Minimum Planing Speed

[76Red18]

I want a lower planing speed for all of those reasons PLUS its almost time to start crusin the beaches in search of the silver king.

[76Red18]

Do es the fin in any way make the stern dig down during a hole shot. I fish the flats often and only have a couple of pot holes that are barely deep enough for me to get up on plane.

[76Red18]

I want a lower planing speed for all of those reasons PLUS its almost time to start crusin the beaches in search of the silver king.

and bikini clad ladies I might add

[Blue197320]

i had the fin on my old 150 evinrude on my 20. i took it off one day and could notice a big differenc in the way it would plane and the attitude of the ride. now ive got trim tabs and a merc 200 so i dont use it now. if you dont have tabs id get one.

[Bushwacker]

The fin works like an airfoil, so it depends how you use it. If you trim the motor down so the airfoil has a positive angle of attack, you'll get stern lift which is why it helps you plane at lower speeds. If propshaft is parallel to surface, you won't get any lift, just a little drag which will knock a couple of mph off your top end. If you trim motor out/up, the foil will have a negative angle of attack and stern will probably dig in.

[76Red18]

Thanks for all the comments. I believe I'm going to try the SE Sport model 300. A little research shows that this model is not the wing design which does have some negatives such as diging during a sharp turn. The narrower design of the SE Sport brand doesnt have the flex of the wing design.

[Blue197320]

i think thats the one i had on my 150. i didnt know much about trim of the boat, but i lost 2 mph without the fin. i went from 38 down to 36 no matter how much i played with the motor.

[76Red18]

i think thats the one i had on my 150. i didnt know much about trim of the boat, but i lost 2 mph without the fin. i went from 38 down to 36 no matter how much i played with the motor.

So maybe I could see top end increase like some of the reviews said. That would be great.

[76Red18]

At high speed the fin should be out of the water so I should be able to use trim the same way I do now. Am I thinking right or will I lose my high speed trim-up ability?

[Bushwacker]

The fin attaches to cavitation plate, so I doubt it'll ever be clear of the water, unless you have motor set really high or on a jack plate! It will not effect your ability to trim the motor out; it may help reduce porpoising, or may allow you to trim out more before that happens. As for different styles of fins, I've seen some, maybe like the one you mentioned, that are relatively narrow but extend further aft, and may generate some lift by capturing/deflecting some of the prop wash. In general a high aspect ratio airfoil (like on a sailplane) is most efficient, i.e., it produces the least drag for a given amount of lift; delta wings, like the Doelfin, are also pretty efficient. I'm not an expert in hydrodynamics, but I believe there are a lot of similarities to low speed aerodynamics, where the flow can be considered incompressible for all practical purposes.

I'd be surprised if a fin actually increased top speed, unless the boat was badly balanced (very stern heavy) to begin with!