induction? ( vented / ported / slotted ) boards : what's the principle at work?

Do they do this?

hehehe! nice one " )


Surfboard fins or induction ports work by re-directing water. Via the conservation of momentum (or force, however you want to figure it), the water re-direction will enable user input to control the surfboard.

A simple example is a twin fin with parallel fins. When the board is on rail, the fin prevents the tail from sliding out by exerting force perpendicular to the fin. The force pushes the tail towards the center of the turn (approximately), which prevents a slide-out. 

Now toe-in the fin a little. The force pushes the tail a little forward of the center of the turn. You turn a little less tightly, but maintain more speed. Generally this works better when the forces of the rail line are also figured in. So, basically, you need something on the bottom of a smooth surfboard to push the tail towards the center of the turn. 

Let’s design an induction port. You will need to FORCE the water into the port to make it work, I think (but I’ve never designed one, so I would guess on a first design). The water needs to hold the rail in, so you want to TURN the water so that it moves towards the outside of the turn. So you need the induction near the rail line, and the water should be expelled to the outside. 

A significant problem may be resistance. The resistance to flow in tubes is not linear, it is a squared relation, so slightly larger tubes will process much more flow ie: a 25% increase in tube diameter will process 50% more flow (and that much more holding power). 

A significant problem may be dynamic range. In faster waves the same board will have a nonlinear increase in its holding power (and corresponding drag). 

OTOH, it could be awesome if you got it all dialed in. The best way to know is to build a prototype or 2 or 3 or 4. 


Herb said he’s built a ton of prototypes and his are opposite your ports’ theorized orientation. 

I think you have got it backwards…



I tell you… words… here’s 1000



Literature from the US Patent Office says that about 3% of the patents granted end up making money for their inventor.

Question for Herb:  Are you applying for a design patent or a utility patent?


As best I can recall, Morey built a surfboard many years ago (70’s?) that had ports connecting between the bottom of the board and the deck. The board was described in one of the surfing magazines and the article included pictures. If I were you, I think I’d be inclined to verify or disprove the existence of said article/board. If verified, it would seem prudent to compare the features of Morey’s board (via the description and the picture(s))with the claims in your patent application. That way, if there is some commonality between the two, you may be able to modify your claims so they will not conflict with any of the concepts incorporated into Morey’s board.

However, having said that, I would suspect that even if there is commonality between the two boards, it wouldn’t surprise me if you were still granted a patent since I suspect that the examiner would probably not be that familiar with the specific contents of all the surfing literature in the public domain–and hence not be aware of Morey’s board. But if that turns out to be the case, the patent may not be of much value since its validity could easily be challenged (esp. if the challenger can obtain a copy of the article).

PS. I’m not trying to intimidate you, just trying to keep you from being blindsided if my recollection is correct…



How or why would you patent something that has been done multiple times over the last 40 or more years and has been well documented in the press?

That would be kind of like "inventing" the supercharger right after Rusty releases the C5, ......its already been done. 

blakestah, you da man! " )

clear, concise explanation, i like that a lot.

janklow disagrees, it would be great to see the basis for taking that position as well (pic doesn’t load too btw)

I think mtb means this induction board by Morey (the Jet board)...


Different yet similar and Im sure Herbs got it worked out.

 As for Induction, my take is that it all surrounds the  Venturi effect, which is this.


 On the left is a simple Tee-piece where water runs down the vertical pipe and air is sucked in the side. Out the bottom, a mix of both (froth).

Top right, how it works on a board, water flows under the board and air is sucked down thru the tube and mixes under the board.     

  Benefit-This might lower the water surface contact area.


Below right, how it works in reverse, if the angle of the hole thru the deck is changed then air isnt sucked down but water can rise up the tube, depending upon the angle of the tube and the shape of the hole on the bottom of the board.

Benefit-This could increase the grip of the board as it sheers off a thin layer of water.


