Moulding GRP Components
for a Self Build Boat

We've reached the stage in this self build boat project in which we move away from building in western red cedar strip and marine ply. Now the composite element of Alacazam's construction begins; time to reach for the chopped strand mat and polyester resin.

Why? Well for the remaining components required to make the hull structure complete - primarily the cabin top, sliding hatch and garage, and cockpit - we've decided to construct them in GRP (Glass Reinforced Plastic), or fibreglass as it's often called.

This is quite a complex process, as for each one we need to make a mould. And for those that require a female mould - like the cabin top for example - we'll need to make a plug, from which we make a mould, from which we mould the cabin top. See, I told you it was complex.

Hers's how we set about it...

The GRP Cabin Top Moulding

The cabin top is located over the galley and navigation area and will provide all-round vision from below.

initial stage of making plug for cabin top mould for sailboatThe initial stage of making a plug for Alacazam's cabin top

And as the forward edge and the sides of the cabin top will sit on the coachroof we used the coachroof as the base for the cabin top plug before it came out of the workshop.

That way the GRP cabin top would fit perfectly. Wouldn't it?

Making the Plug

Chipboard was the main building material for the plug, as you can see in the above image.

stage 2 in making the plug for a sailboat cabin top mouldThe plug for the cabin top mould progresses...
completed plug for sailboat cabin top mouldDone!

The rounded edges of the plug were formed with expanding polyurethane foam as used in the building industry, and sanded to shape.

The entire plug was then filled and faired, and finally given a coat of black mould release agent.

Making the Mould

With the cabin top plug complete, the cabin top mould was then laid-up in chopped strand mat and polyester resin, to form the GRP mould as somewhat proudly exhibited here.

a completed mould for a grp cabin top for a sailboatThe designer poses with the completed mould...

Foam core material was incorporated in the lay-up to provide sufficient stiffness for the mould to keep its shape.

The Cabin Top Emerges

Finally, the cabin top was laid-up in the female mould and later emerged as the finished moulding.

grp cabin top moulding fitted on wood epoxy sailboatThe GRP cabin top moulding fitted on Alacazam's coachroof

As expected it fitted Alacazam perfectly, where it was screwed and epoxied to the coach roof.

With the smooth gelcoat on the outside of the finished moulding, the less attractive inside would later be covered with mural mousse headlining material.

laying up a GRP sliding hatch coverMary lays-up Alacazam's sliding hatch cover. Where did she get those pants?
laying up grp frames for sailboat portlightsMore of Mary's handiwork - the GRP frames for the portlights

In the meantime, Mary was laying-up the fiberglass sliding hatch and garage, and the non-opening portlights for the hull sides aft. These would later be glazed with panes cut from clear polycarbonate sheet, and provide light in the heads, bosun's locker and aft cabin.

completed grp cabin top fitted to sailboat hullLooking good!

Cutting out the holes in the cabin top for the custom-designed windows was another one of those tasks filled with anxiety.

But with the hatch and the windows fitted (manufactured to order by Seaglaze Marine Windows), I think we could be rightly proud of the final result...

The Cockpit Moulding

In a self build boat as in any other sailboat, whether intended for cruising or racing, good cockpit design is fundamental to the overall success of the boat; particularly the slope of the seatbacks, the width of the seats and the distance across the cockpit well.

temporary mould for grp cockpit moulding for sailboatThe mould for Alacazam's GRP cockpit
completed cockpit moulding for sailboatThe completed cockpit moulding

These were all taken account of in Alacazam's cockpit, the mould for which was fabricated in melamine-faced chipboard.

grp cockpit moulding being fitted to sailboatInstalling the GRP cockpit moulding
grp cockpit fitted into wood-epoxy cedar strip sailboat hullHey, we've got a cockpit!

It all looked a little precarious until properly built in. You'll notice an absence of cockpit lockers. I'm not a fan of these, owing to an incident one night sailing single-handed around Cape Trafalgar in my Nicholson 32, Jalingo 2.

Briefly, I was head down in the cockpit locker looking for some warps to tow astern (it was blowing a bit) when we were pooped. About half a ton of water filled the cockpit, much of which ended up in the cockpit locker which did little help my state of anxiety. It won't happen with Alacazam.

And finally...

The last GRP moulding we had to do was the top opening fridge which was later installed in the galley with 4" (100mm) insulation all round.

bespoke grp open top fridge for sailboatThe bespoke GRP top-opening fridge takes shape

Well, actually it wasn't quite the last fibreglass component we had to deal with in this self build boat project. There was the lead-filled GRP encased bulb keel to be built, and this wasn't going to be easy...

Next: Our Self Build Boat Project, Moulding the GRP Bulb Fin Keel

Recent Articles

  1. Hallberg Rassy 42e for Sale

    May 23, 24 03:01 AM

    'Asterie', my Hallberg Rassy 42e is for sale, currently in Greece, but she'll be in Barcelona in a month or so's time...

    Read More

  2. Westerly Oceanranger Specs & Data

    May 20, 24 03:34 AM

    Interested in the Westerly Oceanranger sailboat? Here are the pics, specs and performance predictions you're looking for...

    Read More

  3. Westerly Oceanranger 38 for sale

    May 19, 24 04:09 AM

    'Petrel Blue', an Westerly Oceanranger 38 is currently for sale in Grenada, West Indies...

    Read More