always a hotly debated topic amongst ourselfs

my take on it- sups are just to wide to have big long displacement, you can't displace that amount of water efficiently. even the narrow nosed naish 17 and the jav go to flat fairly quickly. also too hard to handle mostly. oc1 and skis can do big displacement because they are narrower, longer and the paddle power is way up then on sups.

a displacement nose into flat ish bottom asap is the go imho

what do you reckon?-interested in all theories
cheers

teatrea said...

I dont know **** about this , but it wont stop me giving my opinion , i think in a downwind situation a displacement nose is a liability.With wind behing you i would be aiming to skim across the surface as much as possible not burying the nose into waves.So for down wind boards i think flatter the better with a uplifted nose and pin tail.For flat water as much displacement as you can handle on a narrow board.

see told you i dont know **** about it.

teatrea, even on the oc1, it goes a lot quicker when the displacement nose is riding high,but the displacement will let you go through the bump in front down to the next runner. mind you that's a harder thing to do on a sup, so that's a fair point i reckon
cheers

teatrea said...

here is a crazy idea , for flat water boards why not make them more like racing skis maybee a touch wider with a centre keel like a yacht for stability?

You mean just like the Starboard K15 with its center fin in position..

If you take a sneaky look at the rails and bottom of some of these displacement hull type boards you'll see they are doing all they can to make them work as a planing hull.. They want their cake.. and eat it to..

DJ

Firstly: The basic definition as per what actually is a displacement hull. There seems to be much confusion. As per a basic google search and from the Boat US site www.boatus.org/courses/

Planing Hulls--Planing hulls are designed to ride on top of the water, regardless of the weight of the boat. The flatter the bottom, the easier it is to get on plane. Also, less power is needed to attain high speeds with a flatter hull. The trade off is in handling. Flat hulls do not do well in rough water. Many planing boats use a shallow "V" shape to ride better in rough waters. (Sounds like us eh?)

Displacement Hulls-- Displacement hulls typically have a rounded bottom with a tear drop shape running bow to stern. Displacement hulls "displace" or move, an amount of water equal to the weight of the boat. Displacement hulls are very efficient-- most long range cruising boats such as trawlers and many sailboats use this type of hull. But because of their design, displacement hulls are restricted in their speed to the square root of their waterline length times 1.34. Therefore, a 64 foot boat can realistically only expect a top end speed of a little over 10 knots. (Displacement Hulls do not plane!)


SUP do not have displacement hulls. Some boards have a displacement style canoe inspired nose which is usefull for cutting through chop up wind and also to help the board to not stall and to pop back up when poked into the wave in front. These mostly dissapear to flat 12 to 18 inches back from the nose.

Some designs may overcome the poke thing by adding a whole lot of rocker (ie Naish 14" Glide, F16 etc) but these boards from what I understand are slow in the flat and very hard upwind. Pretty much only true downwind boards. (perhaps why SIC made the bullet, a planing hull with a displacement style nose, for more mixed conditions like Australia)

I think of SUP Bottom design to be more like a speed boat, Veed nose to help it onto a plane easily where it becomes more like a surfboard and planes. No doubt true displacement hulls would be faster than what we have now in flat water but until someone works out how to stand on one to paddle impossible.

I think the conspiracy is that the word displacement itself is thrown around as a marketing term rather than an indication of the boards actual design.

Nice post with the definitions in it.
As my non-expert 2 cents, I would suggest that SUP is neither really, in that they are clearly not a displacement hull, but under paddling conditions, they do not really plane either.
Planing implies skimming across the water surface, but SUP boards are not really doing that. They just bob along on top. When they pick up on a runner, the water is still moving faster under the hull than the hull is moving on top of the water.
A third type of hull, the bobbing hull, or possibly a surfing hull. Not a true displacement hull or planing hull.
Distinctly different from the other 2 with the inherent instabliity and intrinsic tendency to capsize. Not really a boat hull at all in that regard, so I wonder if it's even useful to refer to the whole board.
It's really the nose that's being referred to.
Displacement noses "displace" the water at the prow, whereas "planing" noses pass over it.

Al Hunter said...

DavidJohn said...

teatrea said...


With wind behing you i would be aiming to skim across the surface as much as possible not burying the nose into waves.So for down wind boards i think flatter the better with a uplifted nose and pin tail.

see told you i dont know **** about it.

I agree.. (except the pin tail bit).. For real DW'ers give me a board with some rocker.. and a board that jumps onto the plane and surfs like a surf board.

DJ

If I can't prove you wrong nextweek when I get my new 17' I'll be really disappointed

I'm sure your new board will be great.. This is more about a personal taste thing just like Ferrari's and Lambo's.. they're all great.. .. As far as rocker goes it may just come down to having to ride them differently to get the most out of them.

Hey CMC.. I'd call the K15 a full displacement hull because it doesn't have a releasing edge anywhere.. It spreads the water and puts it back again.. The new 'New' is also a bit that way.. Maybe even the Jav although it does have a chopped off tail.. It's also interesting that a dissplacement hull will get planing.. if it goes fast enough..

DJ

latman said...

My take on it is that a SUP is a displacement hull (your weight and the boards weight IS the amount {KG/litres} displaced) but it is very slow and very wide , a true planing hull lifts out of the water and "skims" on the surface which is what a shortboard does (on a wave only)
The difference between a SUP and ski ,Kayak, boat etc (other displacers) is that you need more width for stability (standing gives a High Centre of gravity) compared to sitting in where bum width is enough for balance too. Lats

Hey Lats I was hoping you would comment.

I am happy to take your opinion above most. However, I would have thought that most SUP designs (surf and DW) are designed to 'skim' being on a wave or a runner. The hull design is kind of a compromise of stability, versus flat water run or chop piercing and 'skimming' whenever possible with control. Would you still consider this flat bottom type, as in the red Hobie board above a displacement hull? As I say, for me if you say it is, I am happy to accept that.

Pure flat water boards are of course the exception and DJ's example of the K15 may well be a slow displacement hull. I have never seen one.

I feel OK about being wrong.

PTWoody said...

Just thought I might stick my big nose into this discussion...

Gold !

I like the stability and planing abilities of the Naish 14 & 17. The K15 is quicker than the Naish 14 in the flat, because the K15 is slicing. The flat bottoms feel more user friendly for me.

latman said...

My take on it is that a SUP is a displacement hull (your weight and the boards weight IS the amount {KG/litres} displaced) but it is very slow and very wide , a true planing hull lifts out of the water and "skims" on the surface which is what a shortboard does (on a wave only)
The difference between a SUP and ski ,Kayak, boat etc (other displacers) is that you need more width for stability (standing gives a High Centre of gravity) compared to sitting in where bum width is enough for balance too. Lats

This is a pretty good way to look at it. Spot on i rekon!

latman said...

My take on it is that a SUP is a displacement hull (your weight and the boards weight IS the amount {KG/litres} displaced) but it is very slow and very wide , a true planing hull lifts out of the water and "skims" on the surface which is what a shortboard does (on a wave only)
The difference between a SUP and ski ,Kayak, boat etc (other displacers) is that you need more width for stability (standing gives a High Centre of gravity) compared to sitting in where bum width is enough for balance too. Lats

thats interesting, seems as if dw sup boards are stuck somewhere inbetween planing and displacement without the best of either- to wide to displace properly and never really skimming either
cheers