Roads and Maritime Services issued an alert following a forecast from Bureau of Meteorology warning about dangerous surf conditions for the NSW coast from Ulladulla to Cape Byron.

The deceptively powerful surf conditions will start on Monday and persist into Tuesday.

Skippers and owners of small craft should be on high alert and check the conditions before considering crossing a coastal bar or heading offshore.

Strong winds can also cause dangerous conditions for vessels on moorings which have been poorly maintained.

Roads and Maritime said every skipper is responsible for the safety of their vessel and all on board.

It advises skippers to:

• Check the official weather forecast before and during boating;

• Ensure the boat and its equipment is suitable for the conditions;

• Log on/off with a Marine Rescue NSW marine radio base for every trip offshore;

• Wear a lifejacket.