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Cabo Rudder Alignment & Adjustment

Discussion in 'Cabo Yacht' started by CSkipR, Mar 2, 2017.

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  1. CSkipR

    CSkipR Member

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    IMG_2742.JPG Here is a diagram from Cabo of how my rudders should look. Can someone explain it to me.
    What is the wedge rudder and what is plate rudder? Are these two different types of rudders?
    Which way is the trailing edge of the rudders? The diagram says these are "tow in". How do I measure my rudders to see if they are adjusted correctly?
  2. CSkipR

    CSkipR Member

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    Why would they move this to the Cabo forum. Its a generalized question not specific to Cabo?
  3. PacBlue

    PacBlue Senior Member

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    I will give it a shot.

    Wedge Rudder = Aft Trailing Edge is thicker than Front Leading Edge, plate Rudder has no difference from Leading Edge to Trailing Edge. They probably varied by supplier and/or model.

    Toe-In is fairly common and you really do not want your Rudders without Toe-In (or out, depending on installation) for a fast SF. That means that you would not set up the rudders to be exactly parallel to the boats centerline. Cabo used a nice trick to develop what they concluded as the optimum (least drag, best response) Rudder Toe-In amount by running the prototype at WOT with the Rudder Tie Bar removed to allow them to naturally find their equilibrium position, hence the Toe-In instruction you see.

    How to measure - measure the centerline distance between the Rudder Posts, that is your "X". They want the Aft Trailing edge of the rudders to be "X" + 2-1/2", so since there are two rudders, divide 2-1/2" by 2 and each Aft Trailing edge should be 1-1/4" past parallel. You can confirm this by measuring the total distance between the centerline of the Aft Trailing Rudder Edge as noted = "X" + 2-1/2",
    Capt Fred likes this.
  4. Kevin

    Kevin YF Moderator

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    Trailing edge in your diagram would be towards the bottom of the page. Toe in means the leading edges are pointed towards each other. That contributes to straight line stability.

    Measuring should be fairly straight forward (no pun intended) once you determine which particular rudder shape you have.
  5. CSkipR

    CSkipR Member

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    Thanks guys great info and I think its clearer. So the tow in position means the leading edge of the plate rudder is actually closer together, but you measure the trailing edge so that it is 1.25" further apart from centerline on each side?
    The boat seems to rides bow high would this have an impact?
  6. Capt J

    Capt J Senior Member

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    No, rudders shouldn't have an impact on it riding bow high, that's a combination of props (how much lift they have and number of blades), shaft angle and hull design.
  7. PacBlue

    PacBlue Senior Member

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    Yours is a 43' Cabo? If it is the 43, this is exactly the Bertram 43 Hull without lifting strakes and designed by Dave Napier.

    Typically, weight distribution is the greatest factor for static and running trim. That is what Naval Architects try to balance after the engines and shafts have been designed and put in place to a particular hull. Trim Tabs are used to manually correct any "imbalances' that are present in order to achieve acceptable Running Trim Angles. Most try to target about 3 degrees as near optimum.

    So are you referencing the bow high condition running with full fuel in the cockpit tank? With or without trim tabs? What is the trim level at the dock before you cast the lines of? A trick you can do is to get one of those 0 - 10 degree bubble angle gages that sailboats have to show heel angles and mount one (fore and aft) next to the helm. I think West Marine carries them. https://www.westmarine.com/buy/sun-company--lev-o-gage-clinometers--P002_067_002_504?recordNum=28

    Pick a baseline condition - ideally level the boat while at the dock so that the waterline is basically level, that is, the stern or bow is not sitting lower/higher than the reference water, it is truly parallel to the water. Install the Bubble Trim Gauge at level (Zero) and you can then monitor your Running Trim Angles. You can even use an electronic level as a temporary device. http://www.homedepot.com/p/Johnson-Electronic-Level-Inclinometer-40-6060/202704986

    Now you can begin the game of checking the effects of trim tabs on running trim/rpm/speed. You should find a sweet spot where the Trim Tabs gain a bit of speed at a certain throttle setting, and this is really where your boat is running in a optimized mode. If the measured trim angle seems a bit high, there is probably not much you can do about it, except for getting into some real fun stuff - like adding a bit of hook to the hull bottom surfaces. this consists of glassing in a "wedge" of fiberglass that extends anywhere from 3/8" to 3/4" below the original transom edge, The shape is usually tapered from o' at about 12" forward of the transom to the desired depth below the original hull surface. These are just some of the tricks that builders use on prototypes before they go to production.

    Given that rather long discussion, keep in mind that your 43' loves to have some bow up running trim while it eats those head seas up, and it is a much better situation than having a bow down condition which is typically adjusted with ballast or rocker (the opposite of hook) to the hull bottom.
  8. CSkipR

    CSkipR Member

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    PacBlue,
    Thanks for the information. It is a 43 Cabo. Typically, I lower the tabs before going up on plane. Don't have too but it seems to help get up quicker. The boat has a lot of weight in the stern/cockpit area. Engines are 8 cyl Mans (many 43's have the 6's) and fuel tank under cockpit is 700 gls. Will check out the trim angles when running. Had the boat for 8 yrs and its been a good one.
    Thanks, Skip
  9. Capt J

    Capt J Senior Member

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    Skip, they just seem to like to run that way. They also like the weight aft. Now, I know you always run yours a little slower, but I've always run them 80% load and perhaps it picks up the stern a little with more speed. BUT, I've found that they still like the trim tabs only halfway down for best speed, so it seems that hull just simply likes that running angle. I almost always trim a boat for speed/efficiency, unless it's rough enough that ride takes precedence. Also as you burn off fuel, you'll have to adjust tabs a touch periodically throughout the day. Keep notes on speed and fuel/water load and try it with a near empty water tank and a full one, since it's in the bow area. It has been a very long time and a lot of boats in between since I've run a 43'.

    I'd pick a baseline for the trim gauge with full fuel and water.
  10. CSkipR

    CSkipR Member

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    Thanks guys for the education on rudders. Went to the boatyard today and measured the rudders. From center rudder post to center rudder post was 68" and the trailing edge of rudders were 70.5". It checked out right on the money. Now if I can get them to finish the bottom paint and running gear will be ready to launch.
    Does your boatyard charge you for each day it sits in the yard if they are not working on it? Thank goodness mine doesn't but in south Fl they did.
  11. Capt J

    Capt J Senior Member

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    No and most in South Florida do not charge by the day if the boat yard is doing all of the work or providing the guys doing all of the work.
  12. Capt Maritime

    Capt Maritime Member

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    Good info on rudder angle. I'm hauling the boat soon and am putting my list of items for inspection. I never realized the toe-in design as I just assumed the rudders were parallel to each other. I have a 40 Cabo convertible now, however I had a 1996 35 Cabo previous and had the rudders removed and the glands reworked. Looking at the attached photo they appear to be set up with some toe-in.

    Attached Files:

    Last edited by a moderator: Aug 14, 2022
  13. Capt J

    Capt J Senior Member

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    Yes, you need toe in