Rig Tension for Islander 37

[Beyond]

Hi guys, I've been having trouble locating ideal rig tension information for my 1968 Islander 37. Any suggestions? The shrouds definitely seem loose to me and I'd like to increase the mast rake a bit, but I'm not sure how much rake it should have. The boat seems too tippy and the main sail seems to pillowy when I'm sailing, even in light wind. The main sail is not that old, so I thought tightening everything and pulling the mast back might help.

[Brion Toss]

Hello,
First, let's get rake out of the way. While it can induce or reduce weather helm, it takes large angle one way or the other to do so. Suit the boat's aesthetics, the designer's specs, and any step limitations. Islander masts are typically plumb, or thereabouts.
Rig tune is a somewhat more complex subject, and I can happily recommend my DVD on the topic. You will be aiming for about 10% of rated strength on the lowers, and 15-20% on the uppers, jibstay, and backstay, assuming that all these wires are the correct size.
Beyond that, pillowy sails probably have most to do with running rigging, particularly halyard, outhaul, Cunningham, vang, traveler, and sheet on the main. This is an even more complex subject, so I can also happily recommend that you set up a consultation for details on how to use those tools on your boat.
Fair leads,
Brion Toss