Designing a new type of fishing boat .

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

  1. helen07
    Joined: Sep 2009
    Posts: 38
    Likes: 2, Points: 0, Legacy Rep: 60
    Location: UK

    helen07 Junior Member

    I'm thinking a steel hull designed to cut water from stem to prop then a flat bottom with fins at the outer edge starting above the prop to the transom stern (speed and stability) . A forward wheelhouse and accomadation and in a huge jump from the conventional placing a lifting gantry on the stern thus keeping all the net and dredge activity at the stern of the vessel and hopefully lowering the height needed to bring catch aboard .

    What do those who know think of these dimensions for a displacement hull on a fishing trawler ?
    Length 15 metres
    Width 7.5 metres
    Draft 2.5 metres
    I'm assuming this will give for a very slow boat unless a very thirsty engine is used ?

    It is common belief among fishermen that lifting poles should always be placed a half length of the boat , i find this difficult to believe as the width of a boat is usually approx one third of it's overall length so why can't poles be placed wherever , if it can lift that weight on it's side rail without capsizing then why would lifting the same weight say on the stern for example cause any problems as it would have 3 times the counter balance . Your thoughts on this please .

    An earlier convo on here got me thinking about the so called rule beater fishing boats design and having brought myself up to date with the latest fishing rules i have been designing a hyperthetical fishing boat that is built to adhere to the rules while offering a level of safety and comfort only currently available from catamarans . Catamarans have no fish hold worth mentioning so are not appropriate .

    Emptying nets inside the stern rail should in my mind prolong the life expectancy of a trawler considerably as several tons slamming into the midsection of a hull inevitable takes it's toll on any boat regardless of it's build .

    I am without qualification and so i will be grateful for any criticism also , though it's very early days , my final drawings might one day end up at a shipyard as i have family still at sea .
     
    1 person likes this.
  2. helen07
    Joined: Sep 2009
    Posts: 38
    Likes: 2, Points: 0, Legacy Rep: 60
    Location: UK

    helen07 Junior Member

    has this posted ?
     
  3. apex1

    apex1 Guest

    Yeah has helen!
    Now lets see what the NA community has to say.
    Have some points for your effort and the unusual care you take for the improvement of your husbands and his collegues working conditions.

    Regards
    Richard
     
  4. gonzo
    Joined: Aug 2002
    Posts: 13,950
    Likes: 486, Points: 93, Legacy Rep: 2031
    Location: Milwaukee, WI

    gonzo Senior Member

    My thoughts are that you haven't been around fishermen too much. The dimensions don't mean too much. Can you make a rough drawing? What are lifting poles. Trawlers normally bring the net up the stern ramp. What do you want to change?
     
    Last edited: Oct 28, 2009
  5. helen07
    Joined: Sep 2009
    Posts: 38
    Likes: 2, Points: 0, Legacy Rep: 60
    Location: UK

    helen07 Junior Member

    Reply

    I'm writing for my partner Gonzo who fished for many years and he say's your comment's are to be expected because he did not point out that his aim is scallop and queenie shellfish , dredge and net .
    Did you ever see a UK trawler haul dredgers at the stern ? Americans do it and current rules mean the max spread of dregde gear allowed inside the 3 mile is 7.5metres , at present boats use 2 tow bars with 5 dredges each and haul them up each the side of the boat .
    This means towing a long and short wire to stop gear fouling upon itself . The negative effect of this is that the long dredges cover the same ground as the short and so catch maybe 50% less . A ten dredge tow bar should improve catch by 25% but most boats small enough to fish inside the 3 mile limit could not possibly work a 10 dredge bar .
    To bring the dredgers aboard on the stern it would be neccesary to lift from a point maybe 3.5 or 4 metres above the stern .
    At present he is having difficulty working out exactly how to set up the net gear so it need not be removed while dredging and visa versa .
     
  6. Ad Hoc
    Joined: Oct 2008
    Posts: 6,280
    Likes: 450, Points: 83, Legacy Rep: 2488
    Location: Japan

    Ad Hoc Naval Architect

    Helen

    I don't design fishing boats, but other commercial vessels: passenger, crew, patrol etc. However, Your design will be driven by:

    1) Regulations to satisfy
    2) The max. distance you want to be from shore
    3) The max payload you want
    4) The max speed/range you want
    5) Deck area/storage.
    6) Method of retrieval of nets, just one, or more etc?
    and of course
    7) Cost

    Once you have formulated those in your mind, then the design process can begin. Until then, one is just going around in hypothetical circles.

    You shouldn't discount catamarans too. They are really becoming vogue now. SouthBoats in Cowes on the IoW produce some excellent examples of this.
     
