EN ISO 12215-6:2008

Small craft - Hull construction and scantlings - Part 6: Structural arrangements and details (ISO 12215-6:2008)

ISO 12215-6:2008 concerns structural details and structural components not explicitly included in ISO 12215-5, ISO 12215-7, ISO 12215-8 and ISO 12215-9. It applies to monohull and multihull small craft constructed from fibre reinforced plastics (FRP), aluminium or steel alloys, wood or other suitable boat building material, with a hull length, in accordance with ISO 8666, of up to 24 m.
ISO 12215-6:2008 fulfils two functions. Firstly, it supports ISO 12215-5 by providing further explanations and calculation procedures and formulae. Secondly, it gives a number of examples of arrangements and structural details which illustrate principles of good practice. These principles provide a standard against which alternative arrangements and structural details can be benchmarked, using the equivalence criteria specified in ISO 12215-6:2008.

Kleine Wasserfahrzeuge - Rumpfbauweise und Dimensionierung - Teil 6: Bauanordnung und Details (ISO 12215-6:2008)

Dieser Teil von ISO 12215 betrifft die Bestimmung von Baudetails und Baukomponenten, die nicht ausdrück¬lich in ISO 12215 5; ISO 12215 7, ISO 12215 8 und ISO 12215 9 aufgeführt sind. Betroffen sind kleine Ein¬rumpf- und Mehrrumpf-Wasserfahrzeuge, die aus glasfaserverstärkten Kunststoffen (GfK), Aluminium- oder Stahllegierungen, Holz oder anderen geeigneten Bootsbauwerkstoffen gebaut sind, mit einer Rumpflänge bis 24 m nach ISO 8666.
Dieser Teil von ISO 12215 erfüllt zwei Funktionen. Erstens unterstützt er ISO 12215 5, indem weitere Erklä¬rungen und Kalkulationsschemata und Gleichungen bereitgestellt werden. Zweitens stellt er eine Reihe von Beispielen für Anordnungen und Baudetails zur Verfügung, die Grundlagen guter fachlicher Praxis darstellen. Diese Grundlagen stellen einen Richtwert dar, anhand dessen alternative Anordnungen und Bauteile bewertet werden können, indem die Gleichwertigkeitskriterien, die in diesem Teil der ISO 12215 beschrieben sind, benutzt werden.
ANMERKUNG    Dimensionierungen, die sich aus diesem Teil von ISO 12215 ableiten, sind in erster Linie für Sport¬boote einschließlich gecharterter Sportboote gedacht und sind möglicherweise nicht für Leistungsrennboote geeignet.

Petits navires - Construction de coques et échantillonnages - Partie 6: Dispositions et détails de construction (ISO 12215-6:2008)

L'ISO 12215-6:2008 concerne les détails de construction et les éléments structurels non explicitement mentionnés dans l'ISO 12215-5, l'ISO 12215-7, l'ISO 12215-8 et l'ISO 12215-9. Elle est applicable aux petits navires monocoques et multicoques, en plastique renforcé de fibres, en alliages d'aluminium ou d'acier, en bois ou en tout autre matériau approprié pour la construction de bateaux, d'une longueur de coque inférieure ou égale à 24 m, conformément à l'ISO 8666.
L'ISO 12215-6:2008 remplit deux fonctions. Elle apporte d'abord une aide à l'ISO 12215‑5 en donnant des explications supplémentaires ainsi que des méthodes et formules de calcul. Elle donne ensuite un certain nombre d'exemples de dispositions structurelles et de détails de construction illustrant des principes de bonne pratique. Ces principes fournissent une base de référence par rapport à laquelle d'autres dispositions structurelles et détails de construction pourront se comparer, en utilisant les critères de référence spécifiés dans l'ISO 12215-6:2008.

Mala plovila - Konstrukcija trupa in zahtevane lastnosti - 6. del: Struktura in podrobnosti (ISO 12215-6:2008)

General Information

• Status: Withdrawn
• Publication Date: 31-Mar-2008
• Withdrawal Date: 13-Apr-2025
• ICS: 47.080 - Small craft
• Technical Committee: CEN/SS T01 - Shipbuilding and maritime structures
• Drafting Committee: CEN/SS T01 - Shipbuilding and maritime structures
• Current Stage: 9960 - Withdrawal effective - Withdrawal
• Start Date: 03-Oct-2018
• Completion Date: 14-Apr-2025
• Directive: 2003/44/EC - Approximation of the laws, regulations and administrative provisions of the Member States relating to recreational craft
• Directive: 2013/53/EU - Directive 2013/53/EU of the European Parliament and of the Council of 20 November 2013 on recreational craft and personal watercraft and repealing Directive 94/25/EC
• Directive: 94/25/EC - Directive 94/25/EC of the European Parliament and of the Council of 16 June 1994 on the approximation of the laws, regulations and administrative provisions of the Member States relating to recreational craft
• Mandate: M/075 - Revised mandate to CEN for standardization in the field of recreational craft
• Ref Project: SIST EN ISO 12215-6:2008 - Small craft - Hull construction and scantlings - Part 6: Structural arrangements and details (ISO 12215-6:2008)

