Steel Shrink-Wrap


This is a refinement of conventional welded steel construction. It offers low distortion of the shell plating by minimising the mid-panel welds to the shell. Also it offers the opportunity to use thinner plating and thus save weight and cost. Development of the technique is credited to now retired US boatbuilder Al Sorensen.

Transverse frames are arranged “floating” – not welded to the shell plating. Longitudinal stiffeners are fitted as required to stiffen the shell plating, with minimal welding. Transverse frames are notched for these longitudinals.

This technique could well be applied to plate aluminium construction, with similar benefits. However, plate thickness reduction may not be practicable.

There is a description with several photos on the Glen-L website – see link.

Structural Design

For structural design, it may be necessary to consider the section modulus of the longitudinal as being for the free-standing section only, rather than considering the modulus of the section with a strip of attached shell plate. This is unlikely to be an issue in the smaller vessels.

Crossing Structure

Decks butting up to the shell plating may be an issue. However, these will be longitudinal, and can offer opportunities for masking with fendering, paint lines etc.

Watertight transverse bulkheads may be an issue, but this will be infrequent in the smaller sizes of vessels. There may be scope for building the bulkheads “floating” to the shell, and sealing the joint with mastic after internal surface coating is completed. Whilst not thoroughly watertight, any small leakage would be unlikely to sink the vessel if subject to internal flooding. Gastight integrity should be achieved. It is unlikely that this expedient would be accepted by a regulatory survey authority.

Tank to shell boundaries can be avoided by making the tanks free-standing rather than structural This if often attractive for other reasons, particularly in smaller tanks where internal access is restricted. My personal view is that structural tanks only become worthwhile when a person can climb in through the manhole.


  • Go to Glen-L Steel Shrink-Wrap website page – click here

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