Hi Marcus

Just some general comments.

There has to be harmony between accommodation requirements, mast position and type of rig (type of single-masted  rig = amount of sail forward of the mast: “aerodynamic balance”).

But the geometric centre of the sail has to go where it has to go.

(The balance of a boat is not just a function of the (so-called) “C of E” – the amount of heel often also plays a part which is why it is not unusual for a vessel to develop a lot of weather helm when heeling to a breeze, remedied by reducing\ sail, sometimes in an unintuitive way, with regard to which sails are reduced (main or fore). So I am not sure that I agree with your reasoning. If the boat does not balance well under the current rig that is another matter, and can be taken into account).

To put a SJR with its geometric centre well-forward of where the BM centre was, could be a mistake. Without proper drawings its hard to say, but the “sail imposed on photograph” looks a little too far forward to me.

Eye-balling a photograph can be deceptive and I guess you are on the spot to make the best judegement, but I would be a little bit worried.

You have already reduced the balance down to 30% and anything less I would suggest makes SJR marginally not worth considering. Also, with SJR, you don’t have much flexibility. There is little margin for error, because with SJR you can’t really decide later to alter the rake of the mast, or sling the sail a little fore or aft if it proves necessary to adjust that balance.

The geometric centre of the sail has to go where it has to go. The designer of the sail can advise where that will be, in relation to the geometric centre of the existing BM sail. (In the case of SJR, the two centres will be the about the same, or close to it. With a contiguous sail, the centres might be different, others can advise.)

I would suggest that if you have decided on a SJR sloop, with its high balance requirement, then your mast position has to be determined by that decision, not by accommodation requirements or wishful thinking.

On the other hand, if you have decided first where the mast has to go, then the aerodynamic balance of the sail plan (15%?  20%?  25%?,  30%?  35%?) has to be determined by that decision. If the mast is too far forward for a SJR, then you might need to consider a lower balance type of sail (not SJR) or, alternatively, if you are determined to have a SJR main, and it is too far forward, than you might need to consider adding a mizzen mast and having a ketch or yawl rig.

Summary: if mast placement is a primary requirement, then perhaps you need to keep an open mind as regards the type of rig

PS the mast sounds good. I wish we could get tapered tubes here in NZ. I would go for the longer mast every time, having experienced the difficulty of a mast slightly too short. Its always easier to cut a bit off the bottom later, than add a bit to the top!

Anonymous wrote:

David,

Thanks for the input. One of the features of the SJR seems to be the simplicity of balance of the rig, which gives advantages of less "parrel-stuff". My point of "not being in it for the speed", was merely that I could probably do with i smaller sail ;).
Do you propose that  I use a 220x6 mm for the lower, and 200x5 for the upper tube?

Graeme,

Please, do not stay off the thread! I am very keen on hearing your advice and experience on the subject.

Yes, those sizes will work. Tystie’s mainmast tube is 220 x 5, with an internal doubler that I was never convinced whether it did as much good as having a 10mm wall, but it must have added a little extra strength. It carries a similar sail area. 

Slieve,
Thanks a lot for the calculator, with the help of it, my ruler, pen and scissors I have  made yet on more drawing for the dining room wall.

I am seriously thinking of making a 13.5 meter long mast out of three alu tubes. It probably won't be pretty - but it may actually work.

As you can see I am pretty into the SJR and I think I will explore it a bit further. The latest alternative is 45sqm and is pretty much the same area as when I put in my first reef (which is most often two...). Since I do that at about 10-15 knots of wind, this is not unusual. It's even so that I have started out with that set quite a few times (I'm an early reefer;))

I was thinking that if the Amiina II type SJR is so efficient, maybe I don't need that much cloth...

I was going to stay off this thread from here on, but I have to correct a tiny point of misinformation in David's recent post, which, no doubt sincerely intended, needs to be clarified.

Marcus, I agree with all that David suggests about looking at alternative rigs and not just opting for SJR (which does involve a little more work) when there are many alternatives which may well match your needs. I would go even further and point out that Arne too has a suite of well-proven stock sail plans especially well-documented and tailored to the needs of a first-time sail maker. There are two good reasons for keeping an open mind on plan form at this stage - one is that it will affect where the mast is placed (in respect to your internal accommodation arrangements.)  For example: A Johanna rig and a SJR will give different mast placements. Given that both of these rigs work well, it may be a game changer if one of them put a mast right through a berth or blocked a companionway. The other reason is, because there is probably a little more work in making a SJR than some other sails, you will want to know that you have done your homework and have good reasons for whatever you finally choose.

But David wrote, in reference to SJR, of "the risk of investing a lot of effort trying to get that jib/main combination perfect." That comment is loaded with, no doubt unintended, misinformation. And, if I may gently point out, is not based on David's otherwise very extensive range of experience. Nobody following Slieve's detailed notes has had any problems at all with "jib/main combination". Perfection has yet to be achieved by anyone, but I can tell you from my direct first hand experience, if you were to opt for SJR, that if you follow Slieve's notes carefully you won't have any problems at all in that regard. I am sure David's unfortunate phrasing there was not intended to disparage the idea of SJR but merely to advise you that if you were to go down that road (SJR), to follow Slieve's advice and no-one else's.

Brilliant Slieve, this explains so much. Would you mind posting a copy of the explanation post onto the other thread I just made? For the sake of a tidy collection of documents? Its exactly what I was hoping for. That, and your spreadsheet for Marcus, will no doubt find a place in your revised notes too, which will be a valuable future resource.

Marcus, don't worry about the details of a tabernacle at this stage, you are too bogged down in details. For the moment, just think of it as a practical and do-able extension of the lower mast tube, into which you will give the tube sufficient bury.

step 1 decide how high you are prepared to go with your mast (including base extension, and top extension if you  opt for it)

step 2 get the advice from the boffins regarding your choice of tubes

step 3 decide where you will place the mast (with respect to interior layout)

step 4 decide which type of junk rig best suits, with regard to 3.

After that you can profitably start fussing about the details, such as tabernacles etc