yacht sunk in med

Discussion in 'Boat Design' started by peter radclyffe, Aug 19, 2024.

  1. Stephen Ditmore
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    Stephen Ditmore Senior Member

    Would it help if parts of US 46 CFR § 171.055 were adopted by LY?
     
  2. philSweet
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    philSweet Senior Member

    Regarding the hull side vents - by them selves, they don't indicate a problem. It's what's going on inboard of the vents that matters. If the hull vents for the engine room air exchange are connected to each other right across the beam of the boat with a duct that is built like the hull, and that duct is teed on the centerline to vent into the engine room and equipped with a shut off damper, then it doesn't down flood, and the damper can be triggered with a tip-over switch. This is normal on all kinds of things. I would also expect none of the main engines and main generators to run off engine room air, but the little night generator might. So the combustion air and exhaust shouldn't be a path for downflooding either.
     
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  3. Stephen Ditmore
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    Stephen Ditmore Senior Member

    What I'm wondering is whether we should look at the whole problem in terms of the vessel's ability to trap air as much as keep water out.
     
    Last edited: Sep 8, 2024
  4. bajansailor
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    bajansailor Marine Surveyor

    What an excellent article, thank you Tad.
    It is really bordering on criminal re how the average powerboat can have engine room vents that are essentially just holes in the topsides that are covered by rudimentary cowls.
    If they are knocked down (or even just take a wave on the beam), water will flood in through these vents.
    And very few are ever fitted with remote operation dampers that can close the vents in the event of a fire.

    The RNLI lifeboats in England have amazing Premaberg vents in the superstructure for supplying (and exhausting) air to their engine rooms.
    Single stage air water separators - Premaberg Manufacturing Limited https://premaberg.com/product-overview/single-stage-air-water-separators/

    These vents also filter out (salt) water droplets, giving clean and relatively dry air to the engines.
    The lifeboats also have remote dampers in the vent trunks that can be closed manually, and if the vessel is capsized by a wave they are weighted and will close automatically, and then open again when the lifeboat comes back upright (as they are all self righting through 360 degrees).

    Edit - I forgot to add the Premaberg link earlier.....
     
    Last edited: Sep 9, 2024
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  5. peter radclyffe
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    peter radclyffe Senior Member

    “In adverse weather conditions and where there is the possibility of encountering a severe gust, squall or large breaking wave, all exposed doors, hatches, skylights, vents, etc. should be closed and securely fastened to prevent the ingress of water.”

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    Loose Cannon has obtained the stability information booklet on file with the British Maritime and Coastguard Agency for SV Bayesian, erstwhile SV Salute. It is 89 pages long and highly technical in nature. Reproduced here essentially verbatim is the section of the report entitled “Notes to Master.” Although it too is very technical, some of it should be enlightnening to the a savvy sailing enthusiast. Stand by, more to come: Loose Cannon has shared this report with collaborating naval architects to ascertain to what degree design played a role in the Bayesian catastrophe.

    1. General Instructions

    A stamped, approved copy of this booklet must be kept on board the vessel at all times. It must also be complete, legible and readily available for use. If this booklet is lost or becomes unusable a replacement copy of the approved booklet must be obtained immediately. The loading conditions shown in this booklet represent typical service conditions. Where a loading condition departs from those shown in this book a separate calculation should be made to ensure compliance with the stability criteria.

    2. General Stability Requirements

    It is important to ensure in any sailing condition the stability of the yacht complies with the criteria of section 11 of “THE LARGE COMMERCIAL YACHT CODE (LY2)”. S/Y “SALUTE” is capable of sailing under power provided by the main engines and has to comply with stability requirements for both motor and sailing yachts. In the following tables the compliance with the Code criteria is indicated with regard to loading conditions analysed in this booklet, that are “Maximum Load Condition” (Departure Condition), “Contractual Full Load Condition (Departure condition) and “Light Load Condition” (Arrival Condition).

    [​IMG]
     
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  6. peter radclyffe
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    peter radclyffe Senior Member

    Compliance "With reference to Chapter 11.2.1.2. of LY2 Code, the Light Load condition in this booklet results not to have a positive GZ curve range up to 90 degrees. For this condition GZ is positive up to 84.3 degrees.

    Notwithstanding of that, the actual range stability doesn't affect the safety conduct of the vessel taking into account the Sail System Functioning Logic that is provided on board.

