daggerboard lifting

Discussion in 'Sailboats' started by j.bonner, Apr 7, 2015.

  1. j.bonner
    Joined: Dec 2014
    Posts: 7
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: north carolina

    j.bonner Junior Member

    Would any one have any good ideas for lifting a 300 lb daggerboard?
    The dagger board case protrudes out of the top of the cabin trunk.
    If I use a tackle system, what size blocks? How many?

    I know i could use a crank winch, but i dont like the idea of having to crawl up on the cabin to crank it up.
    Also with either ideas, how can I keep it from sliding out of the boat if the cable or line where to break?
     
  2. Jetboy
    Joined: Feb 2012
    Posts: 278
    Likes: 6, Points: 0, Legacy Rep: 65
    Location: USA

    Jetboy Senior Member

    To keep from falling down - I would build in a pin to hold in place with adequate supporting structure around the pin so that it is very robust.

    For lifting, you just need to decide how much force you want to pull on a rope system and then divide the weight your lifting by the tension to calculate the mechanical advantage you need. Then find the set of blocks necessary. For 300lbs, I'd go with a 6:1 ish set. A main sheet set block set for a beach cat would work for example.

    Reading again - if you mean sliding and falling out of the boat entirely - I would build the case and board in such a way that that is physically impossible. Build the top of the board such that it cannot fit through the hull opening. Basically have a rectangular trunk down until near the waterline, then have your foil shaped opening. The top of the board would be rectangular and not fit through the bottom.

    Otherwise I'd want at least two safety cables.
     
  3. daiquiri
    Joined: May 2004
    Posts: 5,373
    Likes: 247, Points: 73, Legacy Rep: 3380
    Location: Italy (Garda Lake) and Croatia (Istria)

    daiquiri Engineering and Design

    300 lb is a lots of weight to be lifted by hand through tackle and, IMO, a winch is the most practical solution in this case.

    Consider that you shouldn't exceed approx. 35 lbs of manual pull force if you want to get back home at the end of the sailing day with your spine in one piece. It means that you need a mechanical advantage of approximately 16:1 (taking the single sheave/rope efficiency of 85% into account). That's either one very big tackle or a rather complex set of smaller sheaves, arranged in this manner:
    Sheave block.jpg
    And you also have to consider that, depending on how deep is your daggerboard, it might take many pulls to lift it up completely. For example: if it is 3 ft long, the configuration in the picture will lift it up by 1/16 of the available manual stroke, for each pull of the rope. If you can pull the rope over a distance of 3 feet, for example, the daggerboard will lift up by only 3/16 ft. So, without winch you will have to pull the rope 16 times in order to completely lift the daggerboard. That's 16 times x 26 lbs pull - quite an effort.

    Or you can opt for a winch. Your choice. :)

    Cheers
     
  4. j.bonner
    Joined: Dec 2014
    Posts: 7
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: north carolina

    j.bonner Junior Member

    Thatsa lota moving parts. I suppose I could run the winch cable over a block at the top of the case then aft to the cockpit. Put the cable through pipe, glassed to the cabin top.
    As for the case design not allowing the centerboard to exit...too late. Its installed, glassed in, with gally fixtures in place.
    Its just a rectangle box through the boat.


    Might have to just rig safety cables
     
  5. PAR
    Joined: Nov 2003
    Posts: 19,133
    Likes: 476, Points: 93, Legacy Rep: 3967
    Location: Eustis, FL

    PAR Yacht Designer/Builder

    A braked winch is the logical option, though tackle could be arranged, it would need to be a many part system, which introduces a lot of friction, parts to wear and potentially break, etc. A braked winch will easily handle this load and hold it in any position once hoisted or lowered.
     
  6. Jetboy
    Joined: Feb 2012
    Posts: 278
    Likes: 6, Points: 0, Legacy Rep: 65
    Location: USA

    Jetboy Senior Member

    What kind of power do you have on your boat? You could potentially use an electric winch or even possibly a linear actuator mounted in the right orientation. Or mount the winch in such a way that it's inside and uses a pulley to lift the daggerboard.
     
