General Ship Layout

This page is an entry in Shonas Wreck Guide. Any errors or omissions should be sent to the author for inclusion.

INTRODUCTION

This page is intended to broaden the knowledge of would-be wreck divers, giving them an insight into how the wrecks that they dive, once operated as ships.

This page will contain details such as ships machinery layout, boiler designs, engine designs, major identifying features of a vessel etc.


Machinery Layout

This should no surprise to any experienced wreck diver, but most beginners still don't know their arse from their elbow (sorry, I mean stern from stem!)

Typical machinery layout of a Tramp Steamer
Typical machinery layout of a Tramp Steamer.

As can be seen in the diagram above, the main engines are usually situated amidships, with the boiler room immediately forward of the engine room. The engine is connected to the thrust bearing, which transmits power to the propellers along the propeller shaft(s). As the propellor turns, it tries to push the prop-shaft forwards. The thrust bearing effectively transmits this force from the propellor to the bottom of the ship. The thrust blocks are used to spread this force evenly along the thrust bearing.

As the propeller shaft runs through the rear hold, it has to be protected from the cargo, and as such runs through the prop-shaft tunnel which leads from the engine room to the point where the prop-shaft goes through the hull.

The boilers are fueled with coal from the bunkers, either side of the boiler room, and the resulting smoke from the furnaces is vented up through the ship stack(s).

The 'spent' steam from the engines is drawn into the condensors which use sea-water pumped through condensor tubes to cool the steam, turning it back into water before returning to the boilers. This cooling water is pumped from the sea, through the condensors and back to the sea by the circulating pump.

The ships pumps, anchor winches and cargo winches would be steam driven, and run from either the main boilers or an auxilliary boiler (Donkey Boiler). The Donkey boiler could be used in situations where the main boilers and engines were not operational (i.e. when in port loading cargo etc). The Donkey boiler is sometimes seen on the deck, but is more usually seen in the boiler room as a 'small' boiler.


Boilers

Most of the wrecks that we dive as a club are casualties from WW1 and as such are usually fitted with coal fired Scotch boilers, producing steam to drive either a transverse, compound or triple-expansion steam engine. As these boilers are fairly solid, they can usually be identified in the wreckage, giving clues to the general orientation of a wreck etc.

Side view of Scotch Boiler
Side view of Scotch Boiler.

SCOTCH MARINE BOILER - Side View

1 - Water Sides
2 - Furnace Door
3 - Grate Bars or Fire Bars
4 - Combustion Chamber
5 - Fire-Tubes
6 - Smoke-Box
7 - Safety Valve
8 - Main Steam Stop Valve

Front view of Scotch Boiler
Front view of Scotch Boiler.

SCOTCH MARINE BOILER - Front View

1 - Gauge Glass or Water Column
2 - Main Steam, Safety, Auxilary Steam Valves
3 - Pressure Gauge
4 - Surface Blow
5 - Skin Valve (through ship's side)
6 - Bottom Blow
7 - Hydrokineter (to increase water circulation)
8 - Furnaces
9 - Fire-Tube bundles
10 - Main Feed Valve
11 - Auxiliary Feed Valve
12 - Deep Blue sea

The number of boilers in a vessel may range from 1 to dozens depending on the size of the vessel. The wrecks we dive are of the size where two boilers is usually sufficient to power the engine. Each boiler can be single-ended or double-ended (stoke holes at one end or both) which will give an indication of the orientation of the vessel. Generally, for small vessels with a single engine, the stoke-holes will be facing the engine, allowing the engineer to also act as the fireman.

Fresh water is fed into the boiler where it is heated and converted to steam. The live steam is fed to the engine (it may be superheated by passing it back over the furnace again) directly to the high pressure cylinder. This is the smallest cylinder on the engine, and is usually at the front (Triple-expansion engine layout). The steam is exhausted from the HP cylinder into the MP cylinder and in turn to the LP cylinder (cylinder diameters increasing from HP to LP). Once the exhaust valve opens on the LP cylinder, the steam is sucked into the condensors due to the vacuum effect of the condensing steam. The steam condenses to fall as water to the bottom of the condensor, where is can be fed back into the boilers.


Engines

Most of the wrecks that we dive as a club are casualties from WW1 and as such are usually fitted with coal fired Scotch boilers, producing steam to drive either a transverse, compound or triple-expansion steam engine. As these engines are fairly solid, they can usually be identified in the wreckage, giving clues to the general orientation of a wreck etc.

Triple-expansion engine details
Triple-expansion engine details.

Glossary of Steam Engine Components

1 - Thrust Bearing
2 - Crosshead Guide
3 - Valve Link (Stephenson Link)
4 - Crosshead
5 - Eccentric
6 - Crank Throw
7 - Throttle Valve
8 - Connecting Rod
9 - Low-Pressure Cylinder (LP)
10 - Intermediate-Pressure Cylinder (IP)
11 - High-Pressure Cylinder (HP)
12 - Thrust Blocks

Triple-expansion engine animation
Triple-expansion engine animation.

Key

Red - High pressure Steam from Boilers to HP Cylinder
Yellow - Med pressure steam from HP cylinder to MP cylinder
Green - Low pressure steam from MP cylinder ot LP cylinder
Blue - Spent steam from LP cylinder to condensors (-ve pressure)
Brown - Crankshaft connected to thrust bearing and flyweel