Designing a new type of fishing boat .

Discussion in 'Stability' started by helen07, Oct 28, 2009.

  1. Jenny Giles
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    Jenny Giles Perpetual Student

    Using TV shows as a measure of what happens in reality is probably not the wisest course. It might come as a shock, but some of the actors on "Friends" don't actually like each other.
     
  2. helen07
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    helen07 Junior Member

    Thank you Jenny i don't know what i'd do without your unprecedented intelligence .

    I would be very grateful for those pics baeckmo , I am aware the boat envisioned takes huge liberties with possibilities , not least of which is it's virtually being half as wide as it is long . This is obviously not the norm and so i am actually seeking reasonable probabilities that would deny the pursuit of this line of thought forthwith .
     
  3. JRM
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    JRM Junior Member

    Hi Helen

    There is nothing wrong with your basic assumption that if you can lift the gear at the ship side, it can also be lifted at the stern (as far as ship stability and motions are concerned). That is of course why stern trawlers can work.

    I think the problem is that in this case it leads you to design a MONOhull (not a catamaran) with a WIDE stern. On a small boat, that means that the boat will be short and fat.

    1) The wide beam will make the boat "stiff" so that the boat will roll a lot worse than a normal boat. For example google Ramform + Banff + FPSO. That was a ship with a very wide stern that was used in the North Sea and had to be removed from service for modifications because she rolled too much. She was a far larger vessel than any fishing boat (admittedly her crew were not as tough as fishermen).

    2) the wide beam and short length are generally not a good idea. Ask your "other half" about the short "rule beater" fishing boats built in Scotland a few years ago. They were so short and fat (among other things) that they PITCHED when lying to a beam sea.

    3) if you have a wide boat, it is going to take more power to drive through the water than a narrower boat of the same length. That will cost more fuel.

    Some of the Dutch mussel dredgers are boats that are very shallow draft and wide (for working over shallow mussel beds), but I think even the Dutch will agree that they are not very good for open water work.

    The old English sailing trawlers were up to 80ft long and used to drag a beam trawl. The beam would be at least half the length of the boat and they heaved that up to the side of the boat every time they hauled. And they did most of that hauling with a manual capstan. And they boarded the cod end (OK I know its not a scallop dredge) without any poles at the ship side. They had a block and tackle hanging from the mast on the centreline of the boat.

    I think the basic problem with your idea is that it produces a monohull boat that is too wide - which has quite a few problems - as a few of the posters above also indicate.
     
  4. baeckmo
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    baeckmo Hydrodynamics

    I touched upon the proportions issue in a thread on cat's before. It has been shown that when rolling and pitching periods come too close (by shortening and widening hull dimensions), the ship will exhibit a very uncomfortable "corkscrewing" motion in a seaway; it "jerks" in an unpredictable way that makes it difficult to keep on your feet. It seems that our sensor system for balance cannot cope effectively with motion in double directions unless there is a distinguishable difference in period between the two. This comes equally bad in a monohull as in a cat. In addition to that comes the obvious drawback of increasing the required propulsion power. JRM is correctly pointing to similar examples here.

    Sorry, but you'll have to wait for pic's until the guys are back in harbour on thursday or friday now.
     
  5. peter radclyffe
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    peter radclyffe Senior Member

    this is interesting, i recently priced up a new 14 mt wooden fishing boat, without fishing gear & yes, 350 k
    i guess you have looked at mcduffs site
     
  6. peter radclyffe
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    peter radclyffe Senior Member

    you may like to ask napier co arbroath, to price a design
     
  7. Jenny Giles
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    Jenny Giles Perpetual Student

    Sorry if you took my joke the the wrong way. I didn't mean to offend. It just seemed a bit odd to tar all architects, US or not, with the same brush.

    If you have ever watch the UK show Grand Designs you will have seen that "architect-free" designs can be way overblown too.
     
  8. helen07
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    helen07 Junior Member

    Thanks everybody we are now getting to the crux of the matter and Jenny i appreciate what your saying but some go forward with their eyes wide shut and others put to much trust in architects , my Grand design would begin life as a doll's house and then be handed to an architect whom would be asked to use his profesional judgement and skill to turn it into a reality . Words can be misleading but solid matter is impossible to ignore . A few quid for a model boat is nothing if it ensures the real equivalent meets every expectation .

