C470 Air Draft

C470-126, SV Onward, Air Draft
Rigging: Standard mast with in-mast roller furling.

On 4 Nov 07, I made mast height measurements at Great Bridge VA while waiting to make my first transit through the ICW. I wanted to be sure I had good air draft data for piloting under the infamous ICW fixed bridges.

In Nov-Dec 2009, it became apparent that the height boards at many of the fixed bridges in FL below St. Augustine had been modified and seemed to be reading different clearances than on previous transits for about the same water levels. For more information on this issue see data posted on the ICW Cruisers Guide website.

On 20 Dec 09, I went up the mast to replace my anchor/tricolor light that had been knocked over at the E Lyons Bridge at Stuart. I took the opportunity to remeasure the offset between the top plate of Onward's mast and the equipment mounted there. The updated air draft measurements are provided in the following table.

Air Draft / Mast Height


Water to top of mast step


Water to plate at top of mast


Water to top of anchor/tricolor/strobe light


Water to top of annemometer feather


Water to top of Windex


Water to tip of VHF antenna


Updated: 25 /Dec 09