Oil Pressure goone, squealing gone, yay!

JonChristman · Post by **JonChristman** » Sat Jul 02, 2011 7:23 am

We got the boat out on the lake Thursday night and everything was good. It was a great afternoon to be on the water. Oil pressure was in normal ranges, temp was good, and no squealing sounds. The only discrepency I have is speed at this point. Couldn't get much about 3500 on WOT. Garmin showed 18.8kts but Hummingbird showed 25mph... I am inclined to believe the GPS technology rather then the Hummingbird which has the wheel on the bottom of the boat.

Big D · Post by **Big D** » Sat Jul 02, 2011 11:42 am

Jon, that's great news. For future refference, there are differences between the two systems that lead to minor speed discrepancies. GPS measures the time it takes for you to get from point A to point B, then does a simple calculation resulting in your "speed over ground". This does not take into account the conditions/forces the vessel encounters along the way. I like the ETA feature; saves me the trouble of trying to figure out when I'll finally get to a destination. The paddle wheel method however measures how fast water is turning the paddle. If you're heading into a 3 knot current for example, the unit will display that the vessel's speed is 3 knots faster than it actually is. The reading can also be affected by several things such as fouling on the paddle, correct installation, inherent tolerances etc. It's all relative!!

JonChristman · Post by **JonChristman** » Wed Jul 06, 2011 8:26 pm

Yep same concept in the air when flying groundspeed versus airspeed. There wasn't too much water movement that day, and they were off about the same amount on the trip back to the marina. I figure the GPS is probably more reliable on speed that the Hummingbird, but never the less it was a good trip.

prowlersfish · Post by **prowlersfish** » Wed Jul 06, 2011 10:58 pm

And don't forget Knots is not the same as MPH . 1 mph = 1.151 knots

rooferdave · Post by **rooferdave** » Thu Jul 07, 2011 8:48 am

prowlersfish wrote:And don't forget Knots is not the same as MPH . 1 mph = 1.151 knots

I was under the impression that it is the other way 1.15 mph = 1 knot

http://www.militaryfactory.com/conversi ... r_hour.asp

wowzer52 · Post by **wowzer52** » Thu Jul 07, 2011 10:53 am

You are correct rooferdave. When the GPS is set to "miles per hour" the speed is alot more impressive in conversation than when it's set to "knots per hour". I keep mine set at "knots" for my laptop navigation. At 28 knots WOT how fast am I going in mph?...32 mph, now that's impressive in an old boat weighing 16,000lb loaded with 351 Mercs.