3 fin bonzer fin placement

I searched the threads could not find anything , I am looking for fin placement numbers and specs on the side fins. Thanks

What size board are you considering? I don’t have anything for you, just curious myself…

Thinking 7’ egg. But may go as short as 6’6".

Have you seen the stuff at Surfy Surfy?

Hi MarshflyUSA -

I’m no expert so take with a grain of salt. I have measured a few boards in my time though.

On the triangular tri-finned boards one of the issues is fin placement. It is often acceptable to place the leading fin of the rear fin about even with the trailing edges of the side fins. If placing a center box, allow enough room for a bit of adjusting but that’s pretty standard.

On the triangular side keels for about a 7’ board, the side keels wouldn’t be too far off if placed at about 12" up from the tip of the tail. The side keels are generally about 10"-11" long and 3" high. The trailing edges are slightly raked back. The side fins are generally slightly toed in and rather severely canted.

The Surfy Surfy link by Jrandy has some good pics. I’ve mentioned it here before… it is kind of pointless to try to duplicate fin placement from one board to the next unless you’ve got everything else exactly the same. Minor differences in rocker, rail foil, outline and bottom contour will have a big effect and render any fin differences difficult to decipher.

With that in mind, consider a center box. When installing a center box on a bonzer design, you will find it easier if the stringer is left as kind a dome between the concaves rather than a sharp peak. In the pic below, take a good look at how the top of the stringer is left with 1/2"-3/4" of foam on either side of the stringer.

Thanks for the info. What would your opinion be on small wave performance for the bonzer? I have read many takes on the design. Ace had some very insightful conclusions with his variations on the design. I am curious to see if one will go well in the conditions we have in Texas.

John, you are 100% right that taking elements off one board and placing them on a different sized/shaped one creates variables. Same could be said for riders and waves. Your numbers also seem to align well with the info that can be mined from the Campbell brothers themselves:

“The general rule is to place your center fin 5- 3/4” from the tail of your board."

“The Bonzer side fins have a base totaling 9-3/4” on each side, and a maximum depth of only 2-3/4”.”

“Our establishment of the triangular arrangement of the three fins, with side fins placed forward of the center fin. The side fins were placed 10 1/2” to 12” from the tail and 1 1/2” to 1 3/8” from the rail.”

Sheesh… I missed all of that. I was going by what I remembered when some friends brought a broken Bonzer they had retrieved from the jetty at Silver Strand in Oxnard. They asked me to build some sort of knock-offs for them. Mine had smaller runners and less severe concaves.

This was before the magazine and Bing/Eaton/ACE had seen this sort of design but not by much… within the year, the magazine ran their article and the design became somewhat popular.

ACE arguably has more experience shaping this type of design than anybody on the planet.

I thought the rolled spine would be to add hold and reduce lift rather then to make it easier for the installation of a box.

Hola from Ecuador…Not sure about who has done more. I remember the day Eaton said I had shaped more EATON’s than him…I stopped doing them on a production scale a long time ago. So I am pretty sure others have passed me numbers wise? I do not consider machine shapes as numbers shaped though:…To the question of fin placement. I had developed a sliding scale jig FINDICATOR that had marks for different board lengths. This had box and side fins marked. But different tail widths rockers etc dictated where the fins would go. After awhile I never measured anything. Just set the jig slide a little up or down make the dots…seemed to work out pretty good I still use same formulas for other types of boards. So to give some numbers I would need to be back in OB. There seems to be enough info from other sources to get started. Center fin size and shape is other important detail. I had some custom ones that really made a BIG difference in performance. ACE

Hello ACE - I can remember seeing quite a few Eatons with various ‘Bonzer-like’ contours over the years. In my opinion, ghost shapers deserve more credit than they get and in your case, more credit than you give yourself. I’ve also seen evidence (right here on Swaylocks) of your efforts to push the boundaries of the original design. Anyway, hats off to an unsung hero.

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