Freedom 40 Cat Ketch Junk Rig Conversion

  • 09 Feb 2017 21:52
    Reply # 4601283 on 4601043
    Deleted user
    Battens - The following tubing is used to build telescoping antennas so it is designed such that the incrementally larger or smaller tubes slide into each other with a tight fit:

    Aluminum 6061-T8 tubing.  3.65 meters x 50mm od x 3mm wall (also available with a lighter 1.5mm wall in 6063-T8).  Weight for the 3mm wall is 1.24 kg/meter and the modulus is 69 GPa.  The necessary single splice to get to the 4.1 and 4.75 meter battens , given my skillset, would be to sleeve, glue (urethane), and rivet rather than weld section together.  

    They also offer pultruded fiberglass tubing.  To get similar stiffness to the AL tubing I would need  76 mm od x 3mm wall tubes since at 17 GPa, the AL is about 4x stiffer.  Weight is advertised at 1.31 kg/meter, so it is also 6% heavier. I am thinking that the failure mode is a little more dramatic than the AL, too...   

    would the AL tubing discussed above be OK for the boom/battens of both sails?  Are there any good reason to go with the fiberglass over the aluminum?

    Erik



    scratch all the above - turns out getting six meter AL tubing in 2" (50mm) od and varying wall thicknesses from 1.5, 3, and 6mm is pretty straighforward and reasonable in price.  Also the od can be gotten in 1/4" increments, so going to a 2.25" or 2.5" tube is simple.


    e


  • 09 Feb 2017 19:57
    Reply # 4601043 on 1424184
    Deleted user

    Arne  and David - Thanks...

    Some of the points you raised:

    Link - Not sure why the link didn't work- I thought I grabbed the URL by accessing the photo album through the search function, not through my profile as me.  

    Aft set of the sails - I hope my CE calculation of the old sailplan is correct.  It seems to match up close to where the CE is on some of the sailplan drawings I have found on the web.  The new sailplan is designed to move the CE forward by 23cm in hopes of adjusting the present weatherhelm.  With the larger sail area I expect to reef sooner which will allow for moving the CE to balance the boat better, too.  

    Rudder endplates. Something to consider.  Steerage is a wonderful think :)  During our last haulout I took the rudder off and rebuilt as much as I could.  Part of this work allowed me to increase the "throw" on the rudder and we definitely tack easier and turn better when docking.  It will take some playing with the new sails to see if any additional modifications are needed, but I will wait and trial the new sails first.

    Shorter boom/Dmin - The thinking currently is that if the sheet of the lower span with a Dmin of 1.7 is able to pull the associated sheetlets tight when the sails are dropped, then that would hold the sail bundle centerline even if the upper span, with a Dmin=2, two-blocks and sheetlets on that section of the sail don't get tight. There is Plan B and even C....   which includes - a David suggests - the option of simply looping a line around the entire bundle to secure it, which likely needs to occur when anchored anyways.   In any case, the shorter boom may make the stagger work out easier, but it definitely creates more "space" for the sheetlets.

    New Stuff

    Battens - The following tubing is used to build telescoping antennas so it is designed such that the incrementally larger or smaller tubes slide into each other with a tight fit:

    Aluminum 6061-T8 tubing.  3.65 meters x 50mm od x 3mm wall (also available with a lighter 1.5mm wall in 6063-T8).  Weight for the 3mm wall is 1.24 kg/meter and the modulus is 69 GPa.  The necessary single splice to get to the 4.1 and 4.75 meter battens , given my skillset, would be to sleeve, glue (urethane), and rivet rather than weld section together.  

    They also offer pultruded fiberglass tubing.  To get similar stiffness to the AL tubing I would need  76 mm od x 3mm wall tubes since at 17 GPa, the AL is about 4x stiffer.  Weight is advertised at 1.31 kg/meter, so it is also 6% heavier. I am thinking that the failure mode is a little more dramatic than the AL, too...   

    would the AL tubing discussed above be OK for the boom/battens of both sails?  Are there any good reason to go with the fiberglass over the aluminum?

