Paimpol to St Malo – Navigation Calculations

Just thought I would expand on some earlier notes about navigation and the tide.


Here's a sample nav plan.

1st, we've picked our next port (based on talking with others)...St Malo is a must see and we're running out of time for the French side of the channel.

So, the trick is to get to St Malo using the tidal current, which runs West to East starting 4 hours before high tide, turning back to East to West 2 hours after high tide.

Including the hour of high tide, that gives about 6 hours when the tide is running at up to 3 knots in our favor and not going against us at any point.

St Malo is 44km from Paimpol, so we need to make about 7.3 knots to make it. Which is beyond the theoretical hull speed of the boat, but the (up to) 3 knot current + a normal cruising speed of 5.5 under sail makes that quite “doable”.

So, 6 hours prior to high tide at St Malo, plus 1 hour to clear the lock here and get to the channel.
Note the gate (lock) that keeps the water high at all times within the harbor. You can see in this picture water leaking through. At low tide the gates are closed keeping the water high inside the harbor. At high tide the gates are left open so boats can come and go at will. In between the gates work as a lock, lifting and lowering the boats to match the water level on each side to allow the boats in and out of the harbor.

Next step is to determine what time that would be, so you consult a tide book (or your trusty chart plotter), find that high tide is at 10am, which puts your departure time in Paimpol at 3am (a bit early in this example...but we'll still go with that).

Then you check the state of the tide at Paimpol at 3am and find it is dead low tide, which means the only way to leave the port in the channel is via foot (see the low tide pictures of Paimpol)!

Ok, so that doesn't work

You can only leave Paimpol during the 5 hour period around high tide (the lockmaster does work nights)...so that's twice a day. During high tide, the lock doors are left open.

So, leaving at the 1st lock opening prior to high tide, you could get 3 hours of favorable tide, once you fight your way out of the water flowing into Paimpol and get into La Manche.

Then you have a few options. One, favored by someone we met, is to go against the tidal current and use the low speed over ground (SOG) to do a bit of fishing! Another is to find a port within range that you can enter 3 hours after high tide (good luck but sometimes possible) and the last option is to anchor somewhere, which can be a tricky proposition on this coast.

Armando found a good anchorage just 10 miles from Paimpol, so we left on the high tide (no lock skills required there) and made our way there.

I've left out one other step, which is to download a weather (grib) file and make sure the least bad thing that will happen is just wet, cold weather...

Which is, of course, what we're experiencing on this leg.

Then we go back to the original calculations and depart at dead low tide (we've gained 10nm on the original route), which (unfortunately) is at 5am.

If you get to St Malo outside of the lock operating times (I've read the paragraph on that 6 times and still don't get it...but we'll be fine arriving on high tide in the morning), you go to a mooring buoy in a basin and wait for the water to hit the necessary level (no big deal on a rising tide, but on a falling one you better have a good stock of beer aboard!).

And that's how it is done here. So far, we only sailed (most) of the Brest to L'Aber W'rach leg, winds haven't been favorable and the consequences of late arrival are sometimes quite severe.

We also do take note of other harbors en route, so we do have some options if things don't work out.

We're still West of Cherburg (our probable starting point for the Channel crossing), so we haven't yet hit the highest tides or fastest currents yet...hard to believe that given our experiences so far!

-Scott