Trying to understand torque graph.

[colhel]

Our boat has the TAMD41A engine, I found this online and am hoping it will be similar for our engine http://goldcoastpower.com/brochures/VOLVO TAMD41M Brochure Specifications.pdf

What I'd like to know is, what of the four lines (2 solid and 2 broken) will be most relevant to me , also what exp2.5 and exp 2.7 are referring too. Our boat is a Nimbus 3003 which looks like it has a similar, if not the same, underwater profile as most other Nimbusseseseseses (Nimbi) out there. Coming from a raggie background, of course I'm fairly keen on the fuel consumption graph...

Cheers!

 

[Portofino]

Here you are re prop exponant .Disregard the last para on variable pitch .
One assumes the builder and engine supplier have had get together and arrived at a suitable pitch and dia for your boat .

https://www.scribd.com/document/351015951/Marine-Engineering-Significance-of-Propeller-Curve

The graph in your link is from VP sort of hypothetical one size catch all to put something down in the brochure .

How ever the L/ h graph ( which I take you seem more interested in? ) looks like 3200 .
Is that do able knots wise for you ? Seems like approx 33L/h and soon risers over 40 L/has you go higher with rpm .
We don,t know your exact exponant to give any further detailed L/ h info .
Because we don,t know the pitch ,or dia or any other relevant stats on your Nimbus .

Maybe trawl a MBY or similar real boat test .
As you prob know there’s other variables like sterngear fouling and bottom state which effect the consumption .
There are a few others too ,like the engines arn,t exactly fresh out the box so I guess the Hp rating will be down now from when the link you posted was printed over 20 y ago .
So all things considered work on 40 L/ h per engine somewhere arround 3200 rpm

 

[[2068]]

The exp 2.5 dotted line is for the “light duty” engine which you probably have. It exactly matches no boats or propellors whatsoever, but will be a rough guide.

The solid line would be if you took the props off and somehow attached it to a dyno. Solid line is pretty much useless information from a practical point of view.

Exp 2.7 figures are for the “medium duty” engine which tops out at 3200rpm. I would guess you don’t have this engine.

 

[colhel]

That's great. Thanks very much.