Arne Kverneland wrote:

first of all; I am glad I your boat sails better than I feared it would do. 

Thanks Arne. Your initial assessment was pretty close to correct, I think. This boat is not a flyer, especially to windward, and has not yet been tested in choppy or rough conditions. However it was pleasing to find that she gets along OK in light conditions and can go to windward satisfactorily under those conditions without any help from the motor.

Arne Kverneland wrote:

My experience is that I will keep the weight of the mast below 3% (better 2.5%) of the boat’s displacement  -  and then pile on maximum sail area on that stick.

I was pretty sure that would be your choice and I was hoping it would be too. Rough calculations suggest I can increase sail area by about 30% with mast within 3% of displacement (and about the same length as the current BR mast) using your 1.80 AR planform. Although the extra area will not be needed (and may be undesirable) above 10-12 knots of wind, you have given me confidence that when carrying two panels of reef, the rig will still work efficiently and can be used in this way as a working sail.

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

Mast position

I think I will put this question to one side for the moment – there are a number of choices, none of them ideal. Also the questions of sheeting angle and rudder, to be considered later.

(I must comment though on Arne’s Bigrudder idea – one of those brilliant “why didn’t I think of that” ideas that I wish I had seen years ago, when fighting the tillers of conventional kick-up rudders in the up position – or worse (as happened to me) striking a rock with a large fixed rudder and taking it clean off along with all the fittings and part of the transom.)

Arne’s suggestion of a possible small offset in mast position is noted – this may prove to be a very valuable suggestion.

I want also to mull over the possibility of split rig, having noted that Slieve and others are working with 30% and more of balance, allowing the mast to be set further aft – and perhaps also reducing weather helm when off the wind which, I don’t know yet for sure, may be a problem with my boat when trying to utilise all this extra sail area down wind. As interesting as the prospect may be, I am not experienced in sail design or sail making, and would not normally consider jumping straight into a split rig for my first junk sail. Therefore the main point of interest in the split rig, at this point, is mast position.

Sail position

For the moment, my first choice is Arne’s 1.80 plan which appeals to me for a number of reasons, including maximum sail area for length of mast, easier-to-make sail and extremely helpful and detailed instructions for a beginner like me, and well-proven performance. I liked it from the start.

I would now like to look at its application to the Pelorus in more detail and it seems to me the first thing is to find out a little more accurately where the sail should be placed (at least as a starting point.)

The drawings and some of the calculations in my earlier posts had been found to be not quite accurate. One of the errors I have corrected is the CoE of the Arne 1.80 plan – as shown on my now corrected drawing it actually coincides with the original CoE of the Bermudian rig, and gives a lead of about 11.2%

  (To clarify, the original CoE was calculated from measurements I made, using the full area of the overlapping genoa. The CLR was estimated by “balancing on a knife edge” the underwater profile of my drawing, based on a photograph, and did not include the rudder. The drawing is here.)

I think the advice I have been given so far is to move the sail forward a little from where I have drawn it.

Moving the sail forward will increase the lead to something greater than the current 11%

PJR recommends the lead should be 9%.

However PJR also recommends for a junk rig, the CoE should be 6% abaft the conventional CoE. On my boat that would mean moving the sail aft, and also it would contradict PJR's first recommendation, and give a lead of about 5%

Arne (his Chapter 3) advises 0-15% lead, and I note that on a long-keeled vessel he chose 5% - though that was to be a schooner.

The above five sentences seem to yield some contradictions, or at the very least, raise some questions regarding this particular boat.

Question 1: Aside from the question of mast position, should the sail be moved forward a little? Or aft a little? How far? 

How much lead would seem to be about right for this shallow-long-keel single-sail cat rig?

And how wide a range would be acceptable: plus or minus 2% ?

I will try to do a more accurate drawing of Arne’s 1.80 rig (scaled down slightly to provide for 5m battens) as I find now that what I drew is not accurate enough to use for looking at sheeting angles.

Before doing so, I would be grateful for any comments or advice on placement of the sail as in question 1.

As a preliminary step in looking at mast position, the next question seems to be:

Question 2: What is a practical range for the aerodynamic balance of the rig?

PJR suggests 5% - 30% of batten forward of the mast, and seems to prefer around 10%

Arne recommends 5%- 15% for his rig and seems to use 10% as a starting point.

Does 10% seem a good starting point for the Arne 1.8 rig on the Pelorus?

And does plus or minus 5% still seem to be an acceptable range?

What would be the maximum amount of balance that Arne’s planform would tolerate?

Before making a new drawing, and before getting too wedded to a position for the mast, I would be very grateful for any comments arising from the above two questions. (And I mean very grateful. It seems to be a rare privilege for a newcomer to be able to just segway up and start asking direct questions of people who have spent years gaining their knowledge.)

PS A couple of afterthoughts, which can probably be left for the future. We have found now that this hull-type quickly upsets any balance calculations if it is heeled beyond a certain point, so perhaps there is little to be gained by getting too hung up on CoEs and CLRs at this stage.

The CoE of the current rig is probably in about the right position, and to maintain a balanced helm it is found necessary to reef early. Maybe the junk rig will provide a second option in this respect if the rig can be conveniently slung forward or aft, with respect to the mast, while under way, as I understand some junk sailers do when running down wind. Whatever the tackle is used to achieve this (and I would have preferred less tackle rather than more) it might also provide a way of adjusting the lead of the CoE over the CLR when sailing on the wind, in response to this boat's tendency to shift from slight lee helm to considerable weather helm as the wind strength increases from very light to moderate/strong. Maybe I am over-thinking it - comments of experienced junkies would be of interest.

