LOL Talador,
I see you keep using your own physics! :DSeems like you have forgotten how to do this math, or is mixing up the formulas or the units.
1500N of drag is 1500W (2hp) at the speed of 1m/s (~2kn). Not 10 kn.
The formula is
P = F * v
P - Power [W]
F - Force [N]
v - velocity / speed [m/s]
At 5m/s (10kn), the required power is 5*1500 = 7500W or 10hp. Looks reasonable to me.
Rick seems to be a very knowledgeable person, so I think you really should double or triple check your math before you try to school him. =)
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Björn
Who doesn't fly, but did pay attention in physics class. He even thought is was fun.
On Mon, Jan 11, 2016 at 6:03 PM, taladorwood@yahoo.com.au [harryproa] <harryproa@yahoogroups.com.au> wrote:
Rick,
"Basic numbers for 10kts:Calm water drag 850NAdded wave drag for 2m seas 250NAdded wind drag for 20kts on the nose 350NTotal drag 1540N"Do you seriously think 1540N (2 hp) will drive a 60 foot, 5 ton boat at 10 knots into 20 knot winds?I once pushed a big boat with a 4 hp engine on a dingy (lashed to the side) it took forever to get it moving. but eventually yeah I got it moving. Maybe up to 4 or 5 knots in perfectly calm conditions, but any wind and we would have been toast.I bet your calculations are off by 9.8? 20hp driving a 5 ton, 60 foot boat at 10 knots sounds a lot more reasonable. And most of the power boaters I know would kill to get that kind of performance. . . 20 hp is less than 1 gallon per hour. 10 mpg in a boat going 10 knots is very good and doable. You are claiming you can get 10 times better performance than very good, the equivalent to 100 miles per gallon.Talador
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