economical coastal cruiser

Discussion in 'Boat Design' started by sandy daugherty, Feb 11, 2010.

  1. Guest625101138

    Guest625101138 Previous Member

    Take a look at post #26 on this thread:
    http://www.boatdesign.net/forums/boat-design/trimaran-motorboat-stabilized-monohull-29665-2.html
    There are even more pictures if you move around that thread


    It will give you an idea of what is getting attention and development. Usually takes 10 to 20 years before a good concept becomes common place.

    Rick W
     
  2. Brian@BNE
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    Brian@BNE Senior Member

    fcfc - I like your analysis, but don't want to try and replicate it. :!:

    Could you look at the Yanmar in the attached brochure and tell if the same applies? I realise its a larger capacity motor than has been debated above, but it is basically BMW's 2.0 litre diesel for their cars. I thought it should be quite fuel efficient around 2000-2200 rpm because thats probably where highway cruise speeds (and nice fuel economy) occurs in cars.

    Now I'd thought of CPP instead of sterndrive to further improve loading at low rpm as well as prop efficiency, but draft considerations might not allow it. And cost of gearbox for that setup might not cover efficiency gains.

    What am I overlooking?
     

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  3. erik818
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    erik818 Senior Member

    Fcfc,
    I appreciate the "lecture" you provide on diesel engine data. There's always something more to learn.

    Data for outboards are more difficult to find than for diesels, and the only outboard fuel consumption data that I've seen are at maximum power. Diesel engine manufacturers are much more open with motor data than outboard manufacturers. Maybe you have better access to data; my source is mainly the internet.

    I'm stubborn and still think the relation between the outboard and inboard diesel is correct. Unless a gasoline engine suffers less than a diesel at reduced power output, it's still true that for the same fuel consumtion I get 10 hp from the outboard and 17 hp from the diesel.

    What you say is that I should not expect the advertised efficiency as these are for "best conditions", but isn't that true for both diesel engines and gasoline engines?

    The inexpensive Chinese diesel is much heavier than Solé or Vetus, so it's not my choice anyway.

    I agree that sound proofing is important an adds to the weight difference. Of the two boats I have, the larger boat with an old 1-cylinder Yanmar diesel is less noicy than my small open boat with an old Mercury outboard. I had to work a lot with sound-proofing of the inboard. Before I did that the noice was unbearable.

    Erik
     
  4. FAST FRED
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    FAST FRED Senior Member

    One of the design considerations of the stormport boat is as a flats boat minimum draft is required. 8 inches is not required by everyone.

    The Atkin boats were deeper which allowed a greater percentage of the total weight to be carried by the box keel , other modern box keel boats found this to cut wake making and add even more to the vessels efficiency.

    The trailerable boat starting this thread would perhaps be OK with 18 inches to 2ft of draft , which would still get on a trailer with ease.

    The larger box keel would allow for a bigger , slower prop , with the more efficient keel.

    So perhaps 30mpg is only the start ?

    A recent article by N Calder on gen sets claimed that many small motors (like the Kubota) NOT run with a proper load cost 100% to 200% or more fuel per HP at low inefficient rpm's.

    This could perhaps explain how the flats boat could go from 12K to 18K with no more fuel burn, the engine simply was loaded better.

    A CPP would be out of the question cost wise for this size boat , BUT Tom's concept of "overproping" to get the engine load in sync with the cruise rpm would be an effective but inexpensive method.

    One of the early builders of the Rescue Minor , Robb White , built a common shaft drive system based on outboard style propeller mounting.

    This allowed the prop to be changed aground ,in ankle deep water by just pulling a cotter pin as on most outboards.
    Sure would lower the cost of experimenting to find the "Optimum" prop , or setting the boat up for different style cruising.

    ON a larger boat the use of a box over the prop , with a removable bottom would allow in water prop changes .

    Sorta like the box over the prop on many canal boats for clearing trash , but closed on the bottom.

    FF
     
  5. fcfc
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    fcfc Senior Member

    I am not an expert neither a specialist.

    This engine is up to date technology. There is no problem interpreting fuel burn at any speed. (Data are complete). and show good efficiency (better than 230 gr/Kw at 3000 rpm)

    Also, more readeable :
    http://www.rangertugs.com/r/images/r25/media/Ranger25_PerformanceData.pdf

    Although speed and trim are truly and heavily boat related, other engine data is much more independant of the boat.

