Hull Moulds

Recently, I was to make a mould for someone who is making a small bait boat. These moulds (two of them) are for the hulls, which need to be identical. Mt attempts at drawing this out “accurately” in SketchUp didn’t go as well as I’d hoped and I soon gave up on trying that… Having bought some 3in thick softwood and prepared the timber to finished size, I figured that the only way I’d be able to visualise the shape of the stern properly would be to start cutting some wood!

Although the 2.4m length I bought was kiln-dried; like most Scandinavian redwood I have worked with; it felt sticky to the touch and was clearly full of resin and/or sap. Therefore, I gave the wood several days indoors to let it dry out a bit, first – these moulds need to be accurate to within 1mm of each other. Any distortion of the timber would affect the final shape of each hull after vacuum-forming. Or, worst case scenario; the boat doesn’t run in a straight line!

Marking out the first curve.
...And the outline of the bows.

This is where I was pleased to have a 16in bandsaw – the 12in SIP I had before was certainly up to cutting 120mm though, with a sharp 6tpi blade, it still felt like the proverbial ‘hot knife through butter‘ on the Startrite!

Shaping the bows with the table tilted.

I’m not afraid to admit that my bandsawing is far from perfect; I don’t have the confidence to cut within 1mm of a finished line. I had hoped I’d be able to use my 12in. disc sander (Hegner HSM 300) to clean up the cuts – all that did was make a right mess of my sanding discs. I’ve thrown one away and it was a tough job having to clean the replacement! A horizontal belt-sanding machine would’ve been ideal… If only I had access to one! My next best thing was a portable belt sander (Makita 9404) which worked surprisingly well and, with a bit of care, I was able to produce an almost identical pair of hulls.

Using the 100mm belt sander...
...Because this sopping pine clogged my sanding disc in a matter of seconds!!

Several arrises still needed to be rounded over with a 10mm radius (leaving the top edges square). I was only able to use my router for the longer edges and had to shape the end-grain at the bow the good old-fashioned way (…cheap sandpaper with an application of elbow grease!). As my workbench was overcrowded with several half-finished wall cabinets sat on top (!), Bench Cookies came to the rescue and allowed me to do the routing on my mitre saw station!

Bench Cookies to the rescue!!

I think they’ve turned out alright. Having sent the photos across Europe (!!!), I can also say that my ‘client’ is also satisfied with the results. He did have some further cutting for me to do at the other end as well but, as he’s just bought a new bandsaw himself [boys and their toys!!], he’s happy to cut it to final length and make those relatively straight-forward cuts himself (to allow for the motor tubes).

Before rounding off...
...And after - the completed bows!

I hope you’ve found this informative and realise the importance of cutting these bows at an angle – I’ll admit, I got it wrong the first time but, that’s  why, when I’m doing shaped work like this, I try to leave the components over-length for as long as possible. 😉

Thanks for reading.

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