Help with big fish bottom contours

General Discussion
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I’m shaping a longer fish/swallowtail board (the board will be 9’5" long and 23" at the wide point), but one of my main goals is to loosen it up a bit. After some brainstorming, I realized that a TPH (tri-plane hull) might help.

My dad requested a fish/swallow tail specifically. However, after riding a similar board in the water, he was dissatisfied with its stiffness. The board he rode had rounder rails in the middle, with no clear release point, slight belly in the nose, and deep dual concave in the rear.

The new board will be ridden in up to head high Socal surf, and his surfing style isn’t radical–generally beginning with a bottom turn and coming back up to set a high trim line, with a few light turns here-and-there (think 70’s style). Our previous boards resemble stretched-out 70’s style boards–the favorite being a 9’9" with hard down rails, widepoint forward, flat midsection and V in the rear, single fin, and rounded pin tail. He wants to try a fish version now.

Planing speed is a top priority, as is paddling speed. After this is glide. The board I’m designing has harder, down rails to promote release and maneuverability from the rail, suiting his style of surfing. Can I further increase maneuverability though? Isn’t one of the design elements of the fish/swallowtail to increase hold?

Would a TPH be beneficial here?

I figure that a distinct bevel (like in the example photo) will create a plane to more easilty lean on to aid turning, while allowing for the release of water. The flat/concave bottom should allow for easy planing. My idea for bottom contours is as follows: mellow entry concave to a flat midsection, building to a mellow concave through the twin fins. Outside of the concave, the board will bevel to include elements of the V bottom, also building toward the rear.

What do you think? Would the board mix elements of the V bottom and fish in a good way?

Here is a simple drawing:
[img_assist|nid=1075717|title=Countours|desc=|link=none|align=left|width=561|height=640]

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Hi cw,

That s a beautiful shape above.  I wouldn’t expect a nine foot board to have the performance traits of a sub six foot fish(or would I call it a fish) even if you scaled it up, added the big ol crack,and put keels on it.  I think that’s what John said. Probably be a bitchen board, tho. Mike

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In the 1977 design guide PDF I have onhand the design for the 5-6 Lis Fish included a dead-flat bottom with a 4" wide chine that maxed out at 1/10th" and a tucked rail.    I’ve used that layout and it is plenty loose.  In that length.  

It seems to me that the straight lines and keels of the fish design are probably the bigger obstacle to “loose” in the longboard lengths, though.   A 5-6 length needs a little help in the template to develop drive at the rail; a 9+ foot longboard doesn’t need that.    I would imagine that you could retain the width @12" but round the corners; and then use most any fin setup other than a long based keel and that would give you a much looser board without sacrificing too much drive in relation to that necessary for the local conditions.    With that much width, surface area and rail length I don’t think you need to mess around with concave, either.  Personal opinion.  

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So are you saying to keep the bevel/chines, but nix the concave?

Also, does a TPH act as a displacement hull (liddle, etc) due to its convex shape, or does the flat planing area below the chines prevent this?

What was your tail width?

Thanks for the advice.

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LOL, I’m a typical backyard hack so you should definitely consider the source prior to taking any advice from me.  I only chimed in because your question looked lonely.  There are others here who are much more experienced with these designs than I.  

 

I normally do 16" and 17+" tails (@ 12" up) as a matter of routine.  With respect to bottom contours I have come to the opinion that a little goes a long ways, and (FOR ME)  less almost always works better than more.  As I understand it, the general rule of thumb for bottom contours is that narrow tails can use the extra lift from concaves and wide tails can use the additional control from convex.  So with wide tails I favor flat bottoms with just a little vee, like 1/8" or so.  If I use a chine it’s usually real subtle; if I want more control than that I go to using some roll instead.  Sharp release with a tuck in the rail loosens things up a bit, too.  

 

I think that just switching to a rounded tail, like a slightly pinned round tail, will really add some smoothness to the turns on a board that’s intended for that carving style.  I would only use a straight line in the rear of the template on a board that size if I intended it to go straight most of the time.  Frye’s Gliders mostly use a pin tail or a baby swallow.   Then there are the fins and placement.   When compared to a long based keel, breaking the keels up into a quad combo or a 2+1 would loosen the tail up quite a bit, too.  Maybe move the fin cluster up a little due to the length.  You can’t really turn a wide tail from in front of the fins anyway, so moving that sweet spot forward a little will require less moving around once he’s up.  

 

 

 

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Some of the design features of a short fish (or shortboards in general) don't necessarily translate directly to a bigger version.  For one thing, unless you bump out the width, the outline curves are almost bound to be straighter.  The traditional fish design is already pretty straight... it was designed to hold in the tube on sucked out slabby waves in La Jolla area.  A direct proportioning scale would make a 6' X 21" = 9' X 31.5".  Pulling the width in to 23" sounds reasonable but the outline will definitely lose some curve in the process.  

A couple of workarounds might include:

1.  Move widepoint aft so you end up with more curve in the tail outline.

2.  Boost the tail rocker.

Gdaddy already covered some fin options that make perfect sense.  The wide base full keels on traditional fish are bound to be stiff.  Again, on the original fish, they were designed for maximum hold on sucked out tubing waves.  The bottom contours you are asking about are likely going to be less important than rocker, outline and fins.

PS - that's a nice looking shape on the racks! 

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Well thanks for the kind words guys, but that's not my board... it's a reference photo I grabbed from Google. You can see the rest of it here…it is indeed a nice looking board.

Anyways, we talked over the phone, and decided that a rounded pin, like on our previous board, will work better for the application. Thanks for the advice.

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Skip Frye dose make a long board with a deep swallow tail called the Fish Simmons .  It is easy to guess what the influence was in making that board.  Others in The San Diego area also make boards like that. Kane Garden has some up on their web site.   I Like the idea of the bevel in the rear.  Tom Morey does something like that on his Swizzler. If it were me I would do a four fin fish set up like what Mike Hynson does with his fish add a center box then play with different configurations of fins.