pick the thruster.

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Obelix said..
Are these slotbox side bites common with the kiteboards and surfboards, or are they specific to windsurfers?

slotbox is a windsurfing thing.

side bite fins get used on windsurfers, kites, surfboards, sups.

The bottom one.
several are trailing Tri fins .

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Gestalt said.. slotbox is a windsurfing thing. side bite fins get used on windsurfers, kites, surfboards, sups.

It is, but really its a Futures with FCS grubs

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forceten said..
The bottom one.
several are trailing Tri fins .

i guess so or we could say

2 of the photos are twin fin setups or 2+1
1 is a bonzer
2 are widow makers or 1+2
and 1 is a thruster.

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Mark _australia said..

Gestalt said.. slotbox is a windsurfing thing. side bite fins get used on windsurfers, kites, surfboards, sups.

It is, but really its a Futures with FCS grubs

never thought of it that way but your right!

A tri fin board will go fastest with the single fin in place but with blanking plates fitted in the thruster boxes. In this way, you only get the drag from one fin tip and from the fin area of the size of fin used. Thinner fins tend to be faster that fat/thick ones. The torque lift from a relatively long single fin allows the board to ride on its tail more.

When used as a tri fin, you get the tip vortices from three fns which will reduce your top speed.

As others have said, the best compromise when you want the trueing and high wind benefits of a tri fin set up but with speed, then it's best to use a longer single fin but shorter thruster fins. The longer centre fin then gives you more torque lift at the tail.


When it comes to toe in angles for your thruster fins then you can experiment with off set fins from companies like K4.
But bear in mind that most people fine tune their toe in for turning on the wave, not for straight line speed. Increasing toe in for the thruster fins often makes a board slower in a straight line but better on the wave face.
it's worth adding that boards with more Vee at the tail seem to benefit from more toe in than boards with less Vee. It's a myth that all wave boards need toe in for thruster boxes, although some hull shapes definitely do.
Using asymmetric thruster fins starts another whole discussion because they definitely need some toe in just to reduce drag, with 2 degrees usually being the minimum just to set them in neutral...

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Mark _australia said..

Gestalt said.. slotbox is a windsurfing thing. side bite fins get used on windsurfers, kites, surfboards, sups.

It is, but really its a Futures with FCS grubs

Futures fins have less width than sb, sb being the same as US box. FCS grubs are smaller, both length and thickness than any sb I've seen, and no official sb exists so nether do the screws, cobra has has at least 2 versions .Slot Box, invented by Tabou, who did Not copywrite, made first by cobra for many. Made when extra boxes were adding weight. It's initial problem was the screws were overnighted and stripped, still occurs, operator error.
For its intended use it works ok, for me to purchase , I have Flikka, Simmer, Cobra, they are expensive. US box are way cheaper, cut shorter to eliminate a little weight.

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Gestalt said..

forceten said..
The bottom one.
several are trailing Tri fins .

i guess so or we could say

2 of the photos are twin fin setups or 2+1
1 is a bonzer
2 are widow makers or 1+2
and 1 is a thruster.

Some of these boards are surf boards. The terms used are more clearly defined on surf boards. They don't transfer over so keen.Bonzer 3/4/5 variations

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Basher said..
A tri fin board will go fastest with the single fin in place but with blanking plates fitted in the thruster boxes. In this way, you only get the drag from one fin tip and from the fin area of the size of fin used. Thinner fins tend to be faster that fat/thick ones. The torque lift from a relatively long single fin allows the board to ride on its tail more.

When used as a tri fin, you get the tip vortices from three fns which will reduce your top speed.

As others have said, the best compromise when you want the trueing and high wind benefits of a tri fin set up but with speed, then it's best to use a longer single fin but shorter thruster fins. The longer centre fin then gives you more torque lift at the tail.


