Project Mage - Part 1: Sizing, Scaling and Fiddling.

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  • 31 Dec 2018 17:46
    Message # 6977997

    I bought a C&C 25 in September 2018. She's still a sloop rigged bermudan ... for now. 

    Currently getting a sense of the dimensions and positioning.

    Started with a Hasslar/McLeod rig - but I have borrowed Arne Kverneland's work for a revision. I think I like the Ark Rig better since we get terribly light winds in our Mid Summer on Lake Ontario.  

    Photo of my initial sail design. Yellow line is the CLR of the C&C. 


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  • 31 Dec 2018 18:05
    Reply # 6978088 on 6977997
    Anonymous member (Administrator)

    Adam,

    The CE of these sails sits only an inch or two forward of the middle of the sail (boom). Could it be an idea to shift the sail 20-30cm (8-12") forward of the shown position? Then try to draw in a mast which gives a balance between 13 and 15%, and see if that can be done without ripping up too much of the interior.

    Good luck!

    Arne

  • 28 Apr 2021 23:20
    Reply # 10392012 on 6977997

    Hi Arne - I realize it's been a while - moving cities and boats etc., but is there a reason 13-15 lead is reasonable for a JR boat? I think I'm missing a vital piece of information here. 

  • 28 Apr 2021 23:42
    Reply # 10392256 on 6977997
    Anonymous member (Administrator)

    Hi, Adam.
    The 13-15% mast balance I suggested was for the shown sail with a yard angle of 70°. The outer limits for that yard angle is in principle 0 to 17% balance, but with lower balance than 12% you may have to make the mast taller since the halyard angle is best kept within 30° from vertical.

    In case you need to increase the mast balance of the sail, you can increase it up to about 25% by lowering the yard angle to 60°. If you go further than 25% balance, the sail may get unstable (this is outside my area of experience).

    In that case, I suggest you change to the Split JR, SJR. The limit there, I think is around 33-35%.

    Good luck!
    Arne


  • 29 Apr 2021 02:40
    Reply # 10394187 on 6977997

    Thank you Arne for clarifying. 

    We're now up to version 5  - you were tagged on FB for giggles as the sail area calculations made my eyes water just a smidge:

    I've had this a while now but I've been puzzling out a source for aluminum masts (or flag poles etc.)

    So this drawing has a lede of 16%. I'm going to knock this back to 13-15%

    Interestingly having done the SA/Displacement for this potential sail I'm looking at a SA/Disp of 27.74m^2 per ton.

    Based on Arne Kverneland's guide this would push Thaumaturge from "hot" to "incendiary". In May and September this sail would live it's life heavily reefed. However, in the light months of June through August I can imagine this sail taking me up to hull speed in some pretty light conditions. Have I over done it?

    Questions I still have to work out - and welcome suggestions:

    Batten material/dimensions and if anyone is in Ontario, Canada - a source for a mast.




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    Last modified: 29 Apr 2021 02:41 | Anonymous member
  • 29 Apr 2021 03:17
    Reply # 10394557 on 6977997

    Hi Adam,

    just a couple of items to be thinking about. Timber and Aluminium tube generally come in a maximum length of 6 meters, so having the boom and batten lengths a maximum of 6 meters saves a lot of work in constructing the rig. Sailcloth of the type used by most junkies has a width of 1.5 meters. On the rig you show I would suggest a five panel lower section to the sail which should allow the panels to be cut from a single piece of cloth. This would save a lot of work and wastage in making the sail.

    David.

  • 29 Apr 2021 09:42
    Reply # 10398619 on 6977997
    Anonymous member (Administrator)

    Adam,
    Now I had a closer look at your drawings. It appears that some of your dimensions are a bit 'off'.

    To save time, I just imported the C&C25 sailplan from Saiboatdata.com and plonked the JR sitting on my Ingeborg onto it.
    That should give a SA/Disp = 22.9, which is generous but not extreme.
    The question is where you can have the mast. 

    Arne


    Last modified: 29 Apr 2021 10:23 | Anonymous member (Administrator)
  • 01 May 2021 02:29
    Reply # 10416112 on 6977997

    Hi Arne - mast placement is negotiable. The original plan was to use theexisting hatch but that seemed too far from the Bow for good balance. 

    Using the hatch would also destroy the heads and hanging locker while upsetting access to the v-berth. 

    The location in your drawing would put the mast through the middle of the v-berth. I'm ok with that. To do any work I have to remove the original hard plastic headliner and will need to lift the floor of the berth to get at the bilge for a mast step. No matter where that mast goes in the v-berth the same steps apply. Cut. Gut and then drill a hole.  

    Now for me the question is still sourcing the mast and battens. I'll look up your notes on ingeborg to see what you did about battens. 

    Thank you for your help on this - it is very much appreciated. 


  • 03 May 2021 04:42
    Reply # 10432078 on 10416112
    Anonymous wrote:Now for me the question is still sourcing the mast and battens. I'll look up your notes on ingeborg to see what you did about battens.


    I think you said Ontario:

    https://www.metalsupermarkets.com/store-finder/

    shows a number in the Toronto area. They seem to be able to supply various alloys, diameters, wall thickness and lengths.

    Irrigation supply houses have tube up to 30 feet, but I am not sure if the wall thickness will suit.

    Anyway, as Arne has pointed out, a hybrid (aluminum/wood or aluminum/aluminum) mast can get pretty high too.

  • 04 May 2021 22:55
    Reply # 10442152 on 6977997

    Thanks Len - I did find Metal Supermarkets - and their prices are reasonable. 

    On the mast question - I worry about setting up the alignment for adhering a wooden topmast to the aluminium bottom. I don't have access to a yard that would let me do that kind of work for very long so ideally a single piece would be sought. 

    Valmont structures might have what I need. But really I'm hoping the City of Hamilton might have retired posts if I can hunt the right person down to talk to. 


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