S2 6.7 Junk Rig Conversion

  • 02 Dec 2019 00:23
    Reply # 8149264 on 6872873

    I need some advice on mast partners.

    I do not remember any specific scantlings from PJR. I would appreciate any opinion.

    I removed the hatch on my S2 yesterday. Unfortunately there is rot in some of the balsa. Fortunately it is not in ALL the balsa. I will be sure to repair any damaged core.

    Beyond repair I am not sure what I should do. 

    Including the gelcoat but not the headliner the deck is about 18mm thick. About 12mm is balsa. It is about 2.5mm of polyester and fiberglass on each side and just about 1mm of gelcoat. I attached a photo.

    Is it enough to fill in the hatch area with a similar layup? Or does it need to be double this much all the way out to the hull side in each direction? 

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    Last modified: 02 Dec 2019 00:30 | Anonymous member
  • 22 Nov 2019 16:46
    Reply # 8134944 on 6872873

    Thank you Arne, David and Annie.

    I missed the part about Pete recommending biaxial fiberglass. I already put down one layer of fiberglass (woven tape) and epoxy on the inside of the port and starboard tabernacle pieces.

    I am planning on epoxy and fiberglass then two-part polyurethane paint above the deck. I hope this will give me a structure that will last many years without too much maintenance. The price tag on Interlux Perfection is a little shocking. Does anyone have something else to recommend?

    Below the deck I am tempted to use primer and latex paint to save some money.

    I am fairly confident that the epoxy cured properly before the temperature dropped back down to 33 DegF last night. I may bring it inside the house for a post cure.

    I will need to wait for warmer weather or maybe buy an electric blanket before I get anything else done.

    Last modified: 22 Nov 2019 16:50 | Anonymous member
  • 21 Nov 2019 09:43
    Reply # 8132584 on 6872873
    Anonymous member (Administrator)

    David Tyler’s thinking around using glass sheathing makes sense to me.

    I have used glass sheathing on two wooden masts, mainly to get a good protection against abrasion. The first mast was Malena’s hollow mast (1995). The (West epoxy) glassing was then given seven coats of two-pot polyurethane varnish, over twice the recommended. Still, after around 13 - 14 years, the glassing showed signs of coming apart on the sunny side. Since the owner didn’t take action, water ingress led to rot, and in 2011 the mast was scrapped. To me it looked as if the varnish held, but even on 59°N, it let through enough UV radiation to destroy the epoxy underneath.

    The second wooden mast, the one for Johanna (2002), was given the same glassing, but this time the coating was white, two-pot polyurethane paint. I hope that this will hold better. It looked good when I sold Johanna in 2014.

    The two wooden topmasts of my hybrid masts (2013 and 2016) have only been painted with many coats of polyurethane paint, without any glassing. So far, they look good.

    What I want to try is to use polyurethane varnish as resin when glassing. If the stuff penetrates and saturates the glass nicely, then one can have a very strong and long-lasting surface. Since the glass will be invisible on more than 50cm distance, one could  have a nice clear-varnish finish (as on Malena’s mast), which will last ‘forever’.
    I will try this on a piece of plywood, once the temperatures rise again...

    Arne


    Last modified: 21 Nov 2019 09:43 | Anonymous member (Administrator)
  • 21 Nov 2019 08:47
    Reply # 8132574 on 8132472
    Annie wrote:

    To be honest, my own opinion is that if the wood structure is strong enough, all it needs over it is some light glass cloth to provide a hard and thick surface of epoxy.  However, David told me to put bi-axial cloth on the skegs (and rudders and bilgeboards) and Pete said to put it on the tabernacle.  They are the experts, so I did as I was told, but I don't understand how or why this fibreglass adds any real strength to such large pieces of wood.  I don't like using bi-axial cloth because I find it difficult completely to wet out, without there being at least some bubbles left in the matrix.

    I hope that someone with more technical expertise will chip in and enlighten us both!

