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Trim and fit: automated engine trim: set it and forget it?

Ever wonder what kind of fuel savings you might get from running your engine trimmed where it should be? Surely you've noticed that your boat, once on plane, runs more efficiently as you trim up the engine some. Watch your speed increase at the same throttle setting. Feel the bow rise and notice there's less spray washing aft. Trim up just to the point where the prop begins to blow out (you'll hear it) or the bow starts bouncing, or "porpoising." Now trim back down a tiny bit, till you're humming along smoothly.

Based on some research by Mercury Marine, optimal use of trim may result in 15 to 54 percent fuel savings. If you're running 20 miles offshore for dolphin or bolting across Lake Okeechobee for the bass bite, those numbers are significant. Mercury derived its figures while testing the company's new Active Trim system, which is a kind of autopilot option for engine trim. Testers ran a broad range of boats under a worst-case scenario--engine fully trimmed down in manual mode--versus automatically adjusted by Active Trim.

Basically, Active Trim controls trim according to boat speed (computed by an internal GPS) and engine RPM, the way a skilled captain should. As your engine revs up, the system trims the engine down, tucking in the running gear to provide some lift at the stern, helping you get on plane quickly. Once you're running, the system automatically trims the engine up to an optimal, safe position. This lifts the bow and releases the hull to ride on the surface of the water. On the Active Trim control unit, five selectable "trim profiles" are programmed to accommodate a variety of boats, from small runabouts to high-speed offshore rigs. The profiles also offer an owner some customization based on different loading conditions on his boat.

Over the summer, I tested the system on a 27-foot Shearwater bay boat with Mercury's recently released 350 Verado. Active Trim worked as I had been told it would--it trimmed up the running gear to maximize speed at a given RPM. It also knew to trim down when getting on plane. And yet, presumably because of the profile setting, which the Merc technician had set at 2, the boat didn't show any signs of excessive trim, like porpoising. Active Trim permits instantaneous manual override--simply hit the trim switch and you're in control. Curious about fuel savings, I ran the Shearwater for a while with the engine trimmed down and compared the MPG with what we saw under auto mode. Frankly, I didn't notice a big difference--somewhere in the tenths of a mile between 3.1 and 3.2 MPG at 4,200 RPM (perhaps testimony to the brute power of the supercharged 350 and the efficient running surface of the Shearwater). Nils Ackerbloom, Vice President of Shearwater, said Active Trim might contribute more to fuel savings--in boats of this class anyway--during the moments it takes to get on plane.

So I didn't have a real specific fix on our fuel bill, but overall I was duly impressed with the performance of Active Trim. On a crowded waterway, slowing down for wakes demands quite a bit of fiddling with the trim switch. An owner who likes to keep things simple might appreciate having one less thing to fiddle with.

One thing I think is of particular interest to owners of low-deadrise (shallow vee) bayboats, skiffs and bassboats: Active Trim senses when you're making a turn, automatically trimming the engine down some to minimize prop blowout.

Also worth pointing out: The system won't automatically trim the engine down if, while at rest, you've trimmed up past a certain point. For instance, if someone unwittingly cranks the engine while the lower unit is tilted out of the water, Active Trim isn't coming to the rescue. This is actually a fail-safe built to protect you from another potential trouble spot: If you've drifted into shallow water, you might want that engine tilted up to putt back safely into the channel--and you surely don't want it automatically dropping your skeg and prop onto the rocks.

Yamaha has Trim Assist, an auto trim counterpart in its Helm-Master control suite, which uses a different method of computing trim position. The Yamaha version is available for twin and triple engine installations in its high-horsepower four-stroke lineup. Mercury is angling for a wider audience, making Active Trim compatible with any new Merc outboard or stern-drive MerCruiser with SmartCraft.

Will trim automation be a game-changer? For hardcore fishermen who run their boats often, probably not.

But, for casual owners looking to simplify the boating experience and perhaps save a little at the end of the day, this is promising technology.

JEFF WEAKLEY, Editor
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Title Annotation:FS SEMINAR: BOATING
Author:Weakley, Jeff
Publication:Florida Sportsman
Date:Oct 1, 2015
Words:785
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