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Old 06-22-2013, 01:29 PM   #21
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You are a prime candidate for an EGT gauge.

That would allow the engine to not lug at the highest gear you select.
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Old 06-22-2013, 03:04 PM   #22
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egt gauge

What is and how does a EGT gauge work?
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Old 06-22-2013, 04:24 PM   #23
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It's a probe in the exhaust pipe to measure the temp of the exhaust.

To be accurate it should be located exactly where the manufacturer specifies.

If one props the engine for rated rpm at WOT no exhaust gas gauge will be needed. You won't be able to overload your engine except at specified engine speeds (almost at WOT) and for specified periods of time.

But if you over prop your engine you should have the EGT to know when you are overloading the engine. That point may be several hundred rpm below the engine's normal over loading limit conditions.
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Old 06-23-2013, 06:21 AM   #24
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"If one props the engine for rated rpm at WOT no exhaust gas gauge will be needed. You won't be able to overload your engine except at specified engine speeds (almost at WOT) and for specified periods of time."


IF the engine is being operated at max power (the reason you chose to prop it at max rpm) each and every time a displacement boat is stopped or really slowed by a big wave the engine will be in overload.

Only for a part of a min , just as sport fish are overloaded when accelerating from slow speeds.

Overload does not mean the engine will break , it means more fuel is being delivered than there is air to burn it ,, hence big black smoke .

Underload means there is less load on the engine than the fuel mix can deliver , which is a waste of fuel , and MAY harm the engine thru wet stacking , oil dilution from blowby , or cylinder burnishing .

A "proper" load is where the engine is using most (80%) of the power it can produce at THAT RPM.

Since most folks have only 2 or 3 cruise RPM (some only one) the ability tp operate efficiently is a personal choice and skill.
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Old 06-24-2013, 04:56 PM   #25
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Originally Posted by FF View Post
That 20% + difference is the Holey Grail for the electric propulsion folks.

All their schemes and big bucks complexity are geared to capturing that 20% and eventually using it.

I would prefer to use a cruising prop, no complexity , or the 2 speed gear box and have no huge expensive heavy battery sets to drag out and down the dock.

A ZF 2 speed gearbox is OTS and should last the life of the boat , unlike a batt set.
I read the articles by Caulder in ProBoat re: electric propulsion. My letter in this month's issue says it all.

Re: ZF, I contacted them and they had no interest in using their 2 speed gearbox in that manner and would not even comment on my application. They said, as I recall, their gearbox is only to shifted "up" under load not "down" which is what I was proposing to them. Also it seemed that the ratios were all wrong. What I was proposing was starting off in "High" gear and running up to cruise speed at which point the engine would be fully loaded (or nearly so) then downshifting to "low" gear to continue up to flank speed. They dismissed the idea offhand... Their loss
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Old 06-24-2013, 11:14 PM   #26
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Max cruise,Huh? I guess that's why you jet jockeys get the big money!
I don't know about MAX cruise...just cruise. These engines should be quite happy at 2400rpm. I would guess that to be right in the sweet spot of 70-80%. And I have since run the boat there....and I have to say that I am becoming a Cummins convert. They are quiet sweet running engines. Nothing but a low hum at that rpm and a solid 19 knots!!! Now I need to go to boatdiesel to check out the fuel/power curves to see what it is really doing.
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Old 07-23-2013, 08:56 PM   #27
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when I bought my 44 foot send a cruiser with 320 hp. Cats. The po. Had really large props installed that would not let the motors ven approach the recommended the RPM I installed the correct props and really do not see much. difference in low speed cruise and fuel economy but the top speed is greatly increased
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Old 07-23-2013, 10:13 PM   #28
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I said;

"If one props the engine for rated rpm at WOT no exhaust gas gauge will be needed. You won't be able to overload your engine except at specified engine speeds (almost at WOT) and for specified periods of time."

FF replies;
"IF the engine is being operated at max power (the reason you chose to prop it at max rpm) each and every time a displacement boat is stopped or really slowed by a big wave the engine will be in overload."

The reason to prop at wot at the rated rpm has nothing to do w the ability to run the boat at max speed or max engine output. Nothing to do w it at allll. It's a proper adjustment of the load the engine sees that matches the power output to the resistance of the propeller so the engine can be operated throughout it's range of power output and engine speeds so that all is balanced and working together.

If one is going to operate in very large seas at wot for any more than a few moments he's probably an absolute fool. A good skipper will quickly adjust throttle to match conditions. But an over propped boat will be over propped during much of it's upper throttle range and lack considerable power to climb the big seas. Under propping and a speed limiter set only 100rpm over rated rpm would probably be best for that condition.

The reason one props an engine at rated rpm is basically just a test to know the system is operating correctly. Then one can go to the book and see (for example) that one can operate said engine continuously at 150rpm below rated speed and rated speed is 2500 then the engine can be operated at 2350rpm all day long.

If you over prop an engine you may only be able to apply or generate 90hp w a 120hp engine and the engine may still be over loaded at 2000rpm. You may as well through away your 120hp engine and get a 60hp engine if 60hp is all you need.

But most here HAVE the 120hp engine that is putting out 60hp and about 5% more efficiently than it would if it were propped correctly so why do it right? If you NEVER use more than 60hp running it like that MAY not have a significant downside as long as you KNOW your'e not injecting more than the optimal amount of fuel. In other words not running too rich. If you absolutely know that and NEVER run harder than a 60hp load you probably can over prop for a long time but that's just my opinion and you'll need to live w your own opinion.

Motion 30,
Of course. You've opened the door for what the engine has to offer and you'll probably never notice the slight extra fuel you burn and the slightly higher burn rate will only be noticed at very low rpm. At higher speeds you will probably burn less not more. All around a better way to go.
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