When it comes to toe in angles for your thruster fins then you can experiment with off set fins from companies like K4.
But bear in mind that most people fine tune their toe in for turning on the wave, not for straight line speed. Increasing toe in for the thruster fins often makes a board slower in a straight line but better on the wave face.
it's worth adding that boards with more Vee at the tail seem to benefit from more toe in than boards with less Vee. It's a myth that all wave boards need toe in for thruster boxes, although some hull shapes definitely do.
Using asymmetric thruster fins starts another whole discussion because they definitely need some toe in just to reduce drag, with 2 degrees usually being the minimum just to set them in neutral...

While I agree with some.
Experiment, K4 fins are marketed with toe in , with various degree1/2/3, these all have asymmetrical inside , flat, these are the Graham Ezzy Series. YOUR best speed line is it's best to use a long single with short thrusters
Would a three fin cluster of three equal fins produce speed ? Oh it's not going to feel the same, but it's speed we want, not me, but it's the question. I don't think boards need toe in, wave or otherwise. Others using toe in are Witchcraft and Simmer.
cobra use moderate, less than one, others none. I use about 1.75, and both asymmetrical and symmetrical fins.

FOR THE OP, you want symmetrical fins

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forceten said..

Mark _australia said..

Gestalt said.. slotbox is a windsurfing thing. side bite fins get used on windsurfers, kites, surfboards, sups.

It is, but really its a Futures with FCS grubs

Futures fins have less width than sb, sb being the same as US box. FCS grubs are smaller, both length and thickness than any sb I've seen, and no official sb exists so nether do the screws, cobra has has at least 2 versions .Slot Box, invented by Tabou, who did Not copywrite, made first by cobra for many. Made when extra boxes were adding weight. It's initial problem was the screws were overnighted and stripped, still occurs, operator error.
For its intended use it works ok, for me to purchase , I have Flikka, Simmer, Cobra, they are expensive. US box are way cheaper, cut shorter to eliminate a little weight.

It was a joke man :) that really slotbox was not really an invention, it is just like a Futures but with the better retention laterally that we need.

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Mark _australia said..

forceten said..

Mark _australia said..

Gestalt said.. slotbox is a windsurfing thing. side bite fins get used on windsurfers, kites, surfboards, sups.

It is, but really its a Futures with FCS grubs

Futures fins have less width than sb, sb being the same as US box. FCS grubs are smaller, both length and thickness than any sb I've seen, and no official sb exists so nether do the screws, cobra has has at least 2 versions .Slot Box, invented by Tabou, who did Not copywrite, made first by cobra for many. Made when extra boxes were adding weight. It's initial problem was the screws were overnighted and stripped, still occurs, operator error.
For its intended use it works ok, for me to purchase , I have Flikka, Simmer, Cobra, they are expensive. US box are way cheaper, cut shorter to eliminate a little weight.

It was a joke man :) that really slotbox was not really an invention, it is just like a Futures but with the better retention laterally that we need.

Oh I like jokes, let me know when you do another one. appropriate winky face

agree its not a reinvention of a box, it's a variation of a USBox using a cassette ,I say this as most USBox fins with the pin removed fit right in , length an issue maybe, and to actually fit, cut off the tongue and add slots for the screws if a older model.

i may be missing bits here and there on what's been written above and possibly stretching actual knowledge but hopefully not too far off topic,.

Ben Proffitt did a vid of speedsailing various multi-fin and single fin boards. i was impressed and inspired by his results and wish i had the link at the ready. he had great speed on multifins and all recorded speeds on all the config's and had them all tabulated on a dry erase as i remember. differences in speed between variations would not be a concern to freeride environment

but my conclusion was that although multifins may not have the efficiency of a single fin, esp a nice hi-aspect slalom etc - they are not just getting dragged thru despite themselves. there is bit higher pressure under the board and as we know - pressure acts in all directions and so water is escaping from under the board 360 degrees, some even being squished forward, making a little wave ahead of the planing surface. accordingly - the fins should be aligned to the flow and their angle relative the board will depend on where they are located.

if you're ok with that idea, also realize that applies to water very close to the board whereas water a little deeper is un-disturbed. this implies that a normal bite can only be parallel to some of the flow over its surface.

