Advice on large fins please

Advice on large fins please

Post by Lucian Jakubowsk » Thu, 15 Feb 2001 14:18:13


I bought a new 21" race fin for my early planing board.  It got used for the
first time last weekend.  While putting my gear away after I got home, I
noticed cracks had developed on both sides of the fin base.  It's hard to
describe. but imagine the fin being a certain thickness (layer A-fin).
Then, imagine the added thickness necessary to build up each side of the
base (layer B-left and B-right).  The cracks are developing in between the
layer A-fin and layer B-left, . cracks are symmetrical so the plane between
A-fin and B-right is cracked as well.   . get it.?

I've never broken a fin before.  I only weight 150lbs and sailed one 5-15mph
day with this fin.  It should not have cracks as far as I am concerned.
Does anyone know how these large fins typically break with heavy usage?  I
believe my fin box should break out before my fin should break (not that I
want this to happen or anything).    Doesn't this sould like I got a
defective fin?

Any thoughts on whether G10 is the right material for large fins?

Jake

 
 
 

Advice on large fins please

Post by duboi » Thu, 15 Feb 2001 14:03:19

I had a large 54cm fin on my old GO that had developed cracks directly below the
fin base. These cracks were horizontal and only seemd to be in the outer shell
of the fin. The fin was made by Curtis but was one of their lower range. I
immediately changed it against a new fin.
G10 is good for big fins as its pretty strong. But I don't really like G10 as it
tends to be heavy, I usually buy carbon fins for large sizes.

Later,
Francois

Quote:

> I bought a new 21" race fin for my early planing board.  It got used for the
> first time last weekend.  While putting my gear away after I got home, I
> noticed cracks had developed on both sides of the fin base.  It's hard to
> describe. but imagine the fin being a certain thickness (layer A-fin).
> Then, imagine the added thickness necessary to build up each side of the
> base (layer B-left and B-right).  The cracks are developing in between the
> layer A-fin and layer B-left, . cracks are symmetrical so the plane between
> A-fin and B-right is cracked as well.   . get it.?

> I've never broken a fin before.  I only weight 150lbs and sailed one 5-15mph
> day with this fin.  It should not have cracks as far as I am concerned.
> Does anyone know how these large fins typically break with heavy usage?  I
> believe my fin box should break out before my fin should break (not that I
> want this to happen or anything).    Doesn't this sould like I got a
> defective fin?

> Any thoughts on whether G10 is the right material for large fins?

> Jake


 
 
 

Advice on large fins please

Post by Roger Jacks » Thu, 15 Feb 2001 15:35:12

Hello Jake,

Quote:
> I bought a new 21" race fin for my early planing board.

OK, let's see, 21"= 53.3 cm, so I'm guessing it's a 54 cm fin, right?
Or did you purchase some fin that's measured in inches?
Interesting. Most race fins are sized in cm or mm. Only smaller weed and
wave fins are normally measured in inches.

Quote:
>  It got used for the first time last weekend.  While putting my gear away after I got home, I noticed cracks had developed on both sides of the fin base.  It's hard to
> describe. but imagine the fin being a certain thickness (layer A-fin).
> Then, imagine the added thickness necessary to build up each side of the
> base (layer B-left and B-right).  The cracks are developing in between the
> layer A-fin and layer B-left, . cracks are symmetrical so the plane between
> A-fin and B-right is cracked as well.   . get it.?

Sounds like you perhaps didn't fit your fin in the box, and either the
fin is
tapered or not thick enough, or the box is tapered and the fin is only
fitting down in the bottom of the finbox. I.E. the area of the fin root
nearest
the bottom of the board is not being supported by the fin box, due to an
improper
fit between the 2.
Is this a standard depth Tuttle fin, Deep Tuttle, or something else. If
it's a
powerbox, that's an awful lot of fin span for a powerbox. If it's a trim
box
it should be OK, but it's getting near the too much span for the finbox
to
handle situation.
If this is a G-10 fin, with a molded on fin root (Tuttle/Dp. Tuttle/PB
then I would take it back where you  bought it and see what they say.
But if the root was unsupported by the finbox, either due to the fin
root,
or the finbox, that is something that you might consider checking
anytime you
get a new fin. They have to fit tight, or they do not support each
other.
Quote:

> I've never broken a fin before.  I only weight 150lbs and sailed one 5-15mph
> day with this fin.  It should not have cracks as far as I am concerned.

I would agree, it everything fit correctly.

Quote:
> Does anyone know how these large fins typically break with heavy usage?

I've never broken one. Can you tell me by personal email what brand of
fin
it is, and what the material used to mold the fin root is?

