Free wheel prop or lock it?

[mggilmore]

I'm a new owner of a 1987 Ericson 32. I've noticed in the manual that it says to "not" sail the boat with the transmission in forward gear. My question is, does this mean the recommendation is to sail in neutral or reverse? I know that there is a lot less drag on the boat if I sail in neutral but I'm concerned about wear and tear on transmission. Any input ?
Thanks.
Mike

 

[Loren Beach]

You probably have a stock factory Universal M25XP, and the trans. is a Hurth. My manual sez to put it in reverse when under sail.
Loren

 

[exoduse35]

nutral wins! There is very little rotation of the shaft when sailing. and no wear on the transmission.

 

[mggilmore]

Loren,
Thanks for the quick reply, you got the engine and transmission right. Rats, I was hoping neutral was the answer for prop drag reasons. I'm trying to figure out whether to worry about the drag of a 3 bladed Campbell sailing prop (which I'm considering adding to the boat) and if the boat was OK freewheeling I figured the drag wouldn't be as big of a deal.
Mike

 

[mherrcat]

There is an operators manual for the M25XPB engine in the documents and downloads section. It indicates that neutral is OK as is leaving the transmission engaged in whichever position is opposite your direction of travel; so putting it in reverse while sailing would be OK, unless you were sailing backwards...

It also says NEVER leave it engaged in the position that is the same as your direction of travel.

I always leave my M18 in reverse when sailing. The sound of the shaft spinning in neutral kind of bugs me. I'm not too concerned about added drag with the prop locked.

 

[EGregerson]

prop

If u need that extra half a knot to win the cup, leave it in neutral; otherwise reverse is fine. I was sorta amazed how fast the shaft spins when it's in neutral under sail; gives u an indication of just how powerful the drag is on the prop.

 

[bayhoss]

I sail with the trans. locked in reverse. A spinning prop no matter how slow or what direction can still hang and tangle in a crab pot or other matter.

Best,
Frank

 

[Frank Langer]

Hi,
Apparently with our Varifold folding propeller I don't have to worry about this! But just to be sure, I still put it in reverse gear when sailing. There have been long discussions on several websites about whether there is more drag with a regular propeller free wheeling in neutral or locked in reverse, and the emerging consensus seems to be that locked in reverse is better/faster, aside from the issue of potential wear on the transmission.

I have been pleased to note when I dive the boat at anchor to clean the bottom that our folding propeller has actually folded shut the way it is intended; and I can hear it open when I put it into gear, so that's good too.

Fortunately, our boat came with this propeller, so I didn't have to pay the big bucks for it myself.

Frank

 

[gulfcoaster]

We have an E-32-3 1987 as well. #713. There was an article in Yachting Monthly about a year ago. They conducted drag tests with all types of props. A 3 blade fixed prop locked in reverse had the drag equivilant of dragging two 5 gallon buckets on tow lines behind your boat. YuK!! My manual does specify locking in reverse to be correct. We adding a 2 blade flexifold last year.

 

[Maine Sail]

Official word...

Loren,
Thanks for the quick reply, you got the engine and transmission right. Rats, I was hoping neutral was the answer for prop drag reasons. I'm trying to figure out whether to worry about the drag of a 3 bladed Campbell sailing prop (which I'm considering adding to the boat) and if the boat was OK freewheeling I figured the drag wouldn't be as big of a deal.
Mike

Most manufactures agree that forward is bad for gear boxes and Hurth/ZF specifically advises against forward.

Westerbeke / Universal has weighed in, and it is well known. ZF/Hurth or JS gear boxes used on Westerbeke & Universals can be left in both neutral or reverse but never forward when moving forward.

Some others, like hydraulic gear boxes, can not be left in neutral, no lube, so it is always best to consult your individual manual or manufacturer for your gear box. Yanmar's are to be left in neutral only and not locked in reverse.

Every gear box is different so it is always best to ask the manufacturer.

From Westerbeke / Universal:

UNIVERSAL DIESEL WITH HURTH TRANSMISSION

Model HBW-50 (2:1)
Used on Models 12, M2-12, M-18, M3-20, M4-30, M25 and M-25XP

Model HBW-100 (1.8:1)
Used on Models 30, 35, and 40

Model HBW-150 (1.9:1)
Used on Model 50

Model HBW-150 V-Drive (2.13:1)
Used on All of our V-Drive Models

Image Courtesy C-34 Association

 

[Maine Sail]

There have been long discussions on several websites about whether there is more drag with a regular propeller free wheeling in neutral or locked in reverse, and the emerging consensus seems to be that locked in reverse is better/faster, aside from the issue of potential wear on the transmission.

