Cutting through a steel hull for water in and outlets

Discussion in 'Metal Boat Building' started by AWegener, Jul 1, 2007.

  1. SamSam
    Joined: Feb 2005
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    SamSam Senior Member

    I've used the drill bit and file approximately 1 million times. It works. Aside from the usually sloppy hole with an arc welder, all the nubs that need to be filed end up hardened and wreck the file in about three strokes. Sam
  2. alaskatrawler

    alaskatrawler Previous Member

    Hey Frosty

    Lots of amps and good penetration both sides.... it is better than a gappy hole that you would get with the drill bit method. I trust mine more than yours. Have a nice day.

  3. Frosty

    Frosty Previous Member

    I think we are all getting a bit confused with what I said. I have made no such comment that I just drill a hole out and stick a pipe in it.

    If you re-read you will see that I made special concern over the filing of the hole so as to make an appropriate gap required for a proper weld.

    2/3 mm gap around the pipe will give a proper penetrated weld.

    Welding upside down need needs proper ampage and a proper prepared job. Just turning up the ampage to blast away would end up in most of it down your shirt. This will leave big blogs of weld that apparantly cant be filed off with cheap files.
  4. larper
    Joined: Mar 2006
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    larper Junior Member


    Frostys way is my way besides for holes bigger than ~2" i wouldnt use a file. Better of with angle grinder with a very worn/small cutting disk. Lay the grinder down against the plate with the disk flat in the hole. grind to a perfect fit.

    For very nice round holes start with a smalish disk and save another disk just slightly smaller than the finished hole to adjust with a light touch.

    -- Per
  5. MikeJohns
    Joined: Aug 2004
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    MikeJohns Senior Member

    Hey Frosty

    These days with steel hulls it is very common to use a threaded pipe and a Marelon or similar sea-cocks, these are usually threaded , the flange is principally for the bronze seacock and then you have to isolate everything, even at the best of times removal can be a pain . The good Marelon ones can be dismantled and removed almost fully while leaving the flange screwed on, and the ball and body are then easily cleaned and greased so it depends on access and also on protection of the fitting from fire.

    A well built sea-chest or stand pipe well bracketed to the plating and preferably a bulkhead too makes a reliable central control point some of them have a narrow stem and another big seacock between the standpipe and the plating.

    Schedule 40 pipe should do for most of this work and on smaller pipes fillet welds inside and a cover weld outside should do the trick without 100% penetration.
  6. alaskatrawler

    alaskatrawler Previous Member

    When I weld a standpipe into a hull, I drill a hole the size of the OD of the pipe. I set the pipe thru the hole leavig about 3/4 " stick through on the outside of the hull. This is only done on underwater thru hulls. A fillet weld around the pipe (usually with stick electrode) on the inside of the hull and one on the outside makes for a very strong install. I have never heard of a failure using this method.
    If drilling the hole out with drill bits works then go for it. I guess with me it would be a more time consuming method especially drilling thru 1/4" plate like I usually work with. The next time I have to drill into the hull I will try this method to see how well it works.

    1 person likes this.
  7. charmc
    Joined: Jan 2007
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    charmc Senior Member


    Welcome to the forum! In reading the small bit of controversy, "Wachewmeen, urwayisbedderdenmine? Udonnowachewtawkinabowt!", otherwise known as friendly discussion, you need to realize 2 things:

    1. Like many procedures, it's clear that there are multiple ways to accomplish the tasks. Everyone with any experience cutting holes in steel and welding fittings has his preferred methods The ones you use should reflect your skill level and the tools you have at hand.

    2. The controversy is all your fault! You included that one word guaranteed to start a fire anywhere, "best". Like asking what's the best breed of draft horse, or what's the best published design for a 40' seagoing sailing cruiser.

    In the shop I ran, for rebuilding industrial equipment, the oxy torch was the preferred method, finished with a grinder to bevel the edges. Plasma cutter prices were just starting to come down from stratospheric to merely very costly, so we didn't have one. Today a small one can be had for around $350. USD, probably a good buy if you're cutting steel regularly. But I've seen and used every method mentioned; they all work.

    Max, I agree somewhat with Frosty: for a through hull, I'd want a bevelled gap to help get full penetration from both sides.

