Tag Archives: mast-hinge

Your bridges cannot stop me

At Lowestoft I got to drop the mast for a good reason for the first time. I wanted to leave Tammy Norie at the Lowestoft Cruising Club beyond the lifting bridge and then catch a train home to Cambridge, but the bridge wasn’t due to lift for a couple of hours. Not a problem!

Very satisfying after all the work I put in to the mast hinge.

My friend Greg responded:

Dare you to shoot a bridge (sail at it, drop mast and sails, rehoist all without stopping).

Hmm… maybe, with the mast lift on a block and no mast gallows. I’ll have to practise!

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2014-08-05 · 08:32

Mast raising demonstration

Raising the mast and sail now that the hinge has been reinforced.

This is an easy one-person job now, though I have yet to try it in the water. It would be much quicker than shown in the video if I wasn’t fiddling with the sail cover, too.

This video shows an experimental mast gallows made by crossing the oars with a bungie cord. It seems like a good way to keep the mast out of the way while travelling with it down.

30kg force is required to lift the mast when standing on the sliding hatch. I measured this with a 100kg spring balance I found in a hardware shop for £3 — very handy!

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2014-06-21 · 23:42

Making the mast hinge: blood, sweat, and Duralac

I made the mast hinge improvement this past weekend and it was a complete success!

Firstly, we paid a surprise visit to MG Metals who had a very fine piece of aluminium alloy bar. I think they were a bit puzzled by me and Dad just turning up, but were very helpful and sorted us out in five minutes. It wasn’t so easy to buy stainless-steel machine screws. Screwfix seem to have given up selling screws. Fortunately, B&Q had a few. We ended up with 5mm pan-head screws and a few countersunk screws for fixing through the hinge outer.

The first step was to work out an appropriate length for the flanges. We settled on 200mm. Dad suggested we put as six screws through the mast in each flange, and stagger them for strength. I cut a single 200mm flange and we drilled a centred 12mm hole at the top for fitting. Here it is hanging into the mast stub on the hinge pin I’d already had made, with the mast folded down and resting on the back of the boat.

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I found positions for the six screws and drilled 5mm holes in the flange. Then came the nerve-wracking stage of drilling holes in the mast. A committing move. I did this by hanging the flange from the pin on the outside of the mast, aligning it carefully, then duct-taping it into position. I was then able to drill through the screw holes and through the mast. After that, I put the screws through and nuts on the back to test the fit. It took a bit of wiggling and everything was very tight, but I was able to get the pin into position. Here’s the result. 

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At this point I made a second flange, using the first as a template, and repeated the procedure. I also made some thin spacers from plywood so that the flanges didn’t press directly onto the mast. I shaped these with a surform so that their curve fits the mast pretty well, with a flat face against the flange. This gives the flanges a tiny bit of movement but will avoid their edges cutting into the mast when the whole thing flexes. The movement helps with aligning the hinge pin.

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This all took up most of Friday, but we were able to raise the mast on Saturday morning in time for my brother’s family to visit. We did this with guy ropes either side, but it already felt pretty steady, and there was no way that the pin was going to escape.

However, we were unable to drop the tight-fitting mast sleeve over the hinge. My screws had spread the hinge outer a little, and it was already an almost perfect fit. We cured this by drilling the holes for the top four screws to 5.5mm, allowing the hinge outer back to its original position.

My niece was particularly keen on the boat and set to work scrubbing the decks, though I think mostly she liked throwing water around and playing with the pumps.

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On Sunday I made the two upper flanges and spacers, again using the first flange as a template. By this stage I was getting pretty quick, and drilled the mast with confidence. Because there’s a ring here to support the mast sleeve, there was only room for four screws. Also, with the flanges so close together, it became impossible to put nuts on the back of the screws! At this stage, Dad suggested capturing the nuts within the flanges. I drilled 8.5mm recesses into the flanges and (gently) hammered in nyloc nuts, with Duralac to prevent electrolytic corrosion between the stainless steel and aluminium.

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This made assembling the whole thing much easier: I simply had to screw in the machine screws from outside. I also ended up drilling out all the holes to 5.5mm to allow the flanges to move around a bit more and let the pin through without enlarging the 12mm holes at all.

Time for final assembly. I dismantled the whole thing, treated the wooden spacers with three coats of exterior wood preserver, painted Duralac into all the holes, and screwed everything together. Finally, the pin went into place with a few gentle blows from a mallet — just right. Here’s the result.

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The red stuff is my blood. And with the temperature at over 25°C there was quite a lot of sweat involved too.

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And here you can see the screws in place painted with Duralac. Blood, sweat, and Duralac pretty much sums it up.

