Leisure 27 junk rig conversion

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  • 03 Feb 2023 22:21
    Reply # 13084302 on 13055766

    Hi Jon,

    good to know that the mast should be reasonably easy to fit in the forward position.

    As far as deck reinforcement is concerned the actual load laterally at the deck will be in the order of 1500 pounds, assuming a bury of 5 feet and using Arne's sail plan. Allowing a safety factor of two the design load would be around 3,000 pounds.

    My suggestion would be to remove the head lining in the mast area and then build up the thickness of the deck in the raised coach roof with plywood laminates so that the bottom was flush with the side decks. It looks from the photographs as if this will be about 2 inches I would then laminate to the deck a piece of 3/4 inch plywood about a foot wide across the full width of the boat  and a second strip from the front edge of the blocking to the anchor locker bulkhead. Once this is done then the hole for the mast can be cut. I usually cut the mast hole an inch larger than the mast. When installing the mast I wrap the mast in 5mm thick rubber sheet taped together for a tight fit, I then caulk the bottom of the remaining gap with 6mm diameter rope and fill the  gap with thickened epoxy. This gives a flush join at deck level which can be waterproofed with narrow strips of canvas set in clear silicone.

    I have found that this method is very forgiving and gives a clean look to the installation.

    All the best with the conversion, David.

  • 03 Feb 2023 14:52
    Reply # 13083611 on 13055766

    Thanks David - having measured up on the boat now I would agree with you.

    The second mast position suggested by Arne sits just in front of the existing deck hatch as I suspected originally (pictures one, two and three). I suspect a very slight forward rake might be helpful to assist with clearance from the hatch itself. I think the hatch may also need to be reversed to open away from the mast. 

    The internal position of the mast doesn't seem to interfere too much with the berths in this position. I need to revisit this with something like a length of plastic pipe the same diameter as the mast, but it doesn't really impact on access to the berth, but is more an intrusion at about thigh level when lying down which seems to leave both berths useable. 

    The good news is that the mast step location here is basically into a forepeak locker which has no lining, tanks etc. so the bottom of the locker is just the hull moulding - the sides meeting in quite a sharp "v" at the base at this point. See picture here. It looks like this would be a fairly straightforward location to glass in a mast step. 

    The reinforcement to the partners at deck level will require some more thought as internal reinforcement inside the cabin may not be straightforward. My initial thinking was to fabricate a fairly substantial external "plate" supporting a tube through which the mast is stepped. As per the photos the cabin top is raised above deck level in this area and I envisaged that this could sit on top of the raised area with a flange following the same profile and through bolted through the vertical sides of the cabin top (as well as being through bolted around the mast tube). I need to sketch this out probably as I'm not sure the written description makes sense. The deck does seem fairly solid (and the anchor windlass has been bolted through it with a backing pad for many years with no issues!) but it is difficult to know how much reinforcement is really needed here. 



    My only real concern looking at this in profile from the side is whether the mast position is too far forward in relation to centre of buoyancy as the hull really narrows down up forward and is there an issue with having the weight of the mast this far forward? The opened  hatch in the photo gives a good indication of the mast position. That said, I presume it is the centre of gravity of the entire rig (including sail bundle) which is relevant so maybe there is less difference than it would seem between this and Arne's original suggestion with the mast slightly further aft, but more balance on the sail...

    I did occur to me as I was writing this that I neglected to measure the amount of bury this mast position gives, which I will need to check at the weekend, but based on the requirements noted in PJR I don't think this would be an issue.

    Clearly there is a lot of planning and design still needed, but it does seem as if a conversion should be viable which gives me more confidence! 


  • 23 Jan 2023 22:53
    Reply # 13069779 on 13055766

    Hi Jon,

    the mast can be offset to port or starboard, just set the sail on the opposite side of the mast. The sail on Gypsy Rose is on the starboard side of the mast, most set it on the port side.

    My personal opinion is that the forward mast position would be easier to construct and cause less modification of the interior layout.

