Saturday, December 29, 2007

Mistakes and Fixes

To a person, my gangway slip mates have been kind and supportive this week as I removed the new outboard, and the new Garelick bracket and explained how I had installed it wrong.

I discovered that a week ago, after the old Albin inboard was hoisted out of Narrow Escape, and after I remembered to fill up the nearly empty water tank in the bow. The combination of less weight under the cockpit and maybe 150 pounds added in the bow raised the outboard higher in the water. So high that during what was supposed to be another engine break-in voyage, the slightest wake caused the prop to cavitate and the engine to over-speed.

During the first installation I followed the instructions of both Tohatsu and Garelick to position the engine so that the anti-cavitation plate was two inches below the water line. I taped a marked stick to the transom and I filled two large plastic tubs placed on the lazarette with water to simulate the weight of the outboard. Then I made the measurements from the dock. I also assumed, correctly, that the Albin, which was still in the boat at that time, weighed less than I did, and was in about the same fore-and-aft position I would assume when steering with the tiller.

What I didn't think to do was fill the bow tank. And I was surprised at the dramatic effect those extra 15 or 20 gallons of water made when I later did.

In that condition, the graceful transom of Narrow Escape was 14 inches above the waterline, typical of 1960s-era designs.

The Garelick hydraulic bracket has no adjustment. Four pre-drilled holes are provided to bolt it to a transom. And at the other end, the large polypropolene engine mounting board was fixed in position. In fact, in a perverse quirk of design, a series of partial-depth holes were moulded into the back of the board, apparently to lighten it, in such a way that it was impossible to drill alternate mounting holes that would allow the board to be repositioned on the hydraulic frame.

I was able to drop the bracket 2 3/4 inches on the transom, to the point that the bottom of the bracket was flush with the bottom of the transom, after I trimmed the bottom sides of the structural aluminum L-brackets to match the curvature of the transom.

I gained an additional 1 1/2 inches by building my own mounting board out of 1 3/4-inch (8/4 thickness) Honduras mohagany. That process led to the discovery that one side of the Garelick frame was an eighth inch taller than the other. Since the Tohatsu mounting clamp screws had to clear that frame, I made my measurements based on the higher side.

The transom is a half-inch of solid fiberglass and I filled the old holes with Marine-Tex white epoxy, so I'm sure that I didn't lose any strength by having to redo the job. Nor will I have any problem with water intrusion in the transom.

When finished, the anti-cavitation plate was 2 1/2 inches below the water with no one on the boat. Underway at hull speed with me standing at the transom to observe, the outboard was another four inches or so deeper in the water. It's as deep as it can be without moving the outboard bracket so the it extends below the transom, which might cause some drag in some sailing conditions. With crew aboard, it will be even deeper.

On the other hand, with no one aboard at the slip and the engine raised to the top of the 14-inch range of the hydraulic bracket, the tip of the outboard's skeg is a half-inch above the water without having to tilt the engine.

A three-hour voyage under power yesterday, outside the breakwater and across as many boat wakes as I could find, proved the effectiveness of the new mount position. As a bonus, setting the engine about four inches lower on the transom reduced the noise level in the cockpit.

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