I came down the entire St. Lawrence last year. It is a beautiful trip. Current
starts at Montreal where it is about 5 knots and continues with variations until about Rimouski. The current varies a lot and the tidal flow starts below Montreal. At Quebec
city the tide is 18 feet, so the current reverses with the tide. We had about 7 knots current when we departed Quebec
City. Sailboats with an engine
must move with the outgoing tide and stop on the incoming. Very difficult to make this trip without an engine
, hard to sail until well below Quebec City. There are not very many anchoring
opportunities except in some limited areas. Plan on some marinas
. There is an atlas that shows the current flows in relation to the tide, very worthwhile.