DIY hatches / removable panels in welded aluminum floor

Discussion in 'Metal Boat Building' started by Northeaster, Sep 1, 2016.

  1. Northeaster
    Joined: Sep 2011
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    Northeaster Senior Member

    Hi Folks,

    First, I want to thank all members here who have helped me get to this point.
    I have had my home-built 25 ft aluminum powerboat in the water (yet still very unfinished) for over a month and it is running well now. I may look at adding pitch later but currently get 4.5 kts at idle and 23 kts wide open. Videos (not great ones..) of it running can be seen here:

    https://www.youtube.com/watch?v=MXh7niBBAFo

    note - video was done with bare exhaust, etc - now running proper seawater pump, wet exhaust, etc.

    Now, for today's topic- I am currently running temporary osb/very cheap wood floors, just to get it in the water this summer.

    When the boat comes out for the winter, in a couple of months, I will begin working on numerous unfinished items, likely starting with welded floors. Plans (of this slightly older design, originally in wood) only call for 5/8" plywood floors and self-draining cockpit. It would be hard to keep ply floors watertight, with eventual rot, and I have leftover aluminum sheet, so I will likely cut and weld in sections for the floor, using the temporary floor sections as templates.

    Unless someone advises otherwise, I would think I would fully weld in the side sections only, and then fabricate some type of flange and several large removable panels that would go over key areas of the middle such as the steering ram and rudder post/ stuffing box at stern, prop shaft/stuffing box /gearbox, and one or more up front for storage. I will make an aluminum engine box a well to replace the temporary one pictured.

    My goal is not to have a 100% watertight floor (for preventing sinking) but rather to have a floor that is mostly watertight and will shed most rain water to the side, stern and out the (yet to be cut) scupper holes.

    The available hatches I see available in aluminum are very expensive, so I would like advice on how to build my own hatches / larger removable panels. Some hatches / access ports would be quick access kind, perhaps juts the plastic ones to access thru-hull valve for example.
    But removable larger panels would likely be fastened down with screws, bolts, etc with a rubber type gasket perhaps (rather than caulking...) so they could be removed, with some effort, for maintenance or emergency access.

    A related question would be - should I consider spray foaming the inside of hull, and/or the underside of floor for buoyancy and noise reduction? I really hate to foam over hull seams/welds in case I ever need to repair.

    Here's a few pics of the boat and temporary floors.
    Any further help would be appreciated!
     

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  2. mydauphin
    Joined: Apr 2007
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    mydauphin Senior Member

    I also have an aluminum boat. Learned to weld for it. Not hard to make hatches, mine are almost watertight. Use box tubing, make a outer square and then the inner square becomes your hatch. Use flat bar to make lip around outer square. Would make a diagram but on my phone. 5 minutes of cutting 10 minutes of Welding

    On foam, make sure you this above area that is usually wet from bilge. All foam catches some moisture and will lead to poltice corrosion behind it. So paint aluminium before you foam it in. I also test everything I put on my boat with a blow torch, if it burns, it doesn't go on boat. Some foams burn rather well, others don't. The stuff from home depot in red can doesn't maintain a fire, not to bad. I had some from another brand aND a spark from my welder across the room fell on it, and I hadon't a hard time putting it out. I was within a minute of losing boat, the flames were so bad and toxic I could not get near it. So test your foams, cushions too, trust me you will thank me one day.
     
  3. Ad Hoc
    Joined: Oct 2008
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    Ad Hoc Naval Architect

    Just a simple flange edge and panel on top. If you make the bolt pitch 4D max, it'll be water tight.

    No don't use spray foam as noted above. If you really need foam, buy the right stuff, it'll be worth it in the end.
     
  4. Northeaster
    Joined: Sep 2011
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    Northeaster Senior Member

    Thanks for the replies. Sorry for the imperial measurements..

    I have a 2 inch structural T running down each side of the about, each about 16" from center, so current center span is 32", center to center of Ts.

    I thought, at first, I would weld the side panel(s) in and terminate / weld on top center of these tees, which would leave the other half for a center panel to sit, of it were also welded, or screwed down, with only it's thickness (3/16").
    Now, after your comments , I think it would be best to use angle or flatbar as a lower flange to "catch" a thicker hatch / panel, i.e. 3/16" sheet welded on top of or butting up to edge material, i.e. box tubing frame.

    But, with the existing Ts, which would be hard to hang/ weld a flatbar or angle flange to, give the Ts profile, I am wondering how else to do it...

    Or, if the flange material, say angle, was only welded to the top side edge of the T, not touching or welded anywhere else, would this make a strong enough support for the panel? (Of course, the 4 pieces of angle forming a square or rectangular flange would be welded together at corners where they meet)
    Ig anyone has a diagram or picture I would appreciate it.
    Seen a few on the net - some have hinges, etc.
     
  5. Mr Efficiency
    Joined: Oct 2010
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    Mr Efficiency Senior Member

    Hatches need to be flush, or a total nuisance. Unless you need the ability to store large items, screw in flush ports are good.
     
  6. Ad Hoc
    Joined: Oct 2008
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    Ad Hoc Naval Architect

    This may help, from one of my previous boats:

    Bolted hatch detail.jpg

    Simple - nothing fancy needed.
     