Relations

• Replaced By: EN ISO 12215-6:2018 - Small craft - Hull construction and scantlings - Part 6: Structural arrangements and details (ISO 12215-6:2008)
• Effective Date: 07-Jun-2017
• Parent: EN ISO 12215-2:2002 - Small craft - Hull construction and scantlings - Part 2: Materials: Core materials for sandwich construction, embedded materials (ISO 12215-2:2002)
• Effective Date: 22-Dec-2008

Standards Content (Sample)

SLOVENSKI STANDARD
01-julij-2008
Mala plovila - Konstrukcija trupa in zahtevane lastnosti - 6. del: Struktura in
podrobnosti (ISO 12215-6:2008)
Small craft - Hull construction and scantlings - Part 6: Structural arrangements and
details (ISO 12215-6:2008)
Kleine Wasserfahrzeuge - Rumpfbauweise und Dimensionierung - Teil 6: Bauanordnung
und Details (ISO 12215-6:2008)
Petits navires - Construction de coques et échantillonnages - Partie 6: Dispositions et
détails de construction (ISO 12215-6:2008)
Ta slovenski standard je istoveten z: EN ISO 12215-6:2008
ICS:
47.020.10 Ladijski trupi in njihovi Hulls and their structure
konstrukcijski elementi elements
47.080 ýROQL Small craft
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EUROPEAN STANDARD
EN ISO 12215-6
NORME EUROPÉENNE
EUROPÄISCHE NORM
April 2008
ICS 47.080
English Version
Small craft - Hull construction and scantlings - Part 6: Structural
arrangements and details (ISO 12215-6:2008)
Petits navires - Construction de coques et échantillonnages Kleine Wasserfahrzeuge - Rumpfbauweise und
- Partie 6: Dispositions et détails de construction (ISO Dimensionierung - Teil 6: Bauanordnung und Details (ISO
12215-6:2008) 12215-6:2008)
This European Standard was approved by CEN on 3 February 2008.
CEN members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this European
Standard the status of a national standard without any alteration. Up-to-date lists and bibliographical references concerning such national
standards may be obtained on application to the CEN Management Centre or to any CEN member.
This European Standard exists in three official versions (English, French, German). A version in any other language made by translation
under the responsibility of a CEN member into its own language and notified to the CEN Management Centre has the same status as the
official versions.
CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Cyprus, Czech Republic, Denmark, Estonia, Finland,
France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal,
Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland and United Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION
EUROPÄISCHES KOMITEE FÜR NORMUNG
Management Centre: rue de Stassart, 36  B-1050 Brussels
© 2008 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN ISO 12215-6:2008: E
worldwide for CEN national Members.

Contents Page
Foreword.3
Annex ZA (informative) Relationship between this International Standard and the Essential
Requirements of EU Directive 94/25/EC .4

Foreword
This document (EN ISO 12215-6:2008) has been prepared by Technical Committee ISO/TC 188 "Small craft"
in collaboration with Technical Committee CEN/SS T01 "Shipbuilding and maritime structures", the secretariat
of which is held by CMC.
This European Standard shall be given the status of a national standard, either by publication of an identical
text or by endorsement, at the latest by October 2008, and conflicting national standards shall be withdrawn at
the latest by October 2008.
Attention is drawn to the possibility that some of the elements of this document may be the subject of patent
rights. CEN [and/or CENELEC] shall not be held responsible for identifying any or all such patent rights.
This document has been prepared under a mandate given to CEN by the European Commission and the
European Free Trade Association, and supports essential requirements of EC Directive.
For relationship with EC Directive, see informative Annex ZA, which is an integral part of this document.
According to the CEN/CENELEC Internal Regulations, the national standards organizations of the following
countries are bound to implement this European Standard: Austria, Belgium, Bulgaria, Cyprus, Czech
Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia,
Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain,
Sweden, Switzerland and the United Kingdom.
Endorsement notice
The text of ISO 12215-6:2008 has been approved by CEN as a EN ISO 12215-6:2008 without any
modification.
Annex ZA
(informative)
Relationship between this International Standard and the Essential Requirements of
EU Directive 94/25/EC
This International Standard has been prepared under a mandate given to CEN by the European Commission
and the European Free Trade Association to provide one means of conforming to Essential Requirements of
the New Approach Directive 94/25/EC as amended by Directive 2003/44/EC.

