Converting a Pelorus 8m motorsailer

  • 13 May 2017 14:46
    Reply # 4831192 on 4789675
    Anonymous member (Administrator)

    Graeme

    Finding the lead.
    There is quite some guesswork involved in this, but one guideline is important to remember: A long-keeled boat needs more lead than a fin-keeled boat. Since the CE and CLR we are playing around with are only geometric centres, the actual centres of pressures  move around and generally sit well forward of the geometrical CE and CLR.

    I would rather err on the lee-helm side this time. Remember, a sloop JR builds up more weather helm on a reach and run (most on a reach, actually) than a BR. Putting the CE of the JR on the same position as that of the BR sounds like a good idea. Having experience with the original BR does away with a lot of guessing.

    JR sail balance with respect to the mast.
    I suggest you just print out Sheet 1 of that AR=1.80 Master sail. I have just uploaded these master sails again with some extra info on them (no changes to the dimensions). With the printed out sailplan in hand, you can play around with mast position. Nowadays I have settled on tying the halyard to about 5% aft of the middle of the yard. A vertical mast-line through that point gives about 18% balance, so I guess that is the highest balance one can have without designing a sail with a lower yard angle. As for reducing the sail-to-mast balance, I try to avoid having the halyard pointing more than 30° aft of vertical, so if very little balance is to be used, that may call for a slightly taller mast. Again, playing around with that drawing with mast in different positions, will be useful.

    Nowadays I try to start with a sail-to-mast balance of 10-12%, which lets me adjust the balance back and forth a bit to trim out weather or lee helm.

    When I designed the rig for my present boat, Ingeborg. I fitted the sail with 10% balance. This turned out to give more weather helm than I prefer, so the sail was shifted forward to about 13% balance, which corrected the helm issue (the lead was thus increased with 2.4%).

    Mast rake
    I generally aim on fitting the mast dead plumb, but if needed, I would not be afraid of tilting it up to 2° aft or as much as up to 5° forward. I would still rig the sail to sit with a vertical luff and leech, to minimise sheet tangle. The key is to decide on the correct position of the mast top. From there you can play with different mast lines to better suit the deck layout.

    Cheers, Arne

     


    Last modified: 20 Jan 2018 10:19 | Anonymous member (Administrator)
  • 13 May 2017 01:38
    Reply # 4830606 on 4789675
    Anonymous member (Administrator)
    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.

    Last modified: 13 May 2017 07:55 | Anonymous member (Administrator)
  • 12 May 2017 19:57
    Reply # 4830213 on 4789675

    Will do - getting there by the day :)

  • 12 May 2017 18:47
    Reply # 4830010 on 4789675
    Anonymous member (Administrator)

    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...)

    Last modified: 12 Aug 2024 13:27 | Anonymous member (Administrator)
  • 12 May 2017 16:47
    Reply # 4829803 on 4789675
    Arne,

    2-3 percent? Ouch.

    My Joe 17 has a displacement of 500kg (with my modifications maybe 550), and I am installing a 100x4mm aluminium mast, 6 meters long plus 70 cm of wood.

    I have no means to measure the weight of the mast, but I have a hunch that it's something like 5-7 percent of the displacement.

    Am I in trouble here?

    Last modified: 12 May 2017 17:02 | Anonymous member
  • 11 May 2017 15:22
    Reply # 4826946 on 4789675
    Anonymous member (Administrator)

    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


    Last modified: 13 May 2017 08:58 | Anonymous member (Administrator)
  • 11 May 2017 01:12
    Reply # 4825435 on 4789675
    Anonymous member (Administrator)

    I would like to keep this thread going, from time to time, until the process of choosing, making and trialling a junk rig for the Pelorus is done – each type of boat has different characteristics and hopefully it will be a small contribution to this group’s very impressive body of knowledge and experience gained. I have found these longer threads recording the evolution of ideas very interesting to read (huge thanks to the web master) and am very grateful that people who have heard it all before are so patient and willing to take an interest in other people’s projects.

    So I went away for a couple of nights, to begin learning something about how this type of hull behaves under sail. (Actually I also made Stillwater my destination in order to see Linda C-G’s little Herreshoff, soon to be re-launched with its new junk rig. What a sweet little boat.)

    Findings: The Pelorus sails surprisingly well in light conditions – could use a little more sail area I suppose, but in 5,6 7 knots of wind, seas slight, she slips along quite nicely to windward, sailing by the luff tell-tales – guessing maybe 2 ½ to 3 knots at times with that 4-blade propeller dragging in the water, tatty old Bermudian sails and towing a dinghy with a bit of water in it. Light on the helm, slight lee helm in wind under 5 knots, but neutral through to slight weather helm as the wind speed increases. Easy to steer (much better than when under power) comes about easily enough when tacking – and with slightly eased sheets will keep course under these conditions with autopilot off and helm fixed in one position, for up to 30 minutes at a time – more than enough to go below and make a cup of coffee and check the emails! In short, far better than expected. Flat off the wind, with the genoa useless, I could not help thinking how much better she would go with the spread of a much larger junk sail. She is not close winded however – no surprises there, the keel is very shallow (she only draws one metre) so she makes a bit of leeway and the gps track made good shows the best she could do is tack through about 120 degrees. (Pretty much as predicted by Arne.) With better setting sails this might be improved a little. There is certainly no need to have the engine running in order to make progress to windward, however, and while she would never compare with the sort of boats Arne sails, she is good enough to consider more of a sailboat than a motorboat.

