Why Commerical boats around here use L/H props

i have a R/H diesel engine but a Transmission that turns L/H and a L/H prop, When i ask i was told since it was a shrimp boat the commerical guys like the L/H props ? Anyone even heard anything like that, i don't see the advantage between left or right if its a single screw. However i did walk the local boat yard and i would say 75% of the larger commerical boats are L/H props.

My 40 yr old Volvo outdrive came standard w/ LH prop...could it be that it 'walks' in the preferred direction?

With a LH prop the boat pulls to stbd. in reverse.

Boats to your right have the right of way and need to be seen better. So helms are usually on the stbd side.

When landing on the stbd side as you reverse to stop the propwalk pulls your stern nicely.

Most engines are CCW rotating and most gearboxes reverse rotational direction to CW in fwd gear ... CCW in reverse and that produces prop walk to the port side in reverse. Not as described as ideal above. Most modern gears have 2 shafts and 2 sets of gears but the very popular Brog Warner Velvet Drive planetary drive gears rotate their output shaft the same way as the input shaft. Skippers w modern 2 shaft gears will prefer landing on the port side so reversing dosn't leave the stern hanging out away from the float, however the helm is still usually on the stbd side so they haven't got an optimal view of vessels approaching that have the right of way. Hope I got all those directions right.

jeffnick,
Yes

Honey,
Most of those commercial boats are probably quite old and have BWVD gears. Like my Willy. Preferred. But if you have a RH prop and your'e more concerned about graceful landings than legal matters and have a port helm you would consider the RH prop and port helm preferable.

I suspect the designer/manufacturer/builder of the boat puts an engine and transmission (Volvo calls it a "reverse gear") in it and then uses whatever prop causes it to go forward in "forward gear".

Eric X2

On some outboards and I/O's they have dual counter rotating props. I suppose that eliminates prop-walk. I suppose it'd be difficult to do with an inboard, shaft issues I suspect. On a pod drive it could be done, I think.

Oh wait, it's been done on a Zues:


Prop walk gone? But at what cost?

What ever the reason for the starboard prop walk and I am grateful as they usually ask for a starboard tie, which leaves more port ties for ME!

Thanks Tom ... that makes me feel like I just aced a Bio101 test.

Ram,
Who cares about prop walk when the prop rotates. But it would be nice if a boat went straight in fwd gear w/o rudder correction.

There's so much P factor on my 40hp OB skiff that when alone sitting on the stbd side is'nt enough to compensate. The boat still rides high on the stbd side. And I'm sure prop walk plays a part too.

I wonder what those things cost ... not the Zues drive but the counter rotating leg like the Volvo. Do they have a patent or do others not offer it because of the expense. Do some outboards have CR props?

The boat will be created with the engine off center to angle the prop 4 or 5 deg so it will run straight at cruise with no rudder input.

They did it in the 1920's , so todays NA should have a good idea if you ask for it.

Yes FF,
I've seen quite a number of boats w off ctr prop shafts and some w shafts not parallel w the keel. My Willy is on CL and requires port rudder to go straight w/o hydraulic steering. I got hydraulic steering and it's fine except it's not as light as I was expecting.

A three-degree left rudder is necessary on my boat to keep a straight course in powered forward motion. The hydraulic steering makes it unnoticeable, and with hands off the wheel the rudder remains in the same position. The angle is only apparent with the rudder indicator.

Mark,
Exactly.
So if the manufacturer spent a little more effort and put in an offset shaft you'd go straight w a dead ahead rudder. Your 3 degree rudder creates drag ... drag that wouldn't be there if you had a twin w CR propellers. And I think it would reduce prop walk too. As it should be. Same w an Aqua Drive type drive system. As it should be but if they made the perfect boat we couldn't afford it. Each type of build has it's drawbacks.

Most boats would profit from a CPP setup, but who would pay for it?

markpierce said:

A three-degree left rudder is necessary on my boat to keep a straight course in powered forward motion. The hydraulic steering makes it unnoticeable, and with hands off the wheel the rudder remains in the same position. The angle is only apparent with the rudder indicator.

Click to expand...

But you don't know if the rudder indicator is accurate.

It could be 2 degrees 4 degrees or whatever but it is unquestionably there. Just like wing tip vortices will always be at the wing tip w an angle of attack. It's a given. To what extent it exists varies from boat to boat but it is always there. Mark's indicator is probably right but if the rudder input was in the wrong direction then I'd question his indicator.