Reverse rotation?

Rockxx
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Re: Reverse rotation?

Post by Rockxx »

Perhaps I'm looking at this from the wrong end of the boat. My prop turns clockwise when looking forward. Prop is stamped R.
Always figured on a single engine, this was normal.
Rockxx
1972 28' express "Safari"
Single Chrysler 318
Center Hill Lake, Tennessee
EWRice
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Re: Reverse rotation?

Post by EWRice »

Rockxx,
You have a right hand rotation propeller on a right hand rotation engine. IF you have any transmission other than the velvet drive reduction that reverses output rotation in forward, then your engine will be opposite rotation, or ccw as viewed from front of engine.
Muskegon Lake
1972 32' Express flybridge
"AL13"
Twin 318s
On board air & prime 920
1963 Thompson Super Sea Lancer
Graymarine 327
1961 Alumacraft 12'
'55 10hp Johnson
Rockxx
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Re: Reverse rotation?

Post by Rockxx »

EW
I have a Velvet Drive 1-1 transmission. If I'm understanding this correctly, rotation is determined facing aft to stern, which in that case I do indeed have reverse drive.
1972 28' express "Safari"
Single Chrysler 318
Center Hill Lake, Tennessee
Fastjeff
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Re: Reverse rotation?

Post by Fastjeff »

Why they did this is, apparently, is that most skippers prefer to approach the dock on the starboard side. A RH prop swings the stern that way.
At least, that's my theory.

Jeff
"We live at the bottom of an ocean of air, not at the top." General Marvage Slatington
Leviathon
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Re: Reverse rotation?

Post by Leviathon »

I can tell you on my last Single Screw Marinette, I had to swap engines and put in a LH rotation engine with a LH prop, and for what ever reason, I could not get that thing to back out of the slip for nothing. Could not get it to turn worth a darn in reverse. Weird. I guess they made singles RH for a reason.
Steve and Mary Levi
1973 32' Marinette Fisherman
SBC Crusaders
El Ohssa
St. Joseph, Michigan
jmonday
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Re: Reverse rotation?

Post by jmonday »

Ok I have ask this to many boaters in our area and looked for it on line. Does anyone know why if they already had the 318 in production making them why would they have tooled up to make the opposite rotation that had to be more costly then changing the rotation in the gear box?? I do understand the need for both rotations but I work in the automotive world and also see a lot of poor choices in design but this one seems to have had a reason.
Jeff Monday (Blue Mondays)
1973 28 ft Express single 318 1976 StarCraft Islander 1961 Sea Nymph
Lower River rd
Rabbit Hash KY
Fastjeff
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Re: Reverse rotation?

Post by Fastjeff »

Jeff (the other) I too have wondered about that. I guess the trans guys had yet to make the reversing setup in the trans. Hell of a lot easier this way, and less confusing when working on the engines.

Jeff
"We live at the bottom of an ocean of air, not at the top." General Marvage Slatington
barkleydave
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Re: Reverse rotation?

Post by barkleydave »

To begin with there are always exceptions and poor designs.

As a general rule of thumb.

Inboard single screw boats will back to Port in reverse. (Left hand rotation)

This is important especially if you are in the business of moving lots of boats around. Many years ago I worked at a marina and we often had to move boats to different slips and service area. I was 16 and learned very quickly to verify which way she backed prior to putting a boat into a tight situation.

I also once owned a Thompson 15 ft runabout boy was it pretty. One major problem... the helm was on the Port side. Now with a single outboard it always listed to port while running. VERY UNCOMFORTABLE! Reason... prop torque I did not keep it long.




Also for those asking why most boats are Starboard Helm? Reason: You yield to vessels crossing from your right/starboard ... by having the helm on the starboard you generally would have an unobstructed view to Starboard. So why did M put 32's on Port? I do not know sure someone out there does....


Safe boating,

dave
1987 Marinette 29 FB Sedan
Retired Boat Accident UL and USCG trained investigator
Retired USCG Captain
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Re: Reverse rotation?

Post by EWRice »

jmonday wrote:Ok I have ask this to many boaters in our area and looked for it on line. Does anyone know why if they already had the 318 in production making them why would they have tooled up to make the opposite rotation that had to be more costly then changing the rotation in the gear box?? I do understand the need for both rotations but I work in the automotive world and also see a lot of poor choices in design but this one seems to have had a reason.
I have a couple theories on this.
First, it's only been recently that a marine trans was developed that offered a reversing ability as strong as forward gear. Up until that, reverse was always the weak link in a trans.
Second, the early engines used in planing boats tended to be long stroke with very heavy rotating assemblies. This can give you a gyroscope effect and cause strange handling characteristics. The original Chris Craft V8 (825 cubes or something like that) was known for this. Put two side by side turning the same direction and it may get real ugly.
Muskegon Lake
1972 32' Express flybridge
"AL13"
Twin 318s
On board air & prime 920
1963 Thompson Super Sea Lancer
Graymarine 327
1961 Alumacraft 12'
'55 10hp Johnson
javalin390
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Re: Reverse rotation?

Post by javalin390 »

Some very interesting theories and all very plausible. Jeff's idea that the design of the reversible transmission may have come later in the game. And too, the concept of the reverse rotation engine greatly influences handling characteristics on a single screw, and the harmonic dynamics on a twin. Which brings to mind an interesting story from NASCAR and INDY race car legend Smokey Yunick. During the 50's, when Indy was still running the Offenhauser design racecars, the design where the driver sat side-by-side with the engine in the chassis, Smokey figured out that the torque of the Offy engine would centrifugally push the car toward the outer wall. He proceeded to reverse the rotation, grinding a custom cam, reversing the ignition system, etc...The result is, as you would expect, forced the car toward the inside edge of the track, increasing speed and handling prowess. Naturally track officials were scratching their heads not being able to figure out why Smokey's Offy was blowing the doors off other similarly designed Offy's. It's been said that 95% of NASCAR's rulebook was written to counter many of Smokey's ingenious "tricks", his many books are a good read, even if you're not a gearhead.
Jim Elias
1974 37' SedanFlybridge
Twin 360 Chryslers.
Marblehead, Ohio
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