SIST EN ISO 11812:2024

SLOVENSKI STANDARD
01-december-2024
Mala plovila - Vodotesni prostori ter prostori in kabine s hitrim odvajanjem vode
(ISO 11812:2020)
Small craft - Watertight or quick-draining recesses and cockpits (ISO 11812:2020)
Kleine Wasserfahrzeuge - Wasserdichte und schnell-lenzende Rezesse und Plichten
(ISO 11812:2020)
Petits navires - Cavités et cockpits étanches ou rapidement autovideurs (ISO
11812:2020)
Ta slovenski standard je istoveten z: EN ISO 11812:2024
ICS:
47.080 Čolni Small craft
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EN ISO 11812
EUROPEAN STANDARD
NORME EUROPÉENNE
September 2024
EUROPÄISCHE NORM
ICS 47.080 Supersedes EN ISO 11812:2018
English Version
Small craft - Watertight or quick-draining recesses and
cockpits (ISO 11812:2020)
Petits navires - Cavités et cockpits étanches ou Kleine Wasserfahrzeuge - Wasserdichte und schnell-
rapidement autovideurs (ISO 11812:2020) lenzende Rezesse und Plichten (ISO 11812:2020)
This European Standard was approved by CEN on 12 August 2024.

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-CENELEC 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-CENELEC Management
Centre has the same status as the official versions.

CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia,
Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway,
Poland, Portugal, Republic of North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Türkiye and
United Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION

EUROPÄISCHES KOMITEE FÜR NORMUNG

CEN-CENELEC Management Centre: Rue de la Science 23, B-1040 Brussels
© 2024 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN ISO 11812:2024 E
worldwide for CEN national Members.

Contents Page
European foreword . 3

European foreword
The text of ISO 11812:2020 has been prepared by Technical Committee ISO/TC 188 "Small craft” of the
International Organization for Standardization (ISO) and has been taken over as EN ISO 11812:2024 by
Technical Committee CEN/TC 464 “Small Craft” the secretariat of which is held by SIS.
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 March 2025, and conflicting national standards shall
be withdrawn at the latest by March 2025.
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. CEN shall not be held responsible for identifying any or all such patent rights.
This document is read in conjunction with EN ISO 11812:2024/A1:2024.
This document supersedes EN ISO 11812:2018.
Any feedback and questions on this document should be directed to the users’ national standards body.
A complete listing of these bodies can be found on the CEN website.
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,
Croatia, Cyprus, Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland,
Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Republic of
North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Türkiye and the
United Kingdom.
Endorsement notice
The text of ISO 11812:2020 has been approved by CEN as EN ISO 11812:2024 without any modification.

INTERNATIONAL ISO
STANDARD 11812
Second edition
2020-07
Small craft — Watertight or quick-
draining recesses and cockpits
Petits navires — Cavités et cockpits étanches ou rapidement
autovideurs
Reference number
ISO 11812:2020(E)
©
ISO 2020
ISO 11812:2020(E)
© ISO 2020
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting
on the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address
below or ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: +41 22 749 01 11
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland
ii © ISO 2020 – All rights reserved

