Hull shape design advice for 11.5m, 8kts, Fn=0.4

Discussion in 'Boat Design' started by ram68ocean, Jul 12, 2021.

  1. bajansailor
    Joined: Oct 2007
    Posts: 2,922
    Likes: 1,139, Points: 113, Legacy Rep: 37
    Location: Barbados

    bajansailor Marine Surveyor

    That is a very impressive looking vessel for sure.
    But for her to have a 4,000 mile range at 8 knots, burning 0.25 gallons / mile (or 4 miles per gallon approx) sounds rather optimistic to me.
    What make of engine is this, and what are the revs required for the boat to achieve 8 knots?
     
  2. container
    Joined: May 2019
    Posts: 50
    Likes: 26, Points: 18
    Location: new zealand

    container Junior Member

    I may be wrong here but from memory i think it is a scania derated to 550hp. not sure about revs, maybe 8 or 900? It is spinning a 900mm dia. Prop so it will not be much whatever it is. The boat is from the designers of Earthrace so i think they know what they are talking about.
     
  3. bajansailor
    Joined: Oct 2007
    Posts: 2,922
    Likes: 1,139, Points: 113, Legacy Rep: 37
    Location: Barbados

    bajansailor Marine Surveyor

    I am still a bit dubious about these claims - do you have any links re further info on this vessel please?
    And do you know what the load displacement of this sportsfisherman is?
     
  4. ram68ocean
    Joined: Mar 2013
    Posts: 47
    Likes: 2, Points: 8, Legacy Rep: 10
    Location: Europe

    ram68ocean Junior Member

    It looks very cool. I like that sheer line. Thanks for sharing. The consumption is less than half that what I have initially estimated though.
    Is the designer lomocean ? Do you have more info?
     
  5. ram68ocean
    Joined: Mar 2013
    Posts: 47
    Likes: 2, Points: 8, Legacy Rep: 10
    Location: Europe

    ram68ocean Junior Member

    Would diesel consumption change significantly if it had smaller twin propellers instead of one large one?
     
  6. bajansailor
    Joined: Oct 2007
    Posts: 2,922
    Likes: 1,139, Points: 113, Legacy Rep: 37
    Location: Barbados

    bajansailor Marine Surveyor

    Here is a link to her on the Lomocean website (thanks for the mention of them - I have them bookmarked now) - the range is not mentioned though.
    LOMOcean Design | Naval Architecture and Yacht Design - 14.9m - Sea Wolf http://www.lomocean.com/projects/pleasure/14.9m+-+sea+wolf

    All else being equal, the fuel consumption would go up if you have two smaller propellers, when compared against one larger propeller.
     
    Last edited: Jul 20, 2021
    ram68ocean likes this.
  7. container
    Joined: May 2019
    Posts: 50
    Likes: 26, Points: 18
    Location: new zealand

    container Junior Member

    Yup thats her. light ship displacement is ~15t so around 20 with full fuel and water
     
  8. container
    Joined: May 2019
    Posts: 50
    Likes: 26, Points: 18
    Location: new zealand

    container Junior Member

    Attached Files:

    ram68ocean likes this.
  9. ram68ocean
    Joined: Mar 2013
    Posts: 47
    Likes: 2, Points: 8, Legacy Rep: 10
    Location: Europe

    ram68ocean Junior Member

    hello $, thinking now of vessel design cost and times, would anyone know a rough range of what could cost for a design naval architect studio to provide a full design (excluding shipyards scope) for such a vessel? Does USD 200-300 k sounds reasonable?
    Thinking of an established design office medium size up.
    Do you know if there are previous conversations and spreadsheet for a design office to budget and cost estimate the design cost ?
     
  10. bajansailor
    Joined: Oct 2007
    Posts: 2,922
    Likes: 1,139, Points: 113, Legacy Rep: 37
    Location: Barbados

    bajansailor Marine Surveyor

    Re 'such a vessel', are you referring to your original concept, or to the vessel that Container linked to above?

