Wednesday, December 4, 2013

Whale-watch cruise

We are anchored in Winyah Bay, just off the entrance channel west of North Island and not far from Georgetown Light (map).  The actual community of Georgetown, South Carolina, where we stayed on our way north up the ICW, is another ten miles further up the bay.

We had a nice run today from Southport, although in quartering seas of 3' or so, which made for a lot of motion.  Both cats registered their unhappiness by losing their breakfast -- no surprise for motion-sensitive Angel, but these seas even got to George, albeit much later in the morning.

The boat handled it just fine, and the humans were mostly OK too.  Due to the very early start and faced with the prospect of ten plus hours of little to do on the open water, we opted to shower underway, which posed a small but surmountable challenge.

Actually, the majority of blue water boats have small seats or ledges built into the showers, for exactly this circumstance, and we do have such a seat ledge in the guest shower, but, oddly, the builder chose not to put one in the master shower.  Knowing this would become a liability, Louise had shopped around some time ago for an adjustable teak shower stool that at least looked somewhat nautical.

We can adjust the legs of the stool so that it sits half on the shower floor and half on the ledge a few inches above it (the ledge that, we've mused, could simply have been made two feet taller to solve this problem from the get-go).  When it is not being used it lives on the flybridge, where, in its lowest position, it serves as a footrest for the helm chairs.  It's actually intended as an "assistive device" and we've gotten some ribbing from friends about how quickly we are getting old.

The early start also meant leaving the marina in the dark and making our way out into the river before first light, just a few minutes behind the first ferry of the day at 6am.  By the time we passed the Southport waterfront we were actually able to see the water and we had no trouble making our way out the inlet past Bald Head Island.  We passed the ferry, which runs much faster than we do, on its return trip.

I ran most of my pre-departure checklist last night, right after loading the scooter on deck when we came back from a tasty but too-large dinner at Frying Pan Restaurant downtown.  The restaurant, named after the infamous shoal off Cape Fear, is fairly new and had not come up in my search -- I found it on a quick scouting run when I went out for auto parts.  I'm glad I did, as it had a great view, a really nice Christmas tree, and decent food.  They will close for the season in a couple of weeks, after the local holiday flotilla.

Another first for us on today's run, in addition to making use of the shower stool, was having to add fuel to the day tank under way.  I had topped the tank up last night, which means 75 gallons or so.  That would have been enough for today's 75-mile run under many conditions, but we had to wick it up this morning.

On a crossing like this it is impossible to time every factor to be optimal.  We chose today because of reasonably good ocean weather, and we lucked out in having a mostly slack tide at Winyah Bay.  But that meant leaving the Cape Fear River with nearly three knots of current against us.  Our normal cruise RPM of 1800 had us doing just four knots, and we could not afford to burn another half hour of daylight just getting out of the river, so I cranked it up to 2150.

I ended up turning 2000 for most of the next hour, too, and we had sucked down 20 gallons of fuel in the first couple of hours.  Once we were on the long southwesterly leg I was able to drop back to 1900 rpm, which is still burning more than we'd like, but that gave us an arrival estimate near 5pm, and we did not want to chance arriving at the anchorage after sunset.  I put an extra 20 gallons or so in the day tank mid-morning, so we would not risk running low on fuel just as we were trying to negotiate the inlet.

Sometime mid-morning and again mid-day, we spotted several dolphins and a pod of whales.  Both the dolphins and whales came over to check us out, but dolphins lose interest in Vector quickly because we don't move fast enough for our bow wave to be any fun for them.  We spotted another group of dolphins here in the anchorage right at sunset.

After the showers, whale-watching, and getting dinner started, we were wont for things to do.  There is too much motion to tackle boat projects, and cellular data coverage quits a few miles offshore.  We each had a nap, did some route planning, regular engine room and deck checks, and the like, and I typed most of this blog post into a text file this afternoon.  Mostly, we just chatted.

Tomorrow the weather looks good for the next leg, to Charleston, so long as we do not get fogged in in the morning.  It's a shorter day, just 57 nautical miles (around eight hours), so we won't have to leave in the dark.  Our marina reservation in Charleston does not start until the 8th, so we will be anchoring for a few nights first.


  1. You need to put a turbo on that engine or something, 57 miles in 8 hours? You had it up to 2150 RPM, what is the top RPM of this engine?


    1. We do have a turbocharger, and, actually, at 370 horsepower, this engine is oversized for the boat by a wide margin.

      2150 RPM is 80%, which I consider "full speed". The top rated rpm of the engine is 2600, which I consider "flank speed" and only to be used in an emergency.

      Not that the extra RPM will help much, and certainly not at all under normal circumstances. Remember, this is a full displacement boat, as are most long-range (transoceanic) boats. That means that no matter how much HP you have, the boat can never plane (ride above, or partially above, rather than through the water).

      Displacement vessels are speed-limited by their waterline length, not by engine horsepower. There is a complex formula that requires hull-form analysis, but the rule of thumb is that the "hull speed" in knots is limited to about 1.33 times the square roof of the waterline length.

      This is the reason that longer ships can go faster than shorter ones -- every US aircraft carrier can outrun all of the support vessels in its attack group. For Vector, it means we are limited to about 9.3 knots top speed, no matter how many HP we throw at it.

      Honestly, we try to run the boat around 1600 rpm, which is the sweet spot for us -- the balance between speed and fuel economy. At 1600 rpm we burn 4 gph and do 7 knots, or about 1.75 NMPG. If I crank it up to 2000 rpm, we'll burn twice the fuel, 8 gph, but only get another 1.3 knots, for 0.88 NMPG.

      Yesterday the conditions were such that I had to keep it at 1700 most of the day to make it here in the daylight. That's still a lot better than the 1800 we had to turn two days ago to make Winyah bay in the daylight.

      The next time we do this run we will probably go overnight straight between Charleston and Southport, which cuts perhaps a dozen nautical miles off the total, takes one potentially precarious inlet out of the equation, and lets us run the boat at the much more economical cruise speed of 1500 rpm, where we get nearly two miles to the gallon. That would cut the total fuel used between the two points to about a third.

      We're just getting our feet wet, so to speak, with the whole ocean passage and inlet-running technique, though, and we felt it was too early to add nighttime running into the mix. So we opted for the shorter hops and higher fuel use to keep it all in the daylight.

    2. "Square root", not "roof". Sheesh. No way to edit comments, unfortunately.

    3. Thanks for the reply, that was very interesting. I had no idea displacement vessels are speed-limited by their waterline length, not by engine horsepower.


    4. No problem, and I'm glad you brought it up because I would guess many other readers were also wondering.


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