Folding up keel.

Discussion in 'Boat Design' started by BertKu, Jul 26, 2016.

  1. BertKu
    Joined: May 2009
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    Location: South Africa Little Brak River

    BertKu Senior Member

    Thanks CDK, Yes your suggestion is a good one. But it still means that if I hit something under water that also with your proposed keel, quite some damage could be done. Bear in mind +/- 600 kg has be brought to a standstill. The same sort of damage as expected with a telescopic system. Except if I make some sort of protection, which will fold the telescopic keel in. I am philosophizing now, maybe a strong 3 mm stainless steel strip which is like a hinge in the front. If I hit a rock, the hinged strip will push the front of the keel upwards and then the rock will do the rest. Also it will lift the hull up by 12,5 cm, but the boat does not come to a dead stop immediately. The bottom part is a 3 mm stainless steel part in anyway and can take some scraping. Drag could be an issue, but at 4 to 5 knots, I just have get an extra lithium battery to compensate, should that be the case.
    I do not expect problems from the back, except if I am flipping stupid when I reverse. Well, at my age anything can be expected (you get a grin on my face from me now). Daiquiri, the boat is not permanently in the water, thus algae growth etc. is not an issue. PAR, have you been able to come with a better solution? Thanks CDK, time will learn what I will do. Bert
     
    Last edited: Jul 31, 2016
  2. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    Bilge keels can easily fit on the bottom of your boat, being no deeper than the existing keel. No moving parts, the boat can take to a grounding or beach bolt upright and if you bash into something, very little damage if built stiffly. I'd mount them around the most outboard strake at about a 7 degree angle. Given the speed of your boat, I wouldn't bother to "airfoil" them, just radius the leading edge and a modest taper on the trailing edge. If truly concerned about impact damage, attach them lightly, with small penetration screws. This way if you hit hard, one of the keels might fall off, but that's the worst of it.
     
  3. BertKu
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    BertKu Senior Member

    Thank you PAR, I will discuss it with a boat builder, what he would charge me to put it onto the hull. He is the son of the only yacht builder in our town and was a friend of mine, who died 5 years ago and I have kept contact with his son. His son gave up yacht building instead he does fiber glassing to yachts and other projects. Thank you for your help. Bert
     
  4. JSL
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    JSL Senior Member

    Looks like a power boat hull.....If not, it's the first sailboat I have seen with bottom strakes.
    Why is a keel needed.???? A telescopic keel will be trouble... probably seize up on the first day.
     
  5. BertKu
    Joined: May 2009
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    BertKu Senior Member

    Hi JSL, I think you may not have read all the posts concerning this issue. Yes, it was a powerboat, converted to a semi displacement boat with electrical propulsion. A keel is needed as I plan to place an emergency jib on the boat, just in case. I need the keel not to drift when using the jib and also I need to lower the CG, due to the fact that I place a mast and sail which moves the CG up. I like to differ from your opinion that it will pack up the first day. Maybe after 10 years, but then I will have kicked the bucket in anyway or most likely not be able to sail anymore.

    How good are you in designing and making something? When I was 16 I made an electric base, everybody also said, impossible, cannot be done. 40 years ago I made a color TV and wound the deflection coils myself. So far, whatever I have build , has been a success. The list is quite long. Maybe after making a small prototype and do some testing, I change my mind or if PAR suggestion is not too expensive to make and I have spoken to the boat builder what the costs is and how to do it, maybe I drop the idea. For the time being, everything has advantages and disadvantages. Unfortunately I have great advantages if I could build a successful telescopic keel.

    Sorry to disappoint you. Bert
     
  6. BertKu
    Joined: May 2009
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    BertKu Senior Member

    Hi JSL, You know I prefer forum members to give positive criticism , not negative. If you had written, Bert, Bert, the way you have drawn it is too complex and bound to give trouble on long term, why don't you consider something like this sketch. I would have had respect for you, like I have respect for all the other forum members who have given positive criticism, like CDK, PAR, Porta, and a lot of others.
    I hope that you can take my negative criticism on your contribution.
    Bert
     

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  7. JSL
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    JSL Senior Member

    Sorry to annoy you - just trying to help people avoid frustration. The latest shown (hinged, like a fan or folding knife) might work better.
    A good rule in boats (or anything else for that matter) is to keep it simple, such as a one piece hinged centerboard or swing keel as has been in use for decades. But this may not fit with your vessel.
     
