First we radioed we needed a pump and fuel. Response was we can fuel you at your slip. Once docked, they then told us we had to go to the fuel dock to pump out. Second, on our morning of departure, I powered up our electronics and noticed the depth sounder was reading 0.4 ft under bottom. We checked and the tide was going out for 2 more hours. So, we powered up to leave early. By that time, depth sounder was reading 0.0 ft under bottom. We were stirring up mud and aground off and on as we pulled out of the slip into the fairway. Had we not left we would have been hard aground in the slip. Our boat is a GB LOA 47.5 Beam 14.5 Draft 4.5. All info the marina had in advance.