Author Topic: The ventral fin from Larry W. Allison  (Read 35560 times)

Henrik F

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Re: The ventral fin from Larry W. Allison
« Reply #45 on: March 12, 2013, 02:06:00 PM »
Very nice! I really look forward to recieving the new design.

Henrik F
crosswater.se

westbeach

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Re: The ventral fin from Larry W. Allison
« Reply #46 on: March 12, 2013, 05:42:29 PM »
Larry, Looking sharp!! And Mahalo for keeping us in the loop as to what you have been up to. That is what is so great about L.A; He doesn't just put out a product for the masses without first proving his design and making sure it works well. <thumbs up!>

Looks like it's time to get in touch with Larry again. ;) I am considering adding this to my 14' M&M. Thanks for feedback Henrik!

Just wanted to say thanks for being patient my friends. I know some of you have AVS fins on ordr. Didn't forget you, they are being finished this week. Just a few tweaks to fine tune since these are new to the Allison collection. Want to make sure these work to my liking had to spend more water time first before finishing. Hope you Enjoy the ride my friends. Mahalo, Larry

Henrik F

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Re: The ventral fin from Larry W. Allison
« Reply #47 on: July 03, 2015, 02:15:24 PM »
Hello!
I have now, since early 2013, been paddling with AVS fins. Only touring and raceboards. I started doing so because I wanted a bit more tracking and being able to take some more strokes/side before changing.
What I have noticed that came along with the increased tracking was that the boards became MUCH more stabile. Approximately 2 inches more stabile. This meant that I was able to take on much more challenging conditions.
Some other advantages that appeared were that it is so much easier paddling either with the waves coming in from the side in upwind or downwind. Way easier to hold my intended course! I don't get pushed away from or off the waves as much as before. It also increases my ability to surf the raceboards in a, say, 20° angle on the wave. Footsteering doing a DW is also better and if I get up real speed I will stand so far back on the board that I am lifting the ventral fin out of the water which mean I can steer the board as a surfboard. The lifting goes for bouy turns aswell :)
In flatwater I downsize the ordinary centerfin so increased drag is next to nothing. But sometimes I don't because of the increased tracking so it doesn't really matter.
It might get some increased weight but that is nothing I notice on the water.
So far I've had them installed on a Bark Competitor 2012, Fanatic Fly Race flatwater 14' and a Starboard Allstar 12'6x26,5".

Henrik F
crosswater.se

PaddleSpot

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Re: The ventral fin from Larry W. Allison
« Reply #48 on: July 03, 2015, 10:55:29 PM »
You are so right, Henrik F  :)

The real question is "Why don't they put a small centerboard on every touring SUP ?"  This is so obvious... Best tracking, increased stability, and a perfectly balanced board when paddling crosswind...



Check this little video :

Olivier Drut
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deepmud

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Re: The ventral fin from Larry W. Allison
« Reply #49 on: July 07, 2015, 09:34:16 PM »
That's going to be tough on my Blue Planet isup....  8) maybe I can duct tape one on....

blackeye

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Re: The ventral fin from Larry W. Allison
« Reply #50 on: July 08, 2015, 10:29:45 PM »
That's going to be tough on my Blue Planet isup....  8) maybe I can duct tape one on....

Love the idea, but that's going to be tough on my chin or sternum or gut or the jewels at some point.

PaddleSpot

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Re: The ventral fin from Larry W. Allison
« Reply #51 on: July 10, 2015, 01:14:09 AM »
blackeye, it's only a prototype, to test the general concept. My daggerboard is generally either down, or strapped on the deck. But I'm really convinced that cruising SUPs should have a pivoting centerboard, like old woindsurfs. The ventral fin is only a first step in this direction.
Olivier Drut
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deepmud

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Re: The ventral fin from Larry W. Allison
« Reply #52 on: July 10, 2015, 09:18:18 AM »
I think it's pretty cool - I note the placement is forward rather than in the middle - and WAY larger than Larry's fin. Reminds me of the one that Bart de Zwart came up with for his isup in the Arctic.

