Hi Andrew, there is no need to keep posting and re-posting the thread, it gets a bit unwieldy.

The SJR drawing I did shows a mast centreline about 7  inches forward of the original mast centreline, as best I can estimate from the drawing. I can't determine exactly where the hatch frame is.

How far forward can you shift the mast, while allowing for the necessary structure and allowing for the diameter of the mast? 

I would not recommend raking the mast for a SJR. Too many things are compromised and you would need to design a SJR sail especially for it, and then it would be a very complicated sail to loft. Not worth it. There are a lot of good things about making this Amiina sail very simple and easy to set nicely, which you will find out for yourself, but if you alter the proportions, yard angle etc or rake the mast, you will lose all of them. It's a harmonised package, don't fool with it.

If it were my boat (and mine is very similar just a little smaller) I would say put a scaled version of the Amiina Mkll sail, on a vertical mast, minimum 6" forward of the original mast position, and you will be very happy with the result. You will be surprised how good that sail is. Make sure your mast head will be tall enough to allow for it to be higher than the peak of the yard (more is better) and with enough room below the boom for spanned parrel downhauls between the boom and the deck (say, 60% of panel width of clearance). No problem with a hybrid mast or a bottom tube extension, just don't skimp on height. I am sure Slieve won't mind if you want to contact me off line I can give you the dimensions of the Amiina sail, and you can discuss it further with Slieve when he is available. I will only do that on the basis that you do not alter the proportions of that sail without Slieve's approval - if you do, you're on your own. I think that sail has 33% mast balance - it works, anyway. Do not increase the balance from what it is in the drawing. 35% is taking a risk in my opinion.

To answer your other question (how to measure mast rake) I would suggest get the boat level on the trailer (can you assume the bunks are level? Put a spirit level on a bunk?) Then hoist a line with a plumb-bob and measure the offset. Some secondary school trigonometry will then allow the angle to be calculated. But you won't need to do that with SJR.

I wouldn't normally go this far, as I am not an expert, and I don't have a wide enough range of experience, but the Amiina Mkll SJR has been an unqualified success on my boat. In my opinion your rather similar boat, together with its hatch placement etc., just screams out for the same rig, with the mast as far forward as you can cram it, as the simplest and the BEST rig you can put on this boat. If the mast is a couple of inches further aft than ideal then I doubt you will notice the difference on the helm. (You will probably find this boat developes quite a bit of weather helm when over-pressed anyway, so the worse case scenario: a little more weather helm. Probably time to reef by then, anyway. Partly for this reason I would recommend that you do not go overboard with sail area - keep the sail area about the same as the original bermudan area). It's a powerful sail, and the usual argument "junk rig easy to reef so make a bigger sail" needs caution. Slieve will confirm this advice.

I will add that when heavily reefed my Amiina sail does not seem to perform so well, so there is another reason for keeping the working sail area within reasonable bounds. If the idea of maximum sail area for light weather and heavy reefing for medium weather appeals, there is reason for me to believe that the Johanna sail might be the better choice for you, as according to Arne it performs quite well with just the top fan triangle. If so, you might want to consider the bottom paragraph here.

With the above cautions I would say "Go for it". It looks to me like a great little boat, which should make the best of the SJR potential.

(PS Arne's suggeston of a mast placed forward of the hatch, with aft rake, is also worth consideration if you like to have a Johanna sail - plenty of good reasons for that. When there is no wind, the sail will tend to swing, under gravity, to the centre, rather than to swing and lie outwards. So what, if there is no wind? The other consideration is clearance of the boom tip when the sail is payed out, in a big seaway - the aft raking mast gives less boom tip clearance. But the Johanna sail is designed to have plenty of rise to the boom. And you won't be sailing in the ocean. For your little boat and the sheltered waters you will sail in, I doubt if there is any reason not to have an aft raking mast if it happens to meet your other requirements. (Personally I would prefer to keep the weight of the mast as far out of the forward part of the boat as possible, that's the only reason that would make me hesitate). Aft raking mast is a bit unusual for a junk, but so what? So there you are, thanks to Arne's lateral thinking, there is a good second option for you to consider. First, I would want to make a working drawing though, and further consultation with Arne. It's not certain to me that it will work clear of the hatch.)

