Prop Question Please help!

[tsumma]

Hoping one of you folks here that has more boating experience than me can help me out I have a 1993 marada 21 foot open bow with a 5. 0 Ford OMC Cobra setup I just acquired the boat and it has a beat up stainless prop on it. I want to go with an aluminum prop but have absolutely no idea what size or pitch to go with and can't find any definite information online the previous owner said he did not feel like the prop that is on there is is correct. hope I didn't leave out any information that you need any help would be great thank you in advance. I have not had the boat in the water yet the stainless prop is beat up enough that I'm sure it won't perform well so I want to get a prop before I put it in the water to the first time

 

[Maclin]

Welcome aboard!

A 3blade 19 pitch basic aluminum would be a good starting point for you. Good luck!

 

[tsumma]

Thank you! The marina asask me something about prop diameter too if I'm not mistaken

 

[Maclin]

The diameter will be much less of a factor than the pitch. Most 19p props for sterndrives are 14.25-14.5 diameter range. Probably won't find too much variation in the diameter between brands on 3 blade aluminum props. Using a Prop Finder, such as what iboats.com has, will not usually even need the diameter to find your prop, just the manufacturer and engine size.

 

[tsumma]

Thanks again

 

[jimmbo]

The info regarding dia and pitch are on your current prop somewhere. We need to know it and what rpms the engine is currently getting at WOT, and what the WOT rpm range is for that engine, which BTW is 4200 - 4600 rpm. Your engine probably has a gear ratio of 1.5:1, or 1.59:1 so a 19 inch might even be a bit too much prop for the 302. I would think a 17 would be a better place to start

 

[Maclin]

Good points jimmbo. OMC tended to "load up" their Ford 5.0's with the lower numerical ratios. A 17p would be easier on the engine while running it thru the paces, and give good info too regarding under/over propping.

 

[tsumma]

I've never had the boat in the water so I'm not sure of the Rpm's I'll get you the current prop info rho

 

[tsumma]

My current prop is a ballistic 14 3/8 x 21

 

[Maclin]

So, the previous owner was right! that is a lot of pitch, especially for a stainless.

 

[jimmbo]

The Ballistic has very thin blades resulting a relatively light prop. It also has an weird blade shape. WIth the Ballistic, it seems people either love them or despise them. I am not one of the lovers.

I have 1.51:1 gear ratio on a smaller boat with a 5.7, and with a 21 AL I was getting about 4900 rpm. I would be surprised if the OP is running 4000

 

[tsumma]

So maybe do something in between and do an 18? Aluminum of course

 

[tsumma]

So here's the verdict ending up putting a 19 x 14.5 aluminum Quicksilver prop on. Boat gets on a plane easy but only does 3800 rpm and 35mph way toooo slow. Also the boat leans heaver to driver's side under power.

 

[jimmbo]

Is the tach accurate? Mechanical condition of the engine, as in compression? Timing and timing advance correct? Are the throttle valves full open?