Dole fin
Don't confuse what a dole fin is designed to do with a wedge. You are correct in that a dole fin is designed to help an outboard rig plane faster. The reason you weight a boat (or in the case of Malibu, use a wedge) is to increase it's displacement by pushing the hull down into the water. This (usually) creates a bigger wake. Adding weight will almost completely negate the effect of the dole fin as they wil be competing with one another.
Sorry to say it but a rib really isn't an ideal platform to wakeboard from. A tower or extended pylon (if you could fit one or other) would be a waste of money. Have the best fun you can with what you have and save your pennies for a pucker wakeboard boat or, just as good, an late 80's Ski Nautique 2001. Was a ski boat in it's day but the wake it produces is, nowadays, considered too large for slalom ski-ing. For that very reason it makes a great wakeboiard boat. You can pick 'em up for about £4k but shop around and don't buy the first you see.
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Jeff
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