I borrowed picture from KA43 ( thank you ) on another thread to demonstrate new trends in board design

New straight cut in the boards instead of rounded.

Very interesting will be future development. Which one idea works better?

If we try to find scientific explanation behind each one, we could find argument pro and against each.

For example:

1. straight line is shorter then round - so we do minimize the release edge to minimum here (+)

2.For board travelling at the edge to the water surface this straight line create more obvious pivot point (+)

3. Sharp corners ( 90 degree) could create more turbulence and drag that rounded (- ?)


Have you got any your own arguments against or pro new design ?

If I could suggest something to try next:
a)
if could be maybe vents this corners with fresh air across upper surface. If we not disturb the fin to spinning but release some negative pressure from under board cut outs ( worth to try i guess) .
b) Did somebody try already the same with rear edge ? How straight cut works in comparison to rounded at high speeds ( above 30 -40 knots ) ?

What do cut outs do again?

Is it because when the board gets flighty and wants to lift on the back of the planing surface, that it's easier to control because it's between your feet?

Does it make the board easier to trim with fore and aft foot pressure?

I've read somewhere that most of the lift is at the leading edge of the wetted surface, once the water has changed direction and is going along the straight rocker line it doesn't impart much more lift. That any wetted area behind the leading edge is more or less just drag. But you need a certain amount of length because the length of the wetted area varies.


So any shape cutout should work but fashion possibly is laid on top of it all.

I'd reckon they could take those little triangles from the rail, just go straight across with a set square and be done with it.

I just thought it was just for less wetted surface??

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Ian K said..
Is it because when the board gets flighty and wants to lift on the back of the planing surface, that it's easier to control because it's between your feet?

This is exactly how I could see it ( imagine) .If we immerse square sheet at angle in the water -and pull at speed - sheet will pop up to minimum depth ( max efficiency).

If we do the same with round shape - some parts are deeper some shallow . The deeper parts will produce drag and turbulence only.

We could do easy experiment.

If we stand weight - say 10 kg -

a) on flat sheet 30 cm wide and then pull in the water at angle

b) put this same weight on round , circular piece 30 cm diameter or even bigger

which one will be easier / to plane ( oor faster assuming the same propulsion force ) ?

All of the above...
Lesser wetted surface, higher topspeeds, more trim angle control, conventional deck for your mind. Volume when not planing, compromised of course, by cutouts at speed.
See Tem Berkstresser, Berky Boards, East Coast USA, 1991 for the EXACT same bottom shape.

obviously they have been tested and given the thumbs up , personally I prefer them to be rounded from experience as I put some square cuts in and noticed a bit of turbulence , once they were rounded it was fine , after having a good look at the cut outs there rounded

Claims of reducing surface area is usually marketing hype over physics. but....surprisingly it is sort of true but not in the way most think.
Planning surface area is determined by velocity, angle of incidence and weight supported. For a flat plat, lift is proportional to angle of incidence. Double angle = double lift. Drag is not so linear so best L/D angle is about 7 degrees. (NACA drag tests flat plate).
So cutouts reduce the proportion of planning surface area at tail of board (behind centre of weight) thereby increasing the angle of incidence. This increases lift leading to a reduction of the planning surface needed.
Some say the straight cutouts provide a bit of lateral resistance allowing smaller fins & better upwind performance, others say this also affects gybing but in negative way.
The cutouts the majors have use the last few years look more like style/marketing triumphing over good design and clean, pinny tails like Lockwood's Mistrals appear to be just as good.

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LeeD said..
All of the above...
Lesser wetted surface, higher topspeeds, more trim angle control, conventional deck for your mind. Volume when not planing, compromised of course, by cutouts at speed.
See Tem Berkstresser, Berky Boards, East Coast USA, 1991 for the EXACT same bottom shape.

Have you got a picture?

My experience with cutouts is only on big boards where they seem to be more manageable/faster in chop when off the wind. my RRDs 105/122 seemed to hold more speed out of the gybes but this is from a more intermediate point of view. Id like to hear a local PWA sailor report on this like Sean/Julien (QLD) etc...

Again its from my limited perspective comparing it with similar boards i had in the last 5/6 years

Back in the days they knew how to make serious cut outs !

2017 RRD V9 cutouts

What's old is new again. RRD's 2017 cutouts look very similar to Chris Lockwood's minimalist cutouts on his Mistral Slaloms from 2014

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John340 said..


What's old is new again. RRD's 2017 cutouts look very similar to Chris Lockwood's minimalist cutouts on his Mistral Slaloms from 2014

Other than being a cut out they don't look anywhere near the same.

The RRD has a two stepped cutout with the higher cutout travelling all the way up the tail to the midpoint between the straps and that's just one of the differences, I can see at least two more obvious ones.

Sorry, I"m not a picture dude, I"m just an old windsurfer who was riding a 7'7" x 23" twin fin wave board in summer of 1984.
Tem of Berky boards was the first to address the issue of wide boards for light winds, but low top speeds. He made the cutaway's in the late '80's, early '90's with straight parallel cutouts, all the way thru to the deck, so the footstraps were located right at the end of the cutouts.
He mentioned he got the idea from the late '70's, early '80's, from someone else.
There is little new in the world, just a rehash of old designs.

What are they supposed to do? Do they make them easier to handle in chop?

