A replacement of 1-2 diesels of a power boat with a small gas turbine

Discussion in 'Boat Design' started by Stoyan Ivanov, May 10, 2018.

  1. Stoyan Ivanov
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    Stoyan Ivanov Junior Member

    Hi everybody , I am a newcomer here , develop a project of a powerboat ( around 40 ft long , displacement - 12 to , L/B = 4 , projected cruise speed 30-32kn , planned power (Hybrid - 2 x 370 HP Toyota diesels + 1-2 electric motors)
    I have 2 questions :
    1. Do you think a boat with a displacement of approximately 12 to could do a normal planing at a typical cruising speed of 30-32 kn ? And a maximum speed of around 35-40kn ?
    2. Would it be more effective if I replace one or both diesels with a small gas turbine ( 700-1200HP) ?
    My constructor thinks it will . Planned functionality is 70% of the time - cruising , 30% - high speed 35-40kn .
    Would be very grateful to receive your comments .
    Thanks in advance
     
  2. gonzo
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    gonzo Senior Member

    There isn't enough information to answer your question. The shape and other dimensions of the boat will also have influence over your speed and possibility of planing.
    1) A hybrid system will be more expensive, complicated and heavy than a diesel only installation. If you are only looking at cruising speed, it may not be the best option. However, maybe you can post the reasons for your choice.
    2) Define effective. If you are looking for maximum speed with no regard to fuel economy, gas turbines are great. They do require a lot of expensive maintenance compared to a regular diesel though.
    The Statement of Requirements (SOR) is the first thing you need to decide on. That includes every requirement the boat needs to fulfill. Then, some kind of decision matrix, or other method, is used to decide which requirements have to be modified, deleted or added.
     
  3. Yellowjacket
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    Yellowjacket Senior Member

    Most of the CODAG (Combined diesel and gas turbine) approaches end up being the worst of both worlds. Since the turbine is used for high speed dash you end up with a heavy diesel propulsion system that is weighs so much that that it takes a big thirsty gas turbine to push the hull to higher speeds. If you look at some of the more efficient gas turbines for larger boats than is the topic here, if you go all gas turbine, you can generally reduce the displacement by more than 10% and the power required to go fast now is lower so you end up with a 10% worse fuel burn per mile, but you have a higher top speed and a more simple installation. And even at reasonable cruising speeds the fuel burn isn't that bad. Smaller gas turbines aren't as efficient, you need a turbine in the 2500 hp class to get the kind of efficiency to make something like that work. If you can make the boat work with a pair of 370 hp diesels you're going to have a tough time finding a turbine to go with that that is very efficient. Hybridizing with heavy batteries is, for marine applications pretty much a waste of displacement, and if you're thinking about planing with batteries you're just adding way too much weight.

    There are ways to effectively get turbines to work and have some very attractive results, but it isn't obvious unless you look outside the current box of typical CODAG. We've studied it a good bit and have briefed some builders of patrol craft (militaries are willing to spend more than most commercial users) and a one world famous marine architect (he liked it) so maybe we'll see something about this in the near future.
     
  4. Stoyan Ivanov
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    Stoyan Ivanov Junior Member

    Thanks a lot for the comments . I'll try to be much more precise as to parameters .
    1) Shape - similar to Cigarette 38 Top Gun or Baja Outlaw 40
    Length - 40ft , Beam - 9ft , Height - 6,5-7 ft
    Displacement - 12 to , +/- 10%
    Hybrid system inevitable - it will dive as well , but about that later in case you are interested .
    The first and main question is " Can this SHAPE and L/B ratio plane normally at a cruising speed of appr 30-32kn powered by 2 x 370-400 HP diesels ?"
    2) If the answer of the first question is "no" - WOULD IT BE BETTER ( define effective according to my requirements - optimum " power - planing-fuel economy ratio ) to replace one or both diesels with a small turbine ?
    Just need your opinion ' cause I have to make up my mind . And I understand displacement here is bigger than normal for that type of boats .
    Functioning planned - most of the time in cruising mode , maximum speed - only to show style and when with nice girls ))))
     
  5. Stoyan Ivanov
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    Stoyan Ivanov Junior Member

    Hi Yellowjacket , I highly appreciate your opinion .
    The reason for my questions is that I have a bigger displacement for that type of powerboats - 12 to +/- 10% ( pls see my previous post to Gonzo - shape , parameters ) and with this regard I want to insure an adequate power for a normal planing at 30-32 kn with a possibility to effectively reach the maximum speed whenever I like but not too often at all . What my people have calculated till now ( we are still calculating the weights) is that 2 x 370 -400 HP is enough too fulfil the above task . But some say we need much power and my constructor considers replacement of one or both diesels for a turbine ( helicopter) appropriate .
    If this displacement of 12 to can be solved adequately by 2 x 370 HP ( Toyota Land Cruiser or Lexus - V8 ) diesels I would for this length of 40 ft use only diesels because this will be a 40 ft prototype corresponding to a normal transport trailer length . And in this kind of prototype we'll have to test lots of other things .
    For example hybridizing here is inevitable - the boat will dive as well . With this heavy batteries are a fact and planing is one of the issues to be solved correctly .
    I'll have in mind your thinking about CODAG approaches being the worst of both worlds , but I would highly appreciate your opinion of a combination of a 1000 HP turbine with a diesel of e.g. 200 HP only for use as a generator or eventually to replace failing turbine drive in case of emergency . A kind of optimising CODAG for smaller applications if that is possible . On the other side if our next generation boat is 60+ ft long as we think , we'll for sure use a turbine .
    Would be happy to receive your comment on the "2x370HP = 12 to equation" , hope to have a good contact in the future .
     
