Prop selection for mercruiser 3.0 alpha one

[Pbdy Jr]

I just took my searay out on the water and at wot I only got to 4000 rpm at 32 mph. Obviously something isn't right. Currently I have a 14 1/4" 21p mercruiser aluminum prop. 48-832832 cl 21

What should i try for the right pitch to bring the rpm up and speed up. Boat is a 16' searay

 

[alldodge]

Assuming you have a 1:94 drive your prop slip is 21%

I would go down to a 17 pitch and get the r's up closer to 4600, which hopefully get your slip down to at or below 10%, and in doing so bring your speed up around 35 mph

 

[radza002]

What engine do you have?
Is there any damage to the prop?

Even the small 3.0l should be able to push that boat well past 35 mph with the 21P.

 

[Rick Stephens]

Have you verified your tach is reading correctly? And is there any chance that the boat is heavier with water soaked foam? Heavier boat can sneak up on you.

 

[Chris1956]

If a 21P prop gets 4000RPM, a 19P prop will usually produce 4400RPM, and maybe a wee bit more, as you will be more in the powerband. I

f you need more power to pull a skier or want to load up the boat more, a 17P prop will give you aprox 4800 RPM. Since 4800RPM likely a bit over your redline, you will need to watch it, On those sterndrives, I would stick with the 19P prop..

 

[QBhoy]

A compression test and make sure the bottom is clean.

 

[QBhoy]

Presumably the boat wasn't full to capacity or more and you had it trimmed up to try and achieve optimum figures ?

 

[Scott06]

Verify the tach as suggested. Having a similar Sea Ray for a long time I hit 4600 or so with a 19" pitch, used a 18" 4 blade Michigan vortex for water sports if you prefer some low end punch, if you're big like me (260 lbs) a 16" vortex for skiing makes a big difference. Really depends on how you want to use the boat, my typical use was water sports if you just a cruise a 19" 3 blade would be a great choice.