National 12

General Boards => General National 12 chat => Topic started by: philipcosson on July 02, 2021, 12:53:28 PM

Title: mast step position
Post by: philipcosson on July 02, 2021, 12:53:28 PM
OK, I have tried to get this info from searching the forum and elsewhere, but to no avail.


I have noticed that there are two more common mast step positions. A forward position about 110cm from the bow, and a more aft position about 130cm from the bow.


The original Uffa King design was 3 foot 6 inch = 106cm


1/3rd of boat length, which is common in the Merlin, would be 120cm




Is this a design specific difference or does it alter within a hull design?


Is there a commensurate movement of the centre-board?


What are the effects of a more forward mast step and vice versa? Is this to do with benefits of a large jib?
Title: Re: mast step position
Post by: philipcosson on July 03, 2021, 05:37:51 AM
Reading the rules it seems that 1312mm will be the furthest back from sheerline possible


2. Fore Triangle Height - Rule 10.2 Check that the distance from the Sheerline to the point where the extension of the luff of the jib intersects the Mast when held at a downward slope of 2:7 (16 degrees) does not exceed 4575mm.
Title: Re: mast step position
Post by: grazz on July 03, 2021, 09:24:57 AM
Philip
The mast foot position needs to be set to work with the jib-mainsail ratio and also the centre board position and yes it does therefore tend to be design specific. If the mast foot is in the wrong place then you'll either feel weather or lee helm on the tiller. If you let us know the design you have then we (or other N12 owners) can probably provided some guidance. Typically the mast foot is measured from the transom as that is an eaier measurement point
Happy tuning
Graham
Title: Re: mast step position
Post by: philipcosson on July 05, 2021, 06:21:18 PM
Thanks for your patience Graham.