  7. helen07
    Joined: Sep 2009
    Posts: 38
    Likes: 2, Points: 0, Legacy Rep: 60
    Location: UK

    helen07 Junior Member

    An off the peg vessel can be bought new for between 250 - 350k , the changes i have in mind do not interfere with regs . A lower centre of gravity can only improve stability . Rigging is not a problem as such but ideally it would be a simple case of unshackling the dredge bar and hooking up a net , no shore time required . Cats are great but no storage below decks means a run ashore on a daily basis . Distance from shore is limited only by fair weather conditions and the need to land fish while it's still fresh .

    P.S Gemini workboats are by far and away the UK's number one cat builders .
     
  8. baeckmo
    Joined: Jun 2009
    Posts: 1,136
    Likes: 122, Points: 63, Legacy Rep: 1165
    Location: Sweden

    baeckmo Hydrodynamics

    There is one point on towing operation that has a great influence on hull proportions: the "wet end" of the gear, be it a trawl, dredge or else, should move at constant speed. This means that the propeller must work as deeply as possible, where the orbiting velocities of the wave system are low, and the hull must be designed with low pitching and swaying in mind!

    The classical "double-enders", designed with no (or little) regard of political catch rules, but to be good sea-boats and good working platforms, with smooth waterlines were good in these respects. Some of the newer rulecheaters that were designed for maximum displacement on a limited wl length were below expected catching capacity due to a combination of high pitching amplitudes and speed variations when the bluff stem was diving into a wave. In order to compensate for this, the vessels had to be operated with heavy ballast to increase weight.

    The remaining loading capacity was thus reduced, and the result was increased fuel consumption and lower safety margins. In the end, the balance between catch value and costs turned out to be lower than expected!

    This also means that the towing point should be placed as close to the vessels virtual center of movement as possible, in low speeds this is often close to the center of mass. When the heck gantry was introduced on some of the 100 - 130 foot vessels here, the increased movements of the towing point forced the introduction of load sensing hydraulics in the winch power systems.

    My point here is that a fishing vessel has to be a balanced design. There are so many conflicting requirements. Every time you let one requirement dominate your design, all other qualities will suffer!!
     
    1 person likes this.
  9. gonzo
    Joined: Aug 2002
    Posts: 13,950
    Likes: 486, Points: 93, Legacy Rep: 2031
    Location: Milwaukee, WI

    gonzo Senior Member

    My experience working in trawlers with stern doors, is that when you haul in, the boat weather cocks and the stern sinks with the weight. They have to be designed with extra floatation aft. I think they are several advantages to a stern trawler, but in rough weather, they ship seas over the stern very often.
     
  10. Guillermo
    Joined: Mar 2005
    Posts: 3,644
    Likes: 185, Points: 63, Legacy Rep: 2247
    Location: Pontevedra, Spain

    Guillermo Ingeniero Naval

    Worrying for a monohull. Wide beam will induce very high accelerations to work safely on deck.

    Cheers.
     
  11. baeckmo
    Joined: Jun 2009
    Posts: 1,136
    Likes: 122, Points: 63, Legacy Rep: 1165
    Location: Sweden

    baeckmo Hydrodynamics

    There were more of us sharing that experience Gonzo, and it was no pleasure!

    Those trawlers in Sweden that were rebuilt from side trawling to aft gantry's (including side-to-side traverse for towing points), still take the catch onboard midships. The same goes for many of the newly designed boats here. Main reason beeing just the working conditions in the critical moments when you have a freely swinging load to control. It's easier to design a ships side to take the pounding than to avoid crew accidents on a violently heaving aft deck, green with water.

    In this perspective, the British tradition of having the "poles" (as you call them, Helen) amidships, is simply clever engineering, regarding the circumstances. The heck towing arrangement, on the contrary, is depending on "brute force" and high fuel consumption/low fuel prices in order to be competitive.

    Manual work must be placed where ship movements are the lowest in order to reduce accident risks and physical stress on the crew. There are studies showing the impact of ship layout in these respects. The difference for the crew can be quite dramatic; in one of the tests regarding catamarans for coastal fishing (nets and traps), the oxygen consumption (a direct measure of man's work load) was reduced by 20 %, at the same time as the guys had the "catch round" done in shorter time than with the original layout (same weather conditions, same amount of gear to haul)!

    So, if you want your "quality time" together with your husband improved, you also have to care about his working conditions onboard when you are contemplating the vessel design! It's a bold undertaking and you have a long journey to go, but I really wish you good luck!!

    BTW, the overall dimensions you mention are more suitable for a catamaran. I strongly agree with Guillermo's comment here. I think you must sit down with your ol'man and figure out what kind of storage capacity (volume and weight) you need for a "normal" catch, because it has a major impact on the hull design. Before you have figures on this, you are stuck with a lot of guesses, and any progress in the design spiral is impossible!
     
