Commercial vs Recreational outboards

[20lbSloughShark]

I have often wondered what the advantages to each type are. Basically the only real response I have ever gotten is that commercial version outboards have a stronger lower unit than a standard version. That pretty obvious just looking at them. I could understand if you want a strong lower unit for something like pontoons or big boats on the ocean. What makes me wonder is my motor is a 40hp tiller commercial outboard. Its a small-mid range size, which would be weak in a lot of "commercial" applications. The other thing is that it is a tiller, and as far as I know it always has been. When I think of tiller outboards, I think of fishermen. Is there other advantages that you gain in a commercial outboard? I have heard one person say a different gear ratio, but that makes no sense to me when you can just change the propeller. I have always wonder why a regular fisherman would prefer a big paddle of an outboard vs a regular one. I'm not sure how much more it weights, but the lower unit looks huge compared to most 40hp motors.

[bobbymalone]

I thought they were all around "tougher"

and with less fail prone parts and less preventative maintenance required.

[Ufatz]

Well boys, I must confess that after a lifetime of boats and motors, from old WWII nickel plated Johnson 25HP to Cat diesels, I have never heard of a "commercial" outboard motor version of the motor you can buy at your dealer. Have run motors in fish camps in several parts of world and they were always the same as the ones around my docks at home.

You guys maybe onto something and perhaps I have not been paying attention.

[Down Deep]

Yamaha has a commercial 2 stroke engine designed for the world wide market, mainly river boats. It is there Endruo line. They are built for all day use, day after day in harsh water conditions. Over the years, my experience with out-of- the- box outboards has been excellent. The motors built today are vey well built with excellent performance and last years if maintained. I would find it hard to make a case for a commercial application for the seasonal recreational fisherman even if they were obsessed and fished everyday.

[Washing Lures]

The commercial OMC 2 strokes were premix, no oil injection. I think it was the same for the commercial Yamaha. OMC offeres two different fuel pumps, one they call commercial which is a straight fuel pump and the VRO. I switched a previous motor to a commercial pump because of lack of trust in the VRO pump.

[Savage Brewer]

I think when everyone moved to 4 strokes the idea of a commercial engine went by the wayside.

The advantage of a lower gear ratio is that you can turn a larger diameter propeller, that will have less slip.

[20lbSloughShark]

I didn't even think of the pre-mix vs oil injection. I prefer pre-mix, so that's a plus. I don't have too much experience with different boats, but I would think prop slip would me more with larger boats? Maybe I have the terms wrong, when I hear prop slip I think of cavitation, ventilation, and overall lack of "grabbing" the water. I mean my motor makes really good power for the size, I feel it puts out more than most 40hp motors, but I wouldn't stick it on a big 18' fiberglass boat. I don't think I've ever had an issue with a standard motor grabbing the water. I too had never heard of a commercial motor until a few years ago. This motor popped up, was a good deal, and then I saw it. It is a real tank.

[Ufatz]

Okay gents, I learned something today.

[delcecchi]

I didn't even think of the pre-mix vs oil injection. I prefer pre-mix, so that's a plus. I don't have too much experience with different boats, but I would think prop slip would me more with larger boats? Maybe I have the terms wrong, when I hear prop slip I think of cavitation, ventilation, and overall lack of "grabbing" the water. I mean my motor makes really good power for the size, I feel it puts out more than most 40hp motors, but I wouldn't stick it on a big 18' fiberglass boat. I don't think I've ever had an issue with a standard motor grabbing the water. I too had never heard of a commercial motor until a few years ago. This motor popped up, was a good deal, and then I saw it. It is a real tank.

Why on earth would anyone prefer pre-mix to oil injection (except for the scare stories about bad oil pumps probably due to a couple years of OMC)

[Down Deep]

I agree. I would never go back to mixing fuel because it has absolutely no advantage over injection. Those VRO pumps that were dump were made in the early 1990's. OMC also had a big miss with there direct injection motors which put them out of business and then ended up owned by Bombardier who bought it for a song.

