I am planning on shaping a high performance 5 fin bonzer around 6 ft. I like 19.5 X 2.25 double wing swallows. I am wondering about the tail (bonzer) section. How should I place the 2 channels/concaves in relation to where I want my 4 outer fins placed? Also, should the center of the board have any concave? I was thinking of flat entry, with a flat or slight single concave in the middle. I detest double concaves in the middle so I would rather not go that route. Any help would be great.
if you happen to be in so cal (san diego to be exact) i have all kinds of bonzers, from origional 70s bings to current 3 and 5 fins bumble bee types as well as very high performance 5 fins as well, im always happy to loan or show these guys to anyone who is trying to grasp the bonzer shape…its alot to swallow, im not sure if i get it yet…and its been a long time
Find a thread called ‘Lokbox bonzer fin position help’.
That will in turn give you some links to other threads that’ll probably tell you all you need to know.
Somewhere in there is a diagram Burnsie computer drew of the bottom on his bonzer.
It might actually get a bit confusing, because a lot of people have picked the ball up and run with it , put their own take on it , but , you know …
Your flat to single idea sounds about right ( I was in your position about 4 yrs. ago and did heaps of research on the web),but an actual CB bonzer owner will tell you more.
Have fun with it.
all of what you seek is in the archives, just dig for it. Search Bonzer and Burnsie.
Gather water, bend water, compress water, exhaust water…
Gather water, bend water, compress water, exhaust water.................
That’s what I was told when I was riding Bings in the early 70’s… venturi and all… kinda funny now that I know water doesn’t compress.
There are “reasons” why I do not make em ride em anymore also.
This might help
This might help
Hey NuclearFishin , Is this a NZ made bonzer ? Any NZ u rekon can shape good twin keels ? thx …
no, it’s a bonzer shaped by Gary Hanel in San Diego.
Yep , A Gary Hanel taken from a thread on the Surfermag Design Forum.
Plenty of bonzer stuff there btw , Reef. Although you probably know that.
AnDi, Roger Hall would most likely be the man for twin keels in NZ, he’s bin making them since the '70 s.
There’s a few other guys who make a nice quad fish, too.
Yea…this issue of the incompressability of water comes up every so often.
The reality is, you’re not compressing the water. You’re just forcing it to change direction and, to a degree, restricting it’s flow by channelizing it, and increasing it’s velocity. Does it work? I don’t know… but it sounds like it should if you study your physics.
…the bottom is: flat entry then concave in the middle (not more than 1/8 in average boards) then bonzer channels under feet
(not more than 3/16) more deeper under back foot fading out in the very tail
not “gauge” the rails with the channels
keep the thickness (bulk on the stringer not in the rails) in the place you put the back foot then thinned out a lot to the very tail
Below a is link to Eaton’s site,
There is no doubt that Eaton makes nice products, and bonzers are surely one of them. But you simply can’t funnel, channel, etc. flow and expect it get more out of it than was originally there. If you know of a way to do this, copyright it immediately - the world will beat a path to your door.
Basically, every time you touch the flow, you exchange something. At best it’s a zero sum exchange. But given the medium – water- that is, a viscous liquid, it not a zero sum game, not even at best. Channeling flow will not make you go faster, it may do a lot of other stuff, desirable or otherwise, but make you go - no. You could say planing is a kind of ‘channeling’, but the dynamics are very different from ‘squeezing’ and ‘squirting.’ Anyway, in planing you don’t get more out of it than what’s there to begin with, you get far less - but enough.
I’ve been told bonzers like to ‘run’. That they [bonzers] don’t like to turn a lot. I’ve actually never ridden one – but I’ve spoken to many who have. The bottom contours and fins, all tend to make a bonzer want to track-a-line, and do so with some added stability.
Of course, ‘opinions’ differ.
“Channeling flow will not make you go faster, it may do a lot of other stuff, desirable or otherwise, but make you go - no.”
Anyone with a basic understanding of physics knows this…yet some people still swear by Bonzers - and most surfboard manufacturers use concaves… why?
hi Ace, can you please be more specific if possible?
Here we go…
There’s so much excess energy (energy not accounted for under and around the board) that at this time, with the level of sophistication currently practical in terms of its application to surfboard bottoms and waves, there is no way to quantify energy in and energy out and some sum (or difference) of energy. You would have to measure the volume of the concaves as they change from entry to release, figure out the mathematical equasion that expresses that change in volume, then measure velocity and pressure changes (at the same time) of the water as it passes along that channel (and do it at varying distances from the surface of the bottom of the board), then take into account varying degrees of pitch as you move through a turn or angle down the face of a moving, curved plane of inconsistent speed… and that’s just the beginning!
My argument is… If you have a different voume at at the entrance of the channel than you do at the exit, as most bonzers do, you won’t have a zero sum of energy to begin with.
This is not to say that it can’t be calulated. It’s just that today, with what we know (and what we don’t know), for any of us to sit at our computers and, without any data whatsoever, flatly deny that the laws of physics dictate bonzers “don’t work” is absolute nonsense.
Again, I don’t know if the do or don’t. But it’s certainly worthy of investigating. So let’s all build bonzers and it it!
“I’ve been told bonzers like to ‘run’. That they [bonzers] don’t like to turn a lot. I’ve actually never ridden one – but I’ve spoken to many who have. The bottom contours and fins, all tend to make a bonzer want to track-a-line, and do so with some added stability.”
From my experiences on a wide 5’0’’ bonzer 5, this is only true until you get them started turning, at which point mine loves to go rail to rail & carve quite nicely. On steep, fast, straight drops, it has gotten stuck going straight while I lean into the bottom turn, resulting in a pretty impressive fall. I expect this is related to the lift created by the side fins, but could easily be wrong. I see it as both sides being engaged and lifting when going straight. Once on the face of the wave, after a bottom turn, your outer rail is somewhat less engaged in the water, resulting in uneven lift which may be easier to overcome.
I will see if I can figure out how to work a program which is available to us at my university, and I may be able to generate some useful graphics to illustrate what happens when an incompressible fluid flows past foils in a bonzer-type arrangement.
hi Ace, can you please be more specific if possible?
I have gone over this before. Please look it up. It brings back too many painful memories. The main thing I really have to say about “Bonzers” is that, as they were, I do not use THAT anymore. The heading of this was “Theory for Bonzer design?” What I posted was the “THEORY”.
me last week