Mast Gate problem - advice please

[Twister_Ken]

The situation:
Aluminium mast, gate is an opened out part of the luff groove, which normally is partially closed by a s/steel plate. This plate is slotted for a s/steel bolt which can be loosened to allow the plate to be slid back so that luff sliders can get into track, then tightened to clamp the plate in position to keep sliders in groove during normal operation.

Problem:
The threads in the mast that take the bolt have partially stripped (maybe a bit of electrolytic corrosion?). The mast gate plate cannot therefore be clamped tightly and luff sliders escape in hoisting (sometimes) or dropping (often).

Solution:
Presumably to retap the mast to accept the next size up of bolt, but how to prevent this happening again? Or is there another solution?

 

[Sinbad1]

Problem is caused by electrolytic action between aluminium and stainless. There are proprietory barrier creams/insulators to prevent this available through chandlers.

It can be avoided by using monel fixings such as pop rivets but as you need to slide the mast gate open perhaps you could make up a longer piece of either aluminium or stainless gate and rivet one end into position (but not too tight) and drill and tap into the mast at the other end for the bolt/set-screw which will allow the plate to be tighten/loosened and pivoted back/forward into position.

 

[Trilogy]

I had the same problem with a flotilla of Jenneau yachts in Greece.

In the case of the smaller boats, the gate was only about 10cm's above the boom and you only needed to open the gate to remove the sail. The quick fix was to drill a 3mm hole just above the gate and slide a stainless steel split pin into the hole. The 2nd plastic luff slider then couldn't drop below the split pin.

A (slightly) more elegant solution was found for larger boats that required the sliders to pass through the gate for day to day use. I used a plastic bolt 1 size larger than the existing stainless one. Using the hole in the mast as a die, I cut a new thread on the plastic bolt and used that with great success.

Good luck.

Nick

 

[Twister_Ken]

Question to Nick

Just to confirm, you got an oversize plastic bolt and simply twisted it in to the mast bolt hole, relying on the mast to cut a new thread in the bolt?

I also wondered - if I can get a finger or two inside the mast - about the practicality of epoxying an appropriately-sized nut on the back of the bolt hole.

 

[dickh]

You can get some commercial fittings marketed under a variety of names - 'Rivnut' is one which can give a decent length of thread in the mast wall. To be effective on an Al mast they would have to be in Monel - which I dought is made. Perhaps Aluminium ones would be suitable

 

[Trilogy]

Re: Question to Nick

Correct. If you can find a fairly soft plastic bolt, the 'springiness' prevents it from rattling loose.

Good luck

Nick

 

[castelino]

Recoiling or "helicoiling" could be one solution, using stainless steel coils, provided you have sufficient depth for the thread. I have done this very successfully to join the main beams to the hulls on my Tornado catamaran. You will need to apply some liquid insulator to the inserts to prevent corrosion between the Al and SS, and apply heavy duty grease to the bolt threads as a corrosion resistant measure.

Otherwise drill out the threads and put a nut on the other end?

Trevor Castelino Tel: 07989 944379

 

[PuffTheMagicDragon]

Ken, I had the same problem with the Proctor mast of my Centaur. In fact, I almost lost the Stainless steel plate overboard! My solution was to drill the plate itself with two 5mm holes, one above and one below the existing 3/8" elongated hole. I then drilled and tapped the mast for M5; I chose this size thread because with a pitch of 0,8mm there would be 3+ threads in the mast thickness. I can live with this solution because the gate is only opened at the start and at the end of the season since I have converted to slab-reefing. It might not work for roller reefing. Regarding the problem of electrolysis, I did apply a smear of PBC grease - it was handy - but I do not think that it is a problem because it is not as if the metal parts are continually being dunked in salt water. If you get much rain, then it will be even less of a problem; at least that's what I believe!
Fair Winds!

Wally

 

[Guest]

I use a split pin, retained by a lanyard, to close one side of the track just above the gate. Seems to work ok.

 

[bigmart]

The Rivnut Idea should work. I sell these items for fixing Glass Balustrade Clamps to Stainless Tube. If you fancy trying this idea let me know & I will investigate to find out what materials are available.

AS an alternative Chandlers sell a Stopper nut which is designed to fit in the Luff Groove of most masts. Round & flat styles are available. THe only problem is that these devices block the groove so you can't run sliders past them but they are simple & easy to fit requiring no drilling or mods to the mast.