# Rails & water line

Does the apex of the rail radius affect the water line of the board? In other words, if you have a 50/50 rail, does the board sit lower in the water when planing than a board with a down rail?

Yes.

no

OK, thanks.

So this means less rail engagment with the wave, correct? Less rail "bite"? Because the board is sitting higher in the wave.

C

When the board is in movement the hard edge will help to release the water instead of wrapping it . Not so much an issue of waterline during a “float”, but of whether the board is turning on “top” of the water instead of in the water. Planing hulls vs. concaves. Lift or suck. Nose rides, suck. Trim, lift. Rail engagement is relatively the same it is in the function of the rail shape to let the water flow out the back or to “momentarily grab” on to it.

Thanks, TaylorO. Obviously buoyancy and speed have a lot to do with how a board sits in the water, and a rail will have many "water lines" at different times and places in the wave. But you don't think the appex of rail radius has much to do with this? C

The water line is totaly dependent on what you eat and how much you eat !! Right now my water line is saying I am eating to much !!

No because planing is controlled by hull area.

Hypothetical:

Take 2 boards that are the same with totally flat bottoms--except: one has 50/50 rails fore to aft. The other has down rails.

There will be no difference in where they float (same rider, same wave)?

just make 2 and tell us…

To me, floating is neither here nor there. It’s how the board turns, transitions, and trims. And how you want to execute your turns. If the volume is the same in both boards, they’ll have the same overall displacement. Maybe I’m misreading the question.

Totally. It's just one aspect among many.

I began wondering about this watching Terry Fitzgerald and Larry Bertelmann surf videos from back in the day. They look like they're on top of the water, not in it like today's pros. Sometimes it looks like the boards are totally squirrelly. I looked at 1970s boards and saw that they have a lot of volume under the front foot (buoyancy) and down rails and narrow pin tails (reduced buoyancy). These are single fins with "natural" rockers. When the surfer steps on the narrow tail and engages that fin, the board moves radically. But on the wave, not in it.

So I began to wonder if today's boards aren't built to engage the rail. Rail fins, reduced buoyancy, more radical rockers, etc. Good for pumping and vertical surfing but totally different from a 1970s single fin shortboard--less of an evolution and more of a revolution.

( I went back and re-read the original Q…  Sorry, yes when planing.)

As has been pointed out - there is so much going on when riding a wave, the water “line” will move around depending on how you are riding the wave, but…  Say your are going down the line in the pocket, your 50/50 rail will “suck” into the face more (Better for front foot orientation in my experience.), so if you had the exact same board with down/hard/tucked edges it would be wanting to release the water - the harder the edges the more release - so it would not be sucking into the face.  But, I think the notice in the ride is far more significant than the difference you could measure in the water “lines.”

That being said - I love the way those old boards rode the barrel, but to me it looked like they had to work hard to get those things to turn sharp.  It’s been a while since I rode one, but when I tried it after riding a “modern” tri fin, I found the lack of ease in cutting sharp turns to be a bit of a drag, and over powering a single fin to spin out happened.

From what I’ve seen and experienced, it seems modern rails work quite well in the barrel too.  As I’ve blabbed on about in the past, I love my 50/50 rails in the middle, and my 90 degree edges starting about four inches in front of the front fins.  I taper from 50/50 down to 70/30 by the point I add the edges.

TaylorO, My personal boards aren’t all that different. I remember those downrailers feeling “dishy” at times and the turns were way more drawn out rather than a “snap”. You are right about them being front foot centric. Their whole planshape was forward. Today I always have a pronounced belly (on my boards too) at the nose, somewhat of a hull with the rails hard in the last third and they corkscrew up to the nose end of the rail. This works for me so I stick with it. I don’t know if the original question was answered or not.

tblank - What do you mean by cork screw?

I’ll add that I like my rails like they are, and, as opposed to the “70’s” boards with the wide point forward, and a wide nose, I like the wide point back of center 2"-4" and a narrow nose - with vee/belly in the first 18".   It’s working for me… my boards are getting more similar, the latest to the one before, so I feel like I’m getting closer to what I want.

Hi TaylorO, Corkscrew means at the tail the rails are turned down to a hard edge. The nose has a belly (hull entry) so the rails at that end are turned up to meet the deck from the bottom to attain the curve from the belly. Longitudinally, the rails blend from down to up along the length of my boards in a “corkscrew” fashion. My shortest is 7’ 8". I’ve kind of taken a Skip Frye rail and made it to work for me. I like to turn from the center of the rail instead of a pivot. To me, this gives the best of both worlds. Fast trim and faster turns.

Ok - Now I “see” it.  Kinda “cork screws” (I had to think of an airplane doing a “cork screw” roll -as a real cork screw goes round and round to much for me… Ha! Kinda like the “spiral vee” - I still have no idea what that is…) from hard edge at the bottom in the rear to sorta hardish at the nose at the bottom vee/belly comes up.  I’m down with that one… I even went so far as to add a hard lip on the nose from about 6" to 18" to deflect water flow while paddling, and occasionally dropping in.

TaylorO,. How did that bead on the nose work out? Is that the right interpretation? like guys will do after a board is glassed to add a bead of resin at the tail to make a real hard and sharp edge. Never thought about that.

Thanks for asking tblank -  I don’t do resin beads,  I mix up resin (epoxy for me) and then mix in glass bead (Oh, Chris P. if you read this, I steered you a little wrong… Sorry.) and cab-o-sil.  I get it from Tapplastics - it’s “Cab-O-Sil is a superfine fumed silica.”  and “Makes resin thixotropic, without increasing viscosity. Controls sag and allows work on overhead surfaces. Can create non-sag putty. Increases the hardness of resin.” I use about a 50/50 mix for the edges, still sands easy enough, but is much stronger/“harder” than glass beads alone.  I use it to add 90 degree edges in the tail over a 70/30 base (I wrap 3 full layers of 6 oz on both sides… Nice and strong rails… Ha!)

But, the nose thing was a new idea, as I was paddling my 9’3" “heavy gun” and noticed the chop splash wrapping up over the board and into my face… Ha!

It’s working pretty well.  I’ve only ridden the new 11’er a couple times, but I could see the chop slop splashing off to the side quite a bit.  Makes me ponder a full on flip lip…

Roger that on the Cab-o-sil. Used it many times. By “bead” I meant making a hard edge after all sanding has taken place. It is common to plenty of folks. Guys will take a brand new board and immediately tape the tail edge and pour a sharp rail in the tail before even trying it out first.

Three layers of six oz. on your rails? That ought to hold up for quite a while. A 9’3" and an 11 footer? Are you riding giants?