Make a Hydroplane Turn Left and Right

[Terry Heddin]

What's the best setup to make a hydroplane turn right and left? Not racing, just recreational running.

 

[larcor69]

Remove the turn fin but it won't turn very well

 

[John Beardslee]

Mount a straight fin at the CG in the middle (left to right) of the hull. Like you might see on a flat bottom drag boat.

 

[Hydro Junkie]

John, the issue with that is that water will be thrown up against the bottom of the hull. Unlike a drag boat, a hydroplane has "airtraps" that hold air under the hull which, in turn, supports the hull. Unlike air, water will be forced up against the bottom of the boat on one side of the fin, giving the boat an unbalanced force on the bottom. If you have ever watched a stock built Dumas sport 40 1977 Atlas? They tend to roll toward the left due to the turn fin being located on the inside face of the right sponson, throwing water up against the right side bottom of the hull.
I know someone is going to say "What about the round nosed boats from the 50s and 60s? Their turn fins were on the inside of the sponson as well". And while that is true, the fin on those boats were usually no deeper than 6 to 8 inches below the bottom of the sponson. The results of that very shallow fin was that, with the boats jumping around like they did, the fins weren't really that effective until the boats were slowed way down, negating a lot of the water being thrown against the bottom of the boat.