Going Ballistic

[burchas]

Congrats on your new board. I'm a fellow Blackfish fan.

Do try the side fins with a small ventral between them set back in the box. In my experience, that combo is substantially faster.

Tomorrow is one of those surreal days in NYC where it's all of a sudden 57F when it supposed
to be freezing, at least the water will keep you honest at just under 40F...

I was suppose to test stealth twin fin with the kick fin, which is what you were referring
to for fast acceleration with only difference is the center fin is the kick which is the dedicated
fin for that purpose designed to release at the same time with the twins.

Why doesn't it make sense to you PB? this board was conceptualized with those
twins in mind. The asymmetric foils designed to direct water into the channel thus creating a
lift and making the tail release more like a pintail even though it's a very wide tail, at least that's what Larry says.

I'll need to give it a lot more testing and tomorrow with 15knots  side wind probably won't be the day for it

These are 4" deep with 8" base with the combined surface area of 57sqi

[PonoBill]

I know what Larry says, but it doesn't make much sense to me. sounds like a recipe for drag. And I can't find any way to have lift that's in any way significant.

[burchas]

I know what Larry says, but it doesn't make much sense to me. sounds like a recipe for drag. And I can't find any way to have lift that's in any way significant.

To make the point clearer, the twins create a bump under your tail that you ride on, hence the
the better release. You can see the bump behind this Starboard sprint that has the twins installed
on the pic below.

From what I could tell with all the testing on my SIC, there wasn't any speed difference between
the board with or without them, so even if there is some drag one could argue that the better release is compensating for it so in reality you get the same speed but with a lot more stability, once you go into choppy water, this extra stability translates to a lot more speed.

At any rate, I will test the crap out of this board and try to make a video showing the bump
and the lift, see if that channel really holds any water

[PonoBill]

I don't mean to argue the point, since I have no idea what's actually happening other than it works. I'm not academically trained in hydrodynamics, but I've read a lot trying to understand what goes on with all varieties of watercraft. It would be nice if someone on the zone had specific credentials in this stuff, but based on the little I know, the explanation is nonsense. I've heard everything from "the fins increase the pressure" to "fins convert motion through the water into a force called "drive"" and a number of things in between. None of them make the least bit of sense to me, and most are physically impossible.

I'll stick with "it works" until I have time to modify my test tank so it operates usefully with fins.

[burchas]

I don't mean to argue the point, since I have no idea what's actually happening other than it works. I'm not academically trained in hydrodynamics, but I've read a lot trying to understand what goes on with all varieties of watercraft. It would be nice if someone on the zone had specific credentials in this stuff, but based on the little I know, the explanation is nonsense. I've heard everything from "the fins increase the pressure" to "fins convert motion through the water into a force called "drive"" and a number of things in between. None of them make the least bit of sense to me, and most are physically impossible.

I'll stick with "it works" until I have time to modify my test tank so it operates usefully with fins.

I don't mean to argue that point either since it is not my point. This explanation is
coming directly from Larry. Nonsense or not, "it works" as you put it so maybe it's
time to put your logic aside and subscribe to his theory, after all he is dealing
with hydrodynamics for few decades.

Just like you, I'm trying to paint a clearer picture for my sake and other interested parties. This test tank sounds like something handy for that purpose so do tell if
You made any progress on it

[PonoBill]

Nah. I like Larry, and I like his fins. But his explanations make it clear to me that his knowledge is NOT theoretical. He's not alone. I've read explanations from other fin manufacturers that makes it abundantly clear that you don't have to understand how something actually works to make it.

Not just picking on Larry, from fin manufacturers, even big ones, I've read descriptions of fins increasing the water pressure on the lift side (water is effectively incompressible) and that there's a vector force forward called drive generated by the fin (which is why if we put our boards in the water they instantly accelerate away from us to some percentage of the speed of light). That fins reduce drag (which would mean they don't work and don't generate lift when moving). It's an area with much voodoo.

[yugi]

^ Thank you.
Because I couldn’t understand the given explanation of why they should work either. Some stuff is backwards in there. Whaddaya mean “creating a bump under your tail” when the side fins are angled out? In fact I understand JP fins much much better, and everyone talks about the speed (or lack of drag) they have.

Not that I remember all those formulae from my naval architecture classes anyway, I spent far more time at the tow tank and water tunnel building and testing fins (to be tested as miniature keels). I’ve never seem longer formulae in my life. I didn’t know greek had that many letters! Anyway, I’m more a fan of evidence based science.