  6. gonzo
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    gonzo Senior Member

    A displacement of 12 tons is quite heavy for the power available. A Cigarrette 40 will have a about 1400 HP with lightweight engines, at a displacement of 9 tons. Hybridizing is maybe a good option for nature watching where silent operation is important; not for a fast boat. If you add a generator and a battery bank that can run a 500kW electric motor or bigger, the boat will have no room for any interior accommodations. It will also be too heavy .
     
  7. Yellowjacket
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    Yellowjacket Senior Member

    The "hybrid" solution is really only applicable up to hull speed. Putting in more electrical generator and power is pretty much a waste. If you're putting in a gen set and using that to drive at low speed you only want enough power to push you at hull speed up wind. Beyond that the electrical genset and motors are just adding weight. I don't have any idea as to how much power that is for the size of boat you're working on, but if you put more electrical power into the boat you're wasting weight and spending money on something that has little value. Since it doesn't take much power to push you at hull speed, (upwind) then the hybrid stuff can be a lot smaller and lighter.

    Gas turbines in the 1,000 hp class aren't going to be very efficient. Light and powerful, yes, but efficient, not really. If you look at the specific fuel consumption of gas turbines, small helicopter engines typically have a takeoff SFC of about .55 lbs of fuel per horsepower hour, SFC gets better for turbines at higher percentages of power, so you don't want to loaf along on turbines. But at the same time, the helicopter duty cycle is different than a marine duty cycle. In a helo you take off and land at high power for a fairly short period of time, but then you load along at 50% power or thereabouts when you are in level flight. For this reason you really can't operate a helicopter engine at takeoff rated power in a marine application at high a power without shortening the life and if you back off the SFC gets even worse. In order to get reasonable overall performance (that is, not suck fuel like crazy) you need an SFC of about .45 lbs/hp-hr. If you get down to that neck of the woods, the weight you save by getting rid of diesels will reduce the displacement enough that if you want to cruise in the 30-40 mph range the turbine will be in an efficient power band . If you look at the available engines, helicopter engines in general aren't very good since their mission length is short they don't need to be very efficient. The T700 and RTM322 are good (too expensive and too much power for your application) and so it the T800, (a bit too big and really expensive), where the PT6 is less expensive but is also very thirsty, as are the Walter and the Turbomeca engines. You may have a turbine picked out, but I don't see how you're going to get competitive with diesels in this size class vessel. If you were going bigger (say the 65 to 80 foot class) then there are several solutions that make sense, but smaller than that you're going to have 25-50% higher fuel burn than a conventional diesel setup and that's fine if you have money to burn (literally), but most folks would get tired of paying the fuel bills for that kind of boat.

    As to maintenance, turbines are much lower maintenance than a diesel, most maintenance is "on condition", if it doesn't break don't worry about it. Oil changes are in the 1000's of hours period or not at all. In a marine application a good practice is to spray fresh water into the inlet for a minute just before shutdown, but that's pretty much it. When you look at what it takes to keep a diesel in terms of regular maintenance, turbines require very little attention in comparison.
     
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  8. Magnus W
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    Magnus W Junior Member

    So you're looking at a classic powerboat design that needs a combination of high speed propulsion and something air independent (such as electric) so that you can go submerged. And given the weight I guess you'll be carrying some cargo.

    The best knowledge about such vessels can probably be found in the northern parts of latin America. Not sure about how keen the operators are about sharing said knowledge though...
     
  9. Magnus W
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    Magnus W Junior Member

    About turbines. They most certainly have distinct benefits such as reliability, multi fuel compliancy, low weight vs output, short time from startup to full power availability and others. But if you don't need any of said benefits you will pay a cost penalty both in terms of initial investment and running costs.

    Also, I don't completely agree with Yellow on maintenance. I have experience from operating both patrol vessels with turbines (Rolls Royce) and seaplanes with turbines (Pratt and Whitney). Erosion problems aside the salt wreaks havoc on mainly the compressor part of the turbine and if you want to get hours from a marine turbine that are in the neighbourhood of an airplane counterpart it will require regular cleaning (as in every day and after every run). In a large vessel intake air can be routed so that this problem becomes less of an issue, in a small boat (or seaplane) this is seldom feasible.