    Be careful of the joys of sloppiness, though, Frosty. I'd want a snug fit with the bevelling aiding the weld penetration for best overall strength. One shouldn't have to be rebuilding steel plate with weld rod.
  8. Frosty

    Frosty Previous Member

    Ey well as Max would say its a mooch beeter wey that ye ken anyer own way.
  9. SkipperSki
    Joined: Sep 2007
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    SkipperSki Junior Member

    Well Gents, I've read your reply's and I have to agree with Frosty. Any Shipyard welder worth his salt, knows any pipe welded through steel plate thicker than 3/16" will require weld prep around the hole. The thicker the plate would determine either single vee, (1/4"thick) and double vee for thicker plate.
    Now as for drills, and drill over 1/2" is going to require a magnetic base drill motor. For 1/2" thru 1", any hole larger can use a hole saws for at the most 1/2" plate. Any thicker hull plate, would require a cutting torch, or carbon arc/air using a 400 amp. or more welding rig, or plasma arc. Hole saw sets come in the following sizes, 7/8", 1 1/8", 1 3/8", 1 3/4", 2",
    2 1/2", 3", 3 5/8", 4 1/8", 4 3/4" which are bimetal high speed blades, and should use cutting oil.
    Now a welder would sharpen his soapstone, and scribe around the pipe, marking the hole on the hull, and torch cut it smooth with hardly any slag on the other side, and his helper/firewatch would chip it clean.

    The problem with hole saws, are pipe sizes either Schedule 40 or 80 pipe have the same O.D. in each Nominal pipe size as follows;

    pipe in inches. / O.D. in "

    1/2, /___________.840
    3/4, /___________1.050
    1, /____________1.315
    1 1/4, /__________1.660
    1 1/2, /_________1.900
    2, /_____________2.375
    2 1/2, /_________2.875
    3, /_____________3.500
    3 1/2, /_________4.000
    4, /_____________4.500

    Now you can see a hole saw will cut a large hole, than the pipe size you are cutting it for. Any Welder worth his salt can handle that though, Right?
    In most cases in all positions, he would use a fast freeze filler rod, like Fleetweld 5-P, unless the plate was Cor-Ten and then he would use a Low Hydrogen rod, 7018, or 12018, after preheating the plate. Each weld being chipped and wire brushed, before the next pass. And a Welder worth his salt would make it look as though a machine made the welds. And it would be X-ray quality welds for sure.

    Been there done that!
    Last edited: Sep 8, 2007
  10. murdomack
    Joined: Jun 2007
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    murdomack New Member

    This was a well known, if hated, technique in the Oil Industry when access was required into pipes that could still contain residues of highly flameable condensate and was done using an air powered drill. We called it chain drilling. Once the hole was cut, vented dams were installed either side and hot work could be allowed. Nowadays there are portable milling tools that have been developed that make life a lot easier.
    Finishing of the hole could be done by filing, but a pencil grinder with a tungsten carbide cutting tip was much faster. The problem with these is that you have to cover up well as the slivers of metal get everywhere.
    Although I agree with your statement, I would use the drilling method as a last resort.

  11. bananabender
    Joined: Apr 2006
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    bananabender Junior Member

    Holes in steel

    Assuming availability, for holes up to about 40mm there is nothing to beat a magnetic drill and broach, especially for drilling from the outside. Work at any angle, even upside down once the magnet is powered up and the drills used are slow-revving and precise. Any decent tool hire shop should have them although if I was into serious steel building I'd have one in the cupboard. The brand available in Aus. is a "Slugger", costs around A$1500-2000, haven't seen a cheap Chinese one yet.
  12. AdamFrench
    Joined: May 2007
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    AdamFrench New Member


    How about 316 ball valves on the threaded pipe? Close enough to avoid galvanic problems?


  13. Frosty

    Frosty Previous Member

    The point is drilling one hole can not justify the relatively expensive cutting tool for one hole.
    I can cut a hole in the hull before I could wash my hands and get to the shop.

    If I was cutting holes all day long then of course one would buy some serious equipment like the affluent oil companies can.
  14. MikeJohns
    Joined: Aug 2004
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    MikeJohns Senior Member


    No, you have the potential for problems .

    Marelon or similar plastic seacocks are better on the threaded pipe. They are just about indestructable and are fine for vessels in survey in most countries. They are completely inert and cause no galvanic action.

  15. TollyWally
    Joined: Mar 2005
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    TollyWally Senior Member

    "The point is drilling one hole can not justify the relatively expensive cutting tool for one hole.
    I can cut a hole in the hull before I could wash my hands and get to the shop."

    Of course everyone's situation and attitude is different. Me, I don't mind paying for quality tools. Time is money and hassles can make life distasteful. I figure that I'm not paying money for drilling equipment, what I am doing is buying holes. I'll always have to drill another hole sometime, that one will be free. Now that I have a plasma cutter, well what can I say? It's pretty nice.

    Now there are a million ways to go about something, often there is no real "right" way, it's the results that count. So to the original poster, scope out the various techniques, make a choice that fits your situation and pay your money and take your chances. Next time will be easier and better. My .02
    Last edited: Dec 22, 2007
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