Which Mercruiser Prop

[mls]

I am new to this forum and looking for help. I recently bought a 1983 Sea Ray 21' Bowrider with a 260hp, 350 CID Mercruiser and I think an Alpha I outdrive, The outdrive has a sticker on that says 5.7 litre. Someone had stolen the prop and I need to replace it. The owners manual say's to use a 15 1/2" x 15 pitch prop. A friend has a 14 x 17 mercruiser prop he says I can have. Does anyone know if it will work on mine and if so, what would the result be? Better hole shot or better top speed. Also, what would be the advantage of a 4 blade compared to a 3 blade. Thanks.

Mike S.

 

[walleyehed]

Re: Which Mercruiser Prop

On an I/O a 4-bld has more stern-lift, usually better hole-shot, but suffers on top-end.....depends what you want from the boat.
The 14X17 doesn't sound like it was built for sterndrive apps......a bit small on diameter for the pitch for the 5.7.
I don't know your gear ratio, but I would have guessed a 19P would be close. You need to get your hands on the outdrive serial # and find the gear ratio stamped on the outdrive so we can pin it down.

 

[mls]

Re: Which Mercruiser Prop

On an I/O a 4-bld has more stern-lift, usually better hole-shot, but suffers on top-end.....depends what you want from the boat.
The 14X17 doesn't sound like it was built for sterndrive apps......a bit small on diameter for the pitch for the 5.7.
I don't know your gear ratio, but I would have guessed a 19P would be close. You need to get your hands on the outdrive serial # and find the gear ratio stamped on the outdrive so we can pin it down.

What part of Kansas are you from? I too am a Jayhawker from the SE part of the state. Tomorrow I will go out in the COLD shop and look for the gear ratio. Where on the out drive will it be stamped. Thanks.

 

[MikDee]

Re: Which Mercruiser Prop

walleye, I understand you're the prop expert, nice to know, but wouldn't the 4 blade 17" P. prop normally be a bit smaller in Dia. then a 3 blade 17' P. anyway?

and IMO that prop maybe perfect for his boat, considering I'd guess a 14X19", or 13 3/4 X21", either one a 3blade as a good match to start off with on that combo.

I think the 4 blade would do as you say, quite well though, although it may scrub a few mph at WOT

 

[achris]

Re: Which Mercruiser Prop

The ratio on those drives is 1.5:1. The recommended WOT is 4200-4600. I'm guessing that the 15P was probably pretty close. Using a 17P with a 14" diameter will go pretty much similar, as the extra 2" of pitch will make up for the smaller diameter. You will have trouble finding a 15 1/2" prop these days. They were made by Merc for engines put into large boats and generated more thrust than the smaller diameter prop. Most props for the Alpha style drives now are around the 14" diameter, the important number is the pitch. When you put the new prop on, just make sure your WOT is in the recommended range....

Chris.............

 

[mls]

Re: Which Mercruiser Prop

On an I/O a 4-bld has more stern-lift, usually better hole-shot, but suffers on top-end.....depends what you want from the boat.
The 14X17 doesn't sound like it was built for sterndrive apps......a bit small on diameter for the pitch for the 5.7.
I don't know your gear ratio, but I would have guessed a 19P would be close. You need to get your hands on the outdrive serial # and find the gear ratio stamped on the outdrive so we can pin it down.

I found the serial # but couldn't find the ratio stamped anywhere. The serial # is 0302090. Does anyone have a book that could tell me the ratio, the year and if it is an alpha or what. I don't think it has been replaced so it is probably a 1983 but I would like to know. Thanks for all your help so far.

Mike S.

 

[Willyclay]

Re: Which Mercruiser Prop

Try the 14X17 and see what happens. The price is right. Worst case, you can use it as an emergency spare. Adjust from the baseline it gives you. Good luck!

 

[walleyehed]

Re: Which Mercruiser Prop

I'll answer a few questions from the top...
I live in the very NW corner of the state.
As for the diameter, yes, if it's a 4-bld "in most cases-not all though" the diameter will be smaller than the 3-bld of the same pitch.
If the book calls for a 15-1/2X15 which is not uncommon and readily available in aluminum...it would be 15 or 15-1/4 diameter in SS, I would start there. Also, the 17P in 4-bld is going to pull about the same RPM as an 18P, possibly a 19P in 3-bld depending on prop design-a big factor.
You may want to take a look in the FAQ section at Propeller basics....I have explained how blade area and diameter can cross at a point where they are adapted to slug boats and yet still have a place in Light, fast bassboat style hulls.
Diameter is part of the total design, and in the same thoughts, a smaller diameter can place the rpm where it should be at the cost of fwd performance.

 

[mikeyt]

Re: Which Mercruiser Prop

hi walleye

I have a '96 Mariah Shabah 180 c/w 4.3LX Alpha 1 running the stock 14.25 x 21"P aluminum prop. WOT runs at 4750-4800 but i'm not particularly happy with the acceleration from a standing start. I've been trying to decide whether to go with a 20"P 4 blade SS or a 19"P 3 blade aluminum or SS. Any recommendations ?

mikeyt

 

[walleyehed]

Re: Which Mercruiser Prop

The 4-bld in 20P should give better hoe-shot and mid-range...it should also pull about the same RPM on top but you may lose a mph or 2
The 4 will have a bit more initial push and stern-lift, so it could help. This is considering that you stay with the same material and basic blade design.

 

[mikeyt]

Re: Which Mercruiser Prop

The 4-bld in 20P should give better hoe-shot and mid-range...it should also pull about the same RPM on top but you may lose a mph or 2
The 4 will have a bit more initial push and stern-lift, so it could help. This is considering that you stay with the same material and basic blade design.

Thanks Walleye

I was looking at the Michigan Wheel "Avenger" or "Apollo" in 20" - 4 blade design or even the Stiletto Advantage II in 19" - 3 blade. We do a bit of wakeboarding behind the boat and some cruising around the islands but seldom run at more than 35 - 40mph while doing so. Is there any hub issues i should be aware of when changing from the factory unit to one of the above? Would anyone of those 3 props be preferential? Or do you have another prop recommendation?

 

[walleyehed]

Re: Which Mercruiser Prop

The Apollo in 4-bld would be a good prop for 'boarding beings it has a bit more stern-lift...that will keep the wake at a good size and you won't be fighting the throttle back and forth.
When you order the prop, you specify which unit you have to get the correct XHS hub kit.
If you punch in the model, year and choose the size of the prop you want, it will automatically list it with the hub kit for the engine you punched in for the search.

 

[mikeyt]

Re: Which Mercruiser Prop

Thanks again Walleyehed

mikeyt

 

[rndn]

Re: Which Mercruiser Prop

I didn't read all the replies, but my 89 20' Baja used a 19p three blade and a 20p four blade.

 

[Mkos1980]

Re: Which Mercruiser Prop

Boat in sig with Laser II 13 3/4 x 21 and it hits 4600 RPMS at WOT 55.1MPH

When I bought the boat it had a Mercury 14 1/4 by 19 and I was screaming at 5100-5200 RPM's at 47MPH