40 HP Outboard Power Curve

[hwsiii]

I have a power curve excel spreadsheet setup for my 40HP outboard, but I do not believe it is correct. Does anyone have a known good power curve I could compare it to. I know they are all different, but in two cycles they should be fairly close.


Thanking you in advance for your kind help.
H

 

[Silvertip]

Re: 40 HP Outboard Power Curve

What are you plotting -- horsepower, torque, or both and how are you measuring them? What year make and model outboard are you talking about?

 

[hwsiii]

Re: 40 HP Outboard Power Curve

I am Plotting HP, Shaft Torque and Torque. It is a 1995 Force 40 HP with a 2 to 1 gear ratio. I am running a Michigan Apollo prop at 10 3/8" x 14" and I am topping out at speed of 31 MPH @ 4800 RPM with 1600 pounds all-up weight.


H

 

[Bondo]

Re: 40 HP Outboard Power Curve

Ayuh,...

/

There ya go.... That's from idle to WOT... 0hp to 40hp...

 

[hwsiii]

Re: 40 HP Outboard Power Curve

Thanks for the useless information Bondo. It is extremely helpful.

H

 

[Bondo]

Re: 40 HP Outboard Power Curve

Thanks for the useless information Bondo. It is extremely helpful.

H

Ayuh,... I'm sorry you don't see the Humor,....

Why are you posting a Motor Question in the Prop forum to begin with,..??
This belongs in the Chrysler/ Force outboard motor Forum,....
Not up here...

For curiosities sake,...

Just what is this spread sheet going to do for you,..??

 

[steelespike]

Re: 40 HP Outboard Power Curve

I searched on google I did find a torque curve for a 150 Etec vs 150Yamaha
4 stroke. I don't do well posting pics or addresses.I searched "outboard power curve",OB power charts.Outboard torque curve etc. Etec is dfi so I think a different curve than a carbed 2 stroke.I think these things are well guarded factory info.If your presistant enough you might find some independent charts perhaps on the outboard soup up sites perhaps "scream and fly"could put you on to some info.Maybe some before and after dyno tests.
Your speed seems good considering the Force isn't noted for its performance.
Have you fine tuned your setup?I believe the 40 is rated at 5,000 Most motors folks seem to shoot for rpm about 500 above the rated rpm.I don't know about the Force.

 

[hwsiii]

Re: 40 HP Outboard Power Curve

Thank you very much steelespike, I appreciate your searching to try and help. In my opinion they don't post these power curves for one reason, if everybody knew what the differences between each one was, the could make a much better informed decision about which particular motor would best suit their intended uses. They all seem to claim BROAD power bands, low end torque and high speed as their attributes, and you definitely can't get all of this in one motor. That is why I come to this forum, for the knowledge that I gain, just reading all of the different post in different areas of boats and motors.
Bond-o, by having these spreadsheets I will be able to plot RPM versus boat speed and then using Crouch and Savitsky I can show boat speed versus HP at many points in the power curve. I can also use these numbers to predict rudimentary fuel and MPG curves for a vessel that I am going to start building in the next six months. These relationships are an important part of my research into which of two designs I intend on building for economy and seaworthiness in formed seas. One is 25' and the other is 28' and both have similar characteristics but yet are different enough that I want to be sure that I have as much knowledge about the differences I can expect between the power requirements and expectations of cruising speeds and fuel consumption between the two.
BY having these correlations using my spreadsheets i can decide on which HP motor would probably be best for each vessel for fuel economy and my intended speeds as well as how much speed I can expect at different weights when using the boat. They also will help me decide on a starting point for which Diameter and Pitch prop I need for each motor on each boat, although I consider propping a boat correctly is almost a black art. Given the differences in rake(bow lifting or stern lifting), pitch(progressive or not), skew, cupping and all of the other assorted differences between each prop model in any one companies lineup, much less all of the different companies. Just because a prop says it is 10 3/8" diameter and 14" pitch does not mean that it is even CLOSE to the same performance on a particular boat if you even bought those same dimensions in a prop from the same company. That is why I decided to use the prop forum for my question.


H

 

[Randybeall]

Re: 40 HP Outboard Power Curve

On a different tack, if you have calculated that 40 hp is the amount you need to get the speed you need in this boat design.....all you have to do is find gallons per hour for each engine. I believe your looking for information which is not going to directly answer your question.

 

[Bondo]

Re: 40 HP Outboard Power Curve

I believe your looking for information which is not going to directly answer your question.

Ayuh,...

To Me,.. It sounds like Extemely Over-complicating a Simple Issue....

hwsiii,... Are you an Engineer,..??

