Help with Keel

Discussion in 'Metal Boat Building' started by SeaJay, Jun 2, 2010.

  1. SeaJay
    Joined: Jun 2007
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    SeaJay Senior Member

    I could use some advice on the keel for my 46' motorsailer currently under construction. The keel is a lead filled steel form. The steel form consists of a 1/2" thick x 6 ft long foil (NACA 00) shaped plate at the top, and a smaller (4.5 ft) but similar shaped plate at the bottom. Top and bottom plate are connected by a 2.5" round steel bar at the leading edge, angled aft at 15deg., a 1/2" bar at the vertical aft end, and a section of 8" heavy wall pipe more or less centered fore and aft. The top and bottom plates and these elements, form a frame. A 4.5' x 6' x 5/32" sheet of steel is then welded to each side of the frame, and lead is poured inside through holes in the top plate.

    I have very little experience working with steel and was planning to take this project to an outside shop. I can have the foils and side plates CNC cut but I can't find anyone who is comfortable with bending the plates. I don't think the one guy who did say he would "try" it has any idea of the concept of "fair". So my question to you guys. How would you go about bending these 5/32" sheets so that they wrapped closely around the top and bottom foil shaped plates?
    Regards,

    Sea Jay
     
  2. TeddyDiver
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    TeddyDiver Gollywobbler

    Don't have a clue about the question of bending, but why not just a simple plug -> mould -> cast without a steel shell??
     
  3. Stumble
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    Stumble Senior Member

    Particularly since you are already comfortable having an outside shop do the work I would get in touch with Mars http://www.marskeel.com/ and have them do the layup. There doesn't seem to be much reason to spec to a keel manufacturer how do make keels to me.

    On a second note, I am not sure I understand the desirability of having a steel shell around the poured lead, it seems to add complexity, galvanic potential, and add nothing to the final product.
     
    Last edited: Jun 6, 2010
  4. gonzo
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    gonzo Senior Member

    If they can't bend the steel for the keel fairly, what kind of job are they doing with the rest of the hull and deck? I also see no reason to make a steel box and pour lead into it. Either have a box keel integrated with the hull or a lead keel which won't rust.
     
  5. tazmann
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    tazmann Senior Member

    Lots of reasons to go with steel casting lead filled , strength and impact resistant to name a couple.
    Seajay
    Sense your wraping the side plates around and upper and lower profile you may be able to do it without rolling the plates. Starting from the aft end tack it together, then on the front end use a few all threads, blow holes through the side plates for the allthread and use the nuts on both sides to start pulling it in to the profile . start tacking from the aft end working forward as it's pulled in to the profile. It's going to take a lot of pressure pulling in the 5/32" so use large diameter allthread like 3/4 or 1"
    Here is simular situation witout using a top plate and with 3/16" sides
    Tom
     

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  6. SeaJay
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    SeaJay Senior Member

    Thanks for the input guys! Here's some repsponses to your comments...

    Gonzo - The completed hull is composite so this is the only steel work of this sort on the project. I'm with you on the rust but the steel builders on this site will tell you that modern epoxy coatings go a long way towards minimizing the maintence issues. I figure I'm going to have to keep up the bottom paint anyway so it shouldn't be that much more work to see that steel protection is kept up as well.

    Teddy - I'm not sure if the terms "simple plug mold" aren't an oxymoron in this context. Strangely enough I have quite a bit of experience pouring lead but not an 8,000lb casting. I think that type of work is best left to Mars. The advantage of the steel shell is that the lead can be added a little at a time. Sometimes ingots are place in the keel and molten lead dripped over them to "weld" the mass together. This has the advantage of less heat distortion of the plate steel. Elsewhere in the forums are a number of other threads that discuss this method.

    Stumble,

    I did contact Mars and they were very helpful, but their ballpark estimate of $3/lb of finished keel ($24k) + shipping ($5k?) did make me look at less expensive alternatives. Yes, galvanic corrosion does need to be considered but it is not that big of an issue. And although where boat building is concerned, nothing can be considered simple, there isn't actually a lot of complexity in this method, especially for the amature, one-off builder. Lastly, after speaking with Mars, I happened upon a good deal on scrap lead ($.50/lb), and am now the proud owner of 8,000 lbs (eight 55 gal. drums) of the stuff. So I'm into the keel for $4k at this point which leaves me about $25k to have the steel water jet cut, the form welded up and the lead poured before I end up on the wrong end of the buy/build equation. (Believe me, ending up on the right side of that equation doesn't happen very often!)

    Tazman,

    Thanks a million for the suggestion and photo. This is what I was looking for. Expanding on your idea, I think I could cut the 5/16" a little long at the forward end, so that the plates could be pulled up tight against the leading edge. The plates terminate at a fairly shallow angle tangent to the 2-1/2" round leading edge, so they don't have to form a very tight radius. Maybe use bolts at 6" oc with 4" wide strip of heavier backing plate at the leading edge to keep the 5/16" from deforming around the bolts as the side plates are drawn together. Also, I bet that if I placed a 4x6 on the outside of the two side plates, extending above and below the top and bottom flanges, with a heavy all-thread between them, top and bottom, I could clamp the sides tight, tack the sides to the flange and then move the clamp forward for the next tack. Thanks for firing up the old brain cells!

