Small Solutions... Big Results (No. 1)
THE FIRST IN A SERIES OF RETROSPECTIVES THAT LOOK BACK AT THREE DECADES OF FINDING VALUE-ENGINEERED SOLUTIONS...
Preface: This article begins a series that looks back at various value-engineered solutions to problems encountered by the author in the course of several decades of boat and yacht building and shipyard management.
Several years ago, I contracted to plan and supervise the ship-fitting of a 45-metre high-performance littoral patrol vessel from the keel to the main weather deck. The work included the first-ever installation of two Hamilton HT1000 waterjet drives in a fiber-reinforced plastic composite hull.
Engineering isn't always simply about the design of a product but just as often about the planning and execution of the building of that product...Phil Friedman in The Portable Boatyard
The drive units, which were capable of absorbing more than 5,000 horsepower each, were massive ― about 13 tons each. Even the cast aluminum water intake grates weighed more than half a ton each. And both the drive units and their water intake grates had to be bedded and bolted to the vessel's composite hull with hundreds of 19mm and 25mm diameter stainless steel cap screws (bolts).
All the drive train components would be highly stressed under loads, hence installation needed to be flawless. In metal hulls, fit-up is fairly straightforward and final attachment is completed by welding the components to the hull structure. But mating metal drive train components to a molded composite hull becomes much trickier ― partly because elastomeric bedding/bonding compounds have to be employed to fully seal the joints, and such compounds have limited working lives once applied.
Another complicating factor is that a molded vessel hull has an outer surface that is smooth and locally uniform, where it has been controlled by the machined inner surface of a female mold (tool).
In contrast, the inner surface is generally undulating and somewhat rough and uneven due to the nature of building up a fiber-reinforced composite structure a layer at a time.This relatively uneven inner surface works against being able to seat properly the load-spreading backup washers in a through-bolt assembly.
Moreover, the sheer number of bolts involved called for very accurate pre-boring of the bolt holes, if there was to be any chance of getting them all to line up fully at final assembly, whilst maintaining minimum clearances in the bolt holes themselves. (Zero wiggle room for lining up at final assembly.) Sounds like a job for a numerically-controlled robot borer, costing perhaps a million or so dollars... right?
Sometimes the biggest results can be achieved with the smallest of solutions...Phil Friedman in The Portable Boatyard
Instead of looking for a high tech solution, we opted for designing, building, and employing some purpose-specific low-tech tools.
1. We decided to use the castings that needed to be bolted to the hull as self-templates for boring the hundreds of holes required.
2. We designed and built some fully-articulating electro-hydraulic fixtures that would enable us to lift, maneuver, and hold the heavy units in place against the hull while we bored the holes.
Then came the most elegant and inexpensive solution I think I've ever developed for assuring relative boring precision in such circumstances.
3. We had some Delrin bushings machined to fit inside the holes factory-bored into the cast flanges being bolted to the hull. These bushings acted as guides to center and normalize the axis of a 6mm pilot drill bit.
4. We began on each flange by drilling, from the outside inward, four evenly-spaced pilot holes, using the flange as a self-template.
5. We then moved to the inside of the hull and, using a spot-surfacing tool, specifically designed and built for the job, we ground a perfectly centered and very flat round landing area for the wide heavy duty "fender" style washers that would act as backing for the bolted-on assembly.
We built this tool using a standard hole saw and mandrel whose integral pilot bit had been replaced by a smooth 6mm rod. The hole saw itself was stuffed with marine grade plywood filler blocks, cut using the hole saw and built up until the stack stood proud of the saw teeth. This packing stack was then covered with a 16-grit flexible sanding disc. (Cost less than $200 to build a half dozen of these.)
By inserting the pilot rod of the tool in the pilot hole from the inside outward, we were able to grind a perfectly centered and normalized landing flat into the inside of the composite hull skin and, thereby, achieve full contact with the load bearing backing washers.
6. Once the initial locating holes had been bored, we then proceeded to bore and prepare the rest of the bolting holes and insert, on a trial basis, all of the bolts. We then removed all of the bolts except for the four "locator" bolts, which we back off enough to allow the mating surfaces of the hull skin and the casting's flange to be "buttered" with a high-strength elastomeric bedding/bonding compound. After which a half dozen pairs of hands tightened the locator bolts and reinserted and tightened the hundreds of additional bolts (threads bathed in the same bedding/bonding compound) into their respective pre-bored holes ― all completed well within the working time for the bedding/bonding compound.
Every bolt hole lined up perfectly with its mate in the matching casting and every backing washer sat fully flush with maximized contact area on the inside of the hull skin. Later, extensive testing failed to disclose a single leak, proof that, with proper planning and preparation, big results can be achieved well within scheduling and budgetary constraints, provided only that you choose the right small solution. ― Phil Friedman
Author's Notes: This is the first of a series of articles that I believe may be of interest to engineers and tradesman who deal regularly with construction- and manufacturing-related problems and issues. One of my objectives in producing the series is to illustrate how thinking in terms of value-engineering ― seeking to balance cost against first-rate execution ― pays off time and time again.
If you found this article worthwhile, you might want to follow my blog here on beBee, so that you will be notified via email when subsequent installments appear.
You might also be interested in one or more of my eBooks:
The Portable Boatyard (scheduled to be published late Fall, 2017)
For information on securing a copy of one or more of these, email firstname.lastname@example.org and put "eBook" on the subject line.
Are you starting up or currently operating a small business and facing a problem or issue on which you could use some help? Consider our offer below:
About me, Phil Friedman: With 30 some years background in small business and the marine industry, I've worn numerous hats — as a yacht designer, boat builder, marine operations and business manager, marine industry consultant, marine marketing and communications specialist, yachting magazine writer and editor, yacht surveyor, and marine industry educator. I am also trained and experienced in interest-based negotiation and mediation. In a previous life, I taught logic and philosophy at university.
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