Small Cruise Ship, Shallow-Water Ops

Most Boat Trader readers, whether they run on rivers and lakes or along coasts, can probably relate to boats that are purpose-built for their areas of operation. So it is with Grande Mariner, the Blount Small Ship Adventure vessel I’ve been aboard as chief mate this winter. A few weeks ago I wrote about safety operations aboard Grande Mariner. This time I thought I’d tell you about the ship’s shallow-water capabilities. As the brochure says. “Go where the big ships cannot”. That means shallows — rivers, the Intracoastal Waterway, the Bahamas, and even Belize.

In a keel-cooler system, coolant circulates through a closed loop. part of which is exposed to cool seawater outside the hull. Keel coolers eliminate the need for a raw-water cooling circuit, which can suck up mud and sand in shallow-water operations. Diagram courtesy of Fernstrum.

In a keel-cooler system, coolant circulates through a closed loop. part of which is exposed to cool seawater outside the hull. Keel coolers eliminate the need for a raw-water cooling circuit, which can suck up mud and sand in shallow-water operations. Diagram courtesy of Fernstrum.

So what are the design features we’re talking about? Well, all powerboats need engine cooling. In this case, a keel coolers keep two 3412 Caterpillar diesels purring. No raw-water intake sucking up silt for these Cats. Then there’s a reinforced bow, built to ice-cutter specs, along with a bow ramp for driving right up to the beach and hopping off. And there’s a pilothouse that hydraulically lowers to get under bridges. And the draft of this 180-foot boat of 450 deadweight tons? Seven feet. Even the running gear (props, shafts, and rudders) needs special protection.

None of these things is unique by itself, but when you combine all these features with how you have to operate in shallow water, you get a better picture. For instance, we have the capacity to carry about 6,000 gallons of fuel and 6,000 gallons of potable water. We also have holding tanks for treated sewage, fire sprinklers, and gray water. Throw in 90 or so passengers, a crew of 18, and all the comforts of home, and you have a lot going on in a small package.

Grande Mariner draws only seven feet, and can nose into a lot of places where larger vessels can't venture.

Grande Mariner draws only seven feet, and can nose into a lot of places where larger vessels can’t venture.

The sanitation system treats the sewage to something we are told is drinkable (no thanks) but by international law can only be pumped at least three miles offshore. So you have all these tanks carrying all this weight, and you have to plan carefully how much to have on board at any time in order be at the right draft. We have reverse-osmosis watermakers on board, but we have to be careful where and when we operate them. Probably not a good idea to pump the holding tanks at the same time you’re making water. And the intakes for the watermakers are up forward by the anchors. Anchoring happens almost everyday, but we don’t want to pull up the anchor and a cloud of mud for the watermakers to ingest, so every time we handle the anchor or even cross a shallow entrance bar, we temporarily shut down the watermakers. Same goes for the raw-water pumps used for our air-conditioning systems–if we’re kicking up a cloud of dust we cut these off too.

The final consideration when running in shallow water is how fast can you go. Many times we’ve had less than two feet under us, and it’s not unusual to “polish the bottom” on occasion, as we did crossing the Rio Dulce entrance bar. You need to apply power to do this, this but too much power and the boat can “squat” towards the bottom and make matters worse.

So, lessons from a big boat that can be applied to smaller ones: Running in very shallow water takes careful consideration of tankage and overall displacement, what equipment is running and when, tide levels and currents, and how fast to go. Don’t forget a pair of polarized sunglasses to see the shallows better, and a well-calibrated depthsounder.

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