Question about prop and shaft rotations... we have twin engines with
counter rotational engines, 1 clockwise, 1 counter clockwise.... we also
have a LH prop and a RH prop currently not on the shafts... thus the
question...

Trying to confirm that a clockwise turning shaft in forward gear needs a LH
prop and thus a TH prop would go on a counter-clockwise turning shaft in
forward gear... can someone confirm my thoughts???

Thanks for any and all responses... and no I am not the one who removed the
props and failed to record which one came off which side...

My understanding from what I've read ... RH=clockwise and
LH=counterclockwise ... the opposite to your thoughts. At least it's real
easy to find out, and to correct if you get it wrong the first time.

"Tony Abbott" wrote in message
om...
Question about prop and shaft rotations... we have twin engines with
counter rotational engines, 1 clockwise, 1 counter clockwise.... we also
have a LH prop and a RH prop currently not on the shafts... thus the
question...

Trying to confirm that a clockwise turning shaft in forward gear needs a
LH
prop and thus a TH prop would go on a counter-clockwise turning shaft in
forward gear... can someone confirm my thoughts???

Thanks for any and all responses... and no I am not the one who removed
the
props and failed to record which one came off which side...

Bowgus says:

At least it's real
easy to find out, and to correct if you get it wrong the first time.

And please let us know when this trial is - coz it's also great fun to watch
when it is done wrong the first time ;-)

Steve

Tony Abbott wrote:
Question about prop and shaft rotations... we have twin engines with
counter rotational engines, 1 clockwise, 1 counter clockwise.... we also
have a LH prop and a RH prop currently not on the shafts... thus the
question...

Trying to confirm that a clockwise turning shaft in forward gear needs a LH
prop and thus a TH prop would go on a counter-clockwise turning shaft in
forward gear... can someone confirm my thoughts???

Thanks for any and all responses... and no I am not the one who removed the
props and failed to record which one came off which side...



Depends on where you view it from obviously, the usual thing is to view
it from "aft" (that's the back Harry)

Viewed from aft a right-hand propeller turns clockwise & left-hand
anticlockwise.

This causes confusion because some/most engine manufacturers, even
today describe the engine's rotation when viewed from forward (that's
the front Harry) i.e. an engine described as having left hand rotation
at it's output by "some" engine suppliers, will need a right hand
propeller (ask Gould, giggles all round here at the time; amateurs
buying from & then spruiking/spamming for other amateurs:-)). So with
your question Tony, make sure you know which engine "output shaft" turns
clockwise etc viewed from aft!!!!, the output shaft obviously turns in
the same diection as the prop (hopefully:-)), regardless of how the
engine rotation is described. (no point simplifying for Harry & his
tribe of simpletons wouldn't get this not ever, too uneducated &
basically stupid)

With counter rotating twins the preferred setup is to have the right
handed prop (clockwise viewed from aft) on the starboard side (that's
the right hand side of the boat Harry) & the left handed prop
(anticlockwise viewed from aft) on the port side (that's the left hand
side of the boat Harry)

This means that counter rotating twins should have the props turning
out away from each other at the top. So prop walk can be harvested to
advantage when maneuvering (it behaves like a wheel, at the bottom of
the prop the water is denser than the top, imagine Harry upside down).

Say trying to spin the boat to starboard with twins the starboard,
right handed prop (now turning anticlockwise from aft in reverse gear)
will try to walk the stern across towards port, the port left handed
prop (also turning anticlockwise from aft still in forward gear) will
also be trying to walk the stern to port, so even if the boat stays
almost stationary, it will assist the bow to swing to starboard. (again
no attempt to help Harry & his thugs, they're still working on the port
& starboard thing:-) no no seriously for a minute, are your elections
sort of a nation wide IQ test??? it certainly seems that way if you look
at rec.boats, the lib voters are the uneducated winers & the repubs are
the ones who take care of the real things & thankfully for me, the rest
of the free world)

K

Aft looking forward, it is the direction of the top of the shaft.


"Tony Abbott" wrote in message
om...
Question about prop and shaft rotations... we have twin engines with
counter rotational engines, 1 clockwise, 1 counter clockwise.... we also
have a LH prop and a RH prop currently not on the shafts... thus the
question...

Trying to confirm that a clockwise turning shaft in forward gear needs a
LH
prop and thus a TH prop would go on a counter-clockwise turning shaft in
forward gear... can someone confirm my thoughts???

Thanks for any and all responses... and no I am not the one who removed
the
props and failed to record which one came off which side...

On Tue, 21 Sep 2004 23:41:39 GMT, "Tony Abbott"
wrote:

Question about prop and shaft rotations... we have twin engines with
counter rotational engines, 1 clockwise, 1 counter clockwise.... we also
have a LH prop and a RH prop currently not on the shafts... thus the
question...

