Correct prop

[Perroboy]

I have just bought a Destroyer 5.3 with Suzuki DF70 off Fleabay.

Prop is 13 1/2 x15 3 blade.Fuel consumption appears to be crap!!!The previous owners changed the prop from standard.Can anyone suggest a better prop? Not interested in top speed just want to go further than 1 mile per litre at a gentle cruise (17 knots @4000rpm).Or am I being unrealistic?Pretty sure my old DT 75 stroker was as economical as that!!!
Thanks!!

[longjohn]

I think the standard prop for that engine is a 13 1/4 x 17 3 blade. Are you achieving max revs (5800 rpm) at WOT? What are your revs at that speed - most economical speed is at max torque which is usually around 4000-4500 rpm. 1 litre per NM is a pretty much average for most ribs so you are not that far off.....might expect slightly better.

[Perroboy]

Originally Posted by longjohn

I think the standard prop for that engine is a 13 1/4 x 17 3 blade. Are you achieving max revs (5800 rpm) at WOT? What are your revs at that speed - most economical speed is at max torque which is usually around 4000-4500 rpm. 1 litre per NM is a pretty much average for most ribs so you are not that far off.....might expect slightly better.

I do hit 5800 rpm at WOT and a speed of 25knots...ish.

[Erin]

I don't think 1lt/nm is too bad, but I would have thought you should be getting more than 25kts out of it. Perhaps little under propped.

[longjohn]

Originally Posted by Erin

I don't think 1lt/nm is too bad, but I would have thought you should be getting more than 25kts out of it. Perhaps little under propped.

Yes I agree 25 Kts seems slow - your boat is only a little bigger and probably not any heavier than mine with the same engine and I have seen 38 Kts though 35 is more an attainable max