There are a lot of different ideas about boat design for different purposes, and SUP is fully mired in it. One thing that gets confusing is Planing and Displacement Hull SUPs – mostly because it is not really a “thing” when it comes to SUP.
What are Displacement Hulls and Planing Hulls?
There are many types of boats for many types of activities, including SUPs. But for now, let’s take a step back.
Just for clarification – the Hull is the bottom of a boat.
Displacement hulls are designed to move through the water, displacing the water in some (or many) direction(s). Generally these hulls are either U-shaped or V-shaped, though some may be more boxy or even squeezed into an almost Y-shape.
Planing hulls are designed to move on top of the water rather than moving through it. Planing hulls are mostly flat.
Well that solves it! Any flat hull must be planing and any rounded hull must be displacement. If only it were that easy.
You see, in order for a planing hull to travel on top of the water, it must first be traveling at its minimum planing speed. If a planing-hull vessel is moving slower than its planing speed, then it operates like a displacement hull with a shallow draft (depth in the water).
How This Applies to SUP
Brands will frequently refer to their paddle board designs with words like “Displacement Hull SUP” or “Displacement Hull Nose” in an effort to try and differentiate the design from boards with “planing hulls” or “planing noses.”
The problem is, there are very few times where any SUP is actually planing!
SUP is an inherently slow sport. The top athletes in the world are only traveling about 9.8MPH in a 100m sprint. To put that in perspective, the average adult can run a 100m sprint somewhere around 15 MPH. What actually constitutes a boat’s planing speed is complicated. But simply put it’s very rare that SUPs ever reach a planing speed in any situation outside of surfing.
Elite racers in a sprint can get their SUPs to plane for fractions of seconds at certain points during their stroke, but never fast enough to continuously plane their board. The ironic part of it is, these types of race boards are most widely called “Displacement Hull SUPs!”
Outside of Surfing, SUPs behave as displacement hull vessels regardless of the shape of the board.
But what about these different nose shapes?
Yes! Many people will define a “planing hull SUP” or “displacement hull SUP” based on the shape of its nose. They’ll see a rounded, upturned nose like on an all-around or surf SUP and say “ah, that right there is a planing hull board,” and they’ll see the pointed nose of a touring or race SUP (upturned or not) and say, “And that one is obviously a displacement hull SUP.”
Let’s take a look at these boards paddling on the water.
Above you can see what many would call a displacement hull board on the left and a planing hull board on the right. Notice that both boards are displacing water as they move through the water, and neither is riding on top of the water.
The board on the left certainly has a smaller profile entering the water with that sharp pointed nose with almost zero rocker (upturn). The board on the right has a much wider entry profile under the upturned nose, but it’s still displacing water left, right, and center.
“All Inflatables are Planing Hulls”
Going back to what we’ve discussed so far… inflatables, just like hard boards, are going to operate exactly like a displacement hull vessel unless they are surfing.
Here’s two more pictures to compare.
The board on the left is a carbon fiber racing SUP, and the one on the right is an inflatable racing SUP. Both have pointed, elongated noses with narrow water entry surfaces. Both are displacing water left, right, and center as they move through the water. Neither are planing.
Where Does the Planing vs Displacement Hull SUP Idea Come From?
There are differences in nose shapes that frequently get people to call one board a “planing hull SUP” and another a “displacement hull SUP,” even though all of them will move through the water as a displacement hull vessel.
SUP Nose Shape
Surf SUPs will have very thin, wide, upturned noses. This is for several reasons. The thinner board weighs less and has less mass in the nose making it easier to maneuver on the wave face from the tail of the board. The upturned nose shape helps keep the front of the board from pearling while riding down into the bottom of the wave. And lastly, the wider, round shape gives the board volume, buoyancy, and stability while surfing and paddling.
Most all-around SUPs have borrowed this general board and nose shape. This keeps them more easily surfable while their larger size makes them easier to paddle on flat water. The nose rocker also helps the board ride up small chop and wake instead of plowing through it. Note, this is not the same as planing in any sense. These SUPs appear to the lay person to be moving on top of the water, but they are, in fact, moving through it.
Boards with pointed noses and flatter rocker profiles are designed to maximize their waterline length. These SUPS appear to the layperson to be moving through the water. On any vessel operating as a displacement hull vessel, including all SUPs, there is a phenomenon known as Hull Speed. Hull Speed is the maximum speed at which a vessel displacing water can travel before ever increasingly large amounts of energy are required to add additional units of speed. This has to do with how the vessel creates different wakes and the effect of “climbing the bow wake” when you reach hull speed. It is entirely dependent on the waterline length of the vessel. Longer vessels have higher Hull Speeds and thus are easier to paddle at a higher speed. A quick example – a typical 10’6 all-around SUP may have a waterline length of around 10′ (accounting for the rocker in the nose) and thus a maximum Hull Speed of 4.88 MPH. A typical 14′ race SUP will have about 13’6″ of waterline length (though some have a full 14′ depending on design) and thus a maximum Hull Speed of 5.67 MPH.
Rounded hulls vs flat hulls – how have we not even talked about this yet!?
Some touring and racing SUPs (both hard and inflatable) incorporate a rounded shape on the hull of the board – particularly in the first few feet of the nose section – while others have a flatter bottom. This again leads the layperson to see rounded shape and assume displacement hull and flat shape and assume planing hull. That’s not the case.
Rounded nose hulls are designed not to displace water, but to allow the paddler easier steering control and modify the rocker profile. A rounded shape allows the board to move sideways through the water with less resistance than a boxy shape. Modern touring and racing SUPs mostly limit this rounded nose design to the first 2 feet of a 14′ board. After that, the hull is flattened out to provide better stability. Extending the rounded section too far introduces instability and makes the board feel “tippy” or “rolly.” The recent trend in race board design has also been to make the rails of the board more round to aid in this smoother steering and give the board a softer transition from primary to secondary stability. It has nothing to do with designing a board to be a displacement hull vessel or not – it already is!
Why do Brands Make a Big Deal Out of “Displacement Hull” SUPs?
Marketing. Plain and simple.
There are definitely advantages and disadvantages to different designs and shapes, but just remember – all SUPs (other than while surfing) operate as displacement hull vessels no matter what is being done to their shape or how they are paddled. So don’t get taken in by claims that “XYZ nose design” makes a board into a “displacement hull” or “displacement nose” board – especially if the nose isn’t even touching the water!
