hull speed

[sailaway78]

An example

The GPS is pretty smart, but not smart enough to determine how much current is with or against you, same for wind and wave actions. So you get a total of these functions. If current is with you, it is added to speed through the water, against you subtracted. I have seen max. GPS speeds on my 28, range from nearly 19 knots to less than 4 knots. Crossing the gulf last year on TonyB's 39' Allied, we saw speeds under two knots, running that iron genny as hard as it would run.And before some of you jump on me about the 19 knots, this was coming through a flood gate on the Colorado river in Texas, when the river was at full flood. And yes it was scary.

 

[LloydB]

Joe I think this subject

will never be worn out as sailors will always want to know how fast... and there will often be new sailors wanting to know what do you measure 'Theoretical Hull Speed' with?, if you cant use a GPS. And the answer is so obvious that it is often unstated.

 

[Tom]

Who Really Cares??

Usually I don't really care what my speed is at any moment in time. At sailboat speeds I'm not getting anywhere fast. My Knotmeter is broken has been for almost a year and I don't miss it at all. Almost never fire up my handheld GPS I know where I am and where I'm going. Whatever speed I am traveling I won't get to where I'm going until I get there. Flying a plane I worry because the plane will come down when it's out of fuel. Driving a car I worry because I don't want a speeding ticket. In my sailboat sailing my speed is usually determined by wind speed...it's rare that I'm going fast enough to worry about hull speed. Even if I know my speed there is little that I can do to speed up. Adjust the sails until they look pretty and then drink a beer and enjoy sailing. If I'm going fast I'll tack across the lake another time if slow I 'll enjoy the sunset. Be very happy if you are moving fast enough to worry about hull speed. Motoring I look at the tachometer. About 2000 RPM 80% of WOT then whatever speed that is is OK. If I'm too slow I still don't want to go WOT for any long distance and as stated previously going too fast isn't an option in a sailboat. DON'T Worry ,Be Happy

 

[AXEL]

Check the units

I found that my GPS was always showing that my boat speed was much higher than what the knotmeter was reading. Upon some investagation I discovered my GPS was measuring speed as MPH as opposed to KPH. After setting the speed units to knots the GPS and knotmeter made much more sence.