Fin trailing edge from rail

What are the pros and cons of having the edge nearer the rail and when is it too near or too far?

Most reference a shortboard as 1- 1 1/4 " for front fins of thruster. My favourite board is a 6 2 Pang with trailing edge 22mm (7/8") from the rail (hard edge of bottom). My Griffin quad/five fin has similar.

I remember some discussion years ago involving Blakestah but havent been able to find it yet.


Good question Mark - I think I may have been in on that, or he sent me a pm, but my general thoughts are:

To close to rail, loss of fin action too soon

To far from rail, loss of fin rail interaction, but it disipates slower.

I was putting two sets of front boxes in so I could have a “regular” cant, and a supper, 14 degree cant.  The suggestion was setting the high cant boxes a littl bit further in (the RedX boxes were side by side and off set fore/aft)  [I’m looking for the info right now]

Found by going through my history of posts - Thankfully I started it with a clear subject…

From Blakestah:

Fins further outboard than 1.125" from the rail get real
pivot-y/draggy (in turns). The water needs to re-attach behind the fin
before it exits over the rail. If not, you lose the interactions with
the bottom of the board, and a lot of re-direction capability. Moving
inboard will weaken the fin but the interaction will stay basically the
same, and it is much less sensitive than moving it outboard.


These measures are taken from the rear base of the fin to the vertical projection of the rail.

There ya go Mark -

Thank you thats the one. Is the vertical projection of the rail at the widest part of the rails curve. I have been measuring from the hard edge on the bottom wherethe tucked rail meets the bottom. Will try and scan in drawingif unclear.


fwiw, I use the measurement of #2 in your drawing for marking out the rear dot, by laying a carpenters square against the 2 planes, lined up to the corresponding tick on the stringer

Same here Bud - Seemed like the simplest way…

Wonder if lots-o-cant makes much difference?

The twins I make for myself have pretty extreme cant. add to that a pulled in tail with lots of vee means fin tips extending beyond rail line. There is a huge potential to lose drive. IME fin template & placement is crucial, can easily make up for lost drive and then some. nothing that hasn’t been done before I know, but it’s fun to experiment and ‘discover’ this kind of stuff

getting keen on twins Bud, rode a super sweet Larry Bertleman twin in a retro comp a few days ago and loved it, fins were quite back and it surfed well, could push it fairly hard in turns, rocker was nice too...will post a pic, as keen to hear ya thoughts on it.....I have struggled on twins in the past but recently been surfing finless so have found a twinny much easier to adapt to now...previously I was too heavy and powerful in initiating turns and didnt like the freedom felling, keen to hear and see what you riding......


also been riding mini-sims twins too so my surfing has probably evolved a bit towards handling this type of board too but this one sure did go well, especially for its age, weight and in small waves too, pretty sure I am gunna make a newy the same....

sorry to get off topic here, can start own thread....

…I can add several things: one is that is not so good to have a wide tail and very separated fins

is not good isolate multi fins…

Forget about measuring from the rail.   Measure fron the center or stringer.  You'd be suprised how often backyarders and even pros cannot keep their outlines true.  If you measure off the rail you will just compound an existing problem.

Spot on McDing ................

Now taking whatyou  said on board, I measure from the rail with complete confidence and double check by measuring from the stringer.  WHY ??

One thing I've never ever relied on was a stringer as true centre on any blank ... ever !!!

After I prep a new blank I straight edge, (draw) a centre line along stringer which serves as the absolute centre for template drawing and ongoing reference point for shaping purposes ....... never ever lets you down

When drawing up template if board is say 20" wide at widest point .... I measure 10" either side of drawn centre line.

If tail is say 16" wide guess what, I'll measure 8" either side of drawn centre line

All this said always remember to use the same ruler in case of variables between ruler marks / manufacture's error

Using this method, even varying a template at different points delivers mirrowed parabolic outlines on both sides of board and when it comes to cluster placements this method.... hard to get wrong !!!

Go thru exercise of laying a straight edge along a stringer and prepare for your jaw to drop boys ......




Absolutly!   Establish center which may or may not correspond with the stringer.  Take all measurements form there.  Lay out your template based on true center.  During the shaping process check those width dims from time to time and true up as necessary.  Mark the fins based on your center referance point.  Then you can check your dim for fin to rail.  If you've accuratly worked thru the process you will be happy to find that the fin placement on both rails correspond.  No fraction of an inch differance.  You'd all be suprised at how many boards in the rack at  your local surf shop are out.  Get a Pleskunas square.  

I don’t know how many of you guys were shaping back in
the Clark days, but after…
my god were the stringers wonky! I hadn’t used a stringer
straight edge (my term) in years and suddenly I needed to
check every blank that I shaped, even from the same lot.
I just throw it on the deck now to check blanks, but if you
are using blanks from the big 2, (big 3 if you count Marko
and do EPS) they are usually true so you can do a double
check after measuring from the rail. I follow Bill B’s principle
in toe-ing in fins on the nose. Trailing edge is the number I
log in the book. Foamhead & Mcding are right on! Just My 2c…

I use a router and half template to cut outlines so I have a true center line if necessary and can get seriously right on the money. then for fins I still double check both from rail and from center. always been kinda anal about that part. problem is that I’ve never learned how to properly cut an outline with a saw, but I can knock out a good hardboard template in about 30 minutes :slight_smile:

Hey Bud ....

