This isnt going to be a simple straight forward reply .....
Sail dimension data base listing for a Seafarer 34 (sloop or yawl) has that tack angle at 88° and a luff dimension of 36.0 ft. However this implies a
properly/perfectly
raised mainsail, if the mainsail has a luff boltrope (a 3 strand dacron rope inside a sleeve). Measure this tack angle - from the top of the boom to the mast. Additionally however, this 88° will be the for the boom being at it HIGHEST position from the cockpit / cockpit gear. .... the boom can get
lower during normal sailing. This assumes that your mainsail was cut to the exact boat data base specifications and NOT a used sail from some other boat!!!!!!!!
Caution - This 88° is the 'as designed' tack angle ... without normal overtensioning of the mainsheet which will cause that tack angle to
increase; not for an older sail whose boltrope has become shrunken due to age and usage which will cause that tack angle to also
increase. ... this also implies that when raising a boltroped mainsail that the luff boltrope is properly and
additionally 'stretched out' by approximately 1" per 10 ft. of luff length = 3.6" additional stretch after raising to 'just up' - the
proper but relatively unknown way to 'raise' a dacron mainsail that has a boltrope.
If this seems complicated and confusing, go to the head of the class !!!!!
Suggestion: allow an additional 10° of tack angle so that your geometry isnt 'locked in' so that when the sail naturally changes its dimensions due to age, or overzealous tension on the mainsheet, etc. that the mounted gear doesnt become an impediment to the boom. 88° + 10° = 98-100° (approximate) ... maybe.
• raise the present mainsail but 'just up' and without any normal stretch out of the luff ... 'just raised up'.
• check the angle that the top of the boom makes with the mast is near 98-100°
you can cut a large sheet of cardboard to this 98-100° angle and use it as your 'guide' for setting the boom position.
• if that 100° tack angle (top of the boom to mast) provides sufficient clearance for the boom then 'use it'.
A
properly raised boltroped mainsail ... by additionally and
properly stretching out the luff by and addtional ~3.6" after raising 'just up' for your Seafarer will cause the aft end of the boom to be HIGHER than that 100° angle and the 'as set' tack angle will be closer to the 'as designed' 88°. If you use that 100° recommended 'imaginary' tack angle youll probably have sufficient clearance for most normal sailing operation - a high probability of 'maybe'.
IF the mainsail does NOT have a boltrope at its luff; and instead has a (rare) 'Taped' luff - many layers of folded dacron Tape at the luff, then get back to me or PM me for further discussion.
What Im driving towards here and a discussion of the 'foibles' of raising a mainsail that has a 'boltrope' - a 3 strand rope inside a sleeve at the luff, the most common configuration for woven dacron mainsails used for 'cruising' - a discussion of this 'anomaly' can be found here:
How to properly RAISE a woven dacron mainsail - SailboatOwners.com see post #1. This extra stretching of the luff causes the aft end of the boom to RISE. If the sail is
not PROPERLY raised, the aft end of the boom will or can be MUCH LOWER.
I hope I havent made this discussion TOO confusing; but, if your measurements dont include these 'anomalies' you may become 'locked-in' to a quite bad geometry that can easily prevent 'good sailing' and the natural swing and height of the boom. ;-)