All this Time....Dif Pitch than Thought...

[tahoejag]

Few years back ran merc black max 14.21p as oem. Log caught an ear and prop became toast. Picked up used prop, local dlr says its a MW prop and would fit my alpha...says thought is was 21p. Legible stamps on prop only referenced repair #s. One # stamped in the hub could not be cross ref to anything as asked in prior posts and MW themselves. Sitting around forum and browsing net, came across a simple way to measure prop pitch. (Now take into consideration I'm thinking I have 14 1/2x21p 3 bld alum. My #'s are WOT 4900 at 43mph gps, fairly loaded, 4.3l carb., which didn't seem right for 21p). After measuring prop it comes out to be 14 1/2 x 18p. Now #'s make more sense!!! Here's where general open opinions come in. Looking at a Rev4 (Santa is..heehee), aval in 19p and just recently 20p. Was going to go with the 19 until merc thru the 20p in there. Sad thing is that no one around here wants to part with a rev 4 for trial and error purposes and at $500 a pop....Santa says I better be sure! Just curious what the prop guys think??? I am looking for mid range/fuel economy cruising with 20'5' open bow runabout at 2800lbs, 700lbs gear/passengers. I get a one shot deal at this. Merc just had to throw that 20p in there! Thanks all!
John

 

[steelespike]

Re: All this Time....Dif Pitch than Thought...

It is usually suggested to drop an inch in pitch when going to a 4 blade.
So a 20" 4 blade could lower your rpm by 400-500.
Assuming a 1.62 gear ratio your present slip is at a little high 16%.
A more efficient new prop could further reduce slip and the rpm.
Being a repaired prop performance numbers could be skewed a little.
Without the year i'm not sure about your max rpm but the 4900 seems reasonable.
I wouldn't go over a 18" for your 4 blade.
Hopefully someone more informed will be along with a suggestion.
You might want to find a dealer that will let you try some props with the understanding your going to buy.Also wouldn't hurt to have a prop shop confirm your props pitch.

 

[tahoejag]

Re: All this Time....Dif Pitch than Thought...

Without the year i'm not sure about your max rpm but the 4900 seems reasonable.
I wouldn't go over a 18" for your 4 blade.

Sry bout that....boat info is now in signature. Engine range is 44-4800.

 

[jestor68]

Re: All this Time....Dif Pitch than Thought...

If you visit the Mercury prop selector and put in your data for mid range cruise/fuel economy, it tells you to get the 14.6 X 19 pitch Rev 4.

I would spend about $130 for a Solas Rubex 4 (aluminum) and enjoy comparable performance.

Another viable alternative would be to simply step up in diameter to a Quicksilver 15.5 X 18 pitch. The extra inch of diameter will provide greater static thrust(hole shot), better cruise efficiency, and lower the WOT rpm by about 200 rpm. It will work as well as a 4 blade for what you want to accomplish, at a fraction of the cost($160).

 

[tahoejag]

Re: All this Time....Dif Pitch than Thought...

Hey guys, thanks for the feedback! From what I hear and read, thats one hell of a prop! This is one topic that could go on forever...but being in the ballpark now, just a matter of picking a pitch. I'm not about ready to beat myself up with this, like santa said, pick one and have fun with it! :joyous:

 

[jestor68]

Re: All this Time....Dif Pitch than Thought...

Where did you hear that the REV 4 is available in a 20" pitch? According to the Mercury Marine Web site, it is available in pitches 15-25, in two inch increments; which does not include a 20".

 

[tahoejag]

Re: All this Time....Dif Pitch than Thought...

Where did you hear that the REV 4 is available in a 20" pitch? According to the Mercury Marine Web site, it is available in pitches 15-25, in two inch increments; which does not include a 20".

jestor68...your correct, under the rev 4 specs; however deeper into the site of mercurymarine.com, I found this under the news articles - "Mercury adds propellers to popular Enertia, Revolution 4 lineups" Oct 30, 2012

..."The right-hand versions of the new Enertia propellers, as well as the 15-pitch Revolution 4 left hand and 20-pitch Revolution 4 right hand offerings, are available now. The new left-hand Enertia and 20-pitch Revolution 4 propellers will be released in January 2013."

