Hi all
Am currently in the process of building an 8 Foot Gun for Indo,but am not sure where to place the fins.the dimensions are.8 footx2.7/8 x 19 3/4.Single concave to vee with 3 1/2" rounded square tail.Im ok with the standard thruster fin placement on anything up to 6 6" .but not completly sure on an 8 foot gun.My original guess was (front fins .12 5/8" (rear fin 4 1/2".I have been using Probox for the other boards ive done and will most likely be using that set up again.
I went to various surf shops with no luck and carnt seem to find anything on the net.
Any help is really appreciated,as i wana get this right
You might consider a 2+1 setup with side fins at around 15" and a center box as far back as tail thickness will allow. Being able to swap out and change position of center fin really can expand the range of any board.
PM Lee Vanderhurst (LeeV) about his semi-gun. He originally specified a single but later installed side boxes and liked the result.
Hey Bonoski,
I do a lot of guns in that size range for Puerto, Hawaii, Indonesia. Although a bit will depend upon the fin, rocker and type of wave (hollow, big lumpy etc.) your numbers are pretty close. I would say a little bit aft of what you suggest with typical tail rocker, with a minimum of 12" fronts, 4" center.
This is for a thruster set up, rather than the set up John is offering which works quite well also…
George
I have a 7’10" thruster gun that works great and the fins are at 4.5" and 13".
your mileage may vary of course, but that should get you in the ballpark.
Thanks for that George.The tail rocker is at 1 3/4 .The nose lift ive got at 7".
cheers Mick
The rear box sounds good ,but will have to check to see if ive got enough thickness there.
Thanks for your help
Mick
Hi Mick,
That’s a fairly low tail rocker for rounder waves, you probably do not want to over load the fins, so my suggestion would be to favor a further aft positioning, say around 12 or 12-1/2 inches up. Here is what I consider a lower tail rocker board ridden by one of my riders in the same board size range as you:
[img_assist|nid=1067522|title=Oscar at Zicatela, 7'6" pintail thruster|desc=|link=none|align=left|width=640|height=427]
Tail rocker on that board is 2.67" nose 6.85" Of course he is pretty light, about 155 max so the outline is fairly narrow. If you had more tail kick then I would explore putting the fins, especially the sides, further forward… …unless of course you are heavier, say closer to 200 lbs, then the low (1.75") tail rocker is viable. Template also will determine where your feet will be positioned when you make that hard drive to get speed and positioning.
George
Hi George
I thought it kind of strange also .so I rechecked the measurments.I have recently moved from the gararge to a back shed…Turns out the floor isnt level and as such the stands were not level either.i,m talking like 1 1/2" over the length of the blank.So I corrected this and rechecked the tail rocker,with an alloy straight edge and level on the bottom side ,the tail rocker is now 2 7/8 ".which sounds a whole lot bettter. …Something to watch out for in future…
with the tail rocker larger at 2 7/8" what should be the shapers mark on the rear fin and side fins form the tail. I,m 90kg in weight
cheers Mick
Now that you’ve leveled off your blank and get 2 7/8" for the tail
rocker, you’re probably at 6" - 61/4" on the nose rocker. 6"N and 2 7/8" are the rocker dims I (6’3 x 190 lbs) prefer on my 8’ thruster semi’s. Another thing to consider is whether you’re front foot or rear foot heavy. Being a front footer myself, I’ve found 13" and 4 1/2" the sweet spot with that rocker for those full rail, long driving turns…also might think about a rakier fin set to tap that drive…
In keeping with the 2+1 suggestion that John proposed, I had a sailboard from 15 years ago that had a standard single box.
Well it had too much tail area in stronger wind and larger waves, and like most sailboards nowadays would leap out of the water on hard gybes and turns.
Anyway I stuck two cut down (~40%) shortboard thruster sides up around 15" offf the tail, right on the rail with an extreme cant angle.
They looked too small to be of any use, but they worked extremely well, and I don’t think it was just psychological.
Only downside is that they were too close to the rail for any box system
Reason I mention it is because I’ve seen some bonzer(?) pics with higher cant angles on the forums recently
Looking forward to hearing what you decide on, as I’m considering a step up board of similar dimensions
peace out
Hi Mick,
Yeah, that changes the whole deal, glad you checked. You’re around 200 lbs, so with that much rocker, you definitely want the fins up further right around 13" as suggested before, maybe even a little more if your tail is pretty narrow…
Got any pics of the template?
George
I,ll take some picks tmoro and try to upload them.13" for the front fins ,do you think 4 1/2" for the rear fin??
thanks for the advice
cheers mick
Hi George
I was setting out the fins on the Gun this arvo and have decided to go with 13"(front fins) & 4 1/2" rear fin all with probox.That will give me 1/4"to adjust front and rearwards.I was going to put the rear mark of the front fin 1" off the side rail,but then read some shapers put the same mark at 1 1/4" off the rail.Can you tell me the main differance a 1/4" will make. The set up I normally use on thrusters for the front fins is 1" off the rails to establish the rear mark ,and 1/4" toe in.should I use this or the 1 1/4" .Is there anything I need to wary of when shaping the rails on a Gun.I’m use to doing a 35 degree tuck on the bottom rail.
Thanks for your help
Mick
Hi Mick,
Fin position numbers sound spot on, assuming a pretty narrow-ish tail…
I think the fin marks should be close to the rail for a narrow tail and further from the rail for wider tails. Range for this number may be 1" to 1-3/8" for most boards and closer to 1" for gun shapes. What will determine how far specifically will be a lot of factors. It boils down to when (in a bottom turn let’s say,) you want the shore side fin to begin releasing. If the fin is close to the rail, it will release sooner. By “release” I mean the fluid flow on the shore-side fin separates (gets an air source that renders it largely ineffective.)
[img_assist|nid=1067616|title=Oscar at Zicatela, 8'2 bottom turn|desc=|link=none|align=left|width=640|height=361]
Shore-side fin is released.
I do not use the short measurement for toe-in, in my opinion it is inaccurate and does not match well with template and rocker of a specific board. I use a long straight rule (8 foot aluminum) and lay the edge from the rear dot of the front fin, forward toward the nose. I then measure the distance that line is “away” from the nose. For example, I may point the fins right at the nose tip, I call this " +0" off the nose…" For most boards I go +2" to +3" off the nose, and most guns seem to work well at +2". Of course I am assuming a lot here, not knowing the outline, rocker rates, fin template(s) and overall “look” of the board.
A lot of my shaper friends will lay out mock fins out of cardboard and hold them in place, “That looks about right…” and they typically nail it. These are guys who have shaped 40 to 50 years, and their boards work great.
For me it took a lot of riding and video analysis and dead reckoning to figure which board and which position works for my shaping. I say go with what seems right, go with what you know and you’ll be fine at this point.
Hope this helps,
George