ISO 11812:2020(E)
Contents Page
Foreword .iv
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Symbols . 5
5 General . 6
5.1 Loading and measurement conditions . 6
5.2 Requirements for watertight and quick-draining recesses . 6
6 Watertightness requirements. 6
6.1 Watertightness requirements for watertight recesses . 6
6.2 Watertightness requirements for quick-draining recesses . 7
7 Requirements for companionway sills . 7
7.1 Companionway sills . 7
7.2 Quick-draining recess with a reduced risk of flooding . 8
7.3 Sill height measurement . 8
7.4 Minimum companionway sill height for quick-draining recesses . 8
8 Height of recess bottom above waterline for quick-draining recesses .8
9 Quick-draining recesses — Single bottom recess drainage . 9
9.1 Drainage general requirements . 9
9.2 Drain requirements . 9
9.2.1 Number and dimensions . 9
9.2.2 Special provisions . 9
9.2.3 Installation .10
9.3 Drainage calculation requirements .10
9.3.1 Drainage calculation principle and assessment methods .10
9.3.2 Simplified drainage assessment method .11
10 Quick-draining recesses — Multi-bottom recess drainage .12
10.1 Drainage general requirements .12
10.2 Drainage calculations .12
10.3 Drainage requirements for a foot basin .13
11 Owner’s manual.14
11.1 General recommendation for use .14
11.2 Recommendation for use from Table 4 — Companionway opening .14
Annex A (normative) Full calculation method for draining time .16
Annex B (informative) Technical background — Source of the calculations used .24
Annex C (informative) Examples of “quick-draining” recesses .30
Bibliography .32
ISO 11812:2020(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.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular the different approval criteria needed for the
different types of ISO documents should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www .iso .org/ directives).
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. Details of
any patent rights identified during the development of the document will be in the Introduction and/or
on the ISO list of patent declarations received (see www .iso .org/ patents).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and
expressions related to conformity assessment, as well as information about ISO's adherence to the WTO
principles in the Technical Barriers to Trade (TBT), see Foreword - Supplementary information.
This document was prepared by Technical Committee ISO/TC 188, Small craft.
This second edition cancels and replaces the first edition (ISO 11812:2001), which has been technically
revised.
The main changes compared to the previous edition are as follows:
— systematic usage of the general term "recess" instead of "cockpit";
— introduction of the concept of recess open to the sea and recess with reduced risk of flooding;
— clarification of requirements;
— clarification of requirements on engine ventilation openings installed in recesses;
— implementation of multi-bottom recesses or recesses with a foot-basin in the main core of the
standard;
— deletion of "major head losses" (friction in drain pipes) as their effect was very small, but this made
the calculation much more complex;
— improved data for "minor head losses" (local losses) to correspond to common practice;
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www .iso .org/ members .html.
iv © ISO 2020 – All rights reserved

INTERNATIONAL STANDARD ISO 11812:2020(E)
Small craft — Watertight or quick-draining recesses and
cockpits
1 Scope
This document specifies watertightness, draining time and sill heights requirements for watertight and
quick-draining recesses and cockpits in small craft of up to 24 m load line length (see Reference [1]).
Recesses located in elevated parts of the craft are covered by this document.
This document does not specify requirements for the size, the shape and the location of recesses or
cockpits. It only considers draining by gravity, and not by pumping or other methods.
It only considers normal operation of the craft, but unattended craft recess issues are out of scope.
This document does not guarantee that the water contained in a watertight or quick-draining
recess or cockpit will not affect the stability and buoyancy of the craft, which are covered by
ISO 12217 (all parts):2015.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements 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.
1)
ISO 8666:2016 , Small craft — Principal data
1)
ISO 9093-1:1994 , Small craft — Seacocks and through-hull fittings — Part 1: Metallic
1)
ISO 9093-2:2002 , Small craft — Seacocks and through-hull fittings — Part 2: Non-metallic
ISO 12216:2020, Small craft — Windows, portlights, hatches, deadlights and doors — Strength and
watertightness requirements
ISO 12217-1:2015, Small craft — Stability and buoyancy assessment and categorization — Part 1: Non-
sailing boats of hull length greater than or equal to 6 m
ISO 12217-2:2015, Small craft — Stability and buoyancy assessment and categorization — Part 2: Sailing
boats of hull length greater than or equal to 6 m
ISO 12217-3:2015, Small craft — Stability and buoyancy assessment and categorization — Part 3: Boats of
hull length less than 6 m
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at http:// www .electropedia .org/
1) Under revision.
ISO 11812:2020(E)
3.1
design category
description of the sea and wind conditions for which a craft is assessed to be suitable
Note 1 to entry: The design categories are defined in ISO 12217 (all parts):2015.
Note 2 to entry: The definitions of design categories are in line with the European Recreational Craft Directive
2013/53/EU.
3.2
sailing craft
craft for which the primary means of propulsion is by wind power, having a reference sail area
2/3
A ≥ 0,07(m ) , expressed in metres squared, where m is the mass of the craft in the maximum
S LDC LDC
load condition, expressed in kilograms
Note 1 to entry: The reference sail area, A , is defined in ISO 8666:2016.
s
3.3
non-sailing craft
craft for which the primary means of propulsion is other than by wind power, having a reference
2/3
sail area A < 0,07(m ) , expressed in metres squared, where m is the mass of the craft in the
S LDC LDC
maximum load condition, expressed in kilograms
Note 1 to entry: The reference sail area, A , is defined in ISO 8666:2016.
s
3.4
reference waterline
W
L
level of the water on the hull in the fully loaded, ready-for-use condition
Note 1 to entry: The fully loaded, ready-for-use condition is defined in ISO 8666:2016.
3.5
heeled waterline
level of the water on the hull in the fully loaded, ready-for-use condition when the craft is inclined to:
— an angle of 7° for non-sailing craft and multihulls; or
— the level of the sheer line amidships or an angle of 30°, whichever is lower, for monohull sailing craft
Note 1 to entry: The fully loaded, ready-for-use condition is defined in ISO 8666:2016.
3.6
recess
volume open to the air that can retain water within the range of loading conditions and
corresponding trims
EXAMPLE Cockpits, wells, open volumes or areas bounded by bulwarks or coamings.
Note 1 to entry: Where fitted with closure device(s) according to ISO 12216:2020, cabins, shelters or lockers are
not recesses.
Note 2 to entry: A recess can be composed of several recesses connected together.
Note 3 to entry: Cockpits that are open to the sea are considered as recesses. Flush decks without bulwarks or
coamings are not recesses.
3.7
cockpit
recess (3.6) intended for the accommodation of people
2 © ISO 2020 – All rights reserved

