Outboard Engine Testing + weather effects

[kbcone]

I was reading the Merc Verado General Information p 1C-10.

Corporations internationally have settled on adoption of ISO Internal Standards Organization
engine test standards in ISO 3046. Standardizing the computation of horsepower from data obtained on the dynamometer. All values are corrected to the pwer that the engine will produce at Sea Level,at 30% relative humdity at 25 C or 77F temperature and barometric of 29.62 inches of Mercury. More to follow

Summer conditions of high temperature,low barometric pressure and high humidity all combine to reduce the engine power. This in turn is reflected in decreased boat speeds as much as 3-5 km/h or 2-3 mph in some cases.Nothing will regain this speed for the boat but cooler dryer weather.

more

Pointing out the cosequences of weather effects, an engine running on a hot humid day may encounter a loss of as much as 14% of the horsepower it would produce on a dry,brisk day.The horsepower that any internal combustion engine produces ,depends upon the density of the air that it consumes. The density of air is dependent upon the ambient air temperature,the barometric pressure and the humdity(water vapor) content.
more
Accompaning the effects of weather inspired loss of power is a second but more subtle loss.
Consider a boat rigged during cooler .less humid weather with a propellerthat allowedthe engine to turnwithin its recommended rpm range at full throttle.Higher temp.with higher humidity will consequently decrease the available horsepower. The propeller in effect is too large for the atmospheric conditions.Consequently the engine operates at less than its recommended RPM.

The engine rated horsepower is a direct relation to the engine 's RPM.An engine with too large a prop will have a further loss of horsepower and subsequent decrease in boat speed.This secondary loss of rpm and boat speed can be regained to switching to a smaller pitch prop that allows the engine to run at the recoomended rpm.

For boaters to realize optimum engine performance under changing weather conditions,
it is essential that the engine have the proper prop to allow it to operate at or near the top end of the recommended max rpm range at wide open throttle with a normal boat load.Not only does this allow the engine to develpoe full power. but equally important is the engine will be operating in a rpm range that discorages damaging detonation.This of course enhances overall reliabilty and durability of the engine..

[darbikrash]

It seems that everytime I respond to a post like this I regret it, but here goes.

What you say is true, as is the opposite, e.g. motors run better in cooler conditions, as we all know. The ISO standard is a reference to allow apples and apples comparison between engine manufacturers, so consumers like us can compare engines (well not really as the outboard mfgs won't publish the resulting curves).

Air density does have an effect, but so does fuel density, perhaps more so. Hot fuel is less dense than cold, so you get less in the cylinder which means less HP.

Forced induction engines like the Verado you reference are less effected by air density than naturally aspirated engines, as they have a compressor to compress the air, as well as an intercooler to pull some heat out before it goes into the cylinder. Turbos are a great example of a (air) density compensating device, they try to make up for low density air by just spinning faster. Not quite the same story with belt driven superchargers though.

The diesel guys have managed to really reduce (but not eliminate) the influence of weather effects to a large extent. They do this in several ways. 1.) They tend to cool the fuel either using the tank and fuel return line, or a use dedicated fuel cooler. 2.) Some of the more sophisticated engines (like Volvo) use fuel temperature compensation to measure the fuel temp, and then modify the injector profile (pulse duration) to put more fuel in the shot if the fuel is less dense.

I believe Volvo certifies their common rail engines up to 140 degrees F fuel temp without losing any rated HP.

I don't know if the outboard guys do this or not, but it wouldn't surprise me if the Verado does, and if not, they should.

[kbcone]

I DID NOT say anything , I copied the Mercury Service Manual.SEE the FIRST sentence above.
I did not give any opinion...
If you want to take it up with Mercury. Then called them in Fond du Lac,Wisconsin.
I know the techical staff at Mercury is inferior to your mechanical engineering knowledge.

[darbikrash]

darbikrash - 3/21/2008 7:37 PM

It seems that everytime I respond to a post like this I regret it, but here goes.

Yup, I knew it.

kbcone - 3/21/2008 7:47 PM

If you want to take it up with Mercury. Then called them in Fond du Lac,Wisconsin.
I know the techical staff at Mercury is inferior to your mechanical engineering knowledge.

I think that response was a little uncalled for.

[Mr. Demeanor]

Darb. I thought your response was appropriate and rather informative. Not sure why the OP is acting like you peed in hes Wheaties? I would tell a little story of an engine test we were doing on an engine dyno when a weather front rolled through but I am afraid it would be taken poorly ???????/

[kbcone]

Maybe you should have not replied and re-read the opening sentence.

Anyway ,sorry if i ruffled your feathers.

It was strictly information copied by my slow typing with some mispelled words,from the Mercury Service Manual 200/225/250/275
Verado 4 stroke ,starting model year 2005, starting serial number )T980000,
Manual 1 ,Important Information, page 1c-10.

Again, I do NOT have any replies to the content of the Manual.I did not ADD any additional information or make any comments to Mercury Manual.It is verbatum.
ALL of you can form your own opinions.
I thought is was nice to know information.
That will be my last new thread.

[darbikrash]

Not sure why this is so tough.

It was very clear that you were simply quoting the Mercury manual. No one is taking any issue with your post or any of the Mercury info. No one is challenging your facts. In fact, it was useful to me to learn that ISO 3046 was used for outboard engine certs, I did not know this.

I thought it might be interesting to raise the point that fuel temp is a very big part of the variabilty quoted in the Mercury manual.

You can't change the weather, but you can change the fuel temp.

Some might find this interesting, maybe even, God forbid, spur some discussion about taking advantage of this.

Sorry if my post was offensive.

[kbcone]

Very interesting that Volvo compensates for fuel temp.
I looked thru the Verado Service Manual 3-Fuel System ,Starting Year 2005 SN 0t980000, and I could not find any fuel temp sensors.ie talk to the ECM/ECU/PCM.Furthermore, I could not find any fuel temp sensors even on the Yamahas including the HPDI ,which probably has the highest pressure and fuel temp.I grant you they all have fuel coolers which are very critical. Apparently the USCG/cert did NOT want any return lines back to the boats fuel tank,thus we have VST,FSM (Mercury Verado) and water to fuel heat exchangers in all EFI outboard engines.

I also think that a lot of the Mercury information is some what dated. I think most of it came from a book ," MERCURY PROPS ", about 20-30 years ago.They talk about detonation,etc. However the modern EFI OB engines have sensors that will compensate for detonation, increased Manifold temps and pressure.etc.

In retrospec maybe the Mercury Engineers need your inputs. Carl Kiefhaefer is probably rolling over in his grave, beating the casket,with his IRON FIST,since the Verado was designed by Clause Bruester , formerly of Porsche Cayenne V8 design team leader. . C.K. ,,,WHY can't our engineers design a four stroke??They used Yamahas built F225 before the Verado..


http://www.marineengine.com/books/iron_fist.html

http://powerboat.about.com/od/outboa...mercverado.htm