PaddleSpot

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Re: The ventral fin from Larry W. Allison
« Reply #53 on: July 10, 2015, 09:58:07 AM »
The general idea is to counterbalance the effect of the rear fin.  So the closer to the nose the better. The forward position increases the lever, hence allows to reduce the size of the daggerboard. The limit depending on the rocker of the board. The board on the video is a 14' f-one, the one on the picture is a 14' prototype I built last summer, with a rounded hull inspired from canoes. The daggerboard really helps on this kind of shape.
Olivier Drut
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photofr

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Re: The ventral fin from Larry W. Allison
« Reply #54 on: July 10, 2015, 11:23:55 AM »
PaddleSpot: I still love your idea…
I was able to try your ventral fin with a French paddler… it really works great !
Couple of things I noticed immediately when testing it out with huge amounts of crosswinds:
1. More stability, right off the bat.
2. Unnoticeable decrease in speed (Gregg Barton says fins provide less than 1% loss, based on his many tests with Epic Kayaks)
3. Using the ventral fin in conjunction with the rudder made the 18' board turn even faster (nice pivot point)
4. The removable aspect is a BIG PLUS
5. It weight nothing… made out of plywood.

Brilliant, just brilliant Olivier !
I'll have to put one on my new 14' x 25" Starboard Race
Nelo SUP - 14' x 23"
Nelo Surfski 560M - 18'4" x 17"

stoneaxe

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Re: The ventral fin from Larry W. Allison
« Reply #55 on: July 10, 2015, 11:47:36 AM »
We need to get Bill to finish the design of his remote control ventral with auto GPS.
Bob

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lucabrasi

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Re: The ventral fin from Larry W. Allison
« Reply #56 on: July 10, 2015, 11:50:26 AM »
We need to get Bill to finish the design of his remote control ventral with auto GPS.
I just think gps minnkota with that for me.

BroDog

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Re: The ventral fin from Larry W. Allison
« Reply #57 on: July 11, 2015, 05:07:39 PM »
Saw these recent posts and got me fired up to do some ventral fin placement testing today. The board is an unlimited 17.5' I've been riding for the past 1.5 yrs.  It has 2 ventral boxes.  At the time of placing my order, the shaper was insistent the ventral box needed to be further forward than Larry Allison's recommended 20" forward of center.  In the picture, I'm pointing at a second ventral box that was installed later on at 20".  I usually have a small ventral in this box.

Things I noticed with the ventral fin in the front box (furthest forward, 5 ft from center):
1. Tracking is slightly better. Placing the ventral so far forward seems to only have one specific benefit - tracking.
2. Very difficult to turn.
3. More energy is needed to keep the board up to speed. The fin creates front drag or push. Less forward projection.
4. The board became more  susceptible or sensitive to small wakes pushing the nose around and affecting stability. This was in a harbor. Imagine the effect in the open ocean.

The 20" formula for ventral box placement seems like the best compromise placement for improved paddle efficiency.  20" forward of center is right where the paddle enters and begins a stroke, resulting in good push off the ventral fin along with great tracking and stability.

Happy paddling, Bro's!!!

blackeye

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Re: The ventral fin from Larry W. Allison
« Reply #58 on: July 12, 2015, 09:50:07 PM »
blackeye, it's only a prototype, to test the general concept. My daggerboard is generally either down, or strapped on the deck. But I'm really convinced that cruising SUPs should have a pivoting centerboard, like old woindsurfs. The ventral fin is only a first step in this direction.
My apologies, that came off a bit more snarky than I intended. I am very interested in what you have done. I agree, a centreboard is ultimately the way to go.

PaddleSpot

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Re: The ventral fin from Larry W. Allison
« Reply #59 on: August 12, 2015, 11:51:48 AM »
 No offense taken blackeye :D
Olivier Drut
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