8 March 2019

How to build a Dinghy in Cold Moulded Ply.

From the lines of this classic dinghy I have modified myself a rowing and pottering boat for general purpose use capable of being powered by a small outboard (The best outboard for the world and known as the Seagull Plus).
A 1/8th scale half mould was made and sectioned off so that I could make the eight full scale moulds that need to be mounted on a mobile horse in the confined garage space available.
As of the 8th of February I am at the stage of mounting the moulds onto the horse/jig. In order to ensure all is correctly alligned I shall be using spirit level, set square, sight lines and making many adjustments until I am satisfied that the dinghy will be fair in shape from all angles.
14th March and the mould is being built up. The stem, hog, keel and transom are joined together and in place.
17th March and the slats are being added to the mould.
Once the entire mould is covered and faired smooth and rounded, the surface will be sheathed in 1.5mm marine ply laid diagonally in strips two inches wide. Each strip will be stapled in place temporarily and the second and third layers added (glued in place) withdrawing the staples  in the immediate underlayer as the work progresses.
28th March and almost ready to begin laying the ply. Took delivery of ply but the wrong thickness, so the idea of  using 1.5mm changed to using 3mm ply in three layers instead of the intended four layers of 1.5mm ... Fortunately my supplier had a special offer and resultant cost is substantially less.
5th April and I am laying on the 2" wide strips of ply. Because the edges don't lay parallel (due to the compound curvature hull shape) a gap is left to be later filled by a second tranch of alternate strips. Each of these will need to be spiled to fit using a marking gauge.  

11th April and one side covered with the first of three layers of ply. So 1/6th of the way along a road which is probably going to take a month before the hull may be released from the mould.

Half model at 1/8th scale

Scaled up paper patterns from which the full-size moulds are taken

The moulds mounted on a mobile horse/jig

Level and trued up

Ribbands follow the mould shape

Viewed from inside

Transom keel and stem glued together with cascamite resin. The pine slats are to be planed fair to remove as many high spots as possible

Mould (plug) ready for the ply strips but require polythene film interlayer to prevent layup sticking to the slats

The first layer of 2" 3mm ply strips  laid with a gap between - just the bow remains with three to go.

The mobile jig is supported on six castor wheels

Shaping up slowly - Hopefully I shall speed up once the routine is mastered

The 14mm staples just about hold the ply down, but go deep into the layer beneath and can break on removal. I may well find that lifting off from the plug will be tricky. The solution may require remove of the plug in sections from below.  I will try using shorter staples later today.

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