Trying to confirm that a clockwise turning shaft in forward gear needs a LH
prop and thus a TH prop would go on a counter-clockwise turning shaft in
forward gear... can someone confirm my thoughts???

Thanks for any and all responses... and no I am not the one who removed the
props and failed to record which one came off which side...


Here is your difficulty: a clockwise turning shaft, looking forward,
is a counter clockwise turning shaft, looking aft.
For aircraft certainly, the convention is to use the pilot's view,
looking forward, to decide which direction a prop is turning.

Anyway, looking forward, a prop shaft turning clockwise takes a prop
which turns clockwise in forward gear.

Perhaps it would help you to consider a regular wood screw. These are
screwed clockwise. So if you set the point of a wood screw forwards,
the edges of the screw are angled in the same direction as a RH prop.
The head of a woodscrew turns clockwise to screw into wood, and a
RH prop turns clockwise to screw forwards into water.

Clear as mud? I thought so!

Brian W

With counter rotating twins the preferred setup is to have the right
handed prop (clockwise viewed from aft) on the starboard side (that's
the right hand side of the boat Harry) & the left handed prop
(anticlockwise viewed from aft) on the port side (that's the left hand
side of the boat Harry)

This means that counter rotating twins should have the props turning
out away from each other at the top. So prop walk can be harvested to
advantage when maneuvering (it behaves like a wheel, at the bottom of
the prop the water is denser than the top, imagine Harry upside down).

Say trying to spin the boat to starboard with twins the starboard,
right handed prop (now turning anticlockwise from aft in reverse gear)
will try to walk the stern across towards port, the port left handed
prop (also turning anticlockwise from aft still in forward gear) will
also be trying to walk the stern to port, so even if the boat stays
almost stationary, it will assist the bow to swing to starboard. K





The above is basicly correct... but not the full story.
The navy tend to put props on the other way around because props turning
inwards towards each other at the top is more efficient
This is done on the basis that navy ships have tugs etc to assist manouvers
in port.. so they trade the manouverability for better efficiency at speed.
When all is said and done, you will have to fit the props to suit the
engines/gearboxes as fitted to the boat unless you wanna swap them round?

Frequently, I'll read a post discussing prop rotation, where the writer
says that he has twin screw, counter rotating props, which leads to
confusion, as this really doesn't tell you what you need to know.
Ignoring engine rotation ..... In the past, some setups used a left hand
and right hand engine to create "counter rotation", but to my knowledge
this is rare nowadays.
When looking at the prop rotation, you are always looking at the props
from astern of them looking forward.
When going ahead, a RH prop will turn clockwise and a LH prop will turn
counterclockwise.
In twin screw applications there are two possible configurations
......(there's a third and fourth, but these are not worth mentioning G)

"inboard turning" - the stbd shaft has a LH prop and the port shaft
has a RH prop.
"outboard turning" - the stbd shaft has a RH prop and the port shaft has
a LH prop.

Outboard turning is the most frequently seen application. The reason, is
handling, as, for the most part the same boat with "inboard turning"
will handle totally differently from one with "outboard turning" props.

Outboard turning: The individual props, complement the offset thrust of
props with prop walk, i.e., when going ahead on the stbd shaft alone the
offset thrust tends to turn the boat to port while at the same time,
propwalk will pull the stern to stbd, increasing turning rate. Going
astern, the offset thrust/pull and propwalk work together to pull the
stern to port.
The advantages to this are fairly obvious ..... you can use engines
alone to steer both ahead and astern, and to increase turning rate you
can simply add throttle and basically leave rudders "midship" (G not a
practice I agree with in all cases).
Naturally, the degree of ease that a boat with this configuration will
turn or twist, or walk, will depend on other factors as well (prop
spacing, rudder size, hull configuration, etc.).

Inboard turning: Totally different (G normally)! If your one of those
who never learned how and when to use rudders when maneuvering your twin
screw, outboard turning, propped boat, standby, you may be in trouble.
With this configuration, the offset thrust is countered by the propwalk.
What happens when you put the stbd shaft in gear, ahead or astern? You
go straight. Add throttle, what happens? You go straight. Try to twin
screw? You sit there and throw water ahead and astern. Solution? G
That's why they put those rudders back there and you best start learning
to use them under maneuvering conditions.

Now, before someone with a boat with inboard turning props jumps in, in
anger, the degree of how straight your boat will go or how hard it is to
twin screw without rudders, will vary, from what I describe above, to
something just below a poor handling twin screw with outboard turning props,
BTW, there ARE advantages to inboard turning props.

otn

On Tue, 21 Sep 2004 23:41:39 GMT, "Tony Abbott"
wrote:
I have to do this stuff the old fashioned way. Put one prop on one
shaft. Put that engine in forward gear and crank the starter. If the
prop goes the right way, It's good to go.
Dan