I have always thought that fin placement is measured from the the back of fin. The more I thought about it the less this approach makes sense because the base of a fin can vary so much. Now I’m wondering if I’ve been wrong all along. It seems like it would be a lot more consistant if the fin placement was determined from the front (leading edge) of the fin.
DanB,
You are 100% correct. Measurement from tail to LEADING edge of the fin is the ONLY way to properly evaluate fin placement, and how it affects performance. Measurement to the rear base of the fin can only be meaningful if ALL FINS HAVE THE SAME BASE LENGTH !
You are to be congratulated for your “critical observational skill”. You know of course, it’s like saying “The King has no clothes.”
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I have always thought that fin placement is measured from the the back of fin. The more I thought about it the less this approach makes sense because the base of a fin can vary so much. Now I'm wondering if I've been wrong all along. It seems like it would be a lot more consistant if the fin placement was determined from the front (leading edge) of the fin.
Maybe, but if you give a glasser a measurement, he will assume you mean to the rear of the fin, even if you tell him three times that it is the measurement to the leading edge. Even if he writes it down, he will still screw it up. There is no other way.
Now, if you are doing fin/surfboard DESIGN, I encourage you to think about front edge placements. But, when you send that board to the glasser, tell him the measurements from the fin rear. Please.
hth
Wow!
Finally two people that I can relate to, I have always been amazed when people talk about the placement of fins measured to the trailing edge. Yet most people talk about them in this way, which has often left me wondering why?
-Robin
Was measuring to the trailing edge part of Bill Barnfield’s standardization of surfboard measurements? If so, hopefully he’ll post why he chose to promote measuring rear to tail instead of front edge to tail. I suspect he’ll have a reason.
I think alot of shapers think in terms of how far the rear edge is from the tucked rail edge. They use that starting point then factor in toe from there(based on a 4 and 1/2 base length that is). Just a standard I guess. I’m sure Barnfield has a more scientific answer. An easy way to stump alot of shapers is to ask them where they’ve come up with their respective fin placements. They usually go silent for a second as they don’t want to tell you that’s how so and so does it down the street. Another way is to open a conversation on how fin placement effects whether the nose rides high or low lol.
up from the tail is likely to be comon when the fins are
standardized.
like the distance of the toilet flange.
the front or the back seems a short sight when
we take the time to consider,C.O.L.R.
I learned this set of know ship letters from a contributor to sways.
CENTER OF LATERAL RESISTANCE ! ! !
front ? back ? hmmmmmm
C.O.L.R. is way more brainiac…
… ambrose …
your queen is in check
and where’s a dorsal
measured in biology
and its relationship to the tail fin
is there a formula
for the keel - beam - rudder relationship
in marine design?
Aloha MaraboutSlim, Jim, Bill and others.
The use of the rear of the fin as the zero point for fin measurements happened long before I was able to influence anything in surfboards.
While I understand why other locations seem to make more “design” sense I personally don’t think of the singular rear point of the fin location, as anything more than just a reference point.
Just like we use the center tangent point in the bottom rocker to reference rockers from. There are other ways to measure and duplicate rockers but none simpler or easier to reference from and communicate with others as a standard.
The Rear of the fin as the reference point is fine with me.
Here is why.
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The gap from rear to rear is easily the most simple to view and grasp.
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It is the existing standard
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For multi fins the distance the fin is from the outline matters and since the toe in angle pivots from the rear of the fin it is convenient to use the rear of the fin for both toe in, outline distance… and since we are there already, the distance up from the tail at this point just comes along with it.
I agree that the back of the fin’s connection to the overall design of the fin or performance of the board is not specifically relevant to anything. On the other hand, I don’t think any other point on the fin, like the “leading edge from tail” or the “tip of the fin from the tail” has anymore relevance. Here is why…
In sailing yacht design there is a thing called “Center of Lateral Resistance”. A simple but not perfectly accurate way to visualize and feel this is to take the profile of a large sailboat viewed from the side and shrunken down to a much smaller scale, say 12". Cut out a firm plastic template of everything from the water line down.
Sink this under water. Put your finger somewhere near the center and push it forward under water moving your finger around till you can get the template to balance perfectly on the end of your finger while moving forward.
This point where your finger is, is the “Center of Lateral Resistance”. In yacht design you have to design the mast and sails and locate their “Center of Effort” to work in harmony with the hulls “Center of Lateral Resistance”.
