Centreboard case (or thwart),  or side deck,  or waterline,  or cockpit floor?  …

A very good question;   which may well be why (if I am understanding them correctly) all three tuning guides on this site do it by measuring a distance from the masthead (or main halliard sheave) to the transom,  rather than by using the spirit level and plumb line method.

Doing it that way removes any need to have the boat accurately level.

However the actual dimensions given there are for modern masts and modern rig tensions;   with a vintage boat the dimension would be different.    My own approach with a vintage boat is to initially set the rake so that two conditions are both met;   (1) before you set a headsail and before you secure the forestay,  the shrouds are taut with the mast just slightly out of the gate and you need to push the mast forward in order to close the gate,  and (2) with jib or genoa set and with your normal rig tension applied the mast is then just inside the gate,  without noticeably pressing on it.

And,  of course,  but easily overlooked,  ensure that the mast is not leaning to one side!   Use the main halliard,  duly cleated off,  to verify that the masthead sheave is the same distance from each of the side decks (at any convenient but exactly corresponding measurement points).   A few days ago I was assisting a new owner at my club,  and we found that the two shrouds (set up by the previous owner) were set in different holes in their respective adjusters …

If you want to be a perfectionist,  you could also chock the heel of the mast to prevent it moving around in the step,  because the mortise is usually larger than the heel (or heel fitting).    Chock it so that it is hard against the front face of the frame (no. 2 frame),  and exactly on the centre line.

That will be at least approximately right,  but then take her out on the water,  see how she behaves,  and be prepared to adjust the rake in the light of her handling.

If you find she has undue weather helm,  and/or she seems sluggish when off the wind,  rake the mast forward a little.    If she has any tendency to lee helm,  and/or she is disappointing to windward,  consider raking the mast a little further aft.   Continue to monitor how she handles,  and performs,  and be prepared to tweak the rake from time to time until you feel you are getting the best out of her.    In essence this is doing exactly what generations of top racers did in devising the “standard settings” for modern boats,  but it would be a mistake to think that their results on the modern rig are the same that they would have developed using a vintage rig.

It may take you a little time to tweak her to her best performance,  but the sailing and the gradual honing of her performance should be fun.

Good luck,

Oliver

Peter,

While I would agree with most of Oliver’s advice to get a good starting point rather than trial and error even with an older boat it is worth following the tuning advice given on he various sailmakers tuning sheets.  If you have a series 1 square footed mast, the mast must be set hard against frame 2 and chocked centrally in the mast step, attached the shrouds with the mast about 1/3 out of the deck slot, hoist your foresail and tension as normal.  Now hoist a long tape up the mast using the main halyard until you read 18’0″ at the top of the lower black band, lock off the halyard, now swing the tape to the top of the transom (not the horse if fitted – old boats) ideally the reading should be about 21’10” plus or minus 1″.  Adjust the position of the shrouds until you get in this range.  Your should then find the boat is well balanced when sailing with a neutral of tiny weather helm up wind.  When finished note the shroud positions for future reference.

Steve Corbet