looking for specs on propeller: Mercury 48-79572-17

[Hyperacme]

Prop FAQ ...

http://www.mercurymarine.com/propellers/about/how-propellers-work/

http://www.mercurymarine.com/propellers/about/how-to-choose/pitch/

http://www.rbbi.com/folders/prop/propcalc.htm

http://www.boatus.com/boattech/articles/propellers.asp

http://www.miwheel.com/propellers/resources/

http://www.propmd.com/propeller-basics.html

[Neutron68]

In most of those guides, they didn't factor in propeller diameter with respect to engine load and final RPM.
That doesn't seem right.  
A bigger diameter means more blade surface area is pushing against the water.

Only miwheel.com page addressed questions about how prop diameter affected engine load and final RPM.

Eric

[Rich_V174SS]

With the Mercury props I don't think the diameter makes a whole lot of difference because the old-style large ear props didn't have as much (if any) cup around the blade ear whereas the newer more efficient slimmer blade props do. If you check the old prop part number with a Mercury parts place they'll probably tell you the number has changed many times and the most recent number matches up to a current design Mercury Black Max or Quicksilver Black Diamond aluminum prop.

[Hyperacme]

Don't think you have to worry about dia.
Mfg take care of it.
Just worry about pitch.

[Neutron68]

If prop diameter doesn't matter, why doesn't everyone just use a 13 inch prop?

Eric

[Hyperacme]

It matters but you can't choose a 22 pitch prop in a 12, 13 or 14 inch Dia.
You can choose a 20, 22, 24 or 26 pitch prop in the dia. that the Mfg. has tested and found works the best in most cases.

Chart is for a Laser II, for a Mercury 115 HP outboard ....

[Neutron68]

I found a propeller thrust formula on this page: http://www.mh-aerotools.de/airfoils/propuls4.htm

The diameter of the propeller gets squared and is thus a huge factor in calculating thrust!
A 15 inch prop will have more thrust than a 13 inch prop.



where
T   thrust   [N]
D   propeller diameter   [m]
v   velocity of incoming flow   [m/s]
   additional velocity, acceleration by propeller   [m/s]
   density of fluid   [kg/m³]
(air:  = 1.225 kg/m³, water:  = 1000 kg/m³)

[dorelse]

I'll just say this...you can do all the calculations & theoretical stuff you want.  The most valuable thing you can do is try as many props as you can, and pick the one that works best for your needs.

More than likely, a prop for watersports is not going to be a good speed prop, a top speed prop may totally stink until it hooks up, and its going to be different for each boat.  So its just best to try them out and go with the best all-around prop you find.  At the end of the day, they're all a compromise.

[WetRaider]

I'll just say this...you can do all the calculations & theoretical stuff you want.  The most valuable thing you can do is try as many props as you can, and pick the one that works best for your needs.

More than likely, a prop for watersports is not going to be a good speed prop, a top speed prop may totally stink until it hooks up, and its going to be different for each boat.  So its just best to try them out and go with the best all-around prop you find.  At the end of the day, they're all a compromise.

What he said.

[Hyperacme]

You could have a prop shop make you any size prop you like ... But the prop would cost more then your boat did !
and wouldn't perform any better then one you picked up on Craigslist for $75 - $100 ...

TESTING !
Try a few different sizes from different Mfg.
I'll bet the Merc prop performs the best.

Copy and paste from one of my prop testing days ...

http://forum.cgoamn.com/index.php?topic=3265.0

Nice day for prop testing ...
--------------------------------------------------------------------------------

First off ... HUGE THANKS to Dave for the use of his props, and he went the extra mile to stand on shore and wait for me to come in, then did a "Nascar style" prop change.

AND ...
Your CVX looks ABSOLUTELY AEWSOME !
Even with a Johnson on the back ... J/K

I got to WBL early to do some more adjustment to trailer... Didn't help ... OH well ...
Took CV out with a 17P Alm. prop I got with boat and kept as back up ..

All speed readings are GPS ..

Merc 17P alm. - about 47 mph, over reving to 5500 - 5600 rpms

Dave showed up and we got started ...
Wanted to try Lazer II 22p first but we put adtpter in wrong and couldn't get it out ... so ...
on to the Balistic 22P ... but it hit the trim tab so we removed tab and gave it a shot ...

