JR conversion for Marcon Sabre 27

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  • 03 Apr 2017 09:34
    Reply # 4708986 on 4707698
    Richard Oates wrote:It's the balance of the rig that concerns me, will the helm be nice and balanced, it seems almost impossible to predict this. I would love to hear how you get on in the future.
    Richard, while the cognoscenti may experiment with a tad more lead here or a an adjustment of relationships there, I think that it's fair to say that if you follow the 'recipe' in PJR, you won't go far wrong, especially with a boat like yours, that doesn't go out of its way to push any boundaries.  Moreover, once you have rigged your boat, you will find that the sail can be moved around the mast in many different ways, simply by adjusting some of the standing lines.  But I do sympathise with your dilemma: my feeling is that the tanks might be easier to replace (bladder? jerricans?) than attractive joinery.  If all else fails, toss a coin.  Remember, in this naughty world you never know if you made the best decision, only if the one you made is satisfactory!
  • 02 Apr 2017 18:20
    Reply # 4707698 on 4619716

    Frank

    Thanks so much for this comprehensive reply (over which you have taken much trouble) and sorry for the delay in my response. You have certainly worked things out very well. I hope you get the boat in the water soon and can report on its sailing qualities. For me it's a toss up between the mast in the position you have chosen, where it avoids water tanks below but would go through lockers above, or the sloping coachroof where it would be the other way around, 2 water tanks to alter but not the smart lockers above. Such is life. It's the balance of the rig that concerns me, will the helm be nice and balanced, it seems almost impossible to predict this. I would love to hear how you get on in the future.

    Last modified: 02 Apr 2017 18:21 | Anonymous member
  • 27 Mar 2017 10:07
    Reply # 4692367 on 4619716

    Richard

    Re your enquiry as to how partners and mast were fitted in my Sabre 27

    The mast is protected from chaffing / excessive movement at the partners by a thin (~ 3 mm) rubber sheet which is wrapped once around the mast in that area. It is secured by an adjustable  circular s/s clip fitted above the partners casting. The mast can move a little in the partners, it is not a tight fit. As shown in the photo of our boat (photo) a rubber collar then fits over the mast partners again secured by adjustable s/s circular clips to provide a watertight seal.

    I needed to prepare a suitable base to mount the partners casting because there was insufficient flat area on the foredeck. Additionally, to get the CoE of the Junk sail in the right position, I had to rake the mast 3 degrees aft relative to the waterline. To ensure that the partners made even contact with the mast, the partners casting had to sit on it’s base perpendicular to the mast. Adding a circular base allowed me cover both these requirements. The hull had been set up with the waterline horizontal both along its length and across the beam to facilitate the fitting out process. This made setting up the mast a little easier.

    I first made up a simple circular shaped plug then made a mould. I ground down the underneath of my moulding to fit over the raised portion of the foredeck (the king post moulding) and to allow it to sit at the correct angle. This was then bonded to the foredeck using epoxy. Later I cut a circular hole to take the partners casting which has a flange to allow the casting to be through bolted to the foredeck.(photos, image no 9)

     I also prepared the hull for the mast foot, first laminating sever layers of  18 mm marine ply and shaping to fit the hull. This was then bonded to the hull and glassed over. A drainage channel was built in to this base to allow any water that might enter the mast to drain freely.

    The mast with the partners in place was then craned into position and the base passed through the hole in the foredeck. The mast foot fitting (Photos image no 12) was then inserted and attached to the mast foot ( pre - drilled holes, large through bolt). I used temporary stays to hold mast in correct position while I glassed in the mast foot. Later I drilled holes for the through bolts to secure  the partners to the foredeck and bedded the partners casting down on Sikaflex which was also used to seal beneath the bolt heads.

    As to the ease of removing or re-stepping  the mast, I haven't tried that yet but since mast is not a tight fit through the partners it shouldn’t present too many difficulties. Granted, refitting the mast could be a little more tricky, but I think that  if the rubber protective sheet which wraps around the mast, as described above, is fitted once the mast has been re-stepped, (easy to do just need s talcum powder to allow it to slide down the mast and into the partners), there would be sufficient clearance when passing the mast through the partners casting.

    Hope I have covered your enquiry please let me know if you would like more detail on this/ other build topics.

  • 24 Mar 2017 20:56
    Reply # 4688545 on 4684781
    Frank Farrell wrote:All that remains now is for me to get this boat in the water; it has waited long enough. If you want additional information about the conversion - there is much I have left out, I would be pleased to go into more detail.


