Help with Keel

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

  1. rugludallur
    Joined: Jan 2006
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    rugludallur Rugludallur

    Thank you for your kind words, feel free to email me or just post your questions here if you have any.

    Jarl
    http://dallur.com
     
  2. Brent Swain
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    Brent Swain Member

    A hydraulic jack with a flat bar bowstring welded across the top can put a good curve in any plate you want to bend. Once the bottom is welded on, the top is welded to the hull and the ballast is poured in , it is not going anywhere.
     
  3. SeaJay
    Joined: Jun 2007
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    SeaJay Senior Member

    Just a quick update...I ended up with 3/16" plate and as Brent said, it was no problem to bend it around the bottom foil shaped flanges. It's all welded up now and I'm just about ready to start pouring lead.

    Regards to all,

    SeaJay
     
  4. ACuttle
    Joined: Aug 2008
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    ACuttle Marine Design Engineer

    I've worked on a lot of projects involving fairly complex steel forms, but I think that any advice I could give has already been mentioned. Normally I'd suggest just breaking the back of a plate with some rolls but with thing steel in long enough lengths that isn't usually needed, a bit of internal long's can help the plate take the form. Plenty of green-edge is a good way to go so you've got something to work off. Sounds like it's come together well for you.

    I was wondering why you had your plate water-cut, it seems an expensive way to go?

    Hope the pouring goes okay.
     
  5. SeaJay
    Joined: Jun 2007
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    SeaJay Senior Member

    Drew,

    I only had the top and bottom 3/4" foil shapes cut with the water jet. The bottom cut was just the foil shape itself, but the top foil had 5 access holes and the flance had 10 bolt holes. I wanted to achieve two things with the water jet.

    First, I wanted the exact NACA 0010 foil shape that I was able to create on my computer. The water jet is so accurate that when the foil was projected and cut at full scale, you could see the "tangent" lines on the flange where I fudged the CAD drawing a bit.

    Secondly, although the plate was 3/4" thick, I didn't want any heat distortion.

    Both objectives were met.

    I also had the flange shape cut out of 1-1/4" plywood to use as a template to drill the bolt holes through the bottom of the boat...it was very handy. As that shape was cut out of the center of a 4xx8 sheet of plywood, the "hole" that was left now fits securely around the top of the keel, supporting the keel in its vertical position as it stands in a steel frame I made up. This sheet of ply also forms a work platform on top of the whole appartatus upon which the lead pot sits, waiting to discharge molten lead through the access holes in the upper foil into the void of the steel "shell". I think the plywood cuts added about $60 to the cost and were well worth it.
     
  6. ACuttle
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    ACuttle Marine Design Engineer

    Fair-enough - if you can afford it then water-cutting is a good way to go. I was wondering if you'd gone for it all over, which would have seemed like a bit of overkill.

    I think you'd have been alright with a good plasma or laser but as you say it, can be best to be careful.

    Have you been able to check the overall foil shape out for accuracy, now that it's been formed and welded up?

    I've wondered about water-jet for some tight forming work I've got on, but at the end of the day I find it a bit dear for most work.
     
  7. SeaJay
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    SeaJay Senior Member

    Drew,

    I can say that the top and bottom foil shapes are exactly what was in my computer. You pay for the time of the water jet cut so a faster, rougher cut is less expensive. I went for a mid range speed and the cut was very acceptable. (I didn't realize the kerf was so small (maybe 1/16") and it created a little problem where I had the access holes cut about 95% complete. I planned to saw through the connecting pieces with some sort of saw after the sides were were welded on, but the kerf was too small to get a blade in so we used the torch...pretty crude instrument after the water jet.)

    Anyway, the top and bottom plates are near perfect as far as I can tell. The side plates wrapped around them well and at this point I can detect no distortion. The leading edge needs some work. There is a 2" diameter solid bar which forms the structure of the leading edge and the side plates terminate along this bar. It required a lot of convincing to get the sides to lay at a perfect tangent to the bar. There was some distortion at the top and bottom. The top isn't a problem as the top couple of inches gets covered with a welded gusset plate. The bottom will require some work with the grinder. Having said this, the problem was with me trying to bend too thick of a plate around too tight of a radius...the water jet did what it was supposed to do.
     
  8. ACuttle
    Joined: Aug 2008
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    ACuttle Marine Design Engineer

    Yes, I think it must be a pretty good showing if you can see the CAD changes in the CNC cut. I was wondering whether the sides had taken the foil well too, but it sounds like you've done a pretty good job bending to the form, especially given you felt you needed advice at the start of the thread. What kind of radius were you looking to get where you feel it needs some tidying?

    What kind of rough-price are you getting for a job like that? I suspect it will be scarily low to what I'm looking at.
     
