I’ve cut 7 boards now and am starting to get somewhere near what I want - a fast, manoeuverable board that points high yet has enough drive and get up and go to make deeeep takeoffs comfortable (yes - that holy grail of designers everywhere!)
Up to now I’ve been using old-school design - keeping the top deck rocker flat from the tail to 2/3 up. This has worked well with the (2"/5.5") bottom deck curve, (2.75") thickness and deck crowning - to provide decent rail foil (1.5" rails at mid). I’m using vee flat vee bottoms / PUPE / 6oz, 2x6, 1.5" lap.
I’m now looking at moving to the next step and put curve into the top deck rocker - slightly flatter than the bottom rocker so that I can maintain the thickness I want in the mid section.
Any ideas on how much weaker/more flexible the board with the curved top deck rocker will be (if at all)? I’m assuming that the flat top deck and crown provides strength that might get lost in a curved deck rocker.
I looked on Sways for some info on this and the following post was informative but I hope that there might be Swaylockers who have direct experience on this design transition in PUPE:
Discussion Topic: 7’0"balsasandwich riding impressionshttp://www.swaylocks.com/forum/gforum.cgi?do=post_view_flat;post=258790;page=3;sb=post_latest_reply;so=ASC;mh=25;http://www.swaylocks.com/forum/gforum.cgi?post=259734;search_string=domed%20top%20deck;#259734
Thanks
Red
All I can say is that I have gone to an extreme in that direction: Every board I have built has the deck rocker the same as the bottom rocker.
The result is really good, that’s why I keep on doing it, specifically the deck flexes more and the board is thinner in the riding position for any given volume, which improves control.
There’s another more subtle advantage, namely that the feet are always the same distance from the planing surface, it’s like standing directly on the bottom, also good for control
Interesting point. I can see mow that I can keep the deck flatter in the mid section (for stability) and domed in the tail (for response) if I implement top deck rocker and drop the midpoint thickness a bit. This is something I’ve been struggling with (because the rails are just so hard to cut and the foil/volumes are difficult to even out).
My boards are only 6’2" - shorter than yours?
Yes mostly our boards are longer but we are doing a few 6 footers using the same principle.
Don’t the compsand guys often go thinner for flex, with a bit of deck rocker?
Maybe Silly, Bert and co can help.
If the top deck is rockered does the low point of the bottom rocker have to move?
Every rider surely has his or her own preferences but I can tell you this much… a domed deck (convex stringer curve) is stiff. Concave stringer curve promotes flex, convex stringer curve inhibits flex. Many modern boards, when eyeballed from tail to nose along the deck, will have a concaved stringer line on the deck and have quite a bit of flex. I think this is one design aspect of the squared off tail rails I’ve seen - they allow a concave deck curve without having to “turn down” the deck to meet the bottom. The fiberglass shell is definitely a structural component. I have stripped deck glass off dome decked boards and the shell is stiff even with no foam or stringer.
Thanks JohnMellor for the input.
The added flex is something that worries me a bit if it’s going to translate into higher likelihood of snapping. I understand that flex can make a board more robust (reeds bending in the current and all that).
I think there’s more control over rail foiling with concave top deck rocker, but it’s hard to get my head around. I’m thinking of dropping the thickness at the stringer and levelling off the deck in the middle 1/3. I’ll try to keep stringer volume quite uniform to the tail but dome the deck to pull the rails thickness down and achieve a decent rail foil.
If I do this, I haven’t got my head around how to balance the volumes in the nose and tail without carrying more thickness forward than I usually do. More doming in the front 1/3?
Also, because the deck is then “downhill” from the tail to the center I’m wondering if the surfer compensates, leveling the deck and by doing so lifts the low point of the rocker into water intake, rather than having it neutral or in the water exhaust. The board would then seem “flappy” up front?
Seems to me that deck rocker must affect bottom rocker setup in some way?
Hi -
I know that some guys, Rich Harbour for instance, have said they order their stringer profiles based on deck curve.
The blending, foiling and thickness placement are pretty much up to each designer and the variables are infinite.
Have you considered taking various boards and placing a straight edge on the deck along the stringer? That might give you a better idea of how other people are doing it. If a straight edge bridging the thick point and tail is showing daylight under the back foot area, you might measure the space between the straight edge and the board to get an idea.
