bottom contours on single fin surfboards

Ok.  I make several boards a year.  I 'm getting pretty good. In terms of concave.  I’ve made single to doubles,  through to flat or spiral Vee.  I’ve made single to flat, ones with basically a spine that went well above rail line towards the back half of the board…etc. etc.  I’ve also recently discovered that I like boards that are flat…Like really low rocker.  tail kicks that are late and nose kicks that start way back and barely blend up to a late kick in the nose.  A super shallow rocker combined with a moderately deep concave to sunken double is just crazy fast.  Why worry about the nose rocker when you can roll in from outside due to almost no rocker?

I’m getting off topic.  the point is that I like flat boards and I want to make a single fin. 

My next board is going to be a straight single fin.  I’ve made one before for someone else.  that was a mild single to mild Vee out the tail.

Again…Back to the question.   Single concave…I want to do a single fin (6’6" epoxy  light weight but with old school outline. SEE Mctavish Tracker for example click blue link or maybe An Alex knost Brown microwave televison type which actually looks a ton like this video of Tom Wegners single fin he talks about on youtube…click to link to see good video)  with single concave running all the way through.  Actually about 1/16 to 1/8 single concave running right through the tail. or flat in the last 5 or so inches due to the more pinned out tail.   My mind tells me this may be a mistake.  With the singe fin my imaginiation tells me that I need Vee or flat in the last 1/3 of the board to help it transition rail to rail.   But the punchy speed of the single barrel concave intrigues me.   It makes sense with a thruster or quad that the single barrel would work as the rail fins do much of the holding and allow water to channel through.  but with the singe fin set into the trough of a single concave or dropped below rail double?  Would it hang up in the turns because it has a hard time turning over on rail?  Or is it fine because the rail is the fin and the narrower tail should allow for transitional turning anyway?   Has anyone ever done this?  Does it work?  How did it go?    I would prefer experienced answers over theoretical hydrodynamic verbiage. 

Oh and the waves I generally ride are junky to hollow beach break.  I like to go on trips to Puerto Rico, Costa and when I can afford to… Indo.  The board probably won’t see much in the way of long point breaks.  It may however see some dredgy hollow beach break barrels.  And probably more typically punchy twisting beach break slop that can be fun if you are able to move around sections and find the pockets etc. 

To get an idea of the vibe I’m after check this sweet video with Alex Knost and Harrison Roach and a few others.  Twitchy little guy but they really make these boards look super fun.  I want one!  Youtube vid Special K and the Sea Badgers

Thanks guys.



As to your questions about single fins and bottom contours here’s my .02:

I would say a common set-up is a flat-to-vee, or a roll to v bottom for a single fin… but technically do any bottom you want!

As for flat rockers, they tend to be more geared for small-to-med size surf so your ok there if that’s what type of board you surf? For larger waves you might think of using more rocker in middle, nose and tail to get better results.

I would recommend you try a roll to v bottom - where you put a slight roll on the bot edges and it fades to flat in middle the length of board… then shape in a moderate v in tail …the roll will assist in rail movement, and so will the v. Have fun!

I think rocker flatness or curve relates more to wave shape than size. You can have fairly large waves with big, slopey faces and thus not need a lot of rocker. Forgiving point beaks would fit that description. Conversely, small hollow beach breaks would dictate more rocker.

Totally agree Sammy Ive had a midlength board that worked just unreal on pointbreaks with a flatter rocker but not so much on reef breaks. 

At this point I don’t know.  I built this board a few months back for a buddy.  

It’s super flat through a large portion of the board.  kicks late in the nose and spiral Vees through the tail.  The tail kick is 2.5"  The board is 6’9"   We all took our boards to nicaragua and this board was the standout of the trip.  On reef break fast pitching beach break…it was so flat the paddle would get you in super early (so even if it was steep you could roll in from further out and sit on the tail to lift the nose)  and from there…it would just slingshot you into the barrel where its low arc in the rail would sit really nicely in the trough of the barrel.  

I know it’s all preference.  I appreciate the comments guys. Cheers.

Well, as length decreases rocker becomes less of an issue in beach break. I hear friends gripe about pearling too much and they blame their board. Sorry. It’s lack of technique that causes pearling on take-offs. Once you get your board dialed, it becomes second nature.

Avi- I like your “late kick” you described! I did something similar un-unknowingly as the guy I built my first board for was hard to please… he kept say n he liked/wanted a thinner nose and tail! Prior to that I was surforming and sanding in to thin board down. So I regrouped, and decided I needed a point to kick up my tail kick or rocker… so I measured up a foot on
bottom, made a pencil dot there and gradually kicked up and thinned zee tail! I ended up with a rather unnatural hump at zee foot up mark - so I took my surform and
Block and blended it in to the overall rocker and bottom…anyway, my nose rocker looked fine as it was-so I opted to leave it alone and thinned it on deck side when I cut in my eagle beak nose as that type of nose was popular back then. For v I just winged my surform and block at a forty five or so, and I took it up close to third mark you speak of… but I heard for a singles you can take your v all the way up to wide point! Ive tried a board like this and they do turn on a dime. And it’ll even help one adjust while forward up on board…I guess we could scrub v in more towards stringer to deepen vee if you wanted a harder , one? And deepen v in front of fins also…tons of technicalities?!

good thoughts.  Thanks guys.



Have you seen Mandala shapes? I am curious about his tri plane hull single fin board. You might read up on it. There’s also a utube clip where Manual talks about displacement hulls, and tri plane hull…good stuff. Ive never tried the tri plane hull, but I wonderfull exp on a convex bottom
Old William-Dennis board my sisters friend let me borrow…im think n it was an egg shape. Im not sure if it was a displacement hull? Board functioned extremely well for a old board! It had a moderate convex bottom the entire length! And thin eggy round pinched rails.'…one strange look n board that surfed INSANE! Not a lot of rocker …a smooth flowing curve in tail …not a lot of nose flip…