Will a full length rail help?

Discussion in 'Stability' started by Tom Stewart, Sep 26, 2016.

  1. Tom Stewart
    Joined: Sep 2016
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    Location: Houston TX

    Tom Stewart Junior Member

    I have two issues.
    1. Excessive spray over bow.
    2. Vessel configuration makes it a bear in a larger following sea.

    Details:
    Hull: 1983 Henriques Maine Coaster, semi displacement hull, single volvo tamd 63 (318 hp). Large keel.
    15 knot boat at 2100rpm.

    The vessel has a very sharp entry, large keel and relatively flat stern. In anything over 3' sea conditions in the sloppy Gulf of Mexico, the bow catches the wave in front and the stern is caught by the wave behind and pushes it to one side.

    I was thinking about adding a spray rail to the front and saw some posts on the Downeast forum about a full length rail.

    Would I benefit in a following sea by adding a full length rail?

    Where could I find information about placement of the rail? My boat yard is not capable of this project.

    Any suggestions/data would be appreciated.

    Thanks
    Tom
     
  2. gonzo
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    gonzo Senior Member

    I've installed spray rails in several Lobster boat type hulls. The forward section, about 1/3 of the length should taper gently to the static waterline. The rest of the rail follows the waterline to the stern. I install the rails about where the sides start turning and the tangent of the curve is about 60 degrees from vertical. The bottom of the rails is perpendicular to the hull.
     
  3. TANSL
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    TANSL Senior Member

    All that is really interesting but did it serve for something ?. How improved performances of the boats?
     
  4. Tom Stewart
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    Tom Stewart Junior Member

    Thanks Gonzo...based upon your experience, how will that affect the ride?

    Thanks again,
    ts
     
  5. gonzo
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    gonzo Senior Member

    The ride was much drier. Also, the hull got more lift and increase maximum speed about 20%. It also slowed down the rolling a bit. These boats were longlining off the North Carolina coast and a bit of extra speed meant more fishing time.
     
  6. TANSL
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    TANSL Senior Member

    Congratulations as such a simple work has provided impressive results. For a fishing boat, a 20% increase in the maximum speed (say 3 or 4 knots) is amazing.
     
  7. Tom Stewart
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    Tom Stewart Junior Member

    I going to order the rail and install over the winter....will let you guys know what I experience.

    Thanks again,
    ts
     
  8. TANSL
    Joined: Sep 2011
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    TANSL Senior Member

    I guess the width of the rail can be very important, decisive for a good result. Gonzo, with extensive experience in this calculation, could give information in this regard.
    And yes Tom please keep us informed.
     
  9. JSL
    Joined: Nov 2012
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    JSL Senior Member

    By your description you have the classic 'double wedge' hull form - fine deep bow/forefoot with broad flat (shallow) stern. This is a classic form for 'broaching to', a potentially dangerous characteristic where the boat wants to swaps ends or 'spin out' : running in a following or quartering sea can be a real challenge. I doubt an appendage like a rail would make any difference (good or bad) and a deeper skeg/keel might only make it worse. In fact, on 2 'nasty' boats, we cut the skeg in half lengthwise (to 50% deoth) and it made a significant improvement. Based on several 'experiences' with these boat types about the only improvement you can make is to improve the rudder/steering so you can control the boat when she starts to 'go'.
     
  10. Mr Efficiency
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    Mr Efficiency Senior Member

    Haha, it sounds as though you are a little sceptical, and I have to agree it would be a remarkable improvement. The assistance might come from a reduction in wetted area, but realistically there is not much dynamic lift generated at a miserable 15 knots from a spray rail on a relatively heavy boat. However, the issue here is broaching, and I don't see a spray rail changing much in that regard.
     
  11. Mr Efficiency
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    Mr Efficiency Senior Member

  12. Mr Efficiency
    Joined: Oct 2010
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    Mr Efficiency Senior Member

    I'd be interested in hearing what happens when the bow slices into the wave ahead, in a following sea condition, Is there any noticeable "bog", a washing off of speed like an application of brakes ? If so, that in itself worsens broaching, as it acts similarly to a jack-knifing effect, and also keep the bow buried longer allowing the broach to develop. If not, there is probably scope to build extra buoyancy into the bow above the waterline, reducing the bow dip, though that is a major project to execute properly.
     
  13. daiquiri
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    daiquiri Engineering and Design

    I agree with the above comments.
     
  14. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    Welcome to the forum.

    Spray rails are as the name suggests and knock down spray. They will not do anything for the boat's handling, particularly at these speeds. Lift strakes do affect handling, but again, not much at these speeds.

    Simply put, your hull form is the problem and why it's acting the way it does in a following sea. This is a common trait and not easily fixed without major surgery. The bows on these boats tend to "root" around in certain sea states, which is another issue. It's all because of the shapes used, which are likely quite old (pre '63 series testing) and nothing short of a different hull will truly fix these issues.

    With a follow sea, skipper awareness and bearing off a bit, sort of like jibing the boat, so the corner of the transom can meet the sea, seems the best approuch. With a rooting bow, trim changes can help is the forefoot isn't too deep. If the forefoot is deep, sometimes, no trim adjustment will help, in certain sea state condisions.

    I know this isn't what you hoped to hear, but it is a common set of concerns with this type of hull. Can you post a picture?

    [​IMG]

    I'll assume this is the boat you have? These are fairly well regarded, but still suffer from the problems you've discovered. I don't know why old school fishermen still insist on this hull form, but in some area of the country, these are highly prised, in spite of the handling issues they're well known to have, especially the single screw boats. If the boat is powered up to full plane mode, she's a lot better, as you can "carry" the bow so it doesn't root, but following seas are still an issue. In a nutshell, we've evolved past this set of hull shapes and have much better ones now, but some just refuse to "let go" I guess.
     

  15. Alumination
    Joined: Oct 2013
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    Alumination Junior Member

    What has changed with modern hull designs that correct this behavior?

    Are there any hull modifications which can realistically be done to improve his existing hull?
     
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