Quote:
>  I believe my fin box should break out before my fin should break (not that I
> want this to happen or anything).    Doesn't this sound like I got a
> defective fin?

Yes, but it could be an improper fit, which caused the fin root to
separate.
Are the cracks across the axis of the fin, or along the axis of the fin?

Quote:
> Any thoughts on whether G10 is the right material for large fins?

It usually works extremely well, but it does not have the longevity of
a molded or CNC machined carbon fin. G-10 fatigues relatively quickly,
when compared to carbon layups, either molded or molded CNC.
I think I'd take it back and see what the shop has to say.
Regards, Roger

 
 
 

Advice on large fins please

Post by Lucian Jakubowsk » Fri, 16 Feb 2001 12:33:37

Hi Roger,

Yes, the fin is 54 cm or 21.3" inches.  Both measures are written on fin.
It has a standard Tuttle base.

I was impressed with how well the fin root was machined. It fits perfectly
in the fin box.  I had previously bought and returned another brand fin that
would not fit in the box at all.  It was a bit annoying having to return the
one fin since I typically use power box and have never had trouble fitting
fins.

Each crack is about 1.5" x .25" and appears to result from a force
separating laminate layers. A picture is worth a thousand words.  I'll send
you a jpegs of the cracks.

I'll let you know what response I get when I try to get it replaced.

When people break fins, do they typically break between the fin root and
fin?

Jake

 
 
 

Advice on large fins please

Post by randy34 » Sun, 18 Feb 2001 16:57:53

Jake
The fin you have is not good, it should not have these cracks already.
Long fins usually break in the area you described, but only do so when they
are either overstressed, faulty or when you hit the bottom whilest surfing.
G-10 is a good material for a large fin, but may be a bit heavy. Very
importent however is the design of the fin, has it got the right profile
from base to tip ? (NACA -profile)
I know Maui fin co. had a problem with their fins in 1999, they developped a
new material/method for their fins which in hindsight couldn't cope with the
stress a fin is under (size didn't matter either), a lot of the fins broke
and the ones that didn't break (yet) show the same cracks you described.
They replaced most broken fins for  redevellopped fins, these lasted a lot
longer. I haven't heard of 2000's M.F.C. fins breaking so it seems they've
got it under control.
Greetz Randy


Quote:
> I bought a new 21" race fin for my early planing board.  It got used for
the
> first time last weekend.  While putting my gear away after I got home, I
> noticed cracks had developed on both sides of the fin base.  It's hard to
> describe. but imagine the fin being a certain thickness (layer A-fin).
> Then, imagine the added thickness necessary to build up each side of the
> base (layer B-left and B-right).  The cracks are developing in between the
> layer A-fin and layer B-left, . cracks are symmetrical so the plane
between
> A-fin and B-right is cracked as well.   . get it.?

> I've never broken a fin before.  I only weight 150lbs and sailed one
5-15mph
> day with this fin.  It should not have cracks as far as I am concerned.
> Does anyone know how these large fins typically break with heavy usage?  I
> believe my fin box should break out before my fin should break (not that I
> want this to happen or anything).    Doesn't this sould like I got a
> defective fin?

> Any thoughts on whether G10 is the right material for large fins?

> Jake

 
 
 

Advice on large fins please

Post by Bill Kli » Sun, 25 Feb 2001 13:51:47

This question deserves a good reply as I own the company that makes Curtis
Fins. We use several different technologies and have the most experience with
deep fins as Curtis designed the first ones in 1994.

Anyway,

G-10 works good , depending on aspect ratio up to about 58cm.

After that we laminate Carbon with G-10 to stiffen and strengthen. We do pretty
good with this up to about 70cm. I am experimenting with various laminates.

Carbon molded: We have done pretty good with strength up to about 62 to 65.

Heavy sailors and serious racers on wide boards put the most strain on these
fins.

The challenge has been to improve strength, durability and performance as we go
to 66 and 70 cm.

I delayed the introduction of these ( sorry for all the backorders!!)  65 to 70
cm fins so the factory could improve strength.

Our regular CR-7, 10 and 12 fins have been pretty good on strength, surpassing
my own conservative expectations. These fins go to 55. A new carbon CR-12 62
should be strong as well. It is coming out in May. This 3 fin series (used as a
3 fin quiver) does well with the new boards, balancing water depth and strength
from shorter length.

It was nice to win at US and Techno Nationals, then win two of three divisions
at Formula Worlds (second in men's open).

The real challenge is now to keep all sailors on state of the art fins which
are strong and fun for all.

Thanks for allowing me to comment

Bill Kline
Gorge Sport USA
Curtis Performance Fins, Orca Fins, Orca Kite Fins
Hood River, OR USA

ph/541 387 2649  fax/541 386 1715