The “good enough” Johanna-style rig and sailmaking.

Bang for the bucks

Longevity

Totally agree with these, Arne, and I would add:

The 80-20, or Pareto principle

and an old favourite, that needs re--stating once in a while:

Horses for courses

which is perhaps the most relevant in this topic about choosing a rig for a boat intended to go ocean cruising.

"I will stick my neck out and say that I don't believe it would have happened if the sail had not been a SJR and the sheet had run out more freely" is, on the basis of what you told us in that anecdote, speculation. I take back the word "wild". As for the rest of your post David, I will say "fair enough" I did not mean to be offensive and I genuinely apologise if you found it so. It was meant to be a challenge to a statement made. Absolutely not a personal attack.

I confess to having had rather too much to say lately.

Its all good stuff, and nearly all of the advice put forward by Slieve, David and Arne boil down the the proposition that any of the contemporary rigs will work very well indeed on this boat. And the fine performance of Ingeborg and Pango with their forward-placed masts and quite different aspect ratios, adds empirical support.

The SJR will involve more work to install, because of mast placement through an existing hatch, and when mounted above a trunk cabin it is also necessary to remember that with SJR, sufficient clearance under the boom is needed, to allow for Slieve’s spanned parrel-downhauls. 

With that in mind, together with David’s valuable cautionary remarks regarding the special needs of an ocean voyager, I really think Ryan should just follow his heart.

 (Regarding boom clearance, we have a boat in Whangarei with SJR which is taking an alternative route by using standing parrels, as does Wayward, and hopefully there will be reports on that soon.)      

Absolutely not looking for the last word, but I can't let the following go by without a counter comment: Wild speculation tends to taint people’s thinking rather than guide it. The conclusion drawn from the River Rat anecdote, as David has given it, is wild speculation if I ever heard it, unless there is more to be told. Granted, sheeting forces on a SJR are light (especially when conditions are very light) as are all the other forces, relatively. This is sometimes an advantage. In any case, there are plenty of other more likely speculative reasons why James got caught in a gust. River Rat has a rather heavy mast and little boats like that are easy to knock down under any rig.  David’s contributions are generally of the highest order, based usually on his direct experience. But that anecdote is not David at his best, and I think it rather just muddies the water. Perhaps James will clarify it.

PS As David points out, there is a little more mathematics involved in lofting the angle-shelf-cambered SJR panels, and the whole deal involves a little more work - somewhat mitigated by the stark simplicity of the Amiina sail. For the DIY sail maker, Arne's methods and instructions are surely the easiest and the best . In fact, Arne's documentation would be a good enough reason on its own to favour a Johanna rig. Slieve's notes require a little more thought, and are in the process of being updated (hint hint) . I think it only fair though to add that a number of first-time DIY SJRs have been satisfactorily built - and as far as I know all SJRs to date have been amateur built.

Ryan has plenty to think about, but nothing to worry about.

PS since a lot of nice things have been said about the Contessa 26 it might be of interest to someone in NZ to know that there is one for sail on Trademe for $5,000, no engine. The vendor operates under smokescreen, is in fact a serial wheeler dealer and I would expect that to be negotiable.  

https://www.trademe.co.nz/Browse/Listing.aspx?id=2632135495&archive=1 

Ryan,

it is easy to get get discouraged by the thought of getting the trim wrong, or ending up with too high pitch inertia.
Take a look at the sailplan below. There I have drawn in an alternative mast running through the middle of the hatch- This would suit a high-balance JR, a SJR, for instance

I have made a few guesses which hopefully is not too far away: I guess the mass of  the identical masts to be 100kg, and I guess that the boat will pitch or trim down around point A, sitting at the middle of the waterline.

Nose-down trim:
Here I use the aft mast as the reference.
The two masts are standing at 0.76m distance.
That would increase the nose-down moment of the Johanna-style mast with 0.76m x 100kp = 76kpm.
How much is that? Imagine that we hang a 15kg anchor on its roller, in point D.
The nose-down moment from that would be AF x 15kp = 4.71m x 15kp = 71kpm.
Add a few links of chain, and that anchor would do more to trim down the bow than moving the mast to the Johanna-sail position.

Inertia:
The formula for the inertia consists of two links which adds up:

The first link, I call the propeller inertia: Imagine that you try to spin the mastpoles around their CG (point B and C). Since both masts are identical, I disregard it (it’s around 1100kgm²).

