Ive been 'setting up' (and crew on) a C27 for optimized racing trim, etc.
With the std C27 (genoa tracks on the rail), several things are quite important: Slot opening distance, Double genoa tracks or BARBERHAULER, proper/exact forestay tension.
On most boats, the fairlead angle (angle that the fairlead car TO the tack of the forestay makes) that usually sets an 'angle of attack' - or tack to clew angle - normally optimizes at 10degress away from the boats centerline for 'close' pointing, a little more (say 12°) for 'speed' pointing in the higher windranges (~15kts.) ... the 12° needed to 'open' the slot distance for maximum speed in max. windstrength for a 150% genoa. Without the ability to reposition to the 12degree (or more!!!) line the 'slot' will usually 'choke' and what one sees is "clew section" of the sail being 'hooked to weather', and the mainsail easily 'backwinded' ..... boat is slower and aggressively heels with reduces 'pointing ability'.
On the C27 (genoa tracks on the rail) with 150% and at 15kts, we start with genoa sheeted to the rail (at about the 10-12° tack to clew line and all the genoa tell tales flying 'perfect'), and then '
barberhaul' the clew inboard to get the max speed and max. pointing angle (combined VMG). As the sail powers-up and the winch pressure increases, we need to definitely readjust forestay tension (via the backstay tensioner) OR the result of the sagging forestay is to also 'hook up the leech' of the genoa to weather - slow, closes the slot (backwinding) in the higher wind ranges, when you want the slot 'more open'.
So thus far for gaining maximum or optimum out of the C27 with a 150% ...
1. the forestay (backstay) needs to be very carefully tensioned (if too loose, the genoa leech hooks up and can close the slot opening distance),
2. the slot opening distance is very 'finicky' (backwinding - needs to be controlled with a barber hauler, in OR out)....
3. and if too much winch pressure is applied to the jib sheets the forestay increases sag which again or additionally causes the leech to 'hook up' (and we additionally tension the backstay adjuster to match.
To simplify all this - we need to carefully adjust the backstay, jib sheet tension, and most importantly - barber haul in/out to get the optimum slot-opening distance.
With the genoa tracks on the coach roof on the 270, you have just the opposite problem with maintaining slot distance and genoa leech shape .... you probably need to reduce jibsheet tension but that can put a big 'curve' into the leech shape (and the leech exit should be FLAT and parallel to the boats centerline). To do this you'll probably need to install genoa tracks on the rail (or a method to apply a barberhauler from the rail to pull the clew 'outboard') ... and/or barberhaul IN/OUT using the coachroof tracks.
If the genoa is on a furler foil, when racing Id disconnect from the drum and position the TACK of the genoa as absolutely as low to the deck as possible .... artificially 'lengthening' the tracks on the coachroof ... 'more aft'.
Id recommend a set program to figure this all out to gain 'optimum':
1. First, as a 'check', if you are using a woven dacron mainsail ... the main has to set/shaped to perfection BEFORE you do anyother adjustments: How to properly RAISE a woven dacron mainsail -
http://forums.sbo.sailboatowners.com/showthread.php?t=120970
2.
http://i1086.photobucket.com/albums/j449/svAquila/MatchingLuffHollow.gif to be sure that youre running correct forestay tension (and getting correct genoa shape).
3. apply a temporary barber hauler to the RAIL and test (and record) the differences (windspeed vs. pointing angle/boat speed). .... and then make a decision as to if and where to apply additional genoa tracks on the RAIL, etc.
4. dont 'overtension' the genoa sheets without a corresponding increase of backstay tension !!!!!!!!!!
The below pic. shows the approx. fairlead angles for the C270 ..... the coachroof tracks on the 270
seem to be well 'inside' of the normal 10° fairlead-tack angle .... suggesting the need for rail tracks and/or barberhaulers when using a BIG jib.
Simple speak: it 'seems' that the coach roof tracks are 'too far inboard' to be used with a 150% in other than 'very light' wind conditions.
hope this helps.