Searching for fuel efficient powerboat

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

  1. Willallison
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    Willallison Senior Member

    Me too... except I have somewhere to sleep and eat....
     

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  2. sabahcat
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    sabahcat Senior Member

    Another pic I just found

    [​IMG]

    and some more information here http://islandcarabao.com/Design.html (this interweb thing is great)

    Being 64 ft in length and 5 wide I would like to think it had some room in side, though it appears somewhat limited
    [​IMG]

    Plus with the stabilising floats well, it would be stable.

    Any more details on yours Willallison?
     
  3. Willallison
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    Willallison Senior Member

  4. sabahcat
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    sabahcat Senior Member

  5. FAST FRED
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    Location: Conn in summers , Ortona FL in winter , with big d

    FAST FRED Senior Member

    I happen to have a 50 ft Navy Utility that has been modified to a lobster style boat.

    We bought the boat to run the LOOP, and the huge rub rail and insane overbuilding were always a delight.

    7K is 2 1/2 to 3 Gph , as the 6-71 is operating WAY below its optimum efficiency.

    A 2-71 or a 3-71 would be a better displacement engine , but 10-12K at times is fun ! but also 8-10GPH

    A modern 4 stroke of about 100hp would be ideal.

    The amount of room is not what you would expect as the rear 15ft of the boat is open , the interior is small as the boat is low for modest offshore work. And inshore an air height of under 12 ft works quite well.

    A 50 could simply be carved a bit and a 32 ft Airstream ( $3000-4000 used) installed.
    Marine paint on the aluminum and you are almost done.

    As a launch there was no anchoring gear , bow roller or windlass .

    No big deal as the boat gas power hyd steering , so a windlass was simply some hose.

    Most any Auto Pilot will work as all it needs to do is control 1 1/2A solenoid valves.

    Boats and Harbors advertises functioning low time 50's for about $35K unmodified .

    IN FL if you want to see her.
     

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  6. Chuck Losness
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    Chuck Losness Senior Member

    Let's not forget that I am a full time liveaboard and have only been in a marina for 2 days in the last 2 years. The long skinny light weight tri's and cat's have their place but not for me. The anchors and chain alone would overload these boats. As much as I like the fuel efficiency of the cat's and tri's a monohull is a better fit for my intended use.

    FF
    I have noticed the 40' & 50' navy boats in boats and harbors for $30,000 give or take. Over priced. King Cattle Surplus just sold a 40 that they were asking $8500. Don't know what the sales price was. two 40's sold in San Diego a couple of years ago for around $4000 each. My recollection is that the only bidder was some local charity that intended to use the boats in some marine related program. Never heard anything more and have not seen them in use. Thanks for the info on your boat. I agree that a 671 is way too much engine. I think that 65 to 75 hp in a 40 would be more than sufficient for my needs.
     
  7. FAST FRED
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    Location: Conn in summers , Ortona FL in winter , with big d

    FAST FRED Senior Member

    I think that 65 to 75 hp in a 40 would be more than sufficient for my needs.

    Fine , but plan on a 6K cruise and 8K at flank for short periods of time.
     
  8. Chuck Losness
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    Chuck Losness Senior Member

    Just curious on how you came up with your speed estimates with 65 to 75 hp. The info that I have been able to find indicates that the 40's weigh just under 16000 lbs light and have 39' LWL. Using the tables in the nature of boats I calculated that one would need 15 to 20 hp to go 6 knots and around 32 to 36 hp to do 8 knots depending on displacement. Flank speed should be around 9.5 knots. For a comparison, my Gulfstar 37 at 20000 lbs and 34 LWL does 6 knots using around 20 hp and it drags its transom through the water at that speed similar to a semi-displacement hull with an immersed transom.
     
  9. Steve W
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    Steve W Senior Member

    Most sailboaters are used to slow speeds so a 6k cruise speed in a powerboat represents better vmg than even quite a fast sailboat. For me mpg trumps speed any day on the water and on land.
    Steve.
     
  10. Easy Rider
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    Easy Rider Senior Member

    Chuck,
    You're thinking and talk'in full disp and FF is talk'in about his semi-disp boat.
    Big difference.
     
  11. sabahcat
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    sabahcat Senior Member

    How do you figure that?

    As an example, a 50 ft sailing cat would usually have 200kg of anchoring gear(75m of 10mm chain + 80lb anchor)

    It would also have 300kg + in rig, sail and winch weight.

