Retirement has got me looking for projects so....
I have watched for too long the tides not suiting my end of Moreton Bay when I want to go exploring in waters that occasionally are only a few inches deep. I have raceboarded for too long and the easy way out if heading downwind in shallows was to sail backwards doing a twitchy nosewalk. But I want to keep sailing in the same way boats just slide up the centreboard.
I want more!
Call me mad but I have been dreaming of something combining all the best boating bits with the old Mistral Takeoff which had flip up skegs. They did not come back very well after a grounding but this system should. I remember a cool dude from NSW at a raceboard nats decades ago had a hollow ply board and a skeg with a lever up top that he could push to change the angle but I do not think it went to zero depth.

For this system I am carving out the back of a donor board (negotiating a Speed ProAm now but will buy any you have with trashed fin box).
A vertical slot cut right through from the tail (happy to blow some efficiency obviously) with newly built G10 or carbon skeg pivoting on a shaft in red below. Red fin is down, blue up. Control lines not shown, but bungee holding down seems feasible. I even foolishly believe that in light winds the skeg out the back will give some bite with the way the water slides around the tail.

I have even thought of doing double fins that could be shorter like the Ten Cate Leaper?

Very keen on any input and sorry if I have been here before, can't find the old post.

Thanks for looking!!

Like the Mistral from 1979

Would be very prone to spin-out as it would be so easy for air to get sucked down from behind.

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NelsonFoils said..
Like the Mistral from 1979

It's a great idea, except THAT. The centre board doesn't retract into the hull ??

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NelsonFoils said..
Like the Mistral from 1979

No, because it did not go to zero depth, nor return to full depth again. Like the OP said.

The mechanism is intended to work just like a centreboard. It will be crowded up the back end with footstraps on top, but a few ideas are gurgling in my head to fit it all in. Agree with the spinout but the shallow running I am doing will be in slow mode with no back foot pressure.
It brings back memories of sailboarding camps I ran at Lake Coootharaba as a chalkie in the 80's. On one we had the inevitable hammering southeaster all week with rain. There were massive flatwater puddles in the paddock at Elanda Point and we pulled the skegs off the wallies and attached teenie sails which the kids used to plane across the puddles and even across the grass. They would not stop sailing until the laughter got the better of them and they learned to use the tail and the edge for control.

Instead of the slots in the back another possibility is to go with the Dutch leeboards and pack up the sides of the back rails to make outer parallel surfaces with skegs fitted to the outside, held together by a long shaft and oversize washers.

I did inhale in the 70's, sorry, but I really do appreciate the feedback from other thinkers, Thanks!

here a idea use a standard fin and power box ,build a cartridge to hold the fin box that has tapers on the side and pivots at the front top .if you can make the fit right it will pivot up and back to allow the fin to go over the ground and then be pulled back with some bungy cord once clear. this keep the air from getting to the fin and the wedge shape will lock in the fin side way force,or just use a kestral black projects fin they work ok on raceboards.
if its a board with a us box i made a fin out of 9mm ply and two layers glass , good for cruising around

Back in the early eighties the Mistral take off had a twin fin setup were the fins could spring back if you hit ground then spring back to upright. If I remember right you could also adjust the rake of the fin. They did not spring all the way back as the board was in the way.

Last time I sailed at Sandstone, I didn't want to do the walk. I usually do a nose sink too, but that still draw's too much water for there.
This time I stopped and pulled the fin out and put it in my vest. The new One Design LT has a power box with a toggle on the fin bolt to make it easy without a screwdriver.
I couldn't believe how well she sailed on a broad reach all the way to the waters edge in about an inch of water.
If I'd have thought of it earlier, I would have stayed out another hour, maybe more.

I wonder if from the back of the centerboard all the way to the back of the board , have a blade 3" deep or less . That would have to give more than enough sideways grip. I would think its turning ability would be the same if the depth of the blade had similar sideways resistance to the fin. Even if it was harder to turn it could be worth it sailing in 4" of water. You could even mount it in the original finbox without modification.
And no moving parts !

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legless said..
Back in the early eighties the Mistral take off had a twin fin setup were the fins could spring back if you hit ground then spring back to upright. If I remember right you could also adjust the rake of the fin. They did not spring all the way back as the board was in the way.

Yes great pics, that was the Mistral TakeOff. I actually test sailed one in the day, based on Robbie's egg I think.

Love the shallow fin idea. I saw a wally a long time ago for our local waters converted with 4 of these:
https://www.waterskiersconnection.com.au/products/waterski-boots-bindings--accessories/62/white-plastic-bolt-on-fin/2134/
water ski fins screwed directly into the bottom. Never heard how it went.
The toggle screw fins were cool, had one on a Mistral Explosion and often removed to sail all the way to the beach at Lake Cootharaba, but I want to be able to redeploy after crossing shallows, and some shgallows will be "unplanned".
Cartridge idea could be easier to do, like a fin box within a fin box, Thanks!

How about a kicker fin ;)

WTF is that off?

;)))

Genius....fatheads too

The kicker fin is awesome. I have a minimum weight Speed ProAm board for $100 and like the way that the kicker top piece could just be screwed under the footstraps. No destruction (yet). It is similar to the kayak flip up rudder system I was looking at with the steering bits eliminated. (No don't add steering you knob!) - the yellow one. The red one with the big spring might be embarassing.
Another clever guy suggested just hinging the back 300 mm of the board so it all flips up. I have a feeling that would do crazy handling things.
A tinkler tail?

some boats run the keel all along the bottom
ever bin done on surfer or windsurfer ??

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westhammer said..

30years ago I lived just down the road from where those Mountbatten sails where made. I did some testing and R&D for them and remember long convosations about how loose leeches weren't a good idea and will never catch on.( got that wrong) I haven't seen one in years.

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joe windsurf said..
some boats run the keel all along the bottom
ever bin done on surfer or windsurfer ??

Windsurfers go a little crabwise because the fin is symmetrical and it must have an angle of attack to develop lift. Any longitudinal feature on the bottom has to accommodate a certain amount of cross flow.

I suspect that we get some steering behaviour with modern boards from their large cutouts.
Maybe they can still be sailed with no fin?
Extra big, deep cutouts may be the go for extreme shallow water sailing?

Once apon a time I thought a deep V might work. Same principle as a kite board edging. The extra volumne could be advantageous. Would be great in weed.

How about a cat twin hull design where the hulls act as the fin?

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BSN101 said..
How about a cat twin hull design where the hulls act as the fin?

A Hydroplane kind of thing ?

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Imax1 said..

BSN101 said..
How about a cat twin hull design where the hulls act as the fin?

A Hydroplane kind of thing ?

I guess

what about how the Starboard Hypersonic ?
did it steer well with short fins ?

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joe windsurf said..
what about how the Starboard Hypersonic ?
did it steer well with short fins ?

That's a MAD bottom shape. Did they go ok?

never had one, but heard ya love em or hate em
am curious if shape allowed smaller fins ??

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joe windsurf said..
never had one, but heard ya love em or hate em
am curious if shape allowed smaller fins ??

They're all being bought up and used as Foilers now, cheap as chips and work ok for small guy/girl foil board.

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Ben1973 said..

westhammer said..

30years ago I lived just down the road from where those Mountbatten sails where made. I did some testing and R&D for them and remember long convosations about how loose leeches weren't a good idea and will never catch on.( got that wrong) I haven't seen one in years.

Mountfield I think. Always pink and yellow ones I saw