Once this standard is cited in the Official Journal of the European Communities under that Directive and has
been implemented as a national standard in at least one Member State, compliance with the normative
clauses of this standard given in Table ZA.1 confers, within the limits of the scope of this standard, a
presumption of conformity with the relevant Essential Requirements of that Directive and associated EFTA
regulations.
Table ZA.1 — Correspondence between this International Standard and Directive 94/25/EC as
amended by Directive 2003/44/EC

Clauses/sub-clauses of this Corresponding annexes/paragraphs of Comments
international Standard EU Directive 94/25/EC as amended by
Directive 2003/44/EC
All clauses Annex I, Part A, Clause 3.1, Structure The standard provides structural details
for monohull and multihull craft
constructed from fibre reinforced
plastics, aluminium or steel alloys,
wood or similar suitable materials.

WARNING — Other requirements and other EU Directives may be applicable to the products falling
within the scope of this standard.

INTERNATIONAL ISO
STANDARD 12215-6
First edition
2008-04-01
Small craft — Hull construction and
scantlings —
Part 6:
Structural arrangements and details
Petits navires — Construction de coques et échantillonnages —
Partie 6: Dispositions et détails de construction

Reference number
ISO 12215-6:2008(E)
©
ISO 2008
ISO 12215-6:2008(E)
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ii © ISO 2008 – All rights reserved

ISO 12215-6:2008(E)
Contents Page
Foreword. v
Introduction . vi
1 Scope .1
2 Normative references .1
3 Terms and definitions .1
4 Symbols .3
5 General.4
6 Structural arrangement .4
6.1 Stiffening .4
6.2 Hull girder strength.7
6.3 Load transfer.7
6.4 Determination of stiffener spans.11
6.5 Window mullions .13
6.6 Sailboat mast support .14
7 Specific structural details for FRP construction .14
7.1 Local reinforcement .14
7.2 Bonding .16
7.3 Major joints.21
7.4 Laminate transition.25
7.5 Sandwich construction .25
7.6 Attachment of fittings.25
7.7 Engine seatings and girders.25
7.8 Hull drainage .28
8 Specific structural details for metal construction.28
8.1 Design details.28
8.2 End connections.28
8.3 Increased hull plating.28
8.4 Protective keel.28
8.5 Hull drainage .29
8.6 Machinery spaces.29
8.7 Good practice welding standards.29
8.8 Good practice for riveting or adhesive bonding .29
9 Good practice on laminated wood.30
9.1 Edge sealing.30
9.2 Plywood orientation.30
9.3 Local scantlings.30
9.4 Alternative criteria .31
10 Consideration of other loads.31
11 Other structural components .31
11.1 General.31
11.2 Rudder structure and connection.31
11.3 Keel attachment .32
11.4 Introduction and distribution of rigging loads .32
11.5 Other structural components not considered in other parts .32
Annex A (normative) Structural arrangements for category C and D boats.33
ISO 12215-6:2008(E)
Annex B (informative) Determination of shear stresses within a stiffener with glued or
riveted joints. 35
Annex C (informative) Good practice welding procedure . 41
Annex D (informative) Longitudinal strength analysis . 47
Bibliography . 52