Cutouts. On wide boards, they lessen the wetted surface once planing, so you have pitch control, shortening the waterline for the highest possible speed.
Slogging, there is only added turbulence and drag.

Cut-outs balance tail/nose lift.

No cut-outs the board will ride lower/flatter on the water as it generates more tail lift.

With cut-outs the board will ride higher, less tail lift to counter balance nose lift. Some will say it is easier to clear the chop and theoretically more top speed. Others may find it more challenging to control. On some models the downside is planning ability and speed out of the jybes.

In general cut-outs are not used on smaller boards as control is key in challenging conditions but if done well the board will just hover on top of the chop and put a smile on your face

My JP Slalom 84, at 55 wide and supposedly 84 liters, has huge cutouts.
Probably should be bigger for my weight (150 lbs.), and it's one of the earliest planing boards for a 5.8 sized sail.

Surely the design brief for a 84L board is not around early planning. On would imagine that when you take such a kit out you're well powered up and not worried about early planning?

What other similar size gear did you try in comparison?

JP Pro Slalom planes up and get's going fast in winds of 16-22 mph, with a 5.8 4 cam slalom sail. Above 24 in the gusts, I"m on a 5.2. 150 lbs, expert freeride sailor, I haven't raced in 25 years now. Last race was 1990, made finals in Stroh's World Cup Slalom and placed 30th in the Oneill Classic.
Other boards include JPSuperSport109, ExocetSpeedSlider95, TabouSpeedster100, Futura111, and various FSW's of 75-86 liters.

Cool, I must be missing the point, comparing boards from 76 to 111L in 16mph from freestyle wave to slalom... Doesn't seem to be a fair comparative test to me?

Hard to compare.
What criteria are we using?
Really tough when you change sails for approximately the same winds.
And while FSW can plane up almost as soon, some of mine are pro editions, water state can affect early planing and topspeeds.
I'd think, the JP Pro Slalom is only compared to fast freeride or slalom boards in speed.

Curious to know if they actually do hydrodynamic testing in tanks or whether it's all just based on feel and feedback from the test riders?

Is there the same level of scientific RnD in these cutouts that goes into, say, boat building? Like this...

Who's "they".
And do windsurf boards go thru water's as calm as that tank?
Are the rider's of specific weight and skill levels?

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LeeD said..
Who's "they".
And do windsurf boards go thru water's as calm as that tank?
Are the rider's of specific weight and skill levels?

Seriously

"They" being the designers, obviously!

Do you think naval ships and submarines travel through water as calm as a testing tank? Do you think formula one cars and aircraft only ever sit stationary in a wind tunnel? Of course not, but they still use such testing methods to set a baseline so every tweak can be scientifically measured and compared.

Or, do you reckon engineers and designers just build a bunch of full-scale prototypes at ridiculous expense, take them out for a spin and simply postulate whether one design is more efficient and faster than another based purely on feedback from the pilot whose skill level and weight might be different to the pilot who tested the previous proto?

It was an innocent and curious question, which you've failed to answer. You did succeed, however, at giving me a pretty poor first impression of you. You got anything of value to add or are you here to be the latest SB troll?

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N1GEL said..
Curious to know if they actually do hydrodynamic testing in tanks or whether it's all just based on feel and feedback from the test riders?

No by the time you make a scale model and tow it through a tank you might as well just jump on it and try it out. Depends a bit on the cost of the model vs the cost of the full-sized item.

If the cost of tank testing and analysis is anything like automotive wind tunnel testing then you could make a crap load of prototype boards for a fraction of the cost. I know which I would rather do.

I guess the old ways could apply here. Back in the 80's John Gudgeon of Multi Fins (THE fin company back then) in Byron Bay (you old blokes will remember them) was asked by Peter Hart how he came up with new fin designs. He replied "I just come up with stuff that looks new, make a few, give them to the boys to try out and whichever ones they like I make up reasons why they work".
Love rocket science!!!

Oh and for LeeD, yes this is Aussie sarcasm even though its true.

I must admit I do believe Remi.

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mr love said..
If the cost of tank testing and analysis is anything like automotive wind tunnel testing then you could make a crap load of prototype boards for a fraction of the cost. I know which I would rather do.

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Ian K said..

N1GEL said..
Curious to know if they actually do hydrodynamic testing in tanks or whether it's all just based on feel and feedback from the test riders?

No by the time you make a scale model and tow it through a tank you might as well just jump on it and try it out. Depends a bit on the cost of the model vs the cost of the full-sized item.

Yeah, it figures that the cost would out weight any small gain... and of course that would be passed onto us, the end consumers.

I've always sailed without the inserts, but think I'll try them on my bigger slalom board this summer and make my own mind up based on my scientific expertise

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N1GEL said.




Yeah, it figures that the cost would out weight any small gain... and of course that would be passed onto us, the end consumers.

I've always sailed without the inserts, but think I'll try them on my bigger slalom board this summer and make my own mind up based on my scientific expertise

Inserts for the small boards not the bigger ones Nigel.

This board is an old speed board that I reshaped the bottom on many years ago. About 9' long by 16". Started its new life without the cutouts but I could only manage mid to high 38 5x10 and it felt too sticky on the water. To fix that I added the cutouts, which freed the board up and got it into the 42 5x10 mark.
It was having too much flat that got me into the problem and the cutouts that solved it. Great board on a broad course.