Solid RIB tubes

Discussion in 'Boat Design' started by Darbio, Jan 8, 2019.

  1. Darbio
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    Darbio Junior Member

  2. Squidly-Diddly
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    Squidly-Diddly Senior Member

    Make you own honeycomb of jumbo noodles with pvc inserts, then cover that with fabric. If you leave the back end open it will be like one of those fancy rescue RIBs with hull that takes on water ballast at rest, then ejects it as it gets up to planning.
    Being foam, along with multiple attachment points of layers of pvc, should create an very redundant structure. A honeycomb could have a unique angular look, and maybe a flat-top which might be more handy for setting things on than rounded air-tube. Maybe add a semi-ridge flat surface to the top along the sides.
     
  3. Darbio
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    Darbio Junior Member

    That’s an interesting thought! Any pics of the Rescue ribs you talk of? I don’t think I’ve ever seen them..
     
  4. Squidly-Diddly
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    Squidly-Diddly Senior Member

    Avon was the brand. It was a family of their higher end RIBs with deep Vee hulls intended for rough open water use.

    Avon Searider Water Ballast system - RIBnet Forums http://www.rib.net/forum/f45/avon-searider-water-ballast-system-23565.html Note that in reply #7 someone says "yours has been closed off" after pics of transom are posted. But my understanding was the openings were pretty big to allow almost immediately going from planning to ballast then back to planning.

    I guess having water ballast on both sides would be more effective, per weight of water. I guess you also wouldn't need water proof covering for the noodles, although you'd want "solid" covering on the part that normally sits in water to reduce drag. Wrap the noodles in something like this stuff. Suntuf 26 in. x 12 ft. Polycarbonate Roofing Panel in Clear-101699 - The Home Depot https://www.homedepot.com/p/Suntuf-26-in-x-12-ft-Polycarbonate-Roofing-Panel-in-Clear-101699/100049922?mtc=Shopping-B-F_D22-G-D22-22_10_ROOFING-Generic-NA-Feed-LIA-NA-NA-&cm_mmc=Shopping-B-F_D22-G-D22-22_10_ROOFING-Generic-NA-Feed-LIA-NA-NA--71700000044086327-58700004607994977-92700044043517424&gclid=Cj0KCQiAvJXxBRCeARIsAMSkApqmPTvbS3OWYogfVd6wYE2kNW6GnnOU9VDlML8g0m4PWVfPbdmaCAkaAipWEALw_wcB&gclsrc=aw.ds
    Install it "flashed" (as in water goes downhill in roofing) starting front the back and working forward.
     
  5. Darbio
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    Darbio Junior Member

    Thanks for the ideas. I’ll have a think.

    I was thinking about using 50cm diameter poly pipe but I can only find stuff that is 12mm thick. At that size it’ll be too heavy (about 230kg - 200kg heavier than the set of tubes currently on the boat).

    How do I calculate what my outboard could successfully push through the water?
     
  6. Mr Efficiency
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    Mr Efficiency Senior Member

    What makes you think that can take the curve ?
     
  7. Darbio
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    Darbio Junior Member

    I spoke to an engineer who told me it was pretty bendable. At 12mm I don’t think I could bend it myself but a fabricator should be able to.

    Alas, at 12mm it would be too heavy. At 3mm it may be doable! Just to find some pipe of that diameter with that thickness.

    Do you have any insights?
     
  8. Mr Efficiency
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    Mr Efficiency Senior Member

    You could cut a length of the pipe in half and use the inside as a mould to glass up a tube in two halves, bend the inside half into place on the boat, then bend the outside one to that, join them together via a flange.
     
  9. Rumars
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    Rumars Senior Member

    Darbio, here are some options as I see them:

    1. Stuff flotation foam into the tubes. Depending on how much you are willing to work yourself there are two options:
    a.) Take the tubes off the bottom and pay someone to sew all the seams with a sewing machine or
    b.) Sew by hand with the tubes in place. This is strictly DIY, you will probably not find someone to do it for you.
    This option will last until the PVC desintegrates from sun exposure enough to let go of the thread. At that point you are left with nice patterns and can renew the fabric.

    2. Fabricate hollow or foam filled tubes from fiberglass. You need to calculate their weight to see how much this will eat into the boats carry capacity. Might make a 6 person boat into a 4-5 person one.

    3. If you have an Al bottom you can do welded Al tubes.

    What you don't want to do is use some plastic pipe for the tubes because you don't know how you can glue the pipe to the bottom and make it hold and thin walled plastic pipe is usually not rigid enough anyway.
     
