View Full Version : powerbox fins safety
6th October 2009, 01:53 AM
yesterday i lost my [one bolt] powerbox fin while sailing approx i.2kms from shore.
i had put new fin in previous day, tightened only with small screwdriver, i had packed finbox with some fincover material at bottom and side of box so fin was tight fitting. i then tightened securely with small screwdriver.
this is now 2nd one bolt[powerbox] fin i have lost. i have never lost a 2 bolt tuttle fin before.this is despite 95 percent of sailing done using this tuttle system. i have lost bolts from tuttle box on numerous occassions but never 2 simultanously.
for river/lake sailors this one bolt [powerbox] system is probably safe enough,for ocean sailors i would say absolutely no f..king way.
going to get my f2 board converted to tuttlebox after this experience.
lost all confidence in this one bolt [powerbox] system.
i bet there are a few others who dont trust the safety of this one bolt system after similiar bad experiences.
6th October 2009, 02:22 AM
One bolt holds wheels on cars (Hub bearing ) !!! Propellors on planes; UJ`s to box`s ;propellors on boats; seat belts to anchorage point;climbers on walls. List is endless where one bolt suffices perfectly adequately !!!
Put a lock washer on your fin bolt or tighten it up correctly !!!!
Good luck with conversion !!!! You could always fibreglass the fin in just to make sure !!!
Why are you putting spacers in a PB ??? Very unlikely they are needed !!!
6th October 2009, 02:28 AM
I went through a few years with F2's, (three different boards) and never had a screw/bolt come lose. I also have a HiFly (5 years) with a power box. Same thing with Tiga boards and single bolt. Haven't lost a fin in 25 years of windsurfing with approximately 20+ boards.
I guess you are unlucky or too conservative with tightening the screw/bolt. Slip in a stainless lock washer, it's cheaper than converting your box to tuttle.
6th October 2009, 04:03 AM
Been using Powerbox since 1993 and never had a problem combined with Deep Tuttle since 2004 and never had a problem, so I think that Ken's suggestion may be helpful to you, particularly as you say that you've lost bolts even on the Tuttle system.
You might make sure that the bolts are not "bottoming out" in the fin before they are fully tightened in the top of the board. If you remove the brass nut in the PB/TT fin and can see that the fin material is crushed in the area where the fin bolt tightens, this is where the problem may lie.
Other than that, you need to apply more torque when tightening the fin bolt/s.
Hope this helps.
6th October 2009, 09:01 AM
If you have lost 2 fins out of the same board, it would seem to be quite apparent that the fins are not fitting in the fin box correctly.
There should never be any reason to put anything (fin cover material or otherwise) in a correctly fitting Powerbox (or Tuttle box/Deep Tuttle; Tige; Bic Power Trim box.)
The only sort of fin box that needs to be "shimmed" is an "A" or "E" box and then the shim is only to "tighten" the fin in the slot if one or the other is out of spec.
Correctly fitted, the fin bolt simply "DRAWS" the tapered surfaces into full contact.
The tapered surfaces then take all the stress and strain, and the fin bolt (bolts) simply enusres that the tapered surfaces remain in contact.
The reason your fin screw is/was 6 mm x 1.0 with a big #3 Phillips drive in the pan head is so that you would use a #3 Phillips screwdriver (normally supplied with nearly all F2's and Starboards) to tighten them.
Use of a lockwasher will not help if the tapers on your fin do not fit correctly.
Adding a lockwasher will ensure that air can get down the shank of the screw.
You need a seal under the bolt head and washer to seal the fin box from the atomosphere above the tail of the board.
Some times it is necessary to add a little material on/in the fin head tapers or the fin box tapers and carefully file the added material back until you get the good fit (with some "DRAW" to hold the fin tightly in the finbox.
I sailed Powerbox fins for 15-20 years and never lost a single fin.
If the fin "falls out" of your board when you remove the screw (s), then it simply does not fit properly.
If you have to smack it with your hand or with a soft mallet to get it out of the board (after removing the screw (s), then it fits correctly.
6th October 2009, 12:41 PM
Let's cut to the chase - If you "lost" the fin while you were sailing, you didn't have it screwed in properly.
I've sheared at least three powerbox fins clean off at the base (Two on the reef, one on a sea turtle. Sorry, Mr. Turtle!), and the base was still in the box after the collision. I've sailed hundreds of hours on dozens (and dozens) of Powerbox fins, and never lost one out of the box.
