Rudder hum

Exactly. Avila was probably the fastest I ever sailed the 20 upwind. We fell off of "Best point" to chase John Holmberg as he was sailing heavy and needed the boat speed (400lbs TTL crew weight). 20+ knots of wind speed. He was killing us with boat speed if I tried to point as high as the sails would allow.

Matt's point might be valid but I sure hate to add to the helm. I will adjust and sail the Pumpkin Pursuit race next week in SF bay and let you know how it goes.

BTW, my sailing buddy/competition (former H20 NAC champ) removed the EPO3s and put his EPO2s back on. He could not dial the EPO3s in on the H20. The foil is somehow different.

_________________
H18 '85
H18 '89 "Knotty Passion"
H20 '96 "20/20 Vision"
Fleet 259 Central Coast California

Would be a matter of trial and error I guess. Reach / run and let go of the tiller. Slight weather pull. I think you all try to get too neutral. Then steering is push and pull... very difficult and too easy to over steer with no load on the helm.

_________________
Matt Miller
Former - Director of Parts and Accessory Sales
Warranty and Technical Support
Hobie Cat USA
(Retired 11/7/2022)

A small amount of weatherhelm contributes to hydrodynamic lift and little to no extra drag as well.

Matt,

Love your turbulence lesson near the top of page one! Have always wondered if the differences in fresh and salt water result in any speed differences. Maybe saltwater's higher flotation effects cancel out its "heavier" form drag, (having to move a heavier substance out of the way). Then there is "slipperyness". So maybe it all cancels out and zero to negligible difference in sailboat speed in salt vs fresh water?

Propeller driven boats would react differently, as both the hull and powering props are affected. Sailboats are "externally powered". Ah, except for centerboards... complicated!

Waterskiing one day in a fresh water lake immediatly after skiing in a saltwater lagoon, my skis seemed lower in the water and it took longer to get on plane, but they also felt "slipperier", like ice skating instead of roller skating. That is an exaggeration, but sort of... Seems I didn't lean back as much in fresh water.

Interesting question anyway!

The term you're looking for is "kinematic viscosity," which is essentially the "surface friction" of the water against the submerged body.

When naval architects dissect the resistance of a body moving through the water, we break them down into two primary components: viscous resistance (due to the drag of the water on the wetted surface) and wave-making resistance (due to the energy lost in travelling through a viscous fluid, which manifests itself in pressure waves that then become physical waves). At low speeds, viscous drag is most prevalent, but at higher speeds the form drag becomes increasingly more relevant.

Viscous drag is most dependent on a physical relationship known as reynold's number (relating vessel inertia to fluid viscosity), whereas wave-making/form drag is most dependent on a different physical relationship known as Froude's number (relating vessel inertia to gravity). The resistance is simplified to a coefficient of frictional resistance and a coefficient of wave making resistance, each largely dependent on their respective relationships, which are each multiplied by water density, wetted surface area and vessel speed (squared), and added together to find total resistance.

The kinematic viscosity of water doesn't change appreciably with salinity (though it is very slightly higher for salt water, and it does change noticeably with water temperature), and gravity is similarly unaffected by salinity - so at the same speed, in fresh & salt water of the same temperature, the difference in total resistance is mostly a matter of water density vs. reduced wetted surface area. Salt water is ~2.5% more dense than freshwater, but the vessel will have less wetted surface area in salt water than freshwater. If the wetted surface area is decreased by less than 2.5%, the boat will be slower in salt water. If it's more, the boat will be faster. This is entirely dependent on hull form, but crunching some numbers, I would bet that the resistance in salt water is ~1.5% more than in fresh water - resulting in a slower boat.

Of course, that's just the theoretical mechanics of it. Actual experience may differ

Great reading this Matt, thanks for the awesome reply and for letting me stir up your grey matter!

Agree with your 1.5% guess because of all the splashing up on hulls, hitting cross beams, dragging under tramp etc. as equally extra wetted area. (Think 2.5% heavier saltwater hitting the cross beam, just as an example.)

But then centerbooards may provide more lift vs drag in salt, or not?...So anyway, basically negligible differences in speed between salt and fresh water. Darn it, I was looking for something cool here.

Actual results may vary, lol! And then, there are foiled cats... No, let's not go there.

Makes me think of early boat racers pumping out etheylene glycol (antifreeze) for a few mph but how many fish were killed? FPH? (fish per hour? -sorry, bad joke)

Thanks again, love the science, I am geeking out here!