Any thoughts on my side fin/rail angle study, and entry rocker...

General Discussion
1

**Below is an excerpt from my communications with a mentor of mine - hope it makes sense.  **

Curious if any of you have thought to share. Fin/rail angle study Methodology.

Measuring the fin angle was easy - for the rail I chose
to go with 8" centered on the center of the fin, then measure out from
the center to the rail, take the difference, and set it up as an angle
away from the center line of the board.  My thought was: This will give
a better picture, the 8", but it turned out,  my boards, and the
“Blue Hawaii” don’t have much curve in that area anyway.  And by using
the stringer and a base line from which to measure the angle, I was
using the same point of reference for both angles.

**‘R’ = rail , ‘F’=fin, I included the boards length and tail width. ‘o’ is for angle, and the last number are the differnce/sum of the angles - it was part the basis of what we are looking at.
**

“Blue Hawaii” 8’x13" - R=11o, F=2o = 9o/13o

“Hands” 7’5"x13" - R<8o, F=4o - 4o/12o

“Sally” 8’x13" - R=14o, F=4o=10o/18o

“Sway” 6’7"x14" - R=12o F=2o - 10o/14o

“Heavy gun” 9’3"x12" - R=8o, F=2o - 6o/10o

“Chicken Hawk” 7’5"x 15" - R=11o, F=3o - 8o/14o

“Rainbow gun” 10’7"x11" - R=9o, F=2o - 7o/11o

What
I’ll say trips me out Mang - is the “Sally,” which is my magic board,
has not only 4o of “toe,” which I didn’t see coming, and should explain
some of the turning benefits, but so does the “Hands,” which doesn’t
have the tail kick, and thus doesn’t “snap” in the same way at all, but
the “Sally” has radical out ward angle of the rails in the tail area. 
My goal was a tail as narrow as the “Blue Hawaii” (B.H.) up towards the
18" mark, but I wanted the board to be wider for paddling, as I rode
boards wider than the 18.5" wide “B.H.” - the “frankinboard” is around
21" wide - so I made the “Sally” around 20.5" wide, thus the radical
outward rail angle.

The
“Chicken Hawk” and “Sway” are/were (The “Sway” is broken in half at
this time.) ridden as Quads and due to other radical bottom contours (I
think I may have mentioned, but I’ve learned my lesson in regards to an
all around board.) - they have heavy “V” panels from the nose back,
with a 6" wide, 1/2" deep channel, both fading to flat @ the 2’ from
tail mark - what this created is a serious kick/curve spread out over a
smallish area, and they both “stuck”/tracked straight at the bottom of
waves that were thick/over head… Great in small hollow/mush up to
chest/shoulder high… but at some point of speed in the flats, I could
not get them to go on edge to bottom turn, period.  Bummer, but a
lesson to be sure.) And they have wide, for me, tails.

The other
interesting thing is the “Heavy gun” (HG) works well, and is fairly
“plain.” But, it does have some serious “V” hull action up front, but
the “V” spreads away from the rail @ 2’ from nose, and follow what
would look like the outline of a shorter board till it is all flat
around the kick @ 27.75" from tail.  The rocker is nice and smooth
(Sadly/or not hard to know with out a true comparison - the rainbow
gun came out with a little “kick” @ 4’ from the tail too, so there a
flatter spot between that kick and the tail kick…)  I will make
another big gun. 

I can summarize this so far - for an all around board, the 4o seems to make
a difference from the standard 2o - makes me think about using 4-way
boxes some day…

But what about that “radical” rail angle??? 
trippy to me Mang… That board works great and it’s fucking weird… I
should go into my buddies shop and measure some rail angles…  Given
the standard 4.5" w/1/8" off set for side fins = 2o, not much mystery
there, in regards to what most people are doing.  Funny to me that I
must have fucked up the math and set the Hands and Sally at 1/4" off…
and the others since then have used the Barnfield method and all ended
up at 2/3o.  I’d be tempted to try 4o in a big gun anyway, as I’m not
worried about speed, and my goal still is to do turns as best I can
when the waves are big and clean… I told you about full round houses,
lay backs and rail grabs on the heavy gun and the rainbow when the
conditions were right.

The
“H.G.” was a home run out of the gate, and given how well it worked, I
thought I could go a little wider with the rainbow, but I think I’ll
stick to 21" as a max… It’s a tough balance to find: A long thick
board to get in early in 3xoh+, and still be able to push it hard in
turns and have is respond smoothly…  I’m still thinking about putting
two rear fins, to make a quad, on the HG to see how that goes on big
days… 

The thing I thought could be semi “universal”  about Barnfield’s method (For setting side fins to the nose)

  • as the board gets shorter and wider, and considering the fins stay
    near the rails, the toe would increase proportionally, and vise-versa
    as the board gets longer and narrower.