As far as I know "Prop Slip" is a term applied to a prop that has a rubber hub which eventually wears out causing the prop to spin around freely before finally grabbing. Props today have composite inserts which solves this problems.

I know that everyone has their own personal preferences, but the quality of the outboards made in the last 10 years has been outstanding.

[Ufatz]

I believe the definition, or at least one of them, of "prop slip" is when your motor is producing cavitation or the motor is otherwise mounted, probably incorrectly, to have the prop turning in less than solid water i.e. turbid or foamy water at the stern. A prop that is turning in that kind of water is not "biting" solid water as it should and thus not producing the thrust you want or expect. I suppose it COULD also refer to a slipping rubber hub, but I am taking this in the context of larger props, directly shaft driven.

Ya'll boys have it your way.

[delcecchi]

All props slip to some extent. If you have a 20 inch pitch you should theoretically go 20 inches for every revolution of the prop. But you don't, you only go 15 or 16 or 18 inches.

Calculate the top speed of your boat using the RPM your motor turns and the gear ratio of the motor and the pitch of the prop. Compare that to what you actually go.

For example take a suzuki 140 with a gear ratio of 2.59 and a 21 inch prop. At 6000 rpm it should be going 46 mph. In reality it is more like 41 or 42.

[Savage Brewer]

My term of slip has nothing to do with the hub.

Look at motors for pontoons and like the mercury "bigfoot" series.

When you have a heavier load and you need the extra thrust and control a larger diameter prop will have better bite in the water.

But to turn a heavier larger diameter prop you need a lower gear ratio for two reasons.

The torque is multiplied in the gearbox to handle the load, and also you need to control the linear velocity of the tip of the prop, if the props outside edge approaches too high of a linear velocity it will cause cavitation also.

As you notice this has nothing to do with top speed, in fact a larger gearbox will create more drag and a larger diameter prop will not help top end at all.

Larger gearbox also helps with longevity as the gears have more material and the bearings are a bit larger.

Look at a racing outboard vs a bigfoot or other high thrust motor.

In a commercial application it is likely that that boat is probably loaded heavy and they are not concerned about top speed.

Suzuki gets around the gearbox size issue on their larger engines with dual gear reduction.

Most outboards the drive shaft is directly coupled to the crankshaft, which means the it spins at the same speed as the engine and all of your reduction is in the lower unit.

Suzuki does a first stage reduction at the crankshaft of around 1.25:1 (varies by HP) so when your engine turns at 4000 RPM the driveshaft is only turning 3200 RPM. Then the second stage is in the lower unit but is only a 2.08:1 reduction reducing your prop rotation to 1544 RPM.

Final drive ratio winds up around 2.59:1

This allows the Suzuki's to turn a larger prop, which will give you better control and efficiency, but it can hurt the top end speed on some boats.

Most motors to achieve that gear ratio it needs a larger lower unit.

Back to your original question, are you happy with your current motor? If so why change it?

[20lbSloughShark]

Savage, that really cleared it up for me, thanks. I am ok with my current motor, I was just curious. I prefer pre-mix for a number of reasons, but that doesn't mean its better. One is everything I have is pre-mix. My snowmobile used to be oil injected, but I made it run pre-mix after it failed. Oil pumps are very reliable, my snowmobile is just really old. Being that most of my motors are 2 stroke, I can just transfer gas to any of them if I want. The main thing, however, is that I'm familiar with pre-mix. I have limited experience with oil injected 2 strokes. In my eyes, the less moving parts, the better. I mix gas, and haul a$$.

[Black_Bay]

Commercial outboards have stronger gear cases, more stainless steel for saltwater use, heavy duty brackets, sometimes the carbs are modified also. They are made to be beaten up and still work with little maintenance in 3rd word countries.