    There are also similar engines from other manufacturers. Vetus VF4 and Cummions QDS 2.0.

    The only thing I would say:
    There is a significant difference between continous power and max power.
    Engine turn fast. I do not think it is a problem engine side, but propeller side for slower applications, it may not be so good.
    They are newer engine so long term reliability and spare parts availability is currently unknown.


    If you are looking that kind of engines for a slower boat, I suggest you lookat volkswagen marine TDI 100-5, 100 hp at 2600 rpm or Volvo D3-110 110 hp at 3000 rpm. They are same kind of engine, bigger (5 cylinders ie yet more expensive) but turning slower, and so easier to match to a slow turning prop.
     
  6. fcfc
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    fcfc Senior Member

    I would say the key issue is how much are you willing to spend to save fuel.
     
  7. Brian@BNE
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    Brian@BNE Senior Member

    Thanks for the link with the 4BY tabular data. And also for alternatives. I do have a high regard for VW diesels.

    In principle I want to use a high rpm diesel auto engine (marinised by supplier), run it at relatively low rpm but with high load via CPP. Cost of gearbox needed to do this might yet be a problem, I just don't know. Then from time to time run at WOT, hopefully still within limits of CPP. If this could be done in a Bluejacket type hull that pops onto plane early and smoothly then I'd be delighted. But I'm hoping for a higher ratio of LOA/beam than Tom's designs. I'll need to quantify weights of fitout and superstructure to determine weather I can keep displacement low enough to get my long skinny concept to work.

    Once I get to thrust requirements of hull, and know draft, I will research engines and props further. And look at costs as you rightly say, but I'm somewhat aligned to Erik's thinking on budget and am still in 'feasibility' mode. If I pay more but spend wisely I'll get a better boat. A better boat will mean more time on the water. Should then be a happy outcome.
     
  8. fcfc
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    fcfc Senior Member

    You wont get a clear engine side benefit from this. If you look a the previous VW TDI75-4 data, from 2000 rpm to 3600 rpm, from 10Kw to 55 Kw to the prop, engine efficiency is within 10% of the optimum. I fear you will get same kind of result from any automotive derived engine with full electronic control.

    You can get a propeller/hull benefit from this this, because as the boat goes slower, the best efficient prop need to go slower, but have more pitch. In fact, most propellers are optimised for top speed. The gain you will have with a CPP is directly dependant on how often you will accept to go significant slower, for the CPP to have a still measurable benefit while the power has been seriously reduced for a slower speed.

    Say boat top speed 75 hp 12 knots. at this point fixed prop have a slight efficiency advantage on a CPP with a bigger hub and not optimally twisted blades.

    If you reduce speed at 8 kts. With a fixed pitch prop, you will need 20 hp. With the better efficiency CPP at the right pitch, you would need 15 hp. That a 25% increase in efficiency. That tremendous. But for your engine at 15 or 20 hp, you are still within 10% of the best efficient range. The net gain is 5% of the maximum fuel burn. And you have to go to 8 knot to experience it.

    You have saved one liter per hour. How many hours at 8 kts to save the cost of a semi custom CPP system compared to a stock commonly available ZF, technodrive etc ... ?

    PS: this of course fully dependant of the hull and speed range, and size. At this level of power, you can have stock propellers,gearbox, shafting system at low prices. On some boats especially bigger ones when production run is too low to have low priced equipment, it would be fully stupid not to use a CPP. FPP solution being at the same custom or semi custom price.
     
  9. fcfc
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    fcfc Senior Member

    The Ilan voyager is 22 years old. And I have yet to see a yard who have sold 5 units of the same stabilized monohull model, fuel powered.

    You need to think hard on why people want not burn fuel.

    It may be for economic reasons. Fuel is pricey.

    But in that case, a solution which asks to lengthen the hull and use materials or building technics with better performances/weight ratio will unlikely solve money tight problems.

    It may be for religious reasons. Eco warrior religion forbids them to burn fuel.

    In that case, I will be more than happy to sell you one the zillions available coastal cruising sailboats (this thread was about coastal cruiser), that goes from 8 to 300 ft, from bare naked to ultra luxury. from 0 kts to 50 kts.

    Have you any other reason not to burn fuel, except your willingness or your wallet ?
     
