counter rotating - port or stbd?

martini · 25 April 2008, 15:57

Does anyone know if it matters which way round the motors are on a twin c/r outboard set up? Is there an industry standard that everyone sticks to?

Thanks

karlT · 25 April 2008, 17:32

Top of blades moving towards each other. So clockwise rotation on port and anti clock on starboard. Think it has something to do with density of water and surface so any sideways movement of water is pushed together nearer surface?

Dirk Diggler · 25 April 2008, 19:03

Quote:

Originally Posted by karlT

Top of blades moving towards each other. So clockwise rotation on port and anti clock on starboard.

Are you sure about that, it's usually the other way round!

martini · 25 April 2008, 21:17

Google has it 9:0 in favour of counter rotate on the port side. How sure are you Karl?!

I'm still none the wiser about the theory behind it all

Limey Linda · 25 April 2008, 23:22

Quote:

Originally Posted by martini

Google has it 9:0 in favour of counter rotate on the port side. How sure are you Karl?!

I'm still none the wiser about the theory behind it all

Just called my Merc. mechanic who is factory trained and a 20 year offshore racing mechanic. Conventionally most riggers will mount counter rotate to port. Howver on racing boats they do it the other way round. as Karl suggested. Reasons: cleaner water turning towards each other, can mount them higher on the transom and run a higher rpm and the boat will be more stable.
Hope this helps.

martini · 26 April 2008, 07:35

Quote:

Originally Posted by Limey Linda

Just called my Merc. mechanic

You didnt do that just for me did you?!

I dont think we can class my rib as a racing boat so port it is then!

Cheers Limey

Dirk Diggler · 26 April 2008, 13:06

Quote:

Originally Posted by Limey Linda

. Howver on racing boats they do it the other way round. as Karl suggested.

That isn't strictly true.... Turning out is normal, but turning in does sometimes work better, although it nearly always gives trickier handling.

Petrov · 26 April 2008, 14:42

Its ften a counter on starboard gives more bowlift (not in all cases, depends on engine porp etc etc)

Limey Linda · 26 April 2008, 16:56

Quote:

Originally Posted by martini

You didnt do that just for me did you?!

I dont think we can class my rib as a racing boat so port it is then!

Cheers Limey

Right decision I think. I hope you have ordered a factory manual. They have excellent installation instructions. Well worth the money. About $70.00 I think and you can order on line using your engine serial number.

Matt · 26 April 2008, 19:40

Listen to dirk!!!!!

Searider · 26 April 2008, 20:23

Outward turning - clockwise on stb, anti-clockwise on port.

Gives more predictable handling but might not give the best speed.

Imagine the boat in the air leaning over to starboard - only the starboard prop is in the water. If it's turning clockwise it will tend to level the boat. If its turning the other way it will tend to increase the lean.

wavelength · 26 April 2008, 20:31

Quote:

Imagine the boat in the air leaning over to starboard - only the starboard prop is in the water. If it's turning clockwise it will tend to level the boat. If its turning the other way it will tend to increase the lean.

oooh - as explanations go I really do like that one!

Cookee · 28 April 2008, 10:40

As Dirk said turning out is the convention for regular boats - turning in can give more speed as others have said, often with more nervous handling, this is as a result of getting more stern lift with the props turning in - Searider - great story where did you get that one from?

Simon B · 28 April 2008, 12:29

So how do they do it on aircraft with props?

BogMonster · 28 April 2008, 16:52

Quote:

Originally Posted by Simon B

So how do they do it on aircraft with props?

By the time the props touch the water on a plane you have usually got bigger problems to worry about

Cookee · 29 April 2008, 14:19

Quote:

Originally Posted by BogMonster

By the time the props touch the water on a plane you have usually got bigger problems to worry about

............ And they're not that close either!

Searider · 30 April 2008, 08:38

Quote:

Originally Posted by Cookee

As Dirk said turning out is the convention for regular boats - turning in can give more speed as others have said, often with more nervous handling, this is as a result of getting more stern lift with the props turning in - Searider - great story where did you get that one from?

It's just the same as offsetting, in a single installation, a right hand rotation to starboard and a left hand rotation engine to port.

Not really a "story" was just trying to simplify the explanation.

yorfuoj · 30 October 2008, 22:45

clockwise rotation on portside and counter on starboard lifts the bow, this is true on monohulls as on catamarans.

Reciprocating that gives a more level fly, this can be used to compensate for unwanted hull behaviour

Davie · 31 October 2008, 22:34

If the engines are used and before you even think about fitting them. check the propellers are on the correct gearboxes. What happened here was a pair of engines were delivered but the propellers were on the wrong engines. There were no markings saying counter rotation or anything to that effect so engines were fitted and sure enough everything worked but yes they were both running in reverse gear. The standard box was the first to blow. Repaired then did same again. It was only noted when the clockwise propeller was shown that everything clicked what was going on. This was on mercury 200's It takes 5 minutes to check box but time well spent. Think about it its like a double wammy!

Downhilldai · 31 October 2008, 23:59

Quote:

Originally Posted by Davie

.... What happened here was a pair of engines were delivered but the propellers were on the wrong engines. ...

I've heard it all now....