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Old 22-03-2020, 02:12   #1
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Gori folding prop and engine load

Hi there, we've just recently discovered that the Yanmar engine of our 1995 Jeanneau Sun Odyssey 45.1 has a turbo unit. It was filthy to the point of almost being clogged so we detached the unit from the engine, stripped it, cleaned it, reassembled it and put it back on the engine.

People have been giving us various bits of advice of how to keep it from getting into that filthy state going forward. Such as run at max revs for 5 - 10 minutes before you shut down the engine to burn off/blow out the carbon and similar suggestions.

Another bit of advice was NOT to run at low revs or low load and here's where I'd like your thoughts.

We have a Gori folding prop and its design means that it is as efficient in both ahead as it is in astern because the blades fold through 180 degrees. Another feature of the prop is something called overdrive in which the blades are open in the astern position whilst driving the boat forward.

This overdrive setting has about 20% more pitch and is for use in calm conditions or when motor sailing. Overdrive gives maximum speed at lower RPM which saves fuel which increases the cruising range by up to 20%.

In overdrive at 1,400rpm in calm conditions we can reach a speed of 7 knots. My question is given the engineering of the prop, the low revs and decent SOG is the engine now considered to be under enough load and is the low rpm going to soot up the turbo?

Thank in advance, Baz.


Here's a link to a short video which shows visually how it all works.

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Old 22-03-2020, 05:20   #2
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Re: Gori folding prop and engine load

I had a Gori on my last boat and loved it, but I did have an exhaust gas temperature gauge on my list of things to get, since that temperature will tell you what the load is on the engine. I did run it once in overdrive in not-so-calm conditions in order to make it into Falmouth Harbour in Antigua before sunset (it was my first time going in there) and I managed to overheat the engine.

I can hear when my turbo kicks in, and at 1400RPM it is whistling along. Doing low RPMs for long periods many times isn't good, but a subsequent high RPM run or two will dislodge any buildup.
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Old 22-03-2020, 06:09   #3
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Re: Gori folding prop and engine load

You can get a cheap Exhaust temp gauge at Sporty's or other experimental aircraft sites. They are used to adjust engine richness to max temp for economy.

How long is your boat, and what sort of hull? At 45 feet you hull speed is just undet 10 knots, and 7.5 - 8.0 may be your realistic economical cruise. Give some thought to the standard way to judge whether you have too coarse or too fine a prop - Your engine/prop combination sould max out at your recommended maximum RPM for your engine. If it labors (maxes out) at a lower RPM, you need a finer (less pitch) prop, and if it roars past your target you need a coarser (more pitch) prop,

You're not going to change that beautiful very expensive prop, but you can learn where the sweet spot is for engine RPM versus speed through the water, and whether you can reasonably use that overdrive.

I hope you have fun out in calm water doing test runs of RPM versus speed.
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Old 22-03-2020, 09:44   #4
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Re: Gori folding prop and engine load

AJ,

Some of your assumptions are invalid. A diesel engine running at lower speeds, at high load, will not always use less fuel than one running faster, it might just be burning its fuel very inefficiently. Contrary to what many sailors seem to "know" what clogs up an exhaust system the fastest is OVERLOADING the engine, which is what you do while you drive around with your prop in overdrive. Don't do this.

If your engine can not develop full rated RPM at full throttle you are overloading it. Again, don't do this.

When you push a diesel's throttle forward, you are not directly delivering more fuel, or air. You are telling the engine's speed governor what speed to run at. It will supply more and more fuel trying to get to that speed. If it can NOT get to that speed, it just keeps dumping fuel in trying. The fuel mixture gets too rich, and there is incompletely burned fuel, which is soot. Which is what clogs your turbo. (All this is NOT true of computer controlled, common rail engines...)

It is ALSO true that running at consistently too low an exhaust temperature can slowly build up soot. Most marine engine manuals recommend running the engine at full load (Not just full speed!) for 5 to 10 minutes every few hours, at least. Follow this recommendation. I am sure your owners manual has such a recommendation, which is not unique to turbocharged engines.

5 minutes of unloaded, full RPM operation, at the end of a long day of slow motoring will do squat all to burn off the accumulated carbon. In the absence of load, spinning up the engine doesn't generate the heat needed to do what people think it is doing.

Since you say you "just discovered(really?) your engine has a turbo: VERY IMPORTANT with any turbo engine, ALWAYS let it warm up for 3 to 5 minutes at least before pushing the throttle up. Give the oil a chance to flood the high speed bearings in the turbo. Just as important, before you shut the engine down, let it idle for at least 5 minutes. This will give the circulating oil a chance to cool down the turbo bearings. Without this, the really high temperatures in the exhaust system can "bake" the oil and clog up the bearings.
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Old 23-03-2020, 00:03   #5
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Re: Gori folding prop and engine load

Hey billknny, thank you for that info, that's very helpful.


