That'll be barnacles and lack of maint. Seawater is a fluid with a mass of more than 1 Kg per 10cm^3. I have customers that worry about hull shapes etc. Increase the coeff. of friction a small amount has a massive effect. Can't remember exactly now but I think friction is proportional to the square of ... something.
The difference here is that these little beasties magically make a ship run slowly. I would bet real money that their invention was to cover up late delivery or whatever. Basically, an excuse that no land lubber of the time could possibly refute.
The difference here is that these little beasties magically make a ship run slowly. I would bet real money that their invention was to cover up late delivery or whatever. Basically, an excuse that no land lubber of the time could possibly refute.