Conversion of shrimp trawler

Discussion in 'Motorsailers' started by UKSailor, Mar 14, 2011.

  1. UKSailor
    Joined: Mar 2011
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    UKSailor Junior Member

    remember, according to the laws of physics/science...

    It is impossible for a bumble bee to fly....its body is too fat, because its wings are too small...


  2. Sand crab
    Joined: Feb 2011
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    Location: Montana

    Sand crab Junior Member


    Bumblebees can fly but pigs can't. Bumblebees fly because of the ability to generate lift through a lot of horsepower or beepower. To fly, a 1000 lb pig would require a humongous amounts of bee power. Whenever you see a sailboat you immediately notice that the sails are larger than the boat appears and that is because that size is needed to generate horsepower. Use a general rule of thumb of about 5 sq. meter of sail per ton to get you anywhere. More or less. So on a hundred ton vessel thats 500 sq. meters or about 5000 sq. ft. of sail area. Why is it all those pictures just show the trawler standing still? Lets see it moving. I'll bet that trawler wins first place for the slowest sailboat ever. If you want to do the charter sightseeing deal then fine. But if you want to sail then get a sailboat or a motorsailer. That boat is a pig and pigs can't fly. BOB
    Last edited: Mar 23, 2011
  3. YuriB
    Joined: May 2008
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    YuriB Junior Member

    Sand crab, your cat should be a racing monohull yacht with this SA/D, according to the US Sailor calculator ( There is something wrong if the multihull of that SA/D only can make 15 knots.

    270-300sq. meters would be enough for this hull, i guess. This sail area is possible with gaff sails.
  4. Sand crab
    Joined: Feb 2011
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    Location: Montana

    Sand crab Junior Member


    Yuri, About 50% of all cats made go directly charter and the charterers are interested in a lot volume for accomodations. Most of these charter cats have an HFR (hull fineness ratio) of about 8.5. It is because of the realitively fat hulls and other issues that the cats can't obtain higher sustained speeds even though their SA/D is about 22 or so. They were built for comfort not for speed. There are numerous smaller manufacturers that make slimmer hulls and these cats are faster. 20 knots is damn fast even in a cat.
    I did say earlier that I only know cats so I now realize that my sail calculations were a bit high for a mono. But looking at the specs for the Wanderbird trawler we see that is 90' long and a 120 tons. I took out my ruler and I came out with a total sail area of about 100 to 150 sq. sq. meters. That trawler is down to about 1 meter of sail area per ton. Clearly it is way under canvassed. By your estimation for a 100 ton vessel Wanderbird at 120 tons is lacking at least 75% of the sail power it should have. We still have the poor hull shape for sailing so even if the sail area were increased we would have a boat that couldn't go to windward. The OP was under the false impression that the sails on Wanderbird would provide some benefit. I beleive that they are only for show. BOB
    Last edited: Mar 24, 2011
  5. YuriB
    Joined: May 2008
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    YuriB Junior Member

    What Wanderbird is currently has, is probably even less than 150sq.meters, and the sails there are only for entertaining purpose.
    For any other generic hull, 90ft long, 270-300 sq. meters is not a problem. At least an example, old style cutters had enormously long bowsprits with up to 5 triangle sails sitting on it. They were fastest ships for that times.
  6. viking north
    Joined: Dec 2010
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    Location: Newfoundland & Nova Scotia

    viking north VINLAND

    Having some 30yrs. experience in hull conversions (non sail into sail) my starting out knowledge prepared me for realistic performances of the converted vessels. To be fair I started with hulls that had sailing hull shapes to begin with but even with this favourable factor, reality over rides vision. The reality is think MOTORSAILER and working from that mindset engineer to make it as good a sailer as pratically possible.(fuel savings along with customer appeal) There is such a conversion being used here in Halifax harbour as a very successful summer tourist trap. No negative intended as it is performong it's planned usage in keeping the customer satisfied in vision as well as excellent musical and story telling features. (most people don't know the difference, it's the overall experience of the package that counts). Can your conversion be a success, yes, but only if you start out with the right mindset--Think MOTORSAILER. On that note don't compare your proposed project being financially feasible because Greenpeace is doing it. They have an unlimited supply of cash input.---Geo

    A yacht is not defined by the vessel but by the care and love of her owner
  7. keysdisease
    Joined: Mar 2006
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    Location: South Florida USA

    keysdisease Senior Member

    I have actually seen a couple of these conversions and been aboard one. Here in South Florida in the Keys 20 years ago there was a avery active shrimp industry, I know these boats well.

    There were a lot of 85ft ers made in fiberglass by St Augustine Trawlers that I think would be the best candidates for conversion. Larger boats were steel and there are plenty of wood ones but :eek:

    They can be quite roomy and I think convert quite well if you don't try and make one into something she ain't.

    Forget the sails, period.

    Forget adding to the deck house. if you want more accomodation there is awesome cubic in the hull where the holds were.

    Displacement hull, keep the power or similar HP, don't downsize at all or only a little.

    I would think about opening up the deck house as a pilothouse / galley / salon and make new cabins below keeping a pilot berth in the pilot house.

  8. whitepointer23

    whitepointer23 Previous Member

    there are lots of converted fishing boats here in australia, some look original, they have the galley in the wheelhouse and convert the holds into accomodation, don't know how they get rid of the fish smell but they do. these are the best looking conversions, the ones with extended wheel houses usually look wrong, there are some that look alright. i would prefer a rear wheel house than a front one anyday. much more comfortable at sea.

  9. YuriB
    Joined: May 2008
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    YuriB Junior Member

    On the photo is a conversion of the wooden Swedish trawler, which has buidge keel made of concrete and 2 masts with gaff sails.
    Length: 20.7 meters (27m with bowsprit)
    Beam: 5.24 meters
    Draft: 2.70 meters
    Displacement: 75 tonnes
    Tonnage: 44 GT, 13 NT
    Rig: 24 m main mast, 18 m mizzen. Sail area is 270 m2.

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