Anonymous wrote:

Graeme’s suggested HM-style rig is interesting. What about giving the mast a bit aft rake, say 1-1.5 degrees? Start with the mast top in the present position. With a bit luck, the mast will clear the hatch.

I know, I know, aft mastrake has been warned against, but few have actually tried it. My first mast on my dinghy Broremann had it, and there surely was no problem (..the sail with its ‘heavy’ battens is supposed to fall to the CL. in light winds).

As for the mast itself, I have a few comments.

At 42kg the suggested mast will add almost 5 % to the displacement. This is on the high side, although not a show-stopper (and at that price, if you can get it without those cut-outs in it.)

A 120mm x 3.5-4mm mast would be plenty strong enough.

As for these roll-tapered masts; do they have a constant wall thickness? I mean to remember that the wall thickness in the masts from Needlespar increased towards the top. This brings the CG of it up.

On my 7.1m/1400kg Malena I got away with a stout, hollow wooden mast (total 9.4m). Not only was the mast tapered, but so was the wall thickness, at 25% of the diameter. Even with the mast at around 5.7% of the displacement, it worked, but the weight of the mast could be felt.

These days I am pondering more about how to make two-piece masts  (like the one Jami Jokinen made for his boat…). The idea is to make it simple enough to split them for easier stowing and transport.

Anyway, good luck, Andrew!

Arne

Hi Arne. I'm sorry, I wasn't aware of your operation. I do hope you are recovering well.

I must admit I am unsure as to whether the wall thickness is constant. I think they are extruded so I would guess the wall thickness stays the same. The only reason for the wall to thicken would be if they start with a cylindrical tube, which I don't think is the case. I will try to find out.

What I would really like is to use one of their 6m poles. Mainly for the cost but also to make it possible for me to step the mast myself. They are 7m in total and weigh 22kg, 3mm wall thickness. However, the top is 70mm diameter so I'm wondering if it would be too thin with an extra bit attached.

I'm still struggling to understand what factor mast rake plays whether it be forward or aft. Also, as I am going to be doing this work with the boat out of the water, how on earth will I measure mast rake? Is it just a case of putting it perpendicular to the white stripe?

I like the idea of a split rig and am hoping Slieve will be able to help when he returns from holidays. Not least because it will be easier to sew smaller sails. 

I'm playing around with ideas about mast position. Unfortunately I've only got 6" before it impacts the hatch, which I would like to avoid. Although if I can find a hatch which is the same width but shorter, that might help. Trouble is, those hatches are phenomenally expensive.

Can I ask, If I put the mast 6" further forwards and it wasn't enough, what's the worst that could happen, a bit more weather helm? Would the boat become unstable?

The 5 Tonner was a much easier conversion but just much too heavy and expensive for me to contemplate. And so much maintenance with a wooden boat!

Thanks again for your input, It's always exciting.

Cheers

Andrew

I believe Arne does not have access to his CAD software at the present time as he is still recovering from his leg operation, so I am going to be a little bold and steal one of his drawings of a Johanna sail set on a forward raking mast, just to get an idea if this could be a possible option. Again, the CE of the sail is aligned with the CE of the original Bermudan rig, and the result is: the mast goes through the area which I presume is the forward hatch (no photo of the foredeck so guessing).

I am sure Arne could fine tune the rake/aspect ratio/mast balance to achieve a more optimal result, but I have a feeling that best efforts will still leave the mast going through what I have to assume is the hatch area.

I think the result looks rather pretty and you might want to reconsider your wish to retain the hatch. You could run the mast through the hatch, and with this rig you would retain the options of subsequently altering mast rake, and also making small adjustments to the mast balance of the sail – also as you can see, this rig also allows a shorter mast – or more sail area if you want a slightly longer mast. I rather like it.

However, you would need to put the mast supporting structure in the space where the hatch currently sits, and then make a new hatch position further forward. Quite a bit of extra work, but do-able. I don’t think I would want to be without a forward hatch, so you would need to make new “lands” for a hatch which is further forward, and a bit of a scramble to use it.