    Erik


  • 06 Feb 2017 10:20
    Reply # 4593668 on 1424184

    I think this is looking very good, too, and I can't see any way to improve on it. I like the aesthetic appearance, as well as the function. Just one thing: with the single 3:1 sheet and multiple spans, you have got a little less than the PJR-recommended Dmin = 2P. The sheet may not come quite taut when the sail is stowed, but will be OK when sailing. The answer will be to tie a line around the sail bundle and take it out to one side of the boat, to stop the bundle swinging to and fro at anchor. I'd do this anyway, even if the sheet is taut, to save on wear and tear. If you used upper and lower sheets, the spans would be single, so no problem; but as we've said, the rigging can be changed fairly easily, once you are sailing and can see what is actually needed, rather than what appears right in theory.

  • 06 Feb 2017 08:22
    Reply # 4593483 on 1424184
    Anonymous member (Administrator)

    Erik,

    I couldn’t open the link, so I had a look in your album. I guess it is the Weaverbird schooner rig, with all those circles on it?

    I think it looks good. Thanks to the aft-set centreboard on the Freedom, you get away with the rig sitting quite fare aft. I am glad you have been generous with the space between the sails. That will save you from snags.

    I also notice that you have cut off the booms at the clew, the way I do. I am not sure if you need it on your rig, at least if you make it with Weaverbird-style hinge battens. On the other hand, cutting off that corner is quick to do and will not hurt even if the sails do not move forward at the first reef.

    Although this rig should be fairly easy to balance out on any leg, I still recommend the fitting of a generous end plate on that low-AR rudder. There is no such thing as a too good rudder. In case she is slow on tacking as she is, I suggest you start with the rudder, even before you start with the rigging project.

    Is your boat still dragging on a fixed 3-blade propeller? In that case, put a feathering propeller (Kiwi?) on the wish-list to Santa for next Christmas...

    Arne

    PS: Have you considered swapping the two sails to increase the lead, or will the space between the sails be too short, then?

     


  • 06 Feb 2017 06:35
    Reply # 4593356 on 1424184
    Deleted user

    Circles and ellipses Oh my...  

    So I've spent some time hopefully refining the sailplan.  CAD and pdf files are in the Box, a jpg is linked below.  Can somebody confirm that to determine the sheeting angle, a perpendicular line from the deck block to an ellipse defined by the sheetlet is the correct method?

    The pdf/jpg is a bit messy because of all the info on it.  Most of the new drawings are related to making sure the sheeting will work within the constraints of the Freedom, including Dmin, and max/min sheeting angles.  Circles, lines, and ellipses drawn appropriately and hopefully not too confusing. 

    Arne - I borrowed your idea of a shorter boom to both help with the batten stagger and to give the sheets enough room to "fit" between the clew and the deck  

    David/Arne/anybody else for that matter - if you could give the the drawings some level of "blessing"/review that would be great.  I would like to make any final necessary changes this week and start discussing and working on the panel/cloth layout for a hinged/cambered sail.

    Thank's everyone for their help so far!


     Erik



  • 01 Feb 2017 19:41
    Reply # 4581386 on 4579219
    Deleted user
    Arne Kverneland wrote:

    Erik,

    could I suggest you read through Paul Fay's articles about rigging his schooner Ti Gitu? Those sails have very high AR. Paul had a bit of a struggle, to begin with, before he cracked the code:

    http://www.junkrigassociation.org/technical_articles

    Just a thought

    Arne

     


    Thank you Arne - somewhere I had read the article with pictures.  Maybe it was on Pauls site.  Always good to re-read!  


    Evi says hi :)


    Erik

  • 01 Feb 2017 09:03
    Reply # 4579219 on 1424184
    Anonymous member (Administrator)

    Erik,

    could I suggest you read through Paul Fay's articles about rigging his schooner Ti Gitu? Those sails have very high AR. Paul had a bit of a struggle, to begin with, before he cracked the code:

    http://www.junkrigassociation.org/technical_articles

    Just a thought

    Arne

     


    Last modified: 01 Feb 2017 16:18 | Anonymous member (Administrator)
  • 01 Feb 2017 08:30
    Reply # 4579210 on 4578678
    Erik and Evi Menzel Ivey wrote:

    AR - The Version 2 design, which resulted in your push for a higher AR on the main had, I think, about the same AR as you have on Weaverbird.  You've previously stated that you would have gone for a larger AR sail if your mast was taller.   What are the pros and cons and possibly limits of this.  I see that one of Darren's current sail has an AR above 2.9 but for a different planform.  If there is one worry it is that I push the design too far outside some proven standard and end up with unanticipated and worse, non-correctable problems.  

