prop ?

[bark]

I have a prop question for the pros...

I am currently running an aluminium 19 pitch on my 5.0L Mercruiser, It works fine, but was thinking of getting a lower pitch for towing when I have a boat load. What are everyones opinion on what to run?

Pitch?
Stainless?
Composite?

What are the pros and cons of stainless, alum. or composite

Also with the 19 pitch I can do 55mph with two in the boat. I easily hit my max WOT Rpm and was wondering what kind of top speed gains I could see by going to a 21 pitch

Thanks for your input

Bark

[Loudelectronics]

A 19 pitch prop made of aluminum can actually stress enough under high speed loads to equal a 21 pitch prop. So by doing so you probably will not gain any top end with a 21 pitch prop. If you want to tow, then a 17 pitch is a good bet. You have to be careful of your RPMs. Dropping pitch increases RPMs and can damage engine. Increasing pitch may not allow the motor to rev out completly. I had a 17 pitch SS for my Bayliner and really liked the holeshot. SS is the way to go. It does not flex and is tougher when you hit something. Aluminum is just cheap, composite is made to break. I believe on your boat you can go up to a 23" pitch prop. 4.3L???

I could not believe the performance change in my boat when I went to SS. Way smoother througout the RPMS and way better holeshot. I also went with the highfive by quicksilver. 5 blade props are really smooth.

You may want to look at the shifting props. I know of someone with one and it works really well. Higher pitch for up top and lower for pullilng down low.

[JoeCool]

A 19 pitch prop made of aluminum can actually stress enough under high speed loads to equal a 21 pitch prop. So by doing so you probably will not gain any top end with a 21 pitch prop. If you want to tow, then a 17 pitch is a good bet. You have to be careful of your RPMs. Dropping pitch increases RPMs and can damage engine. Increasing pitch may not allow the motor to rev out completly. I had a 17 pitch SS for my Bayliner and really liked the holeshot. SS is the way to go. It does not flex and is tougher when you hit something. Aluminum is just cheap, composite is made to break. I believe on your boat you can go up to a 23" pitch prop. 4.3L???

I could not believe the performance change in my boat when I went to SS. Way smoother througout the RPMS and way better holeshot. I also went with the highfive by quicksilver. 5 blade props are really smooth.

You may want to look at the shifting props. I know of someone with one and it works really well. Higher pitch for up top and lower for pullilng down low.
Not knowledgeable about props and stuff, but I thought if it was stressing under load it should lose pitch and therefor lose speed , no? So upgrading to a stainless would in effect give you added top end for the same pitch. I am also curious to see what you guys say about ceramic, is that an upgrade from stainless, or in between the two?
JC

[Loudelectronics]

You make a good point JC but actually what happens is you loose down low. As the prop spins through the water the leading edge pulls the water through. As it pulls it is actually flexing the prop spreading out the fins. Now this is not consistant as cornering, rough water etc will play a role on the pitch of an aluminum prop. Stainless is not affected.

[Loudelectronics]

Oh and composite props are cheap. The are affordable and disposable if they break.

[yamarider]

One con for SS props is that if you hit something, the SS will take the hit and transmit that force to something else in the driveline. An aluminum prop will bend or break, as it is the weakest link, a SS prop will make something else the weakest link.
It's OK if you know where you're going all the time, but if you travel to different lakes the aluminum would be a safer bet.

:cheers::cheers:

[rubberknob]

changing your pitch will either give you slower to plane but faster top end, or it will be faster to plane and lose some top end. Really you have to find out what works best for you. If your going to be packing a full crew onboard often, or do you ride solo more often?. I would spend the money and get a $tainless.

[bark]

Well I am getting an alum. 21 to put on when we want to just cruise, and I have a 17 to try next time we go pulling. Its not hard to swap props so I figured might as well try a couple and see.

What controls the rpms on an i/o boat? Should they have a governor? Mine with the 19 pitch would rev way past the max WOT if I let it.

I can see why first time I/O owners blow up boats, especially if you came from the old 2 stroke that you can just hammer down

[Loudelectronics]

Bark, is yours the 4.3L merc? The reason I ask is I believe 21 pitch is stock on the 4.3 and 19 is the lowest it can go. You can put a 23 pitch stainless high five and still have tons of go off the bottom. My GF's dads boat has this set up and we can fill it with 7 people, and 600 lbs of ballast and get out of the water very quickly. With the 21 pitch aluminum it would not do this. The problem with pitch numbers are that they are theoretical as there is no actual test to measure them as the media they pass is liquid. Theoretically a 21 pitch prop would move 21" through the water with one revolution. However weight of the boat has alot to do with it.

[bark]

Mines a 5.0L mercruiser, I've found props for it right down to a 15, 17, 19, and a 21.

I'm kinda leary on running stainless. I like the safety factor of the alum. The drive shafts are too expensive...lol

I might give one a try. I'll have to keep an eye out for a deal on one.


Thanks Bark

[Loudelectronics]

I would not be to worried about stainless props. Your skeg takes the brunt of the impact and these are replaceable. We have hit lots of ground with our stainless on both bayliners and never had a problem with driveline issues. The drive line is really tough. The pros far out way the cons with a good stainless. Fuel mileage, better response, smoother, stronger and wont ruin your weekend if you hit something, better holeshot.