  10. FAST FRED
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    FAST FRED Senior Member

    "You have saved one liter per hour. How many hours at 8 kts to save the cost of a semi custom CPP system compared to a stock commonly available ZF, technodrive etc ... ?"

    If you look art the Oxymoronic "Fast Trawlers" now being marketed ,

    almost all will spend 98% of the time at slo cruise , and only hit the pin outside the marina to show off.

    Unfortunatly these have industrial sized engines that suffer from under loading far more than auto transplants.

    The difference of course is the industrial marinization could operate at 90% load 24/7/365 , the auto take out had better not!!

    The owner must realize the difference in operating regime , before purchase.

    FF
     
  11. Brian@BNE
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    Brian@BNE Senior Member

    Heat, electricity and no noise

    For Erik and others in cooler climates, the BlueGen unit might be worth thinking about.
    http://www.cfcl.com.au/BlueGen/
    Some house load, battery charging and heating without noise is very desirable. I think the units are just getting onto the market now but I'm not sure of price.
     
  12. erik818
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    erik818 Senior Member

    I don't understand what type of fuel the fuel cell need. In one place natural gas is mentioned, and there's a 1/2" pipe interface for the gas. Can the gas to run a fuel cell be conveniently stored onboard, or can it be generated from commonly available liquid fuels?

    Erik
     
  13. Pierre R
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    Pierre R Senior Member

    When further away from shore than I can comfortably swim or expect swift rescue, I want the proven time tested technology saving my butt. I have no dilusions about being on the cutting edge of technology when my life depends on it. Many have lost their lives in the development of that technology and I thank them for doing the probing for me.

    I understand that this is a design forum with all intents and purposes aimed at being part of the probe into new technologies but, when someone asks for help on a boat used for coastal cruising we should not assume they want to be at the head of the probe. We should also not assume that novices will know when someone is asking them to spend money to test their own ideas.
     
  14. erik818
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    erik818 Senior Member

    I had to revisit the basic size requirements again. The height restriction given by a standard shipping container door is about 2.2m. For a standing height of 1.9m, there will be no height left for a narrow central hull, unless you’re standing on the bottom of that hull. A central hull that’s wide enough to provide comfortable standing height along the boat will be too wide to meet the fuel efficiency target. The stabilised monohull concept is not compatible with standing height and standard shipping containers at the same time. The lightly loaded planing hull, like in the Bluejacket boats, is better if a container size boat is desired.

    With the height restriction 2.2m it’s not possible to have a bridge / enclosed helm overlooking a standing height saloon to the rear and a barely standing height forward cabin. 2.3m container door width and 30cm wide catwalks on the boat give an internal width of 1.7m, which is too narrow to my liking.

    In my opinion a standard shipping container is just too restricting for a coastal cruiser. There’s too much that has to be sacrificed for the possibility to maybe once in a lifetime fit it into a container. I’m back to 12m * 3m for maximum length and width to keep the project almost realistic, and no definite height requirement.

    Erik
     

  15. sandy daugherty
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    sandy daugherty Senior Member

    back to the question

    I'm still following all this (barely) and have also refined my requirements.

    Ian Farrier writes about using large panels of foam on a half-frame to build his latest designs; I'm led to believe that this method is within my capabilites given the range of talent in my circle of friends. So an optimal shape should be considered: plywood and hard chines are not necessary.

    If the Atkins keel is everything its said to be, then a good cabin can be designed around a well soundproofed small diesel, something that could provide eight to ten knots long range cruise at one gallon per hour. But there don't seem to be any engines in the 25 to 35 hp range with common rail fuel injection, or peizo-electric injection, which could theoretically provide greater economy at middle power settings. Three-cylinder engines seem to run at higher rpm.

    Clearly the design of the boat should accomodate a very large diameter propeller, perhaps a two bladed prop that could be raised to facilitate launching. If not with a CV joint, then perhaps with a design that raisee the whole engine and drive train. Trailerable sailboats have centerboards that weigh twice as much!

    :idea: Yamaha High Thrust engines have 2.92: gear ratios. The 9.9s can carry a 12 inch propeller, SOLAS already makes a prop for max power at around 12 knots. Whats wrong with running THREE $2500 outboards?

    My last question: Could state-of-the-art construction techniques, and fanatical attention to weight, build a David Gerr Northwest 39-ish boat light enough to run at these economies?:?:
     
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