Are you matching the toe and cant of your front and back fins?
I have a wider, thicker shortboard I am pretty sure will be great as a quad, so I plan to do a conversion on it. I was given some recommendations by a die-hard quad-natic and measured them out on the board, but realized that the toe-in of the back fins would be slightly less than that of the foreward fins (but the cant would be the same). I’m not sure if having different AOA’s would create drive (since thruster back fins are set straight and are used to create drive) or create drag (would the optimal angle of the front fins be diff than that of the back fins).
Presuming single-foiled fins to start with (in other words I would be running all side fins and not using thruster “center” fins) and then maybe start sticking some double-foiled fins in the back to feel the difference.
I was wondering if I should just simplify things and run the back fins parallel to the front fins, but then thought this might just result in a looser (too loose) board.
I’ll try to post a pic of the angles mapped out on the board later tonight.
Feel free to digress as I am interested in theory as much as simple “You should do this” statements.
there was a recent thread by oldy called I think “quad fin templates” , which covered a few of these things . [It’s probably on “page 2”, at the moment ?]
And , would you also try the ‘canards’ , if you go with boxes ?
I ask , because at the moment , I have those options on my new “bushfire fish” [have you seen it , by the way ??]
All four of mine are pretty much parallel with each other …pointing towards the nose . [Don’t ask what toe-in that is …]
I have the options now of canard , twins at front , smaller at back , vice-versa , and …5 finner [“of course” …]
Being that the side four fins are all fcs plugged , they have whatever that cant angle is that is built into the fcs plugs . [geez , I’m a technical guy , aren’t I ?!]
anyway , hackman , I hope this helps …this is just what I went with on the prawn , and also on the bushfire ‘fishes’…
Are you matching the toe and cant of your front and back fins?
… I was given some recommendations by a die-hard quad-natic and measured them out on the board, but realized that the toe-in of the back fins would be slightly less than that of the foreward fins (but the cant would be the same). I’m not sure if having different AOA’s would create drive (since thruster back fins are set straight and are used to create drive) or create drag (would the optimal angle of the front fins be diff than that of the back fins).
I like to point the fins at the same spot. The location of that spot depends on many other factors. Other opinions may differ, but this is how I do it.
I use 1 or 2 degrees less cant on the rear fins. I use a ratio to calculate it. If the back of the rear fin is 3/4 the distance from the stringer than the back of the front fin’s distance from the stringer, then I use 3/4 of the cant of the front fin on the rear fin. That’s just an example.
{ Distance2 divided by Distance1 and the 0.xxx multiplied by Cant1 equals Cant2 }
Chip- thanks for the quick reply! The fins already on the board are Futures, but I plan to put FCS fins in (I feel most confident routing and installing those since that is the system with which I have the most experience). I can also fabricate my own fins easily to fit FCS if I want (I knew that would get you drooling!).
I know the FCS plugs have their own cant built in, but I manipulate a few degrees here and there. I’m known for my perfect-match FCS repairs around my area since I measure over and over and over and make templates for each and every board I repair… simple angle tools do not work so well when I have to account for concaves, vee, etc.
Ozzy- killer diagrams and formulas! Thanks for the info. I will definitely study them again this evening when I have more time (“real” job is demanding too much of my time today to really absorb the info).
I have had a few quads made now and like the front fins canted out a few more degrees and the rear fins toed in less (a bit straighter). This board is 6ft and front fins are changed between 6 and eight degrees cant with 4 degrees toe and the rear are 4 degrees cant and 2 degrees toe.
I used Probox on this one so I could play around with the cant. Current ones have 4wfs so I can look at toe as well as cant.
I have tried different fins on this board and find when things get bigger and steeper and a bit hairy I like GR’s in the front at 8 degrees cant and something like a G5 in the rear at 4 degrees cant both single sided fins.
For everyday use I use canard quad front fins with 6 degrees cant and Robin Mairs Eliptical fins (double sided) for rear. A lovely combination. The elipticals are more elegant and seem less tracky to me than the rear canards.
To sum up I think its easier to get a working board that doesn’t track with front fins toed and canted in more than rear. I like the front and rear set to be not too far apart and both sets out on the rails because I like twin fins with a bit of extra drive. I have tried gradually moving the rear fins in towards the stringer but in my limited experience this seems better for more powerful waves and feels more thrusterish.
