Searching for fuel efficient powerboat

Discussion in 'Powerboats' started by Chuck Losness, Apr 29, 2011.

  1. WestVanHan
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    WestVanHan Not a Senior Member

    A friend has a nice 51' sail boat that will need maybe $60k spent on it in the next couple years in mast,rigging,sails,winches (all the good stuff) etc. and he spent $26k on it a couple years ago on the engine.


    That's enough fuel/oil changes to do 45,000+ miles with my 50' and twin 635 Cummins cruising along at 7 knots and my cruising style.
    And I do maybe 500-800 miles a year,sometimes 1000. So now at 34,I'll be quite an old codger before I catch up to his spending.

    But I can't sail to Hawaii,or Mexico- but he doesn't either-and I'm happier on a 747 or A340 anyways.
     
  2. Chuck Losness
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    Chuck Losness Senior Member

    WestVanHan
    Good example of the costs associated with a sailboat that people seem to forget about when comparing to the cost to operate a powerboat.

    Easy
    It would all depend on the hull shape. I don't think that we can make too many generalizations beyond the basic concept without a given boat to work with. I also agree that selling the old engine(s) would offset some of the cost of the replacement lower hp engine(s). My favored repower engine would be a John Deere 75hp 4045 for a single or maybe two Kubota 40hp if twins. Interesting side note about Kubota. I ran into a guy with a kubota based diesel from one of the marine engine suppliers who told me that they made Kubota come up with different part numbers for the marine engine and no cross reference parts list to prevent people from just going to an industrial supplier. The same part from the marine company was significantly higher in cost. Twins would be nice because of the built in get home capacity. If it was a single, then I would have to figure out a get home motor. Could be anything from a high thrust outboard on the swim step to using the generator as a backup. Lots of options to consider. There is no vessel assist in Mexico. You are on your own. That is one reason why lots of cruisers down here travel with at least one other boat. Friends towing another boat into port is not uncommon.
    I also agree with you that the real issues will be in all the little details like you mentioned. Not insurmountable. Maybe one of the NA guys will jump in here and tell us we're nuts or even agree that it might be a workable. I definitely would not do this with consulting with a NA first.
    And all of this is just wishful thinking until I sell my current boat.
     
  3. Guido
    Joined: Oct 2011
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    Guido Junior Member

    Low speed planing boat

    Hy everyone,
    I have a standard planing boat (LOA 10m, Displacement 8 ton, maximum speed 31Knots, cruise speed 26 Knots, minimum planing speed 16 Knots, 2 Yanmar engines 235hp that I must change, V bottom hull, fuel consumption 2,5litre/knot) and I'm looking to modify its performance getting to a lower minimum planing speed (10 Knots), lower top speed (22Knots), lower cruise speed (18 Knots), engines with fewer power (??hp) and lower fuel consumption (1,7-1,8 Litres/Knot?). To get my objectives I'm thinking to work on right balance among engines (Power and Torque) and propellers. I'm looking for a more confortable, economical and quiet cruise.
    Have you got any advice or technical consideration on it?
    Thanks
     
  4. Tad
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    Tad Boat Designer

    I think replacing the bottom on a so-called "planing" hull with one suited to lower speed is entirely feasible. In reality the hull molding is perhaps 10% of the complete boat. Replacing half that is not a big deal and if she was a real fuel hog you might actually improve resale value.

    Figuring out where to cut would be simple working with computer models. Probably I would cut a chine line somewhere above the waterline, I would also add a vertical stem and integral swim step to lengthen the waterline. A chine flat with upturned flange that matches the existing hull would be the joint, everything below could be new. Mold the new bottom on a male mold, vaccum bagged on core-cell or similar.

    Take the hull lines and do an inclining with flotation measurements to establish CG. Then you can calculate new centers and estimate the effect of moving major weights around.
     
  5. Chuck Losness
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    Chuck Losness Senior Member

    Tad,
    Thanks for the suggestions. Being able to do this will expand the boats that I can consider.
    Chuck
     
  6. Willallison
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    Willallison Senior Member

    I remember reading a Proboat article a number of years back in which the builder's of a low speed, economical cruiser (may have even been electric, can't rememebr now...) cut the bottom off it and replaced it with planing sections as they couldn't find a buyer for it in its original guise.
    How things change....

    But whilst it may be feasible... is it sensible? When the 2nd hand market is flooded with inexpensive boats, why go to the hassle and cost of modifying when you can simply replace... and usually for a lot less.
    Of course finding a boat that's suited to lower planing speeds can be problematic, but they are definitely out there.....
     
  7. Tad
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    Tad Boat Designer

    Yes Will, that was Craig Walters electric cruiser.......would be the ducks knuts today.....;)

    No it does not make any sense to spend tens of thousands replacing the bottom of a boat that gets used even 100 hours a year. Payback might start to make sense if you are using her over 500 hours per year.....but it depends on what you pay for fuel......
     
