86formula242ls

I have been having a problem starting my boat on occasion. Once a while I would go to start the boat an nothing would happen. After a few try it would turn over and start. I had this problem in the past which turned out to be the slave solenoid and I did replace it again think that was the problem again. But last weekend after being in the cove for a while she wouldnt turn over. I went to the back and jumped the slave solenoid with a screwdriver and she started right up.
Any suggestions?
Also I just cleaned all battery connections, starter connections and the slave solenoid is new (unless is a lemon)
Thanks