[killarney_sailor]

The waves you will encounter are the result of winds in the last few days. Often the waves may have been generated far offshore (as in hundreds of miles). Sometimes you will get wav trains from more than one direction because of different weather conditions in different areas.

In general, the further you are from shore and the deeper the water the more regular the wave patterns will be. If you check NOAA weather you will see that they give three sets of forecasts: coastal, offshore (to 150 nm as i remember), and high seas. If you compare the coastal and offshore forecast you can see any significant differences.

 

[killarney_sailor]

OK, you are not really talking about waves but about currents. You can get currents from tidal change, oceanic currents (like the Gulf Stream), and from river flows. You need to know what these are at least for convenience and sometimes for safety. We went up the St Lawrence once and used the tidal current at one stage. We were clocking slightly more than 10 knots over the ground upstream (the river current was 1 to 2 knots against us. You can imagine how fast someone going downstream would have gone. For some passes into lagoons in French Polynesia you absolutely have to know the tides or it can be extremely
dangerous.

I did not understand one thing you said. You said you were trying to go into your bay with the flood of the tide. In general this should be a favourable current everything else being equal. Perhaps everything else is not equal. Talk to local sailors and see what they say. In general if you went out with favourable currents and came back 12 hours later they will be unfavourable (6 or 18 hours should be favourable both ways). Often you do need local knowledge or at least a cruising guide for the area. if the currents are a big issue cruising guides and coastal pilots should include the information you want.