Hi All,
Cold Chisel has jumpers, I will take a pic next time I am out sailing and put up on the website
http://www.ec12.co.nz They are hard to see because they are tiny. I would not go with out them, I would find it hard to control the mid to top section of the mainsail without them.
As we all know halfway between the top and bottom of the jumper is the forestay. The forestay wants to pull the top the mast forward, the back stay is pulling it back. Therefore the distance from the top of the mast to the lowers is pulling its self inside out. The jumpers stop this problem dead in its tracks and allow for the back stay and fore stay to be held firmer. It is interesting to note that what appeared to be back wind in the top half of the main was in fact the mast pulsing between mainsail presure and that of the jib. I am incline to agree with a few that a little side flex of the mast is a good thing, jumpers wont effect this if you narrow down the spread to 65degrees. They will stop the forestay effect without influencing the sideway effect.
Regards Phil