Feature 1 | YACHT DESIGN AND CONSTRUCTION

A new ISO 12215-5 for small

craft structures
Jean-Baptiste R. G. Souppez, senior lecturer in yacht design and composite
engineering at Solent University and UK principal expert in small craft structures,
highlights the main regulatory changes to the revised version of ISO 12215-5 for
hull construction and scantlings, and its inherent impact on the industry

I
t is the purpose of international ISO with the 2008 version of ISO 12215-5 part • Direct Test, exp erimentally
standards to provide up-to-date of commercial craft regulations, despite assessing the mechanical properties
and relevant requirements and the standard clearly not being intended as opposed to relying on the ISO
guidelines for industries to ensure the to do so, commercial craft will now default values (kAM = 1);
suitability and safety of their products. fall under the revised scope. Annex  J is • Finite Element Methods, a new and
Since the publication of the 2008 version dedicated to workboats (Souppez, 2018), significant addition to the revised
of ISO 12215-5 for small craft hull subcategorised between charter, light version (kAM = 1);
construction and scantlings, formidable duty and heavy duty craft, each with its • Drop Test, w hich remains
progresses have been made. These cover own additional requirements. While both intended for some very small craft,
the design and analysis of structures, military crafts and vessels operating in and provides a more practical
and a wider and better understood array ice conditions are excluded, considering assessment of the compliance (kAM
of materials and production techniques, the operational profile of workboats not applicable).
particularly for composites. The necessity led to accelerations up to 8g to now be
for a revised standard, more in line with considered (as opposed to 6g previously). In the case of composite craft, a
current industry practice, is therefore Lastly, while racing yachts intended boatbuilding factor was also introduced
undeniable. After several years of work solely for professional use remain outside to reflect both the level of uncertainty
in close partnership with the industry, of the scope, a greater emphasis on inherent to the various methods (hand
the Working Group 18, part of the ISO high-performance and sport sailing craft laid versus infused and prepreg), as
Technical Committee 188 and in charge of has been developed. This will minimise well as the level and depth of quality
the ISO 12215 series of standards, has now weight and maximise performance, control undertaken. This will heavily
published the revised Part 5. With major while demonstrating compliance with penalise the absence of fibre weight
changes to the scope and a large range of ISO 12215-5. fraction check, a critical factor in
new considerations, the new version of composite structures.
the standard will strongly influence the New considerations Additional refinements include
small craft industry. To reflect the progresses made in the inclusion of overhangs in the
structural design and analysis, longitudinal pressure distribution,
New scope particularly in the field of composite together with reduced pressure in the aft
Three major alterations to the scope of engineering, and the advances in of the slamming region. These proved
the standard have been made, with a numerical analysis, six options are now in line with industry feedback and will
significant impact, broadening the range available to assess compliance, as listed enable maximisation of living space.
of vessels covered. below. Each method corresponds to an

“
Firstly, while the standard still applies assessment method factor (kAM) aiming
to vessels up to 24m hull length, as defined to add additional safety margins for the
While
under the Recreational Craft Directive lower analysis levels, and reward more
(Directive 2013/53/EU), it now also advanced methods: professional-use
extends up to an IMO Load Line Length racing yachts remain
of 24m. This is a tremendous step forward • Simplified method, based on idealised
in bridging the regulatory challenges beam theory (kAM = 0.90);
outside of the scope, a
arising from the different definitions • Enhanced method, consisting of a greater emphasis on high-
of 24m, and will typically allow vessels
with large overhangs to remain governed
by ISO 12215-5 despite a hull length in
•
ply-by-ply analysis (kAM = 0.95);
Developed method, relying on classical
laminate theory, and extending the
performance and sport
sailing craft has been
“
excess of 24m. ply-by-ply analysis with the addition of, developed
Then, to address the fact that a number for instance, the Tsai-Hill or Tsai-Wu
of regulatory bodies’ required compliance criterion (kAM = 1);

2 Ship & Boat International November/December 2019

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Furthermore, new considerations 12215-5. Importantly, Part 7 will focus on craft industry for the better part of the
crucial to small craft and sailing yachts the global load cases that are specific and forthcoming decade. SBI
have been developed, including definition so critical in multihull design.
for natural stiffeners on round bilge hulls, On the other hand, the ISO 12215-10 References
and double curvature correction. The will tackle rigs loads and rig attachments • Souppez, J.-B. R. G., 2019. ‘Designing
latter is a considerable improvement, as in sailing craft. This long-awaited the Next Generation of Small Pleasure
the impact of double curvature can be guidance on the loads transferred from and Commercial Powerboats with
major on small craft. rig to hull(s) will further enhance the the Latest ISO 12215-5 for Hull
Lastly, guidance and recommendations design and safety of sailing craft, with Construction and Scantlings’. In the
for the analysis of bulking material (now a strong emphasis on maintaining the Proceedings of the First SNAME/
often used as a thin core alternative or watertight integrity of the hull. IBEX Symposium, Tampa, Florida, US
print through barrier), and the sensible • Souppez, J.-B. R. G., 2018. ‘Structural
reduction in scantlings that can be applied Conclusions Analysis of Composite Search and
to sport racing craft (Souppez, 2018), have The ever-evolving nature of small craft Rescue Vessels under the New BS EN
been provided. design and manufacturing implies that ISO 12215-5’. In the Proceedings of
standards must remain up to date and SURV9 - Surveillance, Search and
Future developments adapt to the changes in the industry. As Rescue Craft. The Royal Institution
New parts of the ISO 12215 standard such, further guidance on the use of of Naval Architects, London, UK,
will be published in the near future, to the standard will be provided during 18/04/2018, pp. 1-4.
provide a more complete analysis of some its lifespan (Souppez, 2019), and the • Souppez, J.-B. R. G., 2018. ‘Structural
specific craft types. regulation will be cyclically revised. For Design of High Performance
On one hand, the ISO 12215-7 now, the recently published new version Composite Sailing Yachts under the
standard will be used to establish loads of the ISO 12215-5 provides a consequent New BS EN ISO 12215-5’. SNAME
for multihulls, and the determination of update on the hull construction and Journal of Sailing Technology,
their local scantlings in relation to the ISO scantlings that will influence the small issue 2, pp 1-18.

Ship & Boat International November/December 2019 3