If you do end up at Mersea on the 29th tides are perfect... high is around 2.30pm which means you will have plenty of water from around 10am-11am... be out on a rising tide and within 1.5hrs past high still with loads of water it will probably be later than you want to stay out this time of year.
Toilets & wash/change facillities at the head of the pontoon open 8am to 6pm.
Do remember to use the slip immediately adj the current lifeboat station down between the stored boats... not the wide but very muddy one opp the junction with Firs Chase.
The preferred slip is here... https://goo.gl/maps/GgV7jzcFWe52
Just one caution on that slip... if you look at the image below and imagine facing the water best to launch over the top of or to the right of the rightmost of the two pairs of metal launch rails. On the left hand one there is nearly always stored clutter (as seen in the image) that covers once the tide is in a bit and could produce a prop tangle situation.