The BoatTECH FilesBy Don Casey and Our BoatUS Tech Editors
Published: August/September 2012
Insight has arrived! Next time you need to do a project or repair aboard your boat, chances are one of our experts already has written an authoritative guide to help you through it.
BoatTECH, BoatUS's vast archive of technical stories, constitutes one of the most invaluable and popular pages on our website. Written by the top technical writers in the country – most are among our own trusted tech team of BoatUS experts – BoatTECH is filled with in-depth advice for members on how to do everything on your boat from plumbing to polish. This month, we're unveiling our all-new presentation of the site. We've made it easier to use, and enriched it with more useful photos and advice than ever before. Here's just a sampling.
Gelcoat Scratch Repair
Surface scratches can be buffed out of gelcoat with polishing compound, but deep scratches must be filled. When the gelcoat surrounding a scratch is in good condition, the filler of choice is gelcoat paste, which provides both filler and finish in a single application – but not in a single step. The surface of the cured paste will be uneven, so sanding and polishing are required to smooth the repair and blend it with the rest of the hull. Except for color matching, gelcoat repairs are easy and straightforward.
Never try to repair a scratch by simply painting over it with gelcoat. Gelcoat resin is too thin to fill a scratch and gelcoat paste too thick. Instead of penetrating scratches, gelcoat paste will bridge them, leaving a void in the repair. To get a permanent repair, draw the corner of a scraper or screwdriver down the scratch to open it into a wide V.
Work the gelcoat paste into the scratch with a flexible plastic spreader. Let the putty bulge a little behind the spreader; polyester resin shrinks slightly as it cures, and you'll sand the patch, anyway. Don't let it bulge too much or you'll make extra work for yourself. Gelcoat Scratch Repair on BoatUS.com/BoatTech
Scope is often defined as the ratio of the length of deployed anchor rode to the depth of the water. That is so wrong! Scope calculations must be based on the vertical distance, not from the sea bottom to the surface of the water, but from the sea bottom to the bow chock or roller where the anchor rode comes aboard. For example, if you let out 30 feet of anchor rode in 6 feet of water, you may think you have the appropriate 5:1 scope, but if your bow roller is 4 feet above the waterline, your scope is actually only 3:1. Scope is required to make the pull on the anchor horizontal; the more upward pull on the anchor, the more likely it is to break out. Minimum scope for secure anchoring is about 5:1, and 7:1 is better. A length of chain between the line and the anchor (at least 20 feet) helps keep the pull horizontal. Anchors Aweigh on BoatUS.com/BoatTech
Think "gasket" when you bed hardware. The mistake most of us make is squeezing the sealant out of the joint by over-tightening. While the sealant is wet, snug the fasteners down just enough to form a continuous bead of sealant around the perimeter of the fitting. Crank down on them only after the sealant has cured for 24 hours (one hour for silicone). Turn the nuts only so you don't break the seal on the bolts. Tightening fasteners after the sealant cures puts it under compression, greatly extending the life of the seal. Bedding Hardware on BoatUS.com/BoatTech
Rolling And Tipping
The key to getting a flawless paint finish is the thinner. Too little thinner and the surface shows brush strokes; too much and the paint sags or runs. Start with the paint manufacturer's recommendation, then test the mix on a glass panel — window glass, not fiberglass. Using a foam roller, roll some paint onto the test panel, then tip it out by lightly dragging a dry badger-hair brush horizontally through it. Give the surface a couple of minutes to level out. Because you have painted glass, all flaws are in the paint. If you see brush strokes — the usual result — add a capful of thinner and test again. Stop adding thinner when the stroke marks disappear. Adding paint, because you have to mix it, is more troublesome than adding thinner, so try not to go too far — evidenced by sagging or running. Rolling And Tipping on BoatUS.com/BoatTech
How Important Is Changing Engine Oil?
Not only does the grit in dirty oil wear precision surfaces, the acids the contaminated oil invariably contains dissolve internal engine parts while the boat sits idle. Frequent oil changes ward off breakdowns and extend the life of your engines by thousands of hours. Engine manuals typically specify changing the oil every 100, 125, or 150 hours, but no less than once a year. If your boating is seasonal, once a year isn't often enough. Change the oil when you commission your boat in the spring, and when you winterize it in the fall. You'll never get a better return on a $40 investment than from changing your oil twice a year, or every 100 hours.
Running the engine is always a prerequisite to an oil change. You want the oil warm enough to flow freely, and you want the contaminants in the oil, not lying in the bottom of the pan. Drain the oil cold and a lot of the contamination stays behind. Because a quality oil filter should be good for 200 to 300 hours of running time, engine manufacturers sometimes specify a filter change with every other oil change. But filters harbor a significant amount of oil. Not changing the filter is like pouring this morning's coffee over an inch of yesterday's coffee remaining in the cup. When you change the oil, change the filter. How Important Is Changing Engine Oil? on BoatUS.com/BoatTech
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