How goes it ma man ?????? Twin fin terrorist of the islands lying to the east of me ... (lol)

Little trick that I learnt by observation only, (not that he would share with me) from a crusty old salt as far as saw cutting template outlines goes ... 

If your right handed, make sure your right hip and right hand are next to the side of the blank / template that your cutting .... visa versa if your left handed.

Use your elbow as a pivot and saw 90 degrees to the ground, (saw straight up down ma man).... after your first blank you,ll put the router back in the box for this job ...... and big smile on ya face !!!

Biggest mistake I use to make was right hand sawing with left hip to the blank ..... always cuts on an angle hard as you might try ... such a simple fix !!!

Oh by the way, next big big big tip, "nice light grip on the saw", once again keep saw 90 degrees to ground .... try it

Take care ma man ....


Ps Many thanx on those fin settings ..... work a treat !!!!!!




how do you know the way you put straight a ruler?


no matter that new straight line, in shortboards (tighter curves) you ll obtain a not so fluid smooth line equal on both sides if the stringer is crooked.

think about it.

so, you should rely on your eyes, feel and experience on the craft to determine a fine shortboard outline

As Mc Ding say, sometimes the outlines measure a bit more in one side due to that (or may be the shaper is not good at all)

Is a compromise between the crooked stringers, a pleasant smooth outline and symmetry.

You can obtain an equal distance from that straight middle line for the side fins but they point out different to the nose.

think about it too

then may be you have a single fin

well, not so good stringers, straight line and single fin in a long board is a tasty cocktail…


hi guys,


not to trying to throw gasoline on a fire here… 

in the case you do have a finished shape that is a little off of symetrical, wouldnt it be better to take the measurment for the fin off of the rail as opposed to the stringer?  in my mind, the relationship between the rail and the fin is more important (or at least has a noticeable impact) than the distance between the fins

if i have my head up my ass please correct me


It's always better to stop for a minute, get out a square and tweak the outline.  At least in the tail area.  If you get one so out that you can't avoid it being asymetrical without completely reshaping into something differant: then Yes better to come in the same distance from the rail to salvage the shape.  What an aspiring backyard shaper reallly needs to do though is learn to keep his outline true.   Some things you can do to develop this skill are:  1.   Skin and take your blank down to thickness (or within a fraction of an inch) BEFORE you cut your outline.   Blocked and leveled so that you have a relatively flat and smooth surface to lay your template on.  2.    Leave your pencil line on the bottom of the blank as long as you can in the shaping process, using it as a point of referance.  3.  Buy yourself a Pleskunas Shapers square or a Versa Square from Greenlight.  Foam EZ also has one that is similar.  Check your outline from time to time during the process to make sure you are still right on.  If you have to crown the deck as on a slab EPS blank do it before you start to turn the rails.   Saving the outline until the last part of the process will give you fewer opportunities to screw it up.  I know this isn't the way alot of guys do it and I don't give a rip.  It's the best way for a beginner or someone with a little experience to turn out a shape that doesn't say "HACK" all over it.  I guarantee you that you can walk into any shop that has inventory boards by three or four shapers in the rack, take a few down and put a square on them and at least two or three will have bumps in the outline or be completly out on one side or the other.  With experience;  Yes!  You can whack out the template first thing like alot of guys do and turn the rail without any marks.  But if the process I described above works, doesn't take any more time and gives you a more accurate shape.  Stick with it until your skills have improved.  Think about it and visualize before you even start     One more thing;  Develop your Shaping method or process and work to perfect it.  Once you've got it; stick to it.  Don't be changing it up every blank.   Lowel

I’m gonna go ahead and say the “center” things is pure crap. We surf off the fin(s) and rails and, as the original question referred to, what about the interaction between the fin(s) and rail…The center is basically irrelevant. Ask anyone who’s found success with asymmetrical boards.

And just to keep stoking the flames of discontent – a smooth rail, symmetry, etc…Way less important to function than a whole host of other hydrodynamic interactions.One of my favorite quotes from Greg L., “Water is pretty forgiving.”And, as I’ve said before – Dale S. “Some things matter more than others.”

Good luck, and have fun.

After I finish shape, and go to lay out my fin placement, I check the symmetry in the tail. If I’m off a 1/16, and sometimes I am, I’ll fix it. I do the same to the widepoint, and if I stand it up and look at the nose it it looks off visually, I know something is whacked, and I’ll do the same… put the square on it and fix it.

To me, there’s no shame in that. The shame is in not making it right… or worse, not
even giving a crap and not checking it at all.

Taylor-------------You miss the point of what I have said altogether.  If you want an asymetrical shape;  Fine!  Shape it that way and do whatevwer you want with regard to fin placement.  If it is your intent to shape a blank that IS symetric; take your measurements off the center and mark your fins based on the trueness of your outline.  If your blank is right on from center the distance from the rail for both (or all four) fins will be right on.  If you do what you are talking about and do NOT consider the true symetry of the blank, mark the fins and glass it;  You have just shaped yourself a DOG.  As I said previously;  only taking a measurement off the rail and disregarding the center referance just compounds an error.