prop shaft spinning when sailing

[nimbusgb]

I had the same with the 2030 and a two blade fixed prop, although it'd start rotating at 5kn.

I fitted a Kiwi. (An expensive fix mind) but you get less drag when sailing and more thrust when on engine.

You might find this interesting! Kiwis are made to autorotate slowly!

 

[nimbusgb]

The theory says locked fixed bladed prop can develop as much as 4 times the drag as a rotating one, practical testing supported the theory.

At 6 knots my old 3 blader locked in gear would have been about the same as a 100 kg pull on the aft rail! The kiwi I have replaced it with now presents a 5kg pull

http://www.kiwiprops.co.nz/documents/Drag-Thesis.pdf

 

[Deleted member 36384]

Mole Grips Do Work To Lock The Shaft and Other Forumites Claim They Use Them

ChrisD the mole grips / wrench does work. There have been a few Forumites who have stated that this is a practice that they use. You would have to search the forum, probable using the words "mole" "shaft" and limit the time to this year to find the Posts.

The posts I have seen referred to Hydraulic Gear Boxes, but the problem is the same anyway. I can not remember what size of shafts they were locking. Obviously the area of shaft that the mole grips grip on may get nicked over time. You could use a leather pad on a dry shaft between the mole grips and shaft to effect the lock without damage.

I do wonder why a gear box would lock up if left in reverse after what is a short sail period as mentioned on this thread. What aspects of the gear box design cause low torque to lock the mechanism? Is it hydraulic locking or mechanical "binding" due the gear mesh manufacturing tolerances i.e. they need a bit of oomph from the engine to start rotating but in a low torque in gear lock the friction is too much for the neutral selector to overcome? Another mystery of the Marine Leisure scene.

The only other post that I can find where someone claims a friend locks his shaft with mole grips

 

[philip_stevens]

Very slight thread drift but why is REVERSE always specified? Surely ahead is just as good and, if it's going to jam, I'd rather be jammed in ahead.

With reference to the VP gearbox, it has cone clutches, and if left in ahead, will wear the cones away - the thrust being "pull" rather than push. In the same way, leaving it in reverse jams the cones together.

Anyway, that is what I was told by VP.

Going to Hiscox books, he always left his gear in ahead so that in an emergency, he could just start the engine and motor away without thinking of gears - this was his thinking. Not mine, as it only takes a second to put it in gear.

 

[vyv_cox]

I do wonder why a gear box would lock up if left in reverse after what is a short sail period as mentioned on this thread. What aspects of the gear box design cause low torque to lock the mechanism? Is it hydraulic locking or mechanical "binding" due the gear mesh manufacturing tolerances i.e. they need a bit of oomph from the engine to start rotating but in a low torque in gear lock the friction is too much for the neutral selector to overcome? Another mystery of the Marine Leisure scene.

In my case at least it's just the selector lever that locks up, you can physically shift the Morse back to neutral but it takes a lot of force and seems like a bad idea. It's far easier and apparently harmless to start the engine with the gear in reverse, upon which the Morse goes to neutral with no effort at all.

Very slight thread drift but why is REVERSE always specified? Surely ahead is just as good and, if it's going to jam, I'd rather be jammed in ahead.

In the case of the Yanmar putting it in forward doesn't lock it. Shaft keeps rotating.

 

[Ubergeekian]

In the case of the Yanmar putting it in forward doesn't lock it. Shaft keeps rotating.

Ah.

<small lightbulb appears above head>

That explains something.

 

[Scotty_Tradewind]

Mine has a water lubricated rear end which ceases when the engine is not running. When sailing with the engine off I therefore engage reverse gear and suffer the loss of half knot in speed. Thats why we were so slow RTIR this year!