Water flow on rails.

General Discussion
1

I know… I must have killed the ‘Lack of attn to water flowing off the tail’ thread with that last comment, sorry Greg.

But does that mean people are thinking about it? I did.

Threads talk of better manufacturing etc allowing high performance boards to be thinner.

Now bring attention back to the water on the rail.

Will boards end up thin with curved-up rails? Decks are getting scooped now.

With the right shape you don’t need the volume, and in high performance boards there is little if any function for water wrapping onto the deck.

With these thinner boards, which parts of the rail will still need some sort of rail shape to function?

2

well one thing i have thought about recently is using more of a boxy rail to have two points of release…OR…a rail that sheds water away from the upper half of the rail…like a sharp rail apex…no water wrap at all…food for thought

3

Dale S. had a 90 degree angled “strake” on the deck of his tri-plane hulls for just that purpose - to keep water from wrapping on to the deck. There is probably a pic in the archives. It is do-able.

4

Based on what I have actually seen in the water and in photographs, if your board is speeding, there is no water wrapping the rails or the tail. The only time I’ve ever seen wrapping is when the board has slowed substantially or you are at the end of a tight radius turn where you can slash the rail into the wave face.

As far as trying to harness this water (or control it) you’d probably be better served by taking off your leash, cleaning the boogers off the bottom, patching your dings, or sanding your fins’ leading edges smooth.

5

That’s a good point about the slash.

Is it the outline shape used to bury that rail, or, even partly, the rail shape?

Boards generally have softer, rounder rails from around the wide point forward, getting a combination of lower, boxier, harder, edgier, toward the tail. Maybe the outline and that soft rail provide a front foot cushion and an easy entry and recovery point.

I think Meecrafty is on the same wavelength.

At what point is the the deck-rail dispensable before it affects performance? Perhaps the thickness of the boards will dictate that.

6

Lee,

you have stated the reality of the “at speed water flow” perfectly. Of course that shatters one of the fondest possessions of many peoples imagination.

7

Water flow at speed definitely allows little water on the deck.

But unless you ride completely off the tail with all water entry behind the widepoint, which is unlikely, then the nose rocker, nose rail shape, even the nose outline are all irrelevant.

In normal surfing it is very relevant.

At speed, most of what is behind the widepoint is release.

At what point on the forward entry rails does the rail shape do nothing? Is it the deck line? The rail wide point?

8

more specific question for more detail …but heres a comment anyway

you can use your rail to release or suck as much water as you want , on this board ive kept the front edge hard , so it releases until the point where ive softend it around the middle and then it starts to wrap onto the deck , if i ran a softer rail further forward it would wrap onto the deck earlier ,in a soft full wave you dont want that , coz it will pull the nose down …

but in fast juice , you have to get the water wraping early because your speed will leave the wrapping water behind and it cant get onto the deck before youve outrun it …next pic shows

so now this same rail set up wont allow water onto the deck at faster speeds , even tho it starts to wrap, the board moves faster than the water can get on the deck …

but a softer rail up front would allow the water to start wrapping early so even at speed it would get over the tail …

your rail set up is essential for creating the theme of the board …

it can be the difference between the board that free falls into the take off and hugs the face straight into a backdoor pit , or free falls into a take off ,slips out and drifts into the path of a thick pitching lip …

or it can be the difference between that fast sensitive small wave board , or the board that bogs at every subtle change in weight and lacks all get up and go , leaving you checking your legrope for that chunk of weed , you swear is slowing you down …

go get your garden hose and squirt it on your board from different angles …

youll freak at how much difference in flow between sections of rail that are only 18" appart …

regards

BERT


9

Wildy, this is good. As long as we are talking.

But, I know I’ve seen plenty of pic’s of speedy short boards with water coming over the last third of the deck, at various angles. This gives me a good excuse to go back to some saved SJ pic’s and study the details.

