Center board and rudder

Discussion in 'Boat Design' started by SeaPig, Dec 18, 2020.

  1. Howlandwoodworks
    Joined: Sep 2018
    Posts: 124
    Likes: 26, Points: 38
    Location: MO

    Howlandwoodworks Member

    gonza,
    Sorry, I think I was sleep posting last night. I meant CLE not CLR and leeward has to do with a landmass.
    SeaPig,
    What I was trying to say was, I think you are on the right track.
     
  2. SeaPig
    Joined: Dec 2020
    Posts: 23
    Likes: 0, Points: 1
    Location: Fl

    SeaPig Junior Member

    All,
    There are definitely modifications going on with this boat. Honestly, the overall lines attracted me to the boat and I purchased it knowing there would be some repair work required.
    Once I get the traveler setup for adjustments under way I’ll see what I can do under just the main for power. If I can get the loading on the rudder under control; “good!” That will take me down the non surgical route recommended to me.
    Correct on the foils comments and discussion. I’ve pulled a lot of info on this from other posts here. I’m not afraid to experiment at this point. Once I get up to some speed 45 degrees to the wind and prior to heeling I’m already in the 15-20 degrees of rudder deflection (push not pull to maintain course). I can feel the turbulence and drag through the tiller. And it makes it difficult to tack because now I’m going towards 45 plus on deflection to get the nose through the wind. Jibes on the other hand are a breeze! Release tiller pressure and away you go!!!!
    I will double my efforts to make some progress.
    SeaPig
     
  3. wet feet
    Joined: Nov 2004
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    Location: East Anglia,England

    wet feet Senior Member

    That would be a nightmare to sail with.Do you have any reason to believe the bowsprit is original?My suggestion would be that you try tacking the jib to the stemhead and maybe adjust the sheeting position to see if the problem disappears.Additionally,the daggerboard looks a bit slender for the size of the case-so maybe a bit more area there would help.
     
  4. Howlandwoodworks
    Joined: Sep 2018
    Posts: 124
    Likes: 26, Points: 38
    Location: MO

    Howlandwoodworks Member

    Echinoderms,

    What fun! You get a boat and a mystery. Sherlock Holmes once said "Come Watson, come the game's afoot". It's from Shakespeare, Henry V, "Before the game is afoot, thou still let'st slip."
    You could get some ideas from some existing boats design. I am not familiar with your boats design but these might give you some clues.
    You mentioned there were some old shrouds/chain plate holes. hmm

    Capri 14.2' Catalina Designed by: (Ted Carpentier/Frank Butler)
    https://sailboatdata.com/sailboat/capri-142-catalina
    Capri 16.5' Catalina
    https://sailboatdata.com/sailboat/capri-165-catalina

    International Jet 14' class Designed by: (Howard Siddons/Uffa Fox)
    https://sailboatdata.com/sailboat/jet-14
    Articles & Docs http://www.jet14.com/the-jet-14/articles-docs

    I once saved a 1954, hot molded, Mahogany International Jet 14' Class from the chainsaw.
    Luckily for me there was still evidence from where the rigging once was.

    John
     

    Attached Files:

  5. SeaPig
    Joined: Dec 2020
    Posts: 23
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    Location: Fl

    SeaPig Junior Member

    I knew I was taking on a mystery. But I also appreciate the wood and overall design so I’m invested until the end.

    nightmare: well, let’s just say the first time out was exciting and wet. I’ll leave it at that.

    I believe the bowsprit is not original, the center board box is not original and the location of the shroud mounts are not original.
    But the looks of the bowsprit is “cool”.... maybe I can figure out how to balance the rig and keep the bowsprit and add MORE sail to justify the sprit!??
    It was along work week, but I did get new sheaves made for my brass cheek blocks to make the traveler system. Small steps in the right direction. Installation and a test sail under main power next.
    Pig
     
  6. Blueknarr
    Joined: Aug 2017
    Posts: 1,030
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    Location: Colorado

    Blueknarr Senior Member

    Amazing how often exciting and wet are used together.

    Suppose it is better than boring and wet
     
  7. wet feet
    Joined: Nov 2004
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    Location: East Anglia,England

    wet feet Senior Member

    If you really want to keep the bowsprit and have a balanced boat you need to extend the boom and buy a new mainsail.Then a smaller jib so that when its a bit breezy you can change down and retain the balance.Is it worth it?
     
  8. SeaPig
    Joined: Dec 2020
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    Location: Fl

    SeaPig Junior Member

    Worth it? Isn’t that always the question when it comes to old boats?
    If moving everything back 24 inches fixes the handling problems, then I get to keep about half the bowsprit. I consider that a cosmetic problem for later. First I’ll get through the experimental phase so I can make a refurbish plan.
    I purchased the boat and planned on
     
  9. tlouth7
    Joined: Jun 2013
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    Location: Cambridge, UK

    tlouth7 Senior Member

    Moving the daggerboard aft will make the lee helm worse! Think of how the rig is trying to blow the bow downwind, and the hull and foils are trying to stop it. Moving the rig aft would be my first approach - this might be easy if there is already a mast step further aft than the current one. Positioning the shrouds may be the biggest challenge. Some rake might help if you can't easily move the step.

