Should I drop in pitch?

[Seasport]

2001 Johnson 150HP with a 14 3/4" x 19" SST stainless prop.<br />21' fibreglass boat, deep V hull (22.5 degrees)<br />AV plate is about 1 1/2" - 2" above bottom of hull.<br /><br />With a light-medium load (three people plus full tank) I can get about 5000rpm @ 44mph (GPS) at WOT with motor trimmed right out. Very light load (just me) I can pull 5200rpms @ 48mph (on a good day with the wind behind me <br /><br />Motor is running sweetly and is mounted in second highest position, i.e. I can only go up one more hole. No ventillation. Boat used for a variety of purposes - general crusing & some skiing.<br /><br />Dealer says this is fine but I figure some more revs would be better for motor. Motor is already mounted fairly high and I might risk ventillation if I raise it to highest slot.<br /><br />I may be able to source a 15" x 15" SST prop at a good price. Would this be going down too far. A 15" pitch on a 150 seems very low. What do you think?

 

[LubeDude]

Re: Should I drop in pitch?

Yes, I would definatly drop to a 17P at least, you will have a better hole shot and your engine will like it better overall. As far as the 15P goes give it a try and see it might be the right prop. Its not the fact that you have a 150, its the weight of your boat.

 

[Seasport]

Re: Should I drop in pitch?

I won't be able to try before I buy. I guess the 15P will give me more like 5600pms but lower top speed. Sound right? I don't really want to drop the top speed. What will this do to fuel economy?<br /><br />Maybe a 17P would be better.

 

[Dhadley]

Re: Should I drop in pitch?

Something doesnt sound right. I run a 19" Turbo on my 93 150 60* on the Dusky and its pig heavy. It'll still turn right at 5800 with an average load. With very deep V's you may be able to mount higher than you think. Especially with a diameter of 14 3/4". What kind of prop is it anyway? Most are 14 1/4".<br /><br />Are you sure the motor is OK? Right top timing etc?<br /><br />We only drop pitch as an absolute last resort.

 

[Dhadley]

Re: Should I drop in pitch?

Something really isnt right. Youre running about 5% slip which I doubt. Are you sure your tach is right?<br /><br />Is it a Teleflex tach? Set on position 6?

 

[Seasport]

Re: Should I drop in pitch?

It's an OMC SST II prop. I'm pretty sure it is a 14 3/4" but will check again just in case.<br /><br />Motor seems to be running like a top. I checked timing & link & sync recently - now all spot on. Good hole shot. Timing was set using analyzer - I need to verify on the water I guess. Certainly runs well.<br /><br />It's the standard OMC tach (is this a Teleflex?). No of poles were set by dealer but I checked and they are set as per shop manual (I think it was 6). I guess I could take the tach out and check the calibration.<br /><br />Dealer says that J 150's typically rev to about 5200 on these boats and 175's to 5500-5600 (presumably with a 19P).<br /><br />How heavy is your Dusky Dhadley? Hull weight on my boat is about 1700lbs so with motor, fuel etc. will be over 2500lbs.<br /><br />The hull has a deep V (22.5 degrees) & a fairly wide planing strake - about 6" wide at the transom if that helps. Maybe I could raise the motor a notch (to the highest position) and see if that makes much difference. How many more revs might I expect if I did this?<br /><br />Thanks for the help.

 

[Dhadley]

Re: Should I drop in pitch?

The Dusky is pretty heavy. Much heavier than newer (its pretty old -- 1986) models. Behind the truck I cant tell much difference between the Dusky or the 22 Hydra Sports.<br /><br />The OMC tach is definately not a Teleflex. Its set correctly on 6. Those tachs (OMC's & BRP's) are very accurate but it may not hurt to verify with a shop tach.<br /><br />Before spending any $$ I'd raise the motor and test. At worst all you gotta do is lower it back down. I hate dropping pitch.

 

[Seasport]

Re: Should I drop in pitch?

I checked the prop again and it's definitely a 14.75x19 SST (part number 176671).<br /><br />I think you're right Dhadley. I'll try raising the motor to the top position and see if I have any ventillation problems. I can't see me getting anywhere near 5800rpms though. May need to go down to a 17" for that.<br /><br />I think the 15" is going to be too low a pitch. I'll get the revs up but at the expense of a drop in top speed and fuel economy.