Funny thing about sailboat masts and bridges: no matter how much clearance you actually have, when you’re standing in the cockpit looking up it always looks like you’re not going to make it. Of course, the people who think to put bridges in our way do try to provide information on how much space is under them, even at various states of the tide. But still every so often the situation is ambiguous, and you’re not sure your mast will fit. Lots of people just hold their breath and take their chances in these situations, like these folk in this video here.
If you watch closely, you’ll see they get some sensors scraped off their masthead. Which, obviously, is not the worst-case scenario.
But there is another way… as I learned some years ago while crewing for tech guru Nigel Calder on a delivery from Maine to Annapolis. We were hoping we could fit his Pacific Seacraft 40 Nada under the bridge over the Cape May canal (to save having to go all the way around outside to get into Delaware Bay), but weren’t at all sure we had clearance. Nigel knew immediately what to do, and in a heartbeat we hauled his buddy Mike to the masthead in a bosun’s chair so we could get a better perspective on things.
As you can see here, it was close, but we fit through, and Mike got to exchange pleasantries with some puzzled pedestrians.
It goes without saying that when doing this you need to approach the bridge in question carefully so that you don’t accidentally behead your crew.
As for those bridges that you can’t fit under, they do have their uses. For example, follow this link here for some hot tips on how to step your mast from a bridge.
As an engineer for naval surface combatants, I regularly bump into the maximum mast height requirement which is usually set based on the lowest bridge that a particular Navy wants to sail their ships under w/o dealing with any kind of mast stepping. As Charlie pointed out, the height above water of any bridge (or other overhead obstacle) is usually listed on the charts. The part of the equation that Charlie doesn’t address is how low in the water your vessel is, i.e. the waterline. When I deal with new construction Naval shipbuiling, the design waterline is very well known and we don’t really have to think about any other possibilities. I recently worked on a mid-life refit program and the waterline of a 20 year old surface combatant is a much more elusive value. The other factor that came into play (and actually helped our casue) was that the obstruction this Navy wanted us to design to was in fresh water, not the seawater the ship normally operated in.