    Last edited: Nov 1, 2009
  12. helen07
    Joined: Sep 2009
    Posts: 38
    Likes: 2, Points: 0, Legacy Rep: 60
    Location: UK

    helen07 Junior Member

    Gonzo it seem's to me that you are the only one here who knows that fishermen consider just being able to keep both feet planted firmly on the deck "comfort" . Hauling the cod end of a 20 fathom queenie net on a stern A frame seems to me of little consequence (dipping the rail is part of the job) . However i would appreciate your thoughts on lifting a 7.5 metre 10 dredge bar weighing maybe 2.5 ton (when full) on a 3 metre high stern A frame . Try to imagine the stern ramp being 7.5 metre wide with a stop each side to prevent the gear from swinging . My only concern is that without trying it there is no way to know how lively a 15m boat would become with 2.5 ton raised maybe 3m above the stern rail . If it can be lifted on the side rail without trouble then i can't see how this would be a problem but i am not a naval architect and was hoping someone might offer an educated opinion that might support or deny the unqualified theory .

    Architects the world over completely ignore the customers wishes whenever possible in order to promote their own designs , in order to prevent this i would submit drawings as specific as possible to an architect so he could test the design for faults and it would prove an expensive mistake to submit a design that works only in theory .

    Sorry beakmo you posted while i was writing this and thank you for your comments .
     
  13. Ad Hoc
    Joined: Oct 2008
    Posts: 6,280
    Likes: 450, Points: 83, Legacy Rep: 2488
    Location: Japan

    Ad Hoc Naval Architect

    helen

    Architects the world over completely ignore the customers wishes whenever possible in order to promote their own designs

    That is a very broad brush you're using!

    A professional naval architect only gives what the customer can afford. That is what the specification and general arrangement are for...it establishes the design intent and the cost, up front. If these are not fixed prior to placing a contract.....then you are at the mercy of everyone.
     
  14. baeckmo
    Joined: Jun 2009
    Posts: 1,136
    Likes: 122, Points: 63, Legacy Rep: 1165
    Location: Sweden

    baeckmo Hydrodynamics

    Connecting to notes on dimensions above, I would give two examples here, just to show that you cannot select main dimensions at random.

    The first is a steel trawler, L 16.8 m, B 5.0 m, D 3.3 m. She has a fully laden displacement of 75 tons (metric) and engine power is 475 hp. This boat has been one of the most successful vessels for her size, fishing in very rough weather conditions. One of her real virtues is the constant speed towing performance, due to her deep draft. The propeller center is 2.7 m down and on one extreme occasion she was carrying a catch of 450 standard 40 kg boxes, including ice (but then she was full up to the coaming).

    The second example was designed to "do the same job", but fit within the 15 m regulation, so she got a wider beam, close to 6 m, and a different (more boxlike) midsection and less draft. Her prop center is nearly one meter closer to the surface.

    Looking at them at quayside there is not much difference, the deck layout very similar (I'll post pic's sooner, its too dark now to take any), shelterdecked with wheelhouse forward and fishing over the transom. But the second has far less trawling capacity due to the shoal operation of the prop and the shape of the hull making it much more sensitive to the wave forces. Her heaving motions aft at the towing points is much more violent than the first one. Both when using bottom trawl and pelagic trawl, the doors are jumping forwards, making the trawl mouth opening and collapsing all the time.

    So, if this is aiming to something real i the future, my advice is that you first go back to Ad Hoc's list of the 7 items that "drive" the design. Your husband is the expert on how to handle the gear he is using, so the two of you should focus on how to use a deck area of ~15 x 5 meters for the handling/stowing of gear, crew and catch. When these things are condensating to some final idea, THEN it is time to seek qualified advice regarding hull shape. Any other strategy will result in backwards engineering and that is really wasting your time!
     

  15. helen07
    Joined: Sep 2009
    Posts: 38
    Likes: 2, Points: 0, Legacy Rep: 60
    Location: UK

    helen07 Junior Member

    I have no basis on which to judge naval architects for or against , but i am an avid viewer of property tv programs and it seems to me every time an architect is given any leeway at all on the design say of a 3 bedroom house the customers ends up with a glass staircase or some other stupid feature that's worth more than the whole rest of the otherwise perfectly average house .
     
Loading...
Forum posts represent the experience, opinion, and view of individual users. Boat Design Net does not necessarily endorse nor share the view of each individual post.
When making potentially dangerous or financial decisions, always employ and consult appropriate professionals. Your circumstances or experience may be different.