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  8. Chuck Losness
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    Chuck Losness Senior Member

    I was not thinking of redoing the entire bottom. Just to try to fair in the last couple of feet into a swim step/hull extension to smooth out the flow and add a little more waterline. You are going to have a swim step anyway so why not make it a part of the hull. Boats cruising here in Mexico all seem to be done by the stern a bit. A little extra flotation aft would help this out. And I wouldn't move any of the major components. In looking at boats in the yards down here some would be better candidates than others.
    And you are correct that it doesn't make financial sense to modify a boat if you are not going to use it much. I am currently putting 200 hours per year on my engine and maybe 30 to 40 hours per year just under sail. I do motor sail a lot. At least 50% of the time that I am under power.
    One of the reasons I am looking for a fuel efficient power boat besides being tried of sailing is because I would like to move the boat back to California to avoid the summer heat and humidity and then return to Mexico for the winter and spring. My usage would at least double, maybe triple if I do this.
    The size range I am looking at is around 40' LOA with at least 36' LWL. So I will keep searching and see what I find.
    Thanks again everyone for your input.
    Chuck
     
  9. Tad
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    Tad Boat Designer

  10. Easy Rider
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    Easy Rider Senior Member

    Because it's not a full displacement hull. But I see no pics of her bottom so I'm just assuming (to some extent) her below the water line form. Seems to me recently I was surprised to find out how close to full disp. the Defever is. This one looks like it's bow down or is it w an inaccurate water line (paint wise). Looks like it would be scary in following seas. Also it seems too wide in the stern to be really efficient.
     
  11. FAST FRED
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    FAST FRED Senior Member

    One of the reasons I am looking for a fuel efficient power boat besides being tried of sailing is because I would like to move the boat back to California to avoid the summer heat and humidity and then return to Mexico for the winter and spring. My usage would at least double, maybe triple if I do this.

    IF you are willing to downsize a bit , there are many boats that can be trailered with ease.

    No disrespect , but a 28 ft Bayliner or similar might fit the bill.

    60mph on the highway at 8-15mpg is a nice way to get to the different locations.

    And the "performance" requirements are very different when the boat does not transit ocean on her bottom.

    FF
     
  12. Chuck Losness
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    Chuck Losness Senior Member

    FF
    I have thought about that. Problem is I live aboard so trailerable boats even with an oversize permit may not be big enough and virtually every marina in
    California requires at least a 35' boat for a live aboard. To cover as many bases as I can I need at least a 35' boat. But I don't want to go too big because as displacement/weight increases so does the power required to move it. Vicious circle with no easy answers.
    And there is the option to make my current boat more of a motorsailor with a slightly larger engine/prop, add a swim step/transom extension and fully enclose the cockpit with sunbrella and windows. Even doing that my cruising speed would probably only increase to 7 knots with a definite increase in fuel consumption and I would still be dealing with a sailboat.
    So back to the search for now for a powerboat.
    Boats on my current short list include Roughwater 35, 36 & 37, Luhrs Alura 35 (would require repower with diesels). the Sea Quest/Sun Yong 37 & 39. Then there is always the possibility that I will run into a very good deal on a typically trawler/motorboat such that I can afford to pay for the extra fuel with money saved on the purchase price. People are working away from boats down here, Not many and mostly sailboats. I hear of a couple each year. The banks just bailout of them because the cost to pay a deliver skipper and crew to get it back to the states plus curing the deferred maintenance in order to sell it aren't worth the hassle.
    I really appreciate everyone's input and suggestions.
    Chuck
     
  13. FAST FRED
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    FAST FRED Senior Member

    "But I don't want to go too big because as displacement/weight increases so does the power required to move it."

    Only true if the boat is blown up like a balloon .

    OF you built a 8.6 wide boat that was simply LONGER the relative weight and power required go DOWN.

    Long Skinny boats are really easy to push at speed with remarkable efficiency.

    If the Length / Beam ratio get above 6 real efficiency becomes possible.

    Here are the lines for a "Box Boat " one slim enough to fit in a std shipping container 7.6 wide 39ft long.

    The concept was to simply use a std box to take the boat to any destination in the world , Big ship handles the ocean , and large distances , cheaper than even sail.

    This is a modification of an Atkin box keel , reverse deadrise design.

    FF
     

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  14. Chuck Losness
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    Chuck Losness Senior Member

    FF
    I have thought of that concept also. Even done some simple crude drawings to get an idea of shape and interior layout. Don't really want to build a boat myself and can't afford to have a boat built. I don't know if the fuel savings would be sufficient to offset the cost to build verses the cost for an existing boat with higher fuel consumption. Probably not. The most I would probably do is take an existing hull like a Willard 40 navy boat and build my own cabin and deck. Could get exactly what I want interior wise doing that. Fuel consumption would hopefully be in the 1 1/2 to 2 gph range at 8 knots. I do like the concept and will probably pursue it further. Instead of an akins box keel which I think would be too flat and pound like the devil, I have thought of a hull design with a shallow keel that the engine would sit down into. Something more like the keel on a sailboat. I'll work on a simple sketch.
    Thanks for the suggestion.
     

  15. sabahcat
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    sabahcat Senior Member

    From another forum I had this from an owner of the pictured vessel.

    [​IMG]

    I like the concept.

    I wonder how a re jigged fatter version with decent accommodation and smaller diesel aiming at a 16 on the fly and a 10 cruise would go?
     
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