10

Bert,

I think the photos illustrate my point exactly. In the first photo the surfer has just come up to the top of the wave, slowing down from his bottom turn. He steps to the nose with the board going somewhat less than full speed in a flat part of the wave. The wrap happens and holds the tail. In the next photo, the board has increased speed and is in a steeper part of the wave to the point where it is efficiently planing; no wrap, the tail rises and the nose dips. The surfer must now do something to slow the board down to find a flatter part of the waveto continue nose riding.

The photos also illustrate some counter intuitive thinking on how a board planes. The only time a board planes in a nose to tail sense, is when you are going straight. Once you put the board on a rail, either to turn or to trim, the planing is from inside rail to outside rail. The root spray (the stuff that mathematically keeps the board up) is coming off the outside rail (note that the spray is squirting off the rail at almost 90 degrees; there is very little if any movement of water from the nose to the tail). The wake is occuring on the inside rail. If you are going slow the wake is displaced less and can break over the board. The “speed” is not really board speed as much as it is the speed at which the water is flowing up the face of the wave (steep waves=fast, mush=slow). That is why nose riding is done on either flatter waves or on the flatter part of the wave.

The whole art of extended nose riding is to keep the board in the portion of the wave that allows poor planing.

The design or shape of the bottom half of the rail will have a significant impact on the efficiency of planing and therefore the hold on the face and the “feel” the rider gets when turning or trimming.

11

My apology at the start of the thread is sincere, Greg. I really hope I haven’t offended you, or anyone, and I stand by my last comment.

Which is what got me thinking of total rail release, which is what I’m trying to work out in my head at the moment.

At what point will the volume of the board dictate the rail design, and what will it look like, particularly centre and forward of centre?

I guess that’s my basic question. Although the mal discussion is interesting, I’m more interested in performance shortboards, perhaps 7’ down.

If I’m going to make a board, it’s going to be out of the box a bit, so I want to bounce ideas here before attempting anything. Too many brains here to ignore.

12

Gotta tune ride of board to the waves you plan to surf.

If you ride speed and juicy waves, you want softer rails, possibly thinner, with the hard edge well back around the back foot.

If you ride slower, mushier waves, are big and ride small boards, you might want harder edges well forwards, boxy but not necessarily thick rails for less water wrap and quicker response.

Wider and narrower, more and less rocker you know, so it just has to be tuned in combination for the target waves.

13

At what point will the volume of the board dictate the rail design, and what will it look like…

Wildy you’ve basically described my biggest dilema when it comes to design…creating volume for better paddling while maintaining a thinner rail x-section…so my compromise is basically fuller decks with a sharp downward drop to the rail top…my near rail rail band can be as high as 45 degrees sometimes but i find the extra foam near the rail to be a negative (loss of sensitivity). Use a more gradual approach between rail and deck and its harder to maintain volume…royal PITA! Now if you want to try a concave deck even more drama…i know bert doesnt believe in thick boards but everytime i go under 2.38 thick the age factor kicks in (its actually harder to paddle here than in many other places in the world)…i guess i’ll have to try a real wide shortie sometime soon…maybe 20.5 and 2.0 thick and see what happens…mucho dilema

(off topic, the other design challenge is your typical convex deck…without convex decks certain things can become soooo much easier…but you either end up with a super thin board or a real fat rail)

14

The last board I rode was a 6’0" x 20 1/2" X 2 1/4" modern thruster fish. I was aprehensive as I was accustomed to narrower, thicker boards. I won it, so I had to surf it to find out more.

It had low boxy rails, fully chined, full single concave to slight v in the last 12", with what looked like a lot of tail lift for such a short board. I’m 45 and weigh about 60kg/130 lbs. And it was poopee by the way, and not feather light.

The thing just flew, caught waves easy, and went in tiny junk to good quality shoulder high waves. I didn’t get a chance to try it in anything bigger.

It made me rethink board volume and rail shape, especially with epoxy composite construction in mind. But by going wider and thinner I started to wonder about deck edges to keep the bottom rail shape full enough to function the way I like.

