I have played around with bonzers in the past and more recently cut bonzer concaves in a twinzer fish...and started wondering if anyone varies the position of the peak of their concaves (see diagram) - I've always done them so the peak is centred in the concave. It sort of makes sense to push this peak out to the rails so the water flow is accelerated out to the inner face of your fins??? I may be showing my lack of knowledge here and you may all be scoffing and thinking does this guy know anything??? Feel free to shoot me down but if you have done it/always do please set my mind at rest???
If it does work - can you push it out so far that it almost becomes a channel???
I've only done the center peaked bonzers on a couple of funboards. They both worked great. My advice would be to try the pushed out concave. You never know until you try.
The peak close to the fins makes a lot of sense. Just like channels.
I would try to make the concave follow the outline, and not a straight line.
You can see the trend in modern single channels which are curved from the middle to the tail. Based on Proctor’s shaper, straight channels work very much on an on-off fashion providing too much tracking and making it marginally stiffer to change of direction. But once the tracking effect is gone, it is gone. You want tracking that would work through the turn and always on, but allowing the flow of the turn, hence the channel/concave following the outline.
I would not make the concave too deep. But keeping it safe is what kills innovation.
i’ve done a couple twinzers like yours. They work well, and that “lip” by the fin does function a little like a channel. In fact, the Simzer i did a while back had it like that.
I have gone back to the central position though as it is easier for me to finish the board as the sander head fits in that shape better, not for any other reason…
I do em sometimes too, they work well, give you more to push against and hold well .....maybe a bit less freedom off the top, but with a quad set up and pulled in tail, they hold very well.....