    I had a chat with Eric Sponberg (who used to post on here quite a lot until he retired and went off sailing around the world) some years ago, about having design drawings done for a vessel, and I seem to remember that it worked out then to around US$ 1,000 per drawing.
    Home https://www.ericwsponberg.com/
    US$200k sounds like a lot for the design fees for a one off vessel around 15m. in length.
     
    ram68ocean likes this.
  11. ram68ocean
    Joined: Mar 2013
    Posts: 47
    Likes: 2, Points: 8, Legacy Rep: 10
    Location: Europe

    ram68ocean Junior Member

    I was referring to the original concept (which i think is comparable to the 15m lomocean vessel). But it is clear now that many compromises will have to be taken from the original brief.
    Glad for Eric, well deserved. US$ 1,000 per drawing sounds rather cheap for high quality drawings, there's lot of work and time put behind the drawings.
    How about:
    review design specs, agree compromises with client
    refine or redo the GA
    create a 3d hull shape, deck, mast
    weight estimate, equipment list
    develop a 3d model with main large and heavy equipment
    regulations compliance
    powering study, cfd,
    chosing an engine and propulsion
    fuel tanks sizing
    motions study
    hull optimisation
    define the structure, 3d and 2d
    fea study for structure, noise and vibrations
    electrical load balance
    integrate all equipment
    schematic of all systems onboard (fuel, water, bilge, exhaust, ventilation, etc.)
    prepare deliverables, reports, admin.
    others​
    It seems that the big of the work is the initial communication with client and understanding their needs and what is able to compromise.
     
  12. ram68ocean
    Joined: Mar 2013
    Posts: 47
    Likes: 2, Points: 8, Legacy Rep: 10
    Location: Europe

    ram68ocean Junior Member

    Hi folks, another question regarding choosing an adequate hull shape.
    I have set the main dimensions as 15m length by 3.4m beam.
    The power boat will have a variable loading condition of volumetric displacement between 11 m^3 (min.) and 19 m^3 (max.).
    Typical speed will be between 6 and 8 knots. And will be exposed to offshore heavy seas.

    Could you advice of adequate hull shapes for this scenario?
    I have attached 4 hulls I came up with. Two hard chine and two sailboat type.

    Assumptions:
    -the GA/equipment is fitting inside. (already pre checked)
    - Zero trim angle assumed for min. and max. loading conditions. (will tackle this next)

    Any thoughts are welcome. Thanks

    upload_2021-9-19_19-56-37.png

    upload_2021-9-19_19-57-8.png upload_2021-9-19_19-59-1.png
     

    Attached Files:

  13. DCockey
    Joined: Oct 2009
    Posts: 5,122
    Likes: 568, Points: 113, Legacy Rep: 1485
    Location: Midcoast Maine

    DCockey Senior Member

    Where is the design waterline? How much of the transom is immersed? A deeply immersed transom at slower speed can result in significant drag.
     
  14. bajansailor
    Joined: Oct 2007
    Posts: 2,922
    Likes: 1,139, Points: 113, Legacy Rep: 37
    Location: Barbados

    bajansailor Marine Surveyor

    This is a rather skinny vessel, with a L/B of approx 4.4 - the 'average' type of power boat usually has an L/B ratio around 3.

    So does this mean that the difference between the lightship and fully loaded conditions is approx 8 tonnes?
    If so, then that is a heck of a lot of difference!

    Re the 'offshore heavy seas', bear in mind that there is a relationship between vessel beam and wave height re waves capsizing a boat - I think it is something like a capsize scenario could happen if the wave height is equal to the beam, and the vessel is caught beam on to the seas.
    Which would suggest that your autonomous vessel could capsize in 11' high waves out in the ocean.

    I have just had a quick scan through the previous 3 pages of this thread, and I see no mention of a catamaran hull form - have you considered this possibility at all?
    Although if you really have to carry a payload of perhaps 8 tonnes, then a catamaran is probably not going to be very suitable.
     

  15. ram68ocean
    Joined: Mar 2013
    Posts: 47
    Likes: 2, Points: 8, Legacy Rep: 10
    Location: Europe

    ram68ocean Junior Member

    How do you set the DWL ? At what loading condition, 50% fuel ?
    I was asking myself about the transom immersion. How much is reasonable?
     
Loading...
Forum posts represent the experience, opinion, and view of individual users. Boat Design Net does not necessarily endorse nor share the view of each individual post.
When making potentially dangerous or financial decisions, always employ and consult appropriate professionals. Your circumstances or experience may be different.