  8. Poida
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    Poida Senior Member

    Could you fit two dagger boards pivoted on the sides of the boat?

    Poida
     
  9. BertKu
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    BertKu Senior Member

    Hi Poida, Yes, that was what PAR also suggested. I had a look at it. It unfortunately does not lower my CG and it will be more complex than a couple of bend 3 mm stainless steel. PAR also suggested something else, which I will investigate first. But it boils down to 2 things, 1)make something what survive, should I hit something. 2nd) make it simple, without too much risk of jamming the keel. Thank you all. Bert
     
  10. BertKu
    Joined: May 2009
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    Location: South Africa Little Brak River

    BertKu Senior Member

    Thank you all for your inputs. Having considered all your very good arguments, I have decided to make it as follow. Putting keels on in an other way, cannot be done by me and the cost is too high too to have it done elsewhere by other companies. From the attached new drawing, you may have to try to judge it in 3 dimensions, the 5 x 12 - 14 cm U shaped and 1 rectangular beam will fold into each other. The ends falls onto the edge of the previous level. It pivots and I don't expect problem because the boat is stored after use at my home.

    Advantages.
    1) If I am too old to sail and like to sell the boat, I may remove the solar system with brackets, batteries and cables. I don't want to get involved with
    the sale afterwards to help somebody with the electronics, fuse system and batteries. Although everything is recorded in drawings and in writing. Maybe also the sail, mast and keel I may remove.
    2) I am able to keep the keel lifted and cruise in shallow waters.
    3) I can add easy some lead, to lower the CG and this system has already lowered the boat's CG, the last thing I want is to have the boat capsized.
    4) I am able to make it and mount it onto the boat myself for substantial less cost.
    5) If I hit something under water, the system will fold in. If I reverse and hit something, I also expect to fold it in, as the speed will be lower then forward propulsion.

    Please, your inputs was very useful for me, thanks for all the information and inputs.
    Bert
     

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  11. Petros
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    Petros Senior Member

    have you studies the strakes, or chine runners, kind of like side fins? They stick out horizontally at the bilge chine line. It is used on a small sailboat with a flat bottom, it puts side "fences" at the bilge chine. It makes the whole hull act like a keel, the flow fences keep the flow attached longer to the side of the hull allowing lateral resistance.

    It is not as efficient as a conventional keel or dagger board, but it works well enough that is is popular with many "micro cruiser" designs. No moving parts, and with a flat bottom allows you to beach it, or use it in the shallows.

    Matt Layton designed the Paradox using side strakes, see the attachment. It seems it could be made to work even better if they were larger. Though according to reports it works remarkably well. there is a youtube video of the Paradox tacking into the wind up a narrow jetty, looking it like it had a keel. Not much noticeable slip or leeway.
     

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  12. JosephT
    Joined: Jun 2009
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    JosephT Senior Member

    Hi BertKu, the fold-up keel sounds feasible to me. However, I would suggest a single, heavy solid keel plate/centerboard vs. your nested U-channel concept. If you live anywhere near salt water those light nested channels are an invitation for a barnacle factory not to mention corrosion between the plates. You'll get more mass/weight out of a single retractable keel that pivots on a well reinforced hinge. I've seen several iterations of the simple design below...worth a consideration.

    [​IMG]
     
  13. PAR
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    PAR Yacht Designer/Builder

    If this powerboat trims like most powerboats, he might have enough lateral area to offer modest windward ability, if he uses chine runners. The after sections would be pretty heavily immersed and runners would help finish this off. Bilge keels would work better uphill, but runners are a less obtrusive option
     
  14. BertKu
    Joined: May 2009
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    Location: South Africa Little Brak River

    BertKu Senior Member

    Thanks, nice idea, but I don't want to make big alterations to the main hull. Also such modifications cannot be done easy by me. Thanks for your input.
    Bert
     

  15. Petros
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    Petros Senior Member

    the chine runners like on the Paradox are your best bet for simple and effective. It will acheive everything you need without extensive mods. Here is a video with the last half showing it going to windward remarkably well. looking at it again it is difficult to believe that it has no keel at all, except for the effect of those tiny chine runners.

    https://www.youtube.com/watch?v=LkaW-fu022w
     
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