iv © ISO 2008 – All rights reserved

ISO 12215-6:2008(E)
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies
(ISO member bodies). The work of preparing International Standards is normally carried out through ISO
technical committees. Each member body interested in a subject for which a technical committee has been
established has the right to be represented on that committee. International organizations, governmental and
non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely with the
International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.
International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2.
The main task of technical committees is to prepare International Standards. Draft International Standards
adopted by the technical committees are circulated to the member bodies for voting. Publication as an
International Standard requires approval by at least 75 % of the member bodies casting a vote.
Attention is drawn to the possibility that some of the elements of this document may be the subject of patent
rights. ISO shall not be held responsible for identifying any or all such patent rights.
ISO 12215-6 was prepared by Technical Committee ISO/TC 188, Small craft.
ISO 12215 consists of the following parts, under the general title Small craft — Hull construction and
scantlings:
⎯ Part 1: Materials: Thermosetting resins, glass-fibre reinforcement, reference laminate
⎯ Part 2: Materials: Core materials for sandwich construction, embedded materials
⎯ Part 3: Materials: Steel, aluminium alloys, wood, other materials
⎯ Part 4: Workshop and manufacturing
⎯ Part 5: Design pressures for monohulls, design stresses, scantlings determination
⎯ Part 6: Structural arrangements and details
⎯ Part 7: Scantling determination of multihulls
⎯ Part 8: Rudders
⎯ Part 9: Sailing boats — Appendages and rig attachments
ISO 12215-6:2008(E)
Introduction
The underlying reason for preparing this part of ISO 12215 is that standards and recommended practices for
loads on the hull and the dimensioning of small craft differ considerably, thus limiting the general worldwide
acceptability of boats.
The objective of this part of ISO 12215 is to achieve an overall structural strength that ensures the watertight
and weathertight integrity of the craft.
This part of ISO 12215 is considered to have been developed with the application of current practice and
sound engineering principles.
Considering future development in technology and boat types, as well as small craft currently outside the
scope of this part of ISO 12215, and provided that methods supported by appropriate technology exist,
consideration may be given to their use so long as equivalent strength to this part of ISO 12215 is achieved.
Dimensioning in accordance with this part of ISO 12215 is regarded as reflecting current practice, provided
that the craft is correctly handled in the sense of good seamanship and that it is equipped and operated at a
speed appropriate to the prevailing sea state.

vi © ISO 2008 – All rights reserved

INTERNATIONAL STANDARD ISO 12215-6:2008(E)

Small craft — Hull construction and scantlings —
Part 6:
Structural arrangements and details
1 Scope
This part of ISO 12215 concerns structural details and structural components not explicitly included in
ISO 12215-5, ISO 12215-7, ISO 12215-8 and ISO 12215-9. It applies to monohull and multihull small craft
constructed from fibre reinforced plastics (FRP), aluminium or steel alloys, wood or other suitable boat
building material, with a hull length, in accordance with ISO 8666, of up to 24 m.
This part of ISO 12215 fulfils two functions. Firstly, it supports ISO 12215-5 by providing further explanations
and calculation procedures and formulae. Secondly, it gives a number of examples of arrangements and
structural details which illustrate principles of good practice. These principles provide a standard against which
alternative arrangements and structural details can be benchmarked, using the equivalence criteria specified
in this part of ISO 12215.
NOTE Scantlings derived from this part of ISO 12215 are primarily intended to apply to recreational craft including
recreational charter vessels and might not be suitable for performance racing craft.
2 Normative references
The following referenced documents are indispensable for the application of this document. For dated
references, only the edition cited applies. For undated references, the latest edition of the referenced
document (including any amendments) applies.
ISO 8666, Small craft — Principal data
ISO 12215-5:2008, Small craft — Hull construction and scantlings — Part 5: Design pressures for monohulls,
design stresses, scantlings determination
ISO 12215-7, Small craft — Hull construction and scantlings — Part 7: Scantling determination of multihulls
ISO 12215-8, Small craft — Hull construction and scantlings — Part 8: Rudders
ISO 12215-9, Small craft — Hull construction and scantlings — Part 9: Appendages and rig attachment
ISO 12216, Small craft — Windows, portlights, hatches, deadlights and doors — Strength and watertightness
requirements
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
3.1
loaded displacement mass
m
LDC
mass of the craft, including all appendages, when in the fully-loaded ready-for-use condition, as defined in
ISO 8666
ISO 12215-6:2008(E)
3.2
sailing craft
2/3
craft for which the primary means of propulsion is by wind power, and for which A > 0,07(m ) where
S LDC
A is the total profile area of all sails that can be set at one time when sailing closed hauled, as
S
defined in ISO 8666, expressed in m ;
m is the loaded displacement, as defined in ISO 8666, expressed in kg.
LDC
NOTE In this part of ISO 12215, non-sailing craft are referred to as motor craft.
3.3
grid
grillage
set of transverse stiffeners that intersect a set of longitudinal stiffeners
3.4
secondary stiffener
stiffening element that directly supports the plating
NOTE In a stiffener grillage, secondary stiffeners usually correspond to stiffeners having the lower second moment of
area, e.g. stringers, frames, partial bulkheads. The spacing of secondary stiffeners generally corresponds to the shortest
unsupported span of the attached plating. In the case of stiffeners with a substantial base width (i.e. top hat stiffeners), the
stiffener spacing will be the unsupported panel span plus this base width.
3.5
primary stiffener
stiffening element that supports the secondary stiffening element
NOTE 1 In a stiffener grillage, primary stiffeners usually correspond to stiffeners which have the higher second moment
of area, e.g. structural bulkheads, girders, web frames. The spacing of primary stiffeners generally corresponds to the
span of secondary stiffeners.
NOTE 2 Some stiffeners, such as bulkheads, deep girders or web frames, may also contribute to resisting global loads.
3.6
stringer
longitudinal stiffener, generally designated a secondary stiffener (3.4), which supports the shell plating
3.7
frame
transverse stiffener, generally designated a secondary stiffener (3.4), which supports the shell plating
3.8
beam
transverse stiffener, generally designated a secondary stiffener (3.4), which supports the deck plating
3.9
web frame
substantial transverse stiffener, generally designated a primary stiffener (3.5), which supports stringers and
less substantial girders and is usually connected with substantial deck beams
NOTE The spacing of web frames is usually greater than (or some multiple of) the frame or beam spacing.
3.10
floor
substantial transverse bottom stiffener, which may be used to link frames and may also be a partial bulkhead
NOTE Floors are often used to support a cabin sole, so the upper edge is generally horizontal. On sailing craft, floors
are traditionally used to support ballast keels.
2 © ISO 2008 – All rights reserved

