positioning of mast…
15th October 2013 at 6:22pm #1078
I read you did a bit of measuring at the Europeans in Carnac whilst waiting for the wind to fill in.
The first figure is bow to mast and the second top of the mast to middle of the transom.
Jim 70cm, 6m 05cm; Keith 70cm, 6m 07cm; Tony Rich 70cm, 6m `14cm; Lee 70cm, 6m 12cm; Nick 68cm, 6m 10cm; Burt 68cm, 6m 23cm; Tom 69cm, 6m 20cm; Tony Woods 68.5cm, 6m 13cm; Will Turner 70cm, 6m 9cm; Andy Turner 70cm, 6m 22cm.
My question is… The measurement from bow to mast, is that bow to ‘front of mast’ ? Or bow to ‘centerline of mast’?
How much would these measurements differ for an aluminum mast?
In the Netherlands we are keen on getting it fairly right when fitting out the older OK’s with newer masts and thus changing mastfoot and deck…
ok club nederland
http://ok-jol.nl/19th October 2013 at 10:35pm #6980NickCraigParticipant
They were positions from bow to the front of the mast
In general, I think people have moved forward around 2-3cm with the move to carbon masts. The carbon masts are lighter so the boat can carry the mast a little further forward.
Best of luck with the fitouts
Nick21st October 2013 at 5:45pm #6981
Thank you Nick for your reply !
Wietze26th February 2014 at 5:40pm #6982
I build a new mast foot into my old OK dinghy. The question is how high I need to position the foot of the mast in order to get the mast (needlespar blacktop) the right height through the deck. The upper side of the lower band needs to be between 265-275 mm above the upper side of the deck. But how do these sizes correspond to the fork and pin for the boom?
Another problem with it is that the mast stands angled on the boat. So where do I measure? On the side (centerline) of the mast or on the backside of the mast?
Hope someone can help me out…
The Netherlands26th February 2014 at 9:54pm #6983
First i would mark the Lower Band on the mast, but be careful here, as the latest rules make reference to the Boom Bolt. (Previously you could lay out the mast on the ground and with the boom at 90deg. to it, the top of the band was the same level as the top of the boom).
Not so now, unfortunately. (Almost, but not quite).
The mast then should be positioned in the boat so that the top of the lower band is 270mm from the deck centreline hight, behind the mast, measured parallel to the mast. The rule says something like ‘from a point at the deck behind the mast, the same measurement as the back of the sailtrack if it was extended’ ;-about 15mm from the ’round’ section of mast.
All it needs then is to put the mast in the boat (at the correct rake) and raise or lower it, to get the 270mm measurement.
If you need to add material to the mast foot or mast step, do make sure that the bottom bearing on the mast will be in the correct position relative to the bearing holder in the bottom of the boat. Because you can’t see it in position, careful measurement is advised. Nasty things happen if it’s wrong!!
Do Check the upper bearing also, that the mast ring is in the right place relative to the deck bearing, and that the bearing surfaces are maximised, fore and aft.
Good luck and hoping that helps,
Bob27th February 2014 at 7:41am #6984
First of all, thanks !! Your comments are a great help…
I think I understand. Can you tell me how the top of the lower band limit corresponds to the center of the boom bolt. I can’t find the ‘new’ rule like you suggest… In the ISAF rules I can only find the 90 degree boom/mast rule… I have an old aluminum boom without a hole for the bolt (it was attached to a wooden mast). I need to get the hole drilled in. Can you tell me exactly where to put it?
Your comment on the upper bearing is not about any distances is it? It’s just about the right fit to make sure there’s enough surface for it to be strong? The entire mast foot will be raised to get the correct position. So the problem with the bearing holder won’t be a problem. We designed that to fit… The deck bearing will be designed and build to match the position of the mast bearing…
Wietze27th February 2014 at 10:34am #6985
It’s so good that you are determined to make very good job of this.
Have a look at Rule 12.3 re. position of Mast Forks (gooseneck) ‘boom bolt hole’ position. (I think you’ll be ok with and existing mast, already measured). I would not be tempted to move the gooseneck, for strength reasons.
Also check boom position relative to the black band on the mast with regard to rule 13.3. ie. the top of the boom must be ‘at or above’ the top of the black band, (at 90deg to mast). Some booms will be above the band some not, but as yours has no hole yet, you can make it right!
The important bit.
Have a very good look at Amended Rule 13.2 (December 2012). It is about the boom black band, which should be ‘2640mm from CENTRE OF THE GOOSENECK HOLE. This replaces ‘from the mast sailtrack – extended’ position. (on my boat I loose about 20mm on the boom black band position using this new method – I haven’t worked out how much sail area that is! but it seems crazy).
Cheers, Bob.27th February 2014 at 10:54am #6986
You are correct about the mast upper bearing, if the deck bearing gives enough support, with plenty of contact all round the mast bearing, with the mast raked, and the lower black band at the correct hight above deck, all is well!
But, be sure about that lower bearing!
Regards, Bob27th February 2014 at 11:26am #6987
The mast will be moved to the front. Problem is there’s not that much room in the wooden 1971 boat. I bought an aluminum mast from Oliver Gronholz. It’s fairly short beneath the deck, thus giving room to move the mast forward. The deck positioning will be between 68-74 cm from stern to front of mast. I enclosed a picture of the (concept) mastfoot that will be placed inside. Sideways movement is almost nothing. And fore and aft movement is like in 1971… It fits nicely… easy within rule margins…
It will be altered a little (minimizing material, without losing strength)
Wietze27th February 2014 at 4:43pm #6988
Wow, that looks good.
Keep going, you’ll be sailing soon!
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