    Which David said that? Fanshi's skegs and rudders would be mega stiff, without any sheathing. I will certainly have advocated thick glass sheathing on underwater surfaces, to provide maximum impact protection against the possibility of bouncing the hull and control surfaces on sharp rocks etc. Biaxial glass is quite thick, and would build up the laminate quickly and smoothly, but its fibre orientation properties are not required. Woven rovings would be just as good. (But having said that, it's much easier to persuade glass cloth to conform to sharp bends such as the leading edge of a skeg, if the fibres are at +/- 45˚).

    I would put unidirectional glass on the bilgeboards, vertically oriented, as they are designed to be relatively lightly constructed for ease of operation, and more stiffness will be a good thing. For tabernacles, I would have thought that heavy glass would be for peace of mind as much as any technical reason. For thick decks, I would put on more than a thin glass sheath, but only to protect against dropped tools and the like. For thin decks, that thicker layer of glass becomes structural as well.

    I have seen a demonstration of how 6mm plywood is made twice as strong by coating it with epoxy on both sides (at Hobart Wooden Boat Festival). Thin glass would have added more strength, but I haven't seen that demonstrated. It's a question of the relative thickness of the glass and the wood, I think. A thick piece of strong wood , as in a tabernacle, would not be further strengthened by adding epoxy and thin glass, but a thin hull of cedar strip planks absolutely depends on layers of glass on both sides, for both point impact resistance, and also overall stiffness and strength.

    Last modified: 21 Nov 2019 09:34 | Anonymous member
  • 21 Nov 2019 06:59
    Reply # 8132472 on 8127143
    Does anyone have a suggestion on when I should use fiberglass? I was planning to just use thickened epoxy to join the sides to the center section. Then I noticed that Annie put glass on the top of the side sections and also on the lower part of the middle section. It appears she let it cure before doing the final assembly.

    I do not completely understand how fiberglass and wood composites work to make stronger materials. I suspect that there should be almost zero gap between the wood pieces for it to be effective. Should I use both glass and thickened epoxy? I wonder if that will make a weaker joint compared to glass alone.


    Well, Scott, that makes two of us.  To be honest, my own opinion is that if the wood structure is strong enough, all it needs over it is some light glass cloth to provide a hard and thick surface of epoxy.  However, David told me to put bi-axial cloth on the skegs (and rudders and bilgeboards) and Pete said to put it on the tabernacle.  They are the experts, so I did as I was told, but I don't understand how or why this fibreglass adds any real strength to such large pieces of wood.  I don't like using bi-axial cloth because I find it difficult completely to wet out, without there being at least some bubbles left in the matrix.

    However, what I do know is that it is the thickened epoxy that makes the joints strong.  The glass, conceivably stiffens up the wood, which will reduce flexing, which will mean there is less stress on a filleted joint.  In theory, the glass is 100% bonded to the wood so filleting to it should work fine.  I've done this lots of times because it's often easier to glass the wood before fabricating whatever it is that you are making, than doing it after.

    I hope that someone with more technical expertise will chip in and enlighten us both!

  • 18 Nov 2019 13:46
    Reply # 8127143 on 6872873

    In case anyone is interested -- I am trying to keep my rig conversion moving along. There was some unusually cold weather here last week and I was not able to do any epoxy work. The photo attached is from two weeks ago when the temperature, according to my cooking thermometer, was just above 40 Deg F. Epoxy seemed to cure without any issues overnight using the West System fast hardener.

    Yesterday I went out in the snow and did some sanding and grinding with the angle grinder. I think I now have the closest thing to a 'good fit' between the sides and center that my skills will allow.

    I am trying to follow the JRA article and the work documented on Voyaging with Annie Hill.

    Does anyone have a suggestion on when I should use fiberglass? I was planning to just use thickened epoxy to join the sides to the center section. Then I noticed that Annie put glass on the top of the side sections and also on the lower part of the middle section. It appears she let it cure before doing the final assembly.

    I do not completely understand how fiberglass and wood composites work to make stronger materials. I suspect that there should be almost zero gap between the wood pieces for it to be effective. Should I use both glass and thickened epoxy? I wonder if that will make a weaker joint compared to glass alone.

    I am seeing some highs up above 40 in the forecast this week. I hope to keep everything inside and warm (~66 Deg F) and then move it outside to mix the epoxy, clamp it and screw it together.

