Help With Economical Semi-Planing Designs

Discussion in 'Powerboats' started by SAQuestor, Apr 5, 2007.

  1. fcfc
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    fcfc Senior Member

    There are also stupid silly figures I do not understand.

    For the Andreyale, when they claim 2nmpg at 15 kts, that 7.5 gph for both engines, 3.75 gph per engine. When I look in the test performance curve, I see 3000 rpm 14.3 kts, 3300 rpm, 16.3 kts. So A wild guess of 3150 rpm for 15 kts may not be too wrong. And when I look at yanmar consumption curve for 3150 rpm, http://www.yanmar.com.au/express/Dealer/Prodspec/ENGINE PDF/4JH3_HTE_TechData.pdf , the manufacturer quoted engine consumption is under 3.75 gph (around 3.5 gph). So all look realistic and match.

    For the Shannon, 18.5 kts at 11 gph, I see from the motorboating test that for 2750, the speed is 16.9 kts and at 3000 rpm, 18.6 kts. So a wild guess of 2950 rpm for 18.5 kts may be true. But when I look at the manufacturer consumption curve http://www.yanmar.com.au/express/Dealer/Prodspec/ENGINE PDF/4LHA-HTP_TechnData.pdf , at 2950 rpm, the fuel burn is over 6.5 gph, not 5.5 gph as claimed. So I fear either the speed at 11 gph is under 16.9 kts, or the fuel burn at 18.5 gph is over 13 gph. Unless of course Yanmar claims that its engine burn more fuel than they actually burn.

    18.5 at 2 nmpg is 9.25 gph. 13 gph is somewhat more than 30% higher.

    Now, if someone could explaine me where is my error ...

    The other speed computation.
    From the test, at 18.5 kts, the Andreyale would have its engines at 3700 rpm. At this speed, the Yanmar consumption is around 5 gph per engine. So that would 10 - 10.5 gph overall.

    At 15 kts, the Shannon 38 engines are at 2400 rpm. At that rpm, it is 4 gph. So 8 gph overall.
     
    Last edited: Apr 8, 2007
  2. FAST FRED
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    FAST FRED Senior Member

    Unless of course Yanmar claims that its engine burn more fuel than they actually burn.

    The engine mfg give the fuel burn at max hp at each point on the rpm graph.

    Since the boats are usually set (propped)to get peak hp at max Rated rpm , any pullback will lower the power the prop can pull at the lower rpm.

    So the Yanmar may be capable of creating 6gph worth of hp , but its only being asked to produce 5gph by the prop requirements at that rpm.

    FF
     
  3. fcfc
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    fcfc Senior Member

    Easy. Just read the consumption curve (4LHA) = 4 gph @ 2400 rpm. Now read the power curve @ 2400 rpm. 130 hp max output. 70 hp propeller curve. Now guess what power 4 gph refer to.


    BTW, what is the budget of a economical semi planning design as per the initial post ?

    Because bean counting the gph for a Andreyale 40 worth half a million $ used
    http://www.yachtworld.com/core/list...units=Feet&access=Public&listing_id=1808&url= is a bit meaningless.
    The owner of such a boat do not count 1, 10 or 100 gph ...

    I have looked in the O1 thread http://boatdesign.net/forums/showthread.php?t=12157 what could be such a beast.
    The only thing I have found:
    1) there is no practical layout.
    2) Budget over 45 000 $
    Machinery 40-50 hp 20 000 $ minimum from air vent intake and cooling water intake to exhaust transom , propeller, shafting and controls.
    Bare naked hull around 10 000 $
    Micelleanous fittings 15 000 $ (deck, interior, minimal electronics).
     
  4. FAST FRED
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    FAST FRED Senior Member

    Its probably cheapest to marinize a truck diesel.

    Most all the bell housings are SAE , so a huge choice of reconditioned marine trannys should keep the cost down.
    100hp to 250hp is easy. in truck hp not Marine rating.

    Instead of a heat exchanger , extra pump and costly wet exhaust , the commercial boat style keel cooler and dry stack is also inexpensive.

    The hull will probably be 5-6000lbs , probably hard to bring in for $10,000 in anything but strip plank wood , Epoxy covered.

    Ideas?

