BR20 tabernacle screws lifting

[Mike R]

This is my first post as a newbie to BR20 Gladys, who I have recently taken over from Matthew P.   I am glad to say that the boat seems to be well set up and a joy to sail, however there is one chestnut that seems to have affected a number of BR20s that still seems to be a problem, which is that the rear tabernacle screws seem to enjoy coming loose.

It is fair to say that there is very little left in the holes to hold the screws, apart from the slivers of tie-wrap that I had to shove down as a quick fix.  The engineer in me would say "bolt it through" but I understand that it is better to pull a few screws in a "mast event" rather than damage the foredeck.   

The screws are already #12 and the holes are worn so I am not sure going up a size is the solution, so I am thinking fill the holes with epoxy, but maybe some sort of glass filler may also be required to ensure the repair will hold a thread?

I look forward to any comments and also any tried and tested solutions/ fillers used.

Also any thoughts on root cause of this problem?

[Llafurio]

I use "Fischer UX  ... R" plugs. They form a nylon knot inside a cavity or on the far side of a wall. I use them also where the locker lid screws on the gunnel inside have lost grip. C.

[Mike R]

Thanks for the tip - did the fitment of Fisher plugs solve the problem?

Has anyone any throughts as to the root cause of the tabernacle screw pulling problem?

The tension in the jib halyard is significantly different depending on whether the jib furled or unfurled.   When the jib is unfurled, the jib boom lifts and nicely tensions the jib outhaul & shrouds and the mast is nicely planted in the tabernacle.  However when the jib is furled, the jib outhaul and shrouds relax and the mast is able to move around in the tabernacle and I guess gives it a knock every now and then.
Is the the cause of tabernacle screws loosening?

Would the fitment of a topping lift to the aft of the jib boom better control the tension in the jib outhaul and help keep the mast planted in the tabernacle at all times?

Any thoughts from the community?

[Llafurio]

Thanks for the tip - did the fitment of Fisher plugs solve the problem?

Yes.

Has anyone any throughts as to the root cause of the tabernacle screw pulling problem?

I have.: The first BRs did not have oblong holes for the tabernacle bolt so did not offer sufficient play for when the mast was pulled forward before the wind when the shrouds were loose. That pulled the rear tabernacle deck screws up. -On the early BRs.

On later BRs, after I had complained, the bolt holes were made oblong, but it still was possible that they were not giving sufficient play at all times in all conditions.

Then, even if your bolt holes are big enough, you yourself do exert a pulling force on the tabernacle deck screws every time you step and unstep the mast while standing inside the cockpit. Just figure out the forces yourself.

You are mistaken if you think the tension of the forestay plays any key role in pulling the tabernacle deck screws up. The stepped mast is to stand firmly on the deck on its own foot, while exerting no vertical forces at all on the tabernacle.

It is a good thing the tabernacle is not through-bolted onto the deck. A falling bolted mast would cause severe damage to the deck. However, it is a common issue on BRs and BRes that the tabernacle deck screws lose grip before long. For some time you can counter that by using bigger and bigger diameter screws, to no lasting effect however, or you can resort to using suitable nylon plugs for the screws. They will hold well, but still will not damage the deck as much as through-deck bolts, washers and nuts would - in case the mast falls.

[Peter Cockerton]

If and when the initial fixing holes will not provide any more grip even with the largest shaft and thread screws I fixed a small pad of marine ply under the deck for the screws to get some byte. Totally agree with thought process on nuts washers and bolts to secure the tabernacle, but I can't see anything different in allowing the screws to pass through the now enlarged holes in the deck and into the wood pad under the deck as long as the screw size is kept sensible and judged to rip out of the pad should the shroud supports fail.

Peter C

[Mike R]

Thank you for your replies.

I opened out the holes to 6mm and Fisher plugs but they are barely holding any torque, so I dont expect them to last long.   Hopefully to the end of the season.

I expect a piece of plywood will be one of my winter projects

[Llafurio]

You must strictly adhere to the plug - screw diameter and length matchings prescribed by Fischer. If the plug twists in the drilled hole while screwing the screw down, use a drop of silicone oil on the screw thread to reduce torque friction.

[Graham W]

My boat suffered from loose tabernacle screw misery a long time ago.  This was partly as an after effect of my mast going over the side when a shroud shackle came undone on Lake Bala.  The wooden capping of my centreboard slot also came loose, because it was secured by bare screws into the GRP centreboard casing.  They weren't able to absorb the lateral forces from the top of the centreboard when sailing hard to windward.  The upshot was that the whole of the wooden capping came off one afternoon off Corfu.

The solution in both cases was wood.  A half inch marine ply plinth was epoxied to the top of the foredeck as a new base for the tabernacle.  And wooden strips (actually pieces of vine trellis donated by a Greek taverna) were fixed under each side of the top of the GRP centreboard case.  In all instances giving the screws something more substantial to bite into but which could still rip out in an emergency.  I've not had any problems in the many years since - crude but effective.

[Mike R]

Returning to the plug option, the smallest Fisher plugs I could find were 6mm x35mm.  The deck is approx 25mm thick, so I took 10mm off the bottom of the plug to fit in the hole and then fitted the existitng self tappers (also approx 25mm).

At the moment when you tighten the screws, the plugs seem to want to just pull out of the holes.

Do these Fisher plugs need to be left full length (35mm) and engaged with a full length screw to make them work - i.e. drill through, don't cut the plug and leave 10mm of screw and plug protruding below the foredeck?

[Llafurio]

... Do these Fisher plugs need to be left full length (35mm) and engaged with a full length screw to make them work - i.e. drill through, don't cut the plug and leave 10mm of screw and plug protruding below the foredeck?

Yes. You must NOT shorten the plug, but adhere strictly to the plug - screw length and diameter matchings which are prescribed and illustrated on the box by Fischer. By shortening the plug you render it useless, because it is the end of the plug which performs the magic of "knotting" the plug around the screw. 

Once the plug has formed the "knot" below the deck, you can either -conventionally- cut the protruding tip of the screw off, or -smarter- take the first long screw out, and replace it with a somewhat shorter version of the same diameter.
https://www.youtube.com/watch?v=SUhbhApHuV4  and  https://www.youtube.com/watch?v=A75-Ks8iXJI .

[MarkDarley]

Something else to check!

[Paul Samoilys]

Graham I have had the same issue in Corfu thankfully not when sailing but when stepping the mast all 6 screws just popped out. Looks like this has happened before and wondering on your marine ply solution.  Do I then have to make all sorts of tricky adjustments as the mast will be half an inch taller?  Any thoughts on whether the Fischer solution might work given the photos?

[Graham W]

Paul,

Yes, from the photos it certainly looks like it has happened before.  I think that you have two options:
1.  Do a better job of filling in the holes with epoxy than whoever did it previously and then try the Fischer solution, sticking strictly to the instructions on screw length outlined by Claus above; or
2.  Still fill in the holes with epoxy but then cover over the whole mess with the 1/2" marine ply.  I wouldn't worry about the effect that this has on the rigging, as the directly affected bits of standing rigging (shroud strops) would need to be checked and adjusted next season anyway.

Good luck!

[Paul Samoilys]

Thanks for the advise Graham.  Any plans for an Ionian sojourn?

[Graham W]

A possible flying visit for a wedding next July.