board stability...

back yard shaper…made 50-60. My newest is 7x21.5x 3. Its super fast and loose…but is little unstable and squirrley on take off and first turn. Almost feels like a proper short board. Looking for a little more stability and consistancy. Any thoughts? a touch of width…heavier glass…less thickness?

sorry for the crappy pictures


How much have you ridden it? I suspect if you give it a proper chance you’re going to love it just the way it is.

Maybe we could discuss some ideas tho. On this one, what is the bottom shape? Deck domed? Rails? Fin locations?

Is it just at takeoff?

thanks for the reply.  The bottom is suttle single all the way through. The deck is a little domed but nothing thats out of the ordinary, and the rails are definitely more on the high performence side. not full, but also not super pinched.  

  when standing up on take off, it just feels wobblie and not very secure. once i make the drop and set the line, she hauls ass

Maybe go with the Thruster option as opposed to the Quad setup.  Usually if they are squirrelly, it is bottom contour related.  

Throw a nubster in the center box and see how it goes.  Quads are usually loose until they get up to speed or are on the face. With a 5 fin, you have lots of variables in fins.  It looks like you have a flat set in the rear.  A 50/50 or 60/40 foil in the rear will change how it surfs.  Mess around with the fins.  Once you get it dialed in you need to document what you did so you have it on record for your next shape as a 5’er.  I see you got Steve to glass it, good choice.  Just my 2c…

i willl try a nubster!! thanks for the advice.  Steve is a great dude and kills it!  ive had boards glassed outher places and steve’s are by far the best

Sometimes you want to change your course right at takeoff, that initial looseness might be a blessing in disguise

another vote for trying double foil rears, which anchor more, cavitate less…fun looking shape

Too many fins!  Put a single 7.5" flex fin in the box, fool around with the position until you find the sweet spot and then you’ll know what your shape is all about. If you want to add more fins from there, you will have a point of reference, i.e., did I make it better or worse.

Honestly i don’t think its a fin thing. The board has a lot of side to side movement when i’m getting up. thats where the instability comes in. Its not a very stable surface as my feet hit the deck. Instead of just popping up and going…Im having to be very carefull at first. Thanks why im thinking if i added a little in the width,or glassed it heavier or beefed up the rails a little would help. other then that, shes good. but hell, maybe that is a fin thing…i am kind of a dummy!!!

Good advice from ST on a nubster.  Had not  thought about that.

You have a deadband.  Twins and quads (which are just a form of a twin) are prone to this when there is a wee bit too much curve in the tail.  If your template were a little wider in the hip, say about 15 inches or so up from the tail, that would make your board a little more parallel from the wide point to the hip and could correct it.  However, if your fins are toed in even 1/2 degree too much, that’ll compound your problem.  Absolutely try your board as a single fin, cause that’ll have no deadband whatsoever.  Then try it as a 2+1.  The thruster is the marriage of a twin fin and a single fin, and there is usually a deadband between the response of the side fins, but the center back fin fills it in.  By changing the fin configurations, you’ll zero in on the cause of the problem.

Oops, just remembered this:

Another problem that we have is that our cambered fins can actually have different zero lift angles of attack for different speeds.  It is possible that your fins are toed in too much at getting on your feet speeds and are aligned just right at cruising down the line speeds.  Roughing up from the 15% to 25% chord on the outside of your fins with some coarse sandpaper can fix this - not a guaranteed fix though cause so many of our fins have ‘mystery foils.’

Thank you, I was thinking the same thing  The back quarter of the board narrows into a rounded pin. Maybe it narrows up to fast and to much. If i relaxed to curve to give the back part of the board a little more width and straighten out the overall back half just a little, maybe that will help with the initial stability.   Thank you guys   Erik

I agree.  Play with the fins and you will figure it out.   Like I said;  usually a bottom contour issue.  Changing the fins to cure the problem are a band aid for the issue.  If you know what causes this you’ll change it up on the next shape.

Heres a picture of the rocker.  maybe a little to much in the tail might lead to a little wobble on standing up? The great Greg Griffin  suggested that on surfer mag forum.

Nah, not too much rocker.  Your rocker looks pretty straight to me in the last foot or so.  Consider that the medium we’re riding curves progressively up the face of the wave.  If our rocker doesn’t do the same, then the water will see a downturned flap.  Boards with this sort of rocker tend to work better lower in the wave.  Your rocker also has more of a continuous curve through the middle.  This rocker is very popular because it works very well for the fly-off-the-top-drive-hard-off-the-bottom professional surfer crowd that everybody wants to copy.  Go to the McTavish website and take a look at the Noosa 66 tail rocker - that is a really good tail rocker.  Then look at this 7’ 6" rocker - the curvature has a nearly linear progression into the tail.  I’ve been using this rocker, in various length, sometimes with the nose cut off for a board like this one, for nearly 30 years.

If the board becomes a rocket as a quad after that initial slow speed instability passes, then it will still likely be one as a 5 fin too, just more stable initially where you want it.

 

I saw over ‘there’ you tried it as a thruster and said it was perhaps even less stable.  Was this with a full size thruster fin?  What fins have you tried, are they considered more raked or more upright? lots of surface area or less so?  Rake and more tip area adds stability and elongates the turning radius.

 

My shortbaord is 6’11x22"x3", similar to your dimensions, and is also a rocket.  I’ve yet to click with it as a quad, as it seems one needs to have one rail engaged, or the other, and there is weirdness in that transition, especially at slower speeds.  While it looks vastly overfinned with 5 fins, the trailer not being full sized, it does not feel like it.  Its still loose and fast with 5, but with a more planted feel in the tail and way more confidence rail to rail , in and through hard turns, but I am not sure I like it more than a thruster set up.

 

I think you can sort out that initial instability with 5 fins and play with their respective sizes template  and foil, and still have something you like once at speed.

 

With regards to the shape itself being the cause of initial instability, have you ridden many boards of these general dimensions?  I mean if there is too much tail rocker your impression would not be that it is a rocket down the line, unless the waves were so punchy any board would feel like a rocket.

 

Carry a fin key with you, stuff a fifth fin in your wetsuit, or two different ones of different sizes.  The days I had serious issues with mine as a quad and put one of those quads in teh thruster box while out in the lineup, and the other in between my shoulder blades, was an eye opener for sure.  

Good luck.

 

 

 

This board had a similar problem where it was too loose as a 2+1 thruster.  I tried adding some camber to the side fins by adding some glass to the inside of the trailing edge, then sanding a nice curve in it.  It worked a little bit, but the danger with that is that will lock the board up when surfing juice.  I ripped that all out and threw in a box.  It works somewhat Ok as a single fin, but is still too loose.  I’m going to reshape the tail as I did with Shaping Screw Up #1 - 6’ 10" x 21 3/4".  You can see how my 9’ rounded pin thruster gun template follows this template perfectly, but doesn’t turn in too much in the back, then another template is used to make a square tail.  A low priority project at this moment, but it will get done.  That’s 60 psi closed cell extruded styrene foam between the bamboo stringers, and the rest of the foam is 40 psi extruded.  I put a lot of effort into making the blank and everything afterwards, so one way or another I’m going to get a good board out of it.  I’ll keep the box in it till I sort out what fin works best and where, then I’ll rip that out and do a permanent installation.

you got it: too much curve, not enough width on the back half outline so boards go too easy on rails. light footed front foot surfer like it (it’s what i need) but heavier more balanced footed rider not.