ISO 12215-6:2008(E)
3.11
girder
substantial longitudinal stiffening element, generally designated a primary member, which supports bottom
transverse frames or floors, other frames and beams
NOTE Bottom girders are sometimes called keelsons.
3.12
bracket
stiffening element, usually of triangular shape, used to reinforce the connection of two stiffeners and to reduce
their span
NOTE Brackets are also used to transmit local loads.
4 Symbols
Unless specifically otherwise defined, the symbols and units used in this part of ISO 12215 are given in
Table 1.
NOTE Symbols and units used only in the annexes are not included in Table 1.
Table 1 — Symbols
Symbol Designation Unit
A Design area of plating/stiffener mm
D
b Spacing between stiffeners mm
b Width of bonding flange mm
w
B Beam of hull, in accordance with ISO 8666 m
H
D Maximum depth of the boat, in accordance with ISO 8666 m
max
E Elastic modulus of stiffener N/mm
f Mechanical property coefficient for FRP and aluminium alloys 1
f Mechanical property coefficient for wood 1
1w
I Second moment of stiffener cm
k , ., k Coefficients for reinforcing thickness calculation 1
0 2
k , k Glue width coefficient 1
j jmin
l Span of stiffeners mm
u
L Length of hull, in accordance with ISO 8666 m
H
L Length of waterline, in accordance with ISO 8666 m
WL
m Loaded displacement mass, in accordance with ISO 8666 kg
LDC
m Trailering mass, in accordance with ISO 8666 kg
T
P Maximum engine power kW
t Bottom plating thickness mm
b
t Thickness of plywood bulkhead mm
BHD
t Total thickness of top hat web mm
w
V Boat maximum speed in calm water knot
max
σ Design direct stress N/mm
d
σ Ultimate direct strength N/mm
u
τ Design shear stress N/mm
d
τ Ultimate shear strength N/mm
u
Ψ Glass content by mass 1
ISO 12215-6:2008(E)
5 General
Where the load and scantling determination have been accomplished for craft with a hull length, L , of
H
between 2,5 m and 24 m in accordance with
⎯ ISO 12215-5 for design pressure for monohulls and scantlings determination,
⎯ ISO 12215-7 for multihulls,
⎯ ISO 12215-8 for rudders, and
⎯ ISO 12215-9 for appendages and rig attachment,
structural arrangements and details shall comply with Clauses 6 to 11.
Where one of the two following methods prescribed in ISO 12215-5 have been used, the craft need only
comply with the requirements of Annex A:
a) for sailing craft with a length, L , of between 2,5 m and 9 m of design categories C and D, where
H
ISO 12215-5:2008, Annex A, has been used;
b) for craft with a length, L , of between 2,5 m and 6 m and of single skin FRP bottom construction, where
H
ISO 12215-5:2008, Annex B, has been used.
6 Structural arrangement
6.1 Stiffening
6.1.1 General
The hull, deck and deckhouse plating shall be stiffened as necessary to comply with ISO 12215-5, by any
combination of longitudinal and transverse conventional stiffeners, structural bulkheads, internal furniture such
as berths and shelves, and internal tray mouldings, providing these may be considered as “load bearing”. The
arrangement is usually made with stiffeners supported by deeper and stronger stiffeners, crossing
perpendicularly.
NOTE For small boats, “natural stiffeners” (i.e. elements that add stiffness, even if not dedicated for the purpose; see
ISO 12215-5:2008, 9.14), e.g. deck edge, round bilges, hard chines, keel, can define panels that need no further
stiffening.
Figures 1, 2 and 3 illustrate characteristic arrangements that comply with good practice. These figures apply
to both sailing and non-sailing craft, and combinations of arrangement within a single craft are acceptable.
Small boats (generally those of hull length less than about 9 m in length) employ natural stiffeners such as
deck edge, round bilges, hard chines, keel, etc. to define panels and then need no further stiffening. Larger
craft generally need to make greater use of the stiffener types described in 3.3 to 3.12.
6.1.2 Equivalence criteria
Other arrangements are possible, but these shall follow good practice principles (as illustrated by Figures 1, 2
and 3) of effective and smooth transmission of stresses due to pressure loads and concentrated loads (mast,
keel, rudder, etc) from the load point into the supporting structure (see 6.3 and 6.4).
6.1.3 Longitudinally framed boat
In the example in Figure 1, the hull shell is stiffened by longitudinal secondary stiffeners supported by
transverse primary stiffeners, such as web frames, bulkheads and deep floors. The example given is typical
for an FRP boat.
4 © ISO 2008 – All rights reserved

