SJR for Serendipity

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  • 13 Jul 2019 23:10
    Reply # 7778468 on 7777985

    She looks good Graeme!!

    I look forward to seeing her when I return to New Zealand.

    All the best, David.

  • 13 Jul 2019 21:46
    Reply # 7778402 on 7777985

    Thanks Arne you are always so helpful, your writings actually a big influence encouraging me to have a go at making a sail. 

    Yes, this little boat does not have the firm sections of Frøken Sørensen but is a bit wedge shaped with a wider stern.


    Weather helm developed when heeling became excessive,  and may have been more if the centreboard was fully down. so I will take your advice and look at improving the rudder with some more blade area.

  • 13 Jul 2019 18:09
    Reply # 7778253 on 7777985
    Anonymous member (Administrator)

    Congratulations, Graeme,

    and thanks to Marcus for the fine photo job! The SJR certainly looks powerful (no surprise), and you will soon tidy up the jiblets. The hull of Serendipity  seems to have one thing in common with my Frøken Sørensen (FS) -  the wide transom stern. This will naturally lead to some weather helm when heeling over. On FS, the builders  (East Germany 1987) had simply given the her a very deep, strong rudder with a good foil section. FS could therefore be knocked over until the cb. lost grip, and still be controllable.

    In case weather helm becomes annoying, I therefore suggest you make a deeper rudder, either by replacing her present blade (if the rest is strong enough), or by starting from scratch.

    Anyway, good luck!
    Arne


  • 13 Jul 2019 13:07
    Message # 7777985

    Serendipity is a 17 foot "Monarch" open top trailer yacht, designed  by Alan Wright.

    As a learning exercise I made a tabernacle, mast and split junk sail. A few days ago Marcus towed me out of the little mangrove tributary and stood by with camera while the rig was hoisted and given its first trial. 

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    The sail is a slightly scaled down copy of Amiina's Mk2 sail, but without the split in the top panel. As can be seen, two of the jib panels are setting badly. I think this is due to their being incorrectly placed and fastened on the battens, as they were fairly accurately made on a simple wooden mould, and all three identical. The green main panels (also 45 degree shelf) were similarly made, but of very light cloth from an old spinnaker.

    The battens and yard are solid timber in two parts, with the sail panels sandwiched between. I followed the method used by James (River Rat) . I think they are rather heavy and I might replace them later with bamboo. (And fix those jib panels at the same time.)

    The mast was made in three over-lapping sections of aluminium tube, made from what I had, and also probably a little heavy.

    The tabernacle is made from aluminium sheet folded into a "top hat" section, and sunk so only the top few inches protrude above the partner. The mast is stepped by walking it up from the heel. This is possible as the "cabin" has an open top. The tabernacle itself could be seen as redundant here, but I had made it so I used it. It does make it a little easier when raising the mast. Also I made the mast a little short and by happy chance, this arrangement has allowed me to raise the mast height.

    The sail drapes pretty well with just the halyard, two spanned parrel/downhauls for the four battens, and a standing parrel for the boom. (The photographs show a standing "Hong Kong" parrel on the yard but it was in fact disconnected, doing nothing and will be removed.) There are two sheets (one for the top two battens and one for the lower three) and this setup seemed to work pretty well so will probably remain.

    The sheet loadings were very light, but at 33% there is still enough imbalance for the sail to weathercock reliably when sheets are let fly. For what should have been a nimble and close-winded boat, Serendipity was making leeway and was slow to come about (though never once missed stays) - and we fairly quickly realised the reason was that the centreboard was only going half down, another thing to fix. Reefing up and down was a cinch, requiring only a tweak on the downhauls to bring the sail back into shape. The rig seems to have no vices and off the wind it brought the boat up to hull speed quickly - I would love to try this rig on a planing hull.

    I thought it went pretty well for a first try. There are some more photographs here, and the bow waves and wakes show that the boat was sailing quite fast at times. The water was flat, but the wind conditions were quite gusty down here in the creek, so we did not venture to raise the last panel. That lower panel was made from tyvek, as an experiment: rather flimsy and I doubt if it will last very long.

    Slieve wrote recently: "I wonder if too much thought goes into the detail such as sheet angle and camber depth, and then we don't focus on the more basic features like mast height and rig height. It's easy to get distracted by the detail and miss the the mundane." Never a truer word was spoken. I made a mistake by not allowing enough mast length for the height of the sail. It was no problem on this day, but when the sail is fully hoisted there is barely enough halyard drift. Luckily, in this case, I can jack the mast up higher in the tabernacle and still have enough bury.  As David T wrote: " ...if possible, it's better to go for more than the absolute minimum drift that the blocks can tolerate."  For anyone making their own first sail, there is a temptation to be greedy with sail area while being as mean as possible with mast height - its a mistake, and a lesson that needs to be emphasised

    Many thanks to Slieve for making his sail design available to me, and for his advice and encouragement. Thanks also to Marcus for photographs here.

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    Last modified: 18 Jul 2019 09:50 | Anonymous member
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