Here's your approximate dimensions for a Saber 34 Mk1 .... just measure along the foot
to arrive at your desired 'markings'.
If these 'marks' will be used for long distance cruising consider to add 'chafe patches' along the foot and leech where the rolled up sail comes in contact with the "roll" .... just triangles 12-18" on an edge patches made from adhesive backed 'insignia cloth'
... just a 'stick on', replaced every 1-2 years, no need to sew down. Sailrite.com has it.
J = 14 ft. (Tack to mast dimension)
LP 150% = 21.2 ft.
(assuming the sail is almost a 'deck sweeper '... clew is fairly low to the deck ..... ) ....
Length (YOUR estimated 'marks')
@ 150% = 22 ft.
@ 120% = 17' 7"
@ 110% = 16.0 ft.
such a sail is possible to an approximate area reduction by 30% maximum:
• IF the sail is constructed with 5-6oz. DACRON cloth or dacron cruising laminate,
• IF you have a reefing
-furling system (need a free rotating 'top swivel')
• IF the backstay tension is at or above 15
-20% wire tension. To INSURE that the forestay doesnt develop significant 'sag' when reefed.
• IF the Sail has a foam luff and/or the sail was 'cut' specifically for roller reefing
• IF When you roll up to 'reef' that roll is TIGHT !!!! ie.: You apply somewhat heavy resistance to a jib
sheet when you pull in the furling line
That 30% max. rolled up reduction is only an estimate of max. 'roll' before the shape develops a 'severe bagginess' in the middle panel section at the position of the 'new' luff area. Many times you cant roll to this 30% max. reduction because of how the sailmaker cut the 'leading edge' shape.
If this sail was a 'stock' sail cut for 'cruising' you 'might' get a 20+% roll-up (120% LP); if this sail was a 'race cut sail' (flattish luff entry shape) you'll probably get up to 30% but with 'some' bagginess behind the 'roll up' developing.
You'll have to 'test' how the sail roller-reefs and then set your 'marks' to those dimensions in its variably rolled up state in close to 'actual' windspeed and sea state conditions to see if you 'can' roller-reef to these area reductions; once 'bagginess' behind-the-luff develops due to 'roller reefing' you wont be able to 'point' as well as before as when the sail was fully 'unfurled'. Only 'trials' in actual conditions will indicate 'how much'.
If you 'can' reef to 30%, consider to use Garhauer EZ glide fairlead car adjusters Garhauer Marine Hardware -5857845
..... to reset the proper car fore/aft position 'from the cockpit'
Hope this helps. ;-)