Yes, with SJR your eggs are all in one basket and no chance of fooling around with these other variables once the mast position is fixed. That will save you a lot of “over thinking”. You simply make the necessary structural improvements necessary to support a free-standing mast and put the vertical SJR mast up against it and – it is what it is.

(In my own boat, which is in some ways a rather similar sort of boat to yours, I ended up with the mast slightly too far forward, with the result that there is a slight lee helm when going to windward in very light airs. But when the wind is strong and the boat is heeling, I get considerable weather helm. Wherever you put the mast, you won’t get perfect helm balance under all conditions. It hasn’t been a problem. Lee helm in light conditions can be reduced to zero by ensuring the board is fully down, and shifting crew weight as far forward as possible in the cockpit. When weather helm becomes excessive it’s usually time to reef anyway, but it can be eliminated by raising the centreboard a little, and shifting crew weight to the rear of the cockpit. Off the wind, the centreboard comes up and you are flying, with the high balance SJR sail the helm is light, and all is good).

If a mistake has crept in somewhere, we have a “saying” in New Zealand which overcomes all problems: “She’ll be right!” I don’t think a couple of inches to allow for important structure is going to matter much - it might result in the right position anyway, without a photo and some precise measurements I am only assuming a slightly less than ideal scenariao. Without photographs or good description of the structure in the area just aft of the hatch it would be unwise to comment further.

Is it solid glass, or core construction in that area?

PS in regard to structure, "She'll be right" does not apply. It's got to be strong enough. I think your first decision is to assess the engineering requirements of having the mast placed where you want it to go. Does that leave enough room aft of the hatch to make a deck beam robust enough to support to forward pressure of the free-standing mast? If not, then putting a mast through the hatch area might be the only option. That's got to be figured out before worrying about what type of rig. If you want to discuss further, then post photos and some precise measurements of the above and below deck in relation to your chosen mast position, hatch etc. or get someone local to discuss these things with, before making your final decision as to where to place the mast.

After that you can worry about rig choice.

Thank you Graeme, that is very reassuring. I'm afraid it is beyond my tiny brain how you calculate the best mast position when you have so many variables, including balance, forward rake etc. And then, once the partners and mast step have been reinforced and probably glassed in, what if a mistake has crept in somewhere.

With sail area etc, I can see you could modify things but the mast position seems to be critical at the outset.

Anonymous wrote:

Here is Medina sail plan showing the geometric centre as designed, in case someone would like to help Andrew with a proposed junk sail with forward raking mast.

If it were mine and if I were to chose SJR I think it would look like this

This shows a SJR sail of approximately the same area as the original rig, with the geometric centre (CoE) aligned with the original centre. The centre line of the mast is shown.

This sail area could be scaled up or down a little, depending on the hight of Andrew's new mast. (Note Andrew, the mast height must be at least as high as the top of the yard, and slightly more would be better. Also, the distance of the boom down to the deck, at the mast, needs to be at least 50% of the width of a panel (or slightly more would be better) in order for the spanned running parrel downhauls to function in the way Slieve specifies. The balance shown here is 33%. Mast rake on this rig  is not recommended.

Note, as this is a smallish vessel, the helm balance can be fine tuned by crew shifting weight from the rear of the cockpit to the front, so there is a tiny amount of wriggle room as to where the mast is placed.

...............................................

If Andrew decides to have a relatively high balanced contiguous sail, with some forward rake as suggested by David, there is possibly of even more wriggle room in mast placement, because the amount of forward rake can be varied a little at the design stage, and once that angle has been chosen and mast rake fixed, there is also the ability to move the sail forward or aft a little, to vary the balance a little if further adjustment is needed.

(Neither of these adjustments (mast rake, and fore/aft slinging of the sail) are possible with SJR.)

So there is something to think about.

Hopefully someone else will chime in with a proposed contigous sail plan to suit this boat.

Thank you Graeme. That's a great start. The mast I'm planning would be 8m above deck level, 9.2m overall. I'll get started on a proper drawing. Unfortunately if the mast moves forwards by more than about 6" then it means taking out the forward hatch, which would be a great shame.