Honestly, you should have someone else show you how to put in fin screws if you're losing them even from tuttle boxes. Especially if you're shimming the fins with fincover material. Not even the worst US/A Box fin would ever need something that thick and spongey.
6th October 2009, 01:01 PM
thanks for advice.i will put seal below washer and tighten with larger screwdriver.
the fin i bought was second hand and was very loose fitting.
i had to pack it with heaps of fin cover sponge.
better to buy a fin to large and then to sand back to fit.
going to put a few layers of nail varnish over my other powerbox fins so they are extremely tight fitting in box.
6th October 2009, 10:07 PM
I should check your box because its very rare to have to shim up powerbox fins; unless its damaged and widened. (I`ve been using PB since it came out and have never had to shim a fin or lost a bolt ???)
One bolt securely will hold fine. Two in not properly and you`ll lose them both .
7th October 2009, 12:03 AM
Can it be, that your screw is a little to short, you cannot feel if she is 3mm or 7-8mm
in the insert. Wolfgang
7th October 2009, 08:47 AM
It's pretty easy to check the fit of all the tapers in a Powerbox fin system.
Simply get a bar of bath tub soap, rub the bar of soap on all surfaces of the fin head
that fit into the fin box. When you are finished rubbing the soap on the fin head, the soap will look dull and whitish/grayish.
Install your fin in the finbox in your board and tighten the fin screw normally. (It does not require any extra torque on the screw as you want to duplicate the conditions that you will normally get when you install your fin.
Remove the fin screw, and knock the fin back a little to separate the "draw" of the tapers.
Now look carefully at your fin head.
All of the places that are in contact between the fin head and the fin box will now be shiny and darker.
Take a single cut file and work off the high spots.
Redo the soap and put the fin back in the box as before.
Install the screw normally.
Remove the screw and knock the fin out of the box.
If you have filed the fin correctly, you should begin to see the high spots spreading out.
If it's a sharp edge or protrusion on the fin or in the fin box, file off the sharp edge or protruding lump/seam until it blends in with the surrounding tapers.
Continue to gently work the high spots out until you have as near 100% contact between the fin head and fin box as you can achieve.
If you find a low spot, it's better to take a filled or thickened epoxy paste (like Marine Tex
or JB Weld (Quick) and smooth on a few thin layers of the filler to until it blends in with the surrounding fin head/fin box materials.
Be careful working anything in the fin box, as it's very difficult to file or shape down inside the fin box. Better to do your "filling" on the exterior tapers of the fin head so they are easy to "work back".
Pay particular attention to the two large flat tapers on the sides of the Powerbox fin head.
These are the ones that provide all the support for the fin.
Also look at the front and rear edges to ensure that they are not preventing the larger tapered surfaces from engaging fully.
You will know when your fin fits correctly.
It will not "fall out" of the fin box without some knocking or tapping with a soft hammer as the "draw" of the tapers will hold the fin in place even without the screw even being installed.
Hope this helps,
7th October 2009, 01:36 PM
I have actually lost a Powerbox fin once, but that was most certainly because of a bolt that was too short. I noticed that the threads engaged just a few turns of the screwdriver, but I was as usual in a hurry to get out.
And then I lost the fin...
I could imagine that it you shim with fincover material that is soft then you may get some play into the system, and that might work out (rocking it from side to side) the bolt eventually. I believe shim materials, if used, should be solid.
You also said that you "packed finbox with some fincover material at bottom". This could be the culprit. A powerbox fin is NOT intended to touch teh bottom of the box, it is supposed to be wedged in between the walls.
But I have never even heared about anyone else that would have needed to shim a powerbox fin.
7th October 2009, 11:33 PM
My experience with power boxes is that the fins ALWAYS fit just right. No shimming or sanding. On the other hand, I usually have to sand either the fin or the box if it's Tuttle.
10th October 2009, 03:33 PM
Hi, for me powerbox is best choiche. Central screw is easier and quicker. No problem with interchange of fins. Two years ago I hitted a rock hardly with a Select 48 Course, head broke, screw curved, but BOARD FINBOX SAFE! I've heard about tuttleboxes broken in similar situations: two thight and hard connection system imho. You save the fin but loose the board, finbox repair is an hard and pricy one!
But: first of all now if I sail in rocky spots I use a longer powerbox fin with a thick rubber spacer (1 cm) under the screw head, so now I have a "fin bumper". Second I was wondering about a cave screw with inside a safety leash (a fishing rope) or something similar to avoid loosing the fin in case of impact (easy when yore trying to ride waves near the shore)...
Nico, Venice, Italy
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