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2019-06-12 Shouldnt the pointy bit be at the front

Well, No!

Oddly contrary to what you might think, with fluid dynamics the ‘pointy bit’ should go to the back. I see so many poorly designed inefficient motor boats these days, that enough is enough. Lets set the world of motor yachting straight once more.

It’s all about the Draaaaaaaaag…

I was always told at a very young age that ‘the out-take of the boat is far more important than the intake’. BUT WHY! The reason is drag. A clean out-take in the water means no tidal vortices pulling the boat back. Not to be confused with Toroidal Vortices, (these are really cool, but require another post). This principle of low drag is seen in nature as well. Birds wings, a ducks waterline and even fish.

A fish has a large head (near flat surface) but tails off to almost nothing causing no unnecessary vortices.

Here’s what is happening

As the water gets dispersed evenly around the front of the boats hull, it splits and goes around the sides. The tricky part is when the water has to come back together at the back. The way to reduce drag and increase speed is to create as little to no vortices as possible at the back of the boat. a vortex is undesirable as it is a void. Like Newtons theory of “What goes up, must come down” in fluid dynamics, all holes must be filled. A vortex is a hole, and is trying to be filled by the closest thing, the boat. This means the boat is being pulled back into the hole made by the vortex. To create a boat with no vortex, you need to reduce the separation of the water causing the hole. This can be done by putting the point at the back, it allows the water to come back neatly without a hole.

http://www.zenithair.com/stolch801/design-wing.html

No vortex, no wash, no fuss.

Does it work? Well, yes. The military create silent submarines using this technique. They also use the weight and water density to be able to travel faster deep under water than they can at the surface (a topic for another day). By controlling how a vortex is created you can use this to your advantage. You can use it to steer a boat, or make a plane fly! A rudder creates drag down one side, making the boat uneven causing it to pull to one side, or the other.

And for the record, a boat should have almost no wake.

In a nutshell. Fluid dynamics… Good Ay!

The Enginer’d