Thursday, February 24, 2011

How Low Can You Go?

What is your air draft?   Really?  How do you know? 

Bryant Vann’s website shows that the designed clearance on a Manatee is 22’-6”.  Based on what I have read there elsewhere and on calculations I’ve made, I’ve assumed that Morning Star’s vertical clearance is closer to 23’…”about” being the operative word. Of course, everybody knows that when you’ve seen one Krogen, - well, let’s just say that they are all a little different.   But our personal limit has been to open any bridge lower than 24’ to allow for discrepancies in bridge measurements as well as a generous “fudge-factor” in my calculations. 

Several weeks ago I set out to prove the height of the mast and to consider ways to lower our air draft.  Since I own a laser transit, it was fairly easy to take a series of measurements and accurately measure Morning Star’s air draft. 





The first step was to set up and level the laser. 
It is important to have a clear view of the water as well as the mast tabernacle. 

Next, measure the elevation of the instrument above the water.

Finally, transfer that elevation to the mast tabernacle.
Once this is done, it is simple to measure the distance from the top of the anchor light  to the mark and add the two dimensions together.  It took longer to carry the instrument from the car to the dock than to actually do the measurement.  The results?  The air draft is exactly 22 feet, at least on Morning Star.  But please, don’t take my word for it.  Measure your own boat.

When we were on the Erie Canal in 2007, we had to lower the mast and boom to meet the 21’ height limitation.  This meant that we couldn’t enjoy the shade under the bimini top on the upper deck.  Since we are planning to head back up  that way this summer, we set out to reduce our air draft.

The first part of the project was to eliminate the need for the mast.  Since we have the dinghy in davits, the only uses for the mast are (1) a place to park the anchor light and (2) to lift the 15 HP outboard on and off the boat.  We started by purchasing and installing a Garhauer motor crane.  What a sweet piece of equpment (Thanks Roger Montembault!).  It’s a huge improvement over the mast/boom combination.  Once that was installed, we took down the bimini top and frame, removed the boom, lowered the mast and removed it from the tabernacle.  A Sawz-All with a metal cutting blade made short work of the butt of the mast.  Before we knew it, we had removed five feet of mast, lowering our air draft to 17’.  While the mast was down we changed the bulb in the anchor light to an LED bulb because of its bright light and low power consumption.

Now, when we approach bridge lower than 24’, we just have to remember to lower the VHF antennas!

Morning Star is canal-ready with her “improved” mast.