I think your having the same problem as me. When i first sailed my boat i had heaps of problems with holding the main sheet and well we finished the nationals with all the sailors saying we're so weak and soft. We came in and one of the sailors found out i didn't have the rached on and it was broken. I went and bough a new block and i could hold on to it all day without any trouble. check if your bock is working properly and if its not that something is seriously wrong!!