Jami, the 6m lower section is the same as on my Frøken Sørensen. It should weigh around 19.5kg. Add to this that little top section of spruce and you are up in, say 25kg.

That should give 5% of the boat  -  the same percentage as the hollow wooden mast I put on Malena in 1995 (about 70kg on a 1400kg Albin Viggen). That boat sailed very well with the rig, although the weight and windage  of the mast could be felt. I sailed happily around for almost five seasons before I sold her.

Your mast may be on the stout side  -  it will surely not break, but thanks to the aluminium, you get all that strength on a small section (= less windage). In addition, remember that your own weight is well over 10% of the boat, so your position in the cockpit will count a lot more than in a 1500 or 3000kg boat.

I suggest you keep on and complete your project ASAP  -  the summer is approaching fast now, and before you know it, it is over.

Now, THAT is what you should worry about!

Arne

Malena in 1999 with her 32sqm muscle rig (SA/disp = 24.8...)

Graeme,

first of all; I am glad your boat sails better than I feared it would do. Thanks for your interesting report.

Now a couple of comments:

Sail area
If you look through my “Junk Rig for Beginners”, you will notice that my first motif for converting to JR was the poor downwind performance of the BR. Since I had been told that reefing was so easy, I gave the first JR quite some sail area (1990). The rumours about easy reefing turned out to be correct, so I have stuck to the practice of rigging with a SA/displacement of over 20. See Newsletter 44 about the first junkrig rally in Stavanger. I guess the big sail areas on my Johanna and Malena was regarded to be a bit less than seaworthy by the British visitors (“fjord flyers”). However, I think Hasler and McLeod created the best all-round JR planform there is with their ‘standard JR’, with several parallel lower panels and two or three fanning top panels. I find that my sails, based on their work, perform very well at any state of reefing. My previous boat, Frøken Sørensen, was unballasted, so a strong breeze was a full gale to her. I bet I reefed her on almost half of my outings, and I never regarded that as an emergency situation.

The size of your JR should therefore be decided with the weight and windage of the mast in mind. My experience is that I will keep the weight of the mast below 3% (better 2.5%) of the boat’s displacement  -  and then pile on maximum sail area on that stick.

Weather helm due to heeling.
I have experienced exactly the same in a friend’s Dufour 36 Classic. When we tried rolling in half of that big genoa instead of the main (in-mast reefing), the boat rightened herself again, the rudder angle dropped to normal, and the speed went up. Best of all, when tacking, the crimped foresail made the job so much easier.

Mast position.
I see a couple of options from my armchair: You can move the mast further forward from your first JR position and even offset it 10-20cm to one side to get it out of your berth. This may call for a little triangular mizzen, with the mast actually clamped to the outside of the transom. The good thing with this option is that there will be plenty of drift for the main sheet.

The other option is to put the mast further aft (and again offsetting it if necessary). This has its advantages and drawbacks. You may either fit a boomkin for the single point sheet (as with that mizzen), or you will need separate port-starboard sheeting (or a sheet traveller from side to side). I would treat the weather helm issue with a new, big balanced swing-up rudder on the transom. This rudder has a good deal in common with the big retractable rudders of the Chinese junks: It not only steers the boat, but also acts as a centreboard.

Hope you got a bit to chew on, there...

Arne

Arne Kverneland wrote:

That boat actually resembles the 37’9” Hartley “South Seas”, 

PS: What is the tidal height in you place? 

Yes quite similar in some ways. The Pelorus has flatter sections forward and seems to stay drier in choppy conditions. I once owned a Hartley South Seas (we shortened it down to 35' by cutting away the overhanging stern) and used it for commercial longline fishing for about ten years - it was a good boat.

In spring tides the range is about 0.3m at low tide to about 3.5m at high tide. The neaps are about 1.1 to 2.7

Arne Kverneland wrote:

Funny that, Graham.

As I understand it, a trimtab works against the rudder (while a servo pendulum tab works with it). Am I right that you don’t tack by just resetting the windvane, but rather lock the trimtab in line with the rudder before pushing the tiller over? In the latter case you have now got a big rudder to help Arion come about.

Arne

The trim tab would work against the rudder if I reset the windvane to tack the boat.  I do that in flat water, though I still give the tiller an extra shove to come about quicker.  But then I can just go back to my cup of tea or whatever.  When I am in the open sea, however, I disengage the windvane, bear away onto a close reach to build up speed, then put the tiller firmly down.  The trim tab is just trailing behind, disconnected from the vane, and you'd think it would feather, and thus be neutral, but it doesn't, at least not much.  Mostly it works with the rudder.  The increased tacking speed is very noticeable and astonished me when I first experienced it.  I used to always wonder, in the open sea, if we would come about or not, but since increasing the size of the trim tab we have never missed stays.  As you say, together they provide a very large rudder.  It was a happy accident.  And when I do have the windvane connected, the boat self steers all the time, even when driving hard downwind.  Sometimes, in light airs on a run with almost no apparent wind, the vane is not powerful enough to move the large trim tab, but then I link my autopilot to the trim tab and the boat sails like it is on rails.