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Old 28-06-2020, 19:24   #91
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Re: Captain/Owner Sleeping at the Helm

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........
Your choice of where to spend energy.

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I like what you did here
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Old 28-06-2020, 19:36   #92
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Re: Captain/Owner Sleeping at the Helm

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Now for you aeronautical types, with a piston driven aircraft engine, can the prop be uncoupled from the engine to truly freewheel if engine quits, or does it continue to turn engine over - albeit at much reduced RPM's than free-wheeling. This would seem to me to create more drag than true uncoupled freewheeling, and feathering the prop would def. reduce drag.

The best alternative though - marine or fixed wing air -seems a fully feathering (or folding) prop.
NO......not on a piston powered airplane. if you have a constant speed prop, you feather it when you lose the engine. If you have a fixed pitch prop, it is not possible to uncouple it from the engine. The pilot just has to slow the plane and the prop will eventually stop.

As to the topic at hand....maybe was a bad idea to just throw the engine levers into reverse without consulting a manual or somebody that knows what they're doing.

IF you find the skipper/captain/owner/HMFIC sleeping on shift? Utilize your best CLR/CRM skills and advocate. Or just throw a bucket of water on him. Either is good.
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Old 28-06-2020, 19:49   #93
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Re: Captain/Owner Sleeping at the Helm

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..........

IF you find the skipper/captain/owner/HMFIC sleeping on shift? Utilize your best CLR/CRM skills and advocate. Or just throw a bucket of water on him. Either is good.
Perhaps try the CLR/CRM skills and advocate method first time and the bucket of water method if/when there is a second time!
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Old 28-06-2020, 20:19   #94
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Re: Captain/Owner Sleeping at the Helm

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Trying to stop thread drift after the first coupe of pages is like trying to stop the tides...



Your choice of where to spend energy.



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Apparently I’m not the only lazy mod.
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Old 28-06-2020, 20:47   #95
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Re: Captain/Owner Sleeping at the Helm

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Only if one he had extensive a very limited knowledge of a horse's salt requirement and very limited knowledge of a chocolate cakes sugar requirement.
There, FIFY
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Old 28-06-2020, 21:09   #96
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Re: Captain/Owner Sleeping at the Helm

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NO......not on a piston powered airplane. if you have a constant speed prop, you feather it when you lose the engine. If you have a fixed pitch prop, it is not possible to uncouple it from the engine. The pilot just has to slow the plane and the prop will eventually stop.
(snip)

So it looks like there is no aeronautical equivalent of a low drag free-wheeling boat prop, as the non-feathering piston driven prop ends up stopped by engine compression, with huge drag, as speed drops. Turbo-propped craft certainly all feather, and have a huge gear reduction between turbine and prop speeds that would slow free-wheeling un-feathered.
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Old 28-06-2020, 23:15   #97
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Re: Captain/Owner Sleeping at the Helm

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It's odd, in the aviation world this isn't a debate, it's a accepted fact that windmilling is more drag. Next time I'm out I'll do a little experiment, ether way don't feel like ty noise, or lack of cooling water in the dripless or spinning that much for ether little or a negative
Yes, and this confuses people. Boat props and aviation props are very different.
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Old 29-06-2020, 01:44   #98
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Re: Captain/Owner Sleeping at the Helm

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It's odd, in the aviation world this isn't a debate, it's a accepted fact that windmilling is more drag. Next time I'm out I'll do a little experiment, ether way don't feel like ty noise, or lack of cooling water in the dripless or spinning that much for ether little or a negative

There is a valid reason for the difference between aircraft props! On an aircraft engine the propeller does not have a gearbox that can be disengaged so the prop is extracting energy from the air flow in order to push the motor through each cylinder compression - hence significant drag! Even on turbines there is a planetary gearbox in which the reduction ratio when driven by the prop requires a large amount of energy hence drag... on a boat the prop has very little resistance to rotation when in neutral....
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Old 29-06-2020, 05:32   #99
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Re: Captain/Owner Sleeping at the Helm

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Only if one had extensive knowledge of a horse's salt requirement and very limited knowledge of a chocolate cakes sugar requirement.
Doesn't it come down to the type of horse's saliva as to the quantity and quality of the salt as it applies to the size and chocolate concentration of the cake
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Old 29-06-2020, 05:36   #100
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Re: Captain/Owner Sleeping at the Helm

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Doesn't it come down to the type of horse's saliva as to the quantity and quality of the salt as it applies to the size and chocolate concentration of the cake


Doesn’t the cake taste better when the horse is supplied with a pink salt lick in place of the normal white or blue?
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Old 29-06-2020, 07:03   #101
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Re: Captain/Owner Sleeping at the Helm

I've had a couple of crew found asleep on watch (I'm up and down a lot, changes of watch and randomly during watch). They got put off at the first opportunity. That meant pulling some doubles. Simply not okay.

I haven't been in that position as crew and fortunately not skippering with owner aboard. I'd want to get off.

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In no means do I want to come off as a know it all. The vibration was obviously the props. I was just showing the boat owner the source.
I'd say the vibration was obviously the drive train and not the props.

There are a number of issues. If there is real vibration there is usually an alignment problem or perhaps a worn bushing or bearing. If it's just noise it's friction you just don't hear with the engine running.

The original manual for my Yanmar 4JH4E says to put the transmission in reverse when sailing. Two years later, Yanmar changed their guidance. I have always suspected the change came from lawyers (liability) and accountants (warranty costs). You do have to (engineering) pay attention to the lubrication system of the transmission. Some don't work with the engine off, which makes freewheeling ill-advised.