Balistic 22P 50.2 mph at about 5200 -5300 rpms, could hardly hold steering wheel with one hand when trimmed out and went in to BAD chime walking, I mean bad !
Once speed/trim angle hit about 50mph and motor was trimmed out I couldn't hold it there for more then a few seconds or I'd have been tossed out of boat ..

Next was an old Merc SS 22P prop that hit 48.9 mph at about 5200 - 5300 rpms, torque steer wasn't to bad, more then I'd like but ...

Dave took his CVX out for a spin on this test but had alarm go off so we limped back to launch. Full of oil and good stream out his pee tube ... Might just be a senseror or bad ground ...

So Dave took his CVX home to get set back trim tab and pound out adtpter stuck in Lazer II, he must have broke every traffic law in the books because he was back in an hour ...

We put the set back TT and Balistic back on and got 49.9mph at 5200 rpms with more of the same torque steer and out of control chime walking, very violent chime walk .. Both times(testing Balistic) it had a lots of bow lift.

Next was the Lazer II 22P - 51.4 mph at about 5200 - 5300 rpms, trimmed all the way it had lots of torque steer but no chime walking. Same as other props up to around 50 mph and trimmed all most all the way it had neutral steering ...Full trim and had to really hang on. At least no chime walking.
Trim tab has notiches so can only go over so far ...

Kind of forgot when/where in the order we did it but tryed one of his 2 blade props ..
2 blade 22P - 50.8 mph at about 5300 -5400 rpms, very little torque steer, but weird noise, maybe vibration, maybe just the way the prop is, coming from motor, worked pretty good and felt very smooth.
Maybe a 23P 2 blade would work ?

Also a Power Tech 22P that only did 48 mph at 5200 - 5300 rpms

Last test was the Lazer II with the set back trim tab - 49.9 mph with bad chime walking ... Don't know what was going on there ...

Some thoughts are my steering is sloppy .. I can turn wheel from the 12 oclock to the 1 oclock without moving motor.

Dave will have some props up "For Sale" soon ... LOL
 

[Neutron68]

Yes, I will definitely try several props and see what happens in the real world.

Earlier in this thread, I asked if anyone thought that the beat-up 15x19 prop I have is worth paying to have reworked.  
If so, I can try that 15x19 in addition to the 15x17 I just bought.

Eric

[Hyperacme]

Depends on how much it costs to fix, if it won't work on your boat and you want to sell it, can you get your money back ?
Save it for a spare to limp home if you hit something with your good prop ...

[Neutron68]

I was quoted $70-$80 to rebuild the 15x19 prop. 
This is an old-style, 15-spline prop (no shaft adapter needed for the 1978 Mercruiser drive).

Any idea why the blades on the 15x19 are long and narrow, compared to the wide blades of 15x17 I just bought?

Eric

[V153]

I was quoted $70-$80 to rebuild the 15x19 prop

That doesn't sound too bad to me, considering I just paid $130 to have a relatively minor ding repaired in my SRX. 'Couse SS is a lil different than alum but still ...

Your 15x19 has a lot more 'rake' than the 15x17. I would clean it up'n run it. If it's too tall have 'em whack an inch of pitch outa it. That 15x17 looks more like a sailboat or poontoon boat prop. No offense to poontoon boats ...

[Neutron68]

Any recommendations for a propeller wrench?

A 1 1/16 socket on a socket wrench?  If so, how deep?

One of those plastic prop wrenchs?

[Jason]

Any recommendations for a propeller wrench?

A 1 1/16 socket on a socket wrench?  If so, how deep?

One of those plastic prop wrenchs?

 I use both. The nice thing about the plastic one is you won't loose an expensive ratchet and socket in the lake. But sometimes you can't get enough torque on those tight nuts. I use a standard 1/2 drive 1-1/16" deep well impact socket.

[dorelse]

I have one like this...

[Jerry]

I bought the right prop, and a prop-lock. (not in picture)

[Neutron68]

Any recommendations for a propeller wrench?

A 1 1/16 socket on a socket wrench?  If so, how deep?

One of those plastic prop wrenchs?

 I use both. The nice thing about the plastic one is you won't loose an expensive ratchet and socket in the lake. But sometimes you can't get enough torque on those tight nuts. I use a standard 1/2 drive 1-1/16" deep well impact socket.

On the socket, how deep is deep enough?

[Neutron68]

I have one like this...

What brand (part number) and cost is that?