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.

Anonymous wrote:

Planform (the outline or geometric shape of the sail)

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 .

I am not sure that is true. There was another sail not long ago, where the top panel was a triangle with no yard that this reminds me of. In this case the top panel is replaced with two lines but the effect would be the same. It looks like the planform has been derived much the same as the first SJR which used string and bamboo sticks to see what would hang straight on its own. I think the friction may be less than it looks at first. The effective yard angle would be fine in strong winds reefed and manageable in light winds where wind pressure is less of an issue. If there is any issue with friction, I would suggest a good downhaul system is the priority.

It seems to hang well in the back yard, even with a breeze. I guess the proof will be on the water as various wind angles. I too will be interested in how well smaller jiblets work. I think the size of the jiblets does not really matter. If they are shaped right, they will provide lift on their own. If they stay out of the way of the mainlets, then the mainlets may perform better with the batten formers as the mast becomes the leading edge and the leeward side of the mast couples with the mainlets better than normal battens would allow.

So far as I can tell, this has got to be one of the simplest systems going, with more conservative sail shaping than the origami (even simpler) perhaps.

I agree with Antoine, it is great to see you have made your own sail and I am sure it will look splendid with those bright colours. I am all for DIY sail making, where possible (while remaining still just a little envious of those who can sport a professionally made one!)

However, I would not have the courage to design a sail first time round, so I applaud your innovative approach, while keeping my fingers just slightly crossed…as I will explain.

For the sake of further discussion, I have approached the idea of a split sail from a somewhat different stand point from yours. Here is my thinking on the split rig.

I rather think that in itself the split does not contribute much, if anything at all, to the performance of the sail. I am not convinced that the “slot effect” of a Bermudan sloop rig,  or “funneling the air" to the main panel luffs has much application to a lug sail – others more knowledgeable than me might disagree. It will be interesting to know how it works out for you, in practice. (I can't foresee any major problems).

Mast balance (percentage of sail outline ahead of the mast centreline).

For me there were two main  reasons for having the split: (1) it was primarily to get the largest amount of “mast balance” possible for a lug sail (about 33% or perhaps a smidgeon more) as I believe that the greater the balance, the best (or at least the easiest) downwind handling characteristics, for any boat with a single sail rig – and (2) following Slieve’s thinking (I copied his sail design), to try to build the best and most accurate camber possible into the forward 33% of the chord, with the hope that this would give a slight edge when it comes to windward performance. I think the result was a moderate success on both counts, but if so, that could only be possible with a mast balance of around 33%. Anything less in the way of mast balance, I felt, would render the sail no better than if it were contiguous and therefore not worth the extra trouble of having the split. That’s where my thinking was a little different from yours. Your thoughts on this later, when you have tried the sail, will be of interest.

Running rigging (in particular, the parrels)

Part of the split junk rig package (as per McGalliard) is the running parrel-downhaul method of setting the sail – which appeals to me intuitively more than the conventional array of parrels which seem to be necessary on conventional sails. (Mind you, I have not tried any other system, so that’s a perception which is quite open to challenge). However, the special symmetrical battens of the aerojunk (either the double wishbone, or the D-former type you have used) seem to eliminate the need for any of these parrels. At the expense of a more sophisticated type of batten, you seem to have simplified the rigging – always a good thing if you can do it without adding to cost or reducing reliability.

Planform (the outline or geometric shape of the sail)

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 . In a normal sail this disharmony would mean much greater forces required to hold the sail in its correct position in relation to the mast – but I presume this problem is solved immediately by the special battens you have made, which do not allow the battens to move forward. It is still possible that with a large halyard angle you will find it a little difficult to raise the last couple of metres of the sail, unless the d-formers are as frictionless as possible. Raising the height of the masthead crane does reduce the halyard angle, so hopefully you have kept your mast as long as practicable.

On the subject of sail aerodynamics I am out of my depth so I will only make a couple of (perhaps worthless) comments. The outline, or geometric shape of the sail is rather different from the McGalliard Amiina Mkll split junk sail which has been replicated quite a few times now and may be considered these days as conventional and fairly well proven. There is some aerodynamic theory behind that shape and I would regard any great departure from it as experimental – so your innovation will be of interest.

My other comment is not intended to be derogatory towards aerodynamic theory – but I can’t help making a converse statement by relating that when I built my sail I made a serious (and stupid) mistake that one would expect to be aerodynamically costly. With the shelf-foot camber and very low batten rise of the Amiina Mkll split junk sail, it is very difficult at first glance to see which is right side up when looking at a completed jib panel. I did not mark them when making them. When I hoisted the sail for the first time, there was a serious diagonal crease in two of the jibs.

Try as I might, there was no way I could pull those creases out, and to me the sail looked terrible. Although it seemed to work quite well despite the creases, I was not happy with it. Months later I woke up one morning with an idea – as one does – it was suddenly blindingly obvious that I must have assembled the sail with two jib panels upside down. I dismantled the sail and unstitched the two jibs (easy to do with zig-zag stitching) and turned them up the other way, sewed the sail together again and – presto – the sail now sets perfectly. I can’t say I noticed much difference in performance, but it does look much better now.

The moral of this long story? Regardless of theory, your sail will work just fine, I am sure. My comments above are to invite discussion and ideas, not to criticise your effort in any way. Well done. I hope your interesting and innovative rig brings you great joy. (Did you enjoy the sewing?)