    Very interesting to hear about all this work, Frank.  Why don't your write it all up as a series for the magazine, including the fit-out?  Of course, you'll probably not have time until you have launched, but that would be even better, because we'd also get to hear how the boat sailed.  (If you could make sure your photos area round 2.5MB - approx 2400 x 1800 pixels - you can be sure of them reproducing well in the paper magazine.)

    It sounds like we may soon have 3 Sabre 27s junk-rigged: it would be fun for you all to get together some time.


  • 24 Mar 2017 20:07
    Reply # 4688428 on 4619716

    Frank

    Thank you very much for your response, (no worries about the delay) this is a great and very useful contribution for me.

    I too have a twin keel Sabre.  I particularly like the mast position you have chosen, going through the foredeck seems infinitely preferable to fabricating partners to fit the inclined forward face of the coachroof.  Your machined partner fitting seems very elegant and simple. One question regarding fitting the mast. Is the partner a tight fit on the mast or relatively loose? If the latter are you fitting wedges? If the former, how is the mast lowered into position without the risk of lateral rotational movement of the tabernacle damaging the deck, I assume it would be hard to lower the mast and keep it in a perfectly vertical position while doing so.

    I am going to have to swot up on all the aspects of mast position. I would favour the position you have chosen although in a reply near the beginning of this thread David seemed to favour a position much further back, through the hatch in fact.  I wonder if this is because he favours a high aspect ratio rig?  Arne earlier on included a sketch (section 2 with a AR of 2.10 S/a 16.1 and a 1.6 degree mast rake. Considering the arrangement of bulkheads below deck this would seem to be very suitable.

    However you mention that Robin found severe lee helm with the first Sabre conversion and corrected it by moving the mast top 18 inches back. With the mast at 10 feet this would equate to about  2.5 degrees compared to Arne’s 1.6. I am imagining the sail now out at 90 degrees on a run, and it seems to me that the critical thing is how the yard is hung from the mast which results in the position the sail now takes up. I guess I need to read ‘The Bible’ on these matters before expecting experts to explain them to me!

    Meanwhile I am pursuing my trimaran project for the time being, I think it will be a good test bed for leaning more about the intricacies of the rig without spending a fortune. It also gives me much more time to get to understand the dynamics of the JR before committing myself on the larger project.

    I’ll start making the tabernacle tomorrow!


  • 23 Mar 2017 10:54
    Reply # 4684781 on 4619716

    Richard

    I’m sorry I’ve been slow to post my response but main problem is what to leave out.

    Having read all the responses generated by your first posting. I think they are a very interesting and helpful contributions as to how you could convert your Sabre 27.

    When I first considered doing the same, about 10 years ago, I contacted Sunbird Marine seeking more information about a junk rig conversion and costs involved. Robin was very helpful and sent information together with an article by Alan Boswell which included pictures of a Junk rigged Sabre 27 by Sunbird Marine. I have uploaded  these pictures together with additional material.  (see photos)

    The mast position for the Sunbird Sabre 27, is just in front of the coachroof on the foredeck. The partners, which is an aluminium casting (image no. 9) is machined to allow the mast and a thin neoprene rubber sheet which wraps around the mast to just pass through the partners. A waterproof collar ( not shown) seals the mast/partners junction. Images 11 & 12 relate to the mast foot, the fitting ( image 12) inserts into the mast foot and is glassed into the hull and the mast is secured by a through bolt. Images 7 & 8 shows the location of the  mainsheet attachment at the front of the cockpit and stowage box for mainsheet. The aluminium mast was fabricated by Needlespar.

    No detail of the sail area were supplied but it appears to be the Sunbird 80’s design with rigid battens and single sheets to a traveler at the forward end of the cockpit. Robin commented that initially the boat displayed severe lee helm but this was corrected by raking the masthead aft by 18 inches. He added that the boat did not appear to follow the usual rules re: positioning  of a Junk rig mast. He did not mention the keel configuration.  He also commented that  the ideal position for the partners would be about one foot aft, which would locate it in the forward end of the coachroof.

    As to my Sabre 27, which is the twin keel version, my first consideration was for an easily handled rig. Having read ‘Voyaging on a small income’ I was convinced  that the Junk rig was the right one for me.  My project started with a bare hull. The original owner had bought this new in 1982, stored it in a barn, but never started the fitting out. I decided to go for the simplest version of the rig and I chose to go with the HM design, flat sail, rigid battens. I followed advice given in  ‘Practical Junk Rig’ to design my rig and have recently had a sail made by a local sailmaker. 