    Trimming the hull forwards (bow down) tends to increase the immersion of the forefoot which shifts the CLR forwards. Unfortunately it also shifts the rig forwards so that must be countered. Worth having in your armoury.

    A larger and better profiled daggerboard within the existing trunk would help. You could definitely get a bit more depth, and less taper would give you more area. I certainly wouldn't cut a new trunk until you know where it needs to go.
     
    bajansailor likes this.
  10. debenriver
    Joined: Sep 2012
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    Location: Rockland Maine USA and Woodbridge England

    debenriver Junior Member

    Oh dear – all this is pretty well known ...

    CLA (CLR) is the geometric centre of area of the underwater profile, including the centreboard. A common way to find it if you don't have a CAD program or similar is to make a scale cardboard cut-out of the underwater shape and balance it on a knife edge – where it balances will be the CLA. It's not the actual centre of pressure of the underwater body – just the simple centre of area (of the flat profile)

    CE is similarly the geometric centre of area of the sail plan. The sail plan is considered to be the mainsail (less any roach) plus the 100% foretriangle (not the actual area of any headsails). Again this not the actual centre of pressure of the sail plan - just a simple centre of area.

    The CE should lead (that is be forward of) the CLA by a proportion of the LWL. For a sloop this should be between 12% and 16%. So the distance between the CLA and the CE should be between 12% and 16% of the load waterline length.

    In a small boat, moving crew weight can shift the CLA. Raking the mast can shift the CE.

    Centreboard area should be about 3.5% of the sail area (again main + 100% foretriangle). Rudder area about 1.4%.

    Cheers -- George
     
    bajansailor likes this.
  11. SeaPig
    Joined: Dec 2020
    Posts: 23
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    Location: Fl

    SeaPig Junior Member

    George,
    I do believe you posted this topic in here somewhere else. Everything you described is what brought me into this forum and set the baseline for the direction I’m taking as I fix up this boat. If (“if if if”) the non surgical options don’t get the Lee helm solved, or at least to the point I’d feel comfortable having a sandwich under way I will post the measurements and math before the saw touches my boat.
    Pig
     
  12. SeaPig
    Joined: Dec 2020
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    Location: Fl

    SeaPig Junior Member

    The cheek blocks are ready.
    upload_2021-2-9_13-15-54.jpeg
    upload_2021-2-9_13-16-47.jpeg
    that little sliver is what’s left of the original 1/4 round and the reason I made new ones.
    Everything is smooth now and ready to go on the boat. If I ever want to I can swap in Harken sheaves.
     
  13. debenriver
    Joined: Sep 2012
    Posts: 7
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    Location: Rockland Maine USA and Woodbridge England

    debenriver Junior Member

    I did a VERY rough sketch of your sail plan and underwater profile. I emphasize the VERY!


    Screenshot 2021-02-09 at 15.02.55.png

    This shows the CE leading the CLA by about 13.6% of the LWL – which is in the normal ballpark and shouldn't result in lee helm normally. In fact i would expect very mild weather helm.

    Mind you the underwater profile doesn't include the rudder or the centreboard. It should absolutely include the centreboard and conventionally, 50% of the rudder. Though it's quite possible these will almost cancel each other out, so you get about the same lead.

    Or of course it could be that I've got the sketch totally wrong! But at least you can see the principle.

    Cheers -- George
     
    Last edited: Feb 9, 2021
  14. debenriver
    Joined: Sep 2012
    Posts: 7
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    Location: Rockland Maine USA and Woodbridge England

    debenriver Junior Member

    Remember the 100% foretriangle is a triangle with the foot from where the forestay attaches to the stem (bowsprit in this case), horizontal back till it hits the mast. The other two sides are the forestay and the line up the mast from the foot to the top of the forestay. This is not the same as the actual headsail area.

    Are you OK with finding the combined centre of area of several areas? It's straightforward moments - the old seesaw problem - If not I can explain. Or there is a good explanation in Skenes Elements of Yacht Design.

    Cheers -- George
     

  15. debenriver
    Joined: Sep 2012
    Posts: 7
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    Location: Rockland Maine USA and Woodbridge England

    debenriver Junior Member

    The centreboard looks to be way too small – but this shouldn't really affect the helm balance that much – it should simply mean that when you try to sail close hauled you simply mostly blow sideways because there is insufficient underwater profile to give enough resistance and lift.

    You really need to do an accurate CLA and CE calculation before doing any surgery or changing anything.

    Cheers -- George
     
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