This page compares a sailboat centerboard vs daggerboard and the advantages and disadvantages of each as well as the techniques involved in gybing. Sailboat rudder design.
The adjustable centerboard or daggerboard’s purpose is to counteract the sailboat's tendency to drift sideways. As well as converting the sideways motion into moving forward under sail it also acts as the pivot point around which the sailboat turns. The [ correct relationship ] between center of effort (CE) and center of lateral resistance (CLR) maintains the balance of the boat negating any excess lee or weather helm. The CLR therefore is moderated by the amount of centerboard or daggarboard exposed to the water when sailing. The following compares the advantages and disadvantages of a centerboard verses a daggerboard.
The [ centerboard ] is a small, retractable keel pivoting up into a case or box on the centreline of a dinghy or cruiser. As its tip moves back and upward it increase or decreases the area of centreboard under the boat altering its position along the fore-and-aft line.
This fore-and-aft movement has an effect on the steering. The turning forces of the jib and mainsail are balanced around the [ pivot point (CLR) ] when it is in its correct position. If the board is raised, it turns away from the wind as the pivot point moves aft. Equally if it is lowered, the pivot point moves forwards with the sailboat tending to turn into the wind.
The centerboard has an advantage over a daggerboard or a fixed keel in that it retracts of its own accord when the sailing dinghy sails into shallow water. The sideways drift of a sailboat or leeway decreases when the boat sails on points away from the wind. Therefore the [ correct angle ] of the centerboard is dependent on the direction of sail.
Lay your sailboat on its side the observe the various positions of the centreboard then mark the casing as a reference to its position enabling quicker setting during sailing.
Watch for any damage around where the it extends through the hull, usually a nylon-based membrane.
[ Sailboat Daggerboards ] move vertically inside their case and when raised, the area under the sailboat is reduced. The daggerboard’s position along the fore-and-aft line remains the same and has no turning effect. It requires only a small opening in the bottom of the hull which eliminates the drag caused by a large centerboard slot.
Jamming is a problem if sailing into shallow water and the grounding is severe causing damage to the hull. If the daggerboard is too high out of the hull when gybing it fouls the boom, causing capsize.
The primary control for changing direction is the [ sailboat rudder ] and whenever the rudder is moved off-centre by more than four degrees it acts as a brake as well as a turning control. Sailboat rudders work efficiently when the sailboat is moving at speed along with the dramatic braking effect so careful handling is required. Remember that the effect of the rudder is reverse when the sailboat moves backwards.
Heeling, when only slight, causes the sailboat to turn, as the previously symmetrical shape of its water plane is transformed into an asymmetrical shape when heeled. When the sailboat is hit by a gust and twists round into the wind, the sailboat rudder controls this heel induced turn.
When the centreboard is down, the sailboat rudder is operated a lot to keep the sailboat on course. If the helmsman finds he is making course adjustments by pulling the tiller towards himself then raising the centerboard slightly will correct the problem and conversely if he is pushing the tiller away, then lower it.
A variety of shapes and sizes of sailboat rudder rudder design aids in the principal task of making large course alterations when tacking or gybing. A secondary function of the sailboat rudder is as a trim tab to correct the balance of the sailboat as it responds to wind and waves.
The transom-hung fixed rudder is the simplest of these, but other dinghies have an articulated lifting rudder which kicks up when striking an obstruction. The modern spade rudder which protrudes through the bottom of the hull is most vulnerable to damage. Therefore to withstand the stresses of sailing it must be strongly constructed.
The sailboat rudder is operated by the tiller, and the rudder’s effect through the water swings the stern of the boat around, with the stern movement corresponding to the tiller’s movement. When the tiller is moved to the right or starboard, the rudder moves to the left or port and swings the stern to starboard and turns the bow to port.
The reverse happens when sailing backwards with the stern moving in the opposite direction to the movement of the tiller, and the bow in the same direction as the tiller.
The correct sailing position is to sit on the windward side of the sailboat with backs to the wind.
A tiller extension is fitted to most dinghies and is attached to the end of the tiller with a universal joint allowing swivelling both horizontally and vertically. This allows control of the tiller while moving around the boat to correctly position weight. Sit with the tiller extension at the side of the body nearest the rudder and grip the extension as you would a dagger, allowing the movement of the tiller away by pushing and towards by pulling.
All the hull underwater parts including the foils must have a perfect finish, free of blemishes that disturb water flow across their surfaces. Check regularly and repair damage without delay by filling and lightly sanding away imperfections.
When in light winds and flat water any small blemishes on underwater surfaces increases unnecessary drag.
When working ashore on the underwater surfaces, place the boat on its side and lower the centreboard fully. Check how rigidly it is held in its case and its protruding angle in reference to the hull. If there is any excessive movement then this causes drag when moving through the water. Test the bend when leaning on the tip and if there is any give in it, replace it with a stiffer board. Any deflection when moving through the water slows the boat.
The centreboard case bottom is usually fitted with rubber or plastic strips, sealing the slot and preventing water turbulence. Check the condition of the rubber strips and whether it fits flush with the hull and how it moulds around the board when lowered.
With a lifting rudder, check the blade has a tight fit in the stock eliminating any sideways movement which causes drag and makes steering difficult.