ISO 11812:2020(E)
3.8
watertight recess
recess (3.6) that satisfies the watertightness and sill (3.24) height requirements of this document, but
not the drainage requirements
3.9
quick-draining recess
recess (3.6) with characteristics and draining capacity that satisfy all the requirements of this document
for one or several design categories
Note 1 to entry: According to its characteristics, a recess can be considered as quick-draining for one design
category, but not for a higher category.
Note 2 to entry: The term "quick-draining" has been chosen to differentiate from the common understanding
term "self-draining", where water can be drained overboard in certain conditions, but without a specified
draining speed, height of bottom or sill, etc.
3.10
recess open to the sea
recess (3.6) where the aft and/or side boundaries are open to the outside of the craft, with a recess
retention height (3.21) equal to zero
Note 1 to entry: Figure C.1 c) gives an example of a recess open to the sea.
3.11
recess bottom
lowest surface of the recess (3.6), where water collects before being drained
Note 1 to entry: The recess bottom can have several levels.
3.12
recess bottom height
H
B
height of the recess bottom (3.11) above the waterline, the craft being upright, at rest and fully loaded
3.13
minimum recess bottom height
H
B min
minimum value of the recess bottom height (3.12) required by this document
3.14
single-bottom recess
recess (3.6) where the bottom has only one level
Note 1 to entry: A single-bottom recess fitted with a foot basin (3.31) is considered as a multi-bottom recess (3.15).
3.15
multi-bottom recess
recess (3.6) where the bottom has more than one level
3.16
bridge deck
area in the proximity of the companionway (3.23) opening and above the recess bottom (3.11), on which
people normally step before entering the accommodation
3.17
interior
inside the craft's watertight envelope
ISO 11812:2020(E)
3.18
watertightness degree
degree of watertightness
capacity of an appliance (3.20) or fitting to resist ingress of water, according to the conditions of
exposure to water
Note 1 to entry: See Table 1 for a definition of the four watertightness degrees.
Table 1 — Definitions of the degrees of watertightness
Degree of watertightness: Definition
1 (waterproof) Constructed to withstand continuous immersion
Provides protection against the effects of continuous immersion in water
2 (watertight) Constructed to prevent ingress of water
Provides protection against the effects of temporary immersion in water
3 (weathertight) Constructed to minimize seepage
Provides protection against splashing water
4 (spraytight) Provides protection against waterdrops falling at an angle of up to 15° from the
vertical
NOTE  Test procedures for watertightness degrees are provided in ISO 12216:2020.
3.19
downflooding opening
opening in the hull or deck (including the edge of a recess) that might admit water into the interior or
bilge of a craft, or into a recess
Note 1 to entry: Those excluded by ISO 12217 (all parts):2015 are not considered in this document.
3.20
appliance
device used to cover an opening in the hull, deck or superstructure of a craft
EXAMPLE Windows, portlights, hatches, deadlights, doors, sliding appliances, escape hatches, washboard,
compass, ventilation grids, loudspeakers, engine control panel, etc.
Note 1 to entry: They can be fixed appliances or opening appliances.
3.21
recess retention height
h
C
height of water in a recess (3.6), when the craft is upright and at design trim assuming that all gates,
doors or drainage openings are sealed, at which the overflow area is greater than 0,005 L B (m )
H H
Note 1 to entry: The design trim is in maximum load condition as defined in ISO 8666:2016.
Note 2 to entry: When h is less than 0,10 m, it is taken as equal to 0,0 m.
c
3.22
drain
outlet of the recess (3.6) enabling water contained to be discharged overboard by gravity
EXAMPLE A pipe discharging overboard above or below waterline; a part of the recess allowing direct
discharge overboard; scuppers and freeing port.
3.23
companionway
opening intended for crew access to the accommodation and fitted with an opening appliance (3.20)
Note 1 to entry: The opening appliance can be a door, a hatch; vertical, horizontal, etc.
4 © ISO 2020 – All rights reserved