A basic rocker template combined with thickness measurements might also help.
Thanks.
Most of the boards I’m looking at have flat top decks.
I have access to rocker templates to help me realize top rocker, thanks to a generous professional shaper.
I’ll probably duplicate my bottom rocker on the top deck for the middle 2/3 and decrease the accelerated curve in the nose and tail.
Since I’m looking at front foot style boards I think I’m going to carry the thickness forward, so I should be able to get volume balance at 12" tail and nose. I’ll just have to finesse the nose and tail to try to get the balance right (wanting a thicker than normal tail to help with wave catching, but I guess it’s not essential)
I’ll start with my standard bottom and see how it turns out.
Funny - the last project is awaiting glass and the next one is kicking in!
Quote:
Also, because the deck is then “downhill” from the tail to the center I’m wondering if the surfer compensates, leveling the deck and by doing so lifts the low point of the rocker into water intake, rather than having it neutral or in the water exhaust. The board would then seem “flappy” up front?
Seems to me that deck rocker must affect bottom rocker setup in some way? If the top deck is rockered does the low point of the bottom rocker have to move?
Honestly I wouldn’t sweat about it at all. . . I understand what you are saying, basically that by concaving the deck fore and aft the surfer will tip forward slightly, and to compensate and avoid this will tend to lift the nose up as he straightens up to keep in balance.
Really that doesn’t happen, all that happens with a deck rocker which is concave is that the board feels more easily controlled and predictable, the rocker will behave as it usually does
To find a deck profile, perhaps you could just take the bottom profile and geometrically flatten it slightly to get the thickness you want in the thickest point.
Another possibility ( closer to what I do, which is to make the bottom and deck rocker identical) is to take the bottom curve and park the identical curve ( for example) two and a half inches above the bottom. . . . this makes a parallel profile, all you need to do then is taper the nose section down until it looks good. You will wind up with a thicker than normal tail, a thin maximum thickness and a semi parallel profile board. . . the nose is likely to look chunky too, like an old school fish where the rail thickness is carried right to the nose.
Just some thoughts but I wouldn’t worry about the deck profile affecting the bottom rocker at all.
Cheers
Roy
Thanks
Yeah, moving the bottom curve up 2.5" to determine the top deck rocker is the way I’ve seen it done.
The challenge for me is doing this on a computer design. Time to test the rocker cut/paste facility! Funny, isn’t it - something relatively simple with wood templates may be more tricky on the computer.
Thanks for the reassurance on not adjusting the bottom rocker.
I’m looking forward to this!
OK so I’ve taken a working 6’2"/ 2.75" thick design that has a flat top deck and I’ve designed in a curved top deck @2.5" that follows the bottom deck rocker.
The picture shows the two profiles compared. The bottom rockers are identical. It’s a tried, tested and proven bottom, so I’m not mucking with that. The red line shows the curved top deck rocker. The green line gives the waterline for the flat top deck board (actually the rail wide points)
In the new board with curved top deck:
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I’ve done what I can to balance the volumes fore and aft by slightly flattening the rocker at the nose and tail (can’t have a 2.5" thick tail!)
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I’ve also domed the deck in the tail and flattened the cross section in the mid section in order to bring up the volume so it’s similar to the original (volume is 39.75 liters for this one vs 41.25 liters for the flat deck model)
Here are the results of volume distribution for the 2 boards. The vertical line gives the center of volume. It’s midway on both boards (within 1/4"). The tail volume is at the left of the pics, the nose volume at the right.
You can see the that the curved top deck rocker spreads the volume about the center, so the volume distribution is bulbed out around the center compared to the flat top deck. This is to be expected because the thickness stays constant through the middle 1/3 of the board when the top deck is curved, as opposed to max thickness at the rocker low point for the flat deck board. I’m excited about what this might do to handling (widen the sweet spot, make turns easier to initiate…?)
BUT the volume in the curved deck board “bulbs” about 2/3 forward, while it “kinks in” about 1/3 forward. Any ideas about undesirable implications there might be for handling?
Any ideas about dealing with this without losing too much volume?