As I’ve mentioned - not
to blow my own horn: who cares, I’m only making boards for me, and when
my buddies are surfing the smaller weaker beach break in the summer,
I’m trying to dawn patrol at the reef for the biggest heaviest waves I
can find on a given day - so I don’t care to much about general mush…
And, the Sally works OK, even in waist high stuff, as long as it’s not
too mushy, but that’s what I have the Chicken Hawk for…

Speaking
of which - I didn’t mention this, as it’s not part of the fin/rail
angle study, but I have though about this a lot since making the CH.  I
made the stringer, and thus the rocker profile in line with what I’d
been doing in my boards (The Sway was a bit of an outlier, as it came
from a production blank and it was all I could do to get what I wanted
out of it - there quite a bit of factory finish, top and bottom,  under
the glass - so the nose flip isn’t what I would have built myself, but
the rocker up to @ the 1’ from nose is OK.).  But, not unlike what I
did with the Sway - a bottom I’m “over,” but thought of like a
hydroplane - I cut in a deep channel around the entry rocker, and
combine that with the heavy “V” panels, and I ended up with “ribs”
parallel to the rails/stringer/entry of the channel in the front which
I think are non-functional, i.e., I could sand them off in the first
foot of the channel about 18" to 30" and it wouldn’t make a difference.
(One side note of totally stoking revelation - I made the nose 11" wide
on the CH, with serious “V” and it worked so good on late steep drops
(On occasion, on such drops on the Sally, I’d see the nose digging in
(The nose was about 13" wide and kind of rounded at the tip.)), so I
did what I did on the CH, and when the Sally was cracked in half on Easter,
and I even considered letting it be, and I got around to fixing the
near snappage (thank god for the “patented” tO 5/8" stringer… Ha!) I
also took @ and 1.5" off each side of the nose of the Sally - fading
in about 18-20" back @ what I consider to be the ridding entry rocker,
and it has worked great since, so I guess it’s now the Sally 1.2…
Ha!) 

Ok Back to the story at hand re. the CH, channel and panel
thoughts… Taking that much out of the entry rocker for a channel,
combined with the V panels, has in effect made a much lower entry
rocker than I’ve used in the past - granted I do have radical nose flip
in the last 6-8" - like 4-6" and, combines with the V, and the
narrowness it fucking rules - and I find I paddle from much further
forward, as the the true geometric apex has moved forward, and it
causes me to catch waves easier.

To summarize that half hour of work - Way lower entry rocker = catch waves that much easier. Narrow nose w/“V” and flip keep from digging in on late drops. (I
use to think those talking about low entry rocker vis-a-vis fish and
the like were full of shit, 'cuz those boards also have wide noses, and
to me that has always sucked.)

**OK - Sway brethren… Thoughts, insights, comments, questions, shit…??? **

**Thanks for letting me play here - If it weren’t for “Uncle” Dale S., Sways, and my newest mentor… I wouldn’t be here doing this… **

Mahalo -

2

I couldnt easily decipher it between Zero’s and O’s and o’s and didnt want to spend the time doing so.

Maybe if you spelled it out for the first 2 boards.

3

Any possibility of a diagram?

kc

ps. If you need one, here’s a tail  template in gif format, if you’re using Windows you can just save the page, open it in Paint and finish the diagram.

4

Well - I saved the tail thing and added to it, but can not figure out how to get it into the tree/pictue thing above. Then I saw the search feature, saved it as a jpeg… and here it is.

You know - the difference between’0’ and ‘o’ is a lot more noticeable while writing here… classic.  I’m gonna replace the ‘o’s’ for degrees with a ‘d’ hope that helps. The last two are the difference/sum.

“Blue Hawaii” 8’x13" - R;11d, F;2d = 9d/13d

“Hands” 7’5"x13" - R;8d, F;4d =  4d/12d

“Sally” 8’x13" - R;14d, F;4d = 10d/18d

“Sway” 6’7"x14" - R;12d F;2d = 10d/14d

“Heavy gun” 9’3"x12" - R;8d, F;2d =  6d/10d

“Chicken Hawk” 7’5"x 15" - R;11d, F;3d = 8d/14d

“Rainbow gun” 10’7"x11" - R;9d, F;2d = 7d/11d

 

The red zone is were I measured the rail angle - degree of angle from tail towards nose - over 8" centered on the center of the fin. The fin angle is the degree of toe.

