How much power

Discussion in 'Boat Design' started by standman, Apr 3, 2019.

  1. HJS
    Joined: Nov 2008
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    Location: 59 45 51 N 019 02 15 E

    HJS Member

    Length - width is of secondary importance. What is important is the relationship between total weight and length.

    JS

    Speed Power 08 05 22.JPG
     
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  2. standman
    Joined: Mar 2015
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    Location: Cebu

    standman Junior Member

    JS,
    Just visited your website and find your "interceptors" very interesting. When you came up with that must have been a eureka moment. I love your designs too, particularly Passagerarbåt Malaysia. That is exactly what I want to build. Anyway, I will get my shipment of core foam next week and will start build immediately.
     
  3. HJS
    Joined: Nov 2008
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    Location: 59 45 51 N 019 02 15 E

    HJS Member

    The boat you showed in your initial mail does not have much in common with, for example, my passenger boat to Malaysia. I hope your project is much more elaborate than what you initially show. Otherwise, you may experience great surprises.

    JS
     
  4. standman
    Joined: Mar 2015
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    Location: Cebu

    standman Junior Member

    Hi JS. Now you worry me, what sort of surprises should i anticipate? You have more pics of your Malaysia Passenger boat? I just want a simple single deck. My thinking is, long slender boat like canoes or those used in paddle boat races do not have elaborate hull shapes yet they perform very well. tried reading your long and shallow, but there is no English version and since it is in PDF form, google cant translate.
     
  5. Dejay
    Joined: Mar 2018
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    Location: Europe

    Dejay Senior Newbie

    That would spoil the surprise now, would it? :)

    There should be a gif for this. A compilation of failures due to boat design.

    What you want to do with the boat? What are your requirements? Where and when do you want to use it? What conditions? What is your experience with designing and building and driving boats?

    Do you have an hydrostatic analysis and an analysis for the stability? Is it going to roll over? Where is your center of gravity? What about structural design? Is it going to break apart? How did you determine how thick your fiberglass and foam core is? What are the exact measurements?

    I'm a newbie who wants to build a boat too so I'm just curious. Like probably everyone else here I love seeing people build boats!
    The more you share the more people can offer advice. And you'll definitely get the "why not buy used / modify / build from existing plans / rent a boat" suggestions. But those are good questions to ask yourself and have answers. And of course people love to critique and nitpick. But like they say, good advice isn't cheap so that's the price you pay hehe.

    As to your question, what surprises, that is a really hard question to answer. In some ways boat design seems like an unsolved problem. You need to put a lot of work into to answer it, either using expensive simulations and calculations or using experience. The former means paying a naval architect. Or learning a great many things and doing the work yourself. The latter means paying for an existing design and maybe modifying it. And even then the best thing you can hope for is a statistical change to not sink to the bottom of the ocean.

    Going in naive and just doing it isn't the worst thing, how else are you going to start such a daunting project? Just don't stay naive and weigh the risks and benefits. Your statement reads a bit like "The foam is coming and I'm gonna start building immediately and I can't hear you lalalalala". There is a joke in there about the sunken cost fallacy. Or maybe you're a pro and I'm way out of line. Anyways, enough rambling from me, but please share more, I'm also considering a trimaran.

    PS: I probably shouldn't mention this on this forum but I've been watching moving pictures on youtube to learn about boat design. I really like this guy. Reading books is more time effective though.
     
  6. standman
    Joined: Mar 2015
    Posts: 23
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    Location: Cebu

    standman Junior Member

    What you want to do with the boat? Passenger
    What are your requirements? 5000KGs minimum 18 knots - 20knots target
    Where and when do you want to use it? I live on an Island in the middle of the Philippines called Cebu. There are over 7,100 islands around and would like to take people around ECONOMICALLY
    What conditions? Since Cebu is in the middle of thousands of islands, rarely will waves exceed 3 ft.
    What is your experience with designing and building and driving boats? I just finished building a cruiser, i uploaded it to my album ( so you may see - ;) ). Also uploading on youtube video of seatrial.

