Shipwrights Calking Mallet

This mallet is used to hammer the cotton calk into the seams of the ship's planks. I've been asked why the mallet is so odd looking. The reason for the shape of the mallet looks different than a normal hammer is because this shape has been proven to be best over the years by calkers.
The mallet is usually made from Lignum Vite or Iron Wood, this is for strength. The mallet has a long head, so you can have the mallet do its job while the calker can keep his elbow close to his side, thus saving energy. The slit running the length of the mallet is not a crack, but a deliberate slit to add bounce to the mallet. Again, this bounce saves energy that doesn't have to come from the calkers arms.
Calking mallets have been made like this for hundreds of years for these reasons as are the calking irons that the mallet strikes.