Tuesday, May 12, 2015

What is Downwind SUP? - Part 1

I've done a few downwind lessons and guided runs with people who are relatively new to this aspect of SUP and I've usually walked away thinking "something got lost in my message and I'm not sure what it is."  I don't like this feeling at all; mainly because I want to be a good instructor, but just as importantly, because I want them to feel what I feel!  I want them to know that feeling and to love it like I do.  So, what's missing?  It hit me one day when driving home from work.  Some people don't know WHY they are downwinding.  They think they are out there for the sole purpose of paddling with the wind at their back because it's faster and easier.  That's not it though, that's just a tiny piece of it.

They are out there to get their board on a plane and keep it there.  The "why" is to feel the surge, the hit of speed that only occurs when riding a wave.  That's what we are trying to do, we are trying to ride waves.  Period.  When we are not on a wave (or bump) we are resting a bit and looking for another one.

If you have downwinded before (and caught a bump) then you know what planing is.  If you have surfed before then you definitely know about planing.  If you have ridden in a high performance ski boat, fishing boat, or pleasure craft then you know what planing is.  Look at the picture below.  This is planing.

Pleasure boat planing.  Look at how much of the boat is out of the water, look at the smiles on their faces!  Why are they smiling?  One reason is that Donzi wants to show you how much fun their boats are, the other reason is that planing means going fast and going fast is FUN.
Let's think about planing the next time we are out in windy conditions.  Sometimes, there's just not enough wind to create the wave energy to get on a plane.  To get the board the board to plane, we need power to create speed.  Speed creates lift, lift creates planing.  Planing creates fun.  Imagine if the Donzi in the picture only had a 25 HP outboard, it would never plane.  What a shame!

One of the best downwind boards on the market, the SIC Bullet.  This is a planing shape, specifically designed for catching and surfing bumps.
  At rest and at low speeds, both the boat and the board are in displacement mode (i.e., not planing).  At high speed, they plane.  The boat gets on a plane pretty easily from it's big V8, in contrast, we cannot plane under our own power, we need lots of help.  We get that help from wave push and gravity when we catch a bump in the ocean or a wave on the beach.  It's energy, and we need it!

Here are some points about planing.  I don't claim to know anything about hull shapes or physics but I know what feels good and I think these points help to explain what planing is:

  • When at rest, a vessels's weight is supported entirely by buoyant force. Simply stated, a vessel will float or remain buoyant when it's weight + cargo weight is less than the weight of the water is displaces.  It's all good. This is us 99% of the time.  This is displacement mode.

  •  At high enough speed, the reactionary force of the water pushing up on the board is great than the force of gravity and the board will plane.  When on a bump, the horizontal force is converted to vertical force upwards.  This lift also decreases the wet surface area of the board and thus reduces friction which helps the board accelerate.  To plane, a speed boats needs a powerful engine, a sailboat needs good sail area, and we need a wave!

It part 2, let's look at the anatomy of a board on a plane and a board in displacement mode.

(Stolen from Area10 on the StandupZone where he is explaining what he considers "planing"):
Well, certainly you can do what I call "surge-riding", which happens quite a lot with raceboards that don't plane easily - you are definitely getting a push but you are sitting high on the bump and going at the same pace as it. But what I think of as downwinding is an experience that is pretty much indistinguishable from surfing: the board is moving far faster than the bump and this allows you to plow over the bump in front and into the next trough, and so on. The board feels loose and free, and is throwing up spray at the sides and you need your foot over the fin to move it around to avoid poking the nose into the bump in front. So I don't know if that is what you'd call planing, but that is what I'm aiming for in my downwinding. You can connect bumps by turning and following the direction of the troughs, or you can do it by getting so much momentum up that you are skipping over them, and that's when the real excitement happens, to my mind.

(Additional commentary from my buddy Daniel Alvarez:  Jeff Burton it's a nice article. It's hard to say much more without getting really technical about hull speeds, weight to power ratios and prismatic coefficients 
smile emoticon. In sailing we refer to most boats as 5 knot shit boxes. Most sailboats can't escape their displacement hull speeds no matter what you do. Enter the ultralight revolution that started in Santa Cruz which designed much lighter boats with big spinnakers to allow them with some swell assistance to sustain prolonged surfs. Sounds familiar? The Santa Cruz ultralights were the original downwinders and popular with many of the offshore downwind races. Now they can be a hate mission going upwind in a blow. SUPs are effectively 5 knot shitboxes under all but perhaps some elite paddlers. So if we want to go faster we need help. Our sail area is pretty limited (though it feels humongous when paddling upwind) so wind alone is not sufficient to get us going that much faster. But gravity is. Being at the top of a wave can provide enough force (with some aggressive paddling) to get the board on a plane and enjoy a nice surf. So on a good downwind run, you can get the exhilaration of surfing without getting worked. Though I have to say, as a longtime windsurfer I sometimes wonder why I'm paddling in a blow. I guess it is just a different feeling and challenge connecting with the waves.)

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