polly balls deflat after going below the surface and become useless. most fish roll dead if you stick them in the head. small vessel, choppy seas and minimum light good luck nailing the head everytime unless you wait until it is boat side, at that point a harpoon should not be necessary. harpoon is not intended to stop the fish cold with a ball or cleat, dart will pull with a decent size fish or a bad stick. use a rigid hard ball and plenty of line (200 ft. min.). use 1/4'' line it will only fill a 5 gal bucket. fight the fish as you would if you were wiring the leader. no hurry to get her onboard after a good stick, play her out until she rolls.
best harpoon - 10' of 5/8'' galvanized steel pipe. thread or weld 18'' SS harpoon shaft on end. 3/4 way towards opposite end (dull end) tape a 12'' flexable stick to the pipe securing both ends of the stick with tape (a paint stirrer works great). place the dart on the end, pull the line tight towards the stick and insert the line between the stick and pipe securing the line so that the dart always has tension so not to fall off. add clip to end of harpoon and secure to 1/4 line, harpoon will be there when the fish is along side. harpoon can be reloaded in seconds if needed. weight of the pipe will sink the dart deep and is extremely accurate especially when fish is straight down.
everything else is expensive and junk