i think there are 2 companies making bites with a twist to account for this - witchcraft and techtonics-produced CNC fin co. designs. i tried some CNC fin co prototypes and they really seemed to work well but my testing was definitely not scientific control/experiment with gps results etc. i simply put in a set and loved how much better i was staying upwind, and felt faster. the last i know of - i believe Robby Swift was riding the tectonics/CNC fin co design.

witchcraft.nu/boards/trifin/

Before any multi fin surf boards came out my first surfboard was an age & it had little nubs the bloke told my dad there like training wheels so he bought it for me .
A 6'2" board for a 8 year old weighing probably 20 kg I was very small
wish I still had it unfortunately it was stolen
It took me a good 10 years before I could duck dive it was a great board they built them to last then

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LNC said..
i may be missing bits here and there on what's been written above and possibly stretching actual knowledge but hopefully not too far off topic,.

Ben Proffitt did a vid of speedsailing various multi-fin and single fin boards. i was impressed and inspired by his results and wish i had the link at the ready. he had great speed on multifins and all recorded speeds on all the config's and had them all tabulated on a dry erase as i remember. differences in speed between variations would not be a concern to freeride environment

but my conclusion was that although multifins may not have the efficiency of a single fin, esp a nice hi-aspect slalom etc - they are not just getting dragged thru despite themselves. there is bit higher pressure under the board and as we know - pressure acts in all directions and so water is escaping from under the board 360 degrees, some even being squished forward, making a little wave ahead of the planing surface. accordingly - the fins should be aligned to the flow and their angle relative the board will depend on where they are located.

if you're ok with that idea, also realize that applies to water very close to the board whereas water a little deeper is un-disturbed. this implies that a normal bite can only be parallel to some of the flow over its surface.

i think there are 2 companies making bites with a twist to account for this - witchcraft and techtonics-produced CNC fin co. designs. i tried some CNC fin co prototypes and they really seemed to work well but my testing was definitely not scientific control/experiment with gps results etc. i simply put in a set and loved how much better i was staying upwind, and felt faster. the last i know of - i believe Robby Swift was riding the tectonics/CNC fin co design.

witchcraft.nu/boards/trifin/

do you have any more details on CNC fin co... unfortunately i have an addiction

Side bites recup some of the lost grip when running a smaller single. If you want maneuverability then you can use a small single with no side bites. It'll be prone to more sudden spinouts and will affect the low end drive.

You need to find balance between your most used sail, side bites and center fin.

Single fin vs trifin speed chase. Witchcraft Chakra 95 with 20cm centre fin and 10.5 pre-twisted side fins (4.5? toe-in...) vs Goya FW 95 with 25cm single fin. Both sailors of similar weight and skill and both powered up on a 5m sail:

When they swapped the result was the same. A part of the difference may have come from the sail but still then the difference is significant. On a broad reach the difference was less, up wind more.

^^ I've got a Goya One FW 85 of similar vintage. Its slow, single fin or with thruster setup.
Try your fin combo in the Goya and see if it goes faster. Or better still, post me a set and I'll do some testing for you. I've got a GPS and cam.

Actually, I think my Goya is a year earlier than the one in the video. It doesnt have any toe-in. On your website it says 'Please note that the side fins only work well for Witchcraft boards or boards with the side fin boxes placed under a 2? toe-in angle to provide the least drag and best turning behaviour.'

Could I expect much, or any benefit from the fins if my board has no toe-in?

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PhilUK said..


Could I expect much, or any benefit from the fins if my board has no toe-in?

No. Unless you modify the fins to turn them inside the boxes. Minituttle boxes are wide enough to do this and have the screw in the centre.








