ship at the greatest width at the section chosen. The breadth extreme is measured to the outside of plating but will also take account of any overhangs or flare.

The ship depth (Figure 3.2) varies along the length but is usually quoted for amidships. As with breadth it is common to quote a moulded depth, which is from the underside of the deck plating at the ship's side to the top of the inner keel plate. Unless otherwise specified, the depth is to the uppermost continuous deck. Where a rounded gunwhale is fitted the convention used is indicated in Figure 3.2.

Sheer (Figure 3.1) is a measure of how much a deck rises towards the stem and stern. It is defined as the height of the deck at side above the deck at side amidships.

Camber or round of beam is defined as the rise of the deck in going from the side to the centre as shown in Figure 3.3. For ease of construction camber may be applied only to weather decks, and straight line camber often replaces the older parabolic curve.

Figure 3.3 Section measurements

The bottom of a ship, in the midships region, is usually flat but not necessarily horizontal. If the line of bottom is extended out to intersect the moulded breadth line (Figure 3.3) the height of this intersection above the keel is called the rise of floor or deadrise. Many ships have a flat keel and the extent to which this extends athwartships is termed the flat of keel or flat of bottom.

In some ships the sides are not vertical at amidships. If the upper deck beam is less than that at the waterline it is said to have tumble home, the value being half the difference in beams. If the upper deck has a greater beam the ship is said to have flare. All ships have flare at a distance from amidships.


The draught of the ship at any point along its length is the distance from the keel to the waterline. If a moulded draught is quoted it is measured from the inside of the keel plating. For navigation purposes it is important to know the maximum draught. This will be taken to the bottom of any projection below keel such as a bulbous bow or sonar dome. If a waterline is not quoted the design waterline is usually intended. To aid the captain draught marks are placed near the bow and stern and remote reading devices for draught are often provided. The difference between the draughts forward and aft is referred to as the trim. Trim is said to be by the bow or by the stern depending upon whether the draught is greater forward or aft. Often draughts are quoted for the two perpendiculars. Being a flexible structure a ship will usually be slightly curved fore and aft. This curvature will vary with the loading. The ship is said to hog or sag when the curvature is concave down or up respectively. The amount of hog or sag is the difference between the actual draught amidships and the mean of the draughts at the fore and after perpendiculars.

Air draught is the vertical distance from the summer waterline to the highest point in the ship, usually the top of a mast. This dimension is important for ships that need to go under bridges in navigating rivers or entering port. In some cases the topmost section of the mast can be struck to enable the ship to pass.

Freeboard is the difference between the depth at side and the draught, that is it is the height of the deck above the waterline. The freeboard is usually greater at the bow and stern than at amidships. This helps create a drier ship in waves. Freeboard is important in determining stability at large angles.

How To Have A Perfect Boating Experience

How To Have A Perfect Boating Experience

Lets start by identifying what exactly certain boats are. Sometimes the terminology can get lost on beginners, so well look at some of the most common boats and what theyre called. These boats are exactly what the name implies. They are meant to be used for fishing. Most fishing boats are powered by outboard motors, and many also have a trolling motor mounted on the bow. Bass boats can be made of aluminium or fibreglass.

Get My Free Ebook

Post a comment