Anonymous wrote:

Is the back stay necessary? Could it be done away with and the mast held up with a pair of side-stays on each each like on my Westerly22 who's deck-stepped mast has "stayed up" for nearly 60 years with out a back-stay? Plenty of room for a junk main on the existing mast, especially on a motor-sailer that isn't looking for racing performance. 

The Westerly 22 has no spreaders while the fisher does. I do not know if that makes a difference. I would think in that case the aft shrouds should be 45 degrees back. The back stay's main purpose is to balance out the fore stay but the fore stay is only there for the jib. So if a jib is not being used anyway, the back stay may not be needed. 

This of course, assumes the current mast position can be made to work. I think it could by varying the sizes of main and mizzen.

Len, yes if you do it that way, by keeping a constraint on sail area in addition to a constraint on batten balance, then you are right: the sail with a higher aspect ratio will have a centre of area which is closer to the mast centre line. You are correct in that case.

I hadn’t thought of calculating it that way – in fact I was looking at Arne’s three model sail plans (AR 1.8, 2.05 and 2.25) in which for comparison all three sails have the same chord length and their centres of area all lie on approximately the same vertical line same - but, of course, they do not each have the same area.

So, following your reasoning and keeping the sail area constant, let us scale down the AR 2.25 sail in Arne’s suite of sails, so that it has the same sail area as his AR 1.8 sail. The scale factor for that area transformation will be 35.31/46.46 which is about 0.76. Using the square root of that, for a linear scale factor, that taller sail will now have a chord of about 4.36. If both sails are now given the same batten balance (let us say 10% of chord) the centre of area of the AR1.8 sail will be 2m aft of the mast centre line, compared with the centre of area of the AR2.25 sail which will be 1.64m aft of the mast centre line. 

So as a result of that drastic change of AR (from 1.8 to 2.25) we can in theory get about 36cm of “wriggle room” when it comes to mast placement – provided the batten balance is not more than 10%. As you have hinted yourself, this is not a very rational way to choose the aspect ratio of your sail, as a number other important factors are also involved.

Furthermore, I think when you were discussing aspect ratio you were doing so in the context of a split rig. A split rig really makes no sense at all unless the batten balance is at least 30% or more, so while we are in the mood to do a little arithmetic, let us also consider the same question in relation to a batten balance of 33%, which is probably the optimum for a split rig. In that case, a change of aspect ratio from 1.8 to 2.25 would lead to the centre of area being 0.85m aft of the mast centre line in the first case, compared with 0.73m in the second case – a difference of 12cm in regard to Arne’s suite of model sails. This is not an exact business, and 12cm is surely within a reasonable margin of error, that is to say: negligible on a 30’ long-keel vessel.

Summary: I think we both agree that the starting point is to have some idea of where the centre of area of the sail plan should probably lie. From there, the goal is to find a sail type which is centred there and, as far as possible, is in harmony with the requirements of the type of vessel, its internal layout, placement of berths, hatches, sheeting position etc. If there is a preferred place for the mast, then this will largely dictate batten balance of the sail, though in some cases a little bit of fine tuning with mast rake and (as you have rightly pointed out) aspect ratio might also make a small difference. If batten balance of more than 30% is dictated by the preferred mast position, then a split rig might be the answer but I would not venture to allow more balance than about 33% (35% if you want to be a pioneer) and in that case aspect ratio would not make a lot of difference in the quest for helm balance. I suppose it could be argued that every little bit helps, so your suggestion was good, and thanks for correcting me.

The important point to keep in mind, in my opinion, is that the split rig may in some cases be the perfect answer (I am very pleased with mine) – but it is probably one of the least amenable to being used as a platform for experimentation and, of all rigs, offers the least amount of opportunity for adjustment later if things don’t quite work out in regard to helm balance.

All this academic stuff is perhaps a little less crucial when it comes to the vessel which is the subject of this thread. The nice thing about this Fisher 30 is that it will have a good auxiliary engine – but more importantly in regard to this discussion, it has a long keel which ought to make it a little bit more tolerant to small variations in the position of the sail plan – and it presents the potential for a ketch rig which, as Arne has pointed out, allows the sheeting of the mizzen sail to contribute towards adjusting helm balance. Personally, I am very much in agreement with Len's sentiments, and would rather love to have a Fisher 30.

Len: "The jiblets could be moved fore and aft to affect the balance and see if some movement would help..." and also "Comments on why this would be really bad..." 

The above is a really bad idea. The reason is that a properly designed split junk sail is already near to the limit of what is possible in terms of aerodynamic balance of the sail itself, and if you step over that limit the rig will become unsafe and not functional. Furthermore, if you go the other way and reduce the aerodynamic balance of the sail, then pretty quickly it becomes unnecessary and pointless to put a split in the sail.