I have not sailed the Goya but have checked out the shape and there is not much in it. I always check out shapes when I get them in. Out of interest but also to be able to advise customers better when they come from other brands. Maybe the older versions had more rocker, I don?t remember. Rocker line and outline between the Chakra and Goya are pretty similar, enough to hardly have any difference is speed. The main difference is the harder rails on the Chakra but that makes it release earlier, not really make a difference once fully planing. They both said the Chakra was sailing more in control and easier to turn. In the end single fins are faster off course but then you need outboard straps and more body tension to keep the board in the water. Trifins have the advantage it is easier to control more fin area so when set up correctly so they do not add drag, this translates into more speed as well whilst sailing more relaxed.

Select to expand quote

Gestalt said..

LNC said..
i may be missing bits here and there on what's been written above and possibly stretching actual knowledge but hopefully not too far off topic,.

Ben Proffitt did a vid of speedsailing various multi-fin and single fin boards. i was impressed and inspired by his results and wish i had the link at the ready. he had great speed on multifins and all recorded speeds on all the config's and had them all tabulated on a dry erase as i remember. differences in speed between variations would not be a concern to freeride environment

but my conclusion was that although multifins may not have the efficiency of a single fin, esp a nice hi-aspect slalom etc - they are not just getting dragged thru despite themselves. there is bit higher pressure under the board and as we know - pressure acts in all directions and so water is escaping from under the board 360 degrees, some even being squished forward, making a little wave ahead of the planing surface. accordingly - the fins should be aligned to the flow and their angle relative the board will depend on where they are located.

if you're ok with that idea, also realize that applies to water very close to the board whereas water a little deeper is un-disturbed. this implies that a normal bite can only be parallel to some of the flow over its surface.

i think there are 2 companies making bites with a twist to account for this - witchcraft and techtonics-produced CNC fin co. designs. i tried some CNC fin co prototypes and they really seemed to work well but my testing was definitely not scientific control/experiment with gps results etc. i simply put in a set and loved how much better i was staying upwind, and felt faster. the last i know of - i believe Robby Swift was riding the tectonics/CNC fin co design.

witchcraft.nu/boards/trifin/

do you have any more details on CNC fin co... unfortunately i have an addiction

i dont have any more detail off hand except it was formed by engineer from annapolis and his friend in outer banks, north carolina. i can prolly get more info on CNC and when i do, will post again. otherwise, i think the thruster fins offered now by tectonics is their design, in production and is how they may be purchased. i'm not certain, but phone call or msg to dennis parton at tectonics, maui would more definitively answer that. it's neither here nor there, but i think their designs may also be OEM on some race sups.

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Witchcraft said..

PhilUK said..


Could I expect much, or any benefit from the fins if my board has no toe-in?

No. Unless you modify the fins to turn them inside the boxes. Minituttle boxes are wide enough to do this and have the screw in the centre.


I have not sailed the Goya but have checked out the shape and there is not much in it. I always check out shapes when I get them in. Out of interest but also to be able to advise customers better when they come from other brands. Maybe the older versions had more rocker, I don?t remember. Rocker line and outline between the Chakra and Goya are pretty similar, enough to hardly have any difference is speed. The main difference is the harder rails on the Chakra but that makes it release earlier, not really make a difference once fully planing. They both said the Chakra was sailing more in control and easier to turn. In the end single fins are faster off course but then you need outboard straps and more body tension to keep the board in the water. Trifins have the advantage it is easier to control more fin area so when set up correctly so they do not add drag, this translates into more speed as well whilst sailing more relaxed.

Thanks for the info.
I eyeballed a 2016 version of the Goya I bought on the beach and it looked to have a reasonable flat planing section, not appreciating it was the 2014/15 version was the one I was going to buy. It certainly turns well enough.

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Mark _australia said..
Still intersted to know if those side boxes are toed in?

K4 once had the popular fins shown with toe in.

some were very small, for sure Simmer do have about 1.5 degree toe in.

Gestalt, How did the bonzer fins you mentioned work? I am toying with the idea of a bonzer 5 fin set up, as i love them on surfboards, but not sure how the can't and toe in angles would translate to a windsurfer.

Efficient single, tiny sidebites, lot's of wind, fast pilot, flatish rockerline, hard rails.