Merc Props - "large blade area" ??

[jtackle]

In looking or a new prop for my 50hp - 4 Stroke, I have learned that there are a 2 different types from Merc.

Using a 12P for an example, one is #48-73134A40 and the other is 48-816702A40. The second one is described as "large blade area", yet is the same pitch.

Question: What is the difference (except for the obvious!). How would one perform compared to the other, both out of the hole and at WOT ?? (since same pitch)

thanks......

 

[walleyehed]

Re: Merc Props -

Re: Merc Props -

Large blade area would be a heavy load, hard pusher at low to mid throttle...
The normal blade area will be the faster prop in most cases due to less drag, unless it's a high-performance prop for very high running heigths...large diameter, but maybe not large blade area.

 

[jtackle]

Re: Merc Props -

Re: Merc Props -


Thx Walleyehed.

The so called "large blade" is 10 3/4" and the "normal"??" is 10 5/8", so we are not talking alot of differerence here in diameter.

Again both a Merc OEM props, and I can find no further info or description. No ref to any "high performance" traits. When I talked to the local dealer he only said that the standard was the larger blade prop (based on the part number I had for it), and knew little else. But when you look at prop web sites, both are listed as available but no more info.

Would the larger blade give me better hole shot but less top end? Or.....?

 

[jtackle]

Re: Merc Props -

Re: Merc Props -

Any more thoughts or inputs from you guys??

 

[walleyehed]

Re: Merc Props -

Re: Merc Props -

It "could" give more speed if it's designed for more lift...that's a problem with alot of dealers..they know they sell props, but can't be sure what they all do....

 

[Boilermaker]

Re: Merc Props -

Re: Merc Props -

jtackle,
Kenny knows far more on this subject then most of us put together.... and MOST of what I know I learnd from reading his and DHadleys' posts, but maybe I can help explain it .

My thinking is that for the AVERAGE (if there is such a thing) BOAT the smaller blade area will, infact give a better holeshot due to a slight amount of controlled slippage.
This allows the engine to get into its "powerband" faster by allowing higher RPM when you open the throttles from a dead stop. This is also why some props have "venting" holes added to the hub. This allows a controled amount of exhust gas to "vent' out in front of the prop blade and fill in an area that is usually a low pressure (vacume) zone.
This allows the blades to "slip" and get the engine RPMs up. Once the boat speed is increased the water rushing over the prop effectivly seals the vent holes and the prop bites hard, and hooks up.

The OEM "large balde area" props are designed for high load applications such as tow boats, pontoon boats, work boats/platforms, large sail boats, ect... This is where you don't need speed and don't want slippage. You want low speed, high pulling power.
I hope that this helps you a bit.
8)

 

[imported_bjs]

Re: Merc Props -

Re: Merc Props -

small gearcase = small dia props most small gearcase dont offer a h/p ss prop so you have to put a prop made for a large gcasei/. have tired alot of props and the larger the diameter the less rpm i turn( that just in my case) maybe with a differnt motor it might be diffi. have a force motormaybe. your motor will be diff. my motor does not like large dia props.

 

[jtackle]

Re: Merc Props -

Re: Merc Props -

thx guys. always helpful...and always educational.