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(I-4-2) Guidelines for Design and Construction of Large Modern

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(I-4-2) Guidelines for Design and Construction of Large Modern Rules for Classification and Construction I Ship Technology 4 Rigging Technology 2 Guidelines for Design and Construction of Large Modern Yacht Rigs Edition 2009 The following Guidelines come into force on July 1st, 2009 Alterations to the preceding Edition are marked by beams at the text margin. Germanischer Lloyd Aktiengesellschaft Head Office Vorsetzen 35, 20459 Hamburg, Germany Phone: +49 40 36149-0 Fax: +49 40 36149-200 [email protected] www.gl-group.com "General Terms and Conditions" of the respective latest edition will be applicable (see Rules for Classification and Construction, I - Ship Technology, Part 0 - Classification and Surveys). Reproduction by printing or photostatic means is only permissible with the consent of Germanischer Lloyd Aktiengesellschaft. Published by: Germanischer Lloyd Aktiengesellschaft, Hamburg Printed by: Gebrüder Braasch GmbH, Hamburg I - Part 4 Table of Contents Chapter 2 GL 2009 Page 3 Table of Contents Section 1 Design and Construction of Large Modern Yacht Rigs A. General ....................................................................................................................................... 1- 1 B. Design and Construction Principles ........................................................................................... 1- 1 C. Materials and Fabrication ........................................................................................................... 1- 11 D. Miscellaneous ............................................................................................................................. 1- 14 E. Certificate ................................................................................................................................... 1- 16 Annex A Documents to be submitted for Rig Analysis I - Part 4 Section 1 B Design and Construction of Large Modern Yacht Rigs Chapter 2 GL 2009 Page 1–1 Section 1 Design and Construction of Large Modern Yacht Rigs A. General B. Design and Construction Principles 1. Scope 1. General 1.1 These Guidelines generally apply to sailing 1.1 Generally, the basic value for all following yachts of L > 24 m, under the condition, that the yacht evaluations is the static righting moment (RM) of the is handled correctly in terms of good seamanship. yacht at full displacement with a heel angle corre- sponding to SWA. 1.2 These Guidelines are generally applicable for bermudian rigs with spars made of carbon fibre rein- 1.2 The "Safe Working Angle (SWA)", which forced plastics or aluminium alloy. will be referred to in the following, generally represents a heeling angle of 30°. However, other angles may be defined as SWA in agreement with GL. GL reserves 1.3 The principles presented in the following are the right to assess the SWA according to the relevant to be used as a general guidance. Any detailed analysis characteristics of the yacht under sail according to Ta- which is leading to different reserve or reduction factors can be submitted on the basis of an equivalent safety. ble 1.1 or special characteristics such as canting keel. 1.4 Scope of these Guidelines are the structural 1.3 Large Cruising Catamarans require a different integrity of one- or multiple-masted, bermudian rigged approach defining a basic design parameter. Where the monohull or multihull sailing yachts including the righting moment is a very common value for monohulls, dimensioning of standing rigging, mast and boom this is not so for "heavy" cruising catamarans. These ves- sections as well as local construction in way of fittings sels often provide excessive stability which makes it im- structurally attached to the spars. practical to work from. Rather a more direct, yet conserva- tive, approach is taken by using the wind pressure directly. 1.5 Upon request, the performance on construc- tion can be supervised by GL. Basis for this is a 2. Load cases relevant shop approval for the typical construction techniques. The survey will be carried out in perio- 2.1 Ordinary sailing conditions dical intervals where an assessment is made whether Upwind beating, reaching and broad reaching under the product under supervision is built in accordance appropriate sail configurations for light, moderate, with approved documentation and the societies stan- strong and stormy wind conditions, such as: dards by random control. – full main, working jib, genoa I or reacher 2. Documents to be submitted – several reef stages main, working jib, reefed jib, stay sail Relate to Annex A for the scope of documents and information required for Certification listed for each – spinnaker only of the different Certification modules. – others and special configurations for special rigs Table 1.1 Yacht characteristics Displacement Typical Purpose Typical Handling Category Characteristics Characteristics Characteristics I Motor Sailer/ Heavy Cruiser Ocean Going Handled by owner / crew II Mid Displacement Offshore Short-handed