  9. SeaJay
    Joined: Jun 2007
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    SeaJay Senior Member

    Drew,

    I just checked the invoice and I paid 1,200 USD for the following:

    3/4" Steel Plate -
    ~ 36 ft. of cut for the foil and flange shapes; 10 each, 1-1/16" bolt holes; ~ 12 ft. of cut for the access holes in the top flange; 20 each, 4"x3"x2" gussets (cut from the scrap)

    1-1/8" Plywood -
    ~12 ft of cut for the flange template; 10 each, 1-1/16" bolt holes; 12 each, 1/4" alignment holes. The flange template was cut out of the middle of a full sheet of ply so the remaining piece is used form a work platform on top of the frame which holds the keel upright.

    The lead pot sits on top of the platform and the molten lead drops directly into the steel shell...or that's the theory at least !:D

    Where I had trouble bending the side plates was at the leading edge where they meet the 2" dia. vertical bar which forms the "nose" of the keel. I knew there was no way the plate was going to wrap around the bar, but wanted to get it to lay at a pretty close tangent, which it did. A little bit of the problem is because there is a very, very slight compound curve in the sides. The keel frame was on it's side when we applied the side plate, and the plate almost bent around the foil just by its own weight. We clamped it down about every 6" and it followed the foil with little resistance until the last inch or so. Like I said earlier, I knew I'd be fairing the leading edge anyway, but I just wasn't sure how much would be involved. The sides show no visible distortion or dimpling...it looks exactly like the computer generated drawing. The real question is; did I draw it correctly in the first place :rolleyes:...I sure hope so! Anyway, it looks pretty so I'm happy.
     
  10. viking north
    Joined: Dec 2010
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    viking north VINLAND

    Thought i'd add this little tid bit of info i read somewhere in the past regarding foils. The leading edge should not be round but parabolic, otherwise it will trigger flow delamination for the rest of the surface of the foil face thus defeating or at least greatly reducing the desired lift characteristic of the foil in the first place. If upon research you discover the same info, it would be a simple matter of moulding the leading edge with thickened epoxy(similar to the thickness of auto body filler) to create the parabolic shape along the leading edge. Just food for thought. Geo.
     
  11. SeaJay
    Joined: Jun 2007
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    SeaJay Senior Member

    Viking,

    You are correct, the nose of a proper foil is not actually round. It is a bit difficult to explain, but top and bottom foil shapes of my keel are close to perect NACA 0010 foils as they were cut directly from the computer generated drawings. There is a 2" diameter bar that forms the leading edge support and holds the top and bottom foils 54" apart in the vertical direction. The skins land at a tangent to the side of the bar, and stand proud of the surface of the bar. The final shape will be formed with epoxy, following the contours of the top and bottom foil.
     
  12. viking north
    Joined: Dec 2010
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    Location: Newfoundland & Nova Scotia

    viking north VINLAND

    Seajay, wasn't trying to be pickey but i've just completed a long self education study into hydrodynamics and keel foils. I am an experienced builder in all mediums and presently into #3 lifeboat/surfboat to motorsailer conversion (presently taking off her lines the old fashion way) and attempting to come up with a full keel (with Brewer bite) foil section, something with more lift than just a flat sided appendage as i used on prev. builds which were acceptiable for (60/40)(70/30) motorsailers. However this is my personal boat with a beautiful schooner style hull (30ft. glass surfboat)and want it to be more of a (50/50) (40/60) design so using all the tricks to get there. It will end up being low aspect but more lift than no foil at all. As soon as i learn how to post photos i will do so in the thread, "What are you building" I use auto wheelweights encapsulated in polyester resin to secure my ballast, works great.Will keep tracking your great build and where i can offer any tricks or help will do so. Geo.
     

  13. SeaJay
    Joined: Jun 2007
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    SeaJay Senior Member

    Viking - no problem, always good to hear from other builders.

    Update to all - This weekend we started pouring lead and got about 2,000 lbs. into the keel. It all went much smoother than I expected. If you've been following this thread, I've got the lead pot sitting on a platform on top of the keel, and the molten lead flows out of a valve at the bottom of the pot and drops into holes cut in the top of the keel. I thought I would have to move the lead pot forward to aft in order to get the lead evenly distributed, but I thought I'd start in the middle so as to keep things balanced. However, the first shot of approximately 300 lbs of lead flowed evenly along the bottom of the keel to a depth of a couple of inches. And, more importantly, there was no distortion of the sides. After seeing the results we started melting and pouring in earnest and are about a quarter of the way done.

    If anyone needs a lead melting pot (AKA The Okie Cooker) and can pick it up in Sacramento, you are welcome to it when I'm finished. We've done as much as 400 lbs and I suspect it will hold at least 600 lbs. However, please be advised that it is VERY MUCH NOT OSHA APPROVED.
     
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