Racing Hull Shape, Swede form -vs- Fish form

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[PauHanaTX]

Maybe too technical of a question for most, but does anyone have any input on what the best racing hull shape is for an 18'er?  From what I'm finding/reading elsewhere on hull designs, it seems that the scull and kayak communities tend to go with the Swede hull shape but it doesn't seem that the paddleboard/SUP designers lean that way.  They seem to be more into the symetrical shapes.

FYI, Swede form shapes place the greater underwater volume aft of the midpoint and fish form shapes place it forward.  When looking at it from above, a tuna fish shape would be in the fish form class.

Just wondering and looking into buying a big one.  I thought of placing this in the shape shack, but there's not much discussion on building 18'ers.

Mahalo,

Dave in Texas 

[CMC]

Interesting comment.

A OC1, Surf Ski, Paddleboard designer I train with mentioned this same principle to me.  Said he believed that SUP race boards would be much quicker and better behaved in the ocean if they were wider behind centre with less nose rocker and rocker apex forward of center.

His comment was that they had been playing with these factors for 30 years and had been where we are now before.

I just need him to want to get involved in SUP design.

[greatdane]

A lot of current race board designs use the Swede concept, Hobie, Bark and the new Naish Javelin for instance.  It certainly gives the boards nose a "finer entry" to use a kayak design term.

[noa]

as far as displacement shapes go in stand paddle boards, we're still in preschool. there is a long way to go still.
so far the ones that have pushed the concept the most in production boards are Starboard. but there is still so much we're going to see.

[PauHanaTX]

I agree, I see a slight Swede form in the Hobie race board, but not in the Barks or Naish, they look basically close to symetrical.  If you look at a Swede form in a scull or kayak it's very prominant and jumps right out at you.  You can clearly see the volume aft of center, and these guys have been at design for about 100 + years???

I'm not saying the SUP guys are wrong in their designs, because no one has done more R & D than Joe, Mark and Robbie, so they know what works, just look at their records.  I was just curious if there is a reason. 

David   

[greatdane]

You are right, it is not as pronounced as a kayak... but both my old 18' Bark and Javelin have the widest part of the boards back of center.   I have had the chance to test 2 prototypes made by Johnson Outdoors (kayak company) and they use the Swede concept in their boards... and they feel fast.  Getting a top speed of 8mph out of a 14 foot X 29" board is no small feat, but we did it on their board design.

[kayak racer]

I'm a racer and race kayaks. The reason why racing hulls are Swede form is to make the hull narrowest at the front so the catch of the paddle can be closest to the centerline of the hull. So it has less to do with the shape of the hull going through the water than it does about paddle catch. A swede form actually prefers to move through fluid space by turning around and being as fish form. To clarify, a fish form and a swede form are the same shape and that shape prefers, due to natural laws of physics and fluid dynamics, to travel in the fish form direction, hence the natural seletion form of, well, fish! Like a weather vane or a dart, the shape forward or backwards in space is the same but naturally it wants to turn into the wind... All major aircraft fuelages are fish form for instance...

[TallDude]

I just got back from a 2 week paddling trip in Lake Tahoe. A good friend of mine there is a boat designer. He's designed some of the most popular power boats on the water today. He showed me some turn of the century boat designs that are identical to current racing SUP hull designs. Piercing bows, long narrow displacement hulls, and a variety of rocker amounts. These racing boats had a top speed of about 5 to 8 mph. So we are just going through the same designs that work for that speed. Once the engines got better and the speeds increased, these low speed designs were for the most part, history. My friend is working on an unlimited SUP design that I can't wait to try. Not to mention he does incredible carbon-fiber work. The big difference between kayak (OC, and Sski) and SUP designs is the leverage points. With the kayaks your in a fixed position. On a SUP, you move forward and back sometimes more than 2 feet or more. On a SUP, your reach is way forward which can make the board react. A dynamic unique to the SUP. I think that we will see more keel designs in the future, and move away from the traditional fins.

[PonoBill]

the dynamics of a SUP and a OC, a scull or a surfski are substantially different, and the paddling characteristics are too. Sculls use oars that are fixed at their pivot. OC, Surfskis and kayaks are all propelled from a fixed position. A SUP is not likely to see as much paddle catch advantage from a swede design. The evolution is going to be different, we won't be repeating the same 100 years of design evolution.

Talldude--when I went looking for hull designs that's exactly where I looked--the non-planing designs of 100 years ago. If you look at the M&M design that is exactly what they did. The underslung piercing bow, minimal rocker and fish design are pure turn-of-the-century.

[PauHanaTX]

I was looking at the M&M 14' Carbon, I don't think it's a fish design, pretty sure it's Swede.  I scanned the image into CAD and it measures widest point well back of center.

At least that's what I got.  It even looks Swede with the naked eye.

[finsider]

When viewed from above (as in when you are standing on the board) the M&M boards are purely swede...but if you are talking about volume below the water line, when viewed in profile like the picture I used from Adios Pantalones' post it would be fish form.

This combination of vertical volume up front and horizontal volume aft seems to be a winner, because the drag produced by the tail wake has much less of an impact on non-planing speed than bow friction does.

PS- I wouldn't compare SUP design to an actual fish shape or airplane hull because SUP boards are mostly affected by the water on one plane(dimension) and not fully submerged.

thats my .02 cents, and most of what I remember from Computational Fluid Dyamics class

[PauHanaTX]

Wow!  In plan view a swede, in cross section a fish...

So, I guess I'll call it a... "Swish"!!!