    FF
     
  5. fcfc
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    fcfc Senior Member

    Can you price a stainless steel dry muffler , ABYC compliant for a 50 hp engine. What size will it eat from accomodation ?
    Same for the sound proofing / thermal insulation / ventilation of a dry system.
    Same for a cupro nickel keel cooler.

    The fact is, at least for france, and certainly for whole europe, that if you do not comply with marine safety and pollution regulations, you will have very big problems entering any marina and trying to get any insurance coverage.
    The problem goes from fire hazard to exhaust smoke to noise to black water.

    And the cooling method of an engine may have an influence on the price, but it does not touch items like engine mounts, gearbox and couplings, remote control and instrumentation, fuel tanks and fuel system (vents,hoses, decks fittings, jauges , filters ...) , propeller and shafting (shaft, stuffing box, stern tube, cutlass bearings, ...) , etc etc etc...

    From my price estimation above, the basic industrial engine was around 5000 $. The marine engine derived from 11 000 $, and the whole thing that you start pressing a button from the helm station, read state from helm, fill fuel from the deck entry, can still speak while it is running, does not smoke black, and finally makes the boat go forward when you push the forward lever is 20 000$.
     
  6. fcfc
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    fcfc Senior Member

    I was speaking of a 31 ft. empty equiped weigth 4800 lbs. But bare naked hull and deck should be in 1000 -1500 lbs only in sandwich.
     
  7. fcfc
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    fcfc Senior Member

    Here, you can see a previsional budget for a 40 ft, single 250 hp engine :
    http://hawk41.awardspace.com/#toplist

    The grand total (without additional electric engines) is over 115000 € = 150 000 $ at current echange rate.
     
  8. FAST FRED
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    FAST FRED Senior Member

    On most workboats the ABYC is not involved and the exhaust is simply routed outside , thru one or two std truck mufflers.
    There is a requirement to heat shield the exhaust against people contact , but thats cheap screening.

    These truck exhausts seem to last for a couple of engines , so SS may be required as eye candy , but not for durability.

    The heat exchanger most often used is simple pipe.

    Our 6-71N with injectors for 180hp only requires 2, 21ft lengths of 1 1/2 pipe , bolted under the hull.
    We sometimes cruise in FL and Bahamas , with no cooling hassles.

    The pipe lasts at least a decade ( ours is over 2 , but well painted), and replacement would cost less than the VAT on a copper keelcooler setup.

    Some folks have used copper pipe , rather than water pipe , but I'm not sure that lasts any longer.

    FF
     
  9. fcfc
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    fcfc Senior Member

    Andreyale 33 already listed in pocket cruiser thread.
    http://www.yachtworld.com/core/list...=126&fromLength=30&toLength=35&currencyid=100

    More than 14 kts cruise with less than 100 hp.

    Economical :D :?: Budget 175 000 to 200 000 $ for a 6 year old used boat.
     
  10. Pericles
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    Pericles Senior Member

  11. fcfc
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    fcfc Senior Member

    As a matter of taste and colour :p , i would prefer this one http://www.cmdboats.com/rw26boxkeel.htm
     
  12. SAQuestor
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    SAQuestor Senior Member

    OK. Nice boat. Using my own labor over a 3 to 4 year build period, can I build one essentially equivalent in size and power for under $60K?

    Leo
     
  13. SAQuestor
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    SAQuestor Senior Member

    Here are a few pertinent pages about semi-planing/semi-displacement hulls from the book Working Watercraft of the World.

    Page 226

    Page 227

    Page 228

    Page 229

    Page 230

    Page 231

    My takeaways from these pages are:
    1. Fine entry.
    2. Flat buttock lines.
    3. Light weight.
    What other important ideas/features did your eyes pick out?

    Best,

    Leo
     
  14. tom28571
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    tom28571 Senior Member

    Leo, Those criteria seem to put us back just where we started. :D
     

  15. FAST FRED
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    FAST FRED Senior Member

    "Using my own labor over a 3 to 4 year build period, can I build one essentially equivalent in size and power for under $60K?"


    Probably , but the shown fit and finish will take years and loads more cash to get.

    If like me , a workboat style , clean and painted , with wood trim will do , it should be simple enough.

    If you need forests if endangered wood species to clad the interior and deck,and magnificent Joinery to show it all off, it would be cheaper just to buy a used one.

    FF
     
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