Running on one engine...

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Mishigas
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Running on one engine...

Post by Mishigas »

I was thinking (always dangerous when that happens) about the proper way to run on one engine if need be. I would think it would be best to pull the dead engine out of gear and place it in neutural to avoid the prop drag but then will the prop free spinning damage anythng? That can't be good for the shaft seals. Anyone here care to comment on this?
Thanks Sandy Kramer MISHIGAS PC34
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Post by duetto »

hi,

seals are water cooled from engine exhaust. not sure how high they need to spin before they overheat. also, not sure in gear locks shaft (i.e. what kind of clutch is it?).

probably chris calvert questions.

john cummings

duetto mv34 #23
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Page 83
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single engine motoring

Post by Page 83 »

A spinning prop develops more drag than the same prop stopped. Sailboat racers go so far as to lock the prop in an optimal position, to gain that last tenth of drag reduction. If it doesn't spin, it doesn't get hot!
Sandy Daugherty "Page 83" PDQ 36026
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Post by ELIXIR »

Agree probably better to lock the shaft by putting it in reverse. That is what I always did on my sailboats. Hopefully you wouldn't need to run on 1 engine often and I haven't tried it but wonder what kind of speed she'll make.
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Post by Guest »

I'm still working on this answer. I was told by another Yanmar / ZF user that the Hydraulics in the tranny would not "Lock" the prop from spinning if left in gear. I have e-mailed PDQ engineering for an answer. Yes, I hope it never comes to running on one engine but $#!T happens, just want to know what to do if it does.
Sandy Kramer MISHIGAS PC34
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Post by Mishigas »

OK, I have heard back from the folks at PSS Dripless and ZF transmissions so here is the deal. If you have an engine go down and need to run on one engine. it does not matter what gear the transmission is in. The prop will "free spin" as the transmission will not engage without engine / hyrdaulic power. According to ZF transmissions, this will not hurt a thing (no need to lock your prop shaft). If your hull speed is under 12 knots, the high speed PSS dripless we have on the new PC-34s will be fine without a water source to lube/cool the seals. In fact the standard PYY dripless (our is the high speed unit) does not require any water source to cool seals. So there you have it. If you ever get in a situation that your Yanmar goes down, you know how to get home without any damage or harm. Now getting into that slip on one screw will be fun....
Sandy Kramer MISHIGAS PC-34 Hull #68
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Post by duetto »

hi,

not everyone has pss seals. i know we have seals from tidesmarine and they caution against overheating on their website.

soooo, i guess it behooves everyone to know what their boat has for seals.
john & diane cummings
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Running on one engine...

Post by Sno' Dog »

I remember a comment from the Ozimeks (m/v 27 Rhumbline) about cruising on one engine to extend range. (That article is still on the PDQ website: "A Path Less Travelled"). In an e-mail exchange, I tried to pin them down a bit, but they were not able to say for sure what, if any, fuel savings were actually realized by single-engine operation.

I'm still curious about this and I'm looking forward to collecting data on Sno' Dog. I gather the general consensus is that there's not much savings to be had UNLESS the boat is equipped with controllable pitch props which can be feathered. But it's good to know, we can play around with this and not do any damage. Apparently, unless we install a shaft brake, we have little choice but to let the prop freewheel.

On the subject of whether stopped or free-wheeling props produce less drag, this has been discussed ad-nauseum -- particularly among sailboaters. I think the reason for this is that there's no simple answer; it depends on many varibles. In general, a low-solidity prop (such as found on sailboats) may produce less drag stopped while a high-solidity prop (more common on powerboats) may produce less drag when spinning free. But then again, it may not -- there's no simple answer. (I can tell you that almost all wind turbine props produce less drag stopped than they do freewheeling -- but that probably won't help you much here!)

I look forward to gathering some data of my own on this subject. Once I do, I'll certainly pass it along.

Henry
m/v 87 Sno' Dog

http://www.geocities.com/snodoglog/
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