Trawler-->Mast & Boom...Sizing

Discussion in 'Stability' started by oldsalt1, Dec 7, 2007.

  1. oldsalt1
    Joined: Dec 2007
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    Location: Boston, MA

    oldsalt1 Junior Member

    I seek advice on whether a large displacement steel vessel requires a steady sail. If so, how does one determine the size of Mast, Boom, and sail area.

    The boat is a steel trawler, 50 feet LOA, 15 ft. Beam, 77,000 NET

    Presently, the trawler has a steel mast and boom that is not working with inoperable hardware. I have found differing opinions as to simply removing or keeping it, making it functional and fitting a sail.

    It takes up a lot of area on the aft deck...but removing something that could be used to control roll in heavy seas may be dumb thing to do. Then again, perhaps replacing something that is 25 years old and steel with lightweight aluminum fitted with a steady sail may be an alternative. Perhaps steel is better. I am not sure with the weight of the mast and boom having any effect on a 40 ton vessel.

    Thus, this OldSalt is lost and confused. I would appreciate any advice you can offer. The boat is in Ft. Pierce, FL.

    Thanks very much!!
     
  2. MikeJohns
    Joined: Aug 2004
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    Location: Australia

    MikeJohns Senior Member

    The mast gives you a lightening cone of protection, a handy mount for a derrick crane and a nice steadying sail.

    I just checked on a stability calc for a similar vessel. The mast was removed and it was around 300kg (660 lb) the centre of gravity of the vessel was consequently lowered 3 inches. Anti roll keels were added to make up for the loss of the steadying sail and decrease in roll inertia. The operators reported the vessel satsfactory but with a more noticably energetic roll.
    This would be from the decrease of roll inertia.
     
  3. oldsalt1
    Joined: Dec 2007
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    Location: Boston, MA

    oldsalt1 Junior Member

    Mike,

    The former owner never had a steadying sail. Without the sail, does the weight of the mast and boom serve to flatten the roll in heavy seas so that the motion is less abrupt?

    I always thought that lowering CG was a good thing which added to the vessels overall postive stability.

    I have also heard that a de-masted boat suffers more roll than one with masts absent sail.

    I am curious, what are anti-roll keels and is it a big project to retrofit to a vessel with a single keel? I have heard of the expensive Naiad Stabilizers which seem to work if one has 40k to invest.

    I have had some write me at my email and state take down the mast, gain some room. Then, the other school of thought is to keep it in place, fit new hardware, and have a sail made.

    I must admit, I thought the responses would surely help me decide. Now, I am actually more confused as to what to do.

    My cruising will be extensive offshore, and stability, seaworthyness are paramount....what a dilemma!!!

    Please let me about the anti roll keels. By the way, where are you located? I have an existing crane on the vessel for transferring loads etc.
     

  4. MikeJohns
    Joined: Aug 2004
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    Location: Australia

    MikeJohns Senior Member

    Ballasted sailing vessels suffer considerably with the loss of their masts, far more than a fishing boat will.

    Anti-roll keels are simply a small bilge keel, they are very common and are often (and easiliy) added to work-boats and military vessels after they enter service to reduce rolling. Particularly troublesome vessels get a V shaped damper, while usually it is sufficient to simply add a long narrow plate normal to the hull surface.


    Roll reduction strategies work in varying degrees with different frequencies and direction of wave train. In instances of beam rolling close to the natural frequency of the vessel mass aloft may actually increase the angle rolled to. In a choppy confused sea the mast along with all the other mass aboard will iron out some of the jerkiness.

    Removing the mast may make good sense if you are fitting deck gear. However you will not endanger your vessel if you do remove it and you may find the vessel is comfortable enough without any other modifications.

    I cannot be any more specific but I and other professionals in the forum can probably answer specific questions if you give sufficient information.

    I have reciprocal licensing with the US but I am in Hobart !
     
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