A slipway is a sloped ramp, usually built from concrete, timber, or steel, that allows boats and ships to be launched, and small vessels to be brought ashore for servicing. A slipway can provide a low-cost method to haul ships out of the water for maintenance or to launch newly built ships. If moderate to extensive civil works are required, then pricing becomes less of a factor in technology selection. New-build slipways have fallen out of favor since the ‘70s due to increasing vessel size.

There are three types of slipway: longitudinal slipway; transverse slipway (side launch); and marine railway, a slipway with a triangular structural frame, which provides a flat surface to mount ship blocking onto.

The primary advantage of a slipway compared with traditional drydocks or shiplifts is the cost of construction, operation, and maintenance. However, slipways can still require expensive civil works and construction of coffer dams.

Marine infrastructure is a once-in-a-generation investment. We want potential clients to be as informed as possible before making a technology selection. Our recommendation is to investigate the three options (slipway, drydock, and shiplift) to determine the best solution for your site.

There are some disadvantages common to all three types of slipway:

1. Environmental pollution is common when performing maintenance on a vessel resting on a slipway or marine railway. Because the vessel rests directly above the water or ramp,  any excess lubricants, spilled fuels, paint, or blast media go directly into the water.
2. The hauling mechanisms for slipways (e.g., winch or windlass) do not typically provide any redundancy. If a mechanism fails, the ship is released or stalled on the slipway, putting the ship, personnel, and other vessels in the channel in harm’s way.
3. Slipways tend to require very shallow ramp angles. This can cause them to be subject to flooding in high tides. Sea level rise may render them useless over time.
4. When launching large vessels, a significant bow wave may occur, disrupting vessel traffic or other activities in the vicinity.

The disadvantages of longitudinal slipways are as follows:

1. A longitudinal slipway requires a relatively shallow angle of approach from land to water, necessitating a long “runway” above and below the waterline. This arrangement is not appropriate for launch/retrieval into a narrow channel or where there is a lot of vessel traffic.
2. The hardstand area requires a long path, meaning more land is needed to bring the vessel safely past the high-tide mark.
3. When a vessel is on the skids of a longitudinal slipway, it rests at an angle. This creates both safety hazards for personnel working on the vessel and complexities for any work that needs to be done, much of which may be better suited to a vessel that is on an even level.

The disadvantages of transverse slipways are as follows:

1. When launching a vessel on a transverse slipway, it is entering the water on its beam, putting it at risk of excessive roll. Vessels rolling over or capsizing during this type of launch are common.
2. Because of the hull shape and the angular orientation of the ramp it is being hauled up, the blocking arrangement for transverse slipways can be complex. This usually requires the addition of another structure, such as a cradle, to support the vessel.

The disadvantages of marine railways are as follows:

1. Providing safe working conditions for personnel requires additional depth below the vessel to launch or retrieve it. This means more dredging and/or a longer underwater approach, exacerbating one of the disadvantages also seen with the longitudinal slipway (discussed earlier). Namely, the arrangement is not appropriate for launch/retrieval into a narrow channel or where there is a lot of vessel traffic. 
2. The wheels used in the cradle frame to roll in and out of the water are greased, causing an additional source of water pollution and maintenance expense.
3. Marine railways are difficult to inspect and maintain. 
4. Silt and debris can cause a derailment. 
5. The rails rust quickly and can only be replaced by dewatering or using divers. 
6. The submerged structure is vulnerable to damage from anchors, dredging, and impacts from deep draft vessels.  
7. Long lengths of rope are typically used in lowering the vessel into the water. If a rope breaks, the stored energy from rope stretch is released, which is a major safety issue.