ISO 11812:2020(E)
Note 2 to entry: There can be several companionways.
3.24
sill
barrier above which water in the recess (3.6) can enter companionway (3.23) openings and downflood
the craft
EXAMPLE Hatches of cockpit companionways.
3.25
fixed sill
sill (3.24) that is a fixed, integral and permanent part of the recess (3.6)
3.26
semi-fixed sill
opening appliance (3.20), movable but permanently installed on the craft that, when in place, constitutes
a sill (3.24) higher than the fixed part of the sill
EXAMPLE Hatches, sliding sills, but excluding washboards.
Note 1 to entry: A lanyard is not regarded as a permanent attachment.
Note 2 to entry: Sliding or hinged doors are considered as a mobile part of a semi-fixed sill.
3.27
washboard
opening appliance (3.20) for companionway (3.23) openings made of several mobile boards sliding in
a rabbet that, when closed, are stacked one on top of each other, and located above the minimum sill
height (3.29)
Note 1 to entry: This is a frequent device on sailing monohulls; boards are added as the weather worsens.
3.28
sill height
h
S
minimum vertical distance from the top of the sill (3.24) to the closest part of the recess (3.6) bottom
Note 1 to entry: See Figure 1.
3.29
minimum sill height
h
S min
minimum value of the sill height (3.28) required by this document
3.30
recess volume
V
C
volume of water that can be contained in a recess (3.6) before discharge
Note 1 to entry: It is the maximum volume, considering any combination of movable coamings, etc., measured
from the recess bottom (3.11) up to the recess retention height (3.21), assuming that all opening appliances (3.20)
and drains (3.22) are closed.
3.31
foot basin
specific recess (3.6) that satisfies the requirements of 10.3 of this document, located between a recess
and a companionway (3.23) opening, and having a lower bottom than the surrounding recess
4 Symbols
Table 2 gives the main symbols used in this document, with their meaning and unit.
ISO 11812:2020(E)
Table 2 — Main symbols used in this document
Symbol Meaning Unit
B Beam of hull as defined by ISO 8666:2016 m
H
F Freeboard amidships as defined by ISO 8666:2016 m
M
h Recess retention height m
C
h Sill height m
S
h Minimum sill height m
S min
H Recess bottom height above waterline m
B
H Minimum recess bottom height above waterline m
B min
k Design category factor —
DC
L Length of hull as defined by ISO 8666:2016 m
H
V Recess volume m
C
t Maximum allowable draining time min
max
t Reference draining time min
ref
d Drain diameter mm
NOTE  Heights measured above the recess bottom have symbols beginning with h, whereas heights
measured above waterline have symbols beginning with H.
5 General
5.1 Loading and measurement conditions
Unless otherwise specifically stated in the text:
— the craft is in fully loaded, ready-for-use condition as defined in ISO 8666:2016;
2 3
— lengths and heights are measured in m, areas in m , volumes in m , time in min and/or s;
— measurements or calculations shall be made with the craft upright and at rest in calm water.
5.2 Requirements for watertight and quick-draining recesses
Table 3 summarizes the relevant clauses applicable to watertight and quick-draining recesses.
Table 3 — Relevant clauses for a recess to qualify as watertight or quick-draining
“Quick-draining” recess
Requirements Watertight recess
Open to the sea Reduced risk of
Others
(3.10) flooding (7.2)
Watertightness 6.1 6.2 6.2 6.2
Companionway sill None Clause 7 Clause 7 None
Height of recess bottom None Clause 8 Clause 8 Clause 8
Drainage None Clause 9 or 10 None None
Strength of appliances ISO 12216:2020 ISO 12216:2020 ISO 12216:2020 ISO 12216:2020
6 Watertightness requirements
6.1 Watertightness requirements for watertight recesses
In watertight recesses, all surfaces and appliances shall have a degree of watertightness 1 up to a
height of h .
C
6 © ISO 2020 – All rights reserved

