Thursday, May 28, 2015

Air Draft

  You may know that we are members of the Americas Great Loop Cruisers' Association. The AGLCA has a members forum on their website that we can use to find out information about "Doing the Loop", or just to discover other tidbits concerning the boating public. Some of the items that members publish makes you wonder how they ever become equipped to leave the dock.
  One recent question a member posted had to do with how he could best measure his "air draft". For anyone who doesn't know, this would be described as the measurement from the waterline to the topmost part of a vessel, or "how much does my boat stick out of the water?"
  The responses were many...and varied; from using string wound around a stick, poles made with tubes filled with water (to ascertain it being level), to using a laser scope. On and on.
  Give this a thought when you consider joining others in a "buddy boat" situation; If a fella can't figure out how to measure how much his boat sticks out of the water, do you really want to be tethered to someone like that on a Gulf of Mexico, or Gulf Stream crossing?
  Wanting to know the height of ones boat is necessary, however, for the very important reason that many bodies of water have bridges on them that don't raise or move. The "Loop" has some low bridges along the route that may determine whether or not you can even make the trip in the boat you have, or at least may dictate which route you take. But this post isn't about informing you how to go about making that Loop trip. That would require research, and I don't do research. It may be about dumb questions, but since I ask the occasional dumb question, I don't want to shoot myself in my own foot.
  Even though our immediate plans don't include leaving Florida waters anytime soon, we still need to know what our air draft is. There's lots of bridges around here.
  We don't drive around saying, "Hey, there's a bridge over there, let's see if we can fit under that!" But for instance, if we want to go over to the Bayside, we need to get under the Seven Mile Bridge, and we can go under at the closest point to us, which is "low", or we can travel nearly three or four miles to the high point passage and not worry about it. We have always gone out to the high point.
  Why go out an hour out of our way when the "low point" is somewhere around 21 feet and are "air draft" is a few feet lower? The answer to that is because there are no markings on the piers at the low points showing the distance between the water and the bridge structure, and we have tides, waves, and strong currents to consider. Plus, we don't ever have to get over to the Bayside in a hurry.
  If we ever have a need to get under a bridge, we would lower our VHF antennas and our wind generators and stern light, maybe even the radar dome. This would get us under any bridge on "The Loop", but not under some of the bridges along A1A. For some of them, the dinghy air draft may be too much.
  One question that was brought up on the AGLCA members forum did prompt a response from me. One guy asked if the extra buoyancy of salt water was significant enough to make a difference in the air draft of his boat. I think it's a good question, I even anticipated having some extra freeboard once we got to salt water, in order to compensate for all the extra crap we had onboard, but it was not to be.
  In fact, before we left St. Louis, we raised our waterline on the boat by an inch. We were floating that much lower in the water after bringing all our "stuff" onto the boat. Chugging along the inland rivers, our waterline for the most part only changed when we ran light on fuel or water. The depth of the water due to floods, etc. is more of a concern.
   With a full load of fuel and water, Swing Set has water lapping right at the edge of the swim platform. When we got to the ocean, this did not change.
  I'm not saying that salt water does not make a boat more buoyant, it does, but it's not enough to make a difference when one is considering whether or not they can take their boat under a low bridge. I wouldn't even let it be part of the equation.
  Swing Set is 17 feet, 6 inches from the waterline to the tip of the wind generator blades. That measurement was made with a  full load of fuel and water. She sits about 4 inches higher in the water with a light load. Does this mean I'd run under a bridge as low as 18 feet without worrying about it? No, it doesn't. I pay attention at anything under 21 feet, and then I still pay attention.
  Do you see where any of my approach to a fixed bridge takes in the consideration of a few inches here or there in relation to fuel and water load, or added salt water buoyancy, or whether I measured the air draft with the boat tipped to one side or the other? Maybe if the boat is squatted down at speed we would have more room to get under a bridge. If nothing else, if you hit something going fast, anything that falls off has a better chance of landing in the water and not back onto the boat.
  The message I have here is: Go slow, give yourself lots of wiggle room, and don't take chances.
  Anyone who knows me also knows I don't take the helm with a slide rule in my pocket and a heat sensor gun on my hip. Hardly. Leave that for the engineer types. But you can measure and calculate only so much down to the nth degree and there is still an unknown out there sometimes. (At this point, I don't even know if I'm making sense.)

  Speaking of air draft, it would appear that we added some to the dinghy with our new bimini top, but not really. The new top is about even with the stern light. Even so, the top easily folds down, and the top part of the stern light comes off. We can get under some pretty low bridges around here which definitely saves us some time getting around in the dinghy.
  We ordered the top from and it was shipped free. I upgraded the material, but still the bows are aluminum. I don't mind the aluminum bows because weight is an issue when we hang the dinghy on our davits.
  The top, and the material to make a new dinghy seat came to just under $300. The little green umbrella that we had been using to give Holly shade on our trips to the beach would blow around in the wind and make her skittish, and our supply of $4 umbrellas was running low. They do tend to rust.
  How many $4 umbrellas can we buy for $300, you may ask? The answer is seventy-five, but then we'd have to get permission from Holly to share her umbrella when we want to get out of the sun too, skittish or not.

  We thought that the marina would be clearing out after the holiday weekend, but it seems like for every boat that leaves to head north, a new one takes its place. The air temperatures are heating up and we are running the A/C full time now, taking advantage of the fact that our electric is included in our rent.
  As we watch some boats depart, I do get a twinge of regret that we are staying put, but as long as it's just a "twinge", it's outweighed by our sense of luxury and contentment here. We have friends coming down for the Superboat races here over the 4th of July and we're looking forward to that. Now that traffic has settled down on A1A, we'll make more trips to Key West on the scooter and maybe take Swing Set to A & B marina for a few weekends this summer. We'll make do.

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