Outboard Engine Gear Case and Propeller Interchange

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Author Topic:   Outboard Engine Gear Case and Propeller Interchange

Tom W Clark posted 12-11-2009 10:49 AM ET (US)
[From some comments made originally by Tom in another discussion, and on requests for more information on this topic, here is some information on outboard engine gear case and propeller interchange and compatibility in the PERFORMANCE discussion--jimh]
GEAR CASE SIZES
Large gearcase motors have hubs of about 4-3/4-inch diameter. This includes MerCruiser Alpha 1 sterndrives and some OMC and Volvo sterndrives as well. For large gearcase motors, generally 135- to 300-HP, the splines are all the same across all manufacturers.
Intermediate gearcase motors have hub diameters of about 4-1/4-inch. Intermediate size gearcase motors have a greater variety of spline designs and the cross compatibility gets more complicated.
Smaller horsepower motors have hub diameters of 3- and 3-1/2-inch.
PROPELLER SHAFT SPLINES
For large gearcase motors, generally 135- to 300-HP, the splines are all the same across all manufacturers. That is not well understood. The primary difference is that OMC and BRP motors have less of the propeller shaft splined than the other manufacturers. Thus propellers that were made to fit OMC or BRP motors have less spline in their hubs to accommodate this. The net result if this difference is that you can put an OMC or BRP propeller on another brand, but you cannot put another brand's propeller on an OMC or BRP motor.
To modify another brand's propeller to fit a Johnson or Evinrude, you would need to either bore out more of the hub to remove about 7/8" of spline, or take it to a propeller shop and have the old rubber hub pressed out and a new OMC-BRP hub pressed in.
The propeller castings of any propeller in its gearcase class will fit any manufacturer's gearcase, though, as explained above, the splines may not work. There is one exception to this rule: Standard intermediate gearcase Mercury propellers will not fit OMC or BRP intermediate gearcase motors. Mercury makes (under their Quicksilver brand) a very few of their propeller models that are machined to a slightly smaller hub diameter leading edge to fit into OMC/BRP motors. Mercury-Quicksilver call these propellers "small labyrinth."
jimh posted 12-12-2009 11:59 AM ET (US)
It looks to me like OMC was very forward thinking in their design. Their propellers can be used on many competitors' engines, but the competitor's propeller could not be used on their engine. That is a very good combination of engineering and marketing. Those guys at OMC were pretty smart.
TransAm posted 12-12-2009 02:39 PM ET (US)
On the contrary. I would view a design that limits interchangeability or otherwise restricts applications as a negative. Perhaps this is why BRP does not advertise the exclusivity of their prop shaft spline design & configuration. Sure, it may steer a BRP customer to their respective prop brand in a quasi mandatory tie-in, but with the increasing popularity of inter-changeable hub systems, most consumers see their way around this inconvenience. For those not concerned with optimum propeller performance and are content with what comes on the boat, this line of marketing will serve some purpose I suppose. As for BRP propellers on other competing brands of engines, I have yet to come across a Yamaha, Mercury or any other brand of engine with a BRP propeller not to say they are not out there.
jimh posted 12-15-2009 12:42 AM ET (US)
I have read your reply several times, but I cannot understand how you make the contrary point. I believe you have failed completely to make a contrary point.
OMC's propeller shaft design with regard to the spines, as very nicely explained above by Tom, allows for a one-way interchange of propellers. OMC was able to keep competitor's propellers from being used on their engines, yet was simultaneously able to permit their propellers to be used on competitor's engines. (I know I already said that, but I am repeating for emphasis.) On that basis, viewed from an OMC perspective, all advantages accrue to OMC.
If you look at the market history, you can see that it was Mercury who had to invent for themselves a new interchangeable hub system in order to make their propellers fit onto other brands. The Mercuryists (a new term for life-long members of the Mercury brand customer club, which is derived from Trotskyists, the followers of Leon Trotsky) will try to tell you that the FLO-TORQ hub was innovation, but really it was desperation. OMC had boxed Mercury into the corner of the propeller interchange ring and was pummeling them with body blows. Before they went down for the count, Mercury had to design themselves a way to get their propellers on OMC propeller shafts. Their FLO-TORQ interchangeable hub was the answer. Was it a good answer? I will leave that for Tom to say. We already know what the Mercuryists answer will be.
Perry posted 12-15-2009 02:00 AM ET (US)
I'm not a Mercury enthusiast but I would have to say that I have seen very few OMC propellers on non OMC motors. On the other hand, I see many Mercury propellers on all brands of outboard motors. I even have one on my Honda outboard right now, it's an Enertia.
Peter posted 12-15-2009 07:25 AM ET (US)
"I'm not a Mercury enthusiast but I would have to say that I have seen very few OMC propellers on non OMC motors."