The aerodynamic balance of the sail (perhaps Arne's "batten balance" is a better term) is an entirely different matter to the helm balance of the vessel, which is what you will be seeking when you convert your Cal 29. Another point: by "CE" I presume you are referring to the geometric centre of area of the sail. When a sail is scaled vertically (to increase or decrease aspect ratio) the geometric centre does not move fore or aft.

I believe that with a contiguous sail it can be possible to sling the sail a little fore or aft, and perhaps to alter the rake of the mast in order to gain a little flexibility with regard to mast position. However, one of the downsides of the split rig is that there is very little flexibility in that regard. I don't think tinkering with the geometry of the sail is a wise idea. 

(Incidentally, I should mention that the SJR proposition for the Fisher 30 was not done with any careful calculation but merely for discussion, as an option to consider if the aim were to make minimal changes to the layout of the vessel. The correct approach for SJR would be to calculate the geometric centre of the area of the proposed sail plan and compare it with the geometric centre of the area of the original designed rig - talking into account any known characteristics of the original design (ie whether the helm balances nicely, or if there tends to be excessive lee helm or weather helm) and from this, a decision is made regarding mast position. My gut feeling with putting a SJR mast on that current mast position is that it may be a smidgeon too far aft, but with that long keel you could probably get away with it. The mizzen sail  might be better reduced to a smaller "riding sail" and might be redundant a lot of the time. I think Arne's suggestion, utilising the existing mizzen sail as a working sail, might be the better solution.)

Back to the Cal 29, Len wrote: I will start a thread when I actually own the boat and have gotten used to things the way they are (the main sail has only a year or two if I am gentle with it).   That is a really excellent suggestion. After a season of getting to know the boat, most of the need to speculate, as above,  or to experiment with sail geometry, will probably disappear. The answers will fall into place.

(An afterthought: this is in no way to disparage the origami concept. This is of interest in its own right - but not as a platform for experimenting in the manner Len was proposing, I would suggest).

Graeme, the maths around the SA/Disp. can be found here. I don’t like this ratio that much myself. The heavier the vessel, the less likely one is to reach a SA/Disp=20. However, on boats of similar displacement, that number can be useful for comparison.

As for ‘quiet’ sail, I don’t mean the cambered sail is flapping in headwind, as it doesn’t do that (watch this short video clip of dropping a panel on my Ingeborg: 

https://bit.ly/3IKesY5).

What I meant was that the cambered panels will ‘plop’ quite loudly if the boat is rolling from side to side with the sail sheeted to the CL. Anyway, this is not good for the sailcloth in the long run.

The CE of my junk sail is sitting closely to the combined CE of the mainsail plus jib of the Bermuda rig. I therefore reckon that the load on the rudder will be determined by how hard one sheets in the mizzen. It may well be an idea to make a new mizzen as a flat triangle, suitable for riding at anchor etc.

I would no doubt add an endplate to both the upper and lower end of the rudder. Combined with the benefits of the mizzen, I think the boat should steer all right.

Arne

Hm, I struggle with this one.
The Fisher 30, with its very low SA/Disp. ratio (around 8.7) is more like an 80% motor-vessel with an aux. rig. I have seen a few of such boats motoring around, but hardly ever with any sail set. However, the Fisher 30 has a decent keel and plenty of ballast, so should be able to carry a much larger rig than the original. A quick, preliminary study tells me that one could fit a JR mainsail with the mast at the aft end of the foredeck. This could end up at 40-42sqm without a too tall mast. By keeping the mizzen un-changed, the total SA should reach about 47sqm (instead of about 30qm) and thus move the SA-disp. up to 13.6, which is decent for a motor-sailer.

Annie mentions that she would prefer a flat sail here.  To me, that depends on how and where one intends to use the boat. If one will be working a lot in light winds and old sea swell, the flat sail will be a lot quieter than a cambered-panel sail. The downside is that this smallish and flat sail will struggle with moving that heavy vessel in anything below wind force 5.

If that Fisher 30 were mine, I would add quite some camber, at least 10%. This sail would outclass the flat one in the close- to broad reach zone (about 160-180 of the 360° circle). I am not talking about racing: I am talking about saving fuel and engine hours. The price to pay with the baggy panels is, as said, the noise if the vessel is rolling in light winds. In those conditions, I would just lower the sail.

The shown sail is actually a slightly scaled-up version of a sail in use.

Arne

..and here is the original 35sqm sail at work on Ketil Greve's boat...