air draft on boats?

Answer 1

Hi,
I assume that you are asking what an air draught is?!
Air draught is the term used to describe the distance from the top of a vessels highest point to the waterline of that vessel. Ship captains should know the height of their highest antennae on the ships' superstructure, for example and Yacht Skippers need to know the height from the tip of their VHF radio aerial to the yachts waterline.
This knowledge is essential and as basic a requirement for navigation as knowing the vessels draught (how deep the vessels keel is).
When navigating under a bridge, Skippers consult several sources of information in order to determine whether or not their vessel can safely pass under the structure at a given time of day.
Basically, one looks at the chart or an Almanac to find out how high the bridge is above a predetermined height. One then determines the current (or intended time's) actual height of tide, adds that height to the known air draught of one's vessel, then works out whether there is enough clearance or not by comparing that figure to the HAT height and the height of the structure above HAT.
This height of the structure (bridge) above the sea / river used to be taken from the MHWS (mean high water springs) of the relevant area and was a useful guide.
However, MHWS is only the average of highest tide states recorded over a period of time. Working from this average could actually cause a vessel to become stuck under a bridge even if the skipper worked everything out perfectly!
Prudent ship captains and Yacht skippers will take HAT (highest astronomical tide) as the level from which to begin their calculations for air draught. HAT is the level of the highest ever recorded tide for the relevant area.
A skipper would have to research this for himself until recently, but thankfully now modern chart publications are stating HAT instead of MHWS. Some almanacs this year for the UK and NW Europe are all using HAT and as of next year this will be a compulsory inclusion in nautical almanacs.
Hope this answers your question.
Best regards,
Geoff
www.sailingunlimited.net

Answer 2

Air Draft

Answer 3

I pnce followed a house boat off the Thames onto the cut at limehouse. They misjudged the airdraft and it got stuck under the bridge in the rising tide.

We scuttled the boat to free it , drag it back and watch it sink.

I think he could have done with asking what air draft was.

Its the height above the water of a unladen boat.

Answer 4

Air draft is the height of the vessel ABOVE the waterline. Great to know when going under bridges!

Answer 5

The draft of a boat is its depth below the waterline.

Or were you asking a completely different question about wind/draughts?

Answer 6

Air Draught, not draft.
As soon as I saw this question I knew most people would get it wrong (they always do) and so I had to jump in and put them all right....or so I THOUGHT!
So thanks Geoff, you've done it again and it's a pleasure to cross your path once more here in yottie answers.
OK, back to the question. If you want the answer then read what Geoff has to say. His answer is PERFECT and I couldn't have worded it better myself.
Sue
x

Answer 7

Like somebody said it is the Distance to the top of mast from water line . remember that when going under bridges the height stated on chart is taken from MHWS (mean high water springs ) or HAT (Highest astrinomical Tide ) , so at all states of the tide lower than MHWS you have extra clearance than stated on chart & can calculate it from tidal curves for the area

Answer 8

Close the ports!

Answer 9

wear a windcheater and a wooly hat,works for me.

Answer 10

and your question is??????????????