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Discussion in 'General Yachting Discussion' started by Ben, Feb 9, 2005.

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  1. Ben, Feb 9, 2005
    #1
    Ben

    Ben Senior Member

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    Hello all, this is my first post, and I thought I'd use it to clear up a few nagging questions that I've not been able to find answers for. I'm quite new to the whole megayacht thing and am trying to gain a basic understanding. ;)

    My previouse experiance is limited to occasional weekend use of an 18ft bow-rider, some years ago. Here goes.....

    First is a simple question, more of a clarification. Does the word "Draft" refer to the depth of the vessel in the water, or the amount of water required to safely use the vessel?

    Next, I'm fascinated by the idea of having a boat with an ice strengthened hull. Is there a difference between 'ice strengthened' and 'ice breaker'? Would it be possible to strengthen, say, a large steel hulled motor yacht for use in icey areas (not ice breaking)?

    I've seen someone refer to 'beam penalties' when berthing a yacht. I understand this to mean that wider yachts will be charged more for a berth, could someone elaborate on the specifics? i.e. how wide and how much extra cost (on average).

    Any help appreciated. :)

    Ben.
  2. JonS, Feb 9, 2005
    #2
    JonS

    JonS Senior Member

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    Draft is the depth of the hull below the water line.

    Would have to pass on the other two for the mo.
  3. AMG, Feb 10, 2005
    #3
    AMG

    AMG YF Moderator

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    Hi Ben and welcome to the Forums!

    As Jon said, the draft, or draught, is how deep the lowest fixed part will intrude below the waterline. In reality, you can drive a fast boat in more shallow waters as long as you can maintain speed and the opposite goes for a displacement yacht which will increase it´s depth-going at speed. The sea itself is not like a dance-floor either and you have to consider swell or wake and ebbtide situations when you compare to the chart.

    The ice-strengthening is used on many yachts and even more on ships and ferries. An ice-breaker has on top of that a hull that allows it to climb and press the ice, combined with ballast tanks to make it roll if needed. On yachts you often have stabilizers that have to be removed if going in real ice and the props are not the best either. Many times the stern on a yacht is straight and not very good if you have to go back through ice. So ice strengthening allows you to go where ice-breakers operate to put it simple.

    The beam penalty is an expression often referred to with catamarans, as most ports where you have the yachts stern to, side by side, are charging as if you were a "normal" mono hull. So if you have let´s say a 30 % wider boat than the average mono-hull, you are charged about 30 % extra since this slip would normally take a much longer/larger yacht than yours.

    /Lars
  4. Ben, Feb 10, 2005
    #4
    Ben

    Ben Senior Member

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    Thanks for the help guys.

    I'm still a little foggy on the specifics of ice-strengthening. :eek:
    The website for Sinbad has pics of the conditions I had in mind. Would you need to worry about the stabilizers and props if you were in those kinds of waters?

    Would anyone know of a website that lays out the classes and ratings (I presume there are ratings?) for ice capable craft?

    Thanks again. :)

    Ben.

    Ps. love the yachts designs Lars. :D
  5. AMG, Feb 10, 2005
    #5
    AMG

    AMG YF Moderator

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    I am glad you like my designs, hope to make some more soon... :)

    On Sinbad, she is a composite yacht and might be strong, but I don´t know how the classifications of FRP-boats ice-strengthening goes. With a bulbous bow and zero-speed stabilizers she is anyhow not made to BREAK ice.

    For your second question, I have not been to a website with this information, but you might find some through Google?

    /Lars
  6. Ben, Feb 20, 2005
    #6
    Ben

    Ben Senior Member

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    Ok. Got a new question for you....

    Why do some boats lean in when they turn (like motorbikes) and some lean out (like cars)?

    I've noticed that it's usually smaller boats that lean in, and larger that lean out, so I have two thories.

    1. The type of propolsion used. Anything with a "leg" leans in, fixed shaft prop' and rudder leans out.

    Or

    2. The type of hull. Planing hulls lean in, displacement leans out.


    So far I'm going with No.2, but they could both be wrong.

    Anyone? :confused:


    Ben.
  7. D'ARTOIS, Feb 22, 2005
    #7
    D'ARTOIS

    D'ARTOIS New Member

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    Depends on the turning direction of propellor......
  8. YachtForums, Feb 22, 2005
    #8
    YachtForums

    YachtForums Administrator

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    As a general rule, this would be correct, but there are some variables.

    A round bilge, displacement hull lacks lateral hydrodynamic support when turning. As a turn begins, water pressure begins to increase along the forward section of the hull and continues to build along the hull side, causing the un-supported weight of the vessel (above the waterline) to shift to the opposite side of the turn. The more top-heavy the vessel is, the more pronounced the lean would be (without stabilizers). Without having a hull form that enables lateral support, the hull will have tendency lean outwards.

    In contrast, planing hulls, which by their very design, offer a planing surface in which hydrodynamic pressure and lift is derived on either side of the hull when turning. As a turn commences with a planning hull, the sharper deadrise of the forward section will allow the hull to begin leaning to the inside, which is coupled with pressure building on the opposite side of the hull (center to aft section) that supports the lean. During the turn, the hull’s main hydrodynamic support will be derived from the mid to aft section of the hull (on the inside of the turn).

    Not to confuse you but, a planing hull can also lean to the outside at high speed. Much of this has to do with weight distribution above the waterline. If sufficient weight is present to the outside of the hull when turning, the hull will typically turn very flat, bordering on an outside lean. And just to mix it up a little more, a displacement hull with a very low Center of Gravity CAN lean inside.

    Often, displacement hulls are used on larger vessels, which may have a higher center of gravity. This configuration will have a tendency to lean out when turning. However, a top-heavy planing hull can lean outwards at displacement speeds TOO. Once a planing hull has achieved plane, it will generally lean to the inside.

    Carl
  9. Ben, Feb 22, 2005
    #9
    Ben

    Ben Senior Member

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    Ok, so not quite as simple as I thought. :eek:

    Thanks for the in depth reply carl, much appreciated. ;) :)



    As a follow on (sort of) what makes a monohull roll?

    If you had a monohull boat parked in small rolling swell, coming in straight at the side (90 deg.) what is making that boat roll (excluding the use of any stabilizers)?

    Is it the water pushing on the side of the boat, or the water lifting one side and then the other, or both of the above, or niether? :confused:

    Thanks again. :D

    Ben.
  10. Ben, Feb 28, 2005
    #10
    Ben

    Ben Senior Member

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    Hi all, me again.... :rolleyes:

    Could someone tell me why some yachts are "MY" and some "MV", and what do they stand for?

    Thanks.


    Ben.