  7. Northeaster
    Joined: Sep 2011
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    Northeaster Senior Member

    Thanks - Yes, that does help.
    I would think I may use a couple of different methods, depending on the frequency of use of the hatch/ access panel.

    For the less used ones I would likely bolt down similar to your drawing.

    For more frequent / daily use ones I would like to employ some type of latch system. Some I see on-line are hinged, but I think that may get in the way for maintenance, etc so I am wondering about extending a small top flange lip on one side, so that the hatch panel would slide in on one side, catching under the upper flange lip, and then use available SS hatch lift / latch handles to secure the other side.

    Please ignore my poor sketch skills and paint program, but I was thinking of something like this.
    Any advice / suggestions for improvement would be appreciated!
    Drawing does not show it, but I would think some type of rubber gasket material would run around the perimeter, and be compressed down while latching.
    I would also add some flatbar stiffeners, under the lid, as it would span approx. 30 inches.
     

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  8. Barry
    Joined: Mar 2002
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    Barry Senior Member

    This will work but it will be hard to have some compression on the left hand side of your hatch on the seal.

    If you make the left side the same as the right side, and if you get the 1/4 turn latches that have an adjustable lower latch arm, and install 4 latches, then when you turn the T handle, the hatch will be pulled tight onto the seal

    One step further is that I would change your lower profile, the green one from an angle into a wider channel. If your tubing is 1 x 1, make the channel 2 inches wide by 1 inch deep ( include an allowance for the gasket/seal) and have the perimeter of the hatch OPENING, ie boat hull part, all joined as one.
    You will get water into the vertical seam between the side of the 1 x 1 and the channel as you will not be able to seal this. So the channel would be then have an opening at the bottom stern side of the perimeter to take it to wherever the bilge pump is or if it is high enough to an overboard or over swim grid scupper.
     
  9. Barry
    Joined: Mar 2002
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    Barry Senior Member

    Aluminum Hatch Profile Option One

    Most of the aluminum boats in the Pacific Northwest use the channel under the lid. Though rather than use a 1 inch tubing as you have indicated in your drawing, they will form the profile edge. The reason is that when you weld your 1 x 1 tubing to the upper plate, the tubing will distort and it will be difficult to have it perfectly flat after. (Coastal Craft, Eaglecraft, etc)
    The channels are scuppered and they use hinges but the reinforcement of the hinges sits up above the height of the floor and are a toe catcher.
     

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  10. Northeaster
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    Northeaster Senior Member

    great info Barry - thanks. Makes a lot of sense to me.
    I did see some pics of edges formed by brake press vs welded and figured I would consider having them bent to shape when the time comes, especially if they are long panels. I have seen figures / calculations before for bend radius and have read that it is essential to find a shop that has experience in bending aluminum and/or will adhere to proper bend radius, including proper dies I believe.

    Still a few months from doing this work and I really just want to have a clear ideas of options and which way I will do it, before starting - for example so I know to allow enough side floor material to weld to the proper stopping point (where it will meet the hatch panel) i.e. terminate and weld at top side edge of Tee vs top middle of Tee which I would do if I were then welding in solid / fixed middle panels, or even drilling and tapping and using half of Tee as flange.
     
  11. mydauphin
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    mydauphin Senior Member

    Tack, hammer, tack, weld, hammer, weld... what was the question?
     
  12. baeckmo
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    baeckmo Hydrodynamics

    Here a couple of pics from my production. One prerequisite (=rules) is that the rubber sealing is confined in a "channel" in the hatch.

    The flush hatch in pic 1 is sealing against a U-profile that creates a channel under the deck surface. The U is drained through the freeboard; in this case a pipe seen in pic 2. Normally I weld the U-channel so that the lower part ends at the skin just below the deck.

    Locking mechanism is an M12 bolt with its head recessed and a clamp with end stops, very simple and effective.

    If you can tolerate a compromise, it is much easier in your case to make the hatch with sloping edges and lying above deck, see pics 5 and 6. The edge meets the deck in locked position, which prevents overcompression of the rubber seal. This variant is actually quite easy on bare toes hitting the edge.....
     

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  13. Northeaster
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    Northeaster Senior Member

    Hi Baeckmo- thanks for the info and pics - a picture is worth a thousand words...
    In your lats example, with the raised hatch, does it just close down on the flat deck or do you have a perimeter of say 1/2" flatbar on it's edge that is positioned vertically where the rubber seal sits?

    This slightly raised approach might work well for me, as the large rectangular hatches will be in the center, and I want to direct water to the sides and then stern, out the scuppers. I had considered a bit of camber, but this should direct water as well.
     
  14. baeckmo
    Joined: Jun 2009
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    baeckmo Hydrodynamics

    Yes, there is a vertical frame (flat bar 50 x 5) around the opening, see sketch below. I also made some hatches with rounded corners, which look better, but at the cost of more welding. The total height of this hatch is ~26 mm above deck Surface.

    The dimensioning to be checked against expected deck loading, of course. Purists may object that the rubber strip is not fully confined where it meets the 45 degree edge, but we never had any problems with this.
     

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  15. Barry
    Joined: Mar 2002
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    Barry Senior Member

    I would try to avoid any raised hatches. Flush is the safest way to go. You do not have to worry about the water pooling as the floor will rarely be horizontal
     
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