The consensus by two Universities, that actually studied this with actual sailboat props, MIT and The University of Strathclyde Ocean Engineering Department is that locked causes more drag. Yachting Monthly also found this, and their findings matched both MIT and The University of Strathclyde.

I did my own study, in water, and made an actual video of it, the only one I know of. The results are not even close! The typical sailboats locked fixed prop can cause significantly more drag.

http://www.youtube.com/watch?v=jI-UG9RSlJo

 

[Loren Beach]

Prior Threads...

http://www.ericsonyachts.org/infoexchange/showthread.php?t=4310&referrerid=28

http://www.ericsonyachts.org/infoexchange/showthread.php?t=571&referrerid=28

When it comes to props, spinning, not spinning, feathering, walking, number of blades, and a few more "etc"... there are a lot of threads here.
:nerd:
It would be quite a labor of love for someone someday... to artfully combine them all into a veritable Mother of All Propellors article!


MaineSail, that's a nice video of your real-world prop drag demo/experiment!

Regards,

Loren

 

[rwthomas1]

I am relatively sure that the reason you do not lock some transmissions in forward is the use of cone clutches in that particular design. A cone clutch will usually grab better in one direction only. So when engaged the input shaft spins the output shaft of the transmission and cone clutch literally grabs tighter and tighter simply due to the direction of the input shaft rotation. Now place the transmission in forward with the engine off and the propshaft is trying to spin the input shaft/engine and the cone clutch is "seeing" that force in the opposite direction of when the engine is running. This can cause the clutch to chatter, slip and ultimately wear out early. Thats why placing the shifter in reverse presents the correct loading to the clutch, trying to spin the prop forwards while in reverse is the same loading as actually being in reverse! Clear as mud, eh? Thats my theory anyway, any transmission experts feel free to chime in. RT

 

[Maine Sail]

I am relatively sure that the reason you do not lock some transmissions in forward is the use of cone clutches in that particular design. A cone clutch will usually grab better in one direction only. So when engaged the input shaft spins the output shaft of the transmission and cone clutch literally grabs tighter and tighter simply due to the direction of the input shaft rotation. Now place the transmission in forward with the engine off and the propshaft is trying to spin the input shaft/engine and the cone clutch is "seeing" that force in the opposite direction of when the engine is running. This can cause the clutch to chatter, slip and ultimately wear out early. Thats why placing the shifter in reverse presents the correct loading to the clutch, trying to spin the prop forwards while in reverse is the same loading as actually being in reverse! Clear as mud, eh? Thats my theory anyway, any transmission experts feel free to chime in. RT

Rob,

Not just for cone clutches. Yanmar / Kanzaki's use cones but cones can jamb and lock in either direction hence their "must be in neutral" marine service advisory that came out in 2008.

Hurth's don't use cones but the spinning/grinding that occurs when the gear box is left in forward, of the clutch plates, allows metal shavings to be shredded off the plates and into the gear box lubricant.

When the gear box runs these metal shavings splash up onto the plates and the thrust washer severely wearing them and leading to slippage and an eventual re-build.

Even short durations of a Hurth/ZF being left in forward should be treated with a changing of the gear box fluid and a draining and flushing out of the bottom drain tapping to clear the box of any metal shavings. If your fluid is not pure pink with a Hurth it is time for a fluid change.

Worn Hurth thrust washer (should be flat):
http://www.pbase.com/mainecruising/image/128333710.jpg

Worn/burned clutch plates from slippage caused by a worn thrust washer:
http://www.pbase.com/mainecruising/image/128333708.jpg

P.S. I wish you guys would turn on the photo linking icon in this forum!!!!!!!!!!!!!!!!!!!!!!!!!!!!! Other forums on this board have it turned on. It looks like this: http://forums.sbo.sailboatowners.com/lbs/editor/insertimage.gif

 

[Loren Beach]

Thread note:
I moved the discussion over external links to its own thread in the Cheers & Jeers Forum. It seems like a better place for it.
I probably should have skipped my parenthetical and unrelated commentary in the first place.
Regards,
Loren

 

[Blue Chip]

Maine Sail maked a good ponit on drag...but I think (emphasis on I THINK) the discussion isn't so much on drag as it is on effect on the equipment.. Right???

