What Prop do I need

[daveb11]

Hi<br /><br />I have recently bought a 15.5ft speed boat with a 1990 Mercury 75hp. Can any body tell me what type of prop ie pitch etc I would be best using. I do alot of waterskiing from this boat so I assume this needs to be taken into consideration.<br /><br />Many Thanks<br /><br />Dave

 

[WillyBWright]

Re: What Prop do I need

What make boat? What is the boat rated for as far as maximum horsepower? Assuming the motor is maxed out, I'd GUESS that a 17 for skiing and a 21 for speed would do well. For a single prop a good average would be a 19. But those are off the top of my head with little information. If the boat is rated for much more than 75, then you'll have to subtract a few inches from those pitches. Other variables affect it as well. If it's a really light boat, then you might want to add a couple of inches. But I doubt a 75 would twist a 23 on most any boat. If it's a 4-stroke, subtract a bunch of inches. Say 13 for pulling and 15 for speed. Again all these are ballpark and you'll never know until you try one.

 

[daveb11]

Re: What Prop do I need

Thanks<br /><br />The boat is a Fletcher Arrowsport (UK Boat) I will try a 19 and see what happens.<br /><br />Thanks again

 

[roscoe]

Re: What Prop do I need

If this Merc uses a small diameter prop of approximately 11 inches, you will need to drop the pitch down quite a bit, I am using an 11 diameter x 15pitch on 16.5 foot rig that weighs a total of 1300 pounds. And that prop is giving me the recommended rmp's.

 

[phatmanmike]

Re: What Prop do I need

drill yerself some vent holes in the prop and you can use it for a better hole shot fopr skiing and tubing and such without sacrificing top end

 

[Trophy23]

Re: What Prop do I need

Hi, Mercury Marine has a great prop selector you can use on their web site. Of course they are selling Merc props, but you can use the same info to decide what type. It takes into account boat type, gear ratio and boat size/weight. here is link: http://www.mercurymarine.com/prop_selector Sorry, don't have my HTML turned on. Anyway, it's a great tool to play with 'what if's too'.

 

[Trophy23]

Re: What Prop do I need

oh, I see the link worked anyway. Also, that link takes into account type of motor too ie : 2 stroke, 4 stroke, and Optimax, etc.

 

[Solittle]

Re: What Prop do I need

Dave - You need to get a prop pitched to give you the max rated rpm at wide open throttle with an average load. Do you have a tach? Sooo - what are you getting now??? <br /><br />Another factor is the position of the motor on the transom. Our experts here at iboats will tell you to adjust this first then find the right prop.