I've been around inboard boats my entire life. I'm a third generation inboard owner. My understanding is they pretty much all were opposite rotation as automobile engines up until the 1970s. Right hand was standard marine rotation, read as clockwise from the stern. Automobile is not only opposite but read from the front, so clockwise from the front. Apparently it is common practice of almost all engines to view engine rotation from the power takeoff end, commonly the rear. I don't know about airplanes.

I tried to see if early screw steamships established the marine rotation, but didn't find anything conclusive. Correct Craft Inboard boats used right hand rotation engines up until the late 1980s, I think. I've heard they did it to counter the weight of the driver causing the boat to roll less. MasterCraft boats never had right hand propellers as far as I know, and I think right hand propellers in single engine inboards has gone away.

Anyone shed any light on why marine engines were traditionally right hand rotation from the stern?

Member 6guns works on ship engines and likely could shed some light on this.

One will find that much of the confusion in the marine industry as to Right Hand / CW, or Left Hand/CCW rotation may have its roots based on the early definitions used by the Detroit Diesel Corporation (from just before WWII) in regards to the way they categorized their engines, AND in the way many in the AUTOMOTIVE Industry talk about engine rotation. Although engine rotation is defined in SAE J 824, let’s just say that because Detroit 2-stroke engines were so popular and universal in their base design, (the WW II standard 6-71 block was 100% symmetrical and could be “mirrored” or flipped around/reversed and the output power could be pulled from either end), Detroit seemed to always use the front end of the engine to describe rotation.

Besides that, general “Automotive Lingo” told us that because you could only “see” the front of your car engine, car buffs would use the front of the engine ( the part that they could actually see turning) to describe engine rotation (Right Hand or CW), although car engines actually met the SAE standard of CCW rotation. Totally different than all other manufacturers of engines, air compressors, hydraulic components, etc., etc., etc.. In otherwords, everyone else views “rotation” by looking at the “business end” or “principal output end” of the engine or other appliance / component to describe “ROTATION” direction. And COUNTER CLOCKWISE / “CCW”, is the standard of the industry from a Briggs & Stratton lawn mower engine (although the flywheel is actually opposite to the output end) to your VW, Lexus, or BMW, and every gasoline or diesel engine in general use today that may be applicable to vessel propulsion.

https://www.sbmar.com/articles...does-my-engine-turn/

I always was schooled that marine prop rotation was chosen to enhance level boat operation with the pilot on the starboard side.

Everything "aircraft" is from back looking forward orientation. (as it should be)

That's the way the Marine's roll.

Twin engine boats (old Chriscraft anyway) had one of each, CW and CCW. They then also had left hand and right hand propellers.

I think the fighter aircraft, the P38, also had opposite rotation on the two engines.

I just checked a spare prop I had for my 1989 Searay and it is a right hand rotation propeller. BTW the dive system was a 5.7 litre Mercruiser Alpha One.

It depends on what side of the equator you’re on!
Kinda like a toilet

when I first joined the CG I was fireman apprentice and worked on Cummins VT903 engines. Same engine that Cummins put in truck engines. Both engines turned CW when viewed from the rear, but one of the reduction gears made that prop turn outboard or CCW(the left engine) this was so the boat had little to no crabbing when both engines were throttled the same.

I have no clue why marine engines turn that way...the engines we had we original issue and if we blew an engine we got a replacement from a large unit that would have cannabalized it from a utility boat that had been decommissioned.

On the patrol boat I was on I was no longer an engineer, but we had two Paxman Valenta engines..they were British and I don’t know which way they turned but I know the ship handled the same as the aforementioned utility boats. And I’ve seen the ship out of water and the props turned outboard...the left prop CCW and the right one CW.( viewed from the rear).both had some kinda giant reduction gear in the engine room, just forward of my berthing compartment.

*edit for spelling

This message has been edited. Last edited by: MikeinNC,

They are view from the flywheel end because that is the same direction they turn the propeller. Left hand rotation from the stern is normal. Most are marinized car engines, so they just add the stuff to marinize them but now change the rotation (for a single engine boat). But boats with twin engines have engines (or gears) that turn in opposite directions so the boat/yacht tracks straight.