[Ufatz]

Good post S.Brewer. Prop "slippage" can be induced by a variety of circumstances. And your points about big slow turning props also appropriate. Have seen big OBM's used to push around small log floats, dock sections at marina's and net pens at fish hatcheries and they have ALL been geared down for maximum thrust....they need "push" not high RPM's for speed.

In my younger days I ripped across the waters in a small Class II ( as I recall) hydroplane and we had a big Merc spinning a small, two blade, stainless prop. Don't recall RPM's etc. as it was a long while back but I DO know that little baby would JUMP right out of the water!!

But until you guys raised the issue I had never heard of a "commercial outboard motor"......even though I often saw them working and knew what made them tick.

[jentz]

There actually 3 different types of outboard,The standard whick 99% of people have,then the commerical and the last is Military.

The commerical have heavy duty stainless steel water pumps,Shot peened driveshaft for longer service life,Better seals on the cowl,Lots more stainless steel fasteners Larger gear cases,Shorter stroke with larger bore and pistons.Depending on manufacter Heavyier shift rods and shift yoke.

[20lbSloughShark]

When you say water pump, do you mean the impeller or the housing? I would think a SS impeller would not be good, but I could be wrong. BTW, does bore/stroke affect 2 strokes in a similar way to 4 strokes? I would think with an outboard you would want the more torque of a small piston/long stroke but I don't have much to base that on.

[20lbSloughShark]

Well, I just found out something I never realized before. According to my model number, my motor is NOT a commercial motor. I'm thinking the transom mount was replaced, but maybe mine is something else. My model number is J40RCR. Johnson 40 hp, the first r means pull start tiller, and the cr means '84. A commercial should have J40RCCR. That kind of messes things up for me. While I am pretty certain its a commercial (large lower unit, as well as the other things stated in this thread), I may have been buying the wrong parts. The reason I found out, is I was trying to get new spark plugs. Rather than do as I was, taking the number off the old plug, I looked it up. As it turns out there is at least 3 different plugs for a 84' johnson 40 hp. A pull start tiller, a 43 cid commercial, and a 45 cid commercial. I have always been running the plug for the regular 40 hp without knowing it. Not only that, it states a narrower gap. The manual I was given with the motor, which does not look that old, states a plug gap of .04. Most places online say to use .03. My motor always did idle a little rough, but I always just figured it was because the carbs are set too rich. I would put in smaller jets, but it always started, and wasn't too concerned with performance. Maybe it can be fixed with something as simple as the correct plug and gap. So is there another way to figure out what motor I have? The plugs I have been running are resistor plugs, specifically QL77JC4. Hopefully this doesn't come across as ignorant, but is it possible to damage electrical parts with the wrong plug? I did have my CDI go bad last year, and it wan't just a simple, one moment it works, the next it doesn't. It continually got harder to start over a period of about 2 weeks. One day I couldn't even get spark. A new CDI fixed that.

[delcecchi]

Just out of curiosity, what made you think you had a "commercial motor" in the first place?

[20lbSloughShark]

Well the first thing was the person I bought if from said it was a commercial motor. I didn't really know what it meant at the time. It sure looks like it could be one.

[CAMAN]

Are you thinking that big white band above the lower unit makes it look commercial? That is an after market extension to allow for use on bigger transoms. Take that off and it looks like any other outboard.

[marine_man]

There should be a welch plug that has a S/N stamped into it on the block... you can compare that S/N against the S/N that's on the tilt bracket to see if they match.

marine_man

[20lbSloughShark]

Thanks, I'll do that. I would definitely like to find out what I have for sure. I don't really care if its a commercial or not, but I was told it was, and have bought parts as if it was.

[20lbSloughShark]

Thanks for the heads up. I looked up the numbers, and they don't match. It does say J40RCRM so I am going to assume it is just a regular motor. I really can't get more info about it, so that's all I can do. Still a very informative thread.