So depending on the angle of the tube thru the board, water flow can either suck or blow. And the holes on the rails do the same. The toe in of the tubes would regulate when each tube becomes more effective as the water flow changes.

 With enough holes thru the board at the front and the back. a board would both suck and blow and do the same if ridden in reverse so Im guessing that Herbs board can be ridden in both directions like a skateboard. 


 Hence the Bart Simpson sticker on Herbs board that says " This both sucks and blows!"

 I reckon it could be a totally new era of surfboard design. Im hoping thats what we are seeing.


But the principle at work is that the design will influence a similar level of control to a board without adding any more drag than a standard finned board, I dont believe that its designed to go faster. Its not a jet effect.

I agree about redirection of the flow of water and what it would/does do on an induction board  – honestly I would’ve thought that’s obvious – and Herb’s orientation of the ports after lot of trial and error speaks for itself – I leave that at that.  I sorta think I differ more with above quote about toe-in on fins though.  I believe toe-in shortens turning radius. But … hell i dunno.

for now i’m assuming all the other ‘induction’ boards said to have been seen in action prior to herb’s post were finless too ? or finned ?

hmmm another detail to consider by patent proponents hehe



not true

As I've posted before, I saw Tom Morey's board (and had read his Surfer Magazine article) back in the early 70s.  Tom was visiting at Caldwell's house, next to Roehner's in Kona on the Big Island. Caldwell's house was directly in front of the Hano's surf break FWIW.

Morey's air ports were made in conjunction with step bottoms and vented at the step.

I saw another board in possession of some hippie a little later, with six or seven steps on a 1/4" concave board.  The concave ran full length, the steps were approximately equally spaced and each step had maybe six ports about 1/8" in diameter.

Five years ago I reshaped a ancient windsurfer hull that had a single step bottom with two large ports in the deck.  Last time I rode that board with a Horan star fin my foot sllipped off and I drove my knee full force (I'm 240 lbs) into the rail.  Still haven't patched that gash but at least I got only scratches in my knee.

So what?  Haven't seen another vented/ported surfboard and it's 37 years later.  They were a hassle to make and you had to be really careful they didn't leak.  Anyone wants to make cute/odd vented surfcraft has my blessing but many of us have better things to do.

perhaps a 3% chance to get a patent that pays off is enough motivation for those who take the time to make 'em work?  " )



I went through some of this when dialing in the surf trux. The setup is that the fins are at 10.5" and 3.5", the rear fin fixed and double foiled, and the side fins are floppy, but end stopped in toe in. Both rail fins rotate freely in toe-in. That is, when you turn, you can only use the inside rail fin (and rear fixed fin), and only when the inside rail fin hits the end of travel. If the end-stop was at 1/8", you could draw a nice line, tight. If the end-stop was at 3/8" or greater, you can certainly turn the nose of the board, but you slide through the turns so hard it is not worth it.  Whereas it is EASIER to turn the nose with more toe-in (ie: spin the board), it is HARDER to turn the velocity of your center of mass. So if you needed to come tightly off the bottom for a vert hit, you could do that more easily on the low toe-in board. The high toe-in board just could not turn fast enough to make the same vert hit. 

And the rest…it is just physics. With no fins or induction ports and a flat bottomed board, you can only slide through turns. The fins provide force towards the center of the turn. If the induction ports don’t do the same thing then they are not very useful. Herb says they are useful - so they must be applying force towards the center of the turn. To apply force toward the center of the turn, you have to re-direct water away from the center of the turn. I am sure Herb will reveal a lot more when he is ready. I know I will be interested - I think it is COOL.


ehem herb? your turn on the mic hehe we’re all waiting 


…TM designed (I dont know if he really was the builder or only the shaper) 3 prototypes not 1

I shaped 1 couple of years ago but not until early last year that I put it on the water.

I decided to go after I saw a Loehr fish with “induction tubes” so I interchanged couple of e mails with GL and Mkee then I built the board

now is my main board for everyday surfing

In the next days I ll try to put it in the photo section