 

[Bolo]

"Reduce drag"

Loren,
Thanks for the quick reply, you got the engine and transmission right. Rats, I was hoping neutral was the answer for prop drag reasons. I'm trying to figure out whether to worry about the drag of a 3 bladed Campbell sailing prop (which I'm considering adding to the boat) and if the boat was OK freewheeling I figured the drag wouldn't be as big of a deal.
Mike

Not being at my boat I had to download the E32-3 manual from the documents section of this web site and it says, in section 3-3 under "When Shutting Down the Engine for Sail", to put the trans in reverse to "reduce wear on the transmission, shaft and strut bearing, AND ALSO TO REDUCE DRAG FOR MORE EFFICIENT SAILING..." That last part I put in caps myself. I was surprised to see that it recommends reverse to reduce drag. That seems to imply that the prop will spin in reverse while the boat is moving under sail?? I thought that in reverse the prop would be "locked" and cause more drag. I usually just leave it in neutral and I notice that there is no mention that neutral would harm anything. I never noticed if the shaft does turn in neutral while under sail but to be honest I never looked!

Also noticed that the manual says you should never rev the engine in neutral. However, an "old salt" in our marina once told me that it's a good practice to "briefly" rev the engine after docking to blow out any carbon build up in the engine and then wait for a minute or so before shut down. Thoughts?

 

[Maine Sail]

"When Shutting Down the Engine for Sail", to put the trans in reverse to "reduce wear on the transmission, shaft and strut bearing, AND ALSO TO REDUCE DRAG FOR MORE EFFICIENT SAILING..." That last part I put in caps myself. I was surprised to see that it recommends reverse to reduce drag.

Don't be surprised, but the manual is wrong on that point. For many years some in the industry tried to apply the helicopter blade theory to sailboat props and many still believe it. It was not until MIT and University Strathclyde actually studied this with real sailboat props that folks finally started to come around. Two different mediums and two drastically different speeds but yet some tried and successfully got a whole industry buying in on this with zero applied testing.

The bottom line is that Hurth says it is fine to either freewheel in neutral or to lock it in reverse and they made the gear box.

Even Dave Gerr, NA, big dog at Westlawn and author of the Propeller Hand Book agrees that a locked prop causes more drag not less, but old wives tales die a slow death...

 

[mggilmore]

Maine Sail,
Interesting test video, a very effective way to show the difference in drag. I read the study done by the University of Strathclyde which also clearly points out the significant difference in freewhelling and locked props. The article can be found through this link if anyone is interested
http://www.kiwiprops.co.nz/documents/Drag-Thesis.pdf

Interesting that I found it on the Kiwi props site because this test plus other info (such as provided by many on this site) has me leaning towards a fixed 3-bladed prop and to let it freewheel to help deal with the drag, seems like a much less expernsive approach.

 

[Seth]

Props

When in doubt, leave it in reverse. It is true some engines are not affected by the lack of lubrication when freewheeling, but it goes against my instincts to have a shaft spinning without lubrication. You will never hurt anything by leaving it in reverse.

My experience tells me there is more drag with a spinning prop than a stopped one, but it may not be as true with a 3 blade which cannot be set in an "aligned", low drag position...

For sure, I believe that with a 2 blade fixed prop locked in a vertical position you will have less drag than you would with it spinning. This is easy to do-when the boat is at rest (or on a cradle), with the engine off and the tranny in neutral, spin the prop so that the blades are up and down (if you are in the water you will need a swimmer to check this!), then take a magic marker and make a mark on the top of the shaft near the coupler (somewhere where you can see it and get to it from one of the access ports or seat lockers).

When you shut the engine down, put the engine in reverse to stop the prop, then neutral. Rotate the shaft by hand until the mark is in the same spot, then lock the tranny in reverse, and leave it alone. Having the blades straight up and down right behind the trailing edge of the keel should really reduce prop drag and enhance sailing performance.

I have heard the research saying a spinning 3 blade is faster than a locked one, but it seems odd to me, and you can't hurt the tranny by leaving it reverse.

I will leave the 3 blade drag argument to smarter folks than me, but for a 2 blade fixed, locked and vertical is fastest and safest for the engine.

Not that I have an opinion:nerd:

Cheers