ISO 11812:2020(E)
6.2 Watertightness requirements for quick-draining recesses
All surfaces shall have a degree of watertightness 1.
The degree of watertightness of appliances installed in the surface of the quick-draining recess shall be
as specified in Table 4.
Table 4 — Degrees of watertightness of appliances
a
Location of appliances in the recess Degree of watertightness
appliance on bottom and sides up to h 2
S min
appliance between h and 2 h 3
S min S min
appliance above 2 h 4
S min
NOTE 1  On engine ventilation openings installed in a recess, a watertightness assessment can be performed using the total
arrangement of exterior grid and internal ducts or swan’s neck of the appliance, with material and connections sufficient to
withstand the associated head of pressure.
NOTE 2  Additional requirements can be specified in other International Standards, such as ISO 12217 (all parts):2015.
a
h is defined in Table 5, the local sill height and h being measured as required by 7.3
S min S min
Opening appliances covering downflooding openings and installed on the surfaces of a quick-draining
recess shall be secured in the closed position by a manually operated mechanical positive device.
7 Requirements for companionway sills
7.1 Companionway sills
Any companionway inside the limits of the recess and those located within an area extending 0,6 m
outside of the recess boundary shall comply with the requirements of this Clause (see Figure 1).
Key
1 sill height
2 front companionway door on bulkhead
3 aft companionway hatch on deck
Figure 1 — Sills considered and sill height measurement
ISO 11812:2020(E)
7.2 Quick-draining recess with a reduced risk of flooding
A quick-draining recess with a reduced risk of flooding does not require a sill for any companionway
opening if it complies with the following criteria:
— the craft is of a fully enclosed type according to ISO 12217 (all parts):2015;
— the recess is open to the sea, as defined in 3.10 of this document;
— all of the recess is located aft of the mid hull length of the craft;
— companionway(s) is(are) installed on the rear face of a superstructure;
— it has the lowest point of the companionway(s) opening higher than [(L /17) + h ] above the
h S min
reference waterline;
— companionway opening appliance(s) is(are) permanently installed, enabling immediate closure.
7.3 Sill height measurement
The sill height is the lowest height of the companionway, as defined in 3.28.
The sill height shall be measured vertically from the adjacent closest point of the recess bottom to the
lowest point of the upper sill edge (see Figure 1).
If a multi-bottom recess is fitted with a foot basin complying with the foot basin requirements of 10.3,
the sill height shall be measured from the foot basin bottom; otherwise the sill height shall be measured
from the closest recess bottom
7.4 Minimum companionway sill height for quick-draining recesses
Table 5 specifies the requirements regarding minimum companionway sill height for quick-draining
recesses.
These requirements do not apply to quick-draining recesses with a reduced risk of flooding.
Where a semi-fixed sill is fitted, the height of the fixed part shall be at least (h /2).
S min
Table 5 — Minimum companionway sill height, h , for quick-draining recesses
S min
Dimensions in meters
Sailing monohulls Non-sailing craft and sailing multihulls
Design
category
minimum sill height, h minimum sill height, h
S min S min
A 0,30 0,20
B 0,25 0,15
C 0,15 0,10
D 0,05 0,05
NOTE  The above requirements may be raised by other International Standards such as ISO 12217 (all parts):2015.
8 Height of recess bottom above waterline for quick-draining recesses
Table 6 specifies the minimum recess bottom height, H , above reference waterline, for quick-
B min
draining recesses.
For a single-bottom recess, H is measured at the centre of the surface of the bottom.
B
For a multi-bottom recess, H is measured at the centre of the surface of the lowest bottom.
B
8 © ISO 2020 – All rights reserved

