I don't have personnel experience sailing in the North Sound of Grand Cayman, but we have been spending a lot of time this year in the Abacos, and there are many days I WISH we had as much water as is charted in Grand Cayman's North Sound!  Some days I feel like we are giving the turtle grass a crew-cut with the keel wings!  It is rather disconcerting to be sailing along at 6 knots and seeing the sand swirl up in the wake behind you...

This advice might not apply to you, you might be completely comfortable with this, but in case anybody else lives in fear of water less than 3 meters deep....

It has taken a bit of attitude adjustment for me to get comfortable sailing in very skinny water. We move around on a rising tide, although with a tide range of about a foot or so this doesn't buy you much in the Caymans, but every inch counts. If there is a risk of coral heads sticking up from the bottom, we ALWAYS move with good light and a bow lookout. Better if your lookout is up high on the spreaders, but I haven't been able to talk Karen into that--yet! We have actually only touched once while sailing in the Bahamas this year, and that was up onto a sand bank at 5 knots with 5 feet of water over it when the charts all said more than 8. 

We look for an anchorage with 9 feet, but we settle for a charted depth of as little as 7 feet.  Yes, that leaves us with six inches to spare at MLW. We haven't done it yet this season, but it is not a disaster to sit on a sand or mud bottom for an hour at dead low water.  We always check with the dinghy around the swing circle of the anchor for surprise shallow spots.

We have become a bit cavalier about bottoms of sand and soft mud, and more that a bit paranoid of rock and coral.  Seems like the right attitude.

We have three different chart sources we use.  Navionics (in the chart plotter and on the PC), the NV paper charts, and the TRANSAS CE charts on the iSailor iPad app.  Each with different survey data. We find the discrepancies frustrating--and educational.  At least in the US southeast, and Bahamas the TRANSAS CE charts have been the most consistently reliable, but none are perfect.

Be sure your depth sounder is accurate.  Makes no difference  if you display the depth of water, or depth under the keel, but check it to be sure you can trust it, and that it can actually tell you the difference between 6.9 feet and 6.6 feet.

We always record a track on the chartplotter.  That way we always know a way back out of whatever trouble we get into.

Bill Kinney

SM#160, Harmonie