Attaching a Spinlock clutch to a dinghy mast.

[ianc1200]

I've bought an elderly SuperNova Mk1 racing dinghy (sort of an updated Laser). The seller pointed out the Spinlock PXR clutch wasn't securely fixed to the mast. It was screwed in with two self tapping screws which were pulling out. My question is how to fix this. Larger screws into the same holes won't work because of the diameter in the Spinlock not large enough to take bigger. The yard rigger man showed me how to do pop rivets but you couldn't get at the tool through the Spinlock. He suggested simply moving the unit up an inch and again using self tapping screws. I've looked at Rubnuts, but you need to drill 8mm holes for a 4mm screw/bolt. Worried about weakening the mast, steels screws into aluminium etc - what is the best way?

 

[dankilb]

I recently went through the same dilemma - but with a much larger mast (41' AWB) and XTS clutches!

I also tried rivets first. With the larger Spinlock clutches you can dissassemble them, so that you're only riveting the baseplate (for access) and reassemble the clutch around that, but I wasn't happy with the result. The 6mm rivet heads weren't happy in the countersunk (M8) holes.

In the end, I went for riv nuts. I used aluminium rather than stainless. I also noted that this was how some of the original factory fittings were attached to the mast. I applied some Tef Gel to the stainless screws to try and reduce galvanic action. Our extrusion is much larger, but I wouldn't imagine the riv nuts contribute much weakness once they're set into the mast and with fasteners through them.

I can't really think of any other way. Self-tappers seem a bodge to me.

The gold standard would probably be to drop a pre-drilled and tapped backing plate down the mast and try to line up the holes by pulling a piece of string through.

 

[northwind]

If you don't wa t to use rivnut, You could fashion a mounting plate out of hpde or wood and rivet that to the mast and then self tappers for the clutch to the mounting plate. Personally I would use Ali rivnuts.

 

[William_H]

I have attached components to CFRP boom where there was some access to open end of boom. I filed down the tip of SS screw on 2 sides to make like a screw driver blade shape to end of srew. Then drilled a hole sideways through the spade shape. I attached string to the hole. By using wire I was able get the end of the string out from inside the mast in your case, so pull the string and with luck you have a screw coming from inside to outside. Times 2 of course. You feed a nut over the string and hopefully can get it onto the thread. Now you can hold the spade shape with pliers while tightening the nut.
You can put a washer on inside under screw head. The down side is you have a nut instead of screw head where it is seen and you may not be able to get a nut into cavity intended for screw head. But it must just solve your problem. ol'will

 

[Neeves]

I like Northwind's suggestion. Make a mounting plate whose fixtures (holes) to the mast will be as far away from the existing holes as possible and then mount the the plate, with the clutch attached, to the mast. We have exactly these for some components to our mast and cross beam. The plates have right angles flanges at each end, like a long flat 'n' to accomodate the curve of the mast (so the flanges and the centre of the plate touch the mast). You could make something similar by buying, scrounging, a rectangular box section and slitting is down the middle of 2 opposing sides.

Jonathan

 

[oldbloke]

It will be fine if you just move it and refix it.
Ideally make sure the new holes are not in line horizontally with the old ones.

 

[Daydream believer]

If you cannot get the head of the pop rivet gun in the hole & it is only a very short distance short of what you need, then put a piece of tube over the rod of the rivet. Then when you push the rivet in the hole it has the effect of extending the length of the nose. The tube must be small enough to fit in the hole. You may be able to do it with a number of small nuts. Obviously you cannot have too many, as the gun will not have enough rod to grip.

 

[dankilb]

Others claim success threading/pulling a bolt through the hole from the inside with a mousing line. I read this when researching how to fix our new clutches to the mast in older threads/posts. One post suggested a dab of epoxy to attach a mousing line to the end of a set screw. The other suggested drilling a hole through the end in order to tie a mousing line through (might be a challenge with M4!). The idea is you pop the line through the hole, retrieve it from a sheave/hole somewhere lower down the mast, attach the bolt/screw, pull it through the hole (here's where I started to think 'easier said than done'!) and the hold the end with grips while tightening down the nut. You then cut off the excess length required to grip the threaded end while tightening. This sounds like a recipe for frustration to me - but thought I'd pass on the method.

 

[Telstar26]

Of course you could just tie the halyard off on the mast step!

The section of the mast below the gooseneck takes a lot of strain when the kicker's on hard, so don't weaken it and make sure the lowers are tight. (If it's an early Giles boat, it may not have lowers, so fit some!)

Geoff, Supernova 357 (the first one!)

 

[ProMariner]

Ex laser sailor, hate rivets in aluminium. I would use machine screws (coated in tefgel) with nuts and washers on the inside. Take the mast step off to access inside the mast, tape a ring spanner to a batten', tape a nut and washer into the ring spanner, and use to put the nut onto the threads while tightening from the outside, it's really not as fiddly as it sounds, and is a rock solid attachment. It's easier if you use slightly longer machine screw than you need, and easier still if you lie the mast down so the cleat is underneath while you start the threads.

 

[PetiteFleur]

I would use Rivnuts - Monel ones if you can get them otherwise stainless steel with plenty of Duralac. I used Rivnuts on my previous 27' boats mast to fit cleats.

 

[ianc1200]

Of course you could just tie the halyard off on the mast step!

The section of the mast below the gooseneck takes a lot of strain when the kicker's on hard, so don't weaken it and make sure the lowers are tight. (If it's an early Giles boat, it may not have lowers, so fit some!)

Geoff, Supernova 357 (the first one!)

Mine is a Giles one (478 I think, certainly 470 something), and has the lowers, but haven't tried it yet and as a gaffer I'll naturally have them too loose....

Have ordered a Rivnut set for aluminium, although tempted to buy the dedicated bracket and pop rivet that on. Although may do what you suggest - discard the Spinlock and just tie the halyard.

 

[Boathook]

If you cannot get the head of the pop rivet gun in the hole & it is only a very short distance short of what you need, then put a piece of tube over the rod of the rivet. Then when you push the rivet in the hole it has the effect of extending the length of the nose. The tube must be small enough to fit in the hole. You may be able to do it with a number of small nuts. Obviously you cannot have too many, as the gun will not have enough rod to grip.

Done exactly the same a few times with some nuts. Be prepared to loose the nuts as they go flying as the rivet sets !