But what fantastic results! We raised the mast, again with guy ropes just in case. It felt rock solid. Once we had it vertical I asked Mum and Dad to be ready on the guys and tried to push the mast from side to side. Nothing. In fact, I was unable to get it to wobble at all in any direction, except backwards in order to fold it away. Here’s a picture of the hinge with the mast raised.

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The mast sleeve slid neatly into place over the whole thing, making everything even more rigid. You can see the sleeve covering the hinge in this picture of the rig reefed down to three panels.


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During that afternoon I had to make several changes to fittings at the top of the mast. No problem: down with the sail, up with the sleeve, and just fold the mast down. No need for help. It feel like about 15-20kg of force: no problem at all. And I’m pretty sure it’ll work just as well on a canal or river.

So now Tammy Norie can duck under bridges with ease, opening up a lot of opportunities for inshore exploration.

Many thanks to everyone who suggested solutions, but especially to Dad who gave me advice at every step of the way and taught me to use his tools. Hurrah for engineering!

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Filed under mast, Repairs and Modifications

Mast hinge design

I’ve had some useful discussions about Tammy Norie’s dodgy mast hinge with members of both the Junk Rig Association and the Cambridge University Yacht Club and have come up with a winning design.

Many people’s first suggestion was to somehow prevent the pin from popping out by using countersunk screws.  The problem with this is that the mast sleeve is only about 3mm thick and doesn’t have a lot of depth for countersinking.  I’m also reluctant to weaken it any further.  It already seems like not enough material to support a wobbling mast.

Another common suggestion was to make the pin longer and somehow shorten or remove it just before dropping the mast sleeve. Various ideas involving springs, bolts, and slots in the sleeve were suggested. The problem there is that if I’m single-handed on the boat on the water then I won’t be able to let go of the mast, remove or adjust the pin, and drop the sleeve in a safe way.  At some point the mast will be insecure.

The best suggestion came from Igor Gotlibovych of CUYC. (Igor is, with two friends, fixing up their yacht Auriga for an imminent circuit of the South Atlantic.) He sent this picture, saying “you could add two of these, riveted to the inside of the lower section of the mast, to provide extra support.”

Junk

In fact, it’s even simpler than that, because the flanges don’t even have to be bent. Here’s the sketch for reinforcing the lower part.

Hinge reinforcement

In fact, since I’m at it, I’ll probably reinforce the hinge connection to the upper part as well, like this.

Double hinge reinforcement version 2

A good thing about this design is that the exact dimensions of the flanges aren’t critical. The plan is to visit a nearby metal merchant and see what pieces of aluminium alloy he has available. It won’t be hard to cut them to shape. I’ll space them out from the curved inside of the mast using wooden padding, which will also provide a bit of compliance while preventing the flanges from grinding away at the mast.

Watch this space for the results.

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The mast hinge saga

Tammy Norie came with a hinged mast of dubious origin with a pin that has been lost.  The hinge is about 1m above the deck. Once the mast is upright on the pin, an outer sleeve about 1.5m long slides snugly over the join. In theory.

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The papers I received with the boat don’t actually match the mast I have. The one that looks plausible says it’s “the Unique Sunbird hinged mast”, but when I asked Robin Blain of Sunbird Marine about it he said it wasn’t one of his. It has a small label saying “Proctor Masts”, but they don’t seem to exist any more. Proctor Masts USA has a link for Proctor UK that goes to Selden. I wrote to them both, but no reply.

One of the first things I did was cut away the badly corroded supporting tube and have a new tube and pin made for me (at very reasonable cost) in stainless steel by the excellent Mackay engineering in Cambridge.

The main problem is that the pin must fit within the sleeve, and so it can’t protrude beyond the holes in the lower section of the mast. This means it only has about 3mm of purchase on each side. We found that if you don’t handle the mast very carefully the pin pops out of the holes and the mast basically falls off.  This is very hazardous to anyone or anything nearby, and could potentially do serious damage to the boat and mast as well.

While Tammy Norie was in the driveway we rigged up a guying system using a ladder.

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We later found that we could support the mast well enough with a person on each side of the boat, but I’m not happy with the hinge at all. I certainly wouldn’t attempt to raise or lower the mast alone while afloat. That’s a great shame, since there’s an obvious advantage to enabling her to duck under bridges.

So although we can get by for now, we are thinking about how to fabricate a better hinge. It must allow for single-handed raising and lowering of the mast on the water (on rivers etc.) and be stronger than the current arrangement.

The best hinge I’ve seen is one used on Marshall Marine’s catboats.

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I wrote to Marshall but they only make the hinge to fit their own smaller masts, and as you can see it doesn’t allow for any cabling in the mast.

So I need to come up with a design that will fit snugly inside the current mast tube and provide extra purchases on the pin. And I probably need to machine it out of aluminium alloy to match the mast.

I’d welcome any suggestions!

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Filed under mast, Repairs and Modifications