Sea Trial!!

Today, 4/29, Potentate left the dock under her own power for the first time with her new engines.  In addition to the Captain (me) and the Chief Engineer (Ray) we had along First Mate Erin and her brother Mark and brother-in-law Mike as crew.  The object of our first cruise was to test the maximum rpm we could turn on the engines under load, as well as burn some paint off the exhaust manifolds.



We are moored at the north end of Lake Union, between the lake and Portage Bay – right between the University and I-5 Ship Canal Bridges.  Our route to Lake Washington takes us through the Montlake Cut past the University of Washington and on into Lake Washington.  In this area we’re restricted to a speed of 7 knots.  The engines are idling a bit fast, so our minimum speed on the way out was just under 6 knots.

I made a spreadsheet to record a few things in increments of 100 rpm, up through what the maximum rated rpm for the engines is, which is 2600.  In addition to our regular gauges, we also have EGT (Exhaust Gas Temperature) and Turbo Boost (the pressure at which the turbocharger forces air into the engine) gauges.  After we cleared the Montlake Cut I began increasing the rpm by increments of 100 until we were going the 7 knots allowed.  Passing Webster Point, we headed north towards Sand Point, away from shore as we were planning to hopefully throw some wake.  At each increment in rpm, I stayed at that speed for 2 or 3  minutes, until it would reach its speed and other readings at that pace.  I used the GPS for recording our speed.

Mark checks the view at our typical 8 to 9 knot cruising speed

As we got up to 8 and 9 knots, our usual cruising speed, it became apparent that we weren’t getting as much boost from the port turbocharger as we were from starboard.  As we increased our speed further to get into the higher ranges of the engines’ horsepower requirements, the difference in boost pressure became more pronounced, with port giving only half of starboard’s boost pressure.  After reaching 2200 rpm with both engines, the port engine was unwilling to go any higher, although the starboard engine would go to at least 2450 or so, as I briefly opened its throttle.  I backed off at that point and we cruised back towards our slip in the 1700/1800 rpm range.

While it’s possible there could be other reasons for the difference in performance, we’re doubly suspicious of the port turbocharger because it’s a replacement that was sent up to us after we had a problem with the first one’s exhaust port, which wouldn’t seat properly to the exhaust elbow, causing a significant exhaust leak.  So this one, although it sure doesn’t leak any exhaust, was not on the engine when it was tested on the dynamometer before being shipped to us.  We’ll be investigating that further.  I don’t think the slight variations in exhaust temperature are significant, but the boost sure is.

All in all, our first sea trial was a success.  We discovered a possible problem with one of our turbochargers, and we definitely burned and scorched some paint in places.  Here you can see some smoke rising from the port exhaust elbow.  The smoke is actually from the lithium grease that coats the gasket between the two flanges, but you can definitely see some discolored paint as well.  The elbow is water cooled from the point where it widens back to the blue exhaust hose.  The smaller black hose is supplying raw sea water, which mixes with the exhaust gases in this elbow before heading on through the hoses and pipes that take it to the stern of the boat.  The insulation is over the exhaust riser, where the temperature inside reached as high as 825 degrees.  The two flanges you can see reached a temperature of 500 degrees as measured by our remote infrared thermometer, so I’ll be ordering another strip of insulation jacket to cover this.  We don’t want to be scorching or setting fire to the underside of our hatches.

The exhaust ports from the engine where they enter the exhaust manifold are also burned to a nice tan.  The exhaust manifold itself is water cooled and maintained its healthy Cummins white color.  There’s still a lot to do, but this was definitely a highlight to experience some fruition of our labors to date!