Too keep it simple for a start lets look at a single fin. It also has a center of lateral resistance and it can be determined via the same process described above. It is this center of lateral resistance that one is feeling when one changes to different fins on the same board.
Add a bit more tip to the template and the CLR changes toward the back of the fin. Narrow the tip and the CLR changes down toward the base. Etc, etc.
When the fin is placed on a board and the board is tilted up on its edge in a turn a certain amount of the bottom of the board is being pushed sideways through the water. This part of the board also has a CLR. More rocker in the tail moves the CLR forward. Concave tails move it back. Narrower tails move it forward, etc, etc.
Combining the fin and the boards wetted surface in a turn, creates a composite CLR that is able to resist the sideways drift of the board and if done well, redirect those forces such that they aren’t wasted sliding sideways, but rather generate forward energy and thrust.
The point on the fin template that one uses to measure the placement of the fins is pretty much meaningless for design reference. If all fin templates had a dot where the CLR was, that would make a good point of reference that would connect to something “design” related. But as long as you know your fins and how they work it is no problem to use the front, rear or tip as a point of reference for where to locate them on the board. Say a fin has a 6" base and you put the fin 6" up. Fine… use the front of the fin and put it up 12". It is just a point in space that doesn’t signal any particular design or performance issues.
Now lets talk briefly about Multi Fins. Some points to consider.
Each fin has a CLR.
The whole group of fins has a CLR. Move the group closer together and the CLR will get taller and more oval. Move them farther apart and the CLR will get more elongated and wider. Move the whole group forward and the CLR moves forward. Move them back and the CLR moves back. Tilt the fins over more and the CLR moves down toward the base more. Straighten them up or hook them in at the tip and the CLR moves up the fin. Change foils and even more variables jump into the mix! Go slow, go fast and it all changes again.
Continuing with the Sailboat analogy, the surfer is kind of like the Mast and Sails. He can move his CE (center of effort) forward or back, sideways and angle the board more or less. All will work good or bad in conjunction with the boards CLR. If the surfer is like the Ho brothers who surf off the tail they will need something a little different than someone like Shaun Tomson who surfed much more off the center of the board. Good shapers know this stuff and have the ability to shape it as planned.
Neither is good or bad, all is good as long as everything is in balance and harmony. As long as your measurement system is easy to use, allows you to quantify the necessary details and universally communicable, the measurement system will be fine.
What one does with all those measurements is the real issue that matters. Most don’t collect the measurements because they don’t know what to do with them nor are they skillful enough to replicate them or make the small specific changes needed while keeping other parameters the same. Shaping machines have done wonders in advancing this as it has removed much of the necessity in having the actual hand skills to do the job. The downside is that it has opened up the same benefits to those making boards in foreign countries where it is much more advantageous to locate the other aspects of surfboard construction. And while everyone’s job got easier here, it handed over the ability to shape good boards to those who will now take the jobs of those who’s jobs got easier.
In the end, unless you know your fin templates well from actual experience, no point of reference is really any better then another.
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In the end, unless you know your fin templates well from actual experience, no point of reference is really any better then another.
I like the short answer best ! [Although the preceeding information is interesting , of course]
chippy
Hey Dan,
Lots of good advice here, but I dont think you’ve been thinking/doing anything wrong. Like BB said, its just a reference point.
But to answer your question, taking fin base length as a variable, when I micro-analyze a fin setup, I measure the distance from the front fin leading edges to the rear of the center. An additional spread measurement which is dependent on placement AND fin base length. Unfortunately, its only informative…havent been able to do anything of value with it. Basically, I just try fins until Im satisfied. Stiff TC redlines fronts with a more flexible center works excellent for me.
Cheers
Aloha Meecrafty
Howz things in Florida?
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I measure the distance from the front fin leading edges to the rear of the center.
I realize you are just measuring for a quick snap shot but wouldn’t it be more telling to measure from the base of the front edge of the front fins to the raked tip of the rear fin, rather than only the base of the rear fin?
I know you said that you were acknowledging fin base length as a variable, but Rake is a huge variable also and will often have a more noticeable effect. Especially on single fins where the tip can be miles away from the base. This is now less so with multi fins, but still is an important factor.
If one were to be looking for the “spread” of the fin area, or the looking for the Center of Lateral Resistance one should take into account the Rake of the rear fins, not just where their bases ended.
