Hi all,
Maybee a sinmple question but I don´t relly get it…
When measuring the rocker, where on the bord is zero rocker? Is it at half board length or at any other point? If zero is further back you get less tail rocker and more nose rocker so to speak. Or at the extreme, if zero is at the tail you get no tail rocker, only nose rocker all the way. Ofcourse It doesn´t affect the shape itself but it does affect the measurment and I am just about to start shaping in boardcad…
Here’s what I do:
Lay the board on your racks, bottom up. Mark the middle point. Put a long aluminum ruler along the stringer, middle of the ruler on middle point of the blank. Put a level on the ruler and add wedges under the nose or the tail untill the ruler is level. Then measure rocker at nose and tail (or wherever else): distance between the ruler and the bottom of the blank.
Ok, so you are basically balancing the ruler on the point which is half-length of the board. So the point half-length and in the middle of the board is your zero-point if I understand correctly. Everything behind halflength is tailrocker and everything in front of half lenth is nose rocker?
That also mean something like 3" rocker on a 6´board is the same as maybee 5" rocker on a 9´board since the distance from boards middle point to nose/tail is longer on the longer board. To get the same curvature I mean…
Same as balsa except without the level. I put a straight edge on the bottom of the board, centered at midpoint. I then adjust the straight edge to where it is tangent with the curve at midpoint.
The leveling method doesn’t work for me because with that method, the position you set the board on the racks will change your measurement. If the board isn’t positioned perfectly level at midpoint to begin with, it will change your measurement.
On the otherhand, Balsa does have a lot more experience than me.
Rocker will always be relative to any method we chose to measure. Position of board on racks or measuring table or device / employing a lengthy straight edge / accuracy in taking measurements / and so many other variables. But, we get to develop a method and variables which ultimately leads to some sort of consistency in measuring rocker. Fundamentally, if you develop a logical and consistent method to measure rocker and stick with that method you will have a system of measure that will provide consistent useable data for design reference.
Develop a method and stick to it. Create a journal or notebook data base to keep records of your rockers. If through experience you want to adjust or modify your method make a note in your records that entries during certain time spans used a particular method to measure. As time goes by your journal will fill in and be a very valuable asset or tool to your shaping.
Developing ones own method seems a good idea. I can imagine that floating the finished board in water and measuring the rocker in that situation would give a more ‘inclusive’ result than the above methods, maybe valid as a final meausurement?
Juan
I came up with this quick´n dirty method which seems to work really good. I want to measure the rocker at the “highest” point along the rocker. That is I don´t want to measure in the middle of a single concave fo example. With this rigg (built in 15 minutes) and a set-square (correct english?) I can easily transfer the rocker to paper and then do the measuring on the paper. I will also make notes about concaves and V each foot or so.
In trying to provide a service to you, I’ll state:
There are excellent threads in the archives that represent
‘the book’ on whats been written on measuring rocker.
You’ll find the ‘book’ on this subject in the archives most notably those
written by Bill Barnfield and fair replies to him questioning his methods.
No where else is this information represented better or more comprehensively
either in print , or otherwise, than whats already in the archives.
Just thought I’d save you some real time!
Yes , the 'is rocker proportional ' thread is a good start , and there are others.
The only beef I have , and I’m no expert , is that is that these methods don’t seem to allow for bottom contours, e.g. if you measure the rocker on a board with significant concave, that gives you the stringer rocker , but not the rail rocker.Possibly difficult if youre duplicating or making a variation of the board.
But ya ,BB’s method has served me well so far.
A straight, long and light piece of timber should do the trick. Make sure your shaping racks are level and lay the board on your racks. Put the piece of timber on your board and press lightly in the middle of the stick until it balances. Now measure your rocker.
Everyone I know of uses BB’s method. It’s an industry standard. The mid point is the standard everyone uses.
Ok, but there is one drawback as far as I see it: If you have a nice shape and want to duplicate it with some changes to the bottom shape it won´t really work. In my case I want to add concave from middle of board and backwards, this is to flatten the rocker in the middle but keep curvature at rails. The board I am measuring has a v in back and concave in front. That means I will measure inside the concave in the front and later need to “add” material there to make it flat.
It can be difficult to recreate complex bottom shapes perfectly. I’ve found that it is easier (less frustrating) to base your rocker off a flat bottom and then add your concaves or vees. I’ve tried to set my rocker and then measure and adjust as I add concave to get the desired final bottom curve, but it can get frustrating and at times will srew up your final thickness making for a board that is too thin. I’ve even had boards with the exact center line rocker that I desired with a full tip to tail concave but ended up with too much rail rocker.
If I know that I want to add a 1/8 concave from center back then I’ll let the rocker line have an extra 1/8 in the tail . It can be difficult to get the rocker to fall perfectly to the numbers you want doing it this way but at least I know that my rail rocker line is close. I’m also looking to have a smooth stinger curve rather than nailing rocker numbers and having a stinger with hills and valleys.
Measureing from mid point and using a laser to measure your rocker instead of a stick will allow you to measure multiple curves. Because the laser sends a flat line you can measure points up and down and side to side.
For instance.. measuring tails with V you can measure the tail tip at the crown and valley, or high and low point. You can measure nose rocker in the concave or at the rail line.
You can measure rockers on bottoms with concave through the middle of the board too.
Working with complex bottom contours will be tricky because you have deck lines and foam volume distribution to deal with. Seeing the finished board in your head and where you want everything first is kind of important. It takes a lot of repetition…. Miles and miles of walking around surfboard blanks.
D.R.
DMP: You have run into the same problem as me, and your solution seems to be good.
DennisRyder: measuring with laser is probably the best, haven´t really thought about that possibility.
Check my simple setup a few posts up. It works really well and gives the rocker as it was cut in the first place. I find it easier to do it that way rather than trying to compensate for concaves and Vee later. I am currently shaping using BoardCad. However if you have tried it you know that it is based on the rocker in the centerline which is a drawback as I see it.
This is why I really like using rocker tables.
I use an elevated chain stay with a dual magneto hoist, this allows the board to center perfectly with out the hinderance of human intervention. Once the board is hovering properly 7 tiny elfs in white gloves run their hands over the board…memorize it…then replicate it on the ELF 4500 RPL. Simple, simple technology.
SO! You got rid of the braided Seal Hair Twine, and the Seal Rib Calipers, eh? Going soft? It’s Seal Pup Season. Get your aluminum bat ready!
I can hear it now, cling, cling, cling. Ah, the sweet music.
Exactly. You measure the flats then add the contours. Simple stuff really. Always do it the simplest method. Always think simplicity. Unless you have 7 elves
I used to be confused about rocker in general. I knew what it was for but got my self over thinking how to control and measure it. Bill Barnfield posted a great description a while back on how to measure rocker. Now when I shape I try to imagine how the rocker is changing from that center point on the blank and how the curve rises and falls depending on where I cut along the stringer.
I also bought a laser line level thinking that it would be a super tool but in the end it sits in a box. I’m sure that if I had gotten a better one (expensive) then it would be used more but my rocker stick is super easy to use, never needs batteries, and cost something like 5 bucks.
Also I was rolling laughing at the other posts. It’s awesome to see the holders of the great knowledge of board building cracking jokes. It reminded me of the story about the kid that ordered a custom board from Brewer. When he went to check out the shaped blank he told Brewer that the board he shaped was too long from what he ordered, so Brewer took out his cut out saw and cut the extra off the tail and handed him the board, done.