    This yacht is provided with a system that constantly monitors the Sail Operating Manual loads and the winches are designed to fully release sheets whenever the allowed static safety loads limits have been surpassed.

    As reported in the Sailing Table, the vessel has been designed to carry different sail sets and a 25-degree steady heel will not be reached provided the details contained within the Sailing Table and Sail Operating Manual are followed.

    It is the Masters responsibility to ensure that the details contained within the Sailing Table and Sail Operating Manual are followed.

    4. Precautions Against Capsize

    Compliance with the stability criteria does not ensure immunity against capsize or absolve the Master from his responsibilities. Masters should therefore exercise prudence and good seamanship having regard to the season of year, experience of the crew, weather forecast and the navigational zone, and should take appropriate action as to the speed, course and sail setting warranted by the prevailing conditions.

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    Before a voyage commences care should be taken to ensure large items of equipment and stores are properly stowed to minimise the possibility of both longitudinal and transverse shifting under the effect of acceleration caused by pitching and rolling, or in the event of a knockdown to 90 degrees.

    All external hull doors and flush hatches…are to be closed and secured.

    In adverse weather conditions and where there is the possibility of encountering a severe gust, squall or large breaking wave, all exposed doors, hatches, skylights, vents, etc. should be closed and securely fastened to prevent the ingress of water. If available, storm boards, blanking plates etc. should be erected and fitted. The amount of sail carried is at the discretion of the Master and his decision will have to take into account many factors.

    5. Angles of Down Flooding

    The angle of down flooding is the angle of heel at which progressive down flooding of the yacht occur due to the immersion of an opening. For this yacht the following openings have been identified as follow:

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    Critical Flooding is deemed to occur when the lower edges of openings have an aggregates area in m2 , greater than:

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  7. peter radclyffe
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    peter radclyffe Senior Member

    The Master should note that the presence of the vent and skylights significantly reduces the ability of the vessel to withstand down flooding and with these openings securely closed the safety of the vessel is enhanced considerably.

    In assessing the risks of down flooding, the Master should be guided by figures indicating the “Maximum Steady Heel Angle to Prevent Down flooding in Gusts” and the “Curves of Maximum Steady Heel Angle to Prevent Down flooding in Squalls” (see figures at pages (below).

    Figures (below) shows the maximum recommended steady heel angle to prevent down flooding in gusts, for the typical service loading conditions. Operation of the vessel at a greater heel angle would result in down flooding if it were to encounter the strongest possible gust in the prevailing turbulent air stream, which could exert a heeling moment equal to twice that of the mean wind.

    Figure (below) shows the maximum recommended steady heel angle to prevent down flooding in squalls, for the most onerous loading condition. Operation of the vessel at a greater heel angle would result in down flooding if it were to encounter the heeling effects of a squall arising from a storm or frontal system which may result in a heeling moment many times greater than that of the mean wind. For this reason the Master should have regard to the maximum steady heel angle curves presented for a range of squall speed.

    By using the readings from inclinometer and anemometer a master is able to determine the degree of risk of capsize in gusts or squalls which may occur in the prevailing weather system. He may then decide to shorten sail together with other actions he considers necessary.

    Additional care should be taken when sailing with the wind from astern, as in the event of the vessel broaching or a gust striking the vessel on the beam, the heeling effects of the wind may be increased to a dangerous level when preceding heel angle was small.

    6. Additional Notes to the Master

    The “Maximum Load Condition” is derived by adding an “Extra Load” to the Contractual Full Load Condition. The amount of “Extra Load” stays for the possible growth in the weight of the boat due to modification or repairing all over its life.

    Limiting KG curves for this yacht are provided at pages 81-82-83 (not shown). These curves include the provision of INTACT and DAMAGE stability criteria for motor yachts contained in the Code.

    If the vertical centre of gravity of any loading condition, after correction for free surface effects, lies below the limiting KG curves compliance with the requirements of the Code for Intact and Damage stability is ensured. It must be appreciated however, that compliance can never guarantee survivability in the event of damage, and good seamanship must prevail under such circumstances.

    This yacht has been provided with 41.31 tonnes of fixed ballast for stability purposes…This ballast is not to be moved or removed without prior consultation regarding the consequences on stability. Should the ballast be required to be removed for survey / repair or any other reason it must be returned to its original position and made secure against movement.