 

[ondarvr]

Re: 40 HP Outboard Power Curve

I'm a little confused, first you ask about a 40hp Force, a somewhat simple low cost brand known for poor fuel efficiency, then you switch to 25 and 28' vessels. The engines that typically get used in this size craft have all of this information easily accessible.

You can't get a generic power curve for an engine, you would need the actual numbers from a dyno test on that motor, anything else would be useless.

 

[hwsiii]

Re: 40 HP Outboard Power Curve

I believe what I am doing is a viable alternative to having the exact power curves for any particular motor and prop combination. They are relative to each other and to the overall combination of my goal. I am also using savitsky's formulas for cross checking speed and HP calculations as well. There are many variables involved exactly as has been posted in replies. I am just trying to get approximate numbers at this time. By also plotting HP and Prop curves I can see if there is enough HP at any particular RPM setting to have residual HP to turn the prop efficiently. I am sorry if this is the wrong place to post this.

H

 

[ondarvr]

Re: 40 HP Outboard Power Curve

It seems to me there would be far too many variables in trying to estimate the power curve of any engine with only the displacement and supposed (advertised) HP. From decades of racing with 2 strokes and 4 strokes I can tell that motors with nearly identical spec's can have a tremendous difference in how and where they produce power.

 

[hwsiii]

Re: 40 HP Outboard Power Curve

Ondarvr, that is a true statement you are making. I am just trying to produce generalities. But if you think it is easy to get power curve information from outboard manufacturers, I have been trying to get power curves on 100 HP motors for a week. Either Mercury or Yamaha, if you can find that information available, please tell me where. You are used to dealing with High Performance motors that have been dyno tested because they are high performance.


H

 

[Silvertip]

Re: 40 HP Outboard Power Curve

You said: "I am just trying to get approximate numbers at this time. By also plotting HP and Prop curves I can see if there is enough HP at any particular RPM setting to have residual HP to turn the prop efficiently."

Since outboards have no transmission, the engine is essentially operating in high gear all the time. With that in mind, what you are trying to do is a waste of time and effort since the manufacturer of that engine has already designed, tested, and manufactured the engine to the parameters they deemed proper for the intended application. There is nothing you can do to change that. But back to your statement. An outboard, regardless of gear ratio, hp, or torque, must be propped so it revs at or near the manufacturers recommended WOT rpm. If it's wrong at that point, it is wrong all across the curve. Overpropped at WOT means it is overpropped at 3500 rpm (or any other point for that matter). Since you are looking at Yamaha for data to compare what you have obtained from testing with your Force, go here, pick an engine, pick a boat, and you will see performance data to compare against. It even includes fuel flow data and loading information. You will not get proprietary data from any manufacturer unless you pay for it.

http://www.yamaha-motor.com/outboard/products/perfbull.aspx

 

[ondarvr]

Re: 40 HP Outboard Power Curve

Ondarvr, that is a true statement you are making. I am just trying to produce generalities. But if you think it is easy to get power curve information from outboard manufacturers, I have been trying to get power curves on 100 HP motors for a week. Either Mercury or Yamaha, if you can find that information available, please tell me where. You are used to dealing with High Performance motors that have been dyno tested because they are high performance.


H

The power curve and/or torque curve graphs have been discussed here before and so far they seem to be a rare item, it's just something they don't want to release. I really don't know why, because with every other type of motor its something they brag about and are easily found. If it could be done on a normal dyno then maybe an independent party would have done it by now.

What good are the generalities, they're just numbers that are known to be wrong in every situation. There's far too much that goes into hull design, props and engines to make any rules that apply without actual testing

 

[Randybeall]

Re: 40 HP Outboard Power Curve

I have thought about what you are trying to do and it is a wonderful idea. A formula which would allow one to predict what engine and prop combination would work on a boat.
'Sorry Charlie' to steal a phrase. That has been tried for many years and there are too many variables in the application. Every hull, even those built in a production line, is different. You can use experience to give you a starting point, or you can calculate drag of the hull after trials in a flow bench, but even major ship manufacturers have made miscalculatons on new designs which took many dollars to reprop an ocean liner.
I understand that you want to be sure about the power curve but I will assure you, if you get enough power to propell the craft at the top speed you want you will have enough to get it there. Where peak fuel efficency occurs will be affected by torque curve but other than that the dynomometer effect will take care of itself. The engine will devolop enough horsepower to turn the prop and will accelerate as you give it more fuel and air. Your real concern is how much horsepower do you need to drive your hull the speed you want. All else is just classroom excersise, or you could dig a ditch and then fill it in with the dirt you just took out. Sorry if this seems rude but it is the way pumps work, go back and read the theory again.