Gravesend Marina

Visited 17/19 Mar. to bend on sails! We shipped the canvas Friday morning and sailed at High Tide 17th - 1h+30m so as to be facing the lock about 45 minutes before high tide. Timing was crucial 

 http://www.gravesendsailingclub.co.uk/gscweb/comment.php?comment.news.61

http://www.portoflondon.co.uk/display_fixedpage.cfm?id=11&site=maritime

This link enables you to access the resources needed to plan trips up and down the river. In our capacity as volunteers and Core Crew, we only need to know as much as is needed to ensure that we can cope with the training element of our work on board. But each crew-member should at least understand how tides work. The estuary is our primary sailing ground and everything works around the tides. Take time to address this part of our work. Learn the ebb and flow and know some basic numbers.

Each time KJ sails, someone has to do the sums. Woolwich was a good case where we had to know what height of water we could float her over the grid, what height the keel would touch, when the keel would be fully engaged, when the grid would dry, when we could walk under the ship to find the leak and how long we had to fix it.

TRAINING EXERCISE

Drying height of the grid we are going on is [nominally] 2.4m. We draw 2.9m. We are afloat over the grid at 5.3m. Sat, tide goes up to 6.8m at 1759z, We have 1.5m clearance on this tide. at 1759z. The 'twelfth' for Woolwich on Sat evening is 0.5m. She drops 0.5 in the first hour and 1.0 in the second. At 2000z she should touch the grid  

KJ has to come off the Woolwich slip on Saturday evening about 1830z so as to be poured down-river to Tilbury. The distance is twelve nautical miles. KJ would make 8kts with that flow. We need to book the lock inbound for 2000 with a strong expectation of being there earlier.

REALITY

Skipper decided to go at 2130z, slipped at 2125z, entered the lock 2130z, cleared it 2150z and punched tide for the next hour, had an hour of slack, then a bit of flood in Galions Reach arriving at the buoy 0045z. had he slipped at 2230 he would've cleared the dock at 2300 into a flow of tide increasing in vigour all the way to Woolwich. The elapsed time would have been two hours instead of the reported three and a quarter hours. The arrival time would have been five or ten minutes later and the crew would not have been frazzled.

Same happened coming down Saturday. Skipper just could not wait. Had her out of the mooring at 1633 one and a half hours before high water at Woolwich. So instead of being a static exhibit for some two hours high in the water she was off before she was seen above dock height. KJ punched tide for two hours before getting the top of tide slack about 1800 at 51-29.05N x 0-12.237E. She entered the lock at 1900 and berthed at 1945. So now we know how long it really takes to get through the lock!