S2 6.7 Junk Rig Conversion

  • 03 Dec 2019 08:54
    Reply # 8163493 on 6872873

    Both skins of the deck are clearly structural. It's not the same as having a thick deck, some core, and then a thin headlining inside. So the question is, how to get a strong join to it? For fastening on deck fittings, the usual way is to make a large hole through one skin and the core, fill the cavity with a strong epoxy and filler mix, then drill through that solid plug for a bolt. That would work, to bond and bolt a thick piece of plywood (18mm or 3/4") over the hatch hole. However, I would rather chisel out the core to a depth of 1 1/2" all the way around, bond in hardwood strips in to fill that cavity, then bond and bolt the plywood on top. Having done that, an extra two squares of thick plywood of smaller size, surrounding the tabernacle, will transfer the load satisfactorily, to the larger square.

  • 02 Dec 2019 21:44
    Reply # 8158580 on 8153183
    David T wrote:

    I think we need more information and pictures to be of specific help to you, Scott.


    Hi David,

    Thank you for taking the time to respond. I will attach all the photos I took when I was at the boat. 

    I am not sure what information to provide. The tabernacle will be buried in the deck approximately 890mm. For selecting a mast I came up with a target yield strength of 1753 kpm. I would like to determine what sort of deck structure I need to ensure that the deck will not crush or collapse if and when the mast really sees that 1753 kpm load.

    If I understand all those numbers correctly then I think the deck will need to withstand a force equivalent to 1970 kg applied sideways. I am not sure where to go from there.

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    Last modified: 02 Dec 2019 21:50 | Anonymous member
  • 02 Dec 2019 09:33
    Reply # 8153183 on 6872873

    I think we need more information and pictures to be of specific help to you, Scott. Generally, though, mast partners on a GRP boat can be made by stacking up layers of plywood locally, not all the way out to the deck edge. A plywood deck beam will help stiffen the whole area, if the boat is lightly built.

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  • 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
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