2 Bladed prop on 100hp Merc. Is that the right prop???

[Chris B.]

I have a 1969 Merc. 1000, 100hp Model 1100109
It has a 2 blade brass prop and in looking through several different forums and web sites I have not seen any of these motors with a 2 blade prop.
Is this an appropriate prop?
Why would a 2 bladed prop be used instead of a 3 or 4?

Also, is the thrust hub difficult to replace?

Thanks, Chris

 

[Barnacle_Bill]

Re: 2 Bladed prop on 100hp Merc. Is that the right prop???

Years ago Merc shipped motors with 2 bladed props. If all you are concerned about is speed then that is the way to go. But if you want to pull a skier or want a better hole shot then you need to go with a 3 or 4 bladed prop. A prop shop has to replace the hub as it takes special equipment.

 

[Frank Acampora]

Re: 2 Bladed prop on 100hp Merc. Is that the right prop???



Back in the day a two blade BRONZE prop was the only way to go for speed applications. The third photo shows a bronze two blade, solid hub, Mercury racing prop. Brass is an alloy of copper and zinc, Bronze is an alloy of copper and tin. Brass will dissociate the zinck from copper especially in salt water while bronze is more stable and resistant to corrosion. (simplified explanation)

Two blade props in larger engine applications do have less parasitic drag and do produce more speed than a three blade, but they tend to vibrate more and that vibration can frequently be felt in the boat.

 

[Texasmark]

Re: 2 Bladed prop on 100hp Merc. Is that the right prop???

Somewhere out there I read that the most efficient prop had the fewest blades. Since vibration would be out of the ball park with one blade, two was the minimum. So if you wanted the most speed that is what you used. All the racing engines of the time, where I was witness to racing, used small, high pitched, high rpm bronze props on special racing lower units.

Most smaller engines used 2 blades and maybe that was for economy as small engines on most boats weren't setup for speed....get you from here to there. Mercury was the only one that had 2 blades on larger production engines. That was until about 1965 when they produced the Mark 1000, the first production 100 hp engine and painted it black rather than the white/white combo that preceeded it....after the green/silver engines of the late 30's. After that something changed and they were shipped with 3 bladess. Kiekhauffer (spelling), Karl I think, was the father of Mercury engines. If you go to the Old Mercury site, you can read up on him and the founding of his company.

Multiple blades grip the water better and are better at pushing heavier loads. Since OMC was running 3 blades on their engines of any size back in the 40's and up, and Merc and OMC were at it all the time, maybe Merc's Lake X in Florida testing revealed that for general usage, it would be best to go with 3 like OMC who had the name for pushing heavy loads....Merc was considered the light and fast engine......I was there. That's the way I remember it. I had 2 props for my Merc engine; one 2, the other 3. I used the 3 (Michigan bronze) when I wanted to water ski as it pulled better......OK!

So, on your '69 it could have been either.

Best I can do and the accuracy of this post is surely questionable. Grin.

Mark

 

[Chris B.]

Re: 2 Bladed prop on 100hp Merc. Is that the right prop???

A prop shop has to replace the hub as it takes special equipment.

Now I'm a little confused (not terribly hard to do now days) about the hub replacement.
Isn't the hub used instead of a shear pin? I don't have ANY experience with thrust hubs so I was assuming that like a shear pin the hub would be sacrificial if the prop hit something hard but if it needs special tools to remove it that means you would be stranded. Am I misunderstanding it's purpose?

Thanks all for the responses, Chris

 

[Texasmark]

Re: 2 Bladed prop on 100hp Merc. Is that the right prop???

Used to be that Mercury, way back in the early days of the badge, used a splined prop shaft and bronze adapter in their props which had rubber inserts (cushioned slip hubs) between the propeller housing and the splined drive hub.

OMC on the other hand used a brass pin called a drive pin, but users (like me) referred to them as SHEAR PINS because at the worst possible time the prop would hit something, even though their props had rubber "pads" too and they would shear, disconnecting the prop from the prop shaft.

When you are on the windward side of rip rap.....aka ROCKS trying to maintain headway as that's where the fish are, and you have a splined shaft with a rubber slip hub vs a SHEAR PIN with a rubber slip hub, the former will hit whatever the obstruction happens to be, if bad enough to cause the hub to slip, your reducing the throttle to idle and immediately back to your power level will restore your drive. On OMC you are in DEEP DUNG because you have to stop the engine, tilt it engine up, get the cotter pin and hug "nut" off, install the new pin, reinstall what you removed, put the engine back in the water, crank it back up if it will crank after being tilted all the way up....iffy at best, and be on your way.....meanwhile your boat is hammering the rocks..............totally sucks!!!!!!!!!! That and their stupid protruding gearbox in the front of their LUs is why I left OMC and went with Merc. Pretty much been there ever since.

OMC has come to their senses and no longer use the pins. Like Merc they use the splined shaft.

In today's market you have two style props to purchase. One is the "old style" rubber slip hub that requires no separate mating hub.

Then you have the new brain storm of the marketing guys that uses a brass impregnated plastic insert, varies as a function of the engine HP and mfgr., that you insert into your prop "shell". So there you have to buy the prop and the corresponding insert.

It is purely for the dealer so that he can have half a dozen props with a couple dozen inserts and fit his half dozen props to most any engine that comes in the shop. Problem I have with that is that it doesn't take a rocket scientist to see that being plastic and brass fingers, if you really whack something with your prop, especially SS props, where the rubber hub would slip and reconnect, the brass fingers are going to rip through the plastic since it is slot locked to the prop shell, and they and the plastic will disintegrate causing you to be without propulsion. But unlike the shear pin of old, now to get back underway, you need an whole new hub. I don't have one, will not have one, and think it is an obination on the boating public from a water safety standpoint.

My 2c and worth every penny.
Mark

 

[jimmbo]

Re: 2 Bladed prop on 100hp Merc. Is that the right prop???

On all of our OMC drive pin engines, the pins were Stainless Steel, not brass or bronze.

 

[Texasmark]

Re: 2 Bladed prop on 100hp Merc. Is that the right prop???

Maybe that's why they were shear pins for us and maybe drive pins for you. All the pins we could get where i lived were in a little tin and were brass. I had a Scott Attwater and it came new with a little holder on the tiller arm with 2 brass pins and 2 SS cotter keys.

Mark