Less depth = Less current ?

[Dale I]

As a river sailor on the St. Johns I am exposed to near constant tidal current and am wondering why the local theory is to stay shallow if trying to make way against the current...and deep water if going with the current. Does the deeper water move faster than the shallow in a tidal change? If so, why? The St. Johns typically ranges from 8-14' deep in the mile wide sections and 22' or so in the middle-channel... Your responses will likely make a difference in this weekends MUG RACE as I will be slogging the 16 miles south into south breezes and against the tide for the first half of the 'tall ship' class of the race.....(unlike 'Ted, from St. Augustine' who will have a downhill sleigh ride for the 38 miles from Palatka to the Buckman Bridge ). See Rudderclub.com for race details...and come on down next year...over 160 boats registered at last count and many more coming.sailjax.com also has other stuff on local events.

 

[LKYusnret]

I'll be there

in my H 260 Baums Rush down hill all the way. Actually I just don't want a DNF.

 

[Dale I]

LKY, Don't cut corners...

Hope you keep an eye on your depth as I have run hard aground many hundred of feet from shore near the points and bends in a Morgan 27...it is a river, you know. Watch the others around you and take care shaving the corners where marked.

 

[Art]

it's all friction

since water velocity must be zero at the boundary (the bottom) and there isn't likely to be a discontinuity in the flow profile the closer you are to the bottom (zero velocity) the lower the velocity is likely to be..this drag can also result in turbulent flow and even create backeddies with a positive push...these are often seen in shallows near shore ...the big down side is that the likelyhood of hitting objects (rocks, and reefs) are greater...so don't go into shallows unless you know what's there...it's usaually a good practice to finish the race with the keel you started with...

 

[nwilson56]

Want to see antoehr Catalina 30 for updtes

I would like to look at a Catalina 30 to see how to update this one I have just purchased. Can youhelp in Jacksonville, Florida 363-0220

 

[Jeff Bacon]

Less depth = more current ....

..... at least that's what I remember from my formative years in kids sailing school. Based on the venturi effect, the water will flow faster over the shallow areas, then slow down when it hits the deeper water again. we were always taught to avoid the shallow areas when sailing against the current. Bernullis principle, maybe ?Jeff

 

[Tim Welsh]

river channel

I think the main part of the channel will have the most current. If the channel gets shallower the current will pick up. But out of the channel in the shallower waters there will be less current I believe. Tim Welsh

 

[MikeH]

Stay shallow if you have the wind

At last there is a piece of my former work experience that I can apply here! I've also been a river sailer for the last 30 years. My old company did a lot of hydraulic engineering on liquid flows in troughs and canals. Art is right; at the boundary layer (where the water meets the bottom) the water speed is essentially zero, with velocity increasing away from it. The highest velocity in a river situation will be near the center above the deepest part. So when sailing with the current, stay in the deepest parts that have good wind. If you're going against the current then stay as shallow as you can while keeping in decent wind. Shore obstructions are notorious for stealing and mis-shaping wind flows, so you usually can't hug the shore unless you're getting wind from the opposite shore. Look at the wind direction and the height of obstructions on land. Don't let the obstructions blanket your wind.Go fast!MikeH

 

[AndyS]

MikeH hit a major point

The effect of shore structures on the wind is huge, you have to watch carefully.Also, as he mentioned, you stay deep going down-current - which means in tidal waters, you have to know when the tide is slack, and when it is at max flood and ebb. When sailing a series of races, the guy who does great one race, then bad the next may well be the one who forgot that the tide was switching and found himself on the wrong side of the course.- AndyS