Most outboard engines run clockwise, but the output is CCW. The outdrive reverses the direction in the right angle gearbox. When I used to rope start my Johnson crossflow V4 it was a CW pull with the right hand, I think? Memory fading...

As for why they changed from CW output to CCW in the 60s? I can only guess, but that’s around the time that reversing outdrives hit the market. Perhaps the right angle gears used to drive from the front of the downshaft so the force on the gear was closer to the carrier bearing. When reversing outdrives were introduced, the horizontal shaft slides, with a gear on each side of the downshaft. Forward direction was moved to the rear gear so the shaft would be fully engaged in the carrier, providing increased durability and stability at high rpm. This of course reversed prop direction to CCW.

That is 100% my speculation, but it sounds good.

There is no G at the end of CUMMINS.

quote:

Originally posted by Lefty Sig:
There is no G at the end of CUMMINS.

Sure there is, Cummings, Georgia...…..and Cummins engine.

I’m referring to single engine inboards, mostly before 1990. The exceptions being Inboard ski boats built by companies that started up after 1970. Pretty sure single engined inboards built by correct craft, century, Chris craft, and marionette, had almost all right hand propellers though the 1980s.

Almost all marine engines turn same as automotive, including those built before 1970. The only reverse rotations I found were in twin engine installations.

To make a reverse engine from standard, turn the pistons around as there is a slight offset in the pin location. Use a different cam, and probably a different firing order.

I worked on boat engines for 20 years.

So which way does a Saab 900 engine rotate? If you aren't familiar with this car, the engine "front" (with the belts and pulleys) is backwards and faces the firewall.

quote:

Originally posted by c1steve:
Almost all marine engines turn same as automotive, including those built before 1970. The only reverse rotations I found were in twin engine installations.

To make a reverse engine from standard, turn the pistons around as there is a slight offset in the pin location. Use a different cam, and probably a different firing order.

I worked on boat engines for 20 years.

You must not have been around single engine inboards. My 1984 Correct Craft Ski Nautique turns opposite to automotive, as do all Correct Craft boats I have observed until 1989. My father's Chris Craft Cavalier solved the reverse rotation problem by turning its 283 Chevrolet motor flywheel forward.

Other engine changes that may be on reverse rotation motors are: crankshaft oiling passages, water circulating pumps, crankshaft seals. Raw water pumps often can just be turned upside down or inlet/outlet reversed, cam gears are usually ground to allow same rotation of distributor and oil pump. Velvet Drive transmission just require oil pump turned to a different position on its mount.

quote:

Originally posted by pbslinger:

quote:

Originally posted by c1steve:
Almost all marine engines turn same as automotive, including those built before 1970. The only reverse rotations I found were in twin engine installations.

To make a reverse engine from standard, turn the pistons around as there is a slight offset in the pin location. Use a different cam, and probably a different firing order.

I worked on boat engines for 20 years.

You must not have been around single engine inboards. My 1984 Correct Craft Ski Nautique turns opposite to automotive, as do all Correct Craft boats I have observed until 1989. My father's Chris Craft Cavalier solved the reverse rotation problem by turning its 283 Chevrolet motor flywheel forward.

Other engine changes that may be on reverse rotation motors are: crankshaft oiling passages, water circulating pumps, crankshaft seals. Raw water pumps often can just be turned upside down or inlet/outlet reversed, cam gears are usually ground to allow same rotation of distributor and oil pump. Velvet Drive transmission just require oil pump turned to a different position on its mount.

This is unique and correct craft did this to utlize a special propeller. Right hand rotation does something in regards to pulling a skier, I cannot remember what it is. After 1989, they used a reduction gear that reversed the rotation, rather than doing it inside of the engine. They did this on correct craft because the driver sat on the starboard side and a right hand rotation gave the starboard side lift, so you'd have a flat wake.

quote:

Originally posted by jimmy123x:
Sure there is, Cummings, Georgia...…..and Cummins engine.

No “s” in Cumming, Georgia.