Prop Diameter Help

[naturecoast1]

I am working with a 1980 Grady White, 4000lb boat, with a MR228 mercruiser. I am trying to arrive at a happy prop selection.

I sent the 15 1/4 X 19 prop to be rebuilt. I now get over-revving and not enough top end. So, the search begins.

My question in about prop diameter. Playing with 15 1/4" props is very expensive as there is a limited number available. What is likely to be the result if I go to a 14 1/2 or 14 5/8 diameter in a 4 blade prop? 3 blade prop? Should I expect to need more pitch, or about the same as with a 15 1/4"?

I live on the west coast of Florida, so good fishing is 15 miles away or more. So, I am trying to optimize top speed and fuel economy. Quick launch and slow trolling are not top issues. I have a 15 1/4 X 17 prop for that.

Thanks, again, for all the help.

 

[LubeDude]

Re: Prop Diameter Help

Being from where you are, I bet you have a flats boat. Your setup is probably maximized for the 15 1/4" prop. I have found the Solas Scorpion to be a great prop, they are available in 15 1/8". You can search around and find a great deal on one, I just got a brand new one for $260.00 plus shipping. They come in even #`s and I`m not sure if they go all the way down to 18-20P or not.

 

[Dhadley]

Re: Prop Diameter Help

A 4000 lb Grady with a I/O? Hummm......most likely not a flats boat. Lol!

Anyway, there are I/O specific props. The X dimension is sorta hard to change so we don't worry about props like a Lightning or TXP that like to be run high. Stainless props with the standard 14 1/4" diameter will work just fine. Don't rule them out.

Let's start at the begining, is the prop you have ss or aluminum? Before it was damaged was it allowing the motor to reach the rpm band you wanted?

 

[naturecoast1]

Re: Prop Diameter Help

OK,
The prop on the boat is a 15 1/4 X 19 Aluminum. Before the damage, WOT rpm was at 4500rpm. A little bit low, but not too bad. Top speed was 28mph by GPS. Now, motor will redline (6000rpm+) if you let it, and top speed is 22 mph.(@5000rpm) I can't honestly say if the prop shop trimmed the blades. Although, the damage was quite minimal (no nicks, no cracks, you couldn't even tell by looking that the prop was bent) so, I don't know why they would have trimmed the blades. But, you never know. I live a long way from a big town, so the props were sent out by a local marina to the machine shop. As a result, I really don't know if the prop was a 19 pitch before the repair or after the repair or never at all.

So, I realize that I am probably going to have to bite the bullet and buy a new, known prop as a starting point.
I am ready to invest in a stainless prop, but am trying to arrive at a good diameter/pitch before I sink the bucks.

I can get a really good buy on a new mercury 4blade prop that is 14 1/2 X 21.($100) It is also aluminum, so I would see it as a tool for arriving at an end. What I am wondering is whether it is a case of comparing apples to oranges and will be consequently of no value in arriving at a proper pitch to spend $300 bucks on a 3 blade stainless.

So, it boils down to this question: will I learn anything by playing with 14 1/2" props (because they are cheap and plentiful) or do I really have to just quit whining and order a 15 1/4 X 19?

 

[LubeDude]

Re: Prop Diameter Help

A 4000 lb Grady with a I/O? Hummm......most likely not a flats boat. Lol!

I hate it when that happens!

 

[Bondo]

Re: Prop Diameter Help

Diameter has More to do with the Blade Design,+ it's thrust Area.......
You Really don't have much Choice,... It's engineered by the designers......

You need to shop the Pitch you need,+ Forget about Diameter.......

 

[Dhadley]

Re: Prop Diameter Help

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