As a wider thinner board would work okay, albeit a little harder to float on, maybe the advantages would be worth it. I’m sure it would restrict the old turn, dig, no paddle take-offs. But I also know a corky board won’t surf as well.

Do the thinner, concave deck boards have a history of breaking due to the lack of domed beam deck structure, or is that structure much less relevant on sandwich? Does that domed shape control the effects full board flex?

I’m going to have to find the balance I guess, and live with it.

15

dont forget how much extra volume gets added by increasing width …

a bit of trick photo editing …

board on left 6’-7" x 21 , board on right 6’-7" x 19 , the blue line shows just how much extra area is added , but also how much extra volume …

leev made the point which the first photos backed up and leev added further to the points about speed and planeing and release at speed …but what about release at planeing speed , or sinking from a lack of planeing speed …

if your board is narrow and thick , it will want to sink as it cant plane as well , but the thicker rails generally being fuller and rounder , will allow water to flow onto the deck easier …

a wider board will plane at lower speeds , wont want to sink so wont allow water onto the deck as much from that aspect , but also will generally have a lower rail because you have more distance to get a clean transition from mid deck to rail …

as well as being a little thinner in general , so those last 2 aspects help cut the water off cleaner and releasing better before it gets a chance to wrap the rail …

the reason for going thinner is because youve added so much extra foam by going wider , you dont want a boat …

the rails have to be thinner , because of the fullcrum affect , your rail is now further away from your centre of gravity or pivot point at your feet , so naturally because of the leverage principal , it will be harder to get onto the rail , because your trying to sink a rail that is further away …

so reducing rail volume proportionatly more , allows the rider to sink the rail with ease again as a trade off …

so now you have sensitivity back , but also a board that planes at low speeds , because it planes with ease , there is no reason it will sink and water run up onto the deck …

result , wont bog and slow in turns …

the whole sandwich concept allows thinner boards that dont flop …

urethane has a limit to how thin you can go before you get a flopper , so it restricts you to certain shapes , how do you get from a thick centre to a realistic functional rail ???

yes you still need a bottom rail , but once you get above the apex of your rail , you dont need the rest …

you know wildy , ive been having similar thoughts lately …

i want to make a board 18mm thick , but was wondering , if i should purposely add volume to the rails to make a realistic rail shape , but then thought that everything above the apex isnt needed , as a rule my apex goes from close to the deck at the nose to the bottom edge at the tail…

i can see a refined standup version of a greenough spoon working well …

i want to go 3/4" thick just to prove something to my self …

that would mean that i at 220 lb /100kg would be riding a board 1/4 of the volume of most other guys …

if it still works in small waves , it will prove volume is worthless …

my only other problem would be dealing with flex , but thats where i had other materials in mind , stuff ive used before , that just didnt work , mainly because i was trying to make “normal” looking boards from it …

like meecraft said , a rail with a second apex, he said more boxy but thin , but you could go even further ,a real defined deck apex …

ok im out for another one …

regards

BERT

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16

Volume might be next to useless once you are planing and up riding, but that part of surfing is only about 10% of my time in the water.

90% of the time, I’m paddling around looking for waves to get to myself, and volume is extremely important!

Also, you are looking at the problem from only your perspective of big guy, slow small waves.

My side is …150 lbs, big fast waves most of the time, I need narrower boards for less planing surface and more control, but need lots of float for long distance paddling, sprint speeds, and vision over the horizon.

Best overall solution so far is around a 7’6" x 19" tri fin around 2.65 thick!

17

some excellent points being made here…interesting fresh thoughts i havent considered in detail…noggin working overtime

18

A way to address both issues at once is the strake, chine, tri-plane/edge board design. you can have a flat deck, thicker and wider at the “top” for low speed paddle ease, and once planning happens, you are “up” on the much narrower bottom. Floats and paddles like a volumus board, but gets on edge like a narrower board. Best of both worlds??? One point to throw in the mix: more volume = hard to “duck dive.”

