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Old 07-08-2008, 07:57 PM   #1
Lt. JG
 
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Default New Prop ??

Need some help with a prop selection. Boat is a Maxum 2300 SCR, 1992. 5.7 Merc with Alpha 1 outboard with what appears to be the original prop. I see no identifing numbers on it and don't want to take it off until I need to or go to change it. So what should I look for? 3 blade, 4 blade? pitch?
Top speed is 39 mph at about 3700 rpms (mind you I think there is a ground short since the gauge jumps at times). I am not looking for more speed but better "lift" or quicker acceleration. Any ideas or thoughts would be appreciated.
Scott
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Old 07-08-2008, 09:56 PM   #2
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well..you probably have a 15x21 prop....if it's a 3 blade....so....I'd probably look at a stainless steel 15x19x4 bladed prop...smoother acceleration and better control at slower speeds...you might also be aware that that's alot of stainless steel swinging around and if your in salt water..your going to have to watch the zinc's closer.....cuz the dissimlar metals will cause dielectric corrosion....

SP
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Old 07-08-2008, 10:37 PM   #3
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Quote:
Originally Posted by seapuppy
well..you probably have a 15x21 prop....if it's a 3 blade....so....I'd probably look at a stainless steel 15x19x4 bladed prop...smoother acceleration and better control at slower speeds...you might also be aware that that's alot of stainless steel swinging around and if your in salt water..your going to have to watch the zinc's closer.....cuz the dissimlar metals will cause dielectric corrosion....

SP
No salt water here in Knoxville, thanks for the info and looks like a good place to start.
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Old 10-27-2008, 11:28 PM   #4
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Default Prop

I use a 19P stainless Rev 4, 4 blade prop on my 5.0L and previously on a 220hp 4.3L and I really like it. Good hole shot and abot 50mph top end. Oh on a 2000 SR and now 2000SR3
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Old 09-16-2009, 12:44 AM   #5
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Default Re: New Prop ??

Hey Chef,

Been awhile but I'm still using that screen for my front window. Thanks again for helping me on that. We've since moved to Tampa, so the screen is nice in the mosquito combat!

I was just doing some research and came across this old thread. I'm putting a new prop on my 1991 2300scr 5.7L Alpha one. I find that I am running a 3x16x16 (for those who were wondering if a 16 will fit on an Alpha one I can say yes and it's not bad) that being said, i"m considering dropping to a 3x16x14 for a little bit more out of the hole.

What did you end up running. I was thinking of a 4 blade, but the prop shop says they don't make them as big so it would be a lot more money to get the same performance out of a 4 blade. I'll probably go the cheap route.

Would appreciate any thoughts or experience.
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Old 09-16-2009, 01:14 PM   #6
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Default Re: New Prop ??

Brownie, you wouldn't want the same dia and pitch for a 4 blade as you have on a 3 blade because with the extra blade your theoretically catching 25% more water as explained to me by my outdrive specialist which puts a lot of torque strain on your outdrive gears.

I have a 1999 2400SCR and went from a 3 x 15 x 15 alum. (that the previous owner had on), to a 4 x 15 x 16 alum. after reading through forums, and seeing it as ok on the Merc prop chart.

After a month my upper gears blew out and I had to replace the alpha 1 outdrive and chose to go with a rebuilt for a total of about $1.9k, hauled, changed out and refloated.

The outdrive specialist (that's ALL he does) said it could've been from age of the outdrive if original, too much gunning it out of the hole, but definitely exacerbated from the torque of the 4 blade. I went with his strong recommendation of going with the Merc factory spec'd 3 x 15 x 17 alum.
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Old 09-17-2009, 12:17 AM   #7
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Default Re: New Prop ??

Interesting. What you're saying makes total sense. Do you find your holeshot has been working well with the last prop you put on?

Was the 4 blade as dramatic a difference as they say?

I replaced the outdrive right when we bought the boat last year. So I feel your pain there. We knew it going into the deal, so no problem. Running great so far, but we don't get out all that much either.

Thanks for the feedback.
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Old 09-18-2009, 06:07 PM   #8
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Default Re: New Prop ??

Our holeshot has been good with all props we've had on, but we felt that we weren't going as fast as we should have been at top speed with the 3 x 15 x 15; about 20mph cruise 32 mph wot at about 3300 rpm. That's why we went to the 4 blade; it added about 5 mph at cruise and wot , but doesn't do much good if it blows up the alpha 1 lol. Since we've gone back to the factory spec 3 x 15 x 17 we're fast out of the gate and seem to be cruising right where we should be, about 24 mph at 3500 rpms. wot is about 37 mph at about 4200 rpm.
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Old 09-19-2009, 01:51 PM   #9
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Default Re: New Prop ??

Maybe this info will help you out on getting the right prop for your boat.

Prop Pitch & RPM's

For safety, and efficient performance, it is critical that your engine operates within the RPM range recommended by the manufacturer.

A change in the prop pitch will increase or decrease the engine RPM's and can be used to bring them into the recommended range. A 2" pitch increase (for example, from 21" to 23") will result in approximately a 300-400 RPM decrease and vice versa.

The correct prop allows the engine's RPM to run within the top end of the manufacturers recommendation.



3 vs. 4 Blade Props

3-Blades
3-blade props are great on most boats as they offer good all around performance, better efficiency, and can achieve higher speeds. Switching from 4 to 3-blades generally requires a 1" pitch increase.

4-Blades
4-blade props work well with bass, pontoon & high performance boats as they provide better acceleration, keep a boat on plane with fewer RPM's, and produce less vibration at high speeds. Switching from 3 to 4-blades generally requires a 1" pitch decrease.

Aluminum vs Stainless Steel

Aluminum
Aluminum props are a great choice for small and medium sized boats. They are inexpensive and under normal conditions can last for many years. When running your boat in an area where striking the bottom is likely, aluminum blades can flex, helping prevent damage to your engine.

Stainless Steel
Stainless steel props are ideal for large or heavy boats and boats running in saltwater. Although more expensive than aluminum, stainless steel props are more durable and will last longer. When running your boat at speeds over 50 mph, stainless props will perform better than aluminum.


Prop Diameter

Diameter is the width of the circle that the prop would make when rotating.

Prop diameter does not affect the fit of the prop on a boat.

The diameter of your prop can vary by up to 1/2" with no discernable change in performance.

Caution: Before increasing the diameter of your prop, make sure there will be enough clearance between the blades and cavitation plate or anode on your engine.

2-Piece Props

2-Piece propellers consist of the outer prop housing and a removable center hub.

The removable hub easily slips into the outer piece, allowing you to have multiple props for different applications at a lower price. When the prop blades become worn or damaged they can be replaced while keeping the same hub piece.

2-piece propellers perform the same as the 1-piece/fixed hub versions.

Prices listed include both the housing and appropriate hub.
Both parts are added to your cart making it easy to find your complete propeller.

you can look for props and buy them at this link: http://boatpropellers.iboats.com/
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