Prop size

[drake]

How do you determine the right size prop for your boat.I have a 50 horse johnson on an 18ft glass boat with no p/t its slow out the hole and builds rpms slow until it gets on plan then its fine.I changed to a 13x14 prop, its better but still no cigar.

 

[Jacques321]

Re: Prop size

Sounds like you're underpowered. It might not be the prop's fault.<br /><br />How much does your boat weigh, and what kind is it?

 

[suzukidave]

Re: Prop size

That sounds like way too much prop to me, especially with that big diameter. I am betting you are overpropped and lugging the motor even if it sounds ok -- what is your wot rpm?<br /><br />I run a 10 5/8" x 13" pitch on a 55hp on a 16' deep v boat. That allows me to hit my rated wot of 5500. Unless your boat is very light/flat bottom or the gear reduction on the johnson is nowhere near the 1.9:1 on mine you should either be running about an 11" pitch prop on an 18' boat with that motor or else getting a bigger motor. The 11" should get you to rated wot, give you good holeshot and top speed of about 24 mph by the way.<br /><br />Before you change props fiddle with the manual trim post a little. Move the post into the transom a notch or two and see what that does for your holeshot (it will cost you a little speed).

 

[MGuckin]

Re: Prop size

Need more info.<br />Weight of average loaded boat?<br />Type of hull?<br />Max WOT RPM?<br />I think a 14" is too much for a 50 hp but that would depend on hull type, weight, the mechanical condition of the motor, the installation of the motor, handling of the boat and the type of prop.

 

[drake]

Re: Prop size

Sorry,it is a 16 1/2 ft boat 60 inches wide,son measured motor too.It is a semi v boat made by cotton cordell, motor mechanicaly sound,dont know how much it weighs.While it does not have a tac you can tell by sound WOT rpms are not quite there.Have put in different manual trim post, motor runs best on second from transom.Picked it up to keep on one of the lakes for striper fishing rigged out with rod holders and shad tank the open design with tall sides does good job except for speed 25mph would be great.My 24'pontoon 50hp will outrun it. <br /> Thanks for the replies

 

[mellowyellow]

Re: Prop size

your ears might be great, but without a tach.<br />it's gonna be tough to give the kind of advice that would help. it's the main measurement needed<br />to answer your question...<br />good luck,<br />M.Y.

 

[suzukidave]

Re: Prop size

get a tach for sure but if you aren't making 25 mph with a 14" prop you are definitely overpropped and running well below WOT. With a 16.5 semi-v your top speed with that prop should be over 30.