    A transom hung rudder is fairly easy to construct and much easier than modifying a fin and skeg. It can be constructed totally separately and then just bolted on. The existing rudder and skeg could then be removed and the hull patched, which is a reasonably easy procedure.

    All the best with the conversion.

  • 23 Jan 2023 16:24
    Reply # 13069025 on 13066138
    Anonymous wrote:

     

    It sure is. I have always liked that (PBO Nov 2011) photo of Poppy squared away. (See her in the background?) That photo says it all. 


    Thanks Graeme - I remember reading that article actually! Definitely a case of "a picture paints a thousand words"..
  • 20 Jan 2023 21:51
    Reply # 13066138 on 13055766
    Anonymous member (Administrator)

     I am not aware aware of any compelling reason why an offset mast has to be offset to starboard.

    Intuitively one would prefer the sail to be on the centreline side of an offset mast, and if you haven't made the sail yet, that can be done - but even that is unlikely to make any measurable difference to performance. 

    I would keep an open mind and consider all options. In the end, your own internal layout priorities, and your tape measure, will decide the mast placement, and thus the rig, I should think.

    ...but I would imagine the junk rig is a bit more efficient than this in terms of presenting the sail to the wind and having more area higher up in the clean wind? 

    It sure is. I have always liked that (PBO Nov 2011) photo of Poppy squared away. (See her in the background?) That photo says it all. 


    Last modified: 21 Jan 2023 01:59 | Anonymous member (Administrator)
  • 20 Jan 2023 12:12
    Reply # 13065178 on 13055766

    Thanks all - some very helpful advice here!

    I will be down at the boat at the weekend so will have a better opportunity to look at this, but I think that revised mast line would be forward of the deck hatch. 

    As per Graeme's notes / sketch I need to work out how the (already fairly tight) system of doors between the heads / wardrobe works with all this. Currently it's a fairly clever arrangement where the wardrobe door (to starboard) can close off the fore cabin leaving the separate heads door (to port) closing off the heads from the main saloon or you can open that door to close off the main saloon giving what's effectively a much bigger heads compartment for changing etc. 

    I will get my tape measure out at the weekend and try and work it out. 

    I hadn't really considered offsetting the mast, but in my head I had always assumed that an offset mast would be offset to starboard given that the sail lies to the port side of the mast so it effectively keeps the sail closer to the centreline - although PJR seems to say the offset doesn't make much difference to sailing performance.

    In terms of sail area my initial view was to err on more rather than less on the basis that it is easy to reef if needed, but I appreciate this can be taken too far! We don't really plan to do much racing, but would want to make sure we get reasonable downwind performance. 

    The existing 135% roller genoa is approximately 20sqm so quite a bit larger than the one shown in brochure plan. And yes it does suck downwind unless you are prepared to fly a spinnaker, which for me is not viable / safe when shorthanded. We do have an asymmetric cruising chute, but that isn't much help either when sailing lower than a broad reach.

    The closest comparison in terms of sail area I guess is sailing goose wing with the genoa poled out, but I would imagine the junk rig is a bit more efficient than this in terms of presenting the sail to the wind and having more area higher up in the clean wind? So on that basis the 37 sqm feels like it should be about right. Ultimately she is not a very easily driven hull so a junk sail which is big enough to sail effectively downwind in very light airs is going to be unrealistically large and I'm probably going to be motoring in that scenario. 

    I have bit of insight into how a transom hung rudder would work as we have self steering gear mounted on the transom which requires quite a long bracket at the top to get the shaft for the self steering gear vertical, so I think it would be possible, but would be quite a big modification and may be easier to redesign the existing skeg / rudder. Leisure Yachts did make a Leisure 29 which is the same hull design but lengthened to give a longer cockpit and this did apparently solve the weather helm issues. 






  • 18 Jan 2023 22:24
    Reply # 13062898 on 13055766

    Arne,

    the rig you have shown is basically the same area as the existing main and No1 genoa, so I have no argument with that. I was just suggesting that if racing against other Leisure 27's a closer match to their spinnaker area may be required for optimum downwind performance. This would mean reefing earlier for points of sail closer to the wind, but no big deal with a junk rig. I tend to reef early on Gypsy Rose as she is very tender, but this makes little difference to her speed.

