My props rotate the wrong way?!?

[kostond]

I was at the marina talking with a friend today when the discussion turned to prop rotation:grin:. I explained to him that the rotation on my boat was the opposite of most boats I see. Viewed from the stern my port prop spins "clockwise" and my starboard prop spins "counterclockwise".

He thought that was all wrong and paraded me down to some of his dock buddies so they could set me straight.

They all seem to think that my configuration renders the boat very inefficient at traveling through the water.

They said that when the props spin like most boats the props are biting into clean water as opposed to the turbulent water found torward the center of the boat.

As evidence they predicted that my boat is sluggish at rotating with one engine in forward and the other in reverse.(it is, which is why I think a previous owner installed bow and stern thrusters)

They also believe my fuel economy would improve because the boat will move through the water more easily. I only averaged 0.8mpg bringing the boat home from NJ a few weeks ago. I honestly expected to get a little over 1mpg.

They just about have me convinced. Any opinions out there?

Nick K

 

[Air O'Nautical]

Would it work to change the transmissions right to left and left to right.
Then, do the same with the props???
Seems like it would work.....but, that could be the wine talking.

 

[The Bill Collector]

my previous SR was a 1989 300 Weekender with T-454's straight shaft. They rotated as yours do..... And when I got my present vessel they run opposite in rotation and it was a real mind over matter to make my hands run the controls appropriately..........

 

[dpmulvey]

Yours are assbackwards Nick. See if you can get it changed. Depending on the transmission, it may be as simple as throwing a switch or a lever.

The matter is not so much clean or dirty water as it is lift. Your rotation was not uncommon 30 to 40 years ago. Then a brain cell set in.

Props rotating from centerline outward provide lift to the stern and get you over the hump quicker.

The opposite is true of props turning inward toward the centerline. They cause suction which counters trying to get on plane. However, friends that had it years ago told me that setup around a dock is unbelievable for quick maneuvering as your are lifting the stern to move the boat.

 

[kostond]

I left out this part of the story earliear but one of the guys said that since I have zf gear boxes they could just reverse the transmission cables. Those boxes are designed to run at full rpm in either direction. It would then be a simple matter of swapping props.

Like I said before not very maneuverable when the engines are opposing thrust. David, what you said about lift has me thinking though. Coming home i found that the more trim tab I gave the boat the faster it went. On plane it definitely drives with a bow up attitude. I wonder if this being caused partly by the suction you describe.

Nick K

 

[Hampton]

That is what I was going to recommend looking in to. Switch the cables, switch the props.

 

[UPfreebird]

Not sure if your boat is the same as a mechanial operation for a machine,...but if we hook up the power backwards,...the motor will spin backwards. Switch them back correctly, and things go in the correct diretion.

But again,...I am not sure if this would work for your application being a gas powered motor and not an electric motor.

Unless your boat is so advanced that you have diesel motors that run to charge an electric motor which in turn spins your prop. Just like a train would do.

 

[Air O'Nautical]

That is what I was going to recommend looking in to. Switch the cables, switch the props.

That sounds much easier and should work.
(dam red wine)

 

[JVM225]

Not sure if your boat is the same as a mechanial operation for a machine,...but if we hook up the power backwards,...the motor will spin backwards. Switch them back correctly, and things go in the correct diretion.

But again,...I am not sure if this would work for your application being a gas powered motor and not an electric motor.

Unless your boat is so advanced that you have diesel motors that run to charge an electric motor which in turn spins your prop. Just like a train would do.

