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Old 10-27-2014, 01:16 AM   #20
makobuilders
Guru
 
City: Canaveral
Country: USA
Join Date: Jun 2012
Posts: 1,438
I've always been told by mechanics that my Jimmies weren't happy unless loaded up, but I always thought that was just a saying. Now per kulas44's explanation I see the actual technical basis for it.

A displacement boat powered to 100% at V/L=1.34 would be running at 50% at V/L=1.15, a typical continuous and economical cruise speed. In my case I ran my boat at 35% load which never varied. Whether in 20ft seas or flat calm or crossing a bar, I never raised my speed. Honestly I never had a need for "reserve power". I suppose on my upcoming trawler (hopefully Jimmy-powered) I will design it for 60-70% powerload at V/L=1.15, leaving it a bit underpowered.

Perhaps we should spin-off a new thread about engine loading and reserve power.
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