There's nothing wrong w/ the sail I got; the boat sails fine with it. However, now that I'm sailing more and more, seeing sail shape with a clearer eye, and have a better idea in regards to trimming, it annoys me that the outhaul is difficult to adjust and that I can't release the tension more on the foot in very light winds, get rid of a couple wrinkles in a good blow, etc. Even after I first got the sail and wasn't able to see those things, I noticed right away how nice it would have been to be able to throw a line around the boom, between the boom and the foot, to hang a cockpit shower bag or a million other things at any point along the boom. Now, it's either over the sail too (which I don't like to do w/ anything heavy) or at the very end of the boom, which usually isn't where I want to hang anything.
Get a loose foot. I shoulda listened. Story of my life.
Actually a shelf foot mainsail is a bit more aerodynamically efficient, especially for the design parameters of effective wind ranges for which the sail was designed. What the shelf foot does is equate to and approximate to the 'winglets' (little vertical mini-wings that are arranged at 90° to axis of the main portion of a wing) that one now sees on large commercial aircraft. Both the winglets and the shelf foot lessens 'short circuiting' of air flow (on the underside of the boom) from the high pressure side of the sail to the low pressure side of the sail .... in the case of a shelf-foot for less air-flow turbulence along the foot of the sail. Plus, with the shelf footed sail the amount of camber and position of maximum draft is carried all the way 'down' towards the boom.
In a loose-foot the amount of camber in the lower panels is tapered more and more 'flat' towards the boom.
The shelf foot usually has a 3-strand dacron bolt rope along the foot edge; provided so that the sail cloth isn't overstretched when the outhaul is fully tight. The loose foot sail without a bolt rope usually always/eventually permanently over-stretches out of shape along the foot in short order - ultimately beyond the 'black band', and if you're racing .... an eventual DSQ due to a sail that is too large for your class, etc. racing measurements.
Most sailors don't release outhaul tension when finished sailing; so, the loose foot will normally be stretched out of shape along the foot much sooner than a shelf foot; plus, will usually develop a permanent 'crease' (girt) between the tack and the clew.
Shelf footed sails usually need to have the foot bolt-rope 'readjusted' at the end of each sailing/racing season - usually the bolt rope needs to be 'eased' or made longer (ditto - the luff bolt rope, especially if the [racing cut or a dacron mainsail that was made well before the year ~2000] sail was made with a 'shortened' luff bolt rope that NEEDS to be additionally 'stretched out' every time the sail is raised - by about 1" extra stretch for every 10-11 ft. of luff length).
There's not much 'easy' re-adjustment/restoration possible to a loose footed sail that's been permanently over-stretched along the foot .... other than 're-cutting' the entire clew and lower leech areas .... or a 'new' sail.
One 'can' use a shelf foot sail sail without connection of the slugs/bolt-rope in the sail track on the boom .... just like how you fly a loose-footed sail; and, you'll get less friction resisting the outhaul !!!!!
Rx: there's really no advantage with a loose footed sail, other than adjustability
of camber along the foot/boom ......... and then only to have the outhaul NOT eased when the sail isn't being flown, which ultimately permanently stretches and permanently distorts the foot of the sail. The shelf foot is more aerodynamically efficient ... but only in specific wind ranges... so if youre 'campaigning' a boat, you'll need *several* mainsails to meet the needs of various wind ranges.
Special Note to 'rbrasi' - from your avatar pic and the 3rd pic in your thread. This mainsail was probably made long before the year ~2000 and most probably has a 'pre-loaded' or 'shortened' luff bolt rope .... as evidenced by the 'significant' droop (aft end of the boom significantly lower than the gooseneck when sailing). To correct this - and which makes your boat aggressively heel-over, have difficulty pointing, etc., I would suggest you go to https://forums.sailboatowners.com/in...insail.120970/
and follow the info in post #1 to affect a correction when RAISING this sail !!!! --- so that the sail is 'properly stretched out' and that the boom is close to *parallel to the horizon* when sailing.
To set the proper initial *outhaul* tension .... use the same 1" additional 'stretch-out' for each 10 ft. of boom/foot length.
Then if you have a speedometer, etc., adjust the outhaul in/out, to get the 'highest' speedo reading when you're pointing or 'close hauled' - that will set the correct outhaul tension for the present/current wind and waves and for all other points of sail.