Propeller walk, rudder, wind and current

The lesson in plain words

1. Current and the ground
   • A current is moving water. It carries you over the ground, relative to the seabed and shore.
   • Steering depends on movement through the water, which flows past the rudder.
   • Heading directly into a 2-knot current at 2 knots through the water holds your ground position while keeping rudder flow.
   • A freely drifting boat in uniform current is carried along without being turned by that current alone.
   • Uneven flow or restraint can make it swing.
2. Wind and windage
   • Windage is the exposed area the wind pushes on: hull sides, cabin and mast.
   • A high-sided boat usually feels more wind force than a low one.
   • With other conditions unchanged, twice the wind speed gives about four times the force.
   • A stopped boat with a high bow often has its bow blown off, or pushed downwind.
   • A tall cabin aft can change this behaviour.
   • Observe your own boat rather than assuming every bow falls away.
3. Opposite naming rules
   • Wind is named for where it comes from: a northerly wind blows from north to south.
   • Current is named for where it goes: a northerly current sets towards north.
   • Set means the direction the current flows.
   • To head into that northerly current, point south.
   • To head into a northerly wind, point north.
4. Approach into the stronger effect
   • For a slow approach, head into whichever affects your boat more.
   • This is not a comparison of wind and current speeds in knots: their effects depend on the boat.
   • Into current, you can keep water flowing past the rudder while making little progress over the ground.
   • Into wind, the wind helps slow your approach.
   • Check how both forces act before choosing a direction.
5. Read moored boats
   • Look at boats free to swing around a single mooring, especially ones like yours.
   • Their bows usually point towards the dominant force.
   • Boats pointing upstream suggest current dominates; boats pointing into wind suggest wind dominates.
   • Different underwater shapes and exposed areas can make neighbouring boats point differently.
   • Boats tied alongside cannot swing freely, so their headings are poor evidence.
   • Confirm with wind indicators and water moving around fixed posts.

Key data

Key points

• Current carries you over the ground; rudder flow depends on speed through the water.
• Wind acts on windage; a stopped high bow often blows downwind.
• Wind is named from; current is named towards.
• Approach into whichever has the stronger effect on your boat.
• Read similar boats free to swing on moorings; confirm with other clues.

Check what you have read

True or false?

Practice case & exam keys

Exam keys

1. 1Current changes movement over ground; steering depends on flow through the water.
2. 2Wind acts on windage; a stopped high bow often blows off, with exceptions for boat layout.
3. 3Wind direction names its origin; current direction names its destination.
4. 4Approach into the dominant effect; use comparable boats free to swing on moorings as evidence.