Imagine that you are in the middle of the ocean and you just don't know where you are and which direction to go, sound scary? Carrying a compass while kayaking is very essential even though you have maps or navigational charts as they are not of any use without compass.
In fact, all those marine charts available are made to be used with a compass. These marine charts show magnetic variation on a compass so a sea kayaker, for instance, can easily navigate using those magnetic navigation directions. The most important rules for using compass use compass before you get lost; if start finding direction using compass after you lost somewhere then it is going to be very difficult for you to find perfect direction and second thing learn to use compass before start kayaking. Constantly refer the compass, and check whether you are going in right direction or not.
One more important thing, trust your compass; it is very easy to trust your instinct but usually get lost because of your instincts only; so trust your compass completely and navigate in right direction.
There are basically two types of compasses: marine and hiking. Hiking compass has a moving needle that points towards the magnetic north of earth, needles is fitted in case which has 360 degrees of full circle.. This case is needed to be rotated to align the needle with north and directions are read from face of case. You can even adjust it to local variance or declination so it will indicate true north than magnetic north. Even most topographic maps are oriented in this way.
A marine compass has disk inside the case which is magnetized and marked with 360 degrees. Unmarked outer case can rotate around the compass card or compass disk, which will point to magnetic north; you can even adjust these marine compasses for little local variances.
A kayak compass generally boasts two types: deck mounted and hand held. A deck mounted compass is a compass that is fixed on the deck of kayak. Use of a deck mounted compass is advisable, since you can read direction while paddling. Many deck mounted compass look like high crowned egg; but they have a compass disk instead of yolk. They are mounted right front of cockpit of kayak, close enough so as to wipe away. Its rubber lined alignment will provide accurate and quick reference line and you can easily understand the direction in which you are going.
The deck mounted compass can be permanently mounted on deck of your kayak, so you don't need remember to carry it with you every time you go for kayaking, but it also has disadvantage you can not remove it for safety. So for that you can have demountable compass, so you can remove it easily whenever not in use.
While buying compass for kayaking, consider few things like readability, means numbers should be easily readable; then it must be easy to install or detach, while installing or detaching it must stay aligned. It would be great if your compass can perform several different functions at a time.