 

[jestor68]

Re: All this Time....Dif Pitch than Thought...

jestor68...your correct, under the rev 4 specs; however deeper into the site of mercurymarine.com, I found this under the news articles - "Mercury adds propellers to popular Enertia, Revolution 4 lineups" Oct 30, 2012

..."The right-hand versions of the new Enertia propellers, as well as the 15-pitch Revolution 4 left hand and 20-pitch Revolution 4 right hand offerings, are available now. The new left-hand Enertia and 20-pitch Revolution 4 propellers will be released in January 2013."

OK....cool. Thanks for that update.

So, you going for the 20 then?

 

[tahoejag]

Re: All this Time....Dif Pitch than Thought...

If you visit the Mercury prop selector and put in your data for mid range cruise/fuel economy, it tells you to get the 14.6 X 19 pitch Rev 4.

I would spend about $130 for a Solas Rubex 4 (aluminum) and enjoy comparable performance.

Another viable alternative would be to simply step up in diameter to a Quicksilver 15.5 X 18. The extra inch of diameter will provide greater static thrust(hole shot), better cruise efficiency. and lower the WOT rpm by about 200 rpm. It will work as well as a 4 blade for what you want to accomplish at a fraction of the cost ($160).

Jester68...After reading the above, I could get 3 to 4 alum props for the $ of a rev 4! LOL. Not sure what the max dia prop a gen II can handle, I know the 14 1/2" looked close, would have to measure.

So, you going for the 20 then?

Leaning more toward the 19p, simply due to the dia, 14.6? thats alot of prop for a 4.3l

 

[jestor68]

Re: All this Time....Dif Pitch than Thought...

The Alpha drive handles up to 16 inch diameters props. If your drive has power steering(flat anode) there is no clearance issue.

Without power steering(3.0L) you have to replace the anode(fin) with one that's set further back for clearance.

 

[jkust]

Re: All this Time....Dif Pitch than Thought...

Assuming a 1.62 gear ratio your present slip is at a little high 16%.

He should have the 1.81 ratio...the 1.62 is for the mpi 4.3.

 

[tahoejag]

Re: All this Time....Dif Pitch than Thought...

The Alpha drive handles up to 16 inch diameters props. If your drive has power steering(flat anode) there is no clearance issue.

Without power steering(3.0L) you have to replace the anode(fin) with one that's set further back for clearance.

Thanks jestor you saved me a trip to the boat, lol. it does have the flat anode with the 1.81.

 

[jestor68]

Re: All this Time....Dif Pitch than Thought...

In addition to my recommendation of the Quicksilver 15.5 X 18; a step further would be the Solas Amita 15-3/10 X 19 to further reduce that cruise rpm while still providing better initial thrust(hole shot) than that old 14.25 X18 pitch. You'd be running at cruise speed turning 300-400 rpm less, while still remaining right in the middle of your WOT rpm range.

Any time you are dealing with weights of 3000 lbs or more, diameter becomes more important. Your 1.81 gear ratio is especially suited for the "larger" props because they turn at a slower (prop) speed.

 

[tahoejag]

Re: All this Time....Dif Pitch than Thought...

Any time you are dealing with weights of 3000 lbs or more, diameter becomes more important. Your 1.81 gear ratio is especially suited for the "larger" props because they turn at a slower (prop) speed.

Gotcha!....I also have the smart tabs that help out alot, and if I may add that I boat alot in a river current of avg 2 - 4mph that often am going against along with the rough waters of the great lakes and the weekend yacht traffic! (boy thats fun!) Get's pretty..say "adventerous" at times....lol.