displacement or planing?

I see a lot of traffic on the net these days looking for hulls. I’m am by no means an expert on surfboard design, but I am an avid student of design and have researched a fair amount. Here is some of what I’ve learned.

Although the recent fascination with hulls has centered around the Greg Liddle “modified transitional displacement hulls”, any surfboard can be considered a hull. There are displacement hulls, planing hulls and as usually is the case, some variant of the two.

As soon as you put an edge at the tail of your board you have created a planing hull. The very nature of the release provided by that edge, by definition puts that board into planing mode. It the edge were left soft and round, you still have a displacement hull. Now whether it is a good one of either type is another matter.

Have you ever seen the old footage of guys towing behind motor boats on their logs? As soon as they get going, the tail end of the board starts submarining and they can literally walk to the nose and go. This demonstrates a the principle of displacement hull theory. A displacement hull has a theoretical hull speed, above which the water actually sucks the hull deeper into the water (I’m simplifying here). Take a sailboat or any other displacement hull and tow it. At anything above the theoretical hull speed, the boat begins to submarine, actually being pulled deeper into the water. Old, soft edged boards are the same, as are any true displacement hulls being produced today. As soon as you put an edge at the tail, you release the water and the board begins to plane. The modern surfboard, most “hulls” included, balance these principles to achieve the desired effect or feel.

Now I’m sure I’ll get some flak for this, but displacement hulls, by their very nature, are not as fast as planing hulls. They may “feel” faster in a section, but without the release, they are constantly dragging more than a sharp edged board would. Now this is not a bad thing. The feeling of a well balance hull is one of the great pleasures of surfing that most people fail to credit. Surfing one well takes a different approach, especially if you are stepping off a thruster. Single fin riders tend to have an easier time.

Another thing I’ll take flak for, and I’m saying it anyway, Greg Liddle did not invent the displacement hull surfboard. He refined it to an amazing degree, made it work in a short package, championing it when it was completely against the trends of the time, but have you ever seen a Weber Foil? Have you ever really looked at almost any board before the mid sixties? All displacement hulls, although arguably not “modified transitional displacement hulls”, whatever that means. Please don’t take this as me dissing Greg Liddle. On the contrary, I think his boards are brilliant and have been a huge design influence for me. It’s just I get a little frustrated when I here people talk about hull this and hull that, without any understanding of what a hull is.



2 thoughts on “Hullls”

  1. What a great summary! I’m not sure what you’ve be reading or where, but I don’t think anyone associated with GL or Greg himself, have ever said he invented the “hull”. There is a very clear lineage from Simmons to Yater to Greenough to McTavish and Keyo to Greg. At the same time there were parallel developments with Frye, Greek, and whoever shaped the Weber’s (Munoz?). I think you got it right that Greg stuck with it and refined the crap out them over the years.

    I’ve always been struck by the fact that “hulls” seem to reject proper hydrodynamic theory; all that curve and drag in the bottom disappears when you put them on a rail. It might be an illusion but I have seen and experienced making sections other boards just couldn’t make. Still, it’s that unique feeling you get on a “hull” that makes me pull it out of the quiver on those special days.

    I’m going to have to drag myself away from the cliffs and visit PB to see your work! Nice site!

    1. Thanks. Chris at Surfindian has some of my shapes at his shop. I’ll have to do a bit of searching for his name, but the Weber foil was developed by an Australian, and was given credit on the lams of the one I saw. I just can’t remember his name. I do recall it was a beautiful shape. Cheers.

Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s