Likewise, I don't think I've ever seen an OMC propeller on another brand of outboard. But I don't think that OMC was really in the universal propeller business like Mercury is now. OMC propellers were marketed as accessories to OMC motors. I never saw OMC marketing literature or advertising with a message to non OMC brand outboard owners that they should consider buying an OMC propeller for their non OMC outboard.
Until the Flo-Torque II hub system came out, I don't recall seeing any propeller advertising by Mercury directed to non Mercury brand outboard owners. This seems to me to be a relatively new line of business for Mercury within the last 10 or so years.
TransAm posted 12-15-2009 09:33 AM ET (US)
Sounds to me like OMC's marketing strategy was more like a failed effort at an "iron curtain" attempting to not allow other propeller inside the OMC curtain. And, since we see very few (if any) OMC propellers outside the OMC curtain, this part of the marketing strategy has worked perfectly, just as the iron curtain was to keep folks from escaping to the west.
We all know free market forces almost always prevail when given the opportunity. By declaring "Tear down this wall, Mr. OMC" President Mercury thwarted the attempted coercion by OMC to keep its propellers on its own engines with a simple, propeller-freedom device known as the Flo-Torque hub.
jimh posted 12-15-2009 09:57 AM ET (US)
Perhaps the present day difference in the marketing of propellers by Mercury compared to BRP can be explained by the nature of the two companies' propeller production facilities. Mercury appears to be the actual manufacturer of their brand of propellers, having a plant and workforce of their own--and these facilities are even in the United States, at least for now--where they make their Mercury propellers. In contrast BRP does not appear to be the original manufacturer of their propellers, and we can assume that they may be sourcing them from another vendor and just passing them through their sales operation. As a result, there may be more room for profit in propeller sales for Mercury, producing a greater incentive to make Mercury propellers fit on more outboard engines.
As a general observation, the current situation in outboard motor propeller testing is something of a new phenomenon. If you went back 20 years I do not think you would find the typical outboard boat owner would be likely to conduct extensive sea trials with many different propellers. Nor would the typical outboard boat owner have the measuring equipment to accumulate accurate data about the boat performance. That just about every present day boat will have accurate measurement of boat speed (GPS receiver), engine speed (digital tachometer), and fuel flow rate (Flow-Scan type sensor) is somewhat of a new notion. Twenty years ago it was unheard of.

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Author	Topic: Outboard Engine Gear Case and Propeller Interchange
Tom W Clark	posted 12-11-2009 10:49 AM ET (US) [From some comments made originally by Tom in another discussion, and on requests for more information on this topic, here is some information on outboard engine gear case and propeller interchange and compatibility in the PERFORMANCE discussion--jimh] GEAR CASE SIZES Large gearcase motors have hubs of about 4-3/4-inch diameter. This includes MerCruiser Alpha 1 sterndrives and some OMC and Volvo sterndrives as well. For large gearcase motors, generally 135- to 300-HP, the splines are all the same across all manufacturers. Intermediate gearcase motors have hub diameters of about 4-1/4-inch. Intermediate size gearcase motors have a greater variety of spline designs and the cross compatibility gets more complicated. Smaller horsepower motors have hub diameters of 3- and 3-1/2-inch. PROPELLER SHAFT SPLINES For large gearcase motors, generally 135- to 300-HP, the splines are all the same across all manufacturers. That is not well understood. The primary difference is that OMC and BRP motors have less of the propeller shaft splined than the other manufacturers. Thus propellers that were made to fit OMC or BRP motors have less spline in their hubs to accommodate this. The net result if this difference is that you can put an OMC or BRP propeller on another brand, but you cannot put another brand's propeller on an OMC or BRP motor. To modify another brand's propeller to fit a Johnson or Evinrude, you would need to either bore out more of the hub to remove about 7/8" of spline, or take it to a propeller shop and have the old rubber hub pressed out and a new OMC-BRP hub pressed in. The propeller castings of any propeller in its gearcase class will fit any manufacturer's gearcase, though, as explained above, the splines may not work. There is one exception to this rule: Standard intermediate gearcase Mercury propellers will not fit OMC or BRP intermediate gearcase motors. Mercury makes (under their Quicksilver brand) a very few of their propeller models that are machined to a slightly smaller hub diameter leading edge to fit into OMC/BRP motors. Mercury-Quicksilver call these propellers "small labyrinth."
jimh	posted 12-12-2009 11:59 AM ET (US) It looks to me like OMC was very forward thinking in their design. Their propellers can be used on many competitors' engines, but the competitor's propeller could not be used on their engine. That is a very good combination of engineering and marketing. Those guys at OMC were pretty smart.