The point was to see if there was a relationship between those two angles in relationship to my boards, especially the 'magic" one(s).

480×552 4.19 KB

5

Toe is all about keeping the angle of attack in the positive. This means the flow vector pointed at the curved side of the fin. Flat sided fins don't like to go into the negative angle of attack zone. Lift goes to zero and drag goes ballistic and your fin stalls. So, your rail curve and your amount of toe along with rocker, bottom contour and overall planing area all have to be considered for what types of turns you plan to make on the board you're designing.

 

Stalling your fins is not always a bad thing. As you approach stall before you wash out, the higher drag values allow fins to grab more water and kinetically pump your board more effectively. Completely washing out alot of people like to describe as tail slides. So, you sometimes want to stall your fins and depending upon how easily you want to be able to stall will also factor into how much toe.

 

I don't design boards. I work with my local shapers to design my boards with inspiration from others. So, I don't have a data base of values to compare rail curve to to angle. But, boards that are primarily focused towards weaker surf and lots of turning will benifit from more toe & cant,  less rocker, more vee and planing area.  Boards that are focused on say Mavrick's will benifit from pretty much the opposite setup if you are looking for maximum control.

6

You’ve got my interest. (Oh lucky you, huh?)

Is this interpretation right?

And if we call the parameter the Taylor Parameter, and plot it
against R-deg what’s it saying? Do we need more numbers to see a
trend or clustering of points?

                                            R        F       Taylor Parameter

Blue Hawaii 8’x13"           11      2        9/13

Hands 7’5"x13"                   8      4       1/3

Sally 8’x13"                        14      4       5/9

Sway 6’7"x14"                   12      2       5/7

Heavy gun 9’3"x12"             8      2       3/5

Chicken Hawk 7’5"x 15"   11     3        4/7

Rainbow gun 10’7"x11"       9     2        7/11

 

... and are you sure the (R-F)/(R+F) parameter is capturing what you're after?

 

kc

 

... and one more plot, its a straight plot of  R-deg v F-deg.

 

7

Hey Tom  - “Howzit?”  Good to hear from you.

Flat sided fins don’t like to go into the negative angle of attack
zone. Lift goes to zero and drag goes ballistic and your fin stalls.

In general - about what you’ve stated, which I quoted above - It would seem like this would apply to the “inside” fin while turning, if the angle of attack became (too) high enough.   Is this correct?

I’m curious to read what others think about the relationship between toe in and rail line - if we could consider other factors being the same - rocker/contours, etc…

On my other thread I ask about toe in relation to bigger surf.  To some degree I think turning ability is a control factor.  To be sure, outline, rocker and bottom contour also work for control, but my goal is to be able to turn under control too.

8

TaylorO

           I like to refer to it as the working fin...but yeah inside works.

With regard to rail angle and toe angle relationship, I think they are complimentary. Tail outlines that work best to control power (i.e shallower angle) will be complimented or gain more control from a fin with less toe. But, lets say you run a less rakey fin you could get away with a little more toe. You would lose some drive but gain control at the extreme ends of the angle of attack range. So, you really need to consider all the factors as a whole and then determine small incremental tweaks until it feels perfect.

 

9

Tom,

What are you thoughts on the idea that the rail angle or curve (and rocker curve) helps to set the angle of attack of the fin. So that a board with a higher rail angle (more curve) will have a similar effect, in terms of chaning AOA, as more fin toe?

10

In extreme it can. If you are hard on rail with your foot pressure equally distributed either side of the center of effort of the fin or more pressure aft of C of E then the rail angle can have affect. But, once you have any pressure forward of the pivot point or C of E or not completely on rail then not so much.

11

Hey KCasey - Love the graphs.  I would love nothing more than for others so send in their numbers, and that data could be added to the graph But for the second graph the Sally has 4 degrees of toe. 

And for the first, what started this was my discussions with my mentor Mark S. about a possible relation between fin toe angle and relative rail angle around the fin area. 

At first I did rail angle - fin angle = I suppose to see how close it got to straight, but then when I was looking at the numbers it seemed the sum of the angles may have more bearing on performance - see my notes about the magic “Sally” board with the most outward angled rails… 

I’m still working on my own thoughts, one is: The larger/wider angle on the Sally may help explain why it works so well - the angles in greater opposition may enhance the effect of the fin on the rail.  Remember the hands model has 4 degrees of fin toe, but the rail line is far less skewed, and that board does not snap around as well as the Sally even though it is shorter an narrower (Granted it has a bottom set up like a HIC converter, and it doesn’t have the amount of tail kick at the 25% of length from tail the Sally has… so they are not like comparing red delicious apples, more like red and granny smith…Ha1)

Tom - run a less rakey fin you could get away with a little more toe. You
would lose some drive but gain control at the extreme ends of the angle
of attack range.