    For ease of construction and wish to have a comfortable forward double berth and with good ventilation from the forward hatch, compromise was necessary and I chose to position the mast partners in the foredeck immediately in front of the coachroof on a circular base which I moulded and bonded to the deck (photo)(Partners supplied by Sunbird Marine see above). I found that to locate the CoE in the advised position (6% aft of CoE for BR  / 9% lead on CLR) and keep the height of the rig and CoE comparable with a BR Sabre 27,  that a low aspect ratio sail seemed the best option. Choice of mast proved more challenging but I eventually decided to have one built by Hawk Marine Products ( who took over from Needlespar).

    Sail area 35 square metres ( same as main and genoa of  Sabre 27 Mk2). Aspect Ratio 1.5, cord of sail 5.5 metres, sailcloth 5.5 oz Terylene,  5 battens in pockets, Transition panel to head of sail (3 triangular panels).  Aluminium yard, single sheets to aft end of cockpit. Overall height of rig above WL 10.9 metres (same as BR Sabre). The overall length of the mast is 10.2 metres, lower section 5.5” diameter aluminium tube 0.25” wall thickness. An internal sleeve , 2 metres in length and of 5” diameter tube of same wall thickness was inserted to reinforce mast through partners. The middle and upper sections are of the same wall thickness and reduce the diameter to 4.5” at the top.

    I found Arnie’s article  ‘Mast Scantlings’ (JR Magazine no 48 ) a very useful starting point for determining the dimensions of the mast. This article can also be found in this website’s Public Domain Files. The only problem I found related to the units of measurement used when I needed to enter data relating to material strength of aluminium.

    I was aware of the possibility of excessive weather helm when sailing off the wind with a low aspect ratio sail ( PJR mentions this situation) and have planned to be able to cant the sail foreword on the mast if required. 

    All that remains now is for me to get this boat in the water; it has waited long enough. If you want additional information about the conversion - there is much I have left out, I would be pleased to go into more detail.


  • 15 Mar 2017 18:42
    Reply # 4668883 on 4619716

    I’ve been away for a while and just seen the new posts, very interested to hear of epoxy moulding techniques and the nearly finished  Sabre 27 junk rig conversion. I would be really interested as to what mast and sail configuration you have chosen and the mast position adapted together with detail of how you arranged the partners and foot. I have nearly decided how to do mine but it’s hard to make the final  choice, there are so many options.

    I have decided to spend this year thinking about the Sabre conversion, work out the details and likely cost and perhaps carry out the work over the winter, otherwise I won’t get much sailing in this year. Meanwhile I have an interesting option. A few years ago I completed a Strike 16 folding trimaran but have always been unhappy with the mast position on top of the cuddy, and indeed with the cuddy itself which is cramped and prevents easy access to the foredeck.  Also I hate the bright white sails which give me a headache in bright sunshine. I think it would make a great JR conversion.  It would be really easy to fit a tabernacle in the foredeck and as the sail area is about the same as my friend David’s Westerly Nimrod (see separate post re this JR conversion) I thought I might adopt the same weaverbird configuration.  It would be an economical way for me to learn more about JRs and improve this boat.

    The tri has an 8 inch draft with no centreplate and relies on the box section of the centre hull and the V shaped amas for lateral resistance. She will be a great boat for the shallow waters of Morecambe Bay.  Being very light and easily driven she should be pretty fast and I am wondering if this has any implications for the sail design. Any comments on this idea will be gratefully received.  Also being a new member I am not sure if this warrants a new thread?


    Last modified: 15 Mar 2017 18:43 | Anonymous member
  • 09 Mar 2017 09:53
    Reply # 4656515 on 4619716

    Could you make an album of photos, Frank? Especially of the deck area around the mast. I'm sure these would be helpful to Richard.

    Good luck for completion and launching this year!

  • 09 Mar 2017 09:05
    Reply # 4656468 on 4619716

    Interested to read about your planned conversion of Marcon Sabre 27. I am also converting a Sabre 27 to Junk rig. I started some years ago and am now nearing completion of the project, aiming to launch this year. I started with a bare hull which the previous owner had purchased from the moulders in 1982. Happy to share experience gained so far.

  • 07 Mar 2017 09:28
    Reply # 4652351 on 4619716

    I was thinking of moulding around the outside of the bucket, as the inner surface is the one that should be smooth, functionally. There wouldn't need to be any moulding across the bottom of the bucket, as we're only wanting the conical portion, so I think release should be straightforward given some PVA coating, but if necessary the bucket can be cut out.

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