Through Hull

Discussion in 'Metal Boat Building' started by Jaro, Nov 23, 2024.

  1. Jaro
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    Jaro Junior Member

    On the boat I have bought, the toilet hull through is just a pipe (visible from outside) welded to hull and inside there is no seacock. My boat has shallow draft so its easy to get above the submerged line, so I am thinking of cutting this pipe out and welding a bigger 6/4" pipe in there to be sure its healthy and place the ball valve above line of submersion, so its not in actuall direct contact with water and can be changed when on water. There is a similar thing on the kitchen sink, where the pipe goes above the waterline and the ball valve is dry. I think there is nothing to crack this way. Do you have ideas about that?
     
  2. Dave G 9N
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    Dave G 9N Senior Member

  3. Jaro
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    Jaro Junior Member

    Dave, the hose from the toilet goes into a big blob of silicone, so that tells me, there was a problem, from outside its welded pipe, but its likelly not too long inside. I would cut it out and weld in one reaching above the waterline. I would not use piece of plastic on steelboat, does not really inspire confidence. I want to go to my boat over the christmass and cut all the silicone out to see whats the solution underneath, but likelly I would have to remove whatever its there.
     
  4. fallguy
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    fallguy Boat Builder

    I am not sure the rules in steel vessels, but drains on fiberglass boats are not supposed to be hard plumbed thru the hull. That means there needs to be some flex. So, these fittings go through sealants.

    I assume this is required so the plumbing cannot result in harming the hull? if damaged, but again, I don’t know all the rules for steel. For my boat, a hard jarring off a wave with a perpendicular drain might result in movement and mechanical fatigue…so flexible sealants prevent such

    I am at a Christmas party and don’t feel like finding the citation, but perhaps a wiser contributor can comment.
     
  5. Jaro
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    Jaro Junior Member

  6. montero
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    montero Senior Member

    Very good idea . Considering that it is important point , I will do tig welding and do some ribs around abutment to reinforce connection just in case. I saw similar solutions and long leverage of the long pipe without any supports awekened my doubts. It will be very rare scenario that somebody/something will hit upper part of pipe but you never know.
     
  7. fallguy
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    fallguy Boat Builder

    I think the bigger concern is metal fatigue. If every wave moves a perpendicular pipe thru the hull, the pipe may end up holing the hull. But there are some experts here with full wisdom on this subject, so give them time to reply.

    The longer the fixed pipe, theoretically, the more torque that can be applied to it…and so each wave moves your longer pipe more..
     
  8. Dave G 9N
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    Dave G 9N Senior Member

    Fallguy had a point about the regulations for composite hulls. A seacock manufacturer mentioned AYBC H27 SEACOCKS, THRU-HULL FITTINGS, AND DRAIN PLUGS so I looked it up. It says that it applies to all boats. There was no distinction between materials except that a wooden boat may use a wooden plug to drain bilge water. The rationale may be that a welded joint can crack in a way that will propagate into the hull and a crack in a fitting will not. AYBC ISO 9093-2 "specifies requirements for the manufacture and installation of non-metallic through-hull fittings and/or assemblies comprising through-hull fittings, seacocks, hose fittings and/or drain plugs and components attached thereto, used in small craft of up to 24 m length of hull."

    AYBC H27 6.1.1 says that the installation shall prevent any movement of the assembly. Sealants fill scratches and other asperities as well as preventing water from entering the joint area. They are not thick enough to tolerate any motion. A gob of sealant is a sign of either poor workmanship during installation or a temporary measure to reduce leakage around a failing through hull. Silicone is also an invitation to paint failure. Stick (ha ha) with polyurethane or epoxy. I don't know enough about that brand to endorse that fitting, they just have a readable set of installation instructions and a decent picture. No amount of extremely low modulus sealant will share any load with the solid materials. The elastic modulus of a glass filled plastic part would be around 7000 MPa, C95400 Ni Al bronze 107000 MPa and silicone rubber less than 2 MPa. No amount of rubbery sealant can share enough load to prevent fatigue.

    It looks like the joint is designed to fail in the pipe fitting without damaging the hull. It appears to me that the intent is to build enough flexibility into the piping to avoid stressing the fitting. A welded pipe needs to be supported mechanically to prevent it from stressing the joint through vibration or impact loading. Vibration might be the larger problem. AYBC H27 does not seem to allow welded pipes in any case. Paragraph "27.6.1.2 The seacocks shall be connected directly." Not directly to something in particular? It seems that the sentence should end with 'to the...'. Figure 1 shows it attached to the hull, so it appears that the seacock is required to be mounted to the hull, not the end of a pipe, but a few words clarifying the point would help.
    This Seacock & Thru-Hull Primer - Marine How To https://marinehowto.com/seacock-thru-hull-primer/ shows one type as the preferred design. The non preferred design as illustrated seems to come with a load bearing collar from some manufacturers. The collar distributes the load much as the flange does.
     
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  9. montero
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    montero Senior Member

    With respect to AYBC H27 , seacock at the bottom seems to be have more point of failure e.g. external plastic grid , external seal, internal seal , nut , thread and
    seacock himself. To eliminate risks of failure , welding standpipe is way to go . Most of them is freestanding , beacause joint strenght and pipe thickness is sufficient.My only doubts are if something really heavy hit the pipe , more movie scenario.
     
  10. Jaro
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    Jaro Junior Member

    Guys, there are already two other hull throughs, one in kitchen and other for sink, which are done this way. My plate is 4 mm. If I weld in 5 mm pipe in and out, its has to be better than anything its there now. I actually think that there is a pipe welded, as seen from outside, its just too short and I dont trust hoses.
     
  11. Jaro
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    Jaro Junior Member

    The longer the fixed pipe, theoretically, the more torque that can be applied to it…and so each wave moves your longer pipe more.. How? Any wave is subject to difraction. It needs to be correct size to do anything in a hole that is 4/6" big. The lenght of the tube itself is inconsequentual, it just needs to go above the waterline.
     
  12. Jaro
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    Jaro Junior Member

    Montero, anything hiting the pipe heavy enough to make correct weld fail, inside the boat in the toilet, is probably an extint piece of megafauna and has power to break through the hull anyway :D
     
  13. Jaro
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    Jaro Junior Member

    When I say 5 mm pipe, I mean thickness of the wall. And I am qualified and have very good machine to work with.
     
  14. fallguy
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    fallguy Boat Builder

    I am referring to a comparison between a longer and shorter pipe welded into the hull. Apply a side force to either pipe and it will be instantly clear which pipe can damage hull easier. The longer. The motion of a ship at sea can apply the same side force which Dave’s comments and citations highlight. Also, any rust or corrosion is greater in certain metals and a more corrosion resistant thru hull would also be safer.

    I’m pretty sure what you want to do does not meet the rules, but if you secure the top of the pipe well enough against shock or a bump or any side force; it might pass.

    Please don’t enter the forum asking for a blessing and then get upset when you don’t get one. Consider a poor weld or someone bumping the pipe far out at sea. Forum contributors have to consider the rules.

    Another question is whether or not you have any vented loops in the intake system.
     

  15. Jaro
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    Jaro Junior Member

    The pipe is inside of the hull. What is the agent of that force? Motion of a sea something that would be a momentum of roughly 2 pound pipe 1 meter long, professionally welded? :D I am not upset, I actually have technical education. I can calculate that moment if I want to. You have presented an argument that is nonsensical. I m merelly asking for what is common. Any hose is more likelly to fail that welded pipe.
     
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