ISO 12215-6:2008(E)
6.1.4 Transversally framed boat
In the example in Figure 2, the hull shell is stiffened by transverse frames (secondary stiffeners) that are
typically supported at the centreline, at the chines or turn of bilge and at deck level. In larger boats, girders
(primary stiffeners) may be fitted, which support these frames and also assist in carrying hull girder loads.
6.1.5 Small, slow boat stiffened by keel, gunwale stringer, structural sole and thwarts
It is common for small craft (i.e. those of hull length less than 6 m) to have no specific stiffeners. However,
components not primarily intended to be stiffeners, such as internal partitions may act as such. These
components may need to be reinforced for this other role as “stiffeners”. In Figure 3, the thwarts, front and aft
locker, cockpit sole and gunwale are used in this way.
6.1.6 Load bearing elements
To be considered as “load bearing”, the supporting member shall be effectively attached to the plating by any
combination of welding (continuous or intermittent), bonding with structural quality adhesive (e.g. use of epoxy
fillets) or fibre reinforced bonding angles or other methods appropriate to the materials. In addition, the
member in question shall be constructed of material acceptable for hull construction in accordance with
ISO 12215-5, and shall be able to carry the forces and moments associated with the effective support
assumption as defined there.
Key
1 transom
2 gunwale stringer
3 bulkhead
4 side longitudinal stiffener (stringer)
5 web frame
6 deep floor
7 bottom longitudinal stiffener (girder or stringer); good practice is to have ends in accordance with Figure 4 a) or 4 c)
NOTE 1, 3, 5 and 6 are primary stiffeners; 2, 4 and 7 are secondary stiffeners.
Figure 1 — Longitudinally framed boat
ISO 12215-6:2008(E)
Key
1 transom 5 bottom girder
2 bulkhead 6 deep floor
3 frame 7 deep floor
4 bulkhead
Figure 2 — Transversally framed boat

Key
1 gunwale stringer
2 keel
3 structural sole
4 thwarts
5 deep floor
Figure 3 — Small, slow boat stiffened by keel, gunwale stringer, structural sole and thwarts
6 © ISO 2008 – All rights reserved

