Yacht Aditi

Getting our bearings

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The hydraulic headsail furling started to open up at sea one day and, after opening the cap on the furling unit and starting to diagnose the problem, a couple of steel bearings dropped overboard and some of the nylon bearings were seen to have been crushed.

Now carrying vital spare bearings, some of which need fitting immediately, as the headsail furling grease had dried out at some stage allowing some balls to drop over the side when the bearing was first loosened. The bearings are a 50/50 mix of 6mm 316 steel ball bearings with a crush rating of 2,040kg and delrin 6mm balls (much lower crush rate but the OEM’s are not heavier rated torlon).

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To the right is the open headsail furling cap sited above the hydraulic gear system in which the roller balls are visible. You can see that without waterproof grease retaining the balls when the bearing opens (due to a loose locknut in this case) the ball bearings simply fall out of their track with a bounce on deck and a plip-plop into the sea below the bow.

 

 

Spare Ribs?

Found one! Fortunately we found a spare rib on which to attach the SSB mounting frame. The mix of aluminium and teak mounting points with their varied expansion/contraction in rates in differing temperatures are a concern but the choices were few:

DSC00330.JPGThere is plenty of space and cool air around the SSB unit which can operate at 125 deg centigrade

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1,700 Newts

Validating the fixing needs of the main SSB did not reveal much. Allowing for the 13.5kg unit a free fall drop of 5 metres resulting in a sudden dead stop (no distance allowed for deceleration) requires an overall fittings strength of 1.7 kilonewtons. The issue is then finding the shear capacity of A4 bolts in kN/mm2.

Stainless steel may have a tensile strength of 500 n/mm2 and an M6 bolt should have , leaving aside 1mm for thread, a total load area of 19mm and therefore tensile strength of 9.5kN. Not the same as shear but the load value indicates a level of comfort spread across 4 bolts.

The weekend? A complete bender!

With wiring unwrapped from all that it seeks to cling to, pull down, get snagged on the interfacing of Wotsit A to Wotsit B, C and D may, fingers crossed, be finished. The last job then is to fit the 14 kilo Icom ‘briefcase’ somehwere cool, near the chart table, near the power source and away from anything else that dislikes heat. Add to that the momentum that this will gain under movement and it turns into a structural engineering problem. The process of elimination begins – can’t drill here, not under the freezer, too low in the bilge, too big a cable run to the antenna, GPS, modem, control unit – eventually it all ends up back at the place we first thought of – the lucky void of dark matter invitingly unoccupied. But could it house water maker parts? Too bad this looks like SSB territory.

What shoe size, style, material and colour? Choices. Much juggling, clamping, drawing and measuring follows. Finally it is decided that the slipper sole will be made of aluminium in a style similar to the hull, joined to a marine ply upper in which the SSB unit can sit and toast away in peace surrounded by a cool clean vertical air flow.

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Bring on the weekend bender! The 5/8″ inch aluminium flat bar is bent to shape to sit on the bulkhead, hull rib structure and to avoid existing power units. Imagination, measure, bend, measure, trial fit, bend, cut, bend, fit, remove for additional drilling and machining.