    Do you have an hydrostatic analysis and an analysis for the stability? "That would spoil the surprise now, would it? :)"
    Is it going to roll over? I hope not
    Where is your center of gravity? towards the center :)
    What about structural design? Calculating based on material tensile strength x3
    Is it going to break apart? I hope not
    How did you determine how thick your fiberglass and foam core is? Calculating based on material tensile strength x3What are the exact measurements?58' length overall x 10' beam ( 48'x3' at waterline - mainhull)

    I'm a newbie who wants to build a boat too so I'm just curious. Like probably everyone else here I love seeing people build boats!
    The more you share the more people can offer advice. And you'll definitely get the "why not buy used / modify / build from existing plans / rent a boat" suggestions. But those are good questions to ask yourself and have answers. And of course people love to critique and nitpick. But like they say, good advice isn't cheap so that's the price you pay hehe.

    As to your question, what surprises, that is a really hard question to answer. In some ways boat design seems like an unsolved problem. You need to put a lot of work into to answer it, either using expensive simulations and calculations or using experience. The former means paying a naval architect. Or learning a great many things and doing the work yourself. The latter means paying for an existing design and maybe modifying it. And even then the best thing you can hope for is a statistical change to not sink to the bottom of the ocean.

    Going in naive and just doing it isn't the worst thing, how else are you going to start such a daunting project? Just don't stay naive and weigh the risks and benefits. Your statement reads a bit like "The foam is coming and I'm gonna start building immediately and I can't hear you lalalalala". There is a joke in there about the sunken cost fallacy. Or maybe you're a pro and I'm way out of line. Anyways, enough rambling from me, but please share more, I'm also considering a trimaran.

    PS: I probably shouldn't mention this on this forum but I've been watching moving pictures on youtube to learn about boat design. I really like this guy. Reading books is more time effective though.[/QUOTE]
     
  7. BlueBell
    Joined: May 2017
    Posts: 585
    Likes: 53, Points: 28
    Location: Victoria BC Canada

    BlueBell Ahhhhh...

    OMG, a match made in heaven you two are.

    I am building a similar boat that has an awful lot in common with the pictured stabilized monohull.

    30' LOA

    600 pounds racing

    kite powered

    WTF is the video all about? Doesn't look like a long skinny boat to me...
     
  8. standman
    Joined: Mar 2015
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    Location: Cebu

    standman Junior Member

    uhhhh... I WILL build a trimaran... meaning NOT YET !!! He asked if i have built a boat, so i am showing him...
     
  9. BlueBell
    Joined: May 2017
    Posts: 585
    Likes: 53, Points: 28
    Location: Victoria BC Canada

    BlueBell Ahhhhh...

    Ohhhhh, okay, sorry, what was I thinking.
    Carry-on.
     
  10. Ilan Voyager
    Joined: May 2004
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    Location: Cancun Mexico

    Ilan Voyager Senior Member

    The shown trimarans are flawed. Not wide enough, and the amas are too far aft and too long. Primitive hull shapes, too much surface and enormous windage. Not enough width. I'm afraid that these shapes on a 50 feet will give a slow terrifying ponder with problems of diagonal stability. That general silhouette is for a 125 meters ferry with dynamic stabilizers, not a simple small yacht.
    There are very successful motor trimarans in the small sizes, thus with similar hydrodynamic requirements to a 50 feet.
    Nigel Irens is the daddy of motor trimaran and has committed two very successful Ilan Voyager and Cable. Ilan Voyager is a simple 70 feet boat with only one Yanmar 4 cylinders of 235 HP. The displacement is around 7 tons. Top speed 28 knots. Able to cruise 2600 NM around the Britain at 21.5 knots mean speed. A simple calculation shows that a 21.5 knots mean speed Ilan Voyager was using around 150 HP.
    It will be more interesting to make a 60 feet as trimarans are rather crampy. Difficult to put nice amenities on these sizes. The ratio of the main hull is around 12 to 18 and the total width ratio somewhere 40-45 %, the displacement of the main hull is 90-95% of the total displacement.
    A thumb rule when motoring is to calculate the cruising speed with 75% of the nominal power in case of a 4S gas engine and 90% with a marine diesel.
    The choice of a trimaran of that size means simple accommodations for 2 or 3. That won't be a floating condo. Any attempt of a big amenities will give a slow unsafe thing named "Gone with the wind" because of the windage.
    Outboards are not the best choice for long range cruising trimarans because of several reasons. First the weight on the transom. Second outboards have inefficient small propellers. Third it has direct seawater cooling and this fact influences the efficiency of engine which runs too cool 50 C instead of the required 85 C of the coolant for the best combustion.
    For a 50 feet tri a motorization to examine is a Mercruiser 6 cylinders 220 HP fresh water cooling with a Bravo 3 transmission. That's pretty cheap.
    Links:

