Looking for replacement prop: mercury 90hp 2 stroke 6 cyl

[thool]

Hello, I am looking to buy a replacement prop for my boat. The engine is a Mercury 2 stroke, 90hp, 6 cylinder, serial number A124458. I believe it is from the mid 1980s, maybe 1986. The prop I removed has the following numbers stamped on it: 48 77348 A40 21P. It has a 15 point spline pressed in.

I'm not exactly sure how to interpret the numbers. Can someone please point me to the proper prop to buy here? Also, what does it come with and what do I need for the replacement?

Thanks!

 

[jimmbo]

Welcome to iboats
This should be helpful
http://forums.iboats.com/forum/gener...ead-this-first

Your current prop is a 21 inch pitch
Your engine has a Full Throttle RPM range of 4500 - 5000.

 

[thool]

Sure, here is what I can answer for 1-4

1) Performance issue you are trying to correct.
No performance issue. The prop has 2 shredded blades, so I would like it replaced.

2) Current prop manufacturer, model, aluminum or stainless as a minimum.
Unknown manufacturer. Prop is aluminum. Model appears to be 48 77348 a40 21p

3) Current prop diameter and pitch (required).
Prop radius appears to be 6 3/8 so diameter is 12 3/4". Pitch is not known, but might it be 21 from the 21p above?

4) Wide open throttle RPM and speed with an average load (very helpful)
I do not know the wide open RPM, but with 2 adult and 2 kids, no wind, and trimmed, the boat maxes out at about 35-37 knots.

 

[jimmbo]

Based on the numbers on the prop, it is a mercury/quicksilver prop. The 21 at the end of the number says it is a 21 pitch.

35 - 37 knots is about 40 - 42.5 mph which with a 21 pitch puts you around 4500 - 4700 rpm allowing for 10% slippage.

What kind of boat is it on? 15 ft?

 

[thool]

Based on the numbers on the prop, it is a mercury/quicksilver prop. The 21 at the end of the number says it is a 21 pitch.

35 - 37 knots is about 40 - 42.5 mph which with a 21 pitch puts you around 4500 - 4700 rpm allowing for 10% slippage.

What kind of boat is it on? 15 ft?

It is on a 15' fiberglass Thundercraft. Open bow and capacity of 6.

So I'm looking for 12 3/4" diameter, 3 blade, aluminum, 21 pitch? Is it fairly standard going from that point? Do I have to buy anything that gets pressed into the hub?

 

[jimmbo]

Your prop has a fixed hub. Mercury and other makers have changed over to replaceable hubs on a lot of props, but not all. I would put a 19 on, it will improve your holeshot. And get a tachometer

Don't lose sleep if the dia is not exactly the same, leave that to the prop engineers

http://boatpropellers.iboats.com/Mer...t_id=045098860

http://boatpropellers.iboats.com/Mer...t_id=045098860

 

[thool]

Your prop has a fixed hub. Mercury and other makers have changed over to replaceable hubs on a lot of props, but not all. I would put a 19 on, it will improve your holeshot. And get a tachometer

Don't lose sleep if the dia is not exactly the same, leave that to the prop engineers

http://boatpropellers.iboats.com/Mer...t_id=045098860

http://boatpropellers.iboats.com/Mer...t_id=045098860

Thanks! I have a tachometer, but don't recall where the needle was during operation. Boat has been out of the water for 6 months now.