Overpowered Boats?

RickB wrote:

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No you didn't increase rpm but your governor increased fuel flow to maintain the rpm you selected.

******** Oooops! I knew that!

Really! My govonor's that smart? So that explains that *...to a degree. So if I have a tailwind and the tach say the same rpm I'm burning less fuel? I thought the governor only came into play to limit max no load rpm. I guess that's why a diesel sounds like it does when it starts up. Sounds like it's under heavy load for a few strokes before it comes up to idle speed. Is that right Rick?

Yachtbrokerguy,

Just because it dos'nt cost much dos'nt mean one should buy and operate the wrong boat. It's obvious that a Krogen39 or a 40 Willard is a good boat for 7 knots and a Fathom 40 is not. It may be "OK" for fairweather conditions to run a planing hull at disp speed but it is far from ideal and you being a broker you know best that it's not good but there are very few Krogen's, Willard's and Fisher's out there. It's kind of a "run what you brung" sort of a thing but that's no excuse to bless it as being good practice or the way it should be done.*

Now you're talking.. Tks Tucker for the wise comment..

Elwin

yachtbrokerguy wrote:
Lets take a typical boater who puts 150 hours per year on their boat. Loopers will do more, ICW north and south will do more but when you look at all the boats for sale, divide the number of hours on the mains by the age of the engine, on average not that many hours per boating season. Boat "A "uses 2 gph and boat "B" uses 3 gph, so one extra gallon for 150 hours, times $5 per gallon to take in some increase, give a fuel cost difference of $750.
Compared with the cost of dockage, insurance, routine maintenance, reserve for repairs, and depreciation, total fuel use should not be the deciding factor.

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nomadwilly wrote:
Really! My govonor's that smart? So that explains that *...to a degree.** ...

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*This film clip explains mechanical governors.* Presumably, some modern diesels have electronic governors?* My JD 4045D has a "proven and reliable mechanical governor."



-- Edited by markpierce on Monday 28th of November 2011 04:34:37 PM

nomadwilly wrote:
So if I have a tailwind and the tach say the same rpm I'm burning less fuel?

I thought the governor only came into play to limit max no load rpm.

I guess that's why a diesel sounds like it does when it starts up. Sounds like it's under heavy load for a few strokes before it comes up to idle speed. Is that right Rick?

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Yes, if you have a tailwind the load on the engine is less and you burn less fuel to turn the same rpm which generally equates to the same speed over the ground.

Max no load rpm is called "high idle" and is one of the governor settings. It kicks in when the rpm reaches the maximum speed setpoint.

The diesel sounds like it is under a heavy load when starting because as it starts it has not reached the rpm set by the throttle lever so is delivering maximum fuel to try and reach the setpoint. More sophisticated governors incorporate a "start limiter" that reduces the amount of fuel supplied at start in order to avoid the starting surge and large amount of unburned fuel in the cylinder. Lehmans with the "cold start" feature over ride the fuel stop so that more than normally allowable fuel can be injected with the idea that if you put enough in some of it is bound to catch fire.

Remember, your throttle lever sets an rpm, not the amount of fuel delivered to the engine. The governor decides how much fuel it will let you have. If you snag a big log or wrap something around the shaft that slows the rpm the governor will add more fuel to try to get back to the rpm you selected. It will keep adding fuel as long as the rpm is low until it reaches the third setting which is the fuel stop. This is the most fuel the governor will let the engine have and that is usually set to prevent torque overloading or smoking.

Yea I notice just about full "throttle" it hits a flat spot. Do'nt know if I learned that in the past and forgot about it or what. Thank's guys and I'm sure a few other guys picked up on this too. So I suppoze if I'm in a car or truck w a stick shift and advance the throttle the mixture gets too rich very quickly. With a boat the rpm can increase and help the situation out. But black smoke only seems to happen w old engines w low compression.*

RickB wrote:
Yes, if you have a tailwind the load on the engine is less and you burn less fuel to turn the same rpm which generally equates to the same speed over the ground.

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*I suppose this is why there is a return line to the fuel tank.

markpierce wrote:I suppose this is why there is a return line to the fuel tank.

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No, the fuel metering is controlled by the governor and done in the injection pump. The fuel return on your engine merely returns the fuel that leaks past the injector components for lubrication and cooling.

In 2-stroke DDs the fuel injector and pump are combined, the fuel return is much greater since the fuel that is "spilled" during metering is returned and that fuel is far more than is burned.

"But black smoke only seems to happen w old engines w low compression."

Black smoke happens with ANY engine fed more fuel than it can burn.

Usually on acceleration, where it is an acceptable overload.

More modern engines marinized from road transport suppliers will frequently have EPA smoke limiting.

Sometimes its just an EPA injector , sometimes its in the electric brain box.