Boatinnoob

I have a 350efi at 260hp with sterndrive ratio of 1.47. At 4800 rpm i get @55 mph. Current prop is a stainless 3 blade with i believe a 24 pitch. I am new to boating so any help is much appreciated

AllDodge

iTrader: (1)

I doubt you have a 24 pitch, probably a 21 or even 19.
With 1.47 I'm guessing a Alpha drive?

Boatinnoob

Yes alpha one gen 2. Boat is in storage will have to take a look at the prop. When i get a chance i will tell u whats written on the prop.

AllDodge

iTrader: (1)

To determine the correct prop U must have a accurate tachometer and speed from a GPS. The boat tach may or may not be accurate, need to check it against a hand held. The boat speed-o is not good enough

Boatinnoob

Ok, took a look att my prop. It is a michigan wheel Rapture14.25" and 19 pitch

AllDodge

iTrader: (1)

With a 19 your golden with only 6% slip at WOT

That is IF the Tach and speed are accurate

Boatinnoob

That prop is almost 20 years old. Could i get better performance from newer props or a 4 blade perhaps? I have no reason to believe the tach isnt accurate, however the speedo does move around. I have just bought a gps unit, unfortunately it is winter and boat is stored so i wont be abke to get a reading until spring on mph

AllDodge

iTrader: (1)

First and foremost you do not know what if anything needs to be changed because your not sure if speed is correct. Not having correct information to work with, then might as well use a dart board.

There is nothing wrong with a 20 yr or 100 yr old prop so long as its within specs. To find out if its within specs take it to a prop shop and have it checked.

The prop is the device which transfers power. Every blade that is in the water creates more drag, and more drag means more power needed to turn it. Going from a 3-blade 19 to a 4-blade 17 may or may not help and can cause other issues. More blades can increases lift, more lift can reduce hull drag, but can also throw the balance off and hull can porpoise.

If you want to buy a prop, go get one and see if it works in the spring, but right now without exact info, I can offer nothing. Maybe someone else can advise where to spend money

SB

iTrader: (1)

If no other crownline peep's chime in, contact FTMBob. He played with 300 million crownline's.

bbladesprops

I think AllDodge makes very good sense, with a few minor additions . Some testing with a few different propellers will help to make a target decision. Realizing what your ultimate goal is, be it speed, economy etc., will get you to the goal. We offer testing of new propellers from more than one manufacturer an easy process. Let us know if that interests you next Spring.
AllDodge, great advice. What is your back round in the marine world?

Brett