the centreboard. What dimensions would an 'average' for this mod. be? ie. how far is the leading edge of the board aft of the c/b bolt position, when fully down ? Six inches? Nine inches? Surely not any more than that?

Cheers,
Bob