I had rather hoped that one of the top racers would step in here …

In the absence of that,  my own amateurish approach would be to try it against the hoisted sail.   First,  check that the foot of your genoa is not undersize,  just in case you ever want to replace it;  it would be annoying to then have to move the tracks.

Then hoist the sail,  or if necessary a borrowed full size sail in good condition,  with the boat ashore and at the right angle for beating to windward,  and see how far aft the fairlead needs to be in order to pull the sail as flat as you can.    Do this with the fairlead as far outboard as possible,  but observing Rule 14.2;   no part of the fitting may extend outboard of the projection of the outer surface of the skin of the boat.    You will find that the clew of the sail comes almost right up to the fairlead when sheeted at a reasonable (vertical) sheeting angle,  with the line of the sheet roughly perpendicular to the luff of the sail;  but check the vertical sheeting angle by the way the sail sets;   nice open leech but with (ideally) no fluttering,  and a good shape to the rest of the sail,  with a very shallow aerofoil shape.

Now set the track so that it is physically possible to mount the fairlead perhaps an inch or two further aft than that,  so that the sheeting angle with the fairlead right aft is clearly too flat;   that will give you ample scope for adjustment aft,  and will still leave generous scope for adjustment forward.

Finally,  mount the track with that aft point as a marker,  parallel to the side of the boat,  and ensuring that at any point on the track the entire fitting complies with Rule 14.2 (above).

Then have fun,  experimenting with the best setting.

Oliver

Just a thought if you find your sail appears significantly under size as a genoa.

There is a third alternative headsail for the class,  the midi,  which is a halfway house between the original small jib and the now ubiquitous genoa which has been permitted since the sixties.   Dimensions undefined by the Rules (so far as I know),  although well understood by sailmakers.

I have no experience whatsoever of the midi sail,  but rumour has it that it is usual to use a separate pair of tracks for this sail,  set inboard.   I gather that Gareth Morris (Vintage Boats Co-ordinator) is something of an expert on this.

Oliver

Middle of the track should be about 50mm aft of the clew with the sail pulled in with moderate tension, so that the position of the fairlead can be adjusted fore and aft to suit the wind conditions. Aft in strong winds to flatten the sail and forward in light winds to give more fullness.  Laterally the track is normall set in the middle of the side deck, bolt the track through the deck and reinforce under the deck with a pad of hard wood or marine ply at least 12mm thick.  Make sure you seal the wood or plywood with epoxy or varnish before fitting and use large washers under the nuts.  I just sold a set of Holt tracks and fairleads on eBay so hope the ones you have are good.

Hi if you look at the attached photo you can see where the tracks used to be fitted on the deck before I modified the boat to below deck sheeting.  The tracks are parallel to the boat centre line.  Only if you use a small midi genny or a jib do you need extra tracks set inboard or at an angle..