To lock the prop or not?

[R.Ems]

Is a freewheeling prop more, or less, likely to become entangled with a rope or net than a locked one?

I would say, more.
But then it would no longer be freewheeling!

 

[vyv_cox]

Is a freewheeling prop more, or less, likely to become entangled with a rope or net than a locked one?

On three occasions we have had rope tangles, all when motoring. None when sailing with a locked feathering prop.

 

[ghostlymoron]

It will suffer premature wear if left to spin, as you rightly say it is due to the lack of water lubrication that the engine would normally provide.

But as others also rightly point out, the shaft speed is so low under sailing rotation the extra wear is likely to be negligable.

Regards the cutlass bearing, in reality it won't make much difference unless you are sailing across oceans. I would definitely follow what the engine/gearbox manufacturer advises as this could have much more expensive and faster damage.

How does the engine provide water lubrication? Mine is a traditional stuffing box with no water from the engine (which I understand is only necessary on a high speed motor boat). So it shouldn't damage the cutless.
Regarding the gearbox, I should do what it advises in your handbook. On my Yanmar 2gm20f, it rumbles a bit when freewheeling, but appears not to have done any damage. Locking the prop shaft is like driving a car with brakes binding and slows you down significantly specially on a long passage - I reckon 1/2 kn at least.

 

[Moodysailor]

How does the engine provide water lubrication? Mine is a traditional stuffing box with no water from the engine (which I understand is only necessary on a high speed motor boat). So it shouldn't damage the cutless.
Regarding the gearbox, I should do what it advises in your handbook. On my Yanmar 2gm20f, it rumbles a bit when freewheeling, but appears not to have done any damage. Locking the prop shaft is like driving a car with brakes binding and slows you down significantly specially on a long passage - I reckon 1/2 kn at least.

Some, not all cutlass bearings have a water injection point that is tapped off a point in the sea water line - the pressure is provided by the raw water pump.

This is typically used where one end of the cutass bearing is 'blind' and has no natural water flow (i.e a long keel yacht or inboard bearing). A typical external P-bracket bearing does not need this as the water can flow through when the vessel is in motion - this is also why the guidance is not to put the shaft anode too close to the P-bracket, as this can obstruct water flow.

Regarding transmissions - again, follow the advice of the manufacturer. If they say to prevent the transmission from rotating when sailing then you should do this. If sailing performance is a requirement, fit a folding prop (or similar). I have rebuilt and replaced many transmissions that failed due to idling.

 

[harvey38]

What does your engine manufacturer say?

Personally, I don't lock the prop as is what Volvo Penta say in the manual. Before I switched to a folding prop we did a wee experiment 'locked and unlocked' - locked we lost 0.5 kt, or 12nm in 24 hours just over two hours drinking time in the pub.

Owning a mobo it hadn't occurred to me that 0.5 of a knot would equate to 12 miles in 24 hrs, a significant impact and quite thought provoking. Thanks for pointing that out ???

 

[ghostlymoron]

Owning a mobo it hadn't occurred to me that 0.5 of a knot would equate to 12 miles in 24 hrs, a significant impact and quite thought provoking. Thanks for pointing that out ???

On 2 week ocean crossing, it's very significant 12 x 14 = 168nm or day to 1.5 extra days.

 

[scottie]

Is fitting water scoops an option to lubricate the bearing it has been used in the past but not shure if still done

 

[Daydream believer]

On 2 week ocean crossing, it's very significant 12 x 12 = 144 nm or day to 1,5 extra days.

I thought that there were 14 days in 2 weeks. I suppose with the current airline delays at departure one might be a bit confused if one's holiday was cut short ?

 

[vyv_cox]

Is fitting water scoops an option to lubricate the bearing it has been used in the past but not shure if still done

I have seen it on a relatively new small mobo but not on a yacht. The boat was probably capable of 20 knots.

 

[cid]

Is a freewheeling prop more, or less, likely to become entangled with a rope or net than a locked one?

Ok .I am no expert BUT I do recall reading that it is a question as to the method of how you stop the shaft spinning. Forget drag. The advice I recall was NOT to put it in gear. Why , when you wanted to take it out you might require force.This will damage the clutch cone. My late friend did this while racing .
Later he had problems and had to have a new clutch cone installed. The cone cost around 800. My research at the time revealed that putting it in gear while sailing and then having to use pressure to disengage it resulted in damaging the cone . Yes the prop spinning would put wear on the main bearing in the gear box, however this would take considerable sea miles ( thousands ) before damage would happen and would cost far less to repair.
.

