Flat boat prop questions

[madman2021]

I have a 18x60 center console aluminum flat boat. It has a 115 yamaha 2 stroke on a 6 inch jack plate. Turning a 13x19p prop I think, have to check on that. I'm turning 4900 rpms at 56 mph. Wot range is 4500-5500. Would like to get 60 out of her.

 

[steelespike]

Re: Flat boat prop questions

The numbers don't add up. I guess you better check the prop size.Doesn't work with a 19 or a 21" prop.
Is the speed by gps?

 

[jestor68]

Re: Flat boat prop questions

Does 18 X 60 mean an 18ft long boat with a 60 inch bottom width?

It would take a 26 pitch to go 54 mph at a 10% slip using your motor's 2.0 gear ratio at 4900 rpm.

Gotta love those speedometers. :facepalm:

Verfify your prop size and rpm, and we can calculate how fast your boat can theoretically go. They generally go a little slower than that in the real world.

But the bottom line here is that your motor rated hp is at 5000 rpm. That means it's doing all it can at 4900 rpm with whatever pitch you're running now.

If you want to go 60 mph, you'll need a BIGGER motor(or possibly a better prop). What's your boat rated for? And what kind of prop are you running now?

 

[madman2021]

Re: Flat boat prop questions

The speed is off a lowrance hds 7 gps.

Yes 18x60 means 18ft boat 60 inch wide bottom.

Boat is rated for 70 hp four stroke. 115 is about the same weight.

Have to check the prop for size and pitch. It's on the bottom of the prop. Fishing now so can't check.