Episode 18 Pole, Son of Pole and Twin Poles

This is not a blog about Polish men, its about building a contraption for stepping* the mast safely.

(*Yachtie phrase, meaning getting the mast up)

I had the following criteria

• It could be operated it single-handedly
• It could be locked off at any point in lowering or lifting the mast, to allow me to scurry about and untangle things*
• It could be folded up for storage
• It was safe
• It was cheap

(* This is inevitable when you consider the rigging's penchant for turning itself into a pile of knotted spaghetti whenever it is demounted)

Firstly, it is necessary to point out that the masts on trailer-sailers like mine, are designed to be lowered and raised. Mine has a pivot pin on the cabin roof, and is designed to be lowered backwards. Once the pivot pin is removed, the mast can be slid forward for transport-by-road. It seems likely that the designers of such systems believed that the typical boat-owner had a family of 7 ft weightlifters conveniently at hand for all such operations.OK, so that's an exaggeration, but getting the mast up or down is a challenge for me and a mate, and that presumes that I have a mate, and that he or she is available and willing to help.

The answer to my lack of mates, of course, is the mast-stepping contraption. This went through several iterations before I got something to work, which I have called Pole, Son of Pole and Twin Poles.

My first attempt was an early variation of a gin pole, using a long piece of timber. Let's call it Pre-Pole. A gin pole is a pole that is supported at one end and held at ninety degrees to the mast. The pole is supposed to be kept in this position by guide ropes secured on the deck. However, the wood in Pre-Pole split, and the mast collapsed onto the boat. Fortunately, my boat is strongly built, and didn't seem to mind, which surprised me almost as much as the mast falling down onto the stern of the boat.

Pole: 18mm aluminium tube with rubber vee-block foot,
showing buckling in the middle

Many, many months later, I revisited the concept with Pole, an 18mm diameter aluminium tube, 3m long from the giant retail hardware store down the road. By this time, I had my furler, which probably added another 30kg to the mast assembly, bringing it up to maybe 60kg, and the corresponding potential to do much damage if dropped.

Like its ancestor, Pole was a gin-pole, supported in the vertical position by guide-ropes on either side. The foot of Pole comprised a rubber vee-block, which, I had hoped, would grip the base of the mast. I drilled a 38mm hole into the rubber vee block to fit it to the end of Pole. The best way to drill a hole into a rubber block, I found, is with a spade drill, which is remarkably easy. The only hard part was sweeping up umpteen rubber shavings off the floor after the event.

If you're paying attention at this point, you might ask how I got a 40mm pole into a 38mm hole. The answer, of course, is that the hole is in a rubber block. One trick that worked well was to squeeze the rubber block in a vice. Drill the hole, release the vice, and the 38mm hole expands to 40mm. But, why not simply get a 40mm spade drill? Because the giant hardware store down the road didn't have anything bigger than 38mm.

Son of Pole before lowering the mast,
showing the yoke at the bow for the furler

Pole did not split, like its timber ancestor, and showed early promise as Pete (a mate, yes I do occasionally have them) and I gingerly rocked the mast and fuller back on its pivot. We almost declared victory, when we noticed that Pole had bent alarmingly in the middle, so we put everything back before Pole would be overcome by Euler's Buckling Load (something I had learned at University) and drop the mast on our heads.

Seeing that Pole was not beefy enough, I then tried Son of Pole. Son of Pole was a 30mm aluminium tube with 3mm thick walls, acquired from a metal merchant in the suburbs for about $30.

Son of Pole, with gin-pole upright and mast fully down.
Note the guide-ropes either side,
which should have kept Son of Pole upright.

Son of Pole did not bend in the middle, like its predecessor, and I successfully lowered the mast and took the photos shown here. However, when I tried to raise it again, Son of Pole inexplicably lent over to starboard, and the foot nearly detached from the mast. The whole thing threatened to collapse, so I got a shoulder under it. This time I was on my own (Pete had better things to do), and suddenly realised that I was stuck with a teetering mast and nowhere to go. Thankfully, a passer-by saw my predicament, rescued me, and helped me get the mast back up.

Now, I knew two things; the 40mm aluminium tube was beefy enough to avoid buckling, and I needed something to stop the mast slewing over to one side. I decided the most robust approach was an A-Frame, with two poles either side. Enter Twin Poles.