 

[KevinV]

I was thinking about this a bit more - if you really do want waterflow through the bearing you could make a T in the hose, then run a small bore hose to the bilge with a valve on the end, allowing a small flow of water through the bearing (so long as the bilge pump works!)
Almost certainly pointless, but just a thought ?‍

 

[vyv_cox]

Ok .I am no expert BUT I do recall reading that it is a question as to the method of how you stop the shaft spinning. Forget drag. The advice I recall was NOT to put it in gear. Why , when you wanted to take it out you might require force.This will damage the clutch cone. My late friend did this while racing .
Later he had problems and had to have a new clutch cone installed. The cone cost around 800. My research at the time revealed that putting it in gear while sailing and then having to use pressure to disengage it resulted in damaging the cone . Yes the prop spinning would put wear on the main bearing in the gear box, however this would take considerable sea miles ( thousands ) before damage would happen and would cost far less to repair.
.

The answer to this is simple and is advocated by gearbox manufacturers. After sailing start the engine in either reverse or forward, which ever locks the prop. Then put it into neutral, without needing any force. We have been doing this for years.

 

[Porthandbuoy]

The answer to this is simple and is advocated by gearbox manufacturers. After sailing start the engine in either reverse or forward, which ever locks the prop. Then put it into neutral, without needing any force. We have been doing this for years.

Now that I like the sound of.
Intuitively it always seemed to me it was the act of engaging / disengaging the gearbox while the engine was stopped that would most likely cause damage. Of course the proper solution would be to fit a feathering or folding prop, but that could turn into something akin to an anchor thread!

 

[onesea]

I lock the prop by putting in reverse,because the rumbling when sailing annoys me.

Thanks Vyv for the excuse to start engine in reverse because I forget to put in neutral

 

[Moodysailor]

Ok .I am no expert BUT I do recall reading that it is a question as to the method of how you stop the shaft spinning. Forget drag. The advice I recall was NOT to put it in gear. Why , when you wanted to take it out you might require force.This will damage the clutch cone. My late friend did this while racing .
Later he had problems and had to have a new clutch cone installed. The cone cost around 800. My research at the time revealed that putting it in gear while sailing and then having to use pressure to disengage it resulted in damaging the cone . Yes the prop spinning would put wear on the main bearing in the gear box, however this would take considerable sea miles ( thousands ) before damage would happen and would cost far less to repair.
.

The gearbox you are referring to is almost certainly a Volvo Penta MS series. From memory, I don't think those transmissions need to be locked in gear so i'm not sure why that was done (I could be mistaken).

The input shaft will be a lot more expensive than a cone replacement, but yes - it would take a lot longe to wear out too.

 

[Poignard]

If engaging a gear to prevent the propeller, why do people think it better to engage reverse gear and not ahead?

 

[vyv_cox]

If engaging a gear to prevent the propeller, why do people think it better to engage reverse gear and not ahead?

Because only one of them locks the shaft. In forward my Yanmar box continues to rotate under sail with my Bruntons prop. To get it to feather I have to select reverse to lock the shaft.

 

[Poignard]

Because only one of them locks the shaft. In forward my Yanmar box continues to rotate under sail with my Bruntons prop. To get it to feather I have to select reverse to lock the shaft.

Thanks for explaining that.

It's not a problem with my gearbox (ZF BW7), either forward or reverse locks the shaft.

 

[Moodysailor]

If engaging a gear to prevent the propeller, why do people think it better to engage reverse gear and not ahead?

In our previous boat with a hydraulic gearbox, neither would work. We had a seperate shaft brake. I do like the shaft brake

 

[zulloboy]

If engaging a gear to prevent the propeller, why do people think it better to engage reverse gear and not ahead?

For Yanmar engines with Kanzaki cone clutch transmissions, the cone assemby engages with helical splines on the output shaft. The direction of the helix is such that the engine torque acting on the cone assembly will push it harder into the mating concave clutch part, thus greatly increasing the clutch grip.
The torques are reversed when the engine is not driving the prop (ie when sailing), and with the transmission engaged in forward the torque from water flowing over the prop tends to drive those mating clutch parts apart which reduces friction and can allow rotation, especially if the cones are slightly glazed. This wil very quickly completely glaze the clutch cones, causing the slipping familiar to any long-term user of these units. With reverse engaged, the torque will tend to drive the clutch parts together, thus preventing rotation.

Cheers, Graeme