Self-tap screws in GRP

[RickJ]

There are several panels in the X (and other boats I assume) that are held in place by self-tapping screws. E.g. internal access panels, side panels on console, etc. You only have to remove and replace a panel a couple of times before at least one screw starts to fall out because the thread has gone or the GRP has cracked.

Are there any good tips for making more reliable fixings? I'm thinking of some kind of captive nut for a proper screw that will go where the self-tap hole is. Or maybe a re-inforcement to the edge of the GRP so the screws will hold properly.

Any ideas welcome! I had a search, esp. in the mods section, but couldn't find anything. Surely this is a common problem?

Cheers

[Night Sailor]

I found that if I discovered panel screws getting loose going into a thin panel, that it helped a lot to put a thin coat of loctite of the appropriate strength on the threads and head bearing surface when reinstalling a panel. If enough failed to hold when doing that, I switched to the next larger screw size, whether metric or US. Sometimes switched thread angles can help, as between sheetmetal or self tapping, or machine. Never had to go so far as to completely go away from screws to bolts or machine screws with nuts of anykind. I consider sheet metal or self tapping screws for holding only light loads in a horizontal plane, but can take a lot of weight if only concerned with shearing forces.

A fellow sailor rehabbing a 30 year old boat found it works great to eliminate screws everywhere he can with a self bonding, double sided tape from 3M that body shops use on assembly of cars. I forgot the number, but he has installed panels, ports, hatches and other hardware with no thruhull or thru deck bolts and it seems to work for him. Surely, a light duty panel could be done that way also.

[Retcoastie]

I had the most problems with the power panels. I seems to be behind them a lot?????

I got a small block of wood about 1/2 inch square and the length of the panel plus a little. I placed the strips behind the plastic panels at the edge of the opening and drilled a little pilot hole where each screw went. Then I took some silicon adhesive, applied it to the strip and screwed everything back together. Once set, the silicon holds the wood in place and now I screw into wood rather that plastic. If those holes ever strip put I'll just pull the wood loose, rotate it one side and start over. So far the wood is holding up fine.

Cheap, easy, effective.

[bastonjock]

i use double sided tape in my body shop,most of todays plastic strips that run along a car door are fixed using this tape,its great for non load bearing stuff

[They Theirs]

Quick Fix:
The ultra-thin interior liner of the powersailor requires a hard backing for mounting almost anything other than Plastic (adhesive stick-on) interior bits and pieces. We found a quick fix using a rectangle/ribbon cut from a thick part of plastic soda bottle.

Poke and screw the sheet metal screw into the bottle and cut a ribbon size large enough from the most flat portion for the bottle. Cut a much larger “Duct Tape” strip, placing the pre-holed and threaded, plastic ribbon on the tape. (With small X cut in the duct tape over the hole in the plastic ribbon with the outside curved side on the Duct tape in the tape) place the sheet metal screw partially into the stripped out interior liner far enough to place the plastic strip with much larger Duct tape covering the strip, through the liner opening (without its cover) carefully matching the screw into the strip of plastic bottle. Fully stick the larger Duct tape inside the liner to hold the plastic strip thread repair…. remove the screw, install the cover and tighten the screws with care.

Tinnorman Nuts for Sheet Metal Screw make a stronger repair, glued inside with epoxy…spring steel can rust over time.

[RickJ]

Thanks for the ideas.

I'll probably use double-sided tape to help with panels that only have to come off to run wiring (i.e. not often).

But I'm planning to re-locate the starter battery in the console, so that plus the main electric panel I regard as "maintenance access". I think I'll go for a reinforcing strip of some kind on those, maybe wood, thicker plastic, or even aluminium. Might have some corrosion problems with ally though

Cheers

[kmclemore]

From an earlier discussion... both of these options make an extremely good mounting in fiberglass:

Actually, there's another choice, and it's a pretty good one - RivNuts. They're rivets that have threads in them.. you install them much like a pop-rivet, but when you're done you have a nicely threaded hole - far better than just drilling and tapping the mast. They're often used in aircraft and I used to use them back when I was racing. Sometimes you'll also see them called either a "Nutsert", "POPnut" or "blind threaded insert".

Nutsert / Rivnut / POPnut:


There's a great animation of the installation here.

Also... along a similar line.. if you want a shock-mounted type of threaded insert, try "Well-Nuts" (also called "Rawl Nuts" in the UK).. they are a brass threaded insert bonded to a rubber t-shaped insert.. when you tighten up they expand and lock into the hole. I'm considering using these to mount stuff to the liner, actually.

Well-Nut / Rawl-nut:

[eric3a]

..

[RickJ]

Hmm, those inserts look interesting, thanks for the tip.

My gut feel is that the Rivnuts would be better, and a quick Google shows that they're available in SS - always a good sign . I guess there's a higher initial cost for the fitting tool though. The Rawlnuts don't appear to need anything special.

[bscott]

Well nuts work best in places that may be stressed because the rubber will flex inside the hole reducing the tenency of the glass to crack. These are used on snowmobile plexiglass windshields which take major hits and vibration.

[Captain Steve]

Kevin, couldnt get on that site unless I was a business and had a specific application. Some areas of the liner have a close gap behind it....how deep do well nuts go??

[bscott]

The well nuts come in various sizes and you can put them on a grinder to shorten them up--they are cheap enough that you can experiment with the lenght of them and the length and type of metal machine screw that you use.

[NiceAft]

If we are talking about holding something very light, why wouldn't these work (the plastic plugs, not the lead one's)? They are cheap and easily acquired.


I have used them for a couple of years now, and I have not had any problems. If you click on the photo below, in order to enlarge it, you will see a solid resin parrot ( it's name is Mac) I attached by using plastic plugs. It has been there two years. I don't have any photo's of other items I attached. I don't see why they would not work on a panel?


Ray

[kmclemore]

Kevin, couldnt get on that site unless I was a business and had a specific application. Some areas of the liner have a close gap behind it....how deep do well nuts go??

Steve, they come in a wide range of sizes... just Google "well-nuts" "rawl nuts" and you'll come up with plenty.

Here's a couple:

• http://www.hansonrivet.com/w71.htm
  
  http://www.imperialinc.com/grp305.shtml

I usually buy 10-32 size, since that will hold nearly anything on the boat you'll want to support on the liner or anywhere, for that matter.

And BTW, Jack-Nuts are another possibility.... see http://www.hansonrivet.com/w70.htm for more info.



Overall, though, my preference is for well-nuts. A jack-nut or an insert can begin to twist in the 'glass if it's not *really* secure. But a well-nut will tend to grip the hole better and is less likely to twist. Plus if offers a cushion to vibration and will reduce cracking of the hole or the surrounding 'glass.

[bastonjock]

i just had a look at the uk Rawl nuts,it states that they also offer a water tight seal

thanks for that one kevin