How much power

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

  1. standman
    Joined: Mar 2015
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    standman Junior Member

    Thanks JS but I will not give up my ambitions. I've proven people wrong all my life and not about to change now. Like they say, better to aim for the stars and strike a goose, than aim for the goose and strike a rock
     
  2. Dejay
    Joined: Mar 2018
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    Dejay Senior Newbie

    Better a sparrow in the hand than to shoot pigeons with a cannonball.
     
  3. HJS
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    HJS Member



    About ignorance: Willful Ignorance Quotes (59 quotes) https://www.goodreads.com/quotes/tag/willful-ignorance

    “We are all born ignorant, but one must work hard to remain stupid.”
    ― Benjamin Franklin

    JS
     
  4. Ilan Voyager
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    Ilan Voyager Senior Member

    Standman NA and NE are professions with hard 4 years studies. And after the NA and NE need to add 5 years of experience as they are rookies. Plus navigation experience.
    You have not the practical and theoretical knowledge for designing a 50 feet trimaran. At 20-30 knots there is not need of dynamic lifting of the ama. In fact you do not want any planing effect even if you are at so called "planing" speeds.
    Even the sailing maxi trimarans, able of 45 knots do not plane even at that speed. Nobody wants to see the wide structure disintegrate by slamming on the sea. You want progressive stresses as water is hard as concrete at any speed above 15 knots and at 45 is like hitting a wall.
    You obtain the speed using very slim; long and light hulls. It's totally different from planing hulls. There is dynamic lift as always as you have speed in the water, but it must be carefully controlled.
    If you have looked closely at the ama of the Ocean Eagle you see that the bottom is drawn to cut the water, with very small and progressive dynamic lift. If you have looked closely to the video of the same boat you see that it's able to make a perfect circle at 25 plus knots in a state 5 sea, it's 2.5 to 4 metres (8 ft 2 in to 13 ft 1 in) waves rather rough. A monohull of the same size at the same speed would be in a deep trouble trying to do this rather dangerous maneuver.
    The video is for connoisseurs...they would appreciate the very small heeling, the absence of roll, the very small pitch, and the absence of yaw. The phugoid is close to zero. That shows the interest of the position and size of the amas acting as roll, pitch and yaw stabilizers. plus the fact that the tri keeps a very steady speed even passing the waves.
    Another video, look at it closely, ask yourself why there is not rear view of the boat...
     
    Last edited: Apr 11, 2019
  5. standman
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    standman Junior Member

    Thanks for the useful information ILAN. I install navigation and Communication equipment on ships including omni sonars and see hull shapes designed by NA's,. Although there are many great NA's and NE's, I have seen designs where I had to scratch my head and ask, you went to school to build this!!?? In fact, the first boat I built, I was told by a couple of NA's that I would not breach 25 knots. While watching the video you linked, another was suggested and has close up views of both hull and ama.

    As I will operate in areas where waves will rarely exceed 1 meter, being able to make perfect circles at 2.5-4m waves isn't even I criteria I seek.(although I know you're pointing out the stability).
    Stan
     
  6. Ilan Voyager
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    Ilan Voyager Senior Member

    Ships and small boats are not in the same league. Configurations that work on ships are useless on small boats. Winds, waves and currents have not the same effect on a ship or a small boat. A 1 m wave is nothing for a ship, but it will have some effect on a 15 m yacht, and it's a big ave for a 20 feet dinghy.
    The configuration you want to use has been tried seriously in real conditions all weather only on ships, and plus exactly on the more than 100 meters Austal Trimarans. And it seems there is a problem of rolling, even with computer driven dynamic stabilizers. Look at that, it's not brilliant. I leave you imagine the same rolling on a 15 m tri.



    The trimaran configuration I showed to you has been a proven concept since 30 years. It works from 8 meters to 60 meters. It's rather straightforward to build.
    Ilan Voyager 21m long, is a very seaworthy and very well behaved boat, economical and fast with only 235 HP. Made in wood an fiberglass epoxy.
    Cable&Wireless has a round around the world record.
    In economical cruising at 15 knots. The 43 meters 75 metric tons displacement Ocean Eagle 43 uses only 1 metric ton of fuel for 238 NM, 1333 liters for 440 km. That is an excellent result. And you have seen how it behaves.
    The con is trimarans are very light boats with no big amenities.
    If I wanted a 15 m boat with nice amenities and 20 knots speed for use on a sweet sea, I would go immediately to a simple 15 m catamaran, using 2 150 HP outboards.
    There are plenty of good plans and I wouldn't spend one hour in the conception and calculations although I can do it. I do not see the interest in wasting time to reinvent what thet have been already done.
    And if I had the money for a motor trimaran I would call Nigel Irens for the design. He has the experience...And he has proven amply his capabilities.
     