    Best Regards to All,

    SeaJay
     
  7. TeddyDiver
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    TeddyDiver Gollywobbler

  8. SeaJay
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    SeaJay Senior Member

    Teddy,

    Thanks for the link. I am familar with the Rutu site. He has done a nice job and there are a lot of good building ideas on his site. One thing I find interesting is the cost of lead. It is hard to say when he purchase his lead at $0.125 / pound (site last updated 2004), but when I bought my lead last summer, scrap prices were up to $1.00 / pound.

    (I really appreciate it when builders take the time to share their work on line. I just don't have the time to build and maintain a website and build this boat, but I will certainly share my experience (limited as it is) to anyone who wants to drop me a note.)

    Here is a link to another guy who poured his own keel...it didn't turn out so well. http://www.riparia.org/ketch/keelpouring.html

    All in all, this looks like more work than I want to undertake. One more advantage (at least in my mind) to the method I'm following is that the keel bolts are not embedded in the lead. The are a lot shorter and relatively easy to inspect and replace.

    Regards,

    SeaJay
     
  9. gonzo
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    gonzo Senior Member

    The impact resistance of lead is very high. It usually deforms which can be fixed by pounding with a hammer. It also, unlike steel, absobs a lot of the energy of an impact.
     
  10. tazmann
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    tazmann Senior Member

    Seajay
    I'm not the best at explaining with the keyboard, Was hoping the picture would help. Several ways you could go about it there, should work out ok without rolling. There will be a lot of pressure on the clamps so make sure they cant slip off and take your head off in the proccess.
    I live in Yettem, about 50 miles south of Fresno, Next time I get up your way I'll give you a haller.
    Tom
     
  11. Brent Swain
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    Brent Swain Member

    Tom got it right. There is no need to roll 5/32 plate. I've pulled it into shape with C clamps and 3/4 inch pipe clamps, using 1/4 plate, for decades.
    Sealing lead inside a steel boat rather than outside , exposed, minimises corrosion.
     
  12. SeaJay
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    SeaJay Senior Member

    Thanks Brent. I was hoping you would weigh in.
     
  13. SeaJay
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    SeaJay Senior Member

    Gentleman,

    I've had the top and bottom foil shapes water jet cut and am ready to start assembling the frame of my keel (see 1st post). I upgraded the top and bottom plates to 3/4" so there is a bit more "meat" to weld the side plates to.

    My questions this evening have to do with protecting the steel during the period of time I'll be pouring lead inside. I'm thinking that I don't want to apply an epoxy finish until all the lead is inside and the entire structure is welded up tight. I'm planning to work on this intermittently throughout the winter and while the work won't actually be outside, it will be subject to dampness. How should I approach this so that I have the minimum amount of work to do when it comes time to applying the actual finish materials?

    Sorry for sounding clueless, but I pretty much know zip when it comes to working with steel.

    Regards,

    SeaJay
     
  14. rugludallur
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    rugludallur Rugludallur

    The molten lead will burn or at least scald any paint, you don't really need to protect the steel at all until after you pour in the lead.
    Any splashes of lead or smaller specs can be pealed off easily since they don't bond to the steel that well.
    You need to make absolutely sure that no moisture can get in between the lead and steel since this will cause a giant galvanic cell and corrode away.
    Once the whole structure is welded up and filled with lead I suggest you have it sandblasted and a full marine epoxy system applied, make sure the primer is applied within 4 hours of blasting and that the surface roughness is sufficient. As you pointed out, make small lead pours but make them big enough so that you are sure each layer is able to bond to the previous one. I also suggest you place as many solid ingots in the keel as can comfortably fit before pouring, the molten lead should bind them all together and fill the voids.

    I suggest you start by melting up the scrap lead into ingots, you will need to have some sort of sieve or sifter to float of any steel or other junk mixed in with the lead, be very careful about not getting any water into a pot of melted lead, water == explosion with molten lead flying everywhere. You can build your own ingot mold easily, just add ends to a steel channel or cut away one side of a square tube or half of a round tube.
    If you are in a hurry you can use a bucket of water to cool the ingots once their surface has solidified sufficiently.

    Here are a couple of pictures, perhaps they help some:

    Dallur Lead Melting

    You can use the previous/next buttons to see more pictures, or if you want a higher resolution picture you can select "Maximize" in the "Click Mode".


    Jarl
    http://dallur.com
     
    Last edited: Aug 27, 2010

  15. SeaJay
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    SeaJay Senior Member

    Jarl,

    Thanks for the suggestions. I spent a little time tonight on your website but I know I'll be back...lots of great informaton there - very impressive project.

    Best Regards,

    SeaJay
     
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