Yes we really did just discover the turbo, we weren't told about it when we bought the boat and prior to having the issue with a hole in the collar of the exhaust mixing elbow we'd never had need to look closely at that area of the engine.


We'll take all of your points on board (no pun intended) but just another question if you don't mind.


You say "what clogs up an exhaust system the fastest is OVERLOADING the engine, which is what you do while you drive around with your prop in overdrive. Don't do this." Does this mean that we should never use the overdrive function? It seems a shame not to use such a feature.



Thanks, Baz
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Old 23-03-2020, 01:25   #6
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Re: Gori folding prop and engine load

AJ-SeaChange:

While billknny has some points to make, his statement "what clogs up an exhaust system the fastest is OVERLOADING the engine, which is what you do while you drive around with your prop in overdrive. Don't do this." is patently incorrect.

When motoring in overdrive you are not (necessarily) overloading the engine. I had a Gori, as have hundreds of others. Most, if not all, of these Gori customers use overdrive and without engine damage.

The issue is that it is easy to overdo overdrive because it seems so easy to get good speed with lower RPMs. Hence my comment about getting an exhaust gas temperature gauge to give you immediate feedback. Ask any commercial truck driver what engine gauge they use the most and it will be the EGT.

If you operate the engine at optimal exhaust temperature it can't tell whether you have a normal prop or have the "overdrive" mode engaged.
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Old 23-03-2020, 04:14   #7
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Re: Gori folding prop and engine load

You overload an engine when you have too much pitch on the propeller and try to run at maximum power. That could be expected to wear on any engine; it's pushing too hard and the load on the pistons, connecting rods, and crankshaft bearings go up. You reduce load by getting a prop with less pitch or by reducing RPM, the prop being the better solution. If your prop already has too much pitch, wide open with the overdrive engaged is the worst situation - think of your car lugging because you tried to leave a light in second gear. There's a point at which the engine stalls from load.

The central point becomes "Treat your engine like you treat your girlfriend," as my machine shop instructor said about his lathe.
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Old 23-03-2020, 04:23   #8
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Re: Gori folding prop and engine load

tkeithlu we're assuming that the engineers that designed the Gori folding prop took all of that into account.


Surely they wouldn't sell much inventory if their props were buggering up peoples engines.
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Old 23-03-2020, 04:30   #9
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Re: Gori folding prop and engine load

I hope you're right, AJ.
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Old 23-03-2020, 08:55   #10
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Re: Gori folding prop and engine load

I had a SO 45.2... loved my Gori ...until it fell off.. as has the case on many others.......
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Old 23-03-2020, 09:06   #11
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Re: Gori folding prop and engine load

Quote:
Originally Posted by s/v michaela View Post
I had a SO 45.2... loved my Gori ...until it fell off.. as has the case on many others.......

Wow!


Did it fall off due to mechanical failure or incorrect installation?
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Old 23-03-2020, 09:26   #12
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Re: Gori folding prop and engine load

No ,, It was installed correctly at the boatyard and worked great for 3 years with 4 or 5 days a week use. This has happened to many gori props if you google search this problem. I believe that there is an inherent issue with the locking ring/set screw cluster. The ring is threaded to the shaft and if it cracks and splits where the set screws hold the hub to the ring then the whole prop just literally falls off the propshaft. at this point Gori will be of no assistance. So believing in the engineering at Gori is wishing on a star...
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Old 23-03-2020, 10:14   #13
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Re: Gori folding prop and engine load

Thanks for sharing that, very useful info to know.


I'm glad that we still have the original prop stowed onboard and as a scuba diver I'll be able to shove that on should the scenario you've described ever happen to us.


Out of interest what prop do you have now?
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Old 23-03-2020, 10:34   #14
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Re: Gori folding prop and engine load

With regard to running high rpm before shutting down to clean the turbo, I suggest that you do not do this. Turbos spin at very high RPMs (Often over 20k RPM) and take awhile to spin down. You likely have oil lubricated bearings in your turbo as part of your pressurized oil system. If you run at high RPM to make your turbo work and burn out any carbon, and then shut down, you turn off the oil flow in the turbo bearings as your turbo slowly spins down. I suggest idling for awhile to allow the turbo to spin down and cool down some before you shut down.

I love my folding prop but, as suggested in earlier posts, I run my Myanmar at about 3k RPM
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Old 23-03-2020, 14:33   #15
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Re: Gori folding prop and engine load

Over drive, over prop, over load, all leads to the same thing. An engine that expires before its time. Over load a turbo engine and you will kill it even quicker. No engine builders and mechanics will tell you it is a good idea to overload a diesel engine. What do they know? The propeller people must know much more about engines right? Overloaded diesel engines are great for one thing. Engine sales.

Maximum fuel economy is a holy grail among sailors. At the same time, fuel cost on a sailboat is one of the lowest expenditures. Particularly when people are running around with over propped engines.
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