I’m wondering if anyone can explain to me what happens when the two side fins of a thruster are closer together vs. farther apart. Not the two different senarios on the same tail, but say a gun/semi gun vs. smaller surf thruster. For instance, my 6’6" semigun (which i have not ridden yet) has the two side fins at 10.25in apart at the front most point. And my buddys flyer (6’2) has his two side fins at 12.75in apart. Yes the flyers tail is wider than mine, but can someone throw some theory at me about this.
one of many threads on the subject ,
this is one fairly recently [from dec15th last year …using the “search” facility]
hope this helps mate …
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Re: [Shaun] space between fins and its effect? [In reply to] Quote | Reply
fins closer to the tail = tighter
further from the tail = looser
fins closer together in a thruster = looser more pivoty feeling with shorter more square turns
example: generally speaking
shortboard 6’3" fins are set around
3 1/2in from the tail trailer
11in front
1 1/8 off the rail
fins towed or pointed 2in off the nose
now a 7’0"
3 7/8 trailer
11 7/8 front
1 1/16 off the rail
same tow
use that as a starting point ride the board and make adjustments
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Enthusiast
Dec 19, 2005, 10:18 PM
Post #10 of 16 (361 views)
<span style="font-size:6px"> <span style="font-weight:bold"> Re: [Shaun] space between [b]fins</span> and its effect? [/b] [<a href="gforum.cgi?post=245131;search_string=fins%20closer%20together;#245106" class="bb-url">In reply to</a>] </span> <span style="font-size:6px"><span style="font-weight:bold"> <a href="gforum.cgi?do=post_reply_write;quote=1;parent_post_id=245192" class="bb-url">Quote</a> | <a href="gforum.cgi?do=post_reply_write;parent_post_id=245192" class="bb-url">Reply</a> </span></span>
…if you ride a small board in small to medium surf (average conditions), and you put your back foot really near the very tail, you should go with :-the fins near the tail…-the front fins near the rear …
…if you stand up further, move your fins in block, ahead…
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Ocean Beach, San Francisco, CA
Barnacle
Dec 19, 2005, 10:41 PM
Post #11 of 16 (353 views)
<span style="font-size:6px"> <span style="font-weight:bold"> Re: [Shaun] space between [b]fins</span> and its effect? [/b] [<a href="gforum.cgi?post=245131;search_string=fins%20closer%20together;#245122" class="bb-url">In reply to</a>] </span> <span style="font-size:6px"><span style="font-weight:bold"> <a href="gforum.cgi?do=post_reply_write;quote=1;parent_post_id=245195" class="bb-url">Quote</a> | <a href="gforum.cgi?do=post_reply_write;parent_post_id=245195" class="bb-url">Reply</a> </span></span>
Quote:
ok here goes: squash 6’6" side fins 2 1/8 from front middle of side fin box to rail. tail is 15.25". Back of trailing fin box 3 1/4 from tail. 1’ between front of side fins.
6’7" Diamond tail. 2 1/4" from front middle of side fin box to rail. tail is 14.25". Back of trailing fin box 3 1/2" from tail. 11 3/4 between front of side fins.
Measurements are generally made from the bottom, rear, of the fins. Not from the center of the box. Classic competition measurements are 10.5 inches for the rail fins, 3.5 inches for the rear fin. But today a lot of variance is found, and the averages on consumer boards are closer to 11.25 inches and 3.5 inches, and quite a few in the NorCal area are 12 and 4.
The Diamond tail board has the fin cluster 1 inch closer together in the fore-aft direction, it should be noticeably looser/twitchier/faster to change directions.
http://www.blakestah.com/fins/
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florianopolis, brazil and bahamas
Enthusiast
Dec 20, 2005, 7:28 AM
Post #12 of 16 (269 views)
<span style="font-size:6px"> <span style="font-weight:bold"> Re: [Shaun] space between [b]fins</span> and its effect? [/b] [<a href="gforum.cgi?post=245131;search_string=fins%20closer%20together;#245098" class="bb-url">In reply to</a>] </span> <span style="font-size:6px"><span style="font-weight:bold"> <a href="gforum.cgi?do=post_reply_write;quote=1;parent_post_id=245282" class="bb-url">Quote</a> | <a href="gforum.cgi?do=post_reply_write;parent_post_id=245282" class="bb-url">Reply</a> </span></span>
look at it this way...
if you have a honda civic - small wheelbase(closer fins) - the car turns very easily, but can be a bit scary at high speeds.
if you have a cadillac - long wheelbase(more space between trailer and side fins) the turns are more drawn out, but smoother at speed.
i have a 6´0" egg with the rear of the sides at 14 3/4 and 1 1/8 off the rails that is a rocket ship, but doesn´t really snap super hard unless you really push it.
hope that makes sense…
From what I’ve heard, the distance between the fins isn’t a factor, since in most turns you’ll only have one fin or the other engaged. What’s the theory on how close a fin should be to the rail though? Does that vary from board to board?
You heard wrong about the distance between the fins. It makes a significant difference.
I meant rather that it was the distance to the rail that was important, so that if you wanted to widen a tail on a board for example, but keep similar turning characteristics, you would keep fin-rail distance the same. Is that wrong?
Yes. The farther apart your fins are, the more the board will track, and as a consequence be more difficult to turn. Especially at speed.