How much displacement not due to boat?

Discussion in 'Sailboats' started by hiracer, Oct 17, 2006.

  1. hiracer
    Joined: Jun 2006
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    Location: Puget Sound, Washington, USA

    hiracer Senior Member

    36' over deck.
    30.3' lwl
    11.5' beam

    34 hp perkins diesel
    99 gallons of diesel
    17 gallons of kerosene for heater
    120 gallons of water
    35 gallons holding tank
    SS arch on stern
    radar
    2 GPSs
    Solar power and smart charger
    full electronics including SSB, navigation instruments, lights, VHF, AC, invertor, CD stereo, microwave, television, etc.
    Monitor self steering
    pressure fresh water
    Pressure salt water for anchor chain
    three anchors and 300' 5/16th chain plus 900' of nylon rode
    Sea anchor and drogue, harness, jack lines, tethers
    8 or 9' roll up Avon with 5 hp yamaha, three gallons of gasoline
    2 20# propane tanks, 3 burner stove with oven
    cooking ware, plates, bowls, cups, etc.
    Food and clothes for four people for 2.5 month summer trip to Alaska
    etc. ????

    Question one: Approximately how much does all this stuff weigh above light boat displacement?

    4,000 lbs, 5,000 lbs, 6,000 lbs?

    Question two: Does the displacement figure provided by N.A. to steel home builder include weight of diesel engine? Does it include interior? What does it include and not include??

    Trying to get the displacement of my boat by going backwards at it. I bought it used from homebuilder.

    Thanks.
     
  2. Trevlyns
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    Trevlyns Senior Citizen/Member

    My understanding (as an amateur designer) is that displacement can be either weight displacement (the weight of an empty yacht) or volume displacement which is the volume of the immersed part of the yacht in “sailing trim.” Generally however, the displacement mentioned in design literature refers to the volume displacement and would certainly include the mass of the engine, all furniture and fittings, designed fuel and water loads, rigging, sails etc. The architect designs the yacht to “sit” at a certain level in the water (the water line) when loaded – that’s why an empty yacht will sit higher than the designed water line. Another reliable guide as to what the yacht can carry is the pounds per inch immersion figure (or metric equivalent). As its title suggests, it shows how much additional weight would be required to sink the yacht 1 inch lower in the water.
    To try and answer question one; I’m sure that all the items you mentioned would be included within the “displacement” specified by your designer. Of course, if you have any further doubt, make contact with the designer.
     
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  3. hiracer
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    hiracer Senior Member

    The design displacement is a little over 17,000 lbs. Actual weight after loading cruising stores is 23,000 lbs.

    How does the designer know how much tankage the home builder will put in? In my case, there is more than 2,000 lbs of tankage alone. I doubt the designer planned that much tankage or that it is factored into the "official" displacement.

    With steel construction, I suspect there is pressure to underrepresent displacement. I gotta believe some of the difference between 23,000 lbs and 17,000 pounds is in cruising stores and tankage.

    Don't builders habitually underrepresent displacement? But we are to believe designers never do?
     
  4. jehardiman
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    jehardiman Senior Member

    Hiracer, the displacement given by the designer is based upon the displaced water with the vessel sitting on her designed waterline with all gear, stores, and crew aboard. This total is based upon the lightship weight (the weight of the hull and all non-removable equipment and minimum fluids) plus the load list. The load list defines the weight of tankage (based upon the designers whim but usually 50%, 75%, or rarely 100%), stores (again some precentage based upon storage volume), outfit (usually some minimum equipment set), and crew. If you have the full builders drawing package it will have the load list and the D&O's which should have the answer to you questions.

    If you know all that you are going to carry, just add it up...normaly stores (ediable food and packaging, paper goods, etc) are expended at ~ 3.5-5 lbs/person/day and drinking/cooking water and beverages are ~ 16 lbs/person/day unless a watermaker is installed in which case it varies from 4-12 lbs/person/day. Crew is 165-200 lbs, and a sea kit is ~100-175/person.

    Gedunk and pogy bait is extra and ~10-15 lbs/person. ;)
     
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  5. Ike
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    Ike Senior Member

    Gedunk and pogy bait. Now there are two words I haven't heard in years.
     
  6. Mychael
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    Mychael Mychael

    .

    And those things would be????

    Mychael
     
  7. jehardiman
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    jehardiman Senior Member


    Personal food, sodas, candy, etc. brought aboard above the normal allowance and stowed in hidey-holes, puka's, and occasionally your rack. Gedunk and mightneeds are one of the major causes of weight growth in boats and ships.
     
  8. hiracer
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    hiracer Senior Member

    I do have those. Just got them a few weeks ago. I'll take a look, thanks.

    But really my reverse approach is to determine, roughly, whether the boat is built overweight. The builder was skilled (owns and operates a steel fabrication/building company) but at 23,000 lbs I'm trying to figure out where the weight is coming from.

    After running the calculations on the tankage, I'm certainly getting strong hints. That's a lot of tankage for this sized boat.
     
    Last edited: Oct 23, 2006
  9. Raggi_Thor
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    Raggi_Thor Nav.arch/Designer/Builder

    In productin boats it's a problem that designers normally mean the boat in sailing condition when they say "displacement", while sales people want that number to be as small as possible so they talk about light ship weight.
     
  10. FAST FRED
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    FAST FRED Senior Member

    "In productin boats it's a problem that designers normally mean the boat in sailing condition when they say "displacement", while sales people want that number to be as small as possible so they talk about light ship weight"

    Except of course on the old Westsails where the farmers thought heavier was better, so the fully loaded ,ready for Cape Horn , non stop, weights were in the literature.

    A great marketing trick was the top of the companionway hatch combing was opened by pushing on a teak 2X4 .

    Felt increadibly substantal like you were going aboard the QM.

    Boob Bait for da Bubbas!

    FAST FRED
     
  11. hiracer
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    hiracer Senior Member

    But my boat is custom, not production.
     
  12. Raggi_Thor
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    Raggi_Thor Nav.arch/Designer/Builder

    Yes, I think the designer should give you a weight estimate for each item in the boat, hull, deck, structure, equipment and then a total displacement or a range, so that you can see how much gear you can have.
     
  13. hiracer
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    hiracer Senior Member

    Well, I got out the plans.

    Arrrgghh! Coffee stains right where displacement is stated. Looks like "17,000 lbs F.W." but not sure at all.

    Brewer's web posting of the design states its displacement as 17,000 lbs. So that confirms something, but not sure what.

    No way a 36' LOD steel sailboat is going to weigh 17,000 lbs fully loaded with cruising stores.
     
  14. Raggi_Thor
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    Raggi_Thor Nav.arch/Designer/Builder

    Why not?
    Can you measure the area of the midship section?
     

  15. naval ark
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    naval ark Member

    The displacement would certainly include the diesel engine, possibly even a little bit of fuel (if you're lucky). It would include some basic interior, but most certainly not include your arch, SSB, microwave, television, etc. It also wouldn't include the 3 anchors, 300ft of chain, sea anchor, roll up Avon, etc.

    It's not unreasonable for a 30ft Lwl steel yacht to displace 17000lbs, as you'll have 4mm plate and relatively little internal structure as the plating will carry a lot of the loadings. However, I would be very surprised if you were anywhere near that figure with the amount of kit that's currently on board!!
     
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