A rudder is one of the most critical parts of a boat. Rudder failure is a common occurrence on neglected or overworked boats and a very unpleasant and potentially dangerous thing to happen when you are out at sea.
It is important for a boat owner to fully understand how their boat’s steering system works. For example, do you know whether your rudder stock is hollow or solid? Is it made from stainless steel or aluminium, or is it composite? More importantly, do you understand how the system can fail? It is always best with boats to leave nothing to chance and and to know how to spot early signs of trouble. This particularly applies to rudders.
The spade rudder system is common on many modern designs of both sail and power boats. This type is known as a balanced rudder, meaning that it pivots at a point well back from its forward edge (whereas transom hung rudders are referred to as unbalanced rudders). This makes it easier to turn than a transom hung rudder. A spade rudder is suspended beneath the hull, well astern of a fin keel.
Spade rudders have a rudder stock which reaches from the bottom of the rudder up into the hull. The stock can be hollow or solid and made from stainless steel, aluminium or composite materials. The rudder blade is built around the stock and reinforced with a frame which is welded to the stock. So when the rudder stock is turned, the frame and blade turn as one. The blade itself is usually made in two halves of fibreglass which are bonded together. The core is usually filled either with foam or plywood and occasionally is a solid laminate.
On most spade rudders, there are two bearings contained in a bearing tube. One of these bearings is at the point where the rudder stock enters the hull and another one higher up at the top of the tube which may also have a seal.
Spade rudders are subjected to considerable stresses and some experts would say are more vulnerable to failure than the old fashioned transom hung varieties. This is partly because they are hidden from sight and therefore difficult to inspect when afloat and partly because there is more that can go wrong if a spade rudder isn’t inspected regularly. The big issue is that it is very difficult to prevent water from getting into the core, causing corrosion and eventually, rudder failure.
Spade rudder checks:
- Check if water continues to drip from the rudder after the boat has been hauled out.
- Check for any rust-like stains on the the rudder surface, which are an indicator of crevice corrosion.
- Bearing failure – check bearings for excessive play when ashore by moving the bottom of the rudder blade from side to side. Up to 2mm play is acceptable.
- Check bearing tube to hull joint for any signs of cracking.
- Check the flexible rubber, bellows type of seal is in good order.
- Stiff steering can be caused by plastic bearing failure. Roller bearings can fail suddenly.
- Rudder stock failure – check seawater has not penetrated the bearing tube which will cause a stainless steel rudder stock to corrode and eventually fail. The rudder stock’s lower bearing where it enters the bearing tube should be inspected for excessive play or signs of crevice corrosion and galvanic corrosion. Check the shaft seal for signs of leaking. If it is leaking it needs to be replaced. Check the upper part of the bearing tube is well supported and not showing any signs of movement.
- Framework failure – check for water penetration into the rudder blade. This can cause corrosion of the metal frame, resulting in the rudder stock breaking away and failing to turn the blade. Check if there is any movement between the rudder and the rudder stock. If so, the rudder will need to be repaired or replaced.
- Delamination – check the rudder blade for bulges which indicates water has penetrated the rudder and is causing delamination. Check the edges of the blade for signs of cracking or splits which could allow water to penetrate the blade.