what pitch do i want?

[brunolund]

my lund tyee 1850 with merc 4.3 lx has a 21 pitch prop, and i can only get 4400 rpm out of it.( so far) my cavitation plate is broken and currently getting fixed. after its back, what rpm should i be getting at wot? is it really bad if i'm not getting what i should, but more than happy with the speed?

also what size prop should i get?? alpha one gen II

 

[tmh]

Re: what pitch do i want?

What is your WOT speed (gps)? With a known speed and prop pitch you can guestimate whether the tach is correct or maybe off a bit. I wouldn't change anything until you know that. If the hole shot is fine and top end is fine then it seems to me you're in good shape. you don't want to be overowrking the engine though. What is the WOT recommended RPM for your engine?

 

[Bondo]

Re: what pitch do i want?

Ayuh,....

4400/ 4800rpms is what you want,.....
I'd run what you've Got....

 

[180shabah]

Re: what pitch do i want?

4400 is fine.

How do you intend to use the boat? If it is just cruising and fishing then just run the 21". However, if you will be doing any watersports, then dropping to a 19" prop or even an 18" four blade will make a big difference and should still keep you WOT in spec.

 

[Chris1956]

Re: what pitch do i want?

Bruno, I had the same drivetrain in a 19 SeaRay Bowrider. I ran a 21" Rapture and would get about 40MPH at WOT with an RPM of 4200-4400

 

[brunolund]

Re: what pitch do i want?

that's what i'm getting, but i can't trim much yet.
my cavitation plate is broke, so it starts cavitating rather quickly. should have it fixed by next week though.

i'm happy with it the way it is, but i want the plate fixed.

 

[180shabah]

Re: what pitch do i want?

that's what i'm getting, but i can't trim much yet.
my cavitation plate is broke, so it starts cavitating rather quickly. should have it fixed by next week though.

Just nitpickin', but that is actually an anti-ventilation plate, and your prop is ventilating, cavitation is a whole different issue having to do with pressure differential, boiling water, and errosion of the propeller.

Also, a quick question, do you know how/why the A/V plate is broken?

 

[brunolund]

Re: what pitch do i want?

true about the ventilationplate. I never actually thought about it before.

i do not know how it was broken, as it was like that when i bought it.
i'm assuming the previous owner used it as a wqay to remove the lower unit with a hammer(probably), or he backed the boat into something while trailering,(doubt it)

the prop it mint, shaft is not bent, and the unit has no leaks.
only about a 6 inch piece is missing, but it goes through where the rear anode is.