TransAm	posted 12-12-2009 02:39 PM ET (US) On the contrary. I would view a design that limits interchangeability or otherwise restricts applications as a negative. Perhaps this is why BRP does not advertise the exclusivity of their prop shaft spline design & configuration. Sure, it may steer a BRP customer to their respective prop brand in a quasi mandatory tie-in, but with the increasing popularity of inter-changeable hub systems, most consumers see their way around this inconvenience. For those not concerned with optimum propeller performance and are content with what comes on the boat, this line of marketing will serve some purpose I suppose. As for BRP propellers on other competing brands of engines, I have yet to come across a Yamaha, Mercury or any other brand of engine with a BRP propeller not to say they are not out there.
jimh	posted 12-15-2009 12:42 AM ET (US) I have read your reply several times, but I cannot understand how you make the contrary point. I believe you have failed completely to make a contrary point. OMC's propeller shaft design with regard to the spines, as very nicely explained above by Tom, allows for a one-way interchange of propellers. OMC was able to keep competitor's propellers from being used on their engines, yet was simultaneously able to permit their propellers to be used on competitor's engines. (I know I already said that, but I am repeating for emphasis.) On that basis, viewed from an OMC perspective, all advantages accrue to OMC. If you look at the market history, you can see that it was Mercury who had to invent for themselves a new interchangeable hub system in order to make their propellers fit onto other brands. The Mercuryists (a new term for life-long members of the Mercury brand customer club, which is derived from Trotskyists, the followers of Leon Trotsky) will try to tell you that the FLO-TORQ hub was innovation, but really it was desperation. OMC had boxed Mercury into the corner of the propeller interchange ring and was pummeling them with body blows. Before they went down for the count, Mercury had to design themselves a way to get their propellers on OMC propeller shafts. Their FLO-TORQ interchangeable hub was the answer. Was it a good answer? I will leave that for Tom to say. We already know what the Mercuryists answer will be.
Perry	posted 12-15-2009 02:00 AM ET (US) I'm not a Mercury enthusiast but I would have to say that I have seen very few OMC propellers on non OMC motors. On the other hand, I see many Mercury propellers on all brands of outboard motors. I even have one on my Honda outboard right now, it's an Enertia.
Peter	posted 12-15-2009 07:25 AM ET (US) "I'm not a Mercury enthusiast but I would have to say that I have seen very few OMC propellers on non OMC motors." Likewise, I don't think I've ever seen an OMC propeller on another brand of outboard. But I don't think that OMC was really in the universal propeller business like Mercury is now. OMC propellers were marketed as accessories to OMC motors. I never saw OMC marketing literature or advertising with a message to non OMC brand outboard owners that they should consider buying an OMC propeller for their non OMC outboard. Until the Flo-Torque II hub system came out, I don't recall seeing any propeller advertising by Mercury directed to non Mercury brand outboard owners. This seems to me to be a relatively new line of business for Mercury within the last 10 or so years.
TransAm	posted 12-15-2009 09:33 AM ET (US) Sounds to me like OMC's marketing strategy was more like a failed effort at an "iron curtain" attempting to not allow other propeller inside the OMC curtain. And, since we see very few (if any) OMC propellers outside the OMC curtain, this part of the marketing strategy has worked perfectly, just as the iron curtain was to keep folks from escaping to the west. We all know free market forces almost always prevail when given the opportunity. By declaring "Tear down this wall, Mr. OMC" President Mercury thwarted the attempted coercion by OMC to keep its propellers on its own engines with a simple, propeller-freedom device known as the Flo-Torque hub.
jimh	posted 12-15-2009 09:57 AM ET (US) Perhaps the present day difference in the marketing of propellers by Mercury compared to BRP can be explained by the nature of the two companies' propeller production facilities. Mercury appears to be the actual manufacturer of their brand of propellers, having a plant and workforce of their own--and these facilities are even in the United States, at least for now--where they make their Mercury propellers. In contrast BRP does not appear to be the original manufacturer of their propellers, and we can assume that they may be sourcing them from another vendor and just passing them through their sales operation. As a result, there may be more room for profit in propeller sales for Mercury, producing a greater incentive to make Mercury propellers fit on more outboard engines. As a general observation, the current situation in outboard motor propeller testing is something of a new phenomenon. If you went back 20 years I do not think you would find the typical outboard boat owner would be likely to conduct extensive sea trials with many different propellers. Nor would the typical outboard boat owner have the measuring equipment to accumulate accurate data about the boat performance. That just about every present day boat will have accurate measurement of boat speed (GPS receiver), engine speed (digital tachometer), and fuel flow rate (Flow-Scan type sensor) is somewhat of a new notion. Twenty years ago it was unheard of.