Twin Poles needed another trip to the metal merchant to buy another 40mm aluminium pole plus something to make the feet with. This delayed progress in weekly increments, as the only time I could get to the metal merchant was before 1100 on Saturday Morning, such were my working hours, and the metal merchant's opening hours. The same applied to the bolt shops, as I tried to source metric stainless steel bolts of the correct length, with or without shanks. The giant retail hardware store down the road does stock stainless steel bolts, but only in packs of three, or five, when you want four, and rarely of the right length or diameter.

Twin Poles: Foot assembly on the
starboard side showing ply board
slotted on to the base of a stanchion
and a chain plate, pivot pin assembly and
aluminium pole

I intended the feet of the A frame of Twin Poles to be supported on the deck either side of the cabin. The wider the feet, the more stable the A frame. However, there was nothing on the boat that would provide sufficient support and articulation. A simple rubber foot could slip, or punch through the deck. The first step was to make up a pivot pin for each foot, which is harder than you might think because everything was arranged at every angle except a right angle. I decided to get a couple of short sections of 70mm square aluminium box section from the metal merchant, cut one side off, drill through holes at the right angles and use M10 stainless steel bolts as pivot pins. I used aluminium because it was light, and quite easy to drill, cut and file.

Twin Poles: Yoke Assembly
part way through operation,
showing line through block on
the anchor plate to control the drop and lift

Next, the pivot pin assemblies needed to be secured to the deck. I didn't want permanent fixings, so opted to use some off-cuts of builder's ply. I realised a secure support could be got by using the ply to bridge between a stanchion and chain-plate. This had the added advantage of allowing all the axes of rotation for the mast and A-Frame feet to be positioned roughly in-line. Further, bring the A-frame feet further aft meant a longer lever arm, and a longer lever arm meant less stress, which meant more safety. I found most of this by experimentation, which resulted in my aluminium poles being about 200mm too short. The short-fall was made up by lengthening the plywood yoke. One pole was fixed to the yoke with two bolts, and the other with one to it be rotated to bring the legs together for storage and transport. Also, some rotation was needed because of the inaccuracy of my measuring, cutting and drilling.

Getting the angles right for the pivot pins was difficult. I pre-drilled the holes in the poles, then found corresponding points in the pivot-pin boxes. The pivot-pin boxes were fastened to the ply boards by a single bolt, which allowed some rotation between the pivot-pin boxes and boards. The rotation was needed to allow the boards to be slid into place. Some precision was needed to allow enough wiggle to allow the boards to be mounted and demounted, while getting the yoke to hold the forestay and furler in the right location.

Twin Poles; view from the stern
showing the hauling line passing
round the cabin top winch and
secured on the port jam-cleat

To prevent scratching the furler, I lined the inner faces of the yoke with an off-cut string of neoprene, held in place by some black goo and covered with a duct tape from an off-cast roll. Unfortunately, the furler didn't escape completely unscathed; when Son of Pole dropped the mast, the furler hit the ground and collected a few scratches.

I secured the spinnaker halyard to an eye on the top of the yoke, which was bolted directly to a corresponding eye on the bottom. The hauling line was secured to the bottom eye. I thought that a direct fixing from one eye to the other would be more robust than something that relied on the plywood in the yoke. In the final assembly, the yoke had no bending moments, and the forces were transferred directly between the halyard fixing points, and straight down the axes of the poles. The structural engineering that I did in the early part of my career came in useful here, as I visualised how the forces would be transmitted through the assembly.

Twin Poles: at the start of the drop

The hauling line passed through a block on the anchor chain-plate, went aft to the cabin-top winch and then further aft to a jam-cleat, where I could lock it off at any point. The photos show the furling line exiting the furling drum next to the hauling line. Its there because I didn't take it off, but it was slack and took no loads.

Easing the hauling line allowed the mast to pivot back. This was a nervy moment for me and I jammed the hauling line a couple of times so that I could go forward and check that everything was secure, and to take photos. As in previous attempts, the mast wanted to slew off to starboard, but Twin Poles held firm.

With the mast fully down, the lever arm of the A-Frame became apparent. I had intended to make the lever arm as long as possible to reduce stress, but had it been any longer, I could not have un-hooked the furler, which was now almost 2m above the cabin roof. Having dropped the mast, I took out the mast pin and shifted the mast and furler forward to rest on the bracket on the bow rails. I then made the boat secure on its trailer and hauled it home, where I intended to do more tinkering.

Twin Poles: Mast safely down

Twin Poles: Mast down,
view from bow showing
the A -Frame and hauling
line head-on