Need some advice on hull action in following seas

Discussion in 'Boat Design' started by 5akman, Sep 1, 2012.

  1. Mr Efficiency
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    Mr Efficiency Senior Member

    Is there a downside to that idea ? More drag ? :confused:
     
  2. 5akman
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    5akman Junior Member

    Great stuff guys! Yes, the engine is under the cabin sole with the tranny right below the cabin bulkhead. The boat does have a very tall mast with lots of bracing along with the stabilizer poles (not all shown in the pics). A fellow fisherman thought that getting rid of the mast/stabilizers and going with a smaller radar "arch" might be a good way to get rid of weight way up high and may counter the need for the stabilizers. Water ballast aft would be a fairly easy thing to add and a current owner of this make/model said it rides much better with a load of salmon on board.
     
  3. tom28571
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    tom28571 Senior Member

    Of course there is bound to be some added drag but, on boats like these, it will never be noticed. What will be noticed is the much better steering control.
     
  4. 5akman
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    5akman Junior Member

    Any idea what issue of PB had the article on the rudder?
     
  5. tom28571
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    tom28571 Senior Member

    It was a multi-part series starting in Dec 05
     
  6. 5akman
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    5akman Junior Member

    Bummer, I just passed along many years of back issues of PB. I'll have to see if they are available online.
     
  7. Frosty

    Frosty Previous Member

    Welding a length of angle iron to the trailing edge of the rudder can improve performance if you have a real crap flat plate rudder.

    Slow rudders need some shape to it. The angle iron imitates that.
     
  8. midnitmike
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    midnitmike Senior Member

    Spray Rails

    Although you've already been given some excellent advice I have a slightly different approach to the problem. For many years I've advocated the use of enlarged spray rails to address many of the problems inherent in some hull designs when faced with the extreme conditions found in our local. Snowball hulls are by design probably one of the best examples of how not to build a slow, heavy fishing boat. In heavy following seas that sharp bow will dig into the wave in front and provide a pivot point upon which the stern can rotate around. Even if the builder goes to extremes to keep the boat light and fast (we have two in our fleet) they can and will broach under the right conditions. My solution has been to build a large spray rail to counter these affects. They not only lift the bow out of the oncoming wave, but enhance the overall stability of the boat both while running and at rest. Once installed you'll be able to remove the old stabilizers and eliminate the associated rigging. I've done two or three Snowballs and the owners absolutely loved the way the boat handle after wards. Here are a couple of pics of the last boat I outfitted with my rail system...it's not a Snowball, but the hull is rather similar. The one significant difference between this rail and one I would build for a Snowball is the I would extend the rail all the way forward to within say two or three inches of the bow. I should note that each rail I've created is designed specifically for that boat, and that boat alone. Since no two are exactly alike in terms of power, weight, and handling I've always found it valuable to take a test ride before I begin the build. This helps me visualize what I want the hull to do as I'm shaping the rail into it's final form.

    Mike
     

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  9. 5akman
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    5akman Junior Member

    Mike,
    How are these different than rolling chocks?

    I could do something like this myself as I used to build glass ocean going sailboats. I'm curious as to what the spray rail is constructed of (material and dims) and what would be the layup schedule on this. I really like the idea of getting the stabilizers off the top of the boat and the possibility of "bettering" the handling of this boat. Since I haul my boat out with a trailer and not travel lift with straps, these rails could work real nice.
     
  10. Mr Efficiency
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    Mr Efficiency Senior Member

    The striking thing about these gillnetter boats is the forward position of the skeg, prop, and rudder. Presumably so the nets never foul on them. Has to be a big part of the problem down sea.
     
  11. midnitmike
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    midnitmike Senior Member

    AK,
    From what little I know of rolling chocks they're mounted under the hull.

    These "Spray rails" are positioned on the chine. This allows the spray rail to serve multiple roles being at the same time a spray rail, rolling chock, and providing dynamic lift to the hull while underway. Boats average a knot and a half increase at cruise...have a very different feel while underway...are extraordinarily stable at rest...and if done right should virually eliminate broaching. If that sounds too good to be true it's only because I haven't noticed or been told of any adverse affects in almost 20 years.

    They have a foam core which makes it easier for me to shape by hand. My standard lay-up is 1.5 oz matte, and two layers of 1708 biaxle. If you have any more questions I'll be happy to answer them via email.

    MM

    midnitmike <at> hotmail
     
  12. midnitmike
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    midnitmike Senior Member

    I'd be interested to know what makes you think the position of the underwater gear has any affect on the hull broaching in a following sea. Just curious?

    MM
     
  13. Mr Efficiency
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    Mr Efficiency Senior Member

    Simply a matter of the centre of lateral resistance being further forward than it might otherwise be. That increases the length of the lever arm between the centre of gravity and the CLR, making broaching more likely.
     
  14. tom28571
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    tom28571 Senior Member

    Well yes, but the rudder and prop being so far forward greatly decreases the steering moment. Both effects increase broaching tendencies but lack of steering control may be the worst offender.
     

  15. 5akman
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    5akman Junior Member

    I hear the advice about being attentive at the helm. What about however, something focusing on the narrow entry of this hull. Would a bulb bow addition do anything for this situation?
     
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