Careful consideration for hand crafted props

19 Jun 2011
Clements propellers are all manufactured through a sand casting method which takes place in two in-house furnaces.

Clements propellers are all manufactured through a sand casting method which takes place in two in-house furnaces.

Clements Marine had a hand in no less than nine propulsion systems of boats on the Seawork pontoon last month, no small achievement for any company.

Andy Childs of Clements told MJ that it is the processes behind the impressive line up (the systems were featured on workboats by Blyth, Alnmeritec, Swiftcat, South Coats, BW Sea Cat, Alicat and Safehaven Marine), that have driven the company forward.

 The entire propulsion package must  work together effectively, so, as managing director Paul Williams explained, ‘Clements likes  to work with not just the customers, but also with the naval architects, engine manufacturers and boat builders, getting together to discuss what is really needed. A recent installation ordered a four blade prop but on talking through the kind of work the boat was going to be involved in, it became clear a five blade system was going to give them a quieter and smoother operation.

‘We try to stop people wasting money too. We have helped customers realise they actually didn’t need to change their propeller at all, and we were able to come up with some suggestions on efficiency to follow up.’

The care put into the manufacturing methods also make the propellers a reliable bet. Mr Childs explained that Clements propellers are all manufactured through a sand casting method which takes place in two in-house furnaces, each of which has the capability to produce a 1.5 ton prop in a single pour. The patterns are CNC machined from aluminium for accuracy, and then after casting the propellers are CNC bored for optimum precision and for accuracy during the finishing process.

It is the hand finishing which really give the blades the edge. First the propellers go through the propeller blade scanning process, to make the accuracy as high as possible (Class I/S). Then, if required, there is a dynamic balancing process during which the unit is fitted onto a mandrel and rollers and the turning action is analysed by a computer which shows up exactly where material needs to be removed from the propeller to achieve the best smoothness and balance.

Then the systems step back from high technology to the age old process of hand finishing. It is hard but accurate work. Propellers are hand machined to minimum Class I or Class S if certification is required.

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