GRP – Moulded

GRP – Components from Moulds

In this section I have used “GRP” as a generic label for the cold layup fibre reinforced plastics.

This technique  is rarely used for home boatbuilding. However, some boatbuilders support use of their moulds by individual owner-builders. Also, redundant moulds can be picked up on an opportunity basis.

A variant on this is for the home boatbuilder to purchase a set of mouldings from the builder/laminator for home completion. A typical exercise of this option is to purchase a hull and deck joined together, with supplementary mouldings either loose or joined as appropriate.

For construction the mould is gelcoated, the laminate built up, internal framing cores added, and then the internal laminate is built up over the framing cores. This follows commercial yard procedure. Internal bulkheads, decks and fit-out follow; normally after removal of the hull from the mould.

The laminate may be built as a single skin, or inter and outer skins around a core.

It is quite practicable to alter mouldings prior to fit-out. This is quite commonly applied by professional builders, particularly for larger vessels, and can be applied quite readily by home boatbuilders.  Mouldings can be cut, spread, and the gap filled in with laminate, commonly with temporary bridging mould, and hand finishing.

The character of a boat can be changed substantially during the fit-out of a GRP hull. See MINIM COVE following.

A Case Study – 16 ft Training Boats

16 ft SEA FOAM 1st Pelican Point Sea Scouts with sister boat

I (Peter Edmonds) was project leader for a batch of 16 ft 6 oar pulling/sailing boats built for the Sea Scouts in 1979. We took a deteriorated clinker hull from a successful existing design, stiffened and smoothed the outside, laid up a mould around this plug, then laid hulls in the new mould. We then fitted out each hull with centreboard case, buoyancy and ballast spaces, thwarts, timber gunwale structure, etc. The plug was discarded. The new GRP boats were substantially lighter than existing timber boats of the class. Handling was improved with some internal water ballast.

16 ft Mould

When I undertook this project I was only a few years into employment in the GRP boatbuilding industry. We arranged a professional laminator to gelcoat the plug as the first stage of building the mould. The rest of the project was carried out with volunteer labour from within the Sea Scout group, with little more than handyman experience.



MINIM COVE is an example of a boat built with a change of concept. The hull is from a displacement motor launch, configured to a gaff rig small dayboat/weekender, with elegant timberwork.



Viking 30 HARALD III is an example of a home completion from a set of hull, deck and minor mouldings. The project took several years.


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