Hull and Fabrication works 2017

Published: Tuesday, 28 November 2017
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Hull and Fabrication works

This year I am taking advantage of the winter layover to get a number of jobs done on the boat, some are new some long overdue. The plan is to have all the work complete before we go to Crick at the end of May allowing us to enjoy the summer cruising.

Zinc Spraying

I chose Debdale wharf as a winter mooring this year as I had booked in to have the boat hull grit blasted, zinc coated and epoxy blacked in November see here. The idea being to prolong the life of the hull and minimise maintence needed over the next 10 years. The boat was built in 1994 so is now 23 years old and most Insurance companys will require a full hull survey at 25 years. By having the work done now and a full hull survey performed this should satisfy the insurance company when the time comes.

Before the hull work was started it made sense to carry out any fabrication or changes so that they were all zinc plated and epoxy painted at the same time. So I had a few bits of work done.....

Replace brass skin fittings with welded

Along the side if the boat are a series of fittings that connect to the various drains and vents. These all consisted of a hole cut in the hull and a brass fitting screwed in with mastic to seal it. The brass fittings are softer than the steel hull and can get snagged and damaged, or in some cases cut through completely. One fitting for the battery gas vent has been cut though twice in the last 2 years.

The brass skin fittings would also be a weak point in the zinc treatment and epoxy blacking. So before the boat was grit blasted all of the brass fittings were removed and welded stainless steel screwed fittings installed. Unfortunately this meant emptying lockers to get access to the inside so the boat was in a bit of a mess.  Once complete the appropriate hose tail are screwed into the inside of the fitting and the drain or vent reattached.

Most of the fittings are located behind cupboards so to get at them the contents of the cupboards had to be emptied and in one case a new access panel cut.

Rear deck drains

This is one of the long overdue items that was originally reccomended by the surveyor when I bought the boat in 1999. On the rear deck there is a lift up hatch to access the rear of the engine bay and the weed hatch. Around the edge of this hatch is a gutter to collect any water from the back deck and this gutter drained through two steel tubes connected to the bottom of the counter. This meant that the bottom part of tubes is permanently submerged but inaccessible so cannot be painted or blacked. This design was common in the 90's but led to a number of sinkings when the tubes rusted through. The solution is to cut off the pipes, weld up the hole at the bottom and drain the gutter through skin fittings that exit above about the water line.

Weed Hatch extension

The Hybrid engine and battery are much heavier than the BMC engine they replaced and this means the boat sits lower in the water than it used too. While the other work was happening I got an extension welded on to the weed hatch to increase the freeboard.

New Deck drains

Weed Hatch extension and new deck drains

Cooling skin Tank

Hybrid marine have updated the hybrid system and now use a water cooled motir rather than the air cooled lynch motor used on Chelonian today. However this would require fitting an additional skin tank for cooling.

The skin tank acts like an underwater radiator on the side of the hull just in front of the propellor. The existing port side skin tank was sized for the original BMC engine and has always been slightly undersized for the Beta43 engine. Normally this is only an issue on rivers or tidal passages where the engine revs and temerature needs to be carefully monitored to avoid overheating.

So rather than fitting another small skin tank for the electric motor a full size tank has been fitted on the starboard side for the Beta engine which should mean that the boat us much better suited for river and tidal work.

The existing smaller port side tank will be reused for the electric motor cooling.

Skin Tank

New Skin tank

Aquadrive

When the hybrid system was fitted there was a manual dog clutch fitted in the prop shaft. The idea was to allow the hybrid to used as a stationary generator by disconnecting the propellor. While this idea worked it was very little used in  practice and the mechanical complexity of the clutch system was never justified. The clutch was removed some years ago but this left a collection of adaptors in the drive train which is less than ideal. 

With the removal of the clutch there is plenty if room to fit any of the available prop shaft flexible joints to replace the R&D coupling that was originally selected for its compact size. So an Aquadrive coupling has been fitted.

Unlike the R&D coupling the Aquadrive also provides a thrust bearing to transfer the push from the propellor to the hull rather than this being transfered through the gearbox and engine mounts as previously. This should make the transmission quieter and reduce wear on the gearbox and engine mounts helping to extend the life of both.

Aquadrive

Aquadrive Coupling

Summary

All of the fabrication work (except for two skin fittings that will be replaced in January) plus the hull treatment was done in November and the boat is back in the water.

Other work already completed includes servicing the spare eberspacher boiler and swapping the boilers over so that the one that was in service can be serviced in its turn.

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