# What is a superstructure volume?

Discussion in 'Class Societies' started by ldigas, Dec 13, 2011.

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### ldigasSenior Member

What comprises the superstructure volume of small/middle motoryachts?

Think of a boat, which has a pilothouse/a cabin (wider than B/4). The flooring inside the cabin are below the main deck. There are also bulwark plates on the side along the length.

Is the superstructure volume only the "exposed part" (and from where?), or is it the complete volume of the pilothouse (from flooring to "roof") which in some cases of let's say fore cabins can be quite large, yet not exposed?

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### hoytedowFly on the Wall - Miss ddt yet?

Count all space within the superstructure not to include overhanging roof edge, if any.

Think of a cube. Everything inside the cube would be the volume.

If the superstructure is 3 meters wide by 5 meters long and 2.5 meters high the volume would be 37.5 cubic meters if all sides are rectangular and there are only 6 sides.

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### hoytedowFly on the Wall - Miss ddt yet?

How far below the main deck is the floor of the pilothouse/cabin recessed?

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### ldigasSenior Member

Yes, I know how to determine a volume of an object My question was - what are the boundaries of that object, are they determined exactly or are they left to the interpretation of the designer?

Let's take a more extreme case. For example, GL Rules for yachts <24m, divides "rooms" into cabins and deckhouses, depending on how much their height is above the main deck (cabins being low, deckhouses high).

If a room at bow is high just enough (0.6m) above the main deck, that would mean its volume is calculated and included in the sup. volume. But that room is practically whole inside the hull, and with the bulwarks practically not exposed at all?

See where I'm going with this ?

I'm using the term "room" here just to avoid confusion with cabin/deckhouse.

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### ldigasSenior Member

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### hoytedowFly on the Wall - Miss ddt yet?

I would count the whole volume above main deck as superstructure, and any volume below deck as below-deck, thereby sub-dividing the space.

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### gonzoSenior Member

The definition of superstructure is the part of a ship above the main deck.

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### YobarnacleSenior Member holding true course

I'm confused why the concern over distinction of superstructure volumne. If you are calculating windage, then yes. An open cabin or wheelhouse door or windows can dramatically increase windage, like a sack full of wind or a small rigid spinaker. Best to keep them closed, also keeps the AC inside which helps keep electronics dry.
If it's calculating gross and net tons, certified quarters, machinery spaces, ballast tanks, voids, and operation spaces (bridge, wheelhouse) aren't included. Tonnage is an old rule of determining cargo capacity for taxes and port fees. One ton = 100 cu ft.
So, why do you want to calculate superstructure volumn?

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### ldigasSenior Member

Just trying to put up a definition which cannot be misunderstood in several ways. What is that bad?
Most of the definitions I've seen are vague at best.

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### daiquiriEngineering and Design

I agree with Hoyt and Gonzo - a superstructure is defined as a structure which rises over the main deck. On the other side, the main deck is defined as the uppermost complete deck running full width from stem to stern.

Now the question is: when a floor (meaning the horizontal sole) of the superstructure is recessed below the mean level of the main deck, does that floor (and the vertical walls connecting it to the deck) count as a part of the main deck, or is the deck to be considered without that floor, which means - a continuous structure with an opening?

Not a trivial question, imho... Ad Hoc, Jehardiman, Alik - your opinions?

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### ABoatGuyMember

In attached red is a superstructure, black deck houses. Yes?

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### YobarnacleSenior Member holding true course

by all means, carry on

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