    A bit of wind was forecast, so I stayed out another day, to see how she would cope with that. The front came across when I was nearly home, so was in sheltered water with almost no sea to contend with. (This report might be a little different if the trial had been out in the Gulf where a nasty chop can build up.) What happened when the first little squall came over (with full sail up) was that she heeled slightly but stood up to it very well – but quickly developed weather helm, more than the autopilot could handle – and required a lot of rudder to keep going straight. In fact the rudder was stalled out, dragging through the water and she was still trying to round up. I am sure Arne will have something to say about that, and the subject of rudders. But I am not sure that the cure is just a more powerful rudder. This is a characteristic of many sailboats which are beamy and shallow in draft – lay them over on their side a little, and they become hard-mouthed.  Kiwis will know that mullet boats, for example, are notorious for it, with big rudders and occasionally two men on the tiller. The quick answer for this boat was so simple I had not really thought of it. I did not want to be teetering around on the foredeck trying to reef the main just at that moment, much less trying to thread a smaller headsail into the boltrope track of the luff spar – all I had available in the cockpit was the roller furling rope for the headsail. This is not a roller reefing gear but a furling arrangement and in theory if you try to reef with it you get a baggy sail just when you want a flat one. Never-the-less, in the first few seconds there was no option and guess what – the semi-furled genoa set perfectly, the weight came off the helm and she picked herself up and went away at a faster speed than before. Note: this is not a problem of sail balance – the area came off the genoa but the result was a reduction in weather helm. It is to do with hull shape when heeled. All she needed was a reduction in sail area and the rudder was once again perfectly adequate and able to be handed back to my friend Ray, the autopilot. I reefed and unreefed from the cockpit three or four times with ease (take that, you junkies!) and felt very pleased and happy. However had the squalls been 25 knots or more she would have been getting out of control and some more drastic sail changing would certainly have been necessary. So I am more convinced than ever that junk rig is the way to go for this boat, that she will sail all the better for quick and early reductions in sail area, especially in conditions worse than the above described. I am not so sure now that the massive increase in sail area that a junk rig could give, is really necessary – she doesn’t seem to want or need a lot of sail area. But it is always good to have plenty of it down wind in light conditions. (Less is more? Not always, my new friend!)

    I am confident now the hull (and rudder) will give adequate sailing performance both on and off the wind (she is my home, my camper van, not my sports car.) I am confident she will be sailed most of the time, though she will motor if necessary, in a seaway, better than a lot of pure sailboats. I found that though she is stiff and can stand up to a gust of wind, she goes far better with a quick reduction in sail. And I have no doubt that a new junk rig will give better performance on all points of sail than the tired, worn-out sails she currently has. (The genoa was torn at the leech and the stitching was sun-rotted from never having had any protection – patched up the day before with duct tape which was coming unstuck and fluttering away from the exposed leech line). I won't argue with the advice that a bigger, transom-hung rudder (like Graham Cox's Arion) would be better, or that a bottom plate might help as suggested by Arne - but I think we will wait and see if those things are really necessary. Have not seen the need so far - but I expect the real test will be tacking under junk rig in a choppy seaway.

    What I really want to know now is, can a junk rig set and sail well with a couple of panels down, so that a two-panel-reefed sail can be the practical working sail – with the extra area up one’s sleeve, so to speak – a reserve for light airs?  In that case I would increase the sail area from the current 27 square metres to about 35 square meters which a low aspect-ratio junk rig would give me on about the current masthead height.

    Or, is it better to make a working sail which maybe sets better unreefed (?) which can be carried without reefing up to, say 18 – 20 knots?  In that case I would opt for just a small or no increase in sail area with either a shorter mast, or perhaps higher aspect ratio – (the latter not for any expected improvement in pointing ability however, in the case of this boat.)

    Two final points (didn’t intend this to be so long and boring). The remainder of the trip comprised the wind dropping away completely, ghosting up into the creek where I live, on the faintest of airs and with a good favourable tide. Had no desire to start the motor, only used it for the last five minutes to enter a tributary so narrow that mangroves brush both sides. I will trade maximum windward performance for shallow draft any day of the week (though adjustable draft would be nice) – and after ten years of commercial fishing and being quite comfortable with a diesel motor, I had forgotten how satisfying it is to sail – I hope I can see the project through and put a junk rig on this boat, I won’t be motoring too much.

    The other point is, I am having a certain amount of bother now deciding where the mast should go. Its not a very big boat, its my home, space is precious and crawling around a mast in order to get in and out of bed is not so easy now for a granddad like me. It is going to be difficult to retrofit a new rig. I started out thinking I would choose a rig and put the mast where it should go. I am now thinking mast position (and rake or no rake) might have to be the starting point and might be the determining factor for what type of junk rig. More questions on that later.


    Last modified: 11 May 2017 01:44 | Anonymous member (Administrator)
  • 05 May 2017 12:28
    Reply # 4815942 on 4815028
    Anonymous member (Administrator)
    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


  • 05 May 2017 12:00
    Reply # 4815930 on 4815387
    Anonymous member (Administrator)
    Graham Cox wrote:

    So a big rudder certainly helps.  

    Thanks, I will certainly keep this in mind. It will be interesting to see what happens with the somewhat smaller rudder of the Pelorus.
  • 05 May 2017 11:21
    Reply # 4815906 on 4815721
    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.
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