Q&A – Mast Height

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Q: What is the tallest mast your boat can have and still cruise the Intracoastal Waterway?

Q: What is the tallest mast your boat can have and still cruise the Intracoastal Waterway?

Butch Griffin

Kingstown, R.I.

A: I assume you mean the Atlantic Intracoastal Waterway, which runs from Norfolk, Va., to the Florida Keys. There are other passages referred to as the ICW — for example, the New Jersey Intracoastal Waterway. It’s a beautiful area, but generally the depths and bridge heights are such that a larger sailboat wouldn’t take that entire route but instead would pass the Jersey coast on the ocean.

The stated minimum vertical clearance of fixed bridges for the Atlantic ICW is 65 feet, except for the JuliaTuttleBridge in the Miami area, which is 56 feet. (The passage offshore from Port Everglades Inlet at Fort Lauderdale to Government Cut in Miami allows you to avoid that bridge.) But the 65-foot rule just isn’t reliable. In the first place, there are bridges that simply aren’t that high — for example, the WilkersonBridge (Mile 125.9), the two fixed bridges above and below Morehead City, N.C., and the SocasteeBridge (Mile 371) in South Carolina, as observed on their tideboards over many years in many conditions.

We gauge fixed-bridge vertical clearances by these tideboards, which are usually fastened to the fenders of the bridge. They have numbers painted on them that are supposed to indicate the vertical clearance at the current state of tide. You can usually tell by looking at the scum line on them whether the clearance is less than 65 feet, even though the tide isn’t high. On our most recent trip down the ICW, this past fall, we observed that many fixed bridges are missing tideboards altogether, or the boards are in disrepair or the numbers unreadable.

Regardless of whether the bridge was constructed with the required vertical clearance, various factors can reduce clearance. The most common is unusually high tides. These can be caused by storms, prolonged winds from certain directions and/or astronomical tides occurring during the full or new moon phases. In a recent trip down the coast we found one supposedly 65-foot bridge with only 63 feet of vertical clearance. The winds had been blowing onshore for days, pushing the water up into the marshes and creeks and rivers.

Also, there sometimes are items hanging below the bridge span that can reduce vertical clearance, such as electric lines, tarpaulins (from repair or paint jobs), and cables. A boat was dismasted in Florida when its mast caught a trailing cable hanging from the span. And if your mast is passing under the bridge span with only a few inches to spare, a boat passing and throwing a wake can raise you enough to jam the mast into a beam.

Another thing to consider is that these bridges are usually arched. Sometimes the stated heights are for the areas near the sides, with more clearance near the middle. Sometimes they may be for the center. Some tideboards have accompanying signs stating “clearance at center” or “minimum clearance.” There usually is a light hanging down from the bridge on a fixed rod to mark the middle of the navigation span. And some bridges pass over the navigable channel at an incline, so that the highest clearance may be to one side.

The bottom line is that, in my opinion, it’s unwise to take a boat with a vertical clearance requirement close to 65 feet down the ICW. In addition to everything else, you’ve got to compensate for the fact that you’ll have extensions atop the mast, such as a VHF antenna, wind vane, and possibly other equipment. Then it’s important to remember that this is supposed to be fun, without the stress of “Will I make it?” day after day. I’d prefer a mast height of no greater than 62 feet, including extensions — the less the better.

If you’re unsure about your mast height, consider getting a professional rigger to go up and measure. The measurement should be taken from the top of the mast to the water surface, and the rigger should measure the height of any extensions. When this measurement is taken, note whether the boat is normally loaded. Full tanks of fuel and water, gear and provisions for a long cruise can push some boats down considerably. But remember that the converse also is true.

Some use the boom to sling weight, such as the tender, out to the side, heeling the boat and reducing mast height. While it makes sense in theory, this not only is time-consuming and a pain in the you-know-what, it also can be dangerous.

The good news is that if your mast is too tall for comfortable ICW cruising, there are relatively safe inlets along the coast, allowing you to sail outside in the Atlantic in many areas. You will have to research and plan carefully, and you may have to wait a while for good weather (critically important), but you can still make the trip if you have the experience, stamina, skill, boat and gear to go offshore.

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