That doesn't work in gasoline engines. Years ago they used to put counter rotating motors on one side in boats with twin engines. They had different components than standard rotation. Then in the eighties someone got the idea that it would be much easier to have both motors standard rotation and have one of the transmissions perform the needed counter rotation.
Then again you have boats like mine that have outdrives and everything spins the same way. A short time later they figured out that they could make one of the props counter rotate by using the lower unit of the outdrive. If I want to change mine to counter rotation I just need a lower unit, one new prop, and switch some things around at the helm.
The OP might indeed be able to swap things around without having to physically switch the transmissions from one side to the other, but I would absolutely check with the manufacturer of those transmissions to make sure that was the case. It is possible that the reverse gears are not the same ratio as the forward gears and swapping cables or switching something will cause undue stress on the transmissions.
I know that if I wanted to just change the rotation on one of my drives I could, in theory, just switch a cable position at the helm and swap out the prop on that side to a counter rotating prop. It would work for a very short time because all I would really be doing is running the one drive in reverse at a much higher RPM for longer periods of time than it was designed to do. The drive would self destruct quickly.
It's possible that the same would be true for transmissions in the OP's boat.
I see that the OP's boat is a 1986. Is it possible that one of his motors is counter rotating? I thought that many of the manufacturers didn't change over to standard rotation in both motors until the late eighties.

 

[Woody]

I would check with SR to see what this boat was designed for/with. There may be hull differences( prop tunnels vs not) that make any changes kind of moot.

 

[billnpat]

I don't know what my rotation is on my 310

how can i check it????????

 

[JVM225]

I don't know what my rotation is on my 310

how can i check it????????

Bill,
Since you list your boat as having V drives then I imagine that the motors are standard rotation, but one of the transmissions (probably the port) and the prop attached on that side of the boat is counter rotation.

 

[kostond]

JVM225, you're spot on about verifying that the gear boxes can work unboth directions. I plan on checking on it. I am not interested in ruining an otherwise perfectly good gearbox. The boat was repowered in 1996 with Volvo penta diesels and new running gear.

The hull does have prop tunnels. I am not sure why it would be a moot point. I have never noticed anyone with late '80's 390 EC's complain about sluggish response during manuevering. From the rubrail down the hulls are the same. Do prop tunnels help or hurt performance?

Nick K

 

[billnpat]

Bill,
Since you list your boat as having V drives then I imagine that the motors are standard rotation, but one of the transmissions (probably the port) and the prop attached on that side of the boat is counter rotation.

I thought it might be also......Thanks JVM...

 

[Jimmy Buoy]

I don't know what my rotation is on my 310

how can i check it????????

Simply check the rotation of each prop. The Stb prop should be RH (right handed turn or clockwise). You can also tell by the angle of the blades which rotation direction will cause the prop wash to go behind the prop.

 

[25thmustang]

My 1987 Vintage boat has counter rotating motors. Although the OP has been repowered, I would imagine a lot of the same vintage Sea Rays would have counter rotating. Found this out the hard way, when doing plugs on my boat.

 

[billnpat]

Got this from boating mag today

Counter-rotating props negate any torque caused by two propellers spinning in the same direction.
This allows boaters better control throughout the RPM range, particularly in rough seas

 

[JVM225]

Got this from boating mag today

Counter-rotating props negate any torque caused by two propellers spinning in the same direction.
This allows boaters better control throughout the RPM range, particularly in rough seas

I don't have much of a problem running at cruising speed, but I can attest to the lousy handling around the dock with both props spinning the same way. Especially when trying to back up.
Years ago I had a Silverton with a single engine and that boat was much easier to back in to a slip than my twin engine Sundancer.
I get a kick out of all the dock chair captains who like to tell me how easy it should be to back my twin engine boat in to a slip with inches clearance on each side. They look at me like I'm crazy when I tell them the props both spin the same way and it handles nothing like a typical twin engine boat.
I love my boat in general. There are a few things about it that I don't like, and the props spinning the same way is right at the top of the list.
I've been keeping my eye out for a good used counter rotating lower unit for a while now. I thought I had one last summer. Even had it shipped to me from the seller I found on Ebay who advertised it as counter rotating. He was wrong and I had to ship it back to him for a refund. At least I found out it was standard before I put it on the boat.

 

[billnpat]

I thought all props ran counter wise.....is it because you have alpha drives?

 

[UPfreebird]

If it goes the wrong way, do you go backwards when you throttle forward?