    Just to be clear -- the photo showing professional quality wood work done in a proper boat shed is from Annie's blog. The photo with misaligned pieces featuring a cooler in the background is mine. I hope it is OK I borrowed your photo here, Annie. Please let me know if you want me to take it down.

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    Last modified: 18 Nov 2019 21:00 | Anonymous member
  • 20 Oct 2019 19:11
    Reply # 8067399 on 6872873

    I decided clamps are necessary. I think I got it to bend without doing any damage. I hope to get it glued together before it is too cold for the fast epoxy!


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    Last modified: 22 Oct 2019 15:50 | Anonymous member
  • 19 Oct 2019 23:49
    Reply # 8066477 on 6872873

    Thanks for the replies. I plan to use tapered pole. The boat came with a gin pole setup that makes it relatively easy to raise the original mast. I hope to re-purpose it for raising the freestanding mast.

    I decided that I would somehow find a 7" pole and then started building a Tabernacle. I learned the hard way that west system slow hardener must be used at 60 deg F or higher. I thought 50 deg F was the minimum. I was wrong!

    I used 2x dimensional lumber which is actually 1.5 inches thick. The article in JRA magazine issue 61 article recommends 2" lumber. I hope 1.5" actual is close enough for my small boat. If anyone thinks this is too lightly built please let me know.

    I am stuck now because I can't think of a way to make the sides of the tablernacle bend for the taper. Do I need to buy something like 10 big clamps to make it bend? I attached a photo.

    Any advice is appreciated as always!


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    Last modified: 20 Oct 2019 00:43 | Anonymous member
  • 26 Sep 2019 03:50
    Reply # 7901363 on 6872873

    Wouldn't the 8" tapered pole you were looking at before, cut down to 24', be better than one of the four straight tubes you are looking at now?

    I am staying away from the mathematics, but just a direct comparison between that and the 7" straight pole (no. 3 on your list that Dave refers to) it would come out slightly lighter, and with a lower c. of g.  The wall thickness is slightly less, but the outside diameter at the base is greater. And its tapered.

    Its actually not that hard to make a mast from two parts. But if you can get a tapered pole which is a little longer than you need, and at a good price - well, I wish I could be that lucky.

    The tabernacle will be an inch wider, but if that is a problem then you can make an aluminium tabernacle (from folded sheet aluminium) which may help.

    With a proper tabernacle I think raising and lowering the mast is still a practical proposition even if the weight ends up around 35 kg. If it is too heavy for you to walk up into position (it possibly would be for me, these days) there are still ways, with or without a strut (sometimes called a gin pole), to apply a little bit of mechanical advantage and get the job done. Here are some examples of raising the mast on a 22' boat, using various forms of mechanical advantage (trailer winch, block and tackle - not shown here but a small electric anchor capstan will also do the job) - and using - and not using a gin pole. 

    https://www.youtube.com/watch?v=Ve8lzTy-7JQ   no gin pole

    https://www.youtube.com/watch?v=C5WdqdlB8Nc  no gin pole

    https://www.youtube.com/watch?v=w0Sc1e3MXyA  gin pole

    https://www.youtube.com/watch?v=l81rwc6-8SM  gin pole part 2

    Not one of these guys has a proper tabernacle. A proper tabernacle is an advantage.

    The junk rig is at a distinct disadvantage here, because of the mast position being a lot closer to the stem head where a turning block would be. If that turns out to be a problem you just have to figure out a  way around it - in one of the examples above, the person pulled from the trailer winch instead of the stem head. There's always a way.

    I think that whatever mast section you choose, provided you decide it is going to be strong enough, you can just stop worrying too much about other issues and push on, confident that you will find your own solutions to the other problems as they arise (and they will arise.)


  • 25 Sep 2019 23:32
    Reply # 7901138 on 6872873

    Hi Scott,

    my suggestion would be not to compromise on the strength. This eliminates the first and last option. The wall thickness is not too important, this requirement is more related to the ease of damaging the section and as long as it is more than about 3.5 mm thick then this should not be a problem. I would go with the third item on the list as the weight is closer to your aim than the second.

    All the best with the project.

    David.

       " ...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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