Thanks - I’ll try this out.

hard on rail with your foot pressure equally distributed either side of
the center of effort of the fin or more pressure aft of C of E then the
rail angle can have affect.

This totally fits into the equation re. the “Sally” as my back foot is almost always behind the front fin, and when I’m going toe side, my toes are on the rail.

Anyone have any thoughts on the entry rocker, or is it such a no brainer, and I’ve been a kook for mixing up rocker and width?

12

Low entry rocker does not plow as much when you are on trim. But, it's harder to fit into tight curved surfaces. So, if you're surfing San-O or Doheny low entry rocker will help. If you're surfing Big Rock or Pipe a little entry rocker can be helpful.

13

Well - I think I mentioned it, but I have been using lot’s of entry rocker, and as I wrote, the boards I made with less seemed to fit OK.

Do you think to little could be part of the cause of not being able to lay a board on edge in the flats after a steep straight drop  - going fast, and… no go… ( I think I mentioned my “hydroplane” bottom design… can’t say it really helped, but may have hurt when It comes to the a fore mentioned situation.)

14

I’ve corrected the mistakes. My apologies, I shouldn’t have attempted the plots without being in a position to give it the time it desired.

It’s an interesting attempt at capturing something with a single number, more data points will (obviously) reveal its value. 

Once again, my apologies for screwing up the plots, your effort deserved better.

kc

 

15

Do you think the plotted points would shift much if you replaced rail angle with rail curve, or would they be essentially the same? What about factoring in distance from rail?

The other thought that leaps into my mind is… .how much simpler would all of this become if we could adjust toe in on a single board, on a single day.

16

If you've got a steep drop you may need the entry rocker. But, then it sounds like the wave backs off real quickly. You say "a steep straight drop and...no go". Do you mean you are going fast and it won't transition onto rail? Or do you mean you are going fast and then slow way down? If it's the former, then you've got too much tail lift occuring. I'd recommend less tail width, more vee and less fin rake. If it's the latter you need more tail rocker and use it to keep the nose from plowing.

17

Do you mean you are going fast and it won’t transition onto rail? Yes, at the bottom of the wave/“in the “flats.””

If it’s the former, then you’ve got too much tail lift occuring. I’d recommend less tail width, more vee and less fin rake. Plenty V, same fins I’ve used in other boards with out this problem.

Tom…  You may have hit the nail on the head.  As I said, the “hydro plane” design caused a massive kick from the front 2/3rds to the last 2/3rds.  I have plans, for more “frankenboard” experimentation, should I decide to bother with it, which, for the sake of gaining knowledge, I probably will, do some re-shaping on the bottom, cutting of some of the bottom curve/kick/ with slight “v” panels through that area - kinda like a “loaded dome.”

KC - Thanks so much for doing that. On the second graph it almost seems obvious, there is a pretty straight line from the HG to the Sally, through the CH…  Interesting.  Could suggest something there.  Would you be willing, if you have the time to update the first graph… Well, as I think about it just a bit, it doesn’t pop out in my mind what to put on the x/y axises, but it seems there’d be a way to compare, perhaps, the spread between the difference and the sum angles in each board, and between boards… might show something… Being a highly visual person, you’d think I’d try this graph stuff myself, but my comp skills are pretty minimal since college, as my “career” only calls for about this level, and “fill in the blank” forms/reports, so, sorry to be such a kook about it.

NJ S - All the fins are pretty close to the same distance from the rail, and it was not one of the factors I was looking at.  (I had a good discussion with one of the fin guys here about the importance of distance from rail - my summary was this: to close to the the rail, taking cant into consideration, and you lose lots of effectiveness (You don’t want the fin sticking out past the rail.),  further in from the rail and the loss of effectiveness is very slow/minimal.)

As for the testing via adjustability… Call 4way fin boxes into play… Maybe some day.

All - One way I’ve thought about this overnight is my classic kook out - It only goes to show that lots of things work pretty good.  All those boards have been great at many times.  And, as best as I can tell, what I’m looking at isn’t the problem with the two “hydroplane” hulls, which wasn’t my initial question anyway.

Many thanks you guys - good to have good, knowledgeable people to work out my thoughts with .

18

deleted