Coastal pleasure cruises / Short-handed or III Light Displacement Club Racing handled by crew IV Ultra Light Displacement Racing Handled by professional crew Chapter 2 Section 1 B Design and Construction of Large Modern Yacht Rigs I - Part 4 Page 1–2 GL 2009 2.2 Extreme conditions RMDesign = righting moment as defined in B.1. [Nm] Extreme conditions may need to be defined in special CoEm/f/s = centre of effort of respective sail: cases, depending on the boat size and type and other CoE = 0,39 P above gooseneck [m] configurations. m (default) 3. Determination of rig loads CoEf = 0,39 I above foot [m] (default) 3.1 Pretensioning of rig CoEs = 0,59 I above deck [m] The pretensioning of the rigging is to be specified by (default) the designer, otherwise pretensioning is set to avoid CLR = The centre of lateral resistance of the under- slack leeward cap shrouds with an appropriate reserve, water body (including appendages) [m] when sailing at heeling angles at or below the "SWA". Am = mainsail area, projected laterally [m2] 3.2 Transverse sail forces 2 Af = foresail area, projected laterally [m ] 3.2.1 Monohulls P = mainsail hoist [m] Transverse forces are determined from righting mo- E = foot of mainsail [m] ment: I = height of fore triangle [m] Each sail's contribution to the resultant heeling mo- ment is assumed to be proportional to the sail’s area SFCm = side force coefficient mainsail = 0,9 and the distance of its centre of effort above the un- SFC = side force coefficient foresail = 1,1 derwater body's centre of lateral resistance, see Fig. f 1.1. The sum of these heeling moments is set equal to 3.2.1.1 Estimation of corresponding apparent the vessel’s righting moment under the conditions and wind speed for upwind cases specific sail configurations being evaluated: Transverse force from mainsail: Ftmf() v[ms]a = SFCf/m⋅⋅⋅ρ A mf 0,5 RMdesign F[N]tm = ASFCFf⋅ 3 CoEmf CLR+⋅ CoE CLR ρ = density of air [kg/m ] ASFCmm⋅ 3.2.2 Multiple-mast rig Transverse force from foresail: For a multiple-mast rig a conservative assumption of ASCFff⋅ the proportioning of righting moment is to be made: FF[N]tf=⋅ tm ASCFmm⋅ For all relevant sail configurations, the fractions of sail area moments (SAM) for each mast from the total Transverse force from spinnaker when "broaching". SAM have to be determined to find the design righting moment for each mast. RMDesign F[N]ts = The sail area moment is defined as: CoEs CLR SAM=⋅ A CoE CLR [m3 ] A = projected sail area CoE CoEm s The sail area moment for each mast is defined as: n 3 SAMijj=⋅∑ ( A CoE CLR) [m ] CoEf j1= i = index for specific mast j = index for specific sail on specific mast Am Af The fraction of each mast from the total sail area mo- ment is defined as: CLR SAM f = i i n ∑ SAMi Fig. 1.1 Centres of effort i1= I - Part 4 Section 1 B Design and Construction of Large Modern Yacht Rigs Chapter 2 GL 2009 Page 1–3 The design righting moment RMdesign for each mast is From this wind speed the sail pressure forces are cal- to be taken the lower of: culated using the equation: 2 – RMdesign = 1,0 ⋅ (RM at SWA) F/2AWSAc= ρ+DS ⋅⋅ – RMdesign = 1,56 ⋅ f ⋅ (RM at SWA) ρ = density of air Windage of masts and rigging (and equipment) and The side force coefficient cs for a mainsail is generally therewith contribution to (each) SAM and/or (OTM) 0,9, for a jib 1,1. These pressure forces are supposed may be taken into account. to act at the sails centre of effort, where the assump- tions for the locations are: OTM = overturning moment, see 3.2.3 Mainsail 45% of mean height for sails with "normal 3.2.3 Multihulls roach" The relevant apparent wind speed, resulting from the Headsail 39% of mean height of triangular sail. true wind speed and the predicted boat speed is used Looking at a different angle of this approach, these sail to calculate the pressure forces for a rig. pressure forces calculated from the design wind speed re- sult in an "overturning moment" (OTM). If really required AWSO =+ TWS cos (TWA) ⋅ BS for reference, the OTM shall be calculated about the ves- sel's longitudinal axis, at an elevation which can be called TWS = True Wind Speed "platform" of the rig, mostly deck or sheerline level. TWA = True Wind Angle What has been found from studies is that obviously the BS = Boat Speed AWS is a conservative value to work with. While bear- ing away from upwind the allowable TWS gets higher This operational wind speed AWS0 is defining the and also the AWS gets slightly higher. But the OTMs safe operational limits for the vessel, equivalent to a stay rather constant or even get marginally smaller. So safe working heel angle on monohulls, which may not actually, for all "upwind sail" configurations, an AWS be exceeded. The operational limits of a rig need to be limit is conservative and serves well for dimensioning defined precisely and followed diligently. purposes. Downwind cases need to be looked at sepa- The design wind speed, which a rig is designed to, rately, at a certain OTM (guideline: similar to upwind) needs to be determined conservatively. As a catama- and a windpressure due to an AWS of 25 kn.
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