User:Noah Sanders/Centreboard

Centerboard

A centerboard is a retractable keel which pivots longitudinally down from a slot in the hull of a sailboat, known as a centerboard case. The purpose is to provide an underwater balancing force that counteracts the lateral force of the sails, preventing the sailboat from capsizing. (5) The ability to retract allows the centerboard to be raised in shallow water, reduce drag when not needed, and to ease the process of hauling the sailboat ashore. Center boards are more prevalent on smaller sailboats due to larger sailboats requiring a fixed, weighted keel due to their size. Centerboards work in the same fashion as a dagger board. The only difference being the method of connection to the hull. Dagger boards are completely removeable and slide verticly into a slot.

Function

A sailboat is only able to sail at most a 45-degree angle from the wind (2). The shape of the sails generates lift, pulling the sailboat forward. Moving the sailboat forward is not the only force that wind exerts on the system. The wind pushes on the hull of the boat and the sails, pushing the sailboat to the leeward side. If the centerboard was not present, the sailboat would slip sideways and would not be able to make forward headwind. The long and thin structure was designed to limit drag in the forward direction, while also increasing drag in an angle perpendicular to forward motion. [3]

When the sailboat is capsized the centerboard can be used to right to sailboat. From the turtled position, where the mast is pointed straight down into the water, climb up onto the underside of the hull and grab the centerboard. Lean backwards, pulling the sailboat on top of you. As the boat rolls over on top of you, transition from pulling on the centerboard

Points of Sail

At each point of sail there is an ideal centerboard depth.[1]Due to the design allowing the centerboard to be fully or partially raised with ease, it is possible to adjust the height while sailing. While sailing close hauled, the centerboard is most important and should be all the way down to prevent the sailboat from sliding sideways, instead of toward the target destination. While on a broad reach, the sailboat is less susceptible to sideways slippage and thus the centerboard can be pulled up slightly. As the sailboat turns downwind onto a reach or broad reach the centerboard can be raised. This is because the further downwind you sail the less slippage there will be. The drag created by the centerboard will still be present, that is why the centerboard should be pulled up, to reduce drag. When sailing dead downwind the centerboard can be pulled up into the hull entirely because you are sailing with the wind directly at your back and no sideways slippage is present. While you can modify the centerboard depth at every point of sail, the benefit is only marginal when going from close haul to broad reach. It is best to only move the centerboard when transitioning from upwind to downwind.

Sources

(1) Lochhaas, T. (2013, July). Using the centerboard of a small sailboat. LiveAbout. https://www.liveabout.com/how-to-use-the-centerboard-2915476 (Lochhass, 2013)

(2) Kantor, J. (2008). Learn sailing right! The national standard for quality sailing instruction. Beginning sailing. United States Sailing Association

(3) J, W. (2002). The physics of sailing. The University Of New SouthWales. https://newt.phys.unsw.edu.au/~jw/sailing.html

(4) Miklosovic, D. S., Schultz, M. P., & Esquivel, C. (2004). Effects of surface finish on areodynamic performance of a sailboat centerboard. Journal of Aircraft, 41(5), 1073–1081. https://doi.org/10.2514/1.777 (Miklosovic, 2004)

(5) Conger, C. (2008, March 11). How sailboats work. HowStuffWorks. https://adventure.howstuffworks.com/outdoor-activities/water-sports/sailboat.html