Depth sounder

This morning at 5:10 we left for Quebec City. We were leaving about exactly one hour after low tide. The book and the Marina said you should wait until one and a half to two hours after low tide to leave. The gentleman in the trawler beside us who had been a river pilot said that he drew 4.5 pieds and had no problem leaving one hour after low tide. To be sure we sent out our personal depth sounder to check it out. You can see her walking out route to make sure there was at least some water. We got to the entrance and had 2 feet. Our motor got to work and did a little dredging and out we popped. Currently we are just opposite a ferry to Ile aux Grues and about 25 knots from Quebec doing about 8.2. Kns. Bon jour