This post is about lift and drag by the numbers.

The lift and drag for fins can be calculated. But few companies share their numbers—if they know them. Here is a table comparing our 4.8″ fin to a typical 4¼” fin. Not that you have to multiply the pound forces by three for a thruster set, and by four for a quad set. Here’s a conversation about fins by the numbers.

Stacy:
So you have numbers that can show that FinSciences fins produce less drag than dolphin fins?

Doug:
Yeah.  I figure surfers might want to compare FinSciences fins to their favorite fins—with some hard numbers. The numbers show that our fins have better side force and less drag than typical dolphin fins out there.

Stacy:
I’m probably going to regret this, but can you explain that “better side force” in a little more detail?

Doug:
Sure, thought you’d never ask!  In general, “side force” is good and we want more of it—a bigger number is better.  Drag is not so good—we want a smaller number.

Stacy:
So side force is like power?

Doug:
Pretty much. Side force is really lift in terms of science.  More side force or lift means more power in turns–more hold and more drive.  What surfers feel when surfing is the ability to plant your foot and make a turn, or hold yourself in the wave without spinning out, or rocket out of bottom turns and cutbacks.  More powerful fins—fins with more lift—will do these things better.

Stacy:
And drag is like hitting the brakes?

Doug:
Right. You want less drag. Less drag means easier paddling, better acceleration, better wave-catching, and higher speeds so you can reach other wave sections and do some aurf aerials.

Stacy:
So we want as much side force, or lift, and as little drag as we can get?

Doug:
Exactly!  Feel like you’re in high-school science class now? I calculated the side force and drag of our fins in pounds. Take our small shortboard fin surfing on a 3-meter wave—at about 20 knots. That fin will generate 19.23 pounds of side force—57.69 pounds of side force for a thruster setup with three fins. Typical dolphin fins are less efficient. A typical 4.25-inch fin on that same wave generates 16.63 pounds of side force—49.89 for three. Big difference.

Stacy:
So what about the drag on those same two fins?

Doug:
Okay, on that same wave our fin generates drag of 1.23 pounds—3.69 pounds for three. The dolphin fin generates 1.33 pounds of drag per fin—3.99 pounds of drag. Drag holds you back, and slows you down. If you want to do aerials, you’ll have to pump harder if you have more drag.

Stacy:
I bet you have a table that illustrates all this stuff.

Doug:
Yep, at the bottom of the post.

Stacy:
Okay.   Fascinating conversation.

Doug:
In another post, we can talk more about drive, how it varies with speed and with turning, and we’ll talk about SUP fin design and development.

Most Surfers, SUPers Want Easy, Fast Paddling 1