Stop the Prop or Not

[Sailfree]

I have just taken delivery of a Jeanneau 43 DS fitted with a 75hp Yanmar engine and a fixed prop. The Jeanneau handbook says when sailing engage reverse to lock the prop. When I do this the gear lever locks in the astern position and I have to start the engine at tickover revs effectively trying to go astern while sailing forwards!. Once the engine is going I can quickly go to neutral and then forwards. Has anyone had any experience of this or can offer advice please.

 

[ubuysa]

I have a 10-year old Jeanneau 45.1 and I also put the gear lever in reverse whilst sailing to stop the prop. BUT I was warned to watch the speed through the water when doing this. I was told by the previous owner not to attempt to move the gear lever unless the speed was less than 4kts to aviod damage to the gearbox. Perhaps this is what causes yours to be "locked"? Maybe you're sailing too fast to move it safely back to neutral?? Try slowing to below 4kts and then move into neutral before starting???

Just my thoughts.......Tony C.

 

[bobfrost]

I tend to leave motor out of gear when sailing so that in event of battery failure I can always slip into gear to bump start.

I don't know if this helps you.

 

[Robin]

Locking the prop gives the least drag under sail. There will be enumerable arguments for and against that but it is nevertheless the general perceived wisdom. Some gearboxes are not designed to run either by prop spin which may result in lack of lubrication, but in any event there will be unnecessary wear on bearings and shaft seal not to mention irritating rumbling noises.

Sticking in gear under sail is normal on some gearboxes, notably Volvos. The gearbox on our previous boat with a Volvo MD22L did that from new, all it takes is a quick 2 second flick of the starter on the switch with the lever as close to neutral (thus tickover) as possible to release it and put it into neutral for starting. If it actually starts whilst doing this it is not a problem as at tickover revs only in reverse it will be simple enough to move it into neutral or ahead as you wish.

We now have a Yanmar 44HP on our current boat which has a Brunton feathering prop and this is locked by stopping the engine in forward gear - yet another variation!

 

[TigaWave]

On the Volvo 2003 43hp with sail drive the instructions strictly said do not leave the engine in gear, I did once and it locked up the gear lever!
On every other boat with a fixed prop I've put them in gear to save noise , bearing wear, and stern gland dripping.
But the Volvo gearbox definately didn't like it.

 

[nealeb]

My Yanmar 3GM similarly locks up in reverse sometimes but starting in gear is no real problem - and my gaffer tends not to be doing high speeds under sail at times when I might want the engine! It is important (at least on my engine) to use reverse and not forward as this tends to pull the cone clutch into engagement; using forwards tends to pull the cones apart so there could be a tendency to slip and hence cause clutch wear.

 

[snowleopard]

Interesting advice on the 3GM. Do you have shaft or saildrive?

 

[ArgoNot]

There is definitely less drag with the prop stopped. How am I sure? When I stop the prop in my aeroplane the glide ratio, the relationship between height lost against distance travelled in a glide, is better ie. less drag.
It has to do with the drag of the disc occupied by a spinning prop against the drag of the individual blades.

 

[rwoofer]

I think you'll find that when a prop is stopped it is effectively stalled and therefore offers less drag than a rotating prop which is acting aero/hydrodynamically therefore creating far more drag.

The same reason why a sail that is stalled offers less power than a sail that is sheeted correctly with good aerodynamic flow.

 

[corncob]

Sailfree, depends on what gearbox is fitted to your 4JH3-TE? Is it the KM4A or the KBW21? You can lock the prop on th KM4a but not the KBW21. KM4a has a cone clutch, KBW21 is muliplate. The KBW21 will need a shaft brake. Its also a no go if you have the KMH4A the hydraulic version! You can check what gearbox you have by checking the engine designation:
1. 4JH3-T(B)E = KM4A
2. 4JH3-TE = KBW21
3.4JH3-THE = KMH4A

I hope this helps?

 

[ArgoNot]

I'd agree that the blades are probably stalled when the prop's stopped, but that's the highest drag configuration of all. However that highest drag configuration of the individual blades is still less than the overall drag of the prop disc, hence a better glide ratio prop stopped or, if you prefer, lift/drag ratio. It's the same thing.

 

[nealeb]

[ QUOTE ]
Interesting advice on the 3GM. Do you have shaft or saildrive?

[/ QUOTE ]

Shaft - saildrive with my long keel would need a leg about 6' long! No idea whether it increases or reduces drag, but I hate the continual rumble in the cockpit when the prop is turning. As opposed to the grumble in the cockpit when the engine is running, of course /forums/images/graemlins/smile.gif

 

[angelsson]

I like to stop my prop for many of the reasons outlined by others here.
I find it is a matter for individual boats and their engine and gearbox configurations.
My gearbox makers advised me not to stop it in gear as I may not get it out again, and cause possible damage.
My prefered method is to use a rod through the flexicoupling, about pencil thin, and made of wood.
It is strong enough to stop the shaft turning, but will easily snap if I need to start the engine quickly, without any damage whatsoever, have tested it and it works fine.
Hope this helps.
Mike

 

[rwoofer]

Can't say I properly qualified to be 100% certain on this point, but if you take the sail analogy then the power developed is far higher when not stalled. If you think of this power as a slowing force, that is how you explain a rotating prop having more drag.