Stuffing box... Sailing.. prop left to spin

[thedude0]

Hi...maybe someone might know.. not sure with the older type of stuffing boxes... which also use a hose from the engine's cooling sytem to lubricate shaft...

if when the engine is not running and the shaft is left to spin whilst sailing ...does this cause any pressure on the shaft packing... since it is not getting the cooling from engine water system...?

[sailing_gal]

Generally, you do not want to leave the shaft spinning while sailing. After you have turned the engine off, move the shift lever to forward or reverse to stop the shaft from spinning.

[thedude0]

I see ok thanks...thing is they say there is generally more drag especially in my case with quite large three blade prop if its not left to spin so i prefer to let it spin if it causes no wear ..

[Wotname]

Also not a good idea to leave in gear if you have a Yanmar. Plenty of threads and info to say it will void your Yanmar warranty etc etc.

[sailing_gal]

You may put it in gear briefly, just to stop the spinning, then put it back into neutral. You should read your engine brochure to see what they recommend. Yanmar has changed its recommendations in recent years, from leaving it in reverse, to leaving it in forward gear when sailing. When I have spoken to Yanmar reps, they say it doesn't make a whole lot of difference.

[thedude0]

my concern is not really the engine or gearbox but the stuffingbox...

[Sailmonkey]

Originally Posted by thedude0

my concern is not really the engine or gearbox but the stuffingbox...

Is your stuffing box a traditional flax packed one?

Does the shaft pass through a deadwood that also contains the cutlass bearing?

My inclination is to say you’ll cause no harm to the stuffing box in this scenario. I plumbed our sterntube to the engine cooling as well, but it’s to keep the bearing flushed free of sediment rather than cool anything.

[Sailmonkey]

Originally Posted by sailing_gal

You may put it in gear briefly, just to stop the spinning, then put it back into neutral. You should read your engine brochure to see what they recommend. Yanmar has changed its recommendations in recent years, from leaving it in reverse, to leaving it in forward gear when sailing. When I have spoken to Yanmar reps, they say it doesn't make a whole lot of difference.

With a big 3 blade prop , putting the transmission in gear briefly, stops the spinning briefly. Once back out of fear the spinning starts right back up.

[thedude0]

Yes it is the compression plate with two nuts type with an inlet hose from heat exchanger...even after hours motoring the shaft remains cold so the water from engine has a substantial effect...however recently when sailing with engine off the packing burnt so that is why i ask...

[Sailmonkey]

Originally Posted by thedude0

Yes it is the compression plate with two nuts type with an inlet hose from heat exchanger...even after hours motoring the shaft remains cold so the water from engine has a substantial effect...however recently when sailing with engine off the packing burnt so that is why i ask...

It got that hot from sailing!!

Maybe it’s too tight!

[thedude0]

no technically speaking it happened just as soon as i started the engine and motored the last bit

[IdoraKeeper]

Old fashioned stuffing boxes must be allowed to drip. No drip=too tight.

[jmschmidt]

As it's been said many times, a free spinning solid prop creates parasite drag equal to the surface area of a solid disk the diameter of the prop. A prop on a locked shaft creates parasite drag equal only to the combined surface area of the blades themselves. A two-blade prop, not much drag if the shaft is locked. A four or five blade prop with a locked shaft, a lot more drag but still not as much as if it were left free spinning. A lot of people don't believe that but it's true. Check with an engineer. A full feathering prop, doesn't matter because it shouldn't spin much, if at all, when feathered. If you transmission manufacture states not to lock the shaft by leaving it in gear when sailing, it's best to install a separate shaft lock and leave the transmission in neutral. Using your shaft to run an electric generator produces tons of drag. The faster you sail, the more electricity it produces same the greater the drag. Where do you think the electrical energy comes from? Same with a wind driven generator on a boat, sail or power, produces tons of drag too. When sailing it's best to lock the prop on a wind generator too. Unless you really need the electricity, run your wind generator when anchored. There is no free lunch in the world of physics.

[Rough Magic]

Second vote for putting the prop in gear to not spin. The chief designer of a major sailboat company told me the same about drag being less locked. And so much less noise.

[Sailmonkey]

Originally Posted by jmschmidt

As it's been said many times, a free spinning solid prop creates parasite drag equal to the surface area of a solid disk the diameter of the prop. A prop on a locked shaft creates parasite drag equal only to the combined surface area of the blades themselves. A two-blade prop, not much drag if the shaft is locked. A four or five blade prop with a locked shaft, a lot more drag but still not as much as if it were left free spinning. A lot of people don't believe that but it's true. Check with an engineer. A full feathering prop, doesn't matter because it shouldn't spin much, if at all, when feathered. If you transmission manufacture states not to lock the shaft by leaving it in gear when sailing, it's best to install a separate shaft lock and leave the transmission in neutral. Using your shaft to run an electric generator produces tons of drag. The faster you sail, the more electricity it produces same the greater the drag. Where do you think the electrical energy comes from? Same with a wind driven generator on a boat, sail or power, produces tons of drag too. When sailing it's best to lock the prop on a wind generator too. Unless you really need the electricity, run your wind generator when anchored. There is no free lunch in the world of physics.

Propeller Drag Test Results

Propeller Drag under sail, Article


Total Jig Drag = measured 12 pounds with no propeller mounted. Jig drag measurement was taken at WOT. (wide open throttle)

Locked Prop Drag = 45-50 pounds: When we subtract the measured jig drag, 50 -12 = 38 pounds measured of actual propeller drag when locking the propeller in reverse under sail.

Freewheeling Prop Drag = 20-25 pounds: 25 - 12 = 13 pounds of actual propeller drag when freewheeling the propeller under sail.

The locked propeller drag is 2.92 times more drag or a 292% increase in drag over a freewheeling propeller when you remove the test jig from the equation!!!!