Square Tail or Pin Tail on Race/Downwind Boards

[JonathanC]

Just an observation, seems that some of the downwind/race boards have square tails - the Naish 14' Glide, Joe Blair 12'6, Stamp while most have pin tails SIC F Series, Bark, Foote etc .

I've been trying to work out the reasoning, square tail makes sense to keep the width and volume in a shorter board or to fit into a "class" such as the 14' Naish, maybe it makes it a little friendlier for stepping back for pivot turns. Maybe it helps catching a wave.

Does anyone have anything concrete about the hydrodynamics though? The other confusing thing is that most racing yachts are squared off too, is this just to keep them stable and provide a usable width, I can't imagine the racing yachting fraternity compromising hull shape in any way if it reduced speed.

I'd love to hear some theories and with any luck some facts..... and get this part of the forum humming again!

Cheers,
            Jonathan

[PonoBill]

there's a thread about this somewhere, I asked this question about a year or so ago. I'm still not satisfied with the answers I got and I'm tempted to fabricate some sort of funky test. I suspect that there's a big tradeoff  that has a lot to do with the kind of motor you are. A square tail enables straighter rails. That should do good things for friction. But it probably also generates eddies when the flow separates, and that would add drag. Pintails apparently keep the flow attached right to the end, but they require substantial curve to the rails.

I suspect that a big guy with a lot of muscle could get more out of a squaretail board while a smaller person with a better power to weight ratio might get more out of a pin. If for no other reason that a wider tail can pack in more floatation and keep the board faltter in the water.

The fly in all this ointment is the Bill Foote Maliko 14 boards, which look like they are raked in the water and go like stink.

[JonathanC]

I remember that other post Bill but I'm the same, didn't quite come out convinced. The big guy/square tail theory makes sense.

Not sure exactly what you mean by "raked", they certainly seem to have beautiful outline shape, tapering back to a pin from way forward. Hope Larry doesn't mind me using his board to illustrate...This is a 15 but pretty much same applies.

[Dwight (DW)]

My personal feeling is the pin creates less wake, but getting to a pin shape creates instability, so you have to add overall width.

Add a square tail, gain stability, and now you can reduce mid width.

So for me, the choice was less tail drag, or narrower mid width.

I don't think sailboats have square tails at the water line. Only at the deck for passenger comfort.

For a flat water racer, I'd prefer a pin, since I'd be standing in the middle the whole time. But on a downwind board, stepping back with a pin can get sketchy.

[jdmotes]

 I'm no racer but one time (a long while back) I read a book on hull hydro-dynamics and the author stated "if your not going to bring the rails together at the rear (preferred-pin-tail) then cut it off straight (square-tail)"...  His reasoning was pintails bring the disturbance (break) back together with the least amount of resistance. The second best way was the cutoff square tail that provided the 'second best' least resistance...          Later,    JD

[JonathanC]

Hi DW, looked at photos of racing yachts, I think you are right about the cut-off hull on the yachts not being at the water line. Despite the hull often being cut off square, it is usually clear of the water at that point. The water line is on the curved section leading up to the cut-off, bit like the Stamps boards seem to be.

Think I agree with you about the wide tail being helpful for wave riding on down-winders, although once again the Foote boards confuse things by having the pinny tail but apparently being lightning fast on downwinders - might be a significant operator skill factor there though...

[PonoBill]

the pintail on a Foote is new--I hadn't noticed that before. If you look at the boards in last year's downwinder test on Ke Nalu you'll see the prior Malikos had an unusual squash tail that looked a lot like the tail Jimmy Lewis is using on his new boards. I'll ask Bill why he changed but getting information out of him is like opening Macadamia nuts.

Here's a link tot he review
http://www.kenalu.com/2009/03/13/2009-stand-up-paddle-race-distance-and-downwinder-board-showcase-part-2/

I vaguely remember a video we shot of the Foote Maliko 14 in the pool at Ponohouse that shows off the odd rake, but I don't know where it is--it's not in Part 1 of the test.

[footemaui]

Pono.. Do the test !!!!!

[Ninth Island]

If you look at all the new Bark 12'6" race boards they have a large square tail. Joe just told me that he will be going to a similar style on his 14' race boards. I just ordered one so we'll see.

[paddledaddy]

My experience with lightweight sailboats is that boats intended to plane early often have a squared off stern with a flat bottom in the aft end. Boats intended to be as efficient as possible without planning often come to a point in the rear and maintain a rounded bottom and side contour (where they actually ride when healed over.) So it seems the pintail paddleboard would maximize efficiency in flatwater while the square tail with a flat bottom would plane more easily on a downwinder. Obviously designers like Foote and others are trying to balance these issues on a downwind board that spends part of the time on plane and part off plane.

[DavidJohn]

IMO.. For planning boards I'd go with a squared off tail and for non plaining boards I think the pin tail would be better.

I think the squared off tail would give better release for the water.

Squaring the tail off is also a way to get a 16' pintail board into the 14' class..  

Also.. Not all pin tail boards have good water release in non planing conditions.. There much more to it than just the shape of the tail.

DJ

[LaPerouseBay]

Jonathan, that footie in the picture is 14 feet.  If we get together on a downwinder while you are visiting, you are welcome to try it.  I'd like to try your f-14.   

 

[noworrieshawaii]

Hey LPB; aka Larry.. is that the same board Rick borrowed on our Makana Landing run?

I'm kinda dying to do a Buzz's to Grandma's paddle one of these windless early mornings.... Wanna go?

[dakine1214]

has any one tried both the F14 and Maliko 14? Curious on which one they like better. I can't decide which way to go. From what i've read the 3 that interest me are a Foote 12-6 and 14' and the F14. Is there a place where i could demo them on Maui. I live on the Big Island and there is no place here I can do that.
Thanks
John

[LaPerouseBay]

Hi Tracy,  yes that's the board.

I'd like to paddle, but I'm off to work at sunrise Mon thru Fri.  I'm hoping for a downwinder this weekend.  The wind should pick up by Sunday.  North shore has waves on the way as well.  Let's keep in touch.

Mid December is the scheduled delivery of my new f-16.  It's a custom lightweight model.  My first order was a 6 month wait and came in a month early.  I'm hoping for an early delivery again.  WOO HOO!!