The other link is the point inertia around the rotation centre, A.

The formula is simply I= m x R². Here m= 100kg and the measured radiuses for the masts are AB= 6.02m and AC = 6.28m

Then the aft mast will have a point inertia around A :

I₁ = 100kg x (6.02m)² = 3624kgm²

The Johanna-style mast will have

I₂= 100kg x (6.28m)² =3943kgm², which is 319kgm² higher.

So what does that tell us? Again, check with that 15kg anchor. Its contribution to the boat’s inertia in the pitchplane will be:

I_anchor = 15kg x AD² = 15kg x (4.84m)² = 359kgm².

In other words; sailing around with a 15kg anchor on its roller will do more to increase the inertia than moving the 100kg mast 76cm forward.

Anyone who prepares for a longer voyage should think of this, and avoid storing heavy stuff near the ends of the boat. As for Alberg 30 and hobbyhorsing. If she has not been known for suffering from it before, any JR shown to you on these pages, will not make her noticeably worse  -  so don’t worry ☺!

Arne

(more details in Arne's sketches section 4, photo25)

Ryan, let me first address the points on which I'm qualified through first hand experience:

Mast position: yacht designers are agreed that the nearer the mast is to the middle of the waterline, the less the boat tends to pitch, and pitching absorbs energy that could otherwise be converted into forward drive. A boat that "hobby-horses" is a slow boat. Also, a mast that is well forward decreases foredeck space, and that is an issue on a cruising vessel that needs to take the easy deployment of ground tackle more seriously.

Number of panels and sheeted points: Amiina and Weaverbird both have five sheeted points, and that's fine in this size of coastal cruising boat. It means the panels are wide, and with cambered panels, it follows that the sail has a greater % of its area at full camber, a lesser % close to battens and uncambered. That's better for performance. Yet for long distance cruising, I feel that one more sheeted point is better for general management of the sail area, especially in tricky, variable conditions, making the steps between reefs a little finer. So perhaps the six sheeted points of Poppy, but with just the single unsplit top panel of Amiina?

Now the points on which I'm only an observer of the SJR, not an owner:

I've sailed on, and alongside, Amiina for relatively short periods, and that's the sum total of my SJR experience. Amiina's current sail is very lightly built, and that's fine for the kind of sailing she does. I can quite see how an ocean-going build of that planform wouldn't be the same animal, at all. Yet I've seen Amiina's upper jiblets flogging when the sail was allowed to twist too much, and thought "ouff! I wouldn't want my sail to be doing that when I'm 1000 miles from nowhere and I can't repair it when (not if) the cloth breaks down!"

I've pushed the envelope on some of my rigs as regards aerodynamic balance area. I find it unpleasant when the sail "snatches" in swirly, unstable winds, when it's too close to  the neutral point between "overbalanced" and "underbalanced". A SJR might well be fine at 33% in steady conditions, I'll accept that, but just anecdotally, I've been aboard Amiina, and alongside her in my own boat, when a gust struck, and thought "ouff! this is pushing the envelope just that little bit too much!" OK, it matters less on a large boat that can take being blown down in its stride, but on a small boat it matters more that there is sufficient tension in the sheet, and little enough friction, that it runs out quickly in a squall. I was there when River Rat got blown down during the Brixham regatta (Magazine 81, p15). I didn't see it happen with my own eyes, but was sailing in the same conditions, with fresh gusts coming off the land, and I will stick my neck out and say that I don't believe it would have happened if the sail had not been a SJR and the sheet had run out more freely.

So, all things considered, I'm going to stick to my guns and say that for ocean cruising and cruising in the wilder areas of the world, I would be content to be sailing under a robustly built SJR - so long as it had aerodynamic balance in the region of 25% - 30%. But I would be more content to be sailing under my current Weaverbird planform with just one more panel and sheeted point.

PS. We might also mention that although the battens of a SJR are simple straight tubes, the sail gets a bit 'technical' in it's design and construction, and is perhaps not to be undertaken as a first JR project. In the same way that the battens of a Weaverbird-type wing sail shouldn't be undertaken as a first JR project. In both cases, I do feel that a little prior rig-building experience is likely to result in a more satisfying rig.