Info Request

[Boater49]

I own a 2002 FourWinns Horizon180(f/s) with a 4.3l MPI MerCruiser engine (rated at 220hp), a MerCruiser outdrive with a 1.62r, and a Mercury 21p Black Max 3 Blade Aluminum prop. The boat and engine weighs approx 2500lb.<br /><br />With a tank full of gas and 2 people, at full throttle I see engine rpms in the 3500 range on plane, Mercury specs say 4400 to 4800 at WOT, why might this be?<br /><br />Could I be over propped at 21p?<br /><br />I have a hard time pulling up a 260lb skier and the tug is noticable.<br /><br />Could I reprop the boat and improve my hole-shot while keeping or improving my top-end (47mph approx)?<br /><br />Any suggestions or info would be helpful?

 

[wdknox]

Re: Info Request

Boater49,<br /> You definitely are over propped. If you are that far away from the recommended RPMs at WOT, I would think you will actually increase top end speed by lowering the pitch of your prop. Not to mention the increase in hole shot. I've seen post on this site that talk about how to prop out a boat. I think you will gain about 300 RPMs for each degree of pitch you reduce your prop. <br /> <br /> Good luck and I hope this was helpful.

 

[Boater49]

Re: Info Request

I tend to agree, but as a newbie I'm uncertain.<br /><br />According to Mercury, I can expect a 150 to 200 increase in rpm for each 1 degree drop in pitch.<br />but that works out to almost 6.6 degrees. I'm wondering if there might be a misadjustment in the throttle cable?

 

[Boater49]

Re: Info Request

FYI, my Dealer tells me that I can go 1 or at most 2 degrees away from factory standard, which would leave me short. Bad info from the Dealer?

 

[Boatist]

Re: Info Request

I think you could go down to a 15 inch pitch and still be about 4700. For sure you could go to a 17 pitch and I think increase top speed and for sure the hole shot.

 

[amtsst]

Re: Info Request

Hey Boater49,<br /><br />I have the exact opposite problem. I have a Merc 260hp on a 23' Century. My Prop is a 17 pitch and I'm over 5100 RPM's wide open. I"m looking for a 21pitch but don't have a lot of $$$.<br /><br />I know I'm way under-propped but this is what was on the boat when I got it. I think the jackleg marina used by the previous owner got the props switched up somewhere. <br /><br />A trade perhaps?<br /><br /> amtsst@yahoo.com

 

[f_inscreenname]

Re: Info Request

Sounds like Blackwater has your fix. I have about 320hp in a 19' boat,I run a 15X19 now.Thinking,maby,of trying a 21 pitch (like the hole shot plus I do 65mph now). I have found its hole shot or top end. Pick one.

 

[495v]

Re: Info Request

Boater49, first off, I think your over-propped. You should probably be at a 19 instead of a 21. Secondly, before spending all kinds of money on props, I would highly recommend you try an external tach or dwell meter and get a more accurate rpm reading. Your gauge may be a bit off and there's an adjustment screw behind the gauge to calibrate it. I run a 350 mag Mercruiser, 310 horsey's on a 21' bass boat that weighs about 2650lbs. I hit low 70's and pull about 4400 rpm's with a 19 pitch SS mirage prop. Check your tach and then go down to a 19 if that's not it.

 

[Boater49]

Re: Info Request

I'll have the Tach checked out to make sure it's accurate, if it is a prop swap maybe in order.