Reduction gear, prop size and draft

[a64pilot]

Originally Posted by ramblinrod

But then again, neutral and reverse is nice. ;-)

You can still have neutral and reverse without gear reduction, need a gear box if you will.
Looking at that motor and set up, it belongs on the farm, running an irrigation pump, not on a boat.

[Cadence]

Originally Posted by Jim Cate

Without wanting to sound snotty, the term "agricultural" comes to mind when viewing that setup. Probably won't see too many of them at the big boat shows, hanging from the stern of fancy yachts!

Lots of vulnerable iron mongery dangling from the engine and mounts.

not my idea of good practice, but ymmv.

Jim

Looks similar to units used to propel barges. But not as stout. and more complex. The ones I'm thing of were generally 671s and the engines sat on desk.

[ramblinrod]

Originally Posted by a64pilot

You can still have neutral and reverse without gear reduction, need a gear box if you will.
Looking at that motor and set up, it belongs on the farm, running an irrigation pump, not on a boat.

"Direct Drive" implies no gearbox.

A device between the engine output shaft and prop shaft that can decouple or reverse the direction of shaft rotation, is not direct drive.

Perhaps what you are referring to is a gear box with 1:1 ratio. This is not "Direct Drive".

[Wotname]

Originally Posted by ramblinrod

"Direct Drive" implies no gearbox.

A device between the engine output shaft and prop shaft that can decouple or reverse the direction of shaft rotation, is not direct drive.

Perhaps what you are referring to is a gear box with 1:1 ratio. This is not "Direct Drive".

I concur and as Atoll posted, the only way to get reverse with direct drive is to have a prop that allows for a full pitch reversal (or engine that will run "backwards").

[Cadence]

Originally Posted by Wotname

I concur and as Atoll posted, the only way to get reverse with direct drive is to have a prop that allows for a full pitch reversal (or engine that will run "backwards").

I've seen one that ran backwards. When the wheelhouse rang for reverse the oiler would have to manually change cams with a lever and restart her, same for forward.

[a64pilot]

Originally Posted by Cadence

I've seen one that ran backwards. When the wheelhouse rang for reverse the oiler would have to manually change cams with a lever and restart her, same for forward.

I think BIG Diesels are that way also.
Back in the 70’s I think Harley Davidson made golf carts, they were two stroke with a belt driven torque converter, like on a snow machine.
Anyway to go in reverse, you took your foot off of the gas pedal, the motor stopped and you flipped a lever, this made the starter, which was also a generator and was engaged continuously run backwards and switched the engine to fire on a second set of points. It ran perfectly fine backwards, or forwards.

[Sailmonkey]

Originally Posted by a64pilot

I think BIG Diesels are that way also.
.

I know BIG diesels are that way.

There is no gearbox on a container ship. Often there is no controllable pitch prop either.

You want ahead, start the engine. You want astern? Stop the engine, wait for it to stop turning, shift the cam, blow down in the opposite direction.

There is no neutral either. But there is quite often a huge directly driven generator that outputs something on the order of 5 megawatts at 80 rpm.

[Olddan1943]

Originally Posted by Sailmonkey

I know BIG diesels are that way.

There is no gearbox on a container ship. Often there is no controllable pitch prop either.

You want ahead, start the engine. You want astern? Stop the engine, wait for it to stop turning, shift the cam, blow down in the opposite direction.

There is no neutral either. But there is quite often a huge directly driven generator that outputs something on the order of 5 megawatts at 80 rpm.

No transmission, no gear box, they must rely totally on tugs OR perhaps this big diesel drives a reversible electric motor.

[Sailmonkey]

Originally Posted by Olddan1943

No transmission, no gear box, they must rely totally on tugs OR perhaps this big diesel drives a reversible electric motor.

The serial hybrid diesel electric ships use medium speed engines, not the large slow turning 2-stoke engines.

At low speeds the huge ships are surprisingly agile. But still must have tugs to be berthed.

[GrowleyMonster]

Originally Posted by Olddan1943

I "visited" am old boat with a one cylinder, air start motor. No reduction gear, no transmission. It had a manual variable pitch prop, controlled by a hand crank.
It had a mast for sailing, he removed it, put on a hollow tube to hold FW for heating.
Was interesting.

I would be very interested in seeing the manual CP prop. Wouldn't mind having one for my upcoming build.

[GrowleyMonster]

Originally Posted by atoll

in the old days they just stopped the engine and restarted it in the opposite direction ,quite easy to do with compressed air start

as technology moved on controllable variable pitch propellors became more common ,allowing the engine and prop shaft to run at set revs and the blades of the propellor rotated in the hub to go from forward thrust ,feathered to reverse thrust,this also allowed adjustment of pitch for differing sea conditions.
with exhaust temperature indicating the load on the engine.

Ships still do that. Direct drive, slow speed diesel, no reduction or reversing gear. Very common.

[Cadence]

Originally Posted by a64pilot

I think BIG Diesels are that way also.
Back in the 70’s I think Harley Davidson made golf carts, they were two stroke with a belt driven torque converter, like on a snow machine.
Anyway to go in reverse, you took your foot off of the gas pedal, the motor stopped and you flipped a lever, this made the starter, which was also a generator and was engaged continuously run backwards and switched the engine to fire on a second set of points. It ran perfectly fine backwards, or forwards.

Yes, I was referring to a reasonably big old diesel. I forgot about the Harley golf cart, a neighbor had for running around his small farm, that reversed that way.