Just a thought…
Bill, Et Al,
The theory of CLR is correct, but as a practical matter, without the luxury of advanced mathmatics, or some means of finding the CLR empericaly, the measurement to the base leading edge was/is the most significant measurement to evaluate the effect of changes in fin position. This technique is what I have used since 1960 in
designing surfboards, and selecting fin position, regardless of fin base length. Generally, forward- looser/easier, rearward- stiffer/ harder, as it relates to turning response of the board. There is always a point of diminishing return as you move the fin too far forward and you begin to lose “hold”, or lateral resistance, and you trigger a spinout. I remain convinced that the measurement to the leading edge of the fin is the best datum point to refer to in the design process, as well as the fine tuning process. By way of example, I once examined a contest board of David Nuuhivas’ and observed that he had scribed reference marks in the side of the box to mark fin positions for various size surf. The reference marks were for the positioning of the leading edge of the fin.
Aloha Bill
I understand your familiarity with using the front of the base of the fin as the reference point. But I don’t understand how 1/4" at the front of the fin is any different then 1/4" at the rear of the fin.
I bow to your legendary status and abilities but are you sure your not confusing being “very familiar” with being “more accurate”?
I have always used the rear of the base so I am comfortable guessing with a fair degree of accuracy where the fin should go relative to the overall fin template. If I were to switch to using the front, it would take me a bit to get used to that but I don’t think I would be anymore accurate or that using the front of the base would improve my guesses over using the rear of the base. I don’t see the magic in the front over the back. I haven’t ever found the material at the front of the fin to be more significant then the material at the back of the fin. More or less material matters for sure. And which end of the fin loses or gains material is important. I guess what I am saying is that I don’t view the leading edge as a more significant ‘tell’ of where the fin should sit. I realize that you or others might and I have no problem with that but since I know the fin I am going to use, I not only know where the leading edge is, but also the trailing edge.
To be honest, neither of us probably guess that often as we have both done enough different boards with different fins to be pretty secure in where we place fins regardless of which end we use to mark the placement dot. If I don’t have a historic reference point, I just size up the whole fin and the board to establish the fin position. The mark, front or rear, is just to remind me where that was once the board is in the glass shop.
I should note here another method used from time to time on single fins. That is laying the fin down on the bottom with the base lined up on the stringer. Then sliding it forward or back to view how much of the tip is hanging over the rail into space. Around 1/3 of the fin depth is a safe average. Adjust accordingly.
mmmmmmm good read.
looking at fin,good.
formulas good.
refrence points,helpful.
in the end
ride good?
not so good.
mark box,good.
glass on?stuck forever.
fin box move a liddle.
micro adjust ? all consuming pastime.
glass on? grind front of fin or back to tune performance.
how much is good
how much is too much?
no substitute for experience.
look at an old Gaglia.
maui way back fin era
whadda trip in time
like a 12 ’ long steel wheel ball bearing coaster
on teddy avenue down hill
whadda turning radius
big honolua with the maui way back
like an 18 wheeler on the grapevine downhill
smoothe,sssmmmmmmooooooootttttthhhhhheeeeeeeeeeeeee YAAAAAAAAA
formulaic design extrapoliates
destined for other than use-fun parameters
are great for labcoat coffee battles.
may the clean labcoats survive the week.
or for fun may the lab coats
be drenched with chocolate and whipped cream
…ambrose…
wowie side push
cool ,never heard it so well put
kudos all
Bill B,
My reasoning behind the choice of the leading edge of fin for evaluation purposes, was that at that time I was experimenting with fin depth, base length, and position. Base length could be as little as five inches, and as much as ten inches, depending on the style of board. I understood even then that the board did not pivot around the leading edge, but somewhere close to it, depending on the AOA, or rake, of the leading edge. Because of the wide variation in base lengths I was working with at that time, I believed the leading edge measurement to be more descriptive of the changes I was making. I agree that with fin base lengths falling into a much narrower range than in the past, there is less of a variation between fins. I think we both suffer a little from “the Devil I know is better than the Devil I don’t know” syndrom. If the leading edge is chosen as the index of position, then I believe the changes made in the other variable aspects of a given fin are more easily understood or evaluated. I too use the fin position in relation to the rail method to this day. It is still my primary method of determining where to place the fin on a given planshape. For years it was one of my “dirty little secrets” in the design process. It was not something I shared with anyone, back in the day. In fact I just shared that point with Keith Melville at his get together on Sunday during the discussion of a particular board, and its performance.
