I know this subject has been thoroughly… churned… around in the past. Usually in posts about Roy’s boards. However I’ve noticed something in my own hollow boards that has made me think about volume distribution more carefully. I’m wondering if this might also be applicable in compsand constructions as well (I have a feeling it is judging by other posts regarding thickness, volume and concave decks… though for other reasons.)
I’m (mostly) a kneeboarder, and I’ve made and ridden a couple of HW fish for kneeriding, one a twin keel, and one a quad, as well as a few standup boards. For the fish I copied dimensions from my PU board that went really well. I rode one of the wooden boards for most of last year in a variety of conditions up to well overhead and barelling. Overall, I loved it - everything other people have talked about, the glide, the feeling of the taught skins, the sound etc.
But… there was something weird and unpredictable about the handling compared with its PU brother, and I don’t think it was the weight, or the fins, but the buoyancy. As expected, because it’s hollow, it felt very buoyant… under my chest when paddling and knees when riding. But the tail was not at all buoyant. I’m guessing that the ratio of buoyancay in the middle of the board to the buoyancy in the the thin part (the tail) is way different in a hollow where only air fills the gaps between deck and bottom, than in a foam board.
On a kneeboard, where it’s not so easy to adjust your weight distribution, this was weird. Normally subtle shifts from knees to ankles were much exaggerated and vis versa. Like a pendulum around the centre of volume. As most of the waves I ride are down the line and sucky, this wasn’t too much of an issue. But on days with more time to turn, it was. The boards I’m currently making - though still foiled - will be much more parallel from tail to front to try and address this. I wouldn’t be surprised if slightly less drawn in planshapes might help too.
Maybe this isn’t so noticeable on a standup board where foot placement is more easily adjusted. Anyone else notice anything like this ?
final note: can’t mention my hws without saying thanks to the swaylocks crew, esp. PJ. Wouldn’t be right!
Well I don’t think you are going to find too many people on here apart from myself, Rhino, and Thefishexperiment. Power Surfboards are the first and only ones designing them, and no previous parallel profile boards have existed to the best of my knowledge.
The advantages of a parallel profile are in line with what you have experienced. . . a tapered board can tend to become ‘stringer sensitive’, which is another way of saying unstable and harder to control. . … . a parallel profile gives a lower centre of gravity, and thus better control.
Hi Dave, thanks for asking, a quick answer as I have some boards to build as you know.
The parallel profile distributes volume more evenly nose to tail, so for any given board volume the maximum thickness of the board is less than for a tapered board, and thus the rider is effectively riding a thinner board ( giving a lower centre of gravity )
For example our first and second 12 foot ‘Future Primitive’ boards had a maximum thickness of 2 inches and two and a quarter, which is thin for a board of that length. … . our 17 footer is only two and a half inches thick.
They are surprisngly tricky to design as the thickness of the board directly determines the rail volume. … . with tapered boards a ‘lump’ of foam can be left in the middle if more volume is desired without affecting the rail volume. … . Parallel profile boards are the Haiku of board design. . .
Parallel profiles aside, what you’ve just said is the essence of my interest in these boards, Roy.
The most challenging class I ever took in college was one where a 5-page paper was due every Tuesday. On Thursday, we had to turn in the same paper, cut down to two pages.
The Professor always said, “Its easy - just take out the lies.” So every topic was distilled to its crucial elements alone. And everyone who passed the class (which is not to say everyone who took it) came out a better writer.
And I have loved, ever since, to apply the same theory of designing and then taking out the lies to architecture, gardening, business, construction…everything I do. If its possible to apply it to surfboards further than I’m currently aware of, I’m interested. I’d long thought that soft rails, single fins, and flat bottoms were about where you’d be, but maybe I need to take out some more lies like foam, glass, lightweight, foil, etc. Or maybe not - but really only one way to find out.
Roy, I get it now, thanks… Correct me if I am wrong though, more interestingly, you construction method, combined with PP equates to a constant flex throughout the board right? This as opposed to a tapered or foiled profile which would yield a varying flex according to thickness (amongst other factors).
