Interesting Comparisons

[qcamel]

Obviously needs to be taken with a slight pinch of salt due to the not completely impartial way the tests are ilustrated but here are some interesting engine comparisons from the Mercury Website.

www.mercurymarine.com

Ollie

[Brian]

Hmm. It is what I thought. A GPH figure is pretty meaningless. On a 300 Verado it varies from 2 to 60GPH.
A MPG or LPM figure is far more meaningful.

[codprawn]

60gph? Surely not - thats well over 200 lph...........

[qcamel]

I know, our friends in the west always talk in GPH, not sure why and like you struggle to see the relevence, however they continue to do it o it must mean something logical...

[ian parkes]

Havin spent some time recently deciding on motors I have found a few tests like that , the type of boat is unknow and i found any figures pretty meaningless .
Unless they do side by side comparisons of different makes on the same boat its hard to get an idea .
power to wieght comparison is about all you can do . Unless you can believe all the vids on the evinrude site .

[Poly]

Originally Posted by Brian

Hmm. It is what I thought. A GPH figure is pretty meaningless. On a 300 Verado it varies from 2 to 60GPH.
A MPG or LPM figure is far more meaningful.

But to include a fuel consumption per distance numer in the spec for an engine would be dependent on the boat and propellor, wheras fuel consumption at any given rpm/throttle position is not.

So e.g. if an engine burns 30 LPH at WOT and on a particular rib tops out at 30 knots it will be using 1L per NM. The same engine on a "better designed" (faster) hull, or with a better prop might give 40 knots at WOT - so using just 0.75L per NM. But put it on a semi-displacement craft and it might not get above 20 knots - and will burn 1.5 L per NM. All the same engine - all using the "optimum" prop for the situation - but very different results and nothing to do with the engine design...

[kitten]

Consuption at a given revs will still depend on the load so you still have the prop hull variable.

[Brian]

Originally Posted by Polwart

But to include a fuel consumption per distance numer in the spec for an engine would be dependent on the boat and propellor, wheras fuel consumption at any given rpm/throttle position is not.



So e.g. if an engine burns 30 LPH at WOT and on a particular rib tops out at 30 knots it will be using 1L per NM. The same engine on a "better designed" (faster) hull, or with a better prop might give 40 knots at WOT - so using just 0.75L per NM. But put it on a semi-displacement craft and it might not get above 20 knots - and will burn 1.5 L per NM. All the same engine - all using the "optimum" prop for the situation - but very different results and nothing to do with the engine design...

But, I already "have" a boat and a propellor. I want to know how far it will go for a specific amount of fuel.

You see my point. "IF a particular rib tops out at..........".
I need to know this before I start my calculation.
Agreed there are a huge number of variations, boat speed, revs, sea state, weather, no. of pax etc. but to say 10 gals per hour, or whatever, gives one NO chance of establishing performance.
But I suppose we are looking at/for diferent things. I want to know the specific performance of that engine on a specific boat. You want to know about the performance of an engine (in isolation).

[Poly]

Originally Posted by Brian

But, I already "have" a boat and a propellor. I want to know how far it will go for a specific amount of fuel.

You see my point. "IF a particular rib tops out at..........".
I need to know this before I start my calculation.
Agreed there are a huge number of variations, boat speed, revs, sea state, weather, no. of pax etc. but to say 10 gals per hour, or whatever, gives one NO chance of establishing performance.
But I suppose we are looking at/for diferent things. I want to know the specific performance of that engine on a specific boat. You want to know about the performance of an engine (in isolation).

Brian - I understand what you want - but I don't think it is reasonable to expect an engine manufacturer to be able to speculate on fuel consumption on a 3rd party boat. IIRC the Yamaha US site does have some comparison for some of their engines on a variety of boats...

On the otherhannd if someone is selling a boat and engine bundle it is not unrealistic to expect consumption per distance values for the sort of set up they are selling you.

[Poly]

Originally Posted by kitten

Consuption at a given revs will still depend on the load so you still have the prop hull variable.

Presumably engine manufacturers measure their quoted fuel consumption in a test tank with some sort of fixed load on? I don't know if that is standardised across manufacturers or not?