- The two main types of hulls for
trawlers are the full displacement and the
semi-displacement. An example of the semi-displacement
hull is the Grand Banks line of trawlers and the Kadey
Krogen 42 is an example of the full displacement hull.
The difference between the two hulls can be simplified by
stating that the semi-displacement hull is designed, that
with enough horsepower it is able to go faster than hull
speed, while the full displacement hull can't exceed hull
speed.Theoretical hull speed is a mathematical function
and can be expressed in the formula:
- Hull Speed in Knots=
Square Root of the Waterline Length * 1.34
- Of course, this speed is not the most
efficient cruise speed: to achieve that use between 1.1
to 1.2 as the multiplier factor.
- An advantage of the full displacement
hull is that the weight of all the equipment, food,
beverages, fuel and other material carried on board on a
long cruise won't greatly affect the performance of the
boat since the design of the boat is to stay at or under
hull speed and thus the extra weight won't be a great
factor in performance. In a planing hull or even a
semi-displacement hull, the opposite is true, as it takes
a lot more horsepower and fuel to achieve planing speed
if you increase the weight.
- Basically, if you want longer range
and more blue water performance go with the displacement
hull boats, if you do more coastal cruising and need more
speed then look at the semi-displacement boats.