ISO 11812:2020(E)
Table 6 — Minimum height, H , of the recess bottom above reference waterline
B min
Dimensions in meters
Design category H
B min
A 0,150
B 0,100
C 0,075
D 0,050
NOTE  Greater heights than these minimum values may be required to fulfil the
maximum acceptable draining time according to Clauses 9 and 10.
9 Quick-draining recesses — Single bottom recess drainage
9.1 Drainage general requirements
Drainage shall only be by gravity.
If there are mobile parts allowing openings in the recess boundary, this requirement shall be verified in
the worst configuration, e.g. if there are doors, they shall be closed.
The drainage system shall be arranged to minimize trapping of water in the recess, in both reference
waterline and heeled waterline conditions.
Connected recesses with the same bottom level shall be treated as separate recesses if the sum of the
areas that link them is < 120 % of the required minimum draining area of the connected recesses.
9.2 Drain requirements
9.2.1 Number and dimensions
A quick-draining recess shall have at least two drains, one port and one starboard, unless one opening
enables drainage when the craft is at heeled waterline according to 9.1 to both port and starboard.
Drains with a circular cross section shall have an internal diameter of at least 25 mm.
Drains with other cross-sectional shapes shall have an internal cross-sectional area of at least 500 mm ,
and an internal minimum dimension of 20 mm.
9.2.2 Special provisions
In case of grids or systems preventing loose objects from falling into the draining system, it shall be
considered that a grid with small holes is more prone to be clogged than the drain itself. The simplified
drainage assessment method of 9.3.2 may be used, if
— the minimum passage dimension inside any part of these devices has at least a section of 125 mm
(or a diameter of 12 mm), and
— the total entry cross-section is at least 1,5 times the internal cross-section of the drain.
Otherwise the drainage assessment shall be performed according to the full calculation method of
Annex A or a test method.
In case of centreboard housings and other types of aperture, these may be used as drains if:
— they are designed for this purpose, and
— they fulfil the other relevant requirements of Clause 9.
ISO 11812:2020(E)
9.2.3 Installation
When the craft is in maximum load condition, the drain outlet running through the hull shall either be
located:
— above the waterline, or
— below the waterline, and be fitted with seacocks unless the drain outlet is an integral part of the hull
extending from the outlet up to at least 0,75 H above the waterline.
B min
Figure 2 shows a drain outlet being an integral part of the hull.
Key
1 waterline
2 top of integral penetration above 0,75 H : no seacock required
B min
3 in this area, the drain is integral with the hull shell
Figure 2 — Drain outlet being an integral part of the hull
All the drain piping system shall have a degree of watertightness 1.
Drain piping shall be protected against damage from loose objects stowed in the craft and against being
kicked or stepped on.
Drain piping installed in the engine room shall be able to withstand 70 °C or be insulated from the heat.
Drain piping shall not trap water.
Drains shall only be used for recess drainage except drains fitted in the centreboard housing or
outboard wells and trunks.
Seacocks, through-hull fittings, and associated components shall comply with ISO 9093-1:1994, if
metallic, and ISO 9093-2:2002, if non-metallic.
9.3 Drainage calculation requirements
9.3.1 Drainage calculation principle and assessment methods
The drainage calculation principle of this document for quick-draining recesses is based on a maximum
draining time approach.
10 © ISO 2020 – All rights reserved

