Thread: Design
View Single Post
Old 02-07-2008, 04:56 PM   #23
Marin
Scraping Paint
 
City: -
Join Date: Oct 2007
Posts: 13,745
Design

Okay. Prompted by what FF said earlier, I just got off the phone with my friend at Northern Lights/Lugger and he explained the difference between what I'm seeing on the brake horsepower/rpm chart and what horsepower is actually being generated by the propeller. So as Eric has been pointing out, at 1700 rpm my prop is NOT generating 70 hp but is putting out considerably less. My friend explained that there is a formula to figure all this out, and it involves knowing the diameter and*pitch and surface area of the prop and*figuring out the cube of something, at which point I said, fine, I understand all that I need to understand.

When I asked him the bit about how the engine would generate 70 hp at 1700 rpm only if it was running at full throttle at that rpm setting, which would mean the boat would have to have way too coarse a prop on it so the engine would only turn 1700 rpm at full throttle, he said, "well.... sort of, kind of, yes and no,*it's not quite*that simple."

He offered to explain it all in detail over lunch sometime.

-- Edited by Marin at 19:16, 2008-02-07
Marin is offline   Reply With Quote