For the mathematically minded amongst us.....

[Lizzie_B]

Doing some passage planning for Florida trip in April (would love have you all along, but no room left)!!!!.
Need to get under a bridge to save me 800 miles and a lot of time!! How many degrees from the vertical angle of dangle would I have to lean a 56 foot mast to make it go under a 46 foot high span?

PS. If anyone would like a freebie sail in USA and has coastal skipper or above,or equivalent experience, then my boat will need moving from Miami to mouth of Potomac River( approx 6 days sail in a straight line, then enjoy cruising in the Chesapeake for as long as you have time) as soon after May 6th as possible, to be in Potomac by end June at latest. Would any one like