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Old 01-11-2015, 01:06 PM   #19
waddenkruiser
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City: Southern Baltic
Country: Europe
Vessel Name: Sømarken
Vessel Model: AMS 40'
Join Date: Jul 2012
Posts: 183
Eric,
no contradiction, this is what I tried to say: engine load and consequently fuel consumption will differ if you have the same engine (and hull) but different propulsion load curves i.e. different WOT rpm due to different screw designs. (I guess that's what you mean with "over propped": engine will not reach its rated max or WOT rpm because the screw / prop is not properly sized resulting in a load curve above engines rated power at engines rated max rpm.)
The over propped trawlers I have seen here in Northern Europe had typically a WOT rpm 5 - 15% below engines "rated WOT". My assumption is that in these cases a comparison of s.f.c. to a vessel with properly sized screw may differ by some 10-20% - that's what I meant with "house numbers" - and if the comparison is outside of that range one should start to think about.


best regards / med venlig hilsen
wadden
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best regards / med venlig hilsen
Wadden
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