Keel is a bottom-most structural member of ship. It acts like a base on which ship is constructed.
It’s the quintessential part of ship. And ship construction starts with this structural member only. It is also called as back-bone (spine) of ship. This structural member bisects the hull into two sections length-wise. It is also protected by keel-guard.
These are placed longitudinally at the base of ship.
Generally, it refers to the centre line.
It distributes local stresses equally in both sides and also provides longitudinal strength.
The width of the keel = 70B (B = Breadth of the ship)
But there is limit also, 750 mm < keel width < 1800 mm
Thickness of keel should be 2 mm greater than adjacent bottom plating.
Types of Keel
- Bar keel
- Flat keel
- Duct keel
This is the first type of keel which is used since first iron built ship. But it doesn’t provide sufficient strength for big vessels.
A bar is placed in the centre of the keel called bar keel.
The either side of the hull attached to the bar keel is called Garboard strake.
Depth of bar is generally 3 to 6 times of its width.
These types of keels are incorporated in ferries or boats that are vulnerable to grounding.
It’s a modern type of keel and used in all types of sea going vessels.
Flat keel would basically mean a single bottom.
The centre girder is attached to the keel and inner bottom plating by continuous welds and there is no scallops in this connection.
It’s a form of flat keel which has two centre girder instead of one.
This is also termed as Box keel because it allows pipes and other services throughout the keel length.
This is fitted from the forward of the engine room bulkhead to the aft of the collision bulkhead.
It facilitates pipe passing through the cargo holds and thus isolating piping from cargo contact.