  7. PAR
    Joined: Nov 2003
    Posts: 19,133
    Likes: 476, Points: 93, Legacy Rep: 3967
    Location: Eustis, FL

    PAR Yacht Designer/Builder

    Why would you use a pulley on a winch? The smallest winches handle 1/4 a ton on a dead pull, so what's the pulley for? Open and closing speeds on most actuators are measured in fractions of a second, so unless the structure is really, really stout to take the slamming loads that shoving 300 pounds back and forth in .5 second will cause, well . . . Check the Dutton-Lainson units.
     
  8. rcnesneg
    Joined: Sep 2013
    Posts: 456
    Likes: 6, Points: 0, Legacy Rep: 58
    Location: Utah

    rcnesneg Senior Member

    I've got a 55 pound lead daggerboard on my pocket yacht. I use a 3:1 tackle to lift it. Because it sticks in the slot a little I suspect it's putting around 100 lbs of force into the system. I'm pulling with about 35 lbs, so I suspect that's correct. It works alright, but you definitely want some sort of cleat. It wouldn't be hard to get, say a 6:1 mainsheet off a hobie cat and hook up a 2:1 or 3:1 cascade on the end of the sheet and have all the power you need. You'll go through a lot of line though, and you need something serious to mount the top of the lift to. In my case, to the top of the stout mast.

    [​IMG]
     
  9. Jetboy
    Joined: Feb 2012
    Posts: 278
    Likes: 6, Points: 0, Legacy Rep: 65
    Location: USA

    Jetboy Senior Member

    For locating the winch in a more convenient location. The OP said he didn't want to go topside to use the winch. Something simple for a hand crank winch could allow you to mount it down below. Like this;
    [​IMG]

    There are many types of linear actuators. I've used them for automotive projects where hydraulics weren't convenient. The biggest downside is not speed - rather it's that they are usually way too slow. The benefit is that they are naturally self braking. I would avoid electronic motors if possible simply due to weight and unnecessary complexity, but it's just another option.
    [​IMG]
     
  10. daiquiri
    Joined: May 2004
    Posts: 5,373
    Likes: 247, Points: 73, Legacy Rep: 3380
    Location: Italy (Garda Lake) and Croatia (Istria)

    daiquiri Engineering and Design

    That actuator is definitely an overkill for a small sailboat with a 300 lb keel.
     
  11. Fanie
    Joined: Oct 2007
    Posts: 4,603
    Likes: 170, Points: 63, Legacy Rep: 2484
    Location: Colonial "Sick Africa"

    Fanie Fanie

    I would think a winch as Par suggested and use a pulley near the deck so the winch remains inside...
    The disadvantage of a block system is a heap of rope.
     
  12. Jammer Six

    Jammer Six Previous Member

    To direct the force.

    Not everything is numbers. It has to work.
     
  13. j.bonner
    Joined: Dec 2014
    Posts: 7
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: north carolina

    j.bonner Junior Member

    I have a geared winch that used to lift the old centerboard, the problem with it is the fact that it is very slow.
    I wonder if a regular boat trailer winch could raise it without too much extra effort, but be faster.
     
  14. daiquiri
    Joined: May 2004
    Posts: 5,373
    Likes: 247, Points: 73, Legacy Rep: 3380
    Location: Italy (Garda Lake) and Croatia (Istria)

    daiquiri Engineering and Design

    There is no free lunch there.
    Power = Force x Speed
    The limit is the human power - at most a hundred watts or even less, for a short time. So you can either use that power to apply a big force at a slow speed, or a small force at a higher speed. In this case the force is given by the keel weight, 300 lb. That is a big force for a human power input, so the lifting speed necessarily has to be low.
    There is no way to get around this elementary law of physics. The only solution for a higher hoisting speed is an electric or hydraulic winch, which can have a higher power rating than human arms. But then you need a power source or a battery bank, do you have a space for it on board?
     

  15. j.bonner
    Joined: Dec 2014
    Posts: 7
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: north carolina

    j.bonner Junior Member

    Yes I have plenty of battery power, 5 big deep cycle batteries.
    4 for electric propulsion and one house bank battery with a solar charger.
    I could install an electric winch. Maybe an atv winch with a remote?
     
Loading...
Forum posts represent the experience, opinion, and view of individual users. Boat Design Net does not necessarily endorse nor share the view of each individual post.
When making potentially dangerous or financial decisions, always employ and consult appropriate professionals. Your circumstances or experience may be different.