lock the prop or not

[lateron]

Following last month's article in Yachting Monthly which demonstrated that a sailing boat's speed will indeed be increased by letting the prop spin [due to less drag], I wondered what people are doing on their own boats.
Without going into all the arguments of a previous thread on this subject, is it safe for a modern Yanmar [say 2004 GM20] diesel to be sailed letting the prop spin. My engine handbook gives no guidance on this and no warning not to let it spin. But I have read warnings or opinions that the gearbox might overheat.

What is current thinking. Recently I've let mine spin, the only downside being slight noise. Answers on a proboard please!

Regards Ron

[pbunning]

Change your prop for a folding prop. Performance under sail will be much improved.

[j]

is it safe for a modern Yanmar [say 2004 GM20] diesel to be sailed letting the prop spin.

Advisory Number: MSA08-003:
DATE February 8, 2008 Dealers and OEMs
TO: All Marine Distributors
SUBJECT: Gear in Neutral While Sailing All MODELS:

All Sailboat Engines

We continue to get questions regarding the correct gear position while sailing with the engine OFF. This advisory is issued as a reminder; Yanmar requires that if sailing with the engine OFF (not running) the transmission shifter must be in the neutral position or internal damage to the gear or sail-drive will result. This damage will not be covered by Yanmar’s Limited Warranty. Please instruct customers and dealers who deliver the sailboat to the customer, of the correct (Neutral) position for the marine gear while sailing.

If the customer desires that the propeller shaft not spin while sailing, either a folding propeller, shaft break, or other suitable device may be used. However, Yanmar accepts no responsibility for the selection, installation, or operation of such devices. Please also refer to Marine service advisory “MSA07-001_Yanmar Sail Drive Propeller Selection” for additional information....

FROM: www.sailnet.com/forums/diesel-engine-forum/63165-yanmar-gear-position-while-sailing.html

[so40gtb]

On our former SO34.2 with a Kiwi prop, we left it in neutral until the speed exceeded 6.5 kt, whereafter we engaged reverse gear to stop prop spin. Given that this was only a top-end connection, I doubt that the transmission's stress limits were ever approached.

On our current SO40 with a Max Prop, we leave the tranny in neutral. I haven't yet checked the shaft to see if it's spinning when the boat's approaching hull speed.

--Karl

[MartyB]

Karl,

I have found that for my boat with a max prop, best to at least put it in reverse initially to get the prop to feather, then N is ok, usually I leave in R when sailing, then I know the MP will not spin.

How are you liking the SO40 vs the 34.2?

Marty

[nornaj]

Guys
On our SO39i with a maxprop, when under sail we place the tranny in reverse to feather the prop (it will also feather in neutral if speed is sufficiently high).
But then it is (usually) impossible to shift the stick back into neutral. So, when we have to start the engine again, we have to do so in reverse.
NornaJ

[windspeak]

Hi now sailing my 43 DS very interesting subject percieved wisdom has always been lock the prop when sailing what a drag!!! it always made some sort sense though less wear on seals, bearings gear boxes etc dose anyone have any idea what the rpm of a free spinning three blade prop might be at 8-9 knots under sail? I would happily take some extra speed and it would narrow the gap re folding prop performance and my fixed lump many thanks for this post i will try it for the rest of the season

[lateron]

Hi........ some replies to my query at last.
I have left the shaft to spin in neutral most of the time recently and I feel the boat does sail faster [ok only a little say 0.3k]. I keep worrying about the speed of the prop spin but interesting to hear the technical advice from Yanmar.
Also if locked I have to almost stop the boat to safely unlock the prop.
I am considering a folding or feathering prop, and I know there is a huge thread about this topic. I was thinking Kiwiprop. Is motoring performance ie reverse ok with folding/feathering props? My only other reservation is folders have moving parts that can go wrong, fixed blade are more simple.
What do you think?
Ron

[Don Reaves]

Motoring in reverse with a Kiwi is much better than with a fixed prop. That's one of its advantages.

It's true that folding and feathering props are more complicated than fixed props. Keep your fixed prop on board as a spare.
Don

[nornaj]

Can only speak to the maxprop.
Have had a maxprop fitted to each of the the three boats we have owned since 1999.
Reverse performance is superb. Bites immediately and backs up straight at low/increasing revs. Prop walk is maintained at slow speeds if desired, just rev her up. Full speed motoring speed is barely affected. Sailing performance is much enhanced.
The problems we have had relate entirely to initial tolerance issues and/or poor installation.
+ installer forgot to put in the locking pins, unit shook itself apart
+ a burr in the hub went un-noticed on installation and prevented prop from opening fully in reverse on occasion
+ an out-of-true key on the shaft made feathering too stiff once the bolts were snugged down (initially blamed on prop, which was unnecessarily sent back to supplier)
Conclusion: properly installed and maintained, a maxprop is a superb modification.
And finally, it is a truly beautiful to look at. It makes a truly sexy piece of coffee table art. Can't say that for the Kiwi. But then either unit should be underwater......... not on the coffee table.
NornaJ

[rene460]

Hi Ron,
It is important to recognise the difference between feathering and folding. Folding giveslowest resistance when sailing if you are in tight racing but forces on blades in reverse also tend to fold blades, so reverse performance is generally poor.
Feathering props have blades that turn when sailing to line up with flow giving much lower resistance than fixed but a little more than a folder. Some feathering designs have separate pitch adjustments in forward and reverse so can be nearer optimum both ways.
I have Autostream feathering type, which is a bit more expensive than some,but is made locally to me and I like to be able to talk to the manufacture. They stripped down a prop for me and carefully explained operation and installation, so I cheerfully paid the price. It is beautifully made, and works a treat both forward and reverse. The Yanmar agent was concerned about pitch and made my try the engine flat out to check max engine revs. I got 3750 rpm which is exactly the right amount above engine max and is the definition of correct pitch and size combination. It is lower pitch in reverse so would not give right revs at max but you do not normally go max engine revs in reverse. It works a treat both forward and reverse as advertised. And wake is much smoother when sailing indicating less drag. To lock or not is probably not an issue, as any turning moment tends to feather blades and remove turning effect, but I usually lock it like several others have suggested. If you like sailing well, go for a good feathering type but if in tight competition you will probably sacrifice reverse thrust for reduced speed when sailing.
Rene460

[so40gtb]

Having had both the Kiwi and now the MaxProp, there is no doubt that both are far superior to a fixed prop. Between the two, the Max has somewhat better "bite" in reverse, but I would give the Kiwi the nod for less prop walk. Not by much, though. The MaxProp's walk to port doesn't last long, but it can be used effectively to nudge the stern to port when maneuvering in tight situations. Of course, the Kiwi costs less and is mechanically simpler.

--Karl

[lateron]

Thanks guys for your advice. I'm leaning towards the Kiwi at the mo. .Hope to investigate fully in time for next season now.How much extra speed do you reckon you can attribute to your folding/feathering props?

Ron

[MartyB]

Depending upon conditions, I have heard .5-1 knot of boat speed. Not that at higher winds it will matter, but in lighter ones, it WILL make difference. For ocean goers, I have heard 20-30+ more miles a day, doing a 2000 mile crossing, that adds up to a day or two sooner getting somewhere.......

Marty

[dublin]

We have been using a kiwi for last three seasons and reckon an increase of up to 1kt. Being impatient people we used to go straight from motoring at crushing speed to sailing. This prevents the prop from fully fathering and at sailing speeds over 5 kts the prop autorotates. This can be prevented by slowing down before turning off the engine. There is a good technical article on this on the kiwi website