Questions on selecting a prop

[moh]

My prop is shot dented dinged and in need of replacement.
I have two different types of days at the lake. The first consists of fishing days with three people. On these days hole shot is less important but a little more top end would be nice. More time is spent cruising the lake. These are the more common types of days. The second type is family outings. On these days we pull tubes water ski and generally have around 5 people on the boat.

I am trying to decide if it would be better to go with 2 aluminum props one for each type of day or one SS prop. I am ok giving up a little performance if I can get two props that fit each situation better. I have no where to start so any advice on prop pitch, 3 or 4 blade and 2 alu vs one ss would be appreciated.

I boat at around 5000 feet in deep mountain lakes.


2) Current prop manufacturer, model, aluminum or stainless and as a minimum.
19p aluminum came on boat

3) Current prop diameter and pitch (required).
19p 14.5 oem

4) Wide open throttle RPM and speed with an average load (very helpful)
4500 rmp speedometer doesn?t work

5) Engine/drive make, model, year, and HP
4.3 mercruiser alpha 1 2002 1.81 gears

6) Boat make model, year, length and weight

Rinker 180 2002 18.5 boat weight 2300 dry 2800-3000 loaded

 

[Silvertip]

Re: Questions on selecting a prop

Is 4500 the "observed" wide open throttle rpm or is that what the manufacturers recommendation is.

 

[df909]

Re: Questions on selecting a prop

Welcome to the board. I just went through this a few weeks ago with my boat. I have a 21' 4.3L with an Alpha 1 drive. Mine had a 3-blade 21p aluminum and SS blade & I didn't have very good hole shot, it didn't plane very quickly, and I couldn't reach max RPM's at wide open throttle.

I switched to a 4-blade aluminum 19p and am very glad I did. The boat planes much quicker, hole shot has improved, and I even have higher top end (go figure). Here on iboats I got part # 1513-143-19 Solas Amita 4 Blade Aluminum 14.25" dia. X 19" pitch SR for only $109.

With the research I've done it really doesn't seem like a huge difference between the SS and aluminum on a 4.3L motor...if you were offshore racing in a 1,000 hp boat, then SS would be better. Also, if you have a pretty large checking account and are willing to hang $600 off the back of your boat, then you can even get a 5-blade.

I, however, didn't want to spend that much on a prop since it's probably going to cut some underwater trees and maybe grind a rock or two. I'm quite happy with the one I got. Good luck.

 

[moh]

Re: Questions on selecting a prop

Thanks for the response. 4500 is where its at now, I think 4800 is the manufactures WOT

 

[df909]

Re: Questions on selecting a prop

If your current prop allows you to get to 4500, that's in the range you should be in. Also, if the prop is really dinged up you can be losing RPM's because of that. So, I imagine a 4-blade 19p will work well for you. It took maybe 5 days for me to get mine through ibaots and I picked the cheapest shipping possible.

 

[hwsiii]

Re: Questions on selecting a prop

Moh, in my opinion you need to know what your prop slip is in order to make a knowledgable selection for a better prop. DF is probably right about a better prop for your boat, but with the prop being dented and dinged up it is very hard to know what true RPM would be if it wasn't that way. Also it would be good to know if your motor is mounted at the right hright for maximum performance.
If you would run the boat with a GPS for WOT max speed and give us those numbers and send us a few pictures of your prop with the dings and dents I could probably help you to make a more informed decision.

You might also read this for a little better understanding of maximizing your speed and fuel economy with different loads and props.

http://forums.iboats.com/showthread.php?t=365653&highlight=hwsiii


H