A change of pace and circumstance
Well it seems I have not posted since November and the arrival of Befur’s trailer. Since then a lot has happened (so Happy Xmas, and Happy New Year)… I have had the fortune to be made redundant, and have (with Louise’s kind support) agreed to turn that into retirement – so from the end of February there will be no more working interruptions, and as I am only “on call” now, progress should be faster. So with the shingles finally subsiding, and hopefully the last of the winter colds and the left shoulder starting to free up, there can be no more excuses – so 2015 looks bright indeed 🙂
The weather has become too cold to continue with the planking (the epoxy gets too stiff) so “retiring” to the machine shop has been the order of the day. This has allowed a number of loose ends to be addressed:
A rev counter: one of the SBA Auctions provided the opportunity to acquire a nice old tachometer with the right kind of speed ranges, and a day’s tinkering, straightening and cleaning have provided a nice tacho for the engine – need to think about drive mechanisms….
Keel Bolts: The hull design calls for a number of keel bolts to be used to attached the stem to hog and hog to the transom.
Metal Supermarket Man tells me that 316 Stainless is the only steel that can be tolerated if there is salt water in the mix, and while we hope there will be no water at all in the keel, it seemed imprudent to choose any other material. The bad news is that 316 is by no means the “free cutting” stainless (308?) so it played havoc with the tooling on the lathe, blunting/breaking the indexable parting tools just parting of the bolts and nuts – so I needed to invest in new parting blades in P35C grade material to cut the tough/hard stainless. (These had to come from Germany!)
Based on this experience I also decided it was time to invest in indexable threading gear, and JB Tools provided tool bars and inserts to do the job – I must confess these made the screwcutting a complete pleasure – images below of manufacture and fitting:
Air and Feed Pumps
So having returned to the machine shop it is time to turn our attention back to Befur’s engine. The remaining components are the ancillaries (feed and air pumps, lubrication system and draincocks).
The word from existing owners of the Leak compound and experts like John King from the SBA is that the engine is capable of running at up to 550rpm, and needs to be run at this speed to extract it’s rated performance, BUT at this speed the cross-head driven boiler feed and air pumps are far from happy. So we need to provide a mechanism to drive them at about 1/3 of engine speed. Also as we need electricity to power the oil-fired burners we have chosen (and for navigation lights, radio etc.) we need an alternator on board; this needs to be driven at perhaps 6-8 times engine speed to operate properly.
So I am planning to build an assembly fitted to the crank ahead of the engine which will incorporate a 2-stage gear-up for the alternator and a worm gearbox reducer for the pumps. A picture of the GA of the assembly from PunchCAD is shown below…
The blue bit is the (commercial) worm gearbox, the yellow the crankshaft from the engine and the grey the alternator. I am agonising about chain v cam-belt drive for the first stage, and will use poly-v belting to the alternator.
The pumps are not shown in this drawing, but will be driven by a pair of scotch-cranks either side of the gearbox.
As part of this process I needed to compute the ram sizes needed for the pump to provide the required feed via this new approach – this transpired to be a horrible set of mixed unit computations as the feed is measured in lbs/hr, the pump capacity in cc’s and the bore in inches (no metric stuff on my mid-40’s Harrison). It took most of the afternoon to create and check a spreadsheet, with Lou cross checking my maths which eventually proved that the original pumps provided about 110% of required capacity, and new pumps with half-inch bores and slightly longer strokes would provide about 101% on the new gearbox – OK I think. Also the torque requirements seem like they are about 50% of the limit for the gearbox (another ebay purchase) – so all should be OK. (Here’s a copy of the spreadsheet (openOffice version shared on google-drive ).
So we are now re-boring and finishing the feed pumps and re-finishing the air-pump (as there are a few surfaces and dimensions “on the bonk!” as an old friend of mine would say….
So this involved using the old 3/8 bores as a reference to rebore the gland counterbores, and reface the mounting surfaces, so that we could bring the axes of all three pumps into line and parallel so that the cross head could be made and the three pumps made to operate “freely”…. A long slow process involving a little shiming at the end to get everything right.
….so sorry for the delay … better progress and reporting from here on!