by Roger » Wed Dec 14, 2005 1:15 am
The higher you mount the whisker pole the higher you can mount your top block, but I suspect the higher you go, the more pitching and rolling you will experience in a downwind run, and more heel in a reach. The lower you can mount your 'power' the greater the effect of the sail as your boat stays more upright and trim. You don't want your boat plowing the water in a nose down trim, simply because the center of effort of your spinnaker is so high. Also you don't want to crank your mast off at the hounds because of all the pull at the mast top where it is not supported by shrouds!
Alternately, the theory goes that the higher you go, the greater the wind power, but somewhere there must be a trade off of lost power due to heeling.
The other item to keep in mind as you install a top block for a spinnaker is whether or not down the road, you plan to use a DRS (Drifter Reacher Spinnaker or Asymetrical spinnnaker. These are usually huge sails to take full advantage of the height of the mast and length of the boat to maximize sail area in really light winds. If for instance when you get your spinnaker and do your calculations, you find that you are only 18 inches or so from the mast top, you should go all the way to the top so that down the road you could use a drifter. I have a used drifter on order (haven't measured the head to midfoot yet) and I haven't fitted it to the mast yet, but from some basic trig, knowing the leech, luff and foot lengths, I will likely need to have a top block at the very highest possible level on the mast.
I note from your message that the whisker pole on a lightning is only 8 inches longer than on the DS. It will be interesting to test these ratio theories.