Fuel economy discussion...more important now than ever!?

Discussion in 'Boat Design' started by Canivour, Jun 8, 2008.

  1. Canivour
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    Canivour Junior Member

    So as fuel prices are rising, more and more in the back of my mind is the thought of efficiency. These questions follow:

    1. Center console vs bowrider vs cabin cruiser hull efficiency at minimum plane speed, cruising speed, and WOT. (we must first compare boats with similar engines, then talk about different set-ups like IO vs OB).

    2. Prop pitch, diameter, and blade number ---many things to consider here (load, acceleration, top speed, minimum planning speed, rough water, but remember the goal is efficiency-or to even simplify more might be to say range or distance, so basically we are looking for the greatest mpg; or least gph at certain speed.) possibly resulting in up to a 30% increase in fuel efficiency some say from proper prop to improper prop, no pun:).

    3. I/O vs OB, I think we can agree that I/O is usually more efficient overall, but we must acknowledge the gains in efficiency of the direct-injection common today in the two strokes now. Also four stroke OBs to be considered.

    4. Size comparison, (like a 4.3L vs a 5.7L in the same 21' boat - - not just WOT)

    5. Manufacturer's styles (glastron's sleeker ssv hull, grady white's deep v, or a more speed oriented four winns liberator, or if anyone is familiar with sanger's older barefoot models).

    Maybe an easy approach is to have people list their boats size, style and gpm or gph at certain speeds. This way as long as everyone is telling the truth we'll have a more accurate discussion.
     
  2. Guest625101138

    Guest625101138 Previous Member

    The Cadence is 20ft long and 2 ft beam. Believed to be the most efficient commercially available prop driven boat. It will amble along at 5kts all day using about 0.2 meusli bar per nm. It can be pushed up to 9kts in a sprint. It will outpace most sailing boats under 30ft over a set course on most days with an engine in good tune.


    Rick W.
     

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  3. masalai
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    masalai masalai

    Canivour , time to think outside the box and design specifically for efficiency. By wandering around this forum you should realise that the hullforms of "yesteryear" are not suited to this - because petrol was cheap ($10/barrel?) and the US$ was strong, so efficiency was NOT a consideration.

    Now you are looking at a foreseeable $200 per barrel and probability of $300 sooner than most would like as the world comes to grips with the fact that the party (of cheap fuel) is well and truly over. This also implies a prospect of significantly increased costs for "petroleum derived products" - "plexiglass", 2 part resins/glues/epoxy, carbon fibre/kevlar and the many other fibres used in boat-building and sail and rope manufacture.

    Start thinking of smaller, lighter fuel efficient diesel/multifuel engines pushing boats at say 15 knots instead of 25 to 60 knots unless you are a multimillionaire seeking to be ostracised, or need to flee from the law with your haul of illegal drugs.:D

    I am in that process of design development for my own use - and for convenience the form will be catamaran around 7000kg fully laden (lightweight construction) and a bit less than 40 ft loa and 25 ft beam with skinny hulls around 2 ft wide... cruise most of the time at 10 to 15 knots burning less than 1 litre per nautical mile.
     
  4. kengrome
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    kengrome Senior Member

    Rick, what kind of hull does Cadence have below the waterline? Is it a simple vee forward that transitions gradually to completely flat at the transom?
     
  5. Guest625101138

    Guest625101138 Previous Member

    Ken
    It is more rounded in the bow than "V". It begins to flatten in the middle but has a rounded chine. The waterline beam is maybe 80mm less than maximum beam with my weight. This means it stiffens a bit as it rolls. It does get very flat in the stern.

    I pushed it up to 16.8kph. Not as fast as my V11A but good for a boat that weighs over 80lb. The drive system is as smooth as any I have built.

    I felt it to be a bit tender compared with my outrigger boats but I would need to roll it at least once before I gained any confidence in its limits. There are optional outriggers but these would not be required in most instances. It would handle 2ft waves beam on without discomfort. It has a large plate rudder and good steering grips that allows a measure of dynamic stabilisation.

    Rick W.
     

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  6. Canivour
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    Canivour Junior Member

    masalai,

    I do indeed plan on exploring the world of new efficiencies, hopefully in the near future as a a professor of Engineering/Technology Education using the university's grants and facilities. Starting with a used vegetable oil converted diesel (I'd like to marinize a 1.9L VW diesel) and someday possibly play with fuel cell technology in a boat.

    As for now though, I am interested in what the average boat owner is doing or can do to get more hours out on the water for the same $$. I mean, I can't even get a straight answer whether a center console or bowrider has a more efficient hull at the same length. I know there are many variables...but that's what this discussion should be about

    - all the variables that when added up may double a boater's time on the water.
     
  7. kengrome
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    kengrome Senior Member

    Efficiency is related to weight and hull shape, not whether the boat is a center console or a bowrider. It's no surprise to me that you're not getting a "straight answer" here. To me your question is almost like asking which car gets better mileage, a left hand drive with cup holders or a right hand drive with a rear window defogger. There is no correct answer to a question like this because it depends upon other factors you're not asking about.