That they work is basically what I wanted to know. I always listen to non-cool-aid drinkers more attentively.

[burchas]

I've read explanations from other fin manufacturers that makes it abundantly clear that you don't have to understand how something actually works to make it.

Talking about SUP alone (not surf) in a single fin setup I would agree with this statement.

Talking about introducing 4 fins to a sup, and not just one board but many different shapes of
boards and make the boards work better, this is no fluke. I don't think you can do it without
understanding how it works, if not on the academic level at least on the experimental level.

It's easier for me to get Larry's logic than your voodoo.

It becomes clearer to me every time there is a discussion about it that people coming from
other water sports (usually surf) have more difficulty making sense of it. Corresponding
with Larry, he makes it pretty clear the whole concept is reactive to the forces generated
by the paddle stroke and not the forces of a wave pushing the board from behind.

Didn't see you once referring to paddle stroke which might be the reason it doesn't make
sense to you, but than again, it seems that most of your paddling is either downwinding
or surfing...

That said, I'll echo your previous statement and say that I would love it if someone with
academic (and practical) knowledge of Hydrodynamics & Physics would help to paint
it in a scientific way that explain why and how it works.

I like to tinker with sh!t and that's why I like this forum, that's how I find out about Larry
and all sorts of great stuff.

[burchas]

^ Thank you.
Because I couldn’t understand the given explanation of why they should work either. Some stuff is backwards in there. Whaddaya mean “creating a bump under your tail” when the side fins are angled out? In fact I understand JP fins much much better, and everyone talks about the speed (or lack of drag) they have.

Not that I remember all those formulae from my naval architecture classes anyway, I spent far more time at the tow tank and water tunnel building and testing fins (to be tested as miniature keels). I’ve never seem longer formulae in my life. I didn’t know greek had that many letters! Anyway, I’m more a fan of evidence based science.

That they work is basically what I wanted to know. I always listen to non-cool-aid drinkers more attentively.

yugi, as a fan evidence based science I'm surprised that the comment stating
voodoo as an explanation is the one making most sense to you... just saying

[yugi]

As has been said: not buying 2 big parts of the given "theory". Really does not make sense to me.

Very happy it somehow works.
Whatever.

[PonoBill]

I didn't mention it because it isn't relevant to what I was talking about. Understand, I'm not saying Larry doesn't have a mental picture of how his fins work and what they do. And I'm certain that his picture helps him design fins and fin combinations that are original, effective, and valuable. But that doesn't mean he really understands the physics behind them.

For thousand of years educated people believed the sun and stars orbited the earth. They looked at strange motions of the planets and the extremely fast rotation of the sun and concluded that planets moved in complex epicycles and the sun was only a few thousand miles away, closer than the moon and much smaller. They weren't stupid, the solutions were elegant. It seemed clear that the earth wasn't spinning--if you dropped something it fell straight. The earth wasn't swept by stupendous wind. They didn't have Isaac Newton to explain momentum. 

All the explanations worked, and were sufficient to chart the stars and planets, predict eclipses and tides. And they were all wrong. Pretty tough to send a probe to Mars if you plot the course with epicycles. It's hard enough when you do know how the solar system works.

The fact that something works is not proof that the explanation is right. Larry's long experience with building fins gives him a mental library of what works, and a heuristic vocabulary to describe why. But it's not correct as far as I can see. And you can do a lot more with the stuff that works if you really understand why it works.

[PonoBill]

Oh, and Larry's separation of fin performance as being pushed from behind vs. being paddled is one of the things that makes me realize that he does know what he's doing. He gets a great outcome. When I said "there's a lot of voodoo" I meant the explanations by all the fin manufacturers that I've read are voodoo.

My interest in the actual physics is mostly personal curiosity.

[burchas]

My interest in the actual physics is mostly personal curiosity.

Maybe one of these days, this personal curiosity will produce a different working theory I can tinker with

[Larry Allison]

Thanks guys for the kind words! Have a Happy and Safe New Years my friends!

[burchas]

Going upwind on the 2017 Infinity Blackfish  - 1 minute video

https://www.youtube.com/watch?v=LqrFA8sr28E

I'll also add it to off-shore's sup upwind thread:
http://www.standupzone.com/forum/index.php/topic,31046.msg340696.html#msg340696