Time for another stupid question......
I dont want a racing boat. In fact I dont want to go fast, so whats this thing called hull speed and why should I want one?
Not actually anything to do with racing.
Its to do with how fast water moves.
Belly flop into a swimming pool. It hurts. This is because the water cant get out of the way fast enough. The water actually feels like a solid if you thump it fast enough.
Yet you can walk through water. This is because the water has enough time to move out of the way.
Same thing happens with a boat hull.
If you push it through the water slowly enough, the water moves out of the way and there is no water heaped up at the sides as happened with the sugar.
If you move the hull faster, it reaches a point where the water cant get out of the way fast enough and the boat starts to ride up onto the water - plane (not as in flying, but as in skimming over the water rather than plowing through it). The speed where the hull is going as fast as it can without piling up water is called its hull speed. This is the speed the hull will go through the water without using loads of effort - which is why hull speed is important even if you arnt racing.
If you have a short, fat boat it will take as long for the water to move out and back in as with a long boat of the same width.
So... theoretically...a 20 foot long boat will have a hull speed twice that of a 10 foot boat of the same weight, draft and width.
In this pic, the round bits of water move the same distance as each boat goes past - regardless of the boats length. However, the longer boat goes further in the same time as its...well...er....longer.
The longer boat has a higher hull speed.