RULES DET NORSKE VERITAS (DNV) = STRUCTURES = - Boat Design Net

Rules for High Speed, Light Craft and Naval Surface Craft, January 2011 Amended July 2011, see page 3Pt.3 Ch.1 Sec.3 – Page 22Fig. 3Hollow landingA 300 Hollow landing301 Hollow landing is similar to crest landing except that the reference area A R is situated towards AP andFP as shown in Fig.3.302 The load combination may be required analysed with actual weight distribution along the hull beam.303 The longitudinal midship bending moment may be assumed to be:ΔM B = -- ( g2 0 + a cg ) ( e r – e w )e r = mean distance from the centre of the A R /2 end areas to the vessels LCG in m.(e r – e w ) not to be taken less than 0.04 LA 400 Hydrofoils401 The calculation of longitudinal strength of hydrofoils shall be effected for the most severe condition. Asa rule this will be considering the craft sustained above the water surface by the foils and supposing it to bestationary in the navigation condition, taking into account vertical acceleration as well as the verticalcomponents of the hydrodynamic action of the water on the foils.A 500 Hogging and sagging bending moments501 For all craft an investigation of hogging and sagging bending moments taking into account anyimmersed/ emerged structures may be required.502 The investigation is in its simplest form to be based on a predicted phasing between pitch/heave and thepassage of a meeting design wave, and shall include the pitch angle and the inertia forces to be expected in thehogging and sagging conditions.503 Tentative formulae for bending moments (still water + wave) for high speed light craft:For monohull craft (in kNm):M tot hog = M sw + 0.19 C W L 2 B C BM tot sag = M sw + 0.14 C W L 2 B (C B + 0.7)M sw = still water moment in the most unfavourable loading condition in kNm 1)=0.11 C w L 2 B C B (kNm) in hogging if not known= 0 in sagging if not known. 2)For twin hull craft (in kNm):M tot hog = M sw + 0.19 C W L 2 (B WL2 + k 2 B tn ) C BM tot sag = M sw + 0.14 C W L 2 (B WL2 + k 3 B tn ) (C B + 0.7)M sw = still water moment in the most unfavourable loading condition in kNm 1)= 0.5 Δ L (kNm) in hogging if not known= 0 in sagging if not known. 2) .Additional correction of 20% to be added to the wave sagging moment for craft with large flare in the foreship.1) Documentation of the most unfavourable still water conditions shall normally be submitted for information.2) If the still water moment is a hogging moment, 50% of this moment can be deducted where the design sagging moment M totsag iscalculated.B tn = breadth in m of cross structures (tunnel breadth)k 2 and k 3 = empirical factors for the effect of cross structure immersion in hogging and sagging waves. If noother value available:DET NORSKE VERITAS AS