My A class out front of the winch factory in our back yard. Silly me did not build the ceiling height tall enough to allow the A to be rigged inside. I'd show you inside but it looks like a teenager's bedroom.

The boat is a Sidewinder. Designer is Frank Russell and built by Steve Arthur. Sails also by Steve Arthur.

The belt drive sheeting system. Winch is deck mounted beside the mast. Idler pulley beside jib radial. The belt is MXL size (2.03 mm pitch) 1/8" width Kevlar reinforced Polyurethane. Breaking strain is about 120 lbs. 

Close up of winch pulley and jib sheet block. The main sheet is the line running past the mast. The two sheet lines are simply tied to the belt. The belt teeth prevents slippage. The pulley is about 1/2" pitch diameter. This requires almost 10 turns to get the required travel so the winch has a large feedback gear to give the extra turns. The winch also has one less gear reduction which speeds up the shaft by a factor of three so that sheeting speed is about normal at about 380 mm per second (6 V).  This is the same as a normal gear ratio standard winch driving a 38 mm drum. To use a standard winch, a pulley of similar pitch diameter to the standard drum could be used. The one used here was the only pulley I could get at the time but larger ones are available. 

Close up of idler pulley and sheet lines block. The bottom line is main sheet. The idler has a ball race with two V seals like the winches have. The use of the Pekabe block allows the idler pulley to only be used to maintain the small amount of tension required on the belt to stop slipping at the drive pulley. The deck structure is not stiff enough for the idler to take the sheet load as well because any flex will reduce the belt tension.  Flex at the Pekabe block is not relevant. The idler is not toothed.