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NACRA beam bolt stripped : need ideas #278335
04/11/15 11:39 AM
04/11/15 11:39 AM
Joined: May 2002
Posts: 217
J
jcasto1 Offline OP
enthusiast
jcasto1  Offline OP
enthusiast
J

Joined: May 2002
Posts: 217
I have a 1996 NACRA 5.5 with a stripped nut inside the hull. Need ideas on repair.

Details : the beams are held to the hulls using two straps at either end of beam. There is a 5/16-18 stainless bolt at either end of each strap that go down into hull. Embedded in the hull is a threaded element (~100% sure it is a nut). One of these nuts is stripped, I need to repair in order to use the boat with fear of total carnage.

This is how I did it last time on a 1987 NACRA 5.7. the nut location was rear side of the front beam :
1. Cut 4” diam hole for inspection port.
2. Remove the stripped nut : this entails digging / grinding out some fiberglass, until you can remove the old nut which is stripped.
3. Make a “washer” of some kind to spread load - I shaped a piece of teak based on copying shape from putty until it fit real snug up in the corner.
4. Use a longer bolt to attach through the strap onto the nut.
Note : Unlike all the other beam strap bolts on the boat now, to loosen this bolt now requires open inspection port, use wrench on nut when turning bolt.

Inside most NACRA hulls are bulkheads, typically one is located near the front crossbeam, the other at the rear cross-beam. While repairing the 5.7, and looking inside other NACRAs at our club, I noticed the forward bulkhead is almost always located towards the front side of the forwardd cross-beam. On the 5.7, this allowed my repair of the bolt at aft side of front cross-beam to be clear of all the extra fiberglass needed for the interior bulkhead to hull joint.

Now – here is the problem with the 5.5 repair. The location of the stripped nut is in front of the front crossbeam.
a) I really do not want to cut a 4 inch diam hole for access, in front of front beam.
b) Even if I do cut hole and gain access, I am concerned that the nut is “buried” under a *lot* of other fiberglass which creates the bulkhead to hull joint. I just think the amount of material I need to remove to get the nut out, while working with one arm, in a very small restricted space, is going to be burdensome.

Alternate approach : drill out the stripped nut (5/16-18), and tap to next larger size (prob. 3/8-16). Has anyone done this?
Pro : easy quick & simple.
Cons : torque of drilling and tapping may turn the nut inside the fiberglass, making it useless. Also, the nut relies on its top surface to create holding power against the hull when bolt is tightened but after drill & tap, the top load-bearing surface of the nut is smaller, making it less effective. And, it is the same material as original which failed, so it will fail in the same way again.

Is there any chance this threaded element which is stripped is not actually just a small nut, but a piece of stainless – like a “tab” or tang”, that will not rotate as easily and has more “meat” than a nut?

Does anyone have other ideas, and especially, experience with this repair of stripped nut on front side of forward cross beam?


Last edited by jcasto1; 04/11/15 11:40 AM.

Jim Casto
NACRA 5.5 & NACRA 5.7
Austin TX
Lake Travis
-- Have You Seen This? --
Re: NACRA beam bolt stripped : need ideas [Re: jcasto1] #278336
04/11/15 11:54 AM
04/11/15 11:54 AM
Joined: Jun 2001
Posts: 890
Dunedin Causeway, FL
David Parker Offline
old hand
David Parker  Offline
old hand

Joined: Jun 2001
Posts: 890
Dunedin Causeway, FL
On my 1998 Nacra 5.0 I've stripped a rear and front beam "nut".
Drilled larger and tapped, both are going strong 5 years later.

Re: NACRA beam bolt stripped : need ideas [Re: jcasto1] #278337
04/11/15 03:13 PM
04/11/15 03:13 PM
Joined: May 2002
Posts: 217
J
jcasto1 Offline OP
enthusiast
jcasto1  Offline OP
enthusiast
J

Joined: May 2002
Posts: 217
I just finished drilling & tapping for the larger 2/8-16 bolt. Bolt seems to be holding fine, same torque as other 5/16-18 bolts.

Update : upon inspection, the bulkhead is centered on the beam location, so the bolts located front and aft of the beam would be clear of the bulkhead, if I cut into boat to fix from inside. However, if bolt inside the beam was stripped, I would be out of luck.


Jim Casto
NACRA 5.5 & NACRA 5.7
Austin TX
Lake Travis
Re: NACRA beam bolt stripped : need ideas [Re: jcasto1] #278339
04/11/15 06:25 PM
04/11/15 06:25 PM
Joined: Jul 2007
Posts: 976
France
pepin Offline
old hand
pepin  Offline
old hand

Joined: Jul 2007
Posts: 976
France
For these kind of issues, as long as the nut doesn't move, the best solution is to use a threaded insert, commonly called helicoil.

Re: NACRA beam bolt stripped : need ideas [Re: pepin] #278343
04/11/15 08:42 PM
04/11/15 08:42 PM
Joined: Sep 2002
Posts: 3,222
Roanoke Island ,N.C.
Team_Cat_Fever Offline
Carpal Tunnel
Team_Cat_Fever  Offline
Carpal Tunnel

Joined: Sep 2002
Posts: 3,222
Roanoke Island ,N.C.
Originally Posted by pepin
For these kind of issues, as long as the nut doesn't move, the best solution is to use a threaded insert, commonly called helicoil.


+1


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The cure for anything is salt water - sweat, tears, or the sea
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If a man is to be obsessed by something.... I suppose a boat is as good as anything... perhaps a bit better than most.
E. B. White

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