Hi Dave, yes a parallel profile board does tend towards a more even or constant flex, compared with tapered boards, however I can’t be sure that it’s exactly constant throughout the board for a couple of reasons:
as the tail gets narrower the board gets slightly stiffer in proportion to the bottom area, as the rail stringers (which are stiffer than the rest of the board) become a larger proportion of the cross section . . … . bottom area is an important factor because increasing it at any point increases the force and leverage which bends the board
the effect of stiffness increasing as a proportion of area as the board gets narrower towards the tail is offset by any horizontal lift area (e.g. a tunnel ) as this area acts like bottom area and thus like a wider tail in terms of the leverage on the board… . . thus the tail can be more flexy even though narrower.
The fin settings can stiffen part of the tail area, partially negating (2) above !
The net result though is a noticeably more even flex pattern than with tapered profile boards which tend to flex more in the tail than in the middle. Having said that, some of our thicker boards have very little flex, the flexiest boards we have made so far were balsa, it’s a lot more compressible than the woods we are using now, so we have to go thinner to get a good flex, and this can bring up buoyancy issues. . . . just a little harder to achieve the flex, but even a stiff woodie has resonance (whoops drifting OT )
Okay, thanks Roy, you’ve said 2 things that (if I understand correctly) appeal to me.
On a parallel profile board flex isn’t 100% constant as narrowing tail/nose planshapes stiffen it up. If you’re not compensating for this with a fin solution (I’m not) then a tapered profile is necessary. My feeling is that the last thing I want is a mid-section that is flexier than in the tail.
I could compensate for the weird buoyancy issues I’ve been having, while still keeping a tapered profile to promote the kind of flex characteristics I like, by adding a lump of foam in the middle. Simple. Not entirely in keeping with the HW ethic I guess, but definitely simple. Didn’t think of that. Thank you.
My original question was, has any other (tapered profile) HWS rider noticed peculiarities in riding that might be attributed to buoyancy? Have you done anything to compensate for that in terms of foil?
Hi Dave, yes a parallel profile board does tend towards a more even or constant flex, compared with tapered boards, however I can’t be sure that it’s exactly constant throughout the board for a couple of reasons:
as the tail gets narrower the board gets slightly stiffer in proportion to the bottom area, as the rail stringers (which are stiffer than the rest of the board) become a larger proportion of the cross section . . … . bottom area is an important factor because increasing it at any point increases the force and leverage which bends the board …
.
Interesting. Could you potentially tune the flex at different points along the board length by modulating the stiffness of the rails, as some of the compsand builders attempt to do?
Hi Tomway, having an even flex, an even flex with a stiff portion at the tail, or a slight increase in flex in the middle is way more efficient IMO than having a more flexy tail and stiffer middle, because it encourages a decelerating rocker. . . more rocker forward and less aft is faster, and allows the rider to use the flex to drive the board better because the flex works from right under his feet rather than having a stiff section which can’t be used to drive a floppier tail section.
That’s why a tapered profile isn’t necessary IMO.
By the way I didn’t mean to suggest adding a block of foam to a wooden board, what I meant by a ‘lump of foam’ is the thick bit in the middle of a tapered foam board.
Your original question I don’t understand sorry, thought I did but don’t. . . . . is your board under buoyant ?
High performance surfers and surfboards don’t agree with your opinion. You’d have to redefine “performance” away from the consensus view. Maybe the hull, trad fish, and longboard crowd could use a little more of it more though. I’d be interested to know about that. I’d think you give away Newtonian and speed the more fore-aft convex flex you allow in the bottom.
Hey Craftee… great photo I think I know that girl, she modelled for my logo!
Hehe… actually, before bad karma springs from his grave, the logo is an Alphonse Mucha painting, played with in photoshop by a friend. The model was probably 70 at the time your photo was taken too. Great find, where did you get it?
Roy, sorry if I was unclear. My precept is simple really: in my experience (I’m no good at theory) a hollow board needs to have a more parallel profile than a foam board - irrespective of flex characteristics etc - because of the way buoyancy distribution differs between foam and air. I notice that the tail on my wood board sinks much more readily than that on a foam board with identical thickness, rocker and foil. I’m not trying to say parallel profiles are generally better, just that I think they might suit hollow boards better than foam ones. I’m wondering if any other riders of tapered profile hollow boards have noticed this - I know there are a few about, but haven’t heard this mentioned before.
I think I know that girl, she modelled for my logo!