    I don't know what they are doing, if anything, but the best way to get better mileage is to slow down. The second best way is to reduce the operating weight of the vessel.

    If you want to talk about major modifications, change the hull shape from a planing or semi-displacement hull to a full displacement hull ... and never push it faster than 2/3 or 3/4 of the boat's calculated hull speed. Use a smaller, lighter, more fuel efficient engine. Don't power against wind or waves, move with them. Use auxiliary sails to reduce the use of the engine, or use sails all the time and never use the engine. Use a slimmer hull.
     
  8. Knut Sand
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    Knut Sand Senior Member

    VW Diesels:
    Isn't some of the newer VW diesels a bit tricky?

    Fuel Cell:
    Some have already done that (sorry for Norwegian text)

    http://www.nettavisen.no/bat/article1136490.ece
    or
    http://www.bellona.no/nyheter/nyheter_2007/norges_forste_hydrogenbat

    Probably not the first to do it either. (Don't laugh....It's the same type of "boat" as I have.... I would not change the diesel engine, even with high fuel cost, the total cost of used fuel in a boat like that is close to neglectable).

    "get more hours out on the water for the same $":
    Easy; don't move....:D Ok to be more serious; Long slender deplacements hulls (Nagnagnag). Fewer planing hulls. (or lighter/ stronger...).
     
  9. Canivour
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    Canivour Junior Member

    ken, your right on my wording, I meant to imply a center cosole with a deep v hull such as grady whites' sailfish vs a performace boat like for instance my liberator. running same cruising speed and same engine. (I am thinking the deep V is less effiecient?)
     
  10. Knut Sand
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    Knut Sand Senior Member

    If identical, the one with the cupholder, as the other one uses some energy for the defogger, making the alternater rotate (slightly) harder....:D

    But then again; the bowrider full may have a slightly larger transverse inertia, making the boat dip the bow somewhat deeper than the center console (in vaves) And this bay cause it to loose some speed. But on flat water; can't see a difference..
     
  11. Knut Sand
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    Knut Sand Senior Member

    Compare two different (planing) hull shapes, why? Kengrome was right spot on with his view. A deep V is "less efficient", but only if you consider the speed/ milage factor, on flat water. A deep V hull is heavier to run, but, it can do so, when the vaves force the other hull, with less V shape to slow down (due to slamming) a planing hull, in sub planing speed, in vaves, do not have sooo much direction stability, so then the fuel consumption to reach a target will rise again.

    So, in some weather conditions everything will change....:D

    Deplacement hulls, deplacement hulls, deplacement hulls......
     
    Last edited: Jun 9, 2008
  12. charmc
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    charmc Senior Member

    Canivour,

    Yes, the discussion needs to be better defined. Liberator makes performance cats designed for high power and speeds in the 70 - 100 mph range. They are not designed for heavy load carrying or slogging it out offshore in heavy seas, things at which a deep vee or modified deep vee monohull excels.

    It would help to define the questions. Are we discussing the best practices for a boater who has a significant investment in an existing boat to continue operating in a world where fuel has doubled or tripled in cost? Are we asking what are the most fuel efficient hull types to sell in the world of costly fuel? Making the topic very specific will make for a more productive discussion.

    Getting back to your first question, you described deck and superstructure types. Each of them can be built on a deep or shallow vee mono or on a cat hull. As Ken pointed out, hull design and weight are more factors affecting fuel efficiency than topsides appearance. And, of course, operator practice. That is the primary factor affecting how the owner of an existing powerboat of whatever design can afford more time on the water.

    An example of the concept Rick Willoughby showed taken to cruiser size, IMO, is the Dashews' Wind Horse. Long narrow hull, easily driven at moderate speeds with moderate power. Designs such as those, and cats designed with the same goals, should have a place.

    Diesel's ability to use recycled cooking oil will be a benefit for some, but I doubt it will be more than a niche supply, as there just isn't enough for it to be a mainstream source of fuel. That being said, compression or combustion ignition engines designed for multiple fuels will probably be an important element of boating's future.
     
  13. Westfield 11
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    Westfield 11 Senior Member

    Until re-cycled cooking oil is approved by the manufacture to not void my engine warranty, I cannot see too many new boat owners switching. For those who own older boats, the question of long term reliability will always remain especially when fishing a hundred miles offshore. Would you take your children that far out with homemade fuel?
     
  14. Nordic Cat
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    Nordic Cat Senior Member

     

  15. masalai
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    masalai masalai

    Nordic, is there any information available on the 1400 cc Mercedes diesel or its smaller stable mate as used on the "smart cars"? - I have seen it as an option for the Ramphos amphibian from Italy but cannot find anyone selling either engine?

    PM me if you have anything please...
     
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