ISO 12215-6:2008(E)
6.2 Hull girder strength
ISO 12215-5 is based on the assumption that hull and deck scantlings are governed by local loads, which is
usually the case for craft of normal proportions and is especially so for longitudinally framed craft.
For the following craft, an explicit longitudinal strength and buckling assessment is recommended:
V
max
⎯ transversely framed motor craft where > 6;
L
WL
⎯ transversely framed sailboats experiencing large rig loads;
L
H
⎯ craft with large deck openings or craft with > 12.
D
max
Annex D gives recommendations for the assessments to be made.
6.3 Load transfer
6.3.1 General
The structural geometry shall be so arranged and detailed as to ensure a smooth transfer of loads throughout
the structure. Concentrated loads (e.g. mast step for a keel stepped mast, mast pillar for a deck stepped mast)
shall be transmitted into the surrounding structure by a series of stiff supporting members. In no case shall
concentrated load points be landed on unsupported plating. In general, concentrated loads shall be introduced
into the adjacent structural elements by shear load carrying brackets, flanges or floors. Knife edge load
crossing shall be avoided (see 6.3.5).
6.3.2 gives examples of good practice load transfer arrangements. Other arrangements need to be specifically
engineered.
6.3.2 Examples of good practice load transfer arrangements
The list below gives examples of good practice load transfer arrangements.
⎯ Stiffeners (generally angle bar, tee section, top hats or flat bars, etc.) and girders (including engine
girders) do not terminate abruptly, but are suitably terminated to develop their bending strength and shear
strength at the supporting member, with brackets or without brackets, but with structurally effective
attachment of web and flange to the supporting member (see Figure 4). Where stiffeners are lightly
loaded, they may have tapered (sniped) ends, provided the slope of the taper is at least 30 % and that the
plating between the end of the stiffener and the supporting structure is designed or able to transmit the
shear force and bending moment of the tapered stiffener [see Figure 4 c)].
⎯ Floors smoothly taper in depth towards that of the attached transverse frame. Where no transverse
frames are fitted, the floor is attached to the side shell over a sufficient length to ensure that the shear
force (due to keel moment or bottom pressure) can be adequately transferred to the side shell (see
Figure 5). The ends of floors or transverse stiffeners for sailboat ballast keel are in accordance with the
requirements of ISO 12215-9.
⎯ Cut-outs and sharp corners are avoided in load-carrying structures such as shell, deck, primary and
secondary stiffening members. Where cut-outs cannot be avoided, the depth of any cut-out does not
exceed 50 % of the depth of the web of the member, and the length of the cut-out does not exceed 75 %
of the depth of the web of the member, unless effectively engineered. Cut-outs shall have radius corners
not less than 12 % of the cut-out depth or 30 mm, whichever is the greater. Cut-outs are avoided within
20 % of the span from the support points and by way of concentrated loads on the member.
ISO 12215-6:2008(E)
6.3.3 Openings in deck and shell according to good practise
Openings in decks and shell have radius corners not less than 12 % of the width of opening, but need not
exceed 300 mm and are not less than 50 mm. This does not apply where the edges are reinforced by a
structural flat bar or equivalent (see Figure 6).
It is also good practice to minimize sharp cut-outs in structurally loaded panels and stiffeners, unless
accordingly reinforced.
a)  Stiffener ending in panel, poor practice and good practice solution

b)  Bracket, poor practice and good practice solution

c)  Tapered ends acceptable provided the vertical load can be taken by the shell
Key
1 risk of crack
h height of stiffener
Figure 4 — Detail of stringer and bracket end

6.3.4 Floating frame systems
Floating frame systems (see Figure 7) are those where one set of stiffeners (the “floated” stiffeners) effectively
sits on top of another set without being directly attached to the hull plating. Only the second set (the “attached”
stiffener) is directly attached to the plating. When analysing such floating frames using ISO 12215-5, the
effective plating of the floating frame is to be taken as zero.
8 © ISO 2008 – All rights reserved

ISO 12215-6:2008(E)
For all materials, particular metal boats or wooden boats that use plywood frames, these “floating” frames are
normally I beams “attached” to a T, L or U stringer. Attention shall be given to the strength of the weld or glued
area between the “floating” frame and stringer, torsional (tripping) or shear buckling of the stringer and the
frame transverse web and knife edge load crossing (see 6.3.5), which requires explicit calculation. By way of
guidance, the weld or glue area shall generally not be less than the stiffener web area, A , given by
W
ISO 12215-5:2008, Equation (48).

a)  Stiffener ending in shell, poor practice and good practice

b)  Deep floor/partial bulkhead
Key
1 hard spot, risk of crack, poor practice
2 reinforced plating, acceptable practice
3 transverse floor or bulkhead, good practice
4 no longitudinal structure at top end of deep floor, acceptable practice
5 cabin sole, deck or longitudinal stiffener on top of floor, good practice
Figure 5 — Detail of stiffener ending on the plating
ISO 12215-6:2008(E)
Dimensions in millimetres
Key
R radius corner
W width of opening
Figure 6 — Deck and shell openings corner radius

Figure 7 — Section of a wooden boat with floating frame
6.3.5 Knife edge load crossing
Knife edge load crossing happens when two load carrying members cross at a right angle. This shall be
avoided as there is a high stress concentration at the point of connection of the two members. In the case of
knife edge load crossing, at least one of the members shall be reinforced as shown in Figure 8.
10 © ISO 2008 – All rights reserved

