I am going with hill marine on props because that is what I have now.. My boat is a 1973 monark with sponsons.. A foot out past the boat.. The prop is well past it.. My issue is prop selection.. I need to be within the 9 inch diameter rule.. I have a 9x7 speed prop from hill marine with extra cup and pitch but today it didn't do as well as it did on the 6.5hp... Speeds were 4 mph to a max of 10-12.. The 11x10 I had would idle at 7 or 8 mph to 14 -15 top... So I know that propeller choice plays a good part in this... I'm thinking of going with the 9x9... But before I do I'd like some help from you guys.. Thank you in advance

Any luck? i am also building/ built a 20 hp surface drive


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Would help to know what gearing and RPM you are pulling. For example a 18 HP MB with 32/50 gearing and a 11x10 prop would push a 1448 Lowe at 22mph with a lite load. This was at 3900-4000 rpm. Running a 9" dia prop, I would think you would need a lot more pitch to make up for small dia. and a more aggressive cup.

Stan,

I can give you some numbers for that Predator on a Backwater SWOMP. Even though it’s a long tail, it’ll give you some numbers to look at.

I had it on a 14x42 Alweld and it ran 20/21 with a 9x6 at 4100. 22/23 with a 9x7 at about 4000. 9x8 would hold a steady 22, but couldn’t handle a load. The 9x7 handled a load decent and the whopping extra speed sure seemed like a lot more than it was.

I thought you had a hunt deck added to that boat and not pods? I don't think you'll hear many positives about pods and a surface drive. I remember seeing the photos on SETX duck hunters. That part looked like it turned out well, but I still think your boat is hurting you way more than you realize.

Have you pulled the governor on that Predator yet? I sold mine to a friend, but it has 50+ hours now of running 4000-4100 with no governor and no problems. If you pulled it, did you add an auxiliary pump? Its needed on these motors.

Here's a link to an old post of his for more information on his setup

viewtopic.php?t=64552

After reading that, I see your 3000-3300 RPMS. You need to by pass the govenor, those low RPMs are killing you!