I use a double braid and bury the cover into the core in a taper splice. I don't weave the cover through the core - just a straight bury to keep things smooth. I lock stitch at intervals along the double braid and once in the buried cover section to keep things secure. I don't whip - this stiffens up the line and screws up how it runs through the blocks. I use 3/8 regatta trophy braid and replace the core with 1/4" spectra. I then splice in 3/16" spectra into the 1/4" with a taper splice.

Doing splicing on old sheets is a lot harder than starting out with brand new line. In fact sometimes if a sheet has been loaded up hard it is impossible (or certainly beyond my skill level) - so do yourself a favor and learn your taper splicing craft with some new line - just sacrifice a couple of feet for experiments.

Splicing robe line or maffioli swiftcord can be a little fiddly. One secret I found is to extract the strands you wish to trim for the taper starting at the end and working back towards where you want to cut. This is different than working with 12 strand single braid high modulus (e.g. spectra or vectran) where you can pull the strands out right where you want to make a cut. The 'fuzzier' robe line seems to snaggle up if you try and pull out a strand all at once.

Use the resources on the yale and samson websites for splicing instructions.

Main sheet size is a trade off - if a sheet is a little larger there will be more friction through the blocks - so it won't unsheet quite as fast and there will be more effort required to sheet in vs. a thiner line. On the other hand - a larger sheet can be more comfortable to pull on under high load. This can make it more likely that the sheet will be played in a puff rather than leaving it where it is and steering. The longer you are on the water the more this can matter - so skinny sheets might be a better choice for buoy racing vs. distance racing.

Chris.