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It's odd, in the aviation world this isn't a debate, it's a accepted fact that windmilling is more drag. Next time I'm out I'll do a little experiment, ether way don't feel like ty noise, or lack of cooling water in the dripless or spinning that much for ether little or a negative
We've been through this discussion on CF a number of times. I've pretty well given up. I remember in Fluid Dynamics under Prof Jacques Hadler (a leading light in propeller design) doing the calculations for this very question. Then we trooped down to the water flow tunnel for testing. Less drag with the prop fixed. It seemed counter intuitive so a bunch of us trooped down to Prof Hadler's office. He pointed out that our calculations showed less drag with the prop fixed. We agreed. He pointed that the water tunnel tests showed less drag with the prop fixed. We agreed. He suggested we needed to work on our intuition.

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It shows the need to do some background work before you accept an offer to crew on a crossing. Inexperienced skippers usually are eager to learn from experienced crew. But some people are so inexperienced that they are unaware of their ignorance.
Absolutely. When talking to crew candidates I am clear that questions are encouraged and that the interview works in both directions. I need to be confident in them, and they need to be confident in me. There are no dumb questions, only stupid answers.
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Old 29-06-2020, 08:15   #102
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Re: Captain/Owner Sleeping at the Helm

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Only if one had extensive knowledge of a horse's salt requirement and very limited knowledge of a chocolate cakes sugar requirement.
Entirely accurate but... the description makes an autorotative landing sound much scarier than it actually is. I hold a commercial helicopter rating, and during training and flight exams I've done around a hundred landings in autorotation - and one for real landing after power loss.

The practice procedure is to chop power to idle (done as a surprise when with an examiner), pitch up slightly if in forward flight to covert the forward kinetic energy into stored potential energy until forward velocity is lowered to the recommended speed for an autorotation (which gives a better glide ratio), set collective pitch for maximum rated rotor RPM (NOT maximum possible RPM unless you want the blades to fly off the hub!), pick a landing site within the narrow glide ratio (about 2 or 3 to 1 - it's like landing the Space Shuttle - not much glide ratio), "glide" to landing, and at about 25 feet above ground level, gradually raise the collective pitch to convert both the stored rotative potential energy in the main rotor, and the forward speed in the glide -- into lift. Then land. Perfectly performed, you touch down with a little forward speed and all the energy in the main rotor bled off. In practice, in that final flare, you twist the throttle back in to restore power instead of touching down. Easy peasy.

When the engine quits, the danger is not lowering collective pitch right way, allowing rotor RPM to drop so far that the main rotor "cones" and the RPM drops so far that the rotor cannot be spun back up. Rotor stall. It's unrecoverable. Then, you're sitting on a lawn dart and you make a smoking hole in the ground. But that's pilot error - not an inherent limitation of the aircraft.

Since the glide range is so narrow, the basic rules is: don't fly over anything you don't care to land on. If you're a prudent pilot, you play hopscotch between potential landing spots. But of all the possible major failures in a helicopter, the least dangerous is an engine failure. Failures of control linkages or a seized transmission invariably have dire outcomes. (Tail rotor failure in cruising forward flight is just annoying.)
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Old 29-06-2020, 09:10   #103
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Re: Captain/Owner Sleeping at the Helm

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Doesn’t the cake taste better when the horse is supplied with a pink salt lick in place of the normal white or blue?
wow, pretty fancy for us boat scum people that thought salt was just "salt"
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Old 29-06-2020, 12:01   #104
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Re: Captain/Owner Sleeping at the Helm

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So you think it was a good idea to slow the boat and risked potential damage to the engines by locking the props contrary to the skippers wishes and the manufacturer's instructions?



Now how do we deal with know it all crew?


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.

Interesting. Then a saildrive installation has just the opposite recommendation for sailing position compared to the Hurth/ZF. One would think that eliminating any rotation during sailing would be the best choice for any gear. And the OP switching to reverse did stop the nasty vibration.
Does that cat always have saildrive and not a standard transmission?



As for drag, it will probably be increased by letting the prop freewheel. When not rotating, the blades are stalled. If spinning, they can produce lift (in reverse) just as an airplane wing produces lift when moving forward but none when sinking straight down.
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Old 29-06-2020, 12:22   #105
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Re: Captain/Owner Sleeping at the Helm

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Interesting. Then a saildrive installation has just the opposite recommendation for sailing position compared to the Hurth/ZF. One would think that eliminating any rotation during sailing would be the best choice for any gear. And the OP switching to reverse did stop the nasty vibration.
Does that cat always have saildrive and not a standard transmission?



As for drag, it will probably be increased by letting the prop freewheel. When not rotating, the blades are stalled. If spinning, they can produce lift (in reverse) just as an airplane wing produces lift when moving forward but none when sinking straight down.
Over time, some things change, others not. What has changed is for example my impression of Covid19, having made a thoroughly premature and off the mark assessment on here somewhere wrt its seriousness back in February ("wouldn't worry too much"). Over time I have become fully educated.

When it comes to rotating vs stationary props however nothing changes, as per all the other conversations on this topic in the past: it would be absolutely against some pretty fundamental conservation of energy laws for freely rotating props to suffer from more friction than stationary ones. You cannot have a boat moving with less effort through the water and leave one big vortex in its wake. Would be too good to be true.
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