If you have the chance to put the Proboxes in its worth it because its easy and you have a good chance of getting a good setup.
Didn’t we have a substantial thread on quad fin positioning about a week ago which included detailed measurements on a Pavel quad fins and positioning…
The search box is at the top. Try searching for posts by lazymodo with the search string “Pavel quad”
Blakesteah- thanks for the direction. I must have missed the thread of which you speak; my professional life does not allow me enough time to really monitor everything that is posted here… I often miss good info as it gets scrolled off the page, sometimes lost to me forever (Refer to statement below).
I tried searching, but the search function on this site spits out more un-related info than I can wade through. Either that or it gets too “tight” and returns few, if any, relevant threads. I’ve always hated the search function here as it is just sub-par compared to some of the other sites I visit.
I also kinda hate the “search the archives” command as everything regarding surfboard design is an assembly of infinite variables and it is all really an evolution and should be revisited, debated, and revisited again soon (of course, the “which merrick should I buy?” and “flyer or flyer II?” threads get a bit repetitive! )
I am also hoping for info on “performance thruster-based quads” rather than “hot-rodded mod fish quads” (not knocking the later at all as I am planning the purchase of one…or shaping myself one… but I needed different info for the project at hand).
Oldy, thanks for the link. I did see and read through that thread, but it does fall under the “hot-rodded mod fish quads”… BUT still useful to take into consideration for this and other projects. Thanks again.
With quad fin set-ups in a stage of evolution we have new things arriving on the scene we have options arriving at a fairly fast pace these days. Lots of shapers here in Santa Cruz are doing quads now and there more boards in the water without center fins all the time. I believe that we aren’t to far away from seeing a quad under a the feet of one of the top 44 on the circuit.
When it comes to fin set-ups for quads I believe there is much more room for experimentation left. At present lead fins run the gamit in configuration from ones with fairly extreme rake to high aspect with cant running anywhere from 5 to 22.5 degrees. I have little doubt that high aspect lead fins facilitate performance the best. Trailers in most cases, though no all, are smaller than the lead fins, (some folks like to stiffen up the board with a most substantial trailing fin in bigger surf)This sort of fin choice stabilize the board and open up the turning arc. Foils on trailers can be single or double depending on what best serves the board and surfer. Cant on trailers can run from 0 to 22.5 degrees again depending on the stick. I had a good talk with Shaud at Rainbow fins yesterday. The guy knows his stuff and is surfing a pretty radical set-up on his quads. It’s what works for him and he’s rides some pretty challenging conditions. I’m not sure but it may well be that canting a larger profile fin out further will produce a quad with super performance. You know I’m gonna try it. The ability to move fins fore and aft that the lokbox system gives has to help tune a set-up in so the system is an excellent choice for a quad. Future is good too but I think that putting deep boxes fore and aft is better than putting shallow ones in aft if you have enough board thickness because it’ll make it easier for to experiment with fin combinations.
If you want lots of lift and speed cant your fins out an run both with single foils.
If you want more drive and a little stiffer feel run you fins more vertical.
If you want to tone down the lift and make the board a little more stable go with double foiled trailers and take some of the cant out of them.
Like Doug Haut says, “Everything works, it just works differently.”
A surfer has to figure out what kind of fin action he wants and work toward a solution. I know there are some generalizations here that may be rather open ended but the variables are infinite. It’s much like shaping a board – everything little thing you change changes everything else.
Fluid mechanics is pretty complex stuff and I’ve got a lot left to learn ~ Off to the fin shop ~
I like to point the fins at the same spot. The location of that spot depends on many other factors. Other opinions may differ, but this is how I do it.
I use 1 or 2 degrees less cant on the rear fins. I use a ratio to calculate it. If the back of the rear fin is 3/4 the distance from the stringer than the back of the front fin’s distance from the stringer, then I use 3/4 of the cant of the front fin on the rear fin. That’s just an example.
{ Distance2 divided by Distance1 and the 0.xxx multiplied by Cant1 equals Cant2 }
This is what I’m talking about. It’s a RipFish Hybrid that just came off the racks 2 or 3 weeks ago.
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