    And diving. Turbines are air cooled and they require vast amounts of air. In order to ready the vessel for submerged operation you need to be able to close the intake and exhaust ports and even though you don't state the targeted depth I suspect it will be both very hard and very expensive to find valves big enough and capable of dealing with the high exhaust temp of a turbine (remember; small boat means short exhaust means hot hot hot).
    In the 90's when I was on subs the single exhaust port was maybe (iirc) 300 mm in diameter (and we had 2 x 1500 hp diesel) with wet exhausts. A single 1500 hp turbine would require about 1,5 times that (no I haven't done the math on it but it seems about right).
     
  10. Stoyan Ivanov
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    Stoyan Ivanov Junior Member

    Hi Magnus ,
    About your first post - your guess regarding the cargo is wrong . The boat will be used for tourist purposes and as an addition to the mega yachts or cruising ships. If you were on subs , you probably know the elements comprising weight , but I'll overlook your perceptive irony saying that the only cargo will be 5 + people and that I don't need the "best knowledge" of the operators you mention because it is not there .
    But my questions had nothing to do with diving and submerging , they are mainly 2 diesels versus a turbine option .
    With this regard I highly appreciate your comments in your second post . I am principally working on the base of 2 diesels with possible power/displacement equation = 2 x 370 HP / 12 to and trying to investigate the option of a turbine replacement in case the power is not enough for normal planing in cruising speed of 30-32 kn .
    And you are right about the ports and a turbine - I also thought I would have a design problem with this regard .
    Anyway , thanks for your attention , would be grateful to receive more comments .
     
  11. Stoyan Ivanov
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    Stoyan Ivanov Junior Member

    Аnd by the way , as I now saw you are from Sweden , the experts with best knowledge on the subject are rather nearer to you ( Nеtherlands and Russia ) , I think .
     
  12. Stoyan Ivanov
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    Stoyan Ivanov Junior Member

    I'll take in mind your consideration that 12 to is quite heavy for 2 x 370 HP . I also doubt about the power equation . But on the other side I don't need a cruising speed of 60-65 mph like Cigarette 40 with a 1200-1500HP . Mine is 30-32 mph , that is the question - could I plane normally at this cruising speed of 30 mph with 2 x 370 HP or I have to increase the power to 2 x 500 or even more . Or I have to use a turbine .
    As you correctly notice , hybridising as planned is mainly for nature watching under the surface , so I don't need speed there - up to 5 kn . With this regard I think that a battery bank with a generator that can run 2 x 50 kW for max several hours under , is enough , even smaller .
    We are working hard on the room issue , on lightening of materials as well . I understand it is risky and not easy , but if it had been easy some people would have already done it . Or the majority of very rich people wouldn't have risked and bought only Cigarettes , Baja and similar ...
    Limit , I guess , is a function of balance ...
     
  13. Stoyan Ivanov
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    Stoyan Ivanov Junior Member


    Yellowjacket , thanks a lot for your detailed comments .
    A hybrid solution is a must for this concept . And it is - moving relatively fast ( from one point to another in an atmosphere of luxury ) with the possibility to go submerged mainly for nature watching ( for max 1-3 hours , with no need of speed there - up to 5 kn) . Put simply - take tourists from the cruising ship or a nice company of people from the mega yacht , have them enjoy the sea view not only in a static way and watch nature under the sea as well .
    The size of boat we now work on is : Length - 40ft , Beam - 9 ft , Height - 8ft . Trailer length for easy transport . 4 people + 1 pilot .
    Electric power will be used when the boat goes submerged with a speed up to 5kn and and in case it is already installed - for hull speed ( 0-6mph and 6-12 mph ) . Having in mind this specific use , I agree with you that I should not waste power or weight at large and find the adequate parameters . That is why for the time being I am focusing on one of the two options - 2 x 25 kW or 2 x 50 kW electric motors ( one for each diesel engine ) . Maybe they will be enough for the above mission .
    As to the turbine option - you have contributed a lot to my decision making , thanks for that . With a length of 12 m - we really cannot be effective with a turbine. But in case of going bigger ( 60 ft+ ) it could be really a viable solution . In that situation I should solve the main question :
    Are 2 diesel engines of 370 HP enough for a boat of 12to to plane normally at a cruising speed of 30-32 kn or we need more power and how much more ?
     
  14. gonzo
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    gonzo Senior Member

    I think that a submersible will increase the weight considerably. For example, all the exhausts, intakes, drains, windows, etc. have to withstand the water pressure without leaking. Have you considered a viewing pod that protrudes from the bottom? It will also add weight, but not as much. Also, if your operating speed wont be over 30kn a Cigarrette type hull is probably not the best option. They have a very deep vee bottom that doesn't handle well at low speeds.
     

  15. Magnus W
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    Magnus W Junior Member

    My comment with regards to latin American expertise was referring to the drug runners that use semi submersibles sometimes based on power boats. A poor attempt of being a little funny.
     
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