View Full Version : skeg and fin box on new ultrasonic 147
11th July 2011, 09:46 AM
I just picked up my new ultrasonic board. Unfortunately, I can't srew in the skeg to get it attached (the recommended Drake 58 inch race fin) in the fin box (deep tuttle). I tried a different deep tuttle fin and it fit better, although not quite right (could screw in one screw tightly), this other skeg fits perfectly in my Exocet board deep tuttle fin box. The skegs are fitting tightly in the US147 fin box although on closer inspection, are perhaps projecting out very slightly, 1 - 2 mm. I can feel some slightly scratchy epoxy resin in the fin box, and a slight ridge on the edge, and a lot of black stuff came off on my hands. Alternatively, it looks like the screw holes on the new skeg are slightly too far apart, but not sure if this might be a result of the skeg not quite fitting. Experiences and fixes for this particular board greatly appreciated.
11th July 2011, 11:26 AM
In order to get your fin to fit in your new US147 you may have to do a bit of filing on the fin head and
perhaps down in the fin box.
You may also have to elongate the screw holes that go through the deck to the fin.
Take a bar of bath soap, and rub it all over the fin head.
Install the fin in the fin box and lightly tighten the screw that yoiu can get in now.
Take a rubber mallet or dead blow hammer and tap the fin front to back gently a couple of times.
Remove the screw and look at the head of the fin.
Where the soap is still whitish and rough looking, your fin head is not contacting the fin box.
Where the soap has turned dark and shiny is where you need to remove a little material to get the
fin to drop into the fin box correctly.
Before you start filing on the fin head, look at the tapered front and rear of the fin head.
f there is a shiny spot on the rear of the fin head part way down the back, get a flashlight and take
a look in the fin box.
If there is a lump of black epoxy material in the fin box, get a round (rat tail) file and lightly file some material off the top of that lump.
Try the fin again.
Your goal is the get the sides of the fin to fin snugly (a light push fit) on the flat sides in the fin box, and
get as much contact as possible on the front and rear tapers of the fin.
Remember to leave the fin standing about 1/32" (0.8 mm) higher than the bottom of the board.
That last little bit will be the "draw" on the tapers and will ensure that your fin fits at the corrtect level
when the screws are snugged up.
As far as the fin screw holes in the US147, take your flashlight and look down through the fin screw holes in your board and determine which way you need to elongate your fin screw holes to match the
fin head holes and brass barrel nuts in the fin.
Again a small round (rat tail) file is the best tool ot use to elongate those holes.
For filing the tapers on your fin head, a fine tooth double cut file or a smooth file are the best.
Be sure to only take off a few strokes of material with the file, then redo the soap and try it in the
'fin box again.
Only file the black shiny spots and you will have your fin fitting perfectly very quickly.
Hope this helps,
11th July 2011, 08:43 PM
Thanks for the details- the new fin fits perfectly in my other (Exocet) board with a deep tuttle fin box, by the way, and the screws line up straight. This would suggest the problem is more with the fin box itself.
11th July 2011, 10:05 PM
Since the fin fits other boards fine, start with the tuttle box first. Do as Roger suggests and look for where the soap is rubbing inside the box. That's where you should do some filing, but only a little at a time. You may have to soap, insert, remove, file, soap ,insert, remove, file, etc a dozen times before you get it right.
If you can get the bolts to line up, try to crank the fin tight with the bolts every other time you soap and file. If you don't, you may over do it and when you finally tighten up the bolts, the fin will be too deep in the box. Been there and done that by mistake. In my case, it was the fin head that I sanded too much, not the box, since I had other fins that fit the box fine.
I have heard that it's not unusual for tuttle boxes to come with some burrs or high spots inside.
12th July 2011, 10:53 AM
Thanks Ken and Roger for the advice. I found today that I can screw both fins in, but only if I don't put them in straight/flush: rather, at an angle, with the back of the skeg high of the board by 3 - 5 mm, (and the front all the way in and flush) I can screw in the fin using both screws. The fin will fit flush in the fin-box, but cannot be screwed in in this position (screw holes on board do not line up with fin). This seems to indicate that the angle of the fin box is crooked, slightly (eg. I'd have to put the front of the skeg further in, and sand down there, to get the back flush; maybe the screw holes are not quite in the right place?).
12th July 2011, 11:28 AM
OK, sounds like the fit of the fin to the finbox is reasonably close.
Maybe a lump of epoxy or something along the back taper/radius of the fin box.
If you need to "move" the fins screws forward a bit, you can simply take a small round file
and elongate the existing holes 3-5 cm.
The fin box is a molded/cast piece so there is no danger of water getting in your new board or anything
like that. Simply move/elongate the fin screw holes until they line up with the drillings in the top of the fin head that lead down to the brass barrrel nuts.
Better to move/elongate the holes than to put alot of bending stress on the screws.
The screws will be alot easier to install and remove as well.
You could also tap the brass barrel nuts out of the fin head and enlarge the top drilling (from the top edge of the fin head down to the barrel nuts) and perhaps change the angle slightly. Reinstall the barrel nuts with a little soap on them so the slide in nicely and everything should line up much better.
Hope this helps,
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