How is the thrust of the props converted to move the boat?

[[2068]]

"The surface of the water actually rises by a millionth of a micron, to compensate for your leg, which is what rafiki called displacement."

Not sure about this one, but isn't the increased displacement caused by leg-in-the-water offset by the decreased displacement caused by boat plus crew minus the leg?

 

[MapisM]

Oi, that's exactly the reason for the 3.7 hundredth of a micron lower waterline!

 

[jfm]

Ermm... I don't think so.
According to my slide rule here, the leg volume would be compensated by a lowering in Deleted User's Ferretti w/line of exactly 3.7 hundredth of a micron.
LOL, how did we get into this...?!?

You are indeed right MapisM on that, BUT, you are assuming mike hasn't driven his Ferretti aground or up the beach . Flowerpower has half-Lakesailored you too! It is all beside the point though, and yes how did we get into this?

 

[MapisM]

You are indeed right MapisM on that, BUT, you are assuming mike hasn't driven his Ferretti aground or up the beach

Darn, I should have thought that you had a sensible explanation...
ROTFL, you can't make this stuff up!

 

[MapisM]

I suspect that you actually said 1000hp just as an example, therefore my numbers are meaningless, but as I said I was bored...

Yes it was just a rough guess...

I just saw your reply above, must have missed it between one page and another.
Anyway yep, that's pretty much what I thought.
But out of curiosity, do you remember what sort of rpm dit actually M1 demand, to cruise at 20kts?
Coming to think of it, maybe 2000rpm/1000hp/200lph was not too far off the mark...

 

[jfm]

I just saw your reply above, must have missed it between one page and another.
Anyway yep, that's pretty much what I thought.
But out of curiosity, do you remember what sort of rpm dit actually M1 demand, to cruise at 20kts?
Coming to think of it, maybe 2000rpm/1000hp/200lph was not too far off the mark...

400lph is exactly right at 20/21kts iirc. RPM @20kts is something like 1650. I'll check other data....

 

[MapisM]

Yeah, by 200lph I meant each side, of course.
Interesting to hear that rpm was that much lower, though.
Obviously the Cat prop demand curves can only give an idea, actual numbers depend also on each hull, weight, props, etc.
Interestingly, at max load those beasts can output 1000 hp already at 1400rpm or so...!