>>Do I need to take the boat out of the water to replace the forestay?
nah. just attach the spinn and jib halyards to something solid (stem fitting, etc) and then harden them up real real tight with a winch. Those will hold the mast in place just fine for you to go aloft. I usually try to get the dock lines bar tight and have crew ready to level out the boat in case some nerd wakes you while you're up. it's no biggie. tape the snap shackles shut though. go aloft on the main halyard. take the tools you need and drop a messenger in case you forget something...the crew can send things up on a messenger. take a separate line to clip into something at the top...some para webbing with a beener works well...I sometimes make a loop I can step into to take the weight off my middle once in a while if I know I'll be aloft for more than a few minutes. tf
