Deck rocker quantification… this one is fairly mysterious and rarely discussed. We all have a grasp of the basics like length, width, widepoint, nose and tail rocker, etc.
So what’s going on here? How to quantify? How will various changes affect ride?
I think that the deck rocker is just the result of bottom rocker and volume distribution. Can be discussed, but i don’t think that you can conclude anything towards the caracteristic of a board if you just have the deck rocker.
This can get really complicated or very simple depending on the application. In most instances deck rocker is simply the translation of the bottom rocker via the 3 thickness points of the shape to the opposite side. In the normal shaping process, this results in different rockers as the nose and tail are blended, mainly because the rail line is defined from the bottom rocker. This is evident on “big guy” shortboards where there’s not enough length to smoothly taper the thickness towards each end. On noseriders, some shapers will vary the tail rocker from bottom to deck. Other designs may have a forward variation of the two rockers for volume, lift, and/or flex characteristics (i.e. step decks). In any case, it’s easy to lose the rail line with contours on both the deck and bottom. I think that it’s more effective to vary thickness, outline, bottom contours than mess with two different rockers trying to effect lift, flex, volume. Most of the old-school hand-shapers say that deck rocker is simply whatever results from blending a given bottom rocker, length, and thickness.
Tough one to quantify. My guide is to keep as close to maximum thickness through the middle third of the board. This means that deck curve only approximates bottom rocker. I can’t use my bottom rocker template to get my top deck without a lot of messing about. The bottom rocker has more curve. Contrary to what PeteC mentioned, I specifically design my deck rocker. But in agreement with what he said, it’s really easy to get wobbles in your rails if your rockers mismatch or you have non-smooth outlines.
Why do I design deck rocker?
- Having deck rocker means you can get more volume out of a particular thickness board or drop thickness without sacrificing volume.
- Deck rocker allows you to move volume fore and aft. This is the same at petec moving thickness. Volume can substitute for moving width forward or back.
- A smooth deck rocker dictates a smooth rail foil.
If I had learned hand shaping first, I may approach things differently. But because I first got computer design and cutting right, and now back into the handiwork, I bring my design attitudes to hand work.
Thanks John for bringing up this design topic for discussion. I thought my previous input needed more expert opinion so I consulted today with a couple of 20K+ shapers on it and got the following: To them, shaping deck rocker was an artistic matter of how the deck “flowed” towards the nose / tail; no bumps or dips. Certain blanks that had almost continuous rocker always wound up with a bump on the deck that had to be blended in as the shape came to form; this is what I meant in my previous post about how deck rocker just kinda falls in place. They agreed that the most important part of any shape is a smooth rail foil / line, as that is the true rocker of the shape. To me, that line is established with the bottom rail band and at least one deck band. It is more apparent with the sharp planer cuts than if rounded. Bottom (or deck) contours are blended in ahead of the rails so as to not change this line. So if we want intentional bumps and dips (i.e. step decks, concave decks), these must be added after the rail line is established. Obviously additional thickness must be considered in advance. Having said all of that about rail line, you can have one that is broken or inconsistent (i.e. wings, etc). But (caution here) you must know exactly where to break the line which is a function of thickness, width, fins, etc. I hope that this discussion brings some insight to newer shapers about why shaping operations have an order and also some depth to their understanding of rocker.
John raises a thoughtful question. My personal process begins with the blank selection. I look for ample thickness and both nose and tail rocker. After glueup, and after the outline is cut, I establish an eye pleasing, smooth, initial deck rocker. I’ll then dial in the thickness distribution (ie, foil) before beginning to do the first rail bands, top and bottom. This method allows me to ‘‘see’’ the finished board, in my minds eye, as I work through the shaping stages. The ‘‘best’’ method, is the one that allows you, the shaper, to end up with the finished board you imagined when you started. Don’t overlook the importance of selection of the proper fin, or fins, as that can make or break a surfboards performance. Many times, it’s the difference between OK performance, and magic.
…I use deck lines with a bit more lift running into the tail …never been a big fan of modern straight super thin tails , and prefer more buoyancy under the back foot…it also seems to allow me to get the bottom contours nicely blended , without running out of foam to do it. Some of-the-shelf PU blanks don’t allow me to do this , and I have to order a blank up to a foot longer to get some meat in the tail.
Thanks for the input. Judging by the attention Terry Martin is giving that reference line, I’d have to say there is more going on than a simple bottom rocker/thickness taper. Otherwise, why pull the deckline reference tape?
Obviously one still photograph doesn’t do the process justice. I know I’ve never seen anybody else doing this. Since TM was an expert, there must be more to it than meets the eye.
I’m pretty sure at least a couple of blank companies reference any rocker tweaks to the deck rocker. My personal experiences reveal that at least some tail flex (or lack of) is related to deck rocker.
Aside from some cryptic ‘proprietary’ rocker posts here on Swaylocks, not much has been offered as far as quantification and the effects of any changes on the ride.
Here’s another deck shot - from the famous Bert Burger thread. This one showing the side to side concave.
