venturi bottom on fish

so, i have been digging in the archives, and was wondering if any of you guys have tried a venturi bottom on a fish?

by this i mean the more sharp edged tail only type, not the concave/bonzer versions.

i recently say a shortboard that had these channel like ventrui grooves in the tail area just ahead of the fins, say 8". one went, in an arc, along the side fin toe angle out the tail. the other started in the center of the fin cluster out the tail in a triangle, say 3" wide at the exit on the tail. and, i remember seeing a shipman twinzer with what i am thinking of.

i have tried concaves on fish but not this. any feedback?

*bearing in mind the outline is basically retro inspired.


hi Native !

yes I have .

My 1975 [thereabouts] Len Dibben [west australian] twin fin "fish / swallowtail has a venturi from parallel with almost the front of the two side fins right back through the tail , similar to Larry Bertlemann’s from around the same time , I think , looking at some magazine photos …


"Bert’'s [?c.1975?] quiver …

(Kirk , was it YOU who was asking about Bert’s designs ? [sorry , I forget , who’s p.m.'ed me ])

anyway , here they are …

And , here’s one in action [at Bells , I think]…

cheeeeers !


Probably more like ‘78. Winter of 76/77 (I think) was when MR made the big North Shore twinnie splash in the mags. That Bertelman quiver was probably about a year later. Could have been Easter 77 but I’m bettin’ 78. One big note on twin bottoms, all those twins of that era had vee (hard to see in that photo but I know they’re there, I picked up and looked at a couple of those Coke-a-cola boards when LB was in FL). Vee was the overall improvment that made the things work. Still is true today. You can add concaves into the mix but the vee has to be in a twin or you have to add a trailer fin (or trailer fins in a 4). Otherwise you get track.

wow…larry bertleman is moving in that picture

thanks chip,

how was it by the way?

thanks greg, i knew about the vee part, most of my boards are quads anyway. just wondered about the venturi thing. i like how the concaves - double into single - are working for me, but just wondered if anyone has tried the venturis. i can see the vee in the top photo, but no other contours.

the more i think about it, actually feeling a difference on a fish, a board that is by design very flat rockered and fast already, is probably minimal.

thanks for your feedback,

"how was it by the way? "

hi Nativeson !

it was like this

…wide , thick, heavy, bad rails… a dog to duckdive …

I nowadays would only use this [if at all !] in waist [?waste?] high and under onshore or semi-onshore summer surf , when I need to remind myself how far surfboard design has progressed !

I much preferred THIS one …thinner , lighter , more vee, a wing to pull in the tail ,and as Greg pointed out , from around 1977-78.

[N.B. - NOT the original fins , unfortunately !]

… I just finished reading an article in november 1978 surfer , where M.R. mentions Reno Abellira riding a small twin fin at the 1976 ‘Coca Cola Surfabout’ [at North Narrabeen] , and how after checking out his board , he got inspired to re-explore short wide flat twin fins again [M.R. was riding McCoy square-tailed ones* in 1970-71 , as were Mark Warren and Terry Fitzgerald ].

  • My brother had one , which became my first board [minus the twinnies …by the time I got it , it had a glassed on wood single fin !!]


…wide , thick, heavy, bad rails… a dog to duckdive …

the last 3 things there that i avoid all together, for sure

I nowadays would only use this [if at all !] in waist [?waste?] high and under surf , when I need to remind myself how far surfboard design has progressed !

sometimes a little torture is good for new ideas huh? i would probably just hang it on the wall, and thank god i have other options. hard to make a good case for bottom contours if the rest of the board sucks.

thanks for the photos.

" hard to make a good case for bottom contours if the rest of the board sucks.

thanks for the photos " …

a] WELL said !!

b] …you’re welcome .


here’s a bonus bert twinnie “cover photo” for you to enjoy !!

…'Flame’s [Larry Moore] legacy lives on …

hi Rob !

just thought you might like to know that the “horrible 1970s twin fin” of mine actually worked really well today …as a kneeboard !

I could feel the “venturi bottom” between the fins actually working well , during bottom turns, and when in the pocket .

Tiny little clean waves [‘head high’ , when kneeboarding !] . It’s probably actually the most memorable two hours of waves [because it was empty , and offshore too !] that I have had on that board . [On a couple of waves I stood up , as well ].

cheers !


great, thanks chip.

it felt a bit faster, i assume?

glad to hear you got some good waves. i am on my way out now for a look at the waves now…

what a great life we have hey?

hi Rob ,

yeah , I’m not really sure if it WAS faster , or just “felt” faster , because of being closer to the water , and also perhaps having my weight more towards the MIDDLE of the board ?

Whatever …it sure felt GOOD !!

interesting anyway.

its funny how in the discourse of an idea, one can think it over, and then be over it at the same time, hey?

seems like everyone else is anyway, lol.

thanks for the feedback.

another Bertleman.

Chip glad you got some waves on the twinnie.

This was Mark’s first twinnie based on the Reno fish.

and this was Reno riding his…

…one more of Reno’s board…

photo : the late Peter Crawford [R.I.P.]

How times have changed for pro surfers eh ? the caption read…

“seven out of ten pro meets are held in sloppy beach breaks”

well, on a wide swallowtail twin fin , anyway.

Here’s a couple of ‘venturi’ shots for you Rob, hope they are helpful ? [as you can see, the board is old , and pretty wrecked. I call it “Orca” , because that red fin you see there almost did away with my manhood and my main artery in the left leg few years back.]

As for a venturi bottom on a “real” fish …

I’d say try it , and see how you like it ! ( I’d be keen to hear your thoughts / feelings after you ride one . )

cheers !


looks like that board could be sanded down, add a layer of glass, and re hotcoat w/ pigment mixed in. you could blend in the blemishes and revive it.

It would actually be cheaper to make a newer , thinner , lighter one that surfs better , Scott. [Pity you don’t live here , I’d give it to you … but, you should see the carnage on the nose !!!]


carnage on the nose eh? wheres the photo? lol… i actually buy boards like that to repair and revive… too bad i dont live there. I like having vintage boards, fun to surf and make good wall hangers too.

hi native !

Time for the yearly ‘follow-up post’ …

DID you ever end up making a venturi fish tail board , or did you just can the idea ?

just curious …

cheers mate !