ISO 11812:2020(E)
The maximum draining time, t (in min), is defined as follow:
max
 
kL××BF×
()
DC HH M
t =min;5 (1)
 
max
V
 C 
 
with the design category factor, k , as defined in Table 7.
DC
NOTE This document considers that the maximum draining time does not exceed 5 min for quick-draining
recesses.
The draining time is the time elapsed to empty the recess between the retention height, h , and 0,1 m of
C
the remaining water height.
The water height shall be measured above the centre of the bottom surface of the recess.
To define the size of single-bottom recess drains according to the requirements of this document for
quick-draining recesses, one of the 3 following methods shall be used:
— a simplified method, as defined in 9.3.2, which provides conservative results;
— an full calculation method, as defined in Annex A, which gives more accurate results;
— a test method, in accordance with a maximum draining time, t .
max
The draining time shall be assessed, by test or by calculation, with every opening appliance closed.
If the draining section of the recess is greater than or equal to 0,05 V , this recess does not require a
C
draining time assessment.
9.3.2 Simplified drainage assessment method
The following calculation method is applicable to single level bottom recesses.
Step 1 – Determine the recess volume, V (m ).
C
Step 2 – Determine the design category factor, k , using Table 7.
DC
Table 7 — Design category factor, k , of quick-draining recesses
DC
Design category k
DC
A 0,30
B 0,45
C 0,60
D 0,90
Step 3 – Calculate the required reference draining time t (min):
ref
 
kL××BF×
()
DC HH M
t =min ;/5 V (2)
 