Hello Mr. Mellor, I’m not sure I understand exactly what it is you are looking for. Are you after a formula of sorts? There have been some very good explanations of “deck rocker” but to quantify befuddles me. Pulling a tape line longitudinally or across the deck is simply a straight line reference to enhance the difference in the line of the deck. Compare and contrast. I’m not trying to tell you anything here as I know you are pretty adept at shaping and drawing pleasant curves. I have a friend that is an engineer for what started out as Rocketdyne and ended up as MacDonnel/Douglas. He helped design the space shuttle main engines. When I posed a formula or ratios for outlines this set him off on a quest. He talked to fellow engineers about this and in terms of surfboards, there are too many things happening for a definitive equation for changing shapes. He jokingly said it “melted his slide rule”. What are we looking for here? I’m curious to find out.
i remember surfding saying that he prefered to order his blanks to a specified deck rocker as to take as little foam off the deck as possible to keep lightweight blanks with light glass jobs somewhat sturdy underfoot
i see deck rocker as the thickness distribution in combo with the bottom rocker. you can drastically alter the way a board feels underfoot and paddling by shifting that thickness distribution - which is visible in the deck rocker - but i confess i very rarely measure deck rocker or thickness distribution - i do it by eye except for a few instances where i was trying to copy a previous board
“”“”““i remember surfding saying that he prefered to order his blanks to a specified deck rocker as to take as little foam off the deck as possible “”””…this has been almost universal practise since blanks become more “close tolerance” (30 odd years ago? ). Blank manufacturers will keep an extensive inventory of all required deck curves for their customers , or cut and glue-up the blank to any provided template.
Hi tblank -
I don’t think very many people measure deck rocker or know why or how it should be measured. I asked this one before after reading a Joe Quigg interview in Surfer’s Journal where he referenced something like “1 1/2” deck rocker."
The photo posted of Terry Martin kept popping up on Facebook to advertise a video on shapers. He seems to be paying a lot of attention to that pulled tape. We all hear stuff like “2 1/2” tail rocker" or “5” nose rocker" as measured on the bottom. I rarely hear anything about the deck. I would have liked to have been there when that photo was taken to hear what he was saying.
Me too Mr. Mellor, me too.
I’ve watched Terry shape many boards, but never seen him measure deck rocker. However, he did a lot custom longboards where customers asked for specific things that they felt were key design features. Terry tried to oblige the best he could, but wouldn’t compromise what he thought was essential to the board performing well. Most of these features were things to enhance noseriding, and many were questionable in my opinion. Those customers would come by and check his work and maybe that’s what the photo is about. Whenever Terry would do a shape for me or my family, I’d only tell him where it would be ridden and nothing else, just let him indulge himself. The best result was a pig double-ender. I’ll send the photo to Josh Martin and see if he knows why his Dad did that tape thing.
On that photo of Bert’s shape, I think that the deck rocker resulted from a thin board design but with thick full rails. The concave in the deck was done after the rails, and is probably for a flex characteristic. I don’t think we can consider these deck cases as a rocker at all really. With respect to Bert’s shape and what red boards posted earlier, it seems to be more akin to shaping bottom contours rather than a defining curve as a bottom rocker is.
deck contour is as much overlooked,as it is trivialized.
One time I said shape the deck outloud and dickie laughed at me outloud.
The deck is the most intimate part of the board,and rocker is just one part.
Placement of thickness throughout the board is controled by deck contour.
Lowered center of gravity forward is the most common adjustment historicly
for nose trim control.Flats on deck are the next .Domes are sensitizing to controls.
Riding prone makes deck intimacy a reality.
deck rocker is a whole study in and of itself.
running a hand down the finished deck, with wax in your hand or before wax
is the gateway to understanding where trim might be.
and now there are no snakes in Ireland
thanks St. Patrick
Hi John -
You’ve seen my deck rocker… Ha!
I certainly put thought and measurement into the deck, but the “rocker” would be reserved for the nose and tail quarters.
As for “quantification;” I’m sure I have numbers, but given the extemeness of my designs, I’m not sure it would mean much to anyone else.
Hi Taylor - Yes and I know you had some specific flex and rail contour ideas under your lid. But seriously… most of us don’t have a clue as to what TM is doing with the pulled tape. How the heck are we going to even begin understanding what you had in mind? HAHA - i have an entire secret file on your boards!
maybe your answer is in the video - have you seen it? Thinking maybe the picture is a screen grab.
Deck rocker on some Mfgs. blanks does NOT always give you the same bottom to work with, I have my rockers dialed in that I consistantly use, but find on cetain blanks that I wind up with too much flat running out the tail and wind up with less tail rocker.
I’ve drawn bottom rockers and then laid a batten along the line only to see inconsistancies of where the thickness flow needs to be altered.
I had a pair of customeres bring me the Clark blanks that they ordered with their interpretation of what they THOUGHT was what was intended, but had a center of the bottom that was lower than the area behind the nose and ahead of the tail, when shaped the bottom was nearly dead flat tip to tip.
I was sent a grab from Oak Foils instagram, they meat of the post was, I always start with the my deck and get it correct before going on to the bottom, like I have said forever, start with a level playing field.
The thicker the intended shape, the less deck rocker that it will appear to have if the bottom rocker remains the same