1966 merc 650 only has 2 blades replacement prop has 3? Why?

[iamwill1973]

I recently acquired a 1966 650 that runs good and I have to take it off the old boat and mount it on my center console I was wondering why it only had 2 blades and the replacements seem to have 3. Thanks for any help you all can give.

 

[steelespike]

Re: 1966 merc 650 only has 2 blades replacement prop has 3? Why?

The 3 blade is a more versatile design. Able to handle loads,hole shot ,hard turns, responce around the dock better.
A good 2 blade would likely be a smidge faster.

 

[Texasmark]

Re: 1966 merc 650 only has 2 blades replacement prop has 3? Why?

For years Merc put 2 bladed props on their engines. Recollecting, it wasn't till they changed colors from white to Phantom Black that they went with the 3 blade on larger engines. Reasons? I agree with Steel. Somewhere I read that a 2 blade prop is the most effecient on a light fast boat, like the race boats of the time and Merc did like to be in the races. I remember they had them on their top of the like the Mark 55 rated at 40 hp and later on their first 6 cyl 60 hp Mark 75 as I recall. Don't know where the 75 designation came from.

OMC on the other hand had 3 blades on most of it's lineup and big cubes. So the OMC could easily plane a 16' wide beam, plywood, fishing boat with 2 or 3 folks, 2ea 6 gallon fuel tanks, starting battery, a bait bucket built into the boat, and all their gear with a palsy 25 hp OB.

Mark

 

[jimmbo]

Re: 1966 merc 650 only has 2 blades replacement prop has 3? Why?

2 blade props were quite common on Mercs, even the inline 6s untill the mid to late 1970s. For a given pitch the 2 blade props were usually about an inch or so larger in diameter than a 3 blade. In 1979 mercury made major changes to the blade design of their aluminium props. A one blade prop would be the most efficient, but the vibration from imbalance would be unacceptable.

 

[Texasmark]

Re: 1966 merc 650 only has 2 blades replacement prop has 3? Why?

A one blade prop would be the most efficient, but the vibration from imbalance would be unacceptable.

View attachment 161603

You must have read the same article as I did as I recall that comment......DOES make a lot of sense. Grin

Mark

 

[iamwill1973]

Re: 1966 merc 650 only has 2 blades replacement prop has 3? Why?

The prop is in pretty good shape would you guys change it to a 3 blade or leave it at 2 and why? I know if you like it and it suits your needs leave it alone but there are definitely advantages to 2 and 3 blades. I have only seen 3 and up props. I have a 16 ft. mitch craft center console that a 1996 mariner 60 hp would push up to 35 mph. I only had a complaint with the hole shot which took a while to get going in my opinion. I am running a vengeance 15 pitch on that engine. I am not sure of the pitch on the old merc.

 

[steelespike]

Re: 1966 merc 650 only has 2 blades replacement prop has 3? Why?

I would do some test runs with the 2 blade.With attention to trim and weight balance.
If the prop is 46 years old it could actually be worn.You might measure the diameter
and see how it compares to the markings.
A new prop may be more technically advanced as well.

 

[Texasmark]

Re: 1966 merc 650 only has 2 blades replacement prop has 3? Why?

When I was a teen I bought a Wizard (Western Auto brand) 25 hp (modeled after the Merc Mark 30) with a 2 blade alum. prop as standard equipment. I ran it on a 14' wooden boat. Later I bought a bronze 3 blade prop; don't remember the pitches. I called the 2 blade my "speed" prop and the 3 blade my "power" prop. We water skied behind that, a Rude 18, and Rude 25. Was fun and yes I ran the 3 blade when playing with water toys.

Mark