  • 18 Jan 2023 07:42
    Reply # 13061837 on 13055766
    Anonymous member (Administrator)

    David,

    as for sail area, I guess Jon should have a say here. Now I had a closer look at the original Bermudan rig. Tracing the sails, the mainsail came out at only 12.7sqm and the shown working jib is only 12.2sqm. It will thus take a large Genoa 1 to reach a sail area of 37sqm. Downwind, these rigs really suck.

    My suggested JR with 37.5sqm in it, although not big, will produce a lot more oomph than the original rig. Upwind, the JR is taller, even with a shorter mast, and downwind that single sail will make much better use of its area than that masthead Bm rig ever did.

    I notice that Jon’s boat sits downriver from Ipswich, almost next to the North Sea, so maybe it makes sense not to overdo it. A SA/Disp of 18.1 isn’t that bad, after all.

    Arne


    Last modified: 18 Jan 2023 14:08 | Anonymous member (Administrator)
  • 17 Jan 2023 20:16
    Reply # 13061241 on 13055766

    Arne,

    that looks like the plan I had imagined. Use of the running tack line adds a lot of flexibility for weather/lee helm adjustment as I have found with Gypsy Rose. The boom can move forward until it is level with the waterline and this provides much more balance in the sail for off wind sailing. Looking again at the boat brochure this position should be forward of the forehatch and it should be fairly easy to reinforce the foredeck to support the loads from the mast.

    The revised mast position should allow better access for the V berth.

    If the rudder gets overpowered by the revised rig then converting to a transom hung rudder should be a fairly easy conversion and would give the rudder more of a lever arm as well as allowing a larger rudder with a good sized balance area ahead of the pintle line.

    Looking at the existing sail areas the main plus no1 genoa have an area of about 37 square meters and a spinnaker of about 50 square meters, so a somewhat larger sail area than Arne has shown, could probably be acceptable for optimum downwind performance.

    David.

    Last modified: 17 Jan 2023 20:47 | Anonymous member
  • 17 Jan 2023 11:47
    Reply # 13060459 on 13055766
    Anonymous member (Administrator)

    Inspired by David’s thinking, I had another go. This time I used the original Johanna 70 sailplan with the same batten length at 4.90m. This was initially installed with the boom overlapping that of the Johanna 60 sail. The mast was then moved forward 49cm until it crossed the 15% ring on the boom. This gave a comfortable halyard angle and increased halyard drift. I therefore lifted the whole sail 150mm to increase clearance over the rail and pulpit.

    On the wind, the steering balance should be very similar to when using that first sail .

    Downwind will call for more rudder input, but I don’t think it is a show-stopper. I have the same setup on my Ingeborg and I can easily sail downwind as long as I don’t set more sail than I can (just) carry when close-hauled.

    However, you can prepare the sail for a plan B  -  using running tack parrels and tack line to shift the boom forward, as indicated on the diagram in thin gray lines (here 5°). The preparation just means you have to make the fore batten pockets and batten parrels fitting the forward-swung position.

    The diagram shows that the initial boom rise of 10° ensures a decent clearance, even when swinging the sail forward.

    The new mast position will, as said, be 49cm forward of the first one (..the distance from bow to mast is now 1.89m..). That may take up a little more space in the V-berth. In case only one berth is to be used, the mast could be moved 120mm to one side, to clear the CL. My solution has been to pad the mast of Ingeborg.

    Finally, I have no idea of where any deck hatch is sitting. Maybe the mast in its new position clears the hatch.

    Arne

    PS: I haven't tried using a running tack parrel to shift the sail back and forth myself, but others like David have done so, and it clearly works.


    (Arne's album, diagram section 7, photo 8)

    Last modified: 18 Jan 2023 08:56 | Anonymous member (Administrator)
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