Identifying LH/RH props & g/box advice

[crofty1984]

I'm familiar with the way that some propellors are "left-handed" and some are "right-handed" I was just wondering which is which. If I stand at the back of the boat and turn the prop clockwise, the boat should move forward (see pic). So do I have a right or left prop?

Also, can someone tell me if I've got this right?
In neutral, the prop should be easy to turn clockwise and anticlockwise.
In forward, the prop should "lock up" clockwise (against engine compression) and freewheel anticlockwise.
In reverse, vice versa.

Thanks,
Dan

[MOTORVATOR]

crofty1984 said:

I'm familiar with the way that some propellors are "left-handed" and some are "right-handed" I was just wondering which is which. If I stand at the back of the boat and turn the prop clockwise, the boat should move forward (see pic). So do I have a right or left prop?

Also, can someone tell me if I've got this right?
In neutral, the prop should be easy to turn clockwise and anticlockwise.
In forward, the prop should "lock up" clockwise (against engine compression) and freewheel anticlockwise.
In reverse, vice versa.

Thanks,
Dan

Viewed from behind a right hand prop will turn clockwise and left hand anti clockwise to drive the boat forward.

Do be careful turning it over in gear because it's not unheard of for an engine to start, but the right hand prop should lock up anti clockwise in forward gear and vise versa for it to be against the engine drive moment. This only for outdrives and outboards of course, a hydraulic box will lock up both ways.

For best handling the props should be mounted turning out at the top for forward motion unless you want to experiment with surface piercing props where those laws don't necessarily apply when exceeding 100 mph!

If they have been fitted wrong previously it's an easy fix to change the controls on each lever to make it right or alternatively in the back panel of the drive.

[MOTORVATOR]

Actually Crofty, if you are getting ready to stick it back in, also make sure that when you engage reverse the leg should lock down whereas in neutral and forward it is free to be lifted up. Bloody annoying if you don't as when you go to reverse the leg will just lift up and not do anything.

[Simpo Two]

MOTORVATOR said:

For best handling the props should be mounted turning out at the top for forward motion

Left and right I can understand, but 'out'?

[MOTORVATOR]

Simpo Two said:

MOTORVATOR said:

For best handling the props should be mounted turning out at the top for forward motion

Left and right I can understand, but 'out'?

Starboard prop should be RH / Clockwise, Port prop LH / Anticlockwise.

There's two reasons for it. Propwalk is then to your advantage based on the side of the boat it is on, so if you use say the stbd engine and not the other the boat will want to turn to port both through propwalk and the fact that the drive is eccentric to the centreline.

If you don't do it you have the two things cancelling each other out and the boat is not as manouervable.

The other reason is that when you set up the two drives you should link them such that when the steering play is taken up there should be a degree or two of toe out and by having them turn outwards it will hold the drives apart rather than allow them to get to a turn in state from the inevitable play in the linkage. She will then a hold a true course given the same revs on each side.

Next time you are following a twin engine up the river and he is veering from one side to the other you'll know that he very likely has a toe in situation.

Or of course he is very drunk.

[Simpo Two]

Ah, 'out' as in towards that side of the boat.

Not applicable to me then as I only have one jobbie and it's in the middle. But propwalk is an issue - one bloke said it was because the water lower down was more dense, someone else said it was caused by the angle of the propshaft. ALl I know is that my father's diesel Freeman 22 had no propwalk that I can recall, but my petrol F23 walked like a bd. What DOES cause it?

[MOTORVATOR]

Simpo Two said:

Ah, 'out' as in towards that side of the boat.

Not applicable to me then as I only have one jobbie and it's in the middle. But propwalk is an issue - one bloke said it was because the water lower down was more dense, someone else said it was caused by the angle of the propshaft. ALl I know is that my father's diesel Freeman 22 had no propwalk that I can recall, but my petrol F23 walked like a bd. What DOES cause it?

There is a thought that the prop has more bite in the lower water referred to as paddlewheel but that isn't scientifically proven.

It's actually the angle of the propshaft that causes propwalk which is why it's more prevalent on boats with shafts rather than say outdrives where you can trim it up to keep an angle of attack in line with the water. In truth though when manouevering you tend to have the drives fully trimmed in so will still see the effect.

The effect is most prevalent when in reverse and at slow speeds but will occur over the full range just at lesser degrees.

Do it in your head with two blades upright rather than more for ease.

Consider then the prop in side on view and what is happening. The propellor will be at an angle off the perpendicular to the water. Now if you look at the path taken by each blade in a single half revolution you can see that one blade is taking a longer path parrallel to the waterline than the other like an X.

So obviously as each blade is still turning in the same distance moved forward along the waterline a degree of assymetric thrust is created between the dropping blade and the rising one, hence propwalk.

Now all that is lovely in theory but in the event we have to take account of the longitudinal thrust being altered slighty by steering input in the case of outdrives and even an offset shaft installation by the boat builder to allow for it. They will even offset weight to one side to allow for torque on some boats which is why sometimes they will tend to lean over if you give a bit of welly in reverse.

So what it boils down to is that whenever you get on a boat before attempting any close quarters work you should have taken care to investigate and note in your mind just how much effect is there forward and reverse so it can be used to your advantage rather than catch you out. Just as important as taking note of wind and tide really.