I actually plot the 20% chord length position on each fin I make, and use that line for design purposes as the center of lateral resistance. The chord length itself is a weighting factor if you want to simplify it to a point, the places on the fin with longer chord lengths matter more wrt lateral resistance, and the rake of the chord length line tells you something about how “pivot-y” or “slow turning” the fin will be.
But the distance to the rail on a rail fin is most relevant to the rear base of the fin. The fin is re-directing water against the hull, and proper fin action requires enough hull to interact with. If you move it too far out you lose it, and if you move it too far in you miss the place where water moves fastest when you turn.
But above all don’t confuse the glasser!
When we started making our first templates, my partner and I wanted to reference our fin root position relative to the center of effort of the fin. Then we found out about industry standard and had the shift our root position relative the the trailing edge at the base. As was mentioned above accurately measuring either the center of lateral resistance or the center of effort is really beyond the scope of most installers. It’s really better to keep it simple and then be able to adjust from there. So, all the fin systems we currently make fins for allow for adjustability to fine tune the best position for each rider and wave condition.
So, the most accurate answer to the topic of this thread is:
Because it’s the industry standard.
Aloha Bill T
Wasn’t this a great thread! No politics, No Epoxy, No Eps, Just plain old surfboard building info. How refreshing!
I understand better now your use of the leading edge to mark the fin position. It stems from your designing of the fins, I think we were kind of confusing “designing” fins and “placing” fins.
I know you realize this Bill but for the sake of others less experienced we should probably mention a common problem using the back of the fin as the index point. That is the little arc at the base, on the back trailing edge of Box fins, that usually isn’t there for glass on templates. This can skew the fin postion for a builder who isn’t aware of this. The glass layup and fillet on a glass on fin creates this arc so it usually isn’t included in the fin template. Where on box fins it is.
Good thread everyone, thanks for the dialogue. I gotta get back to work.
Hey Bill,
yeah total length from front leads to rear rake tip seems like a good way to go.
Looks like Tom nailed the original question.
But, using the leading point would work good for cutaways.
PS Bill,
Ive been in Lake Tahoe for a week and found a local Bike shop that has a large Giant OCR1 at a closeout price…couldnt resist cuz one of my goals this year is to keep my back in better shape with more cycling.
Cant beleive how much Im getting for the dough. Stoked.
Aloha Meecrafty
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yeah total length from front leads to rear rake tip seems like a good way to go.Looks like Tom nailed the original question.
Yup, Tom “has to” get it right cause he is actually trying to live off of his decisions. That makes a big difference. It is always interesting to me how varied the different standards in surfboard making are. (if we can all things “varied”, “standards”)
It is particularily refreshing to discuss this stuff with guys like Thriakill because you can get to the meat of the reasons way and find common ground in the science. Where often the reasons surfboard makers do things a certain way are more based on simply “what they do” and they often haven’t thought about it much or been challenged to explain it.
These kinds of forums are great for this, because the very act of writing causes one to have to compose their thoughts better, to turn them into words. That process demands a good understanding of why one does what one does, especially if one is going to defend or explain it through an extended thread. It is easy to shoot from the hip in conversation, much harder to do that in print…though we do see it from time to time.
Today, the front of the fin is a pretty secure location compared to the rear in things like cutaways etc. Of course, cutaway leading eges might be just around the corner…! And then what!
Bobby Owens was always one to experiment with fins, often ones that had no conventional “rear of base” or “front of base”. When he was one of my team riders we played with a lot of options. In the end though, all fins if they attach to the board, eventually have a rear of base, somewhere.
Having a good understanding of fin shapes and how they interact with boards, riders and waves is essential regardless of which part of the fin is used to mark the index point on the board. Understanding the CLR is really what that is all about and regardless of how one arrives at understanding the impact of this force, be it science, intuitive, pre-marked on fins etc. The CLR is the thing one primarily feels when one “feels” their fin.
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PS Bill,Ive been in Lake Tahoe for a week and found a local Bike shop that has a large Giant OCR1 at a closeout price…couldnt resist cuz one of my goals this year is to keep my back in better shape with more cycling.
Cant beleive how much Im getting for the dough. Stoked.
Bike shop quality bikes are amazing in their quality, price performance ratio. Of course, this is all thanks to Asian manufacturing. Soon we will see a similar impact on quality and pricing of surfboards for the same reasons.