    With regards to dimensions - unfortunately i'm in touch with my partner only trough txt at the mo but i asked what was the most comfortable boat he ever worked , it turns out it was a Dutch beamer 20m length - 6.5m beam - 2.5 draft , he said the test of a good boat is the Irish sea because being such a small stretch of water it gives a more violent motion , a boat doesn't so much rise and fall with the water like it does in the North sea , instead smaller waves slam into the boat .

    I've ruined this now because he want's to know what i'm up to , i was hoping to impress him with my ideas .

    Peter Radcliffe have you investigated the possibility of having your boat built in the Baltic states ? Latvia and the likes have huge shipyards and the average wage there is just £150 a month ! , I have discovered by accident while researching boats that many of the yards closer to the UK actually buy hulls built in the Baltic to increase their own profit margins . Of course steel and wood are very different and i would expect wood to cost considerably more in this day and age but i thought it might be worth mentioning ?
     
  9. Jenny Giles
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    Jenny Giles Perpetual Student

    My Grand Design is an underground house. If an architect dares to interfere, well, hey, I already have the hole dug, so watch it you bow-tied git! :)
     
  10. helen07
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    helen07 Junior Member

    I think maybe i've cracked it !

    Only the tow bar needs 7.5 metres deck space so dredgers can be emptied , so why not simply take a hull like the one pictured in the link below which is supposedly very fuel efficient (it's 15m L , 5m W ,and 2.7 draft) , then just create a 7.5 wide platform at deck height on the stern like a shelf ?

    http://www.fiskeskibe.dk/upfiles.aspx/91/5F20CB10C8D44AFBB2EC11A490C59E9C.JPG

    It seems viable to me but like i said i'm no expert so what do you all think of this ?
     
  11. JRM
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    JRM Junior Member

    Now you are talking Helen

    This way allows the underwater hull and most of the above water hull to be "normal" proportions, but wider higher up where you need to land the beam/dredges.

    Main thing you need to be careful about is the "outriggers" or "overhang" at the stern are not
    a) too close to the water
    b) too flat
    c) too flimsy

    .....or the sea will slam under them and cause a lot of problems you dont want

    However, it is an idea worth persisting with. Aircraft carriers have wide square bows (for launching aircraft) above a narrow fine bow, so the principle is used already (they manage to get their deck many metres above the sea and still have to be careful about wave slamming under their overhangs).

    If you go on with suggesting hull proportions, listen to what baeckmo says - he seems to know a lot about fishing boats as well as ship/boat hull design.

    By the way - in your previous post you referred to a Dutch BEAM trawler. Trust you know that (deep draft hull) is not the same as a Dutch MUSSEL dredger (shallow draft).
     
  12. helen07
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    helen07 Junior Member

    Thanks JRM , the dimensions of the Dutch beamer are given , apparently it was originally a mussel dredger , 2.5m seems pretty shallow for a 20m boat , a fluke design maybe ?
    I would guess the deck on the boat pictured would only be maybe half a metre above waterline and so the extensions would definitely dip in poor conditions . Obviously this would cause drag but if designed correctly (by a pro) might it not act as a sort of stabiliser by increasing displacement when the boat rolls , if you get what i mean ?
     
  13. peter radclyffe
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    peter radclyffe Senior Member

    thank you Helen, yes latvia is cheaper
    but i dont want a boat built
    i am an s. f. i .a builder
     
  14. helen07
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    helen07 Junior Member

    Peter i feel a little put out here because i can't offer any advice in return for the advice i get . I took a look at the boat you are building and was very impressed . It got me to thinking about a guy who many moons ago bought a similar looking boat and had another of his hair brained ideas for money making schemes .
    He dug a hole , covered the boat in vaseline , dropped it in the hole and concreted around it . He then removed the boat and used the impression as a fibreglass mould . He was a long long way away from being a perfectionist but he did manage to sell 2 copied hulls before he moved on to his next adventure , selling ice to eskimoes or something similar (he was that type of guy)
    I only mention this because it seems likely someone with your skills might very well make something of his idea if you were inclined to try .
     

  15. peter radclyffe
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    peter radclyffe Senior Member

    thanks Helen, what a great idea, good luck to him, i am not qualified to advise you on your design even tho ive studied all i can about them, i prefer a boat with deep draught tho i know this is not possible in most of our harbours, thinking more about latvia, i could not trust them to build it without me overseeing it or a surveyor, the logistics can work for someone who knows the terrain , & for all i know they build good boats, however, i cant gaurantee an unknown build, & you know how hard it is to get any boat right let alone a fishing boat with all its various systems, there is also the wolfson tank testing unit at southampton which you may know of
     
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