Center board and rudder

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

  1. SeaPig
    Joined: Dec 2020
    Posts: 17
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    Location: Fl

    SeaPig Junior Member

    A bigger board is definitely needed. In order to do that I need to build a new trunk and this would be the time to move the trunk back. Here are pictures from today. The yellow shock cord is strung across the hulls center of resistance. I took it out today and did some turning trials in the canal. It’s right on where the boat pivots in the water during a turn.
    upload_2020-12-19_11-41-23.jpeg
    upload_2020-12-19_11-42-7.jpeg

    here is a closer look at some old wood in front of what I assume is a new build center board.
    upload_2020-12-19_11-43-23.jpeg
    I was planning on making a 4sq foot center board. Messabout says up to 5 sq ft..... if I go with an 18 inch chord then that will be about a 4 ft long board total for my 4sq ft dagger. Anything bigger than that would be a hassle to manage on a dinghy.
    It also needs to be thicker than 1/2 or 3/4 which is what the hull exit is right now.
     
  2. philSweet
    Joined: May 2008
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    Location: Beaufort, SC and H'ville, NC

    philSweet Senior Member

    Okay, I think this can be dialed in without major surgery. I'm in general agreement that the bowsprit is an add on, and that the centerboard area is too small.

    The first thing to look at is the mainsail and the traveler system. You need to be able to sheet the boom several degrees to windward of the centerline. So add a line loop through small blocks that let you pull the traveler car uphill.

    You may want to fit a vang for downwind sailing.

    You will need to add reefs to your jib, or get a second headsail. With the balance problem you have, you can't reef the main first, you have to reef or change the jib first. This is perfectly normal in this kind of setup. The traditional way is to have the jib tack on a horse so you just pull it in to the bow and change it or reef it. Reefing a jib is done just like a mainsail. But I prefer to add a pennant to the reefing tack and hoist the reefed jib almost all the way back up to the halyard block. This depends a bit on the jib sheet lead. If you go with a second jib, make it a balanced boom jib and you can control it with one line and the whole thing is self contained, leaving nothing on the deck when not in use (just an attachment point on the bowsprit). The second jib on my 16'er was 16 sqft.

    With lee helm, you are utterly killing the undersized centerboard because the rudder load is adding to the centerboard load. Before getting too crazy cutting new slots, just get the lee helm solved with sail balance and reduce sail if your centerboard stalls. You might need to do this well before you run out of righting moment in light to medium airs, but reef down early, jib first, and keep the existing centerboard operating not stalled.

    When the problem is reduced to "I'm having to reef in winds less than 10 knots to keep the board working", we can start to figure out what you need for more board. With versatile sail options, it ought to be about 3.25 sqft. But if you can make one the fits in the slot that is 2.75 sqft, I think I could live with that.

    Don't worry about the foils being flat. Just put the correct profile on the leading and trailing edges, and leave the sides flat - you'll be fine.

    The current centerboard is raked aft. If you can easily change this, send it straight down.
     
  3. SeaPig
    Joined: Dec 2020
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    Location: Fl

    SeaPig Junior Member

    philSweet
    Do you think a straight board made of spruce strips will stand up to the stress?
    The current board is only 5/8 thick(so Home Depot off the shelf 3/4). I can probably get up to 2 sq ft. Anything bigger and it will probably break under way.
    I’ll build something to test a larger board for sure.
    Also, I can make an adjustable mast step to play with moving the mast up to 15 inches back. (There is evidence of old shroud mounting point further back on the hull that would match moving the mast back.)
     
  4. sharpii2
    Joined: May 2004
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    Location: Michigan, USA

    sharpii2 Senior Member

    The Lee helm is probably being caused by the board not having enough area, combined with it being ahead of the hull's CLR.

    When the board stalls, the hull probably takes over, which makes the situation worse.

    Increasing the area of the board can accomplish two things:
    1.) effectively move the combined CLR forward.
    2.) make the board's CLR a much larger portion of the combined CLR, which would make the hull's CLR less relevant.

    The area of the board can probably be significantly increased by changing its profile shape to that of a rectangle with rounded corners of maybe two inches of radius.

    You might get away with making it maybe 6.0 inches deeper.

    You can change the material it is made of if necessary.

    As for sailing it as is, I would try sailing it with a slight bow down trim, and when reefing, I would drop the jib first.

    I once had a light beam center boarder with a relatively high house somewhat forward. That, combined with its light weight and relatively high bow, made it seemingly impossible to come about. It would make it to almost straight into the wind, then hesitate, then fall off on its old tack.

    The problem was cured by holding the jib on the old tack. This caused it to force the bow onto the other tack.

    This technique proved so reliable that, with the help of a crew mate, I was able to tack it up a channel that was only a
    few boat lengths wide. People came out of their cabins to watch.

    I just came up with another simple thing you could do. Why not rake the mast back a few degrees?
     
    Last edited: Dec 21, 2020
    bajansailor likes this.
  5. SeaPig
    Joined: Dec 2020
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    Location: Fl

    SeaPig Junior Member

    Sharpii2,
    With both your ideas and philSweet’s I have put together a pretty good size punch list to test on the water.
    I started with raking the mast back to the end of its adjustment. A quick move of the mast step back and I can again adjust the rake out on the water as I look for adjustment.
    The traveler is just a 24 inch track with a free sliding anchor. I’ll get something together so it can be adjusted and I have enough resin and glass that I could do a profile change to the existing dagger board.
    As for your description of the tack hanging up and then falling back to its original line; yup that happens.

    Could someone describe what the center board stall feels like? That is new to me and I’m probably missing it.
     
  6. sharpii2
    Joined: May 2004
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    Location: Michigan, USA

    sharpii2 Senior Member

    My experience is that a board stall is very subtle.