    ILAN - Nigel Irens Design http://www.nigelirens.com/boats/power-boats/ilan/


    [​IMG]

    Cable & Wireless Adventurer - Nigel Irens Design http://www.nigelirens.com/boats/power-boats/cable-and-wireless/

    [​IMG]

    As you can see the shapes have nothing similar with the other drawings of this thread.
    On a Ocean Eagle 43 have a look on the design, and have a close look on the amas bottom. You are looking at the work of experienced NA, top engineers and a first class shipyard. People who know their jobs...
    [​IMG]

    To show the seaworthiness of that shape in a state 5 sea.


    A link of a general exposition on motor trimarans rather in the ship size.
     
    Last edited: Apr 10, 2019
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  11. HJS
    Joined: Nov 2008
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    Location: 59 45 51 N 019 02 15 E

    HJS Member



    Before the final form was determined, many tests were done with the ama form and placement. It turned out that this was of utmost importance for total wave formation and drag. If ama placed closer to the center the transverse stability got to low, the ama ended up in the main hull trough.

    Air resistance cannot be lower than in this concept. It turned out that the boat went slightly faster towards the wind than with the wind. The wings create a lifting force that reduces the drag of the water. The lifting force can be compared to a low-winged aircraft. This is called ground effect, a well-known phenomenon that can be calculated.

    The power figures shown in the diagram in post 16 are input values measured at the energy source, the batteries.

    JS

    fartstor.jpg
     
    Last edited: Apr 10, 2019
  12. DCockey
    Joined: Oct 2009
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    Location: Midcoast Maine

    DCockey Senior Member

    Doug Read of Maine Maritime Academy has been working on the design of a lobster boat with a trimaran hull as a lower resistance alternative to the traditional "semi-displacement/semi-planing" monohull lobster boats. Above the deck the boat looks like a traditional lobster boat, but below the deck it has a narrow center hull and two amas aft. The proportions of the center hull and amas are similar to the photos JSL posted. Doug worked on the design of the US Navy LCS Indepenence design which is a trimaran, and used the knowledge he gained from that project on his "green lobsterboat" project to optimize the hull configuration. He has done comparison wave and tow tank testing of an iteration of his trimaran design and a current lobster boat hull and found a significant reduction in resistance. A "half-scale" technology demonstration boat is almost complete, and is expected to be tested this summer.
    Green Lobster Boat | Maine Center for Coastal Fisheries https://coastalfisheries.org/collaborative-research/green-lobster-boat/
    New lobster boat design could increase fuel efficiency by 25 percent https://bangordailynews.com/2013/07/23/news/hancock/new-lobster-boat-design-could-increase-fuel-efficiency-by-25-percent/
    ‘Green’ lobster boat passes seaworthiness tests http://islandadvantages.com/news/2013/jul/18/green-lobster-boat-passes-seaworthiness-tests/#.XK5KWndFyUk
     
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  13. standman
    Joined: Mar 2015
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    Location: Cebu

    standman Junior Member

    Hi Ilan,
    Thanks for the comments. I chose that particular ama design to provide some dynamic lift. You suggest a more tear drop shape like below? Too much surface but they are just skimming the water. As for windage, about 40% is in water and it is what I feel is comfortable height from water level ( about 4.5' on bow to about 2.5ft. towards the stern
     

    Attached Files:

  14. standman
    Joined: Mar 2015
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    Location: Cebu

    standman Junior Member

    Hi JS,
    Your real world experience to me thumps any theories. What is your suggestion on ama shape / design?
    Stan
     

  15. HJS
    Joined: Nov 2008
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    Location: 59 45 51 N 019 02 15 E

    HJS Member

    My suggestion is that you put down your ambitions to design your boat yourself. You do not have the necessary knowledge and experience.

    In my concept, the design of the ama and its location differs from what most people have achieved. It is based on accurate calculations of static and dynamic forces under different loads. Ama moves at very high relative speeds, which is normally called planing speed.

    Therefore, the ama must be designed for this particular speed in relation to length, static and dynamic lifting force and drag. Added to this we have to take account the interference between the main hull and ama.

    JS
     
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