Speed to RPMs

[aholst1]

Finally broke down and bought a chartplotter (after 1 1/2 years) of current boat ownership and a lifetime of boating...Not only do I know where I supposed to be, I now have a "speedometer"
The boat: 89 Santego 2757, twin 4.3L Mercs w/A1s
On plane at 3400 - 3600 rpm or 22 - 25 mph
WOT at 4800rpm for 32 - 34 mph
Full fuel tanks, 15 gals of water, 2 humans on board plus gear.
Speed variance due to a windy day on the with the bridge enclosure zipped up tight.
Does the speed match the rpms?
Thanks,
AJ

 

[night moves]

Your speed and RPM relates to your boat. Other boats of your size and weight maybe the same, but with boats theres always lots of variables. Big yacht type boats, with lots of horse power may not vary much. A smaller boat, speed and RPM change by weight, water surface, drag-bottom surface, wind, well tuned engine(s),did I miss any thing? Back in my boat racing days, I had small counter weights that I could move pending on how the water surface was. This would help the speed by changing the atitude of the boat. This was important in a short course. Get to know your boat again with your new toys - keep notes! (wheres the spell check?)

 

[Unknown]

Yeah, each boat will be different in terms of speed versus RPM, especially if the props on there aren't the same type as originally installed...

But, your boat should be consistent, so you can roughly relate your RPM to your speed over the water (NOT OVER GROUND!) each time...