Doug asks: Do you have the dimensions of your mast's sections handy?

I am afraid I did not note measurements at the time. I have just been up to the boat (which is under a tarpaulin) but measured the top and bottom sections of the mast by using a piece a string and getting the circumference. The bottom section is about 4.25" (about 107mm) diameter and the top section is about 3.5" (about 90mm) diameter.  The centre section was obviously somewhere in between. I guess the wall thicknesses are about 2mm.  (The centre section was long enough to extend completely to the foot, so the bottom section is, in effect, double skin.) The result is a mast which I consider a little too heavy and probably over-strength for my boat. 

I would like to replace it with a lighter mast, and keep this one as a possible mizzen for a bigger boat.

This is starting to digress from the subject of Steven's thread.

If you don't mind, I am going to see if I can copy this conversation over to a new thread.

Since I don't have the meat to put a tabernacle into, I'm looking at doing some low-angle shrouds from the hulls to the mast only about 600 mm above the foot of the mast stepped on the forward crossbeam- all of the sail would be above the stays. It will be rather strange in appearance, I need to make up some sketches.

I saw this arrangement in the Decathlon sports shop on an inflatable dinghy - it sounds like the kind of thing you’re thinking of.  But there’s a YouTube video of a very interesting mast step arrangement that might provide some inspiration also [edit - this is it https://youtu.be/6vNtklr4W04?feature=shared] - also see image below.  I have no info on either of these arrangements but they each act in the way you are talking about, supporting a mast close to the bottom end 

Doug: Steven, your mast appears to be several sections of telescoping aluminum tube, can you share any details, please?

I too would be interested in the details of Steven's mast.

Doug, if you are looking for ideas, I have made a couple of masts from telescoped, differing sections of aluminium tube, and found it not too difficult.

Ideally, I suppose, one tube should fit nicely into the next one, but sometimes you have to make do with what you have. With my scrap pile of tubing I found in each join, the annular gap between the two tubes was too great, and some packing was needed. Here is a schematic diagram: 

In one case, where the gap was small, I stuffed the gap with epoxy-saturated short-pile synthetic carpet - it was just because that's what I had on hand - and jammed the two tubes together before the resin cured.

In another case I made a strip of wooden battens (laid out on a strip of duct tape) wrapped it around the smaller tube and epoxied it in place, filling the gaps between the strips with epoxy filler, sanding it down until the fit was nice.

(As a matter of fact, you can cast the epoxy with the two tubes assembled, to get a perfect and perfectly concentric fit, but ideally you want to be able to get it apart again so that's a bit risky. I've done it though, using baking paper as a release agent. Probably not necessary to go to those lengths for a small mast.)

On the other mast I made the annular packers from wood and also incorporated the cone-shaped fairing which smooths the transition between the two diameters (necessary, for two reasons). The wooden packers looked like this (schematic):

The fairing serves two purposes: (1) to smooth the transition between the two diameters and (2) to prevent the small diameter tube from "telescoping" down into the larger tube due to the downward force of the halyard.

Metal fastenings (rivets etc) are not necessary, and undesirable. 

The overlap between the two tubes needs to be "sufficient" (10% didn't look enough to me so I doubled it, although in theory it should be enough). The main stress on the joint, I believe, is rotational, so some kind of adhesive is necessary. (Junk rig puts rotational forces onto the mast). I used epoxy glue (carefully cleaned and primed with liquid epoxy) and it has proven strong enough, but I now believe this is the wrong material to use and it has been suggested that a polyurethane rubber glue such as Simsons would be more appropriate. I coated the faired joins with an overlay of glass cloth and epoxy - this is now showing signs of movement/stress on the surface, maybe better coated with something a little more flexible, or not coated at all.  Not sure. 

3-piece alloy tube mast for Serendipity

These are just ideas that have worked, maybe there are better ways, anyway it is not difficult to make a "tapered" alloy mast from scraps of tube of varying diameter, and timber topmast sections using the same principles have also been successfully made and reported. Hope that gives you some ideas.

Anonymous wrote:

On Miranda, my AeroJunk Etap 23, I used this halyard system. The halyard went to the mast top to a double block, down to a single block on the top batten (Yard), back up to the double then terminated at the rear end of the yard. 

Paul McKay

I dropped my mast yesterday and did as you showed. So much easier! I can easily lift everything with an 8mm halyard now..I love the etap rig.

As already discussed on another forum, your sail is outside the norm when considering the relationship between yard angle and mast balance, as shown on your sketch diagram, which will result in a larger than normal halyard angle

Len wrote: I am not sure that is true.

I think it is still true in principle - probably more correct to say that in the case of the aerojunk rig it is somewhat irrelevant.

In any case, I stand corrected. There is something in what Len is saying.

The conventional junk sail (including the SJR) hangs from the halyard and is held to the mast by an array of standing and running parrels which handle the horizontal forces on the sail bundle, which would otherwise tend to swing forward - and to keep these horizontal forces easily manageable there needs to be some harmony in the outline shape of the sail, the relationship between yard angle and mast balance, yard attachment point and height of crane etc. This harmony also serves to ease the effort of hoisting that last metre or so when the angle the halyard tackle makes with the vertical is at its greatest.

However, as Paul Mc's photo shows, evidently the aerojunk sail is set up quite differently, with a different halyard arrangement and also requiring no parrels - rather more akin to the gaff sail, with its throat and peak halyards, and the role played by its yard throat and boom throat in holding the sail from moving forward on the mast. Evidently the aerojunk sail design thus somewhat more free from the normal constraints on junk sail outline shape. I guess that is what sets the rig apart from the others, the key feature of the aerojunk rig being the double wishbone cross bars - or the D-formers in the case of Steven's rig and Miranda's latest rig - which play that same mechanical role as "throats" in maintaining the correct fore and aft position of the sail.  (I think we see the same mechanism at work in David T's junk soft wingsail).

I can see now that Steven's sail is within that category, and get a better understanding of Paul Mc's article on his "hybrid junk" on P9 or Magazine #84

Looking forward to successful trials.