    When I first sailed my light, beamy center boarder, I had perfect weather, an ideal wind, blue skies and puffy white clouds.

    Even so, the boat was barely moving. First, I thought I was aground. But the chart said I had at least 7 ft underneath me. 4.5 ft was my maximum draft.

    I had the sails sheeted in too tight, and the boat was moving sideways at least as much as it was moving forward. My bad.

    Generally, if the sails are full and the boat is barely moving, then the board is probably stalled.

    First thing, releave the jib sheet. Then relieve the main sheet. Pull the main sheet in until the sail stops fluttering. You should feel and/or hear a flop as the sail fills. The boat should then start moving. Then do the same with the jib.

    Next, you will have to play with it, as you slowly work your way to pointing as far up wind as you can, by adjusting first the tiller then the main sheet, then the jib. Make sure the boat keeps moving forward while you do this. Eventually, you will reach a point where the boat can point to windward no more and keek going. It is then that you know that you have reached the limit of your boat's pointing ability.

    Be careful how far back you move the mast. Your boat does not seem to have a back stay. Instead, it seems to have back shrouds. If you move the mast back to far, you will have to move these back shrouds aft as well.

    Your probably better off just raking the mast aft.

    You should probably not rake it any further aft than the point where you can draw a line dead vertical from where the back shrouds attach to where the masthead is.
     
    bajansailor likes this.
  7. SeaPig
    Joined: Dec 2020
    Posts: 17
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    Location: Fl

    SeaPig Junior Member

    I read all your posts again and I did another survey. I wanted to see how close raking the mast could bring the sail plan to the CLR. Here is what I found, that leads me to believe the bow sprit is probably added and the boat maybe had a center board and not a dagger board.
    upload_2020-12-22_10-19-20.jpeg
    old back shroud scars on the hull.

    these scars are 24 inches aft of the new ones.
    The tested CLR is 24 inches aft of the center of the dagger board trunk.
    The full sail pan center is sitting 24 inches forward of the tested CLR.

    seems too convenient for all of these to match up? On top of that, the sprit is very shiny and new, so probably an addition.

    with your description of the center board stall, I believe that has happed to me.
     
  8. Eric Lundy
    Joined: May 2017
    Posts: 31
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    Location: Vermont

    Eric Lundy Junior Member

    "here is a closer look at some old wood in front of what I assume is a new build center board."

    What it looks like to me is that the mast step was moved. Is that "old wood" in front of the trunk the old mast step? Considering the changed shroud location and the look of the current mast step was the mast replaced at some point? Just curious.
     
  9. SeaPig
    Joined: Dec 2020
    Posts: 17
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    Location: Fl

    SeaPig Junior Member

    Eric,
    Good question; and all part of the mystery. I’m guessing it’s a new mast. The old wood looks like part of a center board trunk? That’s why I’m looking at the CLR. If it’s the front of an old center board box tat held a triangle board, that could explain the now dagger board box being so far forward. It does open up the cockpit. Combined with moving the mast forward, there is comfortably room for two in there.
    Unless I find who did the refit in 2016, I’m just guessing.
     
  10. SeaPig
    Joined: Dec 2020
    Posts: 17
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    Location: Fl

    SeaPig Junior Member

    All,
    A quick update...
    I fell down the eBay rabbit hole and found some brass cheek blocks to trim the traveler. They will look nice, but the sheaves are over 2/3 worn through. I believe I can mount them to use for the testing. However I did start looking at rebuilding them and that led me to getting a drill press set up. On top of that the weather stinks.
    Real news when I get something done.
    Pig
     
  11. Howlandwoodworks
    Joined: Sep 2018
    Posts: 110
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    Location: Columbia MO

    Howlandwoodworks Member

    Welcome,
    What a nice boat.
    Looking at it from my couch. Is the round hole the mast step or the rectangle keyed one aft of it? It also looks like there was something even back aft of the rectangle oak keyed mast step at one time by the staining on the top of the keelson.
    The dagger looks like something has been added to the top keeping it from sliding all the way into the slot. If it slid down deeper one could pivot the dagger fore and aft and then be fastened in place with a wedge and line. Depending on the direction it was slid in or by reverse its orientated it would allow for even more adjustment to the CLR.
    I have a Int Jet 14' that I can steer by just moving my weight forward or aft in the cockpit if I am single handed it. I have to move way forward with a 120 genoa or larger if I am alone. With two persons on board all is well.
    May you have some great adventures.
    John
     
  12. gonzo
    Joined: Aug 2002
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    Location: Milwaukee, WI

    gonzo Senior Member

    Pushing sideways is not a good indication of where the center of lateral resistance is. The centerboard and rudder are foils and the CLR is very dependent on the profile of the foil. The CLR will be forward of the center when pulling sideways. The hull will also have the center at a different place. An easy way of getting some weather helm is to rake the mast aft.
     
  13. Howlandwoodworks
    Joined: Sep 2018
    Posts: 110
    Likes: 23, Points: 28
    Location: Columbia MO

    Howlandwoodworks Member

    What I was getting at it seems to me that your mast has been moved forward twice and the dagger board alteration has shortened it and in doing so it has lost its intended mode of operation.
    I think both have been altered from there original design and in the process moved the CLR aft. In turn giving it a leeward helm.
     
  14. gonzo
    Joined: Aug 2002
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    Location: Milwaukee, WI

    gonzo Senior Member

    Moving the CLR aft gives the boat a windward helm. Lee helm makes the boat round up.
     

  15. wet feet
    Joined: Nov 2004
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    Location: East Anglia,England

    wet feet Senior Member

    That description is precisely the opposite of the way those terms are understood in this country.We say it is weather helm when the boat is trying to round up and lee helm when it tries to bear off.
     
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