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Guest 18th February 2007 05:53 PM

F 161 and fin
 
I sailing my f 161, is a great board.
But the fin "vibra" or "entra en resonancia" or zumba". Sorry but my english. Any comments?

o2bnme 19th February 2007 12:43 AM

RE: F 161 and fin
 
vibration sounds like the word we would use in English. Are you hearing a whistle as well or just feeling the resonance?

Guest 19th February 2007 06:45 PM

RE: F 161 and fin
 
I hear a noise like a whistle.

o2bnme 19th February 2007 08:08 PM

RE: F 161 and fin
 
Roger Jackson has posted instructions on how to do this in other posts. I'll let his words speak to the 'how.'

http://www.star-board.com/forum/view...hread_id=21526

Quote:

Yes, you can take a sanding block and put a flat (better still a tiny radius) on the traling edge and tip of your formula fin without affecting the performance of the fin to a degree you will be able to tell.
We've been "blunting" the TE of fins that "whistle" for years with no affect on the performance.
Run the sanding block (with 240 or 320 grit abrasve paper) down the TE of the fin with the block perpendicular to the fore and aft axis of the fin. 2-4 passes down the fin will take the sharp edge off. Then turn your sanding block to a 45 deg. angle and "break" the sharp edge where the tiny flat meets the foil of the fin. Just once or twice down the fin and you will have a nice 45 deg. chamfer that won't cut you if you happen to rub your leg or arm against it.

Guest 19th February 2007 10:16 PM

RE: F 161 and fin
 
Thanks a lot.

Roger 19th February 2007 10:59 PM

RE: F 161 and fin
 
Hi Guest,
Getting rid of the "super thin" trailing edge (TE) on the fin should stop the noise and vibration.
If doing the above procedure once eliminates some of the noise, but not all of it, repeat the procedure.
Another thing to look for is a little bit of "concave" just in front of the trailing edge.
If you have a little concave on both sides of the fin, just in front of the TE, you probably need to "blend" the concave in with the rest of the foil.
The fin guys use a flat diamond impregnated file to take care of this problem, but you could use a good sanding block and get about the same result.
Get a straight edge (or better still a hardened and ground dowel pin) and check the back part of the foil on both sides of your fin.
Ideally, if you place the straight edge (or dowel pin) perpendicular to the vertical axis of the foil, you should not see any light as you slide the straight edge (or roll the dowel pin) down the fin.
If you see an area of light (where the straight edge or dowel pin does not contact the foil surface) you have a concave area in the foil.
If the concave is on both sides of the fin, then the foil can be "too thin" to prevent vibration/noise even though the TE is thick enough.
So, work out any concave areas between the high point of the foil (usually about 30% back from the leading edge (LE) and the TE of the fin.
This may shorten the overall width of the fin slightly, so don't overdo your filing/sanding. Just work the little concave areas out until there is a straight line of smooth foil surface from the high point to the TE.
Then do the blunting procedure above until your noise/vibration goes away.
Normally these little "concaves" have resulted from the hand shaper (the guy who finished the fin when it was manufactured) gettting a little too agressive when shaping the back of the foil.
This can occur on CNC fins as well as hand shaped fins as the CNC machine does not do all the finish work. A hand shaper must go in and "blend" all the little "lands" between the CNC tool cuts.
On molded fins, this normally does not happen, and there is very little finish work done on the foil of molded fins after they come out of the mold.
Some CNC fins require very little "foil finish work" as this is a function of the "feed set over" used.
The more "passes" the machine makes, the less blending of the lands between the cuts or passes is needed.
Custom CNC machined fins from craftsmen like Dennis Parton at Tectonics require almost no blending, but the fin stays in the CNC machine 2 or 3 times longer and machine time=more costly, but better quality with a more precise foil.
Hope this helps,

Guest 20th February 2007 05:48 AM

RE: F 161 and fin
 
Hi Roger.
Take note that fin is Drake R19 ??it??s possible this mistake in finish?
Regards.
ARG-61

Roger 20th February 2007 07:12 AM

RE: F 161 and fin
 
Hi Arg-61,
Yes, if the fin sings, there's something not quite right with it.
I think most of the Drake fins are molded (someone correct me if
I'm wrong here) and the R-19 Formula fin that is supplied with the F-161 is just as susceptable to tiny errors (that could make the fin sing) as any other "production" fins.
The mold was made from a Deboichet plug I'm sure, but even with a very precise mold, there can be some warpage, over finishing, etc. that could induce the concaves or too thin trailing edge that causes the fin to vibrate enough to make the noise.
The Drake R-19 is still a "production fin" not a custom Deboichet R-19, or a C3 or a Kashy fin.
So, there certainly is more tolerance for "imperfections" in a $150 molded production fin than a custom, hand made, hand finished
fin that costs 2-3 times as much.
So, if it sings, I've given you suggestions on how to make it quiet and fast.
Hope this helps,

konstas 21st February 2007 12:54 AM

RE: F 161 and fin
 
hi Roger
please can you explain me which is the trailer edge or if you have a photo can you send it

konstas 21st February 2007 12:54 AM

RE: F 161 and fin
 
hi Roger
please can you explain me which is the trailer edge or if you have a photo can you send it


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