ref C
V
 C 
 
NOTE This document considers that the maximum draining time does not exceed 5 min for quick-draining
recesses.
Step 4 – Determine the required diameter, d (mm), of the pair of circular drains
With Table 8, by interpolation if necessary, determine the d value from the required value of t
ref
According to 9.2.1, the value of d shall not be taken less than 25 mm.
For other drain arrangements than those in Table 8, one of the 2 other methods from 9.3.1 shall be used.
ISO 11812:2020(E)
Table 8 — Drain diameter, d, as a function of t and typical drain arrangements
ref
Typical drain
Value of t (min)
ref
arrangement
a
Case 1 10,5 7,3 5,4 4,1 3,2 2,6 2,2 1,8 1,6 1,3 1,2 1,0 0,8 0,7 0,5 0,5 0,4 0,3 0,3
b
Case 2 7,6 5,3 3,9 3,0 2,4 1,9 1,6 1,3 1,1 1,0 0,8 0,7 0,6 0,5 0,4 0,3 0,3 0,2 0,2
Diameter d
25 30 35 40 45 50 55 60 65 70 75 80 90 100 110 120 130 140 150
(mm)
a
Typical drain arrangement "Case 1": 2 freeing ports, above waterline, no flap.
b
Typical drain arrangement "Case 2": 2 drain outlets, above waterline, no elbow, smooth drain entry and no grid.
NOTE 1  Considering main parameters in calculations, these two typical arrangements are the most conservative.
NOTE 2  Case 2 with outlets below waterline is less conservative than Case 2 itself.
10 Quick-draining recesses — Multi-bottom recess drainage
10.1 Drainage general requirements
Multi-bottom recesses shall have a drainage system complying with the requirements of 9.1 and 9.2.
The draining time shall be either tested or assessed by calculation according to the method of 10.2.
When a multi-bottom recess is fitted with a foot-basin, it shall also comply with 10.3.
10.2 Drainage calculations
This subclause provides the step by step method to calculate the draining time of multi-bottom recess.
Step 1 – Calculate the total volume, V , of the multi-bottom recess.
C
Step 2 – Calculate t related to V using Formula (1).
max C
Step 3 – Calculate the time t to drain the volume V from h to the highest bottom level.
ref1 1 C
Step 4 – Define the sub-volumes V to drain for each remaining drainage system.
n
Step 5 – Calculate the draining times t of each sub-volume V (see Formulas in Clause A.3).
refn n
Where one of these sub-volumes V is open to the sea, no drainage calculation is required and
n
t = 0.
refn
Step 6 – Calculate the sum of t ; when considering multiple sub-volumes draining at the same time,
refn
the longest draining time obtained shall be used in the draining time sum.
The maximum time elapsed to empty a multi-bottom recess from the retention height h to a level
C
of 0,1 m of remaining water height shall be less than t calculated in step 1 of this process.
max
The remaining water height shall be calculated in the last sub-volume to drain.
Figure 3 provides an example of assessment for a multi-bottom level recess arrangement, where:
a) the volume Vc is split into sub-volumes V , V , V , V and V according to the respective bottom levels;
1 2 3 4 5
b) t , t , t , t , and t are the draining time of the respective sub-volumes V , V , V , V and V ;
ref1 ref2 ref3 ref4 ref5 1 2 3 4 5
c) the longest draining time sum from [t +t +t ] or [t +t +t ] shall be less than t .
ref1 ref2 ref3 ref1 ref4 ref5 max
12 © ISO 2020 – All rights reserved

ISO 11812:2020(E)
Figure 3 — Example of multi-bottom recess arrangement assessment
10.3 Drainage requirements for a foot basin
A foot basin is intended to reduce the sill height relative to the recess bottom. These additional
requirements are intended to minimize ingress by ensuring the water drains quickly before reaching
the level of the sill.
The foot basin shall drain a volume of not less than h × multi-bottom recess total area.
S min
In addition to the requirements of 10.1 and 10.2, as a specific recess of a multi-bottom recess, a foot
basin shall comply with the requirements of Table 9.
Table 9 — Requirements for a foot basin
Characteristics of the
Requirements
a
foot basin
Minimum width ≥ 90 % of the maximum width of companionway opening
The length of the upper part of the foot basin (normal to the companionway width)
b shall be:
Length
between 2 × h and 4 × h
S min S min
The depth (below upper level of the adjacent recess bottom) shall not be less than:
c
Minimum depth
1 × h
S min
The volume shall be at least:
d
Minimum volume
3hw× idth
Smin
Location Immediately in way of companionway opening(s), see Figure 4
The grating permeability shall be:
equally spread on the total area of the grating,
Grating permeability
≥ 25 % or a specific draining time calculation is made considering the minor head
b
losses at grating level according to A.5.2
Sill height measure-
The sill height shall be measured from the bottom of the foot basin
ment
Companionway opening appliance(s) shall be permanently installed, enabling immedi-
Companionway door
ate closure
a
If the total drainage area is >25 % of the foot basin bottom area, a device protecting water surging from below shall be
provided.
b
This requirement prevents the water rebounding on the grating and flooding inside the interior.
c
The length and the width of the foot basin is measured at the minimum depth required h .
S min
d
To calculate the volume of the foot basin, the depth used is the lowest of the actual depth and the actual sill height.
ISO 11812:2020(E)
Key
1 companionway opening 4 width of companionway opening
2 actual sill above foot basin bottom 5 width of foot basin
or ab
...