ISO 12215-6:2008(E)
Key
1 stress concentration (knife edge load crossing), poor practice
2 bracket transferring the load from the horizontal plate to the vertical plate, good practice
3 reinforcement with an L shaped stiffener or tabbing (for use in lightly loaded areas only), acceptable practice
Figure 8 — Sketch showing knife edge load crossing
6.3.6 Equivalent criteria
Other arrangements are possible but these shall follow good practice principles (as illustrated by Figures 4
to 8) of effective and smooth transmission of stresses, generous radii, use of connecting brackets, gentle
tapering of material, avoidance of stress concentration features and careful placement of any lightening holes.
6.4 Determination of stiffener spans
6.4.1 General
In order to establish whether a stiffener complies with the requirements of the ISO 12215 series (see
ISO 12215-5:2008, Clause 11), the spacing and span of the stiffener being considered shall be established.
The spacing is the distance between successive stiffeners, measured perpendicular to the stiffener axis. The
span is the distance between support points (see ISO 12215-5:2008, Clause 9). It is important to appreciate
that span exercises a very strong influence on the bending strength and deflection of any stiffener.
In order to simplify the calculations, the ISO 12215 series considers stiffeners as isolated beams under a
uniformly distributed pressure load. ISO 12215-5 provides guidance on locating support points for isolated
stiffeners (see ISO 12215-5:2008, Figure 11).
In reality, small craft structures often comprise a set of transverse stiffeners that intersect a set of longitudinal
stiffeners. This may be termed a “grid”. Each point where a transverse member crosses a longitudinal member
is termed an “intersection point”.
In some cases, it is correct to take the stiffener span as the distance between adjacent intersection points, but
in other cases this is too optimistic. The support which one set of crossing members offers to the other set is a
complex function of the relative flexural rigidity (EI) and the grid dimensions between well defined supports
such as bulkheads, side shell, partitions and other very deep members. This subclause provides procedures
for determination of stiffener spans.
6.4.2 Deep stiffeners crossing shallow stiffeners
Where one set of members have a depth of at least twice that of the other set, these deeper stiffeners are
called “primary members” and the shallower stiffeners are called “secondary members”.
The span of primary members, l , is the grid dimension in the direction of the primary member.
u
The span of secondary members, l , is the spacing of the primary member.
u
EXAMPLE Side transverse frames 120 mm deep, spaced 900 mm, run from the deck edge at side to a sharp chine,
for a distance of 1 900 mm. Longitudinal side stringers 50 mm deep are spaced at 300 mm between centres.
ISO 12215-6:2008(E)
The transverse frames are the primary members, with a span l of 1 900 mm and a spacing b of 900 mm.
u
The longitudinal stringers are the secondary members, with a span, l of 900 mm and a spacing b of 300 mm.
u
6.4.3 Stiffeners crossing similar depth stiffeners
6.4.3.1 General
This arrangement is commonly found in small craft as a tray moulding (see Figure 9) and is often referred to
as “egg-box” style. Neither set of members can be categorized as primary or secondary as the degree to
which one set supports the other is indeterminate by simple means of assessment.

NOTE The tray moulding shown is pre-moulded with glued flanges, but it may also be laminated in situ.
Figure 9 — “Egg-box” style tray mouldings
In such cases, the procedure described in 6.4.3.2 and 6.4.3.3 shall be adopted.
6.4.3.2 Stiffeners running in the shorter of the grid dimensions
The span used to determine the design bending moment and shear force shall be taken as 60 % of the grid
dimension.
The design pressure shall be obtained using a design area, A , based on the stiffener spacing and 60 % of
D
the grid dimension.
6.4.3.3 Stiffeners running in the longer of the grid dimensions
The span to be used to determine the design bending moment and shear force shall be taken as 150 % of the
distance between intersection points.
The design pressure shall be obtained using a design area, A , based on the stiffener spacing and 150 % of
D
the distance between intersection points.
EXAMPLE An egg-box consists of 75 mm deep top hat sections running in both directions. The top hats are spaced
600 mm apart for both sets. The grid is 2 300 mm long × 1 700 mm wide.
For the stiffeners running in the 1 700 mm direction: Spacing = 600 mm, span = 0,6 × 1700 = 1 020 mm.
Design pressure based on design area of 600 mm × 1 020 mm.
For stiffeners running in the 2 300 mm direction: Spacing = 600 mm, span = 1,5 × 600 = 900 mm. Design
pressure based on design area of 600 mm × 900 mm.
12 © ISO 2008 – All rights reserved

ISO 12215-6:2008(E)
6.4.3.4 Cautionary note
The method described in 6.4.3.2 and 6.4.3.3 is a considerable simplification of the real behaviour of grids.
EI
Depth is used as an indicator of flexural stiffness, . The procedure assumes that the dimensions of the
l
u
grid, and in the case of the method described in 6.4.3.2 and 6.4.3.3, the number of stiffeners and member
layups, in the two directions, are broadly similar: this presumption explains why in this case the shorter grid
dimension is used, since for similar layups the grid will be stiffer in the short direction and attract greater stress
(analogous to plate equations).
6.4.3.5 Example of a grid that may not fit within the governing assumptions
A grid where the condition specified in 6.4.3.4 would not be satisfied would be one which runs, for example,
for 6 000 mm in one direction wit
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