DWL mast height for O'Day 39
- Thread starter Rgluv2sail
- Start date
Air draft (or air draught) is the distance from the surface of the water to the highest point on a vessel. Good to know since in 2014, the USCG reported that 1.2% of the collisions it investigated in the recent past were due to vessels attempting to pass underneath structures with insufficient clearance Marine Safety Alert 090-14: AIR DRAFT IS CRITICAL!" (PDF) (Press release). United States Coast Guard Inspections and Compliance Directorate. 2014-09-09. Retrieved 2015-02-15. It can be estimated in a couple of ways:
1. Calculate it as follows = I for a masthead sailboat of 50.02 ft SailboatData.com - O'DAY 39 Sailboat) + height of appendages like VHF aerial, navigator lights, wind instruments attached to the top of the mast + distance from base of mast to the waterline (measure this by laying a board or fishing rod horizontal from the base of the mast with a bobber on the end and drop it down till it hits the water, then take it on land and measure it).
2. Take photo of the boat in the water then past it into a drawing document, such as Excel, and based on your boom length of 14.17 ft SailboatData.com - O'DAY 39 Sailboat or other known length measurement with a pair of dividers and measuring scale on the drawing.
1. Calculate it as follows = I for a masthead sailboat of 50.02 ft SailboatData.com - O'DAY 39 Sailboat) + height of appendages like VHF aerial, navigator lights, wind instruments attached to the top of the mast + distance from base of mast to the waterline (measure this by laying a board or fishing rod horizontal from the base of the mast with a bobber on the end and drop it down till it hits the water, then take it on land and measure it).
2. Take photo of the boat in the water then past it into a drawing document, such as Excel, and based on your boom length of 14.17 ft SailboatData.com - O'DAY 39 Sailboat or other known length measurement with a pair of dividers and measuring scale on the drawing.
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Your boat is a Mast head rigged boat. The "I" dimension is 50.02 ft 15.25 meters. This puts the length of your mast at approximately 50 ft. Say 51ft to be conservative. How much free board (distance from the water to the deck) say 4 ft. You can get a tape and measure it standing on your dock.
Now I suspect you have a 3ft wire VHF antenna on the mast head. Maybe you don't. I would add 3ft to cover what is often called a "Bridge feeler/sensor".
Your up to about 58ft at this point. If you want to be conservative, Avoid bridge heights of less than 60 ft. If you must run up a river under a bridge, be sure that it is at low tide (check first if there is a channel that will let you navigate up the river with your 6.3ft draft). If your a little unsure, approach the fixed bridge dead slow and check the clearance with the "Bridge feeler/sensor".
Now I suspect you have a 3ft wire VHF antenna on the mast head. Maybe you don't. I would add 3ft to cover what is often called a "Bridge feeler/sensor".
Your up to about 58ft at this point. If you want to be conservative, Avoid bridge heights of less than 60 ft. If you must run up a river under a bridge, be sure that it is at low tide (check first if there is a channel that will let you navigate up the river with your 6.3ft draft). If your a little unsure, approach the fixed bridge dead slow and check the clearance with the "Bridge feeler/sensor".
For a bridge feeler/sensor consider having one of your crew climb the mast and raise his/her arm above the mast appendages.
Good to hear that you did the calculations. It is always a positive to know your boat and to have the confidence to give it the power under a bridge when the crew is looking up and wondering what is the captain doing.
I had that experience with my Brother-in-Law. The look in his eyes as we glided under the bridge he was sure was obstructing our passage.... Priceless.
I had that experience with my Brother-in-Law. The look in his eyes as we glided under the bridge he was sure was obstructing our passage.... Priceless.
I utilized the "bridge feeler/sensor" unintentionally one day while sailing to Boston Harbor from my local yacht club. There was a bridge spanning my route that I had sailed under many times, and I had verified the air draft before leaving the slip, and noted that the tide would be high, but no worries. Until I heard the VHF antenna go "ting" as I sailed under the bridge. I hadn't noticed that the tidal RANGE was two feet higher than normal.
The O'day 35's Mast is 47' 2" - Passing under the Port Mayaca Rail Road Bridge (49') for the first time was exciting.
Afterwards, it was time for a glass of scotch.
Afterwards, it was time for a glass of scotch.