    Last edited: Apr 12, 2019
  7. HJS
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    HJS Member

    As in any boat design, certain criteria must be determined. The first is payload and speed. In this case, it must be determined how many passengers the boat should take. In this way, maximum and minimum total weight can be estimated at first. This can then form the basis for a more detailed calculation.
    The presumption is that neither examples of Nigel Irens nor the Green Lobsterboat are suitable examples. They probably lie outside the appropriate payload, number of passengers.

    JS
     
  8. Ilan Voyager
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    Ilan Voyager Senior Member

    HJS you are right. Meantime everybody is wasting time as nobody has idea of the real SOR and furthermore the real budget.
    It remains that like in hundreds of similar threads in this forum, some amateurs without real knowledge and know-how believe that they can design boats because they can get shapes with a computer. Alas for them, NA is a profession, rather complex, requiring a deep knowledge far beyond drawing.
     
  9. HJS
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    HJS Member

    Just because it looks like a boat it is maybe not a boat.
    Maybe not even a floating object.;)
    JS
     
  10. Dejay
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    Dejay Senior Newbie

    You mean to say it's an Underengineered Floating Object? :)

    EDIT: I also flirting with the idea of designing my own boat. Or at least heavily modifying a similar design. I am going to look into consulting a naval architect but it might come down to a cost benefit question.
     
  11. standman
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    standman Junior Member

    Payload was already incorporated on the 5,000KGs displacement and so has speed (20Knots)
     
  12. standman
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    standman Junior Member

    Catamarans are of Polynesian decent and when they were conceptualized and built, There were no NA's. Here in the Philippines, Outrigger bancas (trimarans) are dominant for hundreds of years and i bet 90% of them weren't designed and built by "deep knowledged" NA's. Many of these people who have knowledge handed down from other/older builders actually build better bancas than their "supposed" better NA's. In fact an Australian NA decided to join the annual banca race and his "deep knowledge" didn't even get him a place.
    I am admittedly your so called amateur. Built only 1 boat from scratch. Thus I come here seeking knowledge and not discouragement or gibberish comments. If you have nothing good to say.....
     
  13. kerosene
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    kerosene Senior Member

    Usually I share the attitude in your post. But the individuals in those threads typically have extremely limited boating experience and zero boat building experience.

    It is right to make all those points but at the same time it is easy to end up a bit too cynical.
    I have seen dive boats in Belize that perform just fine despite being designed by the builders.

    OP has proven not to be a dreamer without ability to also execute. That separates him from 99% if the "I want to design a boat" posters.
    Also if I am reading it right he has a feel for the practical build process in his locale (there are other Cebu folks on the forum btw).

    It is good to point out the obvious: catalogue design by pro is in the end cheaper. Etc.
     
  14. Mr Efficiency
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    Mr Efficiency Senior Member

    What 5 ton boat will do 20 knots (cruise, not top speed) with 200 hp ? Admittedly he is talking diesel, and can run higher in the rev range without killing the fuel consumption, or the engine, but it (the speed)seems a tad optimistic to me.
     

  15. Ilan Voyager
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    Ilan Voyager Senior Member

    A well designed multi light and long and with aerodynamics better than a Mennonite barn does it. Most motor multis do not fill these requirements.
    An example.
    Kurt Hughes Multihull Design - Catamarans and Trimarans for Cruising and Charter - 46' Cruising Catamaran https://www.multihulldesigns.com/designs_stock/46pwrcat.html
    46' power catamaran in composite.
    Twin staterooms forward and a spacious bridgedeck salon area define this 46' power catamaran. As well it has an extensive aft deck lounge for entertaining. Construction is knitted glass roving and foam core. Advanced engineering keeps the weight down and the aerodynamic house cabin helps reduce drag at speed. Both combine to give surprising speed and economy. Unit #1 was designed with surface piercing props, but I believe a standard 3 blade prop will provide a more cost-effective and reliable solution. The hulls are semi-planing, providing a smoother ride than a full planing configuration, and better economy at the lower speeds. Expect 100 hp per side to give between 23 and 25 knots depending on loading. Full loaded 5,382 kg.

    Ilan Voyayer 21 m about 7 tons fully loaded. 235 HP. Top speed 28 knots, long range cruise speed 21.5 kn using 150 HP (1 liter of fuel per NM) over 2150 NM without refueling. Ratio max width at waterline/length of the main hull 17/1

    Thin, long and light hulls are very efficient if you stay within very strict parameters, and stringent requirements with discipline.
    It'a anecdotal, but I saw in Russia in 1991 a small mono on foils, 40 feet 4 tons 240 HP Volvo 38 knots top speed, 32 knots cruising. Able to cruise at 28-30 knots in 3 feet waves. That was a proto nicely built in alu, foils in titanium. A true flying carpet, very smooth.
     
    Last edited: Apr 17, 2019
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