Fitting a Yanmar and Aquadrive

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Stern tube details :

A GRP or similar composite stern tube is recommended (unless an alternative is already installed) as it is so easy to bond into place. I used a carbon-fibre/epoxy composite, which sounds very technical, but is in fact part of the mast of a windsurfer. Testing an offcut it seems to be incredibly strong. My tube (shown below) is 640 mm long, 38mm dia at the lefthand end (inboard) and 44mm dia at the ouboard end. The red tape marks the position where it enters the hull and the forward end of the skeg. Ready-made GRP stern tubes can be bought from suppliers such as Lancing Marine or ASAP Supplies.

stern tube

The tube needs a cutlass bearing at the outboard end - either a standard bought component or one can be turned up from a suitable material such as Vesconite - a material which doesn't swell in water like most plastics do, and which happily copes with aggresive environments. My last boat had a Vesconite cutlass bearing, which showed no measurable wear after 6 years of use. The bearing can be an interference fit in the tube, and you might want to fit a stainless grub screw just in case.

At the inboard end a stern gland has to be fitted to keep the water out. There are several different types.I initially planned to use the traditional type which is bonded to the stern tube. Epoxy resin is excellent at bonding the metal stern gland housing to the composite tube, provided it is thoroughly degreased with acetone or SP Systems solvent. It helps to apply a coat of epoxy resin to the mating surface and abrade it with coarse glasspaper while the resin is wet - this ensures the epoxy has absolutely clean, unoxidised metal to adhere to. After discussing with a number of people I decided to use a stern gland with a rubber hose connector - the short length of tough reinforced hose allows the gland to float around the end of the stern tube. This would be the best solution for engine installations that don't use an Aquadrive, as the greater freedom of movement of the prop shaft will result in less stress on the whole drive train. This is the type shown here (though in reality it would be fitted with a screw-cup greaser - see the photos of the real thing on the following pages):

stern gland

www.corribee.org - inboard engines