  10. Darbio
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    Darbio Junior Member

    Cheers Rumars - good suggestions!

    the hull is fibreglass so it’s a no go on the aluminium sadly - otherwise that will what I would do.

    getting the tubes sewed is an interesting idea. I wonder if this could be adapted to hold air? See the seams in place and then paint the holes with a sealant of some kind. Maybe, but maybe not!

    Another thing I have been contemplating is making the tubes more angular and fabricating something out of fibreglass, wood and/or HDPE.

    I’ve uploaded a couple of first drafts but need to do the maths on how much each material would weigh and cost.

    As I see it a few options:

    1. wood and fibreglass
    2. Hdpe sheets (what thickness sheeting would be required for the walls?)
    3. Constructed from foam and then coated in fibreglass or some kind of fabric.
     

    Attached Files:

  11. Rumars
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    Rumars Senior Member

    Yes, sewn tubes can hold air. All you have to do is glue a strip of PVC over the threads. Of course the glue is strong enough by itself so no manufacturer uses sewing.
    You could also take the tubes apart, clean the glue residue of the seams and reassemble by welding or new glue.

    The simplest way to fabricate fiberglass tubes is to use XPS. Glue sheets to the desired thickness with epoxy, sand out the desired shape, laminate over with epoxy or xps safe poly resin, fair and paint.
    One thing you have to understand, with fiberglass tubes there is no spring and give, you have to use fenders while docking. If those things are important to you then you have to use foam into flexible covers.

    HDPE is heavy and can not really be glued to the bottom. I would not bother with it at all.
     
  12. Darbio
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    Darbio Junior Member

    Do you think this is achievable for a DIYer? I've put patches on but I'm not sure how you keep everything in line when doing this and stop it from sticking to itself - especially with the cylindrical tubes. I'm sure there is a nack!

    I saw a photo on the henshaws website of this and definitely looks like it would work. Is the idea that you use just foam? No wood etc? Lay fibre glass over the top and then sand the glass down? I suppose this makes it just like any other boat being that you have to take care of the sides. I like this idea as I can fashion lockers into the tubes and make them useful for something - seeing as they take up space.

    Yeah, at 960kg per cubic metre it really is very heavy...
     
  13. Rumars
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    Rumars Senior Member

    Yes, reglueing can be done, but you do need some practice first. I would be more concerned about removing all the previous glue residue.
    Fiberglass is double the weight of HDPE but that is not the most important thing.
    You can not just fashion lockers into the tubes. Not if you want to use XPS and a light layer of glass. If you want lockers you need to design the tubes such as to have the buoyancy and the needed stiffness.
     
  14. Darbio
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    Darbio Junior Member

    How heavy per cubic metre would a fibre glass/foam sandwich be? And what is the most important thing to think about?

    Surely adding weight will cause the boat to handle significantly differently?
     

  15. Rumars
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    Rumars Senior Member

    The important thing us how much material you use and what the finished product weighs. PVC inflatable material has a weight range from 600-1400 g/sqm, normally around 1000 g/sqm. So your goal is to not significantly add to this weight. A cylinder of 50cm diameter 1m long has a volume of 0.2 cubic meter and a surface area (without top and bottom plates) of 1.57 sqm. If you use foam that is 30kg/cum to fill the space the foam alone weighs 6kg. The fiberglass skin ads to that, let's say 400g/sqm total (glass plus resin). So total weight would be 6.6kg plus fairing and paint vs. 1.6kg for the PVC version. Now say that ~7kg per meter is to much so you want hollow tubes made out of sandwich grp. So 400g outside skin + 400g inside skin plus 800g foam (10mm of 80kg/cum) = 1.6kg/sqm or 2.6kg for the sample cylinder. That is only 1 kg over the PVC version vs. 5kg over for the foam filled one.
    The big question is how low can you go on the scantlings and have a safe boat. (Meaning reduce fiberglass weight and/or go for thinner foam core). That would have to be calculated. If you change the shape of the tubes from round to D, incorporate lockers, etc. all has to be calculated. You can go seat of the pants and hope all will be well, but if the thing desintegrates in service you will not have anyone to blame but you.

    What you do is your decision. If the PVC is already sun damaged and worn pour in place urethane foam can extend it's life for s few seasons. If the PVC is actually fine and only the glue let go maybe it is worth a shot at completley reglueing or welding. Sewing and filling with a foam like plastzote or evazote another option as is fabricating rigid tubes. You have to ask yourself what you want and how much it is going to cost you to do it.
     
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