    My 50ft Powercat, based on a sailing boat, carries the same sort of anchoring gear but does not have the 300kg+ in rig, sail and winch weight.

    The same comparison can be done on pretty much any design as regardless of whether it is power or sail, it will have been designed to carry anchoring gear

    How did you work out that they are overloaded?
     
  12. Chuck Losness
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    Chuck Losness Senior Member

    Sabahcat
    I was referring to the latest long skinny trimaran that was posted and to similar ultra, ultra light displacement tri's and cat's. Not your typical cruising cat or tri that would probably have 4 to 5 times the displacement of the pictured tri. I am sure that your 50' power cat displaces far more than 3 tons.
    Your typical cruising boat in my area carries considerable more ground tackle than what you mentioned. On my current boat I have all total 300' of 3/8 chain, 600' of 1/2 rode and 200' of 5/8 rode, and a 44lb bruce, a 39lb bruce and a 22lb danforth. Some of my friends think I am light on my chain for my second bow anchor, only 50', and that I should have at least 100'. They also think that I should carry at least another 45lb anchor of a different style and another danforth. Nobody here uses 10mm/1/4" chain for their anchors. The minimum size you see is 5/16 chain and most long time cruisers use 3/8 chain. I don't know the weather conditions that you face in your area so please don't take offense or think that I am being critical of your choices. I am not. I am only relating what is used by cruisers on the west coast of Mexico to deal with the conditions that we face.
    And yes I think that if you put adequate ground tackle for even that lightweight 64' boat it will be overloaded.
     
  13. sabahcat
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    sabahcat Senior Member

    They obviously are considerably heavier and have considerably more draft requiring deeper anchoring depths and scope.

    Having a 3 ft draft it seems silly to anchor in any more than 15 to 20 ft (6m) so 5:1 scope is 30m making 75m of chain more than adequate.

    Check your maths Chuck.
    10mm chain IS 3/8th. (3/8th = 9.5mm)

    And yet, right at the pointy end is a seemingly sizable anchor for such a light vessel and still the bows float free.
    [​IMG]
     
  14. Chuck Losness
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    Chuck Losness Senior Member

    sabahcat
    My mistake on the chain size not being familiar with metric. Sorry.
    I don't disagree with your thoughts on scope and I routinely anchor in 15 to 20 feet and even less. My boat only draws 5'. I typically use a little more scope but not enough that it would make any difference. Except in the summer, July, August & September. During these months I typically put out all my chain, 200' on my main bow anchor, and still try to anchor as shallow as possible. The Sea of Cortez gets two really nasty winds in the summer months. Chubascos and El Ephantes. These winds can not be forecasted with any certainty.
    El Ephantes are a gap wind caused by localized atmospheric pressure differences between the west coast of Baja and the Sea of Cortez. They can blow at any time of the day or night and routinely reach 50 to 60 knots with little or no warning. They just hit you like they are shot out of a gun. They typically last for 2 to 3 hours and die off as soon as the pressure differentials equalize.
    Chubascos are much more complex and I don't know if I really understand exactly how they are caused. I will give it my best shot. These winds only happen at night and also come without warning. The extreme daily land temperatures along the Arizona, California and Mexican borders creates a thermal low in the 990 to 1000 millibar range. It is known as the "Yuma Low". This low sucks warm, moist tropical air from the pacific ocean off southern Mexico. As it funnels up the Sea of Cortez this warm moist tropical air rises in huge thunder clouds over northern mainland Mexico. This is a daily occurrence. Sometimes this warm air cools very quickly and falls back to land and fans out in all directions. Wind strength is typically 40 to 45 knots but 50 to 60 knots is not unusual. Usually lasts about 4 hours from 11pm to 3 am.
    We also get northers in the winter months caused by high pressure over the great basin in the US, 1035 millibars or higher, and lower pressure in the 1015 to 1020 range in the Sea of Cortez. The weather forecasters are pretty good about predicting these winds but can be way off in wind speed. I typically increase my scope to 8:1 to 10:1 in northers. Wind speeds range from 20 to 25 knots to over 50.
    As you can see, adequate ground tackle is important to me. Backups are necessary. And it's all very heavy.
     

  15. sabahcat
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    sabahcat Senior Member

    Thats OK and, reading your post again you did put a clarifier in there as well, which, gong on what you say sounds a more than fair enough decision.
    If I was in the land of predominately wind and rough I would have a somewhat different vessel want as well

     
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