Sailing life entails many words that at first make no sense; in this article, I will explain the difference between two types of underwater foils, centerboards and daggerboards.
On a sailboat, the difference between a daggerboard and a centerboard is how they are moved into position. A daggerboard is lifted and raised vertically (up and down) through a slot in the hull; a centerboard, on the other hand, pivots or swings into place.
That was the short answer. There are many more commonalities and differences worth discussing, such as the differences in performance and what happens if your daggerboard hits a reef? Will it break your hull?
Keep reading to understand all you need to know about daggerboards and centerboards!
The centerboard is mounted horizontally on a rotating bolt at the foremost part of the foil (keep reading to understand what a foil is). It folds into a comparatively much longer slot in the hull than a daggerboard.
A centerboard comes in many different shapes and sizes, it can be combined with an already existing keel, or it can be larger and be more of a stand-alone type.
How is a centerboard operated?
The centerboard is operated through a lifting line fastened at the end of the centerboard fin(board); this line is manipulated either by hand or by a winch and, once fully retracted, will be tied to a cleat.
The daggerboard, on the other hand, is mounted vertically inside a sliding slot in the hull, it gets it name from the movement, much like the stabbing motion of a dagger.
The board is stopped from moving too far and falling out because the top part is wider than the lower part.
How is a daggerboard operated?
It is manipulated much like the centerboard, through a lifting line and a winch. But instead of being attached through a bolt and swung into position, it is lowered down into place.
What are the differences?
Since the differences mainly lie in the way of deployment, there are not that many big difference, but some smaller once worth noticing are;
The daggerboard doesnt have to be either fully up or fully down; this means the sailor can adjust the depth and effects to his or her needs. To low and there will be unnecessary drag, to high and there will be too little lift and too much drift to windward.
On the other hand, the centerboard pivots into position and is only really efficient as a foil once fully deployed.
Reducing the draft of a boat is very important if you want to sail in very shallow waters such as the Bahamas or if you want to beach your cat.
Once retracted, there is also a decreased chance of getting stuck or tangled up in a fishing net or other semi-floating objects and sometimes hard to see.
On boats where the keel is the lowest point on the boat, the propeller will be protected, but on ships where the center or daggerboard is the lowest spot, then retracting it will make it vulnerable to damage from whales, fishing nets, or coral. You will also not be able to beach your cat since the weight of the ship will be loaded on top of your prop shaft and most certainly will break it.
Once the boards are in a fully lifted position, there is an argument to be made that the centerboard, which has a much larger slot, will have higher drag. This is true, but only if the slot is poorly design and not hydrodynamically smooth, causing underwater turbulence.
A well-designed centerboard should be able to reduce the amount of drag to the same as a daggerboard.
What are the similarities?
Both systems can be mounted in pairs and at an angle; this makes the boards work much as an airplane wing does. Once the water starts passing around it, it will create higher water speeds on the upper side, lowering the pressure and increasing lift.
This makes for less underwater surface, decreases drag, increases speed, and fuel efficiency.
One issue often discussed on forums and with boat people is that a centerboard is safer since if an underwater object hits it, it will fold back into its slot, and no damage will be done. This is true to a degree but worthy of some explanation.
Firstly this is mainly a theoretical argument since an object is not certain to hit the board from straight on; this means that the idea of folding is no longer possible. The next thing to understand is that daggerboards are made to break; this is a safety aspect and makes sure that the hulls stay intact and that the boat will stay afloat.
This is similar to modern mini keels on catamarans; they too are constructed to detach if hit hard enough, the keels fall off, but the hull stays intact.
Both systems offer a risk of getting stuck; some say this is a bigger issue with daggerboards, and they more often fail than the centerboard style. This is not something that I have been able to confirm through any data, and looking at the design of newer daggerboards; there is no real reason to think that this should be the case.
There are many different systems on a sailboat, and everything that can move will sooner or later stop moving due to rust or being filled up with salt and sand. So will too these boards; this means extra time for maintenance and extra money to be spent keeping the systems in good shape.
Compared to each other many would argue that the centerboard is a somewhat simpler system and that they need less maintenance; I would say it is more up to the specific design than whether or not it is a centerboard.
Catamarans and Monohulls
The basic function of a foil is the same whether you’re on a catamaran or a monohull, although some aspect is specific for a cat.
A catamaran will always have two boards; these can be used together or separately. Since a catamaran behaves very differently in big seas than a monohull, the use of foils, especially during heavy weather, is essential to understand if wanting to stay safe.
One situation when catamarans can capsize is while being pushed horizontally by a big breaking wave hitting it from the side. If both boards are down, this will decrease the possible sliding motion and therefore increase the likelihood of capsizing.
This is a complex issue and if you want to undestand capsizing in detail i suggest you read this article;