    This yacht is fitted with a swinging keel. Total weight of keel (structure and ballast) is about 52.3 tonnes. When keel is up, the vessel is operated as Motor yacht; when down she is considered a Sailing yacht. All loading conditions included in this booklet are referred to both keel positions, through appropriate indication “Centerboard UP” or “Centerboard DOWN”.

    [​IMG]
     
  8. peter radclyffe
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    peter radclyffe Senior Member

    usting Conditions

    When sailing in a steady wind the vessel heels to the angle at which the heeling arm curve intersects the GZ curve. When struck by a gust the heel angle will increase to intersection of the gust heeling arm curve with the GZ curve. The heeling moment increases in proportion to the square of the apparent wind speed. The derived angle of steady heel for this yacht is indicated in figures above. Provided the yacht is sailed at a steady angle of heel less than this value it should be capable of withstanding a wind gust equal to 1.4 times the actual wind velocity (i.e. twice the actual wind pressure) without immersing critical down flooding openings…Heel angle is shown on the curves of maximum Steady Heel angle to prevent down flooding in squalls.

    [​IMG]
    Squall Conditions

    Curves of Maximum Steady Heel Angle indicate the range of mean or steady heel angles beyond which the vessel will suffer down flooding in the event of a squall.

    Operation of the vessel in cyclonic conditions particularly in the hours of darkness, where severe squalls are imminent, requires the recommended maximum steady heel angle to be reduced depending on the mean apparent wind speed in accordance with the curves presented below.

    [​IMG]
    Example A) The Yacht is reaching, with a steady apparent wind speed of 15.3 knots. The mean heel angle is about 20 degrees. Forecasts and visible cumulo-nimbus clouds suggest squalls may be imminent. By plotting the heel angle and wind speed (point A on plot above) the indication is that the vessel will be in danger of heeling to the down flooding angle in squall of 30 knots. In order to increase safety from down flooding, say, to withstand squalls up to 40 knots, sails should be handed or reefed to reduce the mean heel angle to 11.5 degrees (point A1 on plot above) or less.

    Example B) The Yacht is beating in gusty conditions with a mean apparent wind speed of 28 knots. The mean heel angle is 10.5 degrees. No squalls are expected. The heel angle is significantly less than 17.2, the Maximum Recommended Steady Heel Angle, and there is therefore a good safety margin against down flooding in a strong gust. Plotting these values of wind speed and heel angle (point B on the above plot) also indicates that the vessel should not be vulnerable in down flooding in a squall unless it resulted in a wind speed in excess of about 50/55 knots. There is thus no need to reduce the sail area on the grounds of stability.

    [​IMG]
     
  9. BlueBell
    Joined: May 2017
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    BlueBell . . . _ _ _ . . . _ _ _

    Let's not forget this important piece when looking at all the data presented because the keel was UP:

    "This yacht is fitted with a swinging keel. Total weight of keel (structure and ballast) is about 52.3 tonnes. When keel is up, the vessel is operated as Motor yacht; when down she is considered a Sailing yacht. All loading conditions included in this booklet are referred to both keel positions, through appropriate indication “Centerboard UP” or “Centerboard DOWN”."
     
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  10. Stephen Ditmore
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    Stephen Ditmore Senior Member

    Thank you for posting this excellent info, Peter. My first impression is that some of this vulnerability should have been rectified as a matter of design (not simply documented in the stability book).
     
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  11. peter radclyffe
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    peter radclyffe Senior Member

  12. peter radclyffe
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    peter radclyffe Senior Member

    , english subs
     
  13. peter radclyffe
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    peter radclyffe Senior Member

    it appears as Tad pointed out, that the reason the centreboard made such a noise is primarily because the c/b case was not tall enough, maybe this was changed to get more accomodation, perhaps another case of the interference by internal designers who know little of seaworthiness requirements
     
  14. Stephen Ditmore
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    Stephen Ditmore Senior Member

    What I'm feeling a need to know is what the intact stability characteristics look like relative to heel to port with the tender platform door in the side of the hull open and with the keel up. What I'm suggesting is that "intact" be taken to mean that the bulkheads isolating that foyer deck be considered the true hull shell.
    That the downburst may have compromised the canopy over the forward sunken cockpit needs to be further investigated. Besides the possibility of downflooding, was analysis ever done of stability with that area flooded?
     

  15. Stephen Ditmore
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    Stephen Ditmore Senior Member

    I've played with the idea of a ketch (or yawl) with a freestanding wing mast aft that rotates underway but locks down on centerline at anchor. Would that accomplish the same thing?
     
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