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Old 04-02-2014, 12:33 PM   #12
Ski in NC
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City: Wilmington, NC
Country: USA
Vessel Name: Louisa
Vessel Model: Custom Built 38
Join Date: Jan 2014
Posts: 5,404
Originally Posted by manyboats View Post
Diesel and gas are almost the same re efficiency at full bore.
Not close at all.

370hp Mercruiser 8.1 @ full power 30.1 gph: 12.3hp/gph

380hp Cummins 5.9 @ full power 20.1 gph: 18.9hp/gph

Pretty substantial difference.

Using 2.7 exp load curve

Merc at cruise 197hp 19.6gph: 10.1hp/gph

Cummins at cruise 208hp 10.4gph: 20.0hp/gph

Merc data from a Sea Ray 380 test report, Cummins data from qsb5.9 performance curve.

You can see the hp/gph drop towards cruise with the gas engine, it improves a little with the diesel. I don't have any data at hand to look further into the lower rpm numbers.
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