Wow, that is commitment, no fence sitting there.

I still like the old bombora step hulls

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col5555 said..
Now this a cutout !

Now lets compare this to the latest Xfire. Here all cutouts seems tiny

98 liters is around 62 cm wide, so not much cutout is needed. 43cm tail.
If the board has a wide tail, say 50cm's, then a bigger cutout is needed.

Below are my 2 latest incarnations of tail cutouts. As LeeD mentioned the cutouts need to be tuned to the boards width and outline and generally as you go narrower in the tail you would reduce the cutout size or eliminate them completely. I am not an engineer and only have a fairly simplistic comprehension of the theory and have arrived where I am through that simple understanding and trial and error. Those who are way more qualified than me please jump in and call BS if anything I am saying is crap.

Planing hulls generate a higher proportion of lift from the leading edge of the planing surface and the amount of lift decreases the closer you get to the trailing edge, especially the outboard surfaces of the rear. So it makes sense to me that to get the most efficient lift to drag ratio you need to balance the width of the leading edge with that of the tail. On a pintail speed board for example you have already removed a lot of surface area from rear of the board with the narrow tail so are less likely to need cutouts at all to get the lift drag balance optimised. Wider boards though and especially wide tailed boards designed for lighter winds where you want the tail width to enable larger fins and bigger sails, you can get noticable top speed gains with cutouts by removing surface area from that low lift area of the board. It is worth remembering though that although the board is producing less lift from the rear end of the planing surface it is still producing some lift so cutouts will impact the way the board trims. So for me that has been where the bulk of the trial and error has been, tuning the tail cutout size and shape along with the outline with the aim of getting the right balance between lift, drag and board trim. Strap placement and mast track position along with rocker all come in to the equation so it gets very complicated and you can really screw up.
What is the perfect cutout shape????? I am sure lots of people have strong opinions on that and I am not even going to try and go there. What I am currently doing appears to work great on my boards and as I always have I will continue to learn something every-time I try a variation. It's all good fun.

If we looks then closely of similar size ( medium size) boards - some may have this " returinig to the rear surfaces" - creating cavity
some like yours above don't have any - just clean cut off.







I wonder what effect it may have if we eliminate those pieces. If that could make a board faster ( but maybe less forgiving at gybing)

We also we could compare where this incision begins .
Similar size boards
At my Isonic 97 it starts very early - almost at fron end of fin



at RRD XFire 98L cut out starts very late - at the end of fin box

Funny was thinking about the cutout thing and remembered my old 1998 model Protech had squarish ones. I never really got on with it as it felt draggy to me and stuck to the Protech's without the cutouts. I remember it came about as a evolution from the flapper design other boards had.

If yuo make the inserts in front good 1cm shorter, water and airbubbles go over the cut out ,there is always a vacuum. The vacuum takes air from the end in front,it begins the rotation over the inserts to the end of the inserts, No vacuum where the cut out start,only rotation.The inderts should be
good 1cm deeper than the bottum- Air goes under the inserts in front, the begin of the rotation, Wolfgang

Good you knew about Parton. I had several of his course slalom, and indeed course slalom in those days, board widths 68-72, didn't really require cutouts for upwind and downwind sailing. However, used for lighter wind slalom, across the wind, and broad reaching, cutouts did help a lot in top speed.
Tem Berkstresser was the owner of Berky Boards, just up the coast from Florida and probably a few year's older. They made the first generation snub nose boards, around 217 in length, volumes 86, 104, 120, and customs in between and above. Tem was the very first who made cutout tails, but he cut them out through the deck, since thought in those days was to have the backstraps slightly more forwards, the back screws maybe 9" off the tail, so you didn't need a full width deck at the rear of the board to stand on.

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LeeD said..
Good you knew about Parton. I had several of his course slalom, and indeed course slalom in those days, board widths 68-72, didn't really require cutouts for upwind and downwind sailing. However, used for lighter wind slalom, across the wind, and broad reaching, cutouts did help a lot in top speed.
Tem Berkstresser was the owner of Berky Boards, just up the coast from Florida and probably a few year's older. They made the first generation snub nose boards, around 217 in length, volumes 86, 104, 120, and customs in between and above. Tem was the very first who made cutout tails, but he cut them out through the deck, since thought in those days was to have the backstraps slightly more forwards, the back screws maybe 9" off the tail, so you didn't need a full width deck at the rear of the board to stand on.

Are these the sort of through deck cut outs you are talking about?









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Those are just wings, to break the contact of the water to loosen up the board during jibes.
Tem Berkstresser's boards of the late '80's, early '90's were like a modern cutout on a wide slalom board, only going up thru the deck, with the straps located just in front of the cutouts.

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LeeD said..
Those are just wings, to break the contact of the water to loosen up the board during jibes.
Tem Berkstresser's boards of the late '80's, early '90's were like a modern cutout on a wide slalom board, only going up thru the deck, with the straps located just in front of the cutouts.

These are Tem Berkstresser boards and I know they are wings. But I've got no idea what your talking about without a picture.

Yeah, you kids haven't been through it, so it's hard to grasp the concept.
Think of 3 fingers behind your footstraps....all parallel of course. And he took the idea from some board in the '50's.

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LeeD said..
Yeah, you kids haven't been through it, so it's hard to grasp the concept.
Think of 3 fingers behind your footstraps....all parallel of course. And he took the idea from some board in the '50's.

I suspect we will have to wait another 50 years for the concept to be used again

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LeeD said..
Yeah, you kids haven't been through it, so it's hard to grasp the concept.
Think of 3 fingers behind your footstraps....all parallel of course. And he took the idea from some board in the '50's.

I'm not a kid and I have been through it, just find a photo to back up your verbal diarrhoea.
I'm not going to start on snub nose.

Anything under 50 year's of age is a kid.
Do you think they had cell phones in 1989?
Go to archives for Windsurfing Mag, USA.
Just IMAGINE, modern cutout board, cut it out thru to the deck, footstrap inserts 1" in front of the cutout.

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LeeD said..
Anything under 50 year's of age is a kid.
Do you think they had cell phones in 1989?
Go to archives for Windsurfing Mag, USA.
Just IMAGINE, modern cutout board, cut it out thru to the deck, footstrap inserts 1" in front of the cutout.

Do these count?

I had this cell phone in 1983.

And this one in 1987.

Nice.
Picture taking technology still eludes them in 1989.

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LeeD said..
Nice.
Picture taking technology still eludes them in 1989.

Kinda like intelligence - every now and again it skips a generation.

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LeeD said..

Just IMAGINE, modern cutout board, cut it out thru to the deck, footstrap inserts 1" in front of the cutout.

pictures or it didn't happen!

Did the War of 1812 really happen? I didn't see the video.
Did the Persians really have a fighting force? Show me a video.

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LeeD said..
Did the War of 1812 really happen? I didn't see the video.
Did the Persians really have a fighting force? Show me a video.

They had cameras by the time of the invention of the windsurfer. I have seen the pictures. It happened!

Show us the pictures!!!

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LeeD said..
Do you think they had cell phones in 1989?

as per other responses - it was called AMPS ... en.wikipedia.org/wiki/Advanced_Mobile_Phone_System