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best fin box for hitting obstacles
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joethewindsufa



Joined: 10 Oct 2010
Posts: 1143
Location: Montréal

PostPosted: Tue Nov 15, 2016 6:19 am    Post subject: best fin box for hitting obstacles Reply with quote

a couple of years ago hit a rock with a US/Euro based fin and catapulted ending up with a hole in the nose ... and a chipped fin

last weekend I hit a rock at full speed/planing with a PB/powerbox fin and the fin broke OFF with NO damage to the board + lost the $90 fin

now if i had to choose, i prefer the loss of a fin

i can only imagine what would happen with a solid hit using a tuttle or DT fin Embarassed

does this mean : the PB fin is the best option in an area with imminent danger of hitting something ??
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cgoudie1



Joined: 10 Apr 2006
Posts: 2395
Location: Killer Sturgeon Cove

PostPosted: Tue Nov 15, 2016 11:53 am    Post subject: Re: best fin box for hitting obstacles Reply with quote

Making the design criteria lean towards hitting something
without destruction might not be the best for performance, and since
your intention is to ride, rather than run aground, I know how I'd
approach fin design, but.............

The best box for hitting things right now is the standard Chinook slot
box, because the fin tab is the weak link and it usually breaks off doing
little damage to your board. The maximum fin length it will tolerate
structurally is around 16 inches (41 cms) though.

Trim Boxes are similar to slot boxes.

Years ago (with slot box fins), the industry developed a tab nut, that would
pull through the slot when a slot box fin impacted something. I tried those
and discovered that they broke free way too easy (like sitting on the beach)

I have seen the rear sections of boards completely torn away with Tuttle box
impacts, though the more typical destruction is for the bolts to pull through
the top of the board. Power Boxes typically pull the single bolt through the
deck also if the impact is strong enough. Shearing a fin off was lucky
on your part. But, if the fin is just drilled, for the bolt, rather than having a
barrel nut in the fin for the bolt to attach, those threads will strip loose,
the fin will pull out, and the board will survive (you might even be able to
retap the fin for a larger bolt, if you don't lose it in the impact.)

In your case, you might consider sawing through 1/2 of the bolt so that it
breaks rather than your board. I've seen this done with varying degrees
of success (and an occasional lost fin).

30 years ago or so, Mistral had a spring loaded rear fin, that folded up
so that you could run your board into the beach, that wasn't a great idea either.

-Craig



joethewindsufa wrote:
a couple of years ago hit a rock with a US/Euro based fin and catapulted ending up with a hole in the nose ... and a chipped fin

last weekend I hit a rock at full speed/planing with a PB/powerbox fin and the fin broke OFF with NO damage to the board + lost the $90 fin

now if i had to choose, i prefer the loss of a fin

i can only imagine what would happen with a solid hit using a tuttle or DT fin Embarassed

does this mean : the PB fin is the best option in an area with imminent danger of hitting something ??
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dllee



Joined: 03 Jul 2009
Posts: 5054
Location: East Bay

PostPosted: Tue Nov 15, 2016 12:37 pm    Post subject: Reply with quote

The only good choice is not hitting anything bigger than light eel grass.
Weak box, you lose fin, you rip box out.
Medium box, you lose fin, you rip box out, you can get launched.
Strong box, you lose fin, you rip box out of the board, and you get launched big time.
Not every hit is the same, and for sure, you will encounter different degrees of hitting something.
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joethewindsufa



Joined: 10 Oct 2010
Posts: 1143
Location: Montréal

PostPosted: Tue Nov 15, 2016 1:32 pm    Post subject: Reply with quote

as you say - best solution - know your waters and avoid obstacles

with bigger fins I tend to go in deeper waters
this was on-shore and using 34 cm fin - waist-deep waters
it was a BIG rock $%^&*
marker had moved %^&*(

lesson learned @ a cheap price Embarassed

@slinky in next comment - NO DAMAGE to the box
thanks for asking
no need to bring post to the top


Last edited by joethewindsufa on Tue Nov 15, 2016 6:17 pm; edited 2 times in total
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wynsurfer



Joined: 24 Aug 2007
Posts: 940

PostPosted: Tue Nov 15, 2016 3:43 pm    Post subject: Reply with quote

One reason I like the a box is that the fin does not fall off when you break the front tab, so at least you can sail back to shore.

Are you sure there is no damage to the power box? I would think there most likely is. There may be no damage to the board, but the box could be cracked around the bolt hole. make sure it is okay because if it leaks you know what will happen.
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skyking1231



Joined: 10 Jul 2000
Posts: 264

PostPosted: Tue Nov 15, 2016 8:22 pm    Post subject: Reply with quote

Dont foreget....not all fins are created equal. Different manufacter....and different designs. Some will sheer off alot easier than another design of the same box type.
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boardsurfr



Joined: 23 Aug 2001
Posts: 1249

PostPosted: Tue Nov 15, 2016 9:05 pm    Post subject: Reply with quote

I had a pretty bad encounter with a rock just below the surface last year. Once I realized what I had hit, I was darn glad that the fin came out of the fin box cleanly. It was a weed fin from CNC fins, manufactured by Tectonics Maui. I'm sure the fin coming out was only possible because Tectonics did not use the brass nut, but instead put the thread directly into the base of the plastic of the base.

I found the fin, rebuild it with some marine tex and sandpaper, and kept using it for a while. The thread still held well enough .. until the day of the OBX long distance race. I probably should have used a longer screw after loosing the first one.
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grantmac017



Joined: 04 Aug 2016
Posts: 935

PostPosted: Wed Nov 16, 2016 1:25 am    Post subject: Reply with quote

I think on fins that use a barrel nut you could easily make one from either round Delrin or possibly micarta rod which would then break away under impact. I doubt it would work with deep tuttle though since the box takes so much of the load.

-Grant
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mudshark



Joined: 08 Feb 2006
Posts: 7

PostPosted: Thu Nov 17, 2016 1:08 am    Post subject: best fin for hitting obstacles Reply with quote

Wow I just hit a turtle when I was starting to carve my jibe on Monday. We both lost. Lost my power box G10 fin and I don't think the turtle is too happy. If he died I would have liked to have eaten him I hear they taste like bald eagle. It looks like the box is ok and so am I just down a couple hundred bucks. I've put the fin thru the back of the board in the past with the old style fin boxes.
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beaglebuddy



Joined: 10 Feb 2012
Posts: 1120

PostPosted: Thu Nov 17, 2016 2:09 am    Post subject: Reply with quote

One thing to consider is if you just have a US fin box the replacement fins can be cheap, just ordinary surf board fins new and used ones are plentiful and cheap.
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