Hull Speed

[CapnHand]

Sure 'Canadian Sailcrafts made (make?) great boats' and all that but never mind the CS BS for now. Yes, there is more wetted surface in fw that slows you down. Yes, there is more waterline in fw that makes you faster. So, my question is; would a given monohull sailboat be faster in fresh water than salt water?

[Sailormann]

Sure 'Canadian Sailcrafts made (make?) great boats' and all that but never mind the CS BS for now. Yes, there is more wetted surface in fw that slows you down. Yes, there is more waterline in fw that makes you faster. So, my question is; would a given monohull sailboat be faster in fresh water than salt water?

CS is making sailboats again and the world is a better place as a result As far as the fresh vs salt speed differential goes, there may be a difference, but it's going to be pretty negligible. If a displacement hull is sitting an inch or two lower in the water, it may go 1/10th of a knot faster, IF you are moving through perfectly flat water. I don't think that you could find that flat water anywhere though...

[sailaway21]

But the hull speed is a theoretical maximum based on hull length. Back in the real world; for a given hull, the more she displaces, the slower she is going to be. So, what little hull length gained by your fresh water allowance is mostly consumed by your greater friction losses from a greater surface area. And since the difference in potential speed is negligible to begin with, vis-a-vis fresh/salt, we've probably rung about all we can out of this topic.(g)



but I could be wrong. (g)

[tomaz_423]

One think is sure about fresh and salt water - (This if from my Laser sailing times): You need more speed to start planning in fresh water.

[MeanzBeanz]

You REALLY notice it at low speeds on certain sailboards as well

[MeanzBeanz]

Originally Posted by sailingdog

tim-

It is far more likely that the knotmeter is less accurate than the GPS.

Yes but we are talking about speed through the water (log), not over the ground (gps). Calibrating your knot meter with a two way run (average of the two allows for tide current etc.) using the GPS is going to give you the best shot at accurate boat speed measurements.

One caveat is if you are sure you are in completely slack water. Then the gps speed is good for hull speed... but then if your log is calibrated they should match.