    Erik

    I think you've reached the comfortable limit with your foresail, at AR = 2.6

    Although PJR has two diagrams of sails with AR = 2.78 (fig 6.9 and 6.11) I don't know if such sails have ever been made and tried. I think it would be difficult to sheet such high sails.

  • 01 Feb 2017 01:50
    Reply # 4578678 on 1424184
    Deleted user

    David - (your latest reply caught me mid draft on my response.  Ships crossing in the night and all that...)    

    Schooner Rig:  I will stop taking sailing jargon freedom with the Freedom sail plan - until further notice the mizzen is now the mainsail and the main is the foresail and we are officially a Schooner.  Hi :)

    Sheet purchase:  We have a pair of Andersen 46 two-speed self-tailing winches, one for each sail.  I definitely understand that a 3x1 sheet by itself would not work well.  Our current sails trim in fine with that amount of purchase and the winches.  

    Halyard Purchase: Along the same vein...  I was hoping to get away with a single or double purchase halyard.  As is, I can winch the girlfriend to the top of the mast and she may be similar in weight to the junk sail (now that will put pressure on me to keep light sails). But as you say, running rigging changes are relatively easy. 

    Top Sheet Batten:  Check!

    AR - The Version 2 design, which resulted in your push for a higher AR on the main had, I think, about the same AR as you have on Weaverbird.  You've previously stated that you would have gone for a larger AR sail if your mast was taller.   What are the pros and cons and possibly limits of this.  I see that one of Darren's current sail has an AR above 2.9 but for a different planform.  If there is one worry it is that I push the design too far outside some proven standard and end up with unanticipated and worse, non-correctable problems.  The sheets - I would love to do a single sheet and will try it, but can live with a double if necessary.  So no worries there.  Unmanageable reefing is less acceptable.  I have re-read the very helpful limits you advised here regarding P/B and camber.  The design still seems to still fit within those limits for a 8% camber that is made up of 4% sail cloth cut and 4% hinges. 

    P of 1.6m:  See above.  It is my preference to have fewer panels to save weight and allow for simpler sheeting.

    Top Sheet Batten sheet standoff:  I am thinking of using a "flicker" as is often used for a fat headed BM.  Some incarnation such as this:Selden Backstay Flicker for boats up to 30 ft. (9 meters) 

    Sheets, Dmin, and other scary things:  Six point, three part sheeting system.  Bottom equal power three point span (Page 68, Figure 4.28 in PJR with a Dmin of 1.75). Upper three points with an anti twist (Page 64, Figure 4.14 or 4.16) for a 1/3+, 1/3, 1/3-, 1/2++, 1/2, 1 pattern. 

      

    Annie - I have been struggling with where to stow the sheets and halyards and you have inspired me to re-think the problem.  Bags don't work, and a tall box would not either.  But it may be that a shallow, almost false bottom, in the front portion of the cockpit floor may work.  We will see.  


    Darren - Please come visit!!!


    Erik



  • 31 Jan 2017 22:17
    Reply # 4578401 on 1424184

    Now I've had a look at version 3, and it's looking better. Maybe you can use a single 3:1 sheet, so long as you have a large selftailer, but I'd still prefer upper and lower sheets, for better control of twist when reefed. It doesn't matter too much, it's relatively easy to try different sheeting options. 

    [remember to take the link URL from your public profile - the planform link is not readable]

    [Raven is now definitely a schooner, not a schetch or a ketch. Can we call the after sail the mainsail and the forward sail the foresail, in line with this?] 

       " ...there is nothing - absolutely nothing - half so much worth doing as simply messing about in junk-rigged boats" 
                                                               - the Chinese Water Rat

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