Is a walkway around a deckhouse always necessary?

I maybe should have been clearer in my initial question. I'm specifically looking at catamaran and trimaran designs, not a monohull, so in my case the forward deck access would be through a door with a similar design to a Chris White or Gunboat forward cockpit.

But the question about whether a catwalk is essential for some other reason (e.g. maybe insurers need it, or some regulation requires it) is really about working through the criteria that the catwalk typically serves and checking whether all those criteria can be met in other ways.

 

That's a good point. In my case I'm thinking of a catamaran or trimaran with a large living space surrounded by windows, so natural light should be plentiful.

 

Could you share some examples or pictures of boats that have increased the interior volume by using a flush deck?

 

You get better answers when you state the "context" of your question up front.

 

Tartan 10, Cal 25 SF Bird

 

Also the Cal 28

 

My remark goes also for multihulls. Any companion way should have a sill. In multihulls, there should be a recess "a footbath" before the companionway. The sill height is then interpreted as the footbath depth. The footbath should be drained, according to its volume. The control authorities in Europe, prior to the marketting of the Lagoon 77, made this very clear. It was also the case for all the Lagoon catamaran with fore companion way.

Under which regulations will fall your boat ? Technically speaking, the deck should give direct access to all boat maneuvers, as pointed out by Will in the comment #5, including sail control, mooring points and man over board recovery. In the absence of catwalk, either you go by the roof top, either you go by a fore companionway, either both.

EN ISO 15085 - Man-overhead prevention and recovery
3.6 working deck
external areas defined by the boat builder for people to stand or walk during normal operation of the boat.

NOTE 1 The working deck is normally composed of rigid parts of the boat, such as decks, coach-roofs, superstructures, flying bridges, etc. but may also consist of flexible parts, such as trampolines and nets.
NOTE 2 On some boats the working deck is limited to the cockpit, the foredeck only being used for access to strong points.
NOTE 3 Unless specifically stated by the boat builder, areas having an inclination of more than 25° to the horizontal in a longitudinal direction, or more than 30° in a transverse direction, are not considered to be part of the working deck.

The minimum dimensions of the catwalk of a recreationnal craft is 150mm according to ISO standard. A smaller width disqualified the given deck zone as being part of the "technical deck". In the cases where there is no catwalk, or if the catwalk width is smaller than 150mm, the roof top may be considered as part of the deck, to give access to the fore mooring point. In that case, means of prevention should be present, including anti-slip surface, and eventually footstops, hooking points, guard rails/lines.

 

The challenge here is that standing on the deckhouse roof puts you rather high up, considerably above many pontoons or quays.

Could you rapidly move from bow to stern or vice versa while holding a dockline without letting go?

 

Rolling your ankle a few miles out is scary, or a few hundred miles out....when I was a nimble young sailor I would have said cool. After 40, the ability to hop and skip around a deck substantially diminishes.

 

Thanks Alan, that is exactly the information I was looking for.

Does this mean that ALL of those means of prevention listed must be included, or is this an example of some means of prevention that could be used. For example, if there are hooking points are guard rails still reqired?

Also, what determines the "design category" of a vessel used in those tables?

 

That's a useful criteria that I hadn't thought of in that way.

 

A quick internet search will describe each design category, A being ocean crossing vessels D being inshore protected waters with different wind and sea states to be operated in.

 

Yes, you're right Waterwitch. Please find downbelow the definition of all the design categories :

To use the tables 3 and 4 given in the post #22, you shall :
- determine the design category of the boat ( ! Besides being related to the navigation conditions, the stability index of the boat, called STIX, establishes properly the design category of a recreationnal craft <24m )
- choose an option
- verify all mean of prevention marked in the table.

For example, the very beautifull 15' sailing monohull "Sally Gee", showed in the post #3, may be in D design category ( a feeling... only stability calculation can tell ).
Only one option in available, the option 6. So to be ISO compliant regarding the man-over board prevention, the deck of the boat should be equipped with :
Slip resistant surface -> present on the roof top, so roof top is part of the deck
Handholds -> in that case, It may be considered that the bulwark can be used as handholds. De facto, it may be used as is. Are the handholds on the roof really usefull, or are they more used as footstop ? I don't know.
Mean of re-boarding -> Considering the low freeboard, it may be considered that it is not necessary to add a specific re-boarding ladder. You may use the rudder and adjacent rail to re-board.

It should be noted that, with option 1, hooking points & gard rails are mandatory, if the boat is intended to be ISO compliant.

 

Actually there is a very good engineering reason for 'catwalk' side decks. If you look at a f/glass hull newly uprighted before the deck is attached you will see the topsides at deck level have almost no strength in the horizontal plane unless reinforced by horizontal structure. If the you take a forty footer, say, and place a three foot high pilothouse directly on it, the pilot house itself, if long enough, will also have very little stiffness along it's bottom edge. (Unless a whole load of costly and heavy reinforcement engineering is added.) Join the two and you have a vertical to vertical joint with no horizontal stiffness.

Traditionally boats were built with deck beams and structural deck that held the top strakes in place horizontally against the pressure of water when heeled, forming, essentially the third side of a triangle with two sides and a top. (And against the twisting of the mast and rigging) A really strong and stiff structure. Deck houses etc were built over strong reinforcing of the required gaps in the deck.

It is somewhat strange that so many boats are still built with low coach roofs or almost flush decks today when they are aimed at cruisers who want to see the world but then have to sit below where they can see almost nothing when eating. (But that is another hobby horse!)

Looking at the hulls of a catamaran you will see that they have almost flat vertical topsides that would flop around terribly if not stabilised by the attachment of horizontal deck.