19
Quote:
i want to go 3/4" thick just to prove something to my self ...

Bert,

Take a look at the modern skimboard. 3/4" thick and relies heavily on width for planing. Rails are hard down turned with a sharp edge. This is primarily for planing on the sand, but the rails seem to work fine on the wave also.

Some other things to notice: How can a skimboard do bottom turns and cut backs without fins? My theory is that the rail is so thin it penetrates deeper into the water and acts as a fin. So applying these rails to a surfboard might allow for smaller side fins, which would reduce drag without comprimising drive.

There are lots of other things that can be learned from skimboards.

20

I wouldn’t say volume is worthless. Thickness is really just for float while you rest or to keep you out of the cold water when you’re trudging to stay in the lineup, but basically it is a concept that relates to paddling and sitting NOT riding or planing through a turn.

We really are just balancing planing and displacement. When I was just a pup out sailing with my pop, we would have discussions on speed. I asked him what would be the easiest way to make his displacement hull faster? If we jump overboard (change the waterline), he replied, the boat would float higher and have less surface area wetted (drag). He had a swing keel and he had me take the tiller and went down and cranked it up while we headed downwind. Same weight (waterline was the same) but less frontal area, and less SURFACE AREA wetted as it cranked into the hull equalled more speed.

Now an important consideration that I haven’t heard much discussion about is this: What is the dynamic of the board and wave when you start to plane? The tail lifts onto the surface of the wave and is elevated so you are moving at the same speed as the energy moving thru the water. Watch what happens when people don’t catch waves. The tail stays down in the water and the lack of forward push in the internal wave hump can’t overcome all the surface area that is wetted and the frontal area angle of attack so the tail never lifts and stays buried and the frontal and wetted surface area is never overcome by the surface angle of the wave. The wave swallows the board starting at the tail. Did we use to call this mushing out? Of course in a bigger wave this is desirable, but again it is a balance of displacement and planing. Remember watching beginners on a bigger day on longer boards with wider tails and the tail lifts up over their heads and pearl, bail off or over the falls upside down and backwards 360? If you figure it out at this point, that little pintail back at the surfshop starts looking better and better. (Or stomp on the tail or stand up toward the tail earlier) When the wave breaks this bouyancy issue becomes more of a factor. Fill a tennis ball with water and throw it into the breakers, you’ll never get it back, but a bouyant ball will ride in pushed by the energy hump. The water molecules are just lifting and lowering in a ferris wheel type of motion and are not traveling towards shore. So float is good for heading into shore after you’ve had a good session.

My son surfed a VERY small board successfully by SINKING it just before the takeoff paddle and using what little bouyancy/flotation he had and was effectively using ALL the planing surface of that board to “jump” up onto the surface of the water. Instead of leaving the nose up and dry and trying to drag the board from the entry to the tail up onto the tail planing surface. Certainly blew my mind, when he would challenge the older battleship pintail dudes out at Trestles, by taking off further in and deeper in the pit. He would also maintain his position by just sitting on the board if the wave was breaking on him or more toward the shore and keep his tail down, while his friends would try to paddle through and out and get pushed back towards shore.

Take a gease pencil and mark the surface level of the water in a tub. Then sit on in it. That is how much water you DISPLACE locally and will give you a good visual aid of what you are PUSHING through with every paddle stroke. It’s good to be young and innocent and light and skinny and summer vacation and…

You can learn a lot by observing rocker shape and widths and rider weight on a small day where a wave starts to form and then backs off. A light rider allows the board tail to lift and plane sooner. Where a heavy guy on a banana rocker board or too narrow won’t catch the wave until it is almost shorebreak with the tail imbeded in the wave.

The board/rider force will be pushing down due to gravity so water will displace exactly where it is pushed and as it cannot compress it will be frontwards, backwards and to the side. So now we are at what Bert said and what we do with the displaced water is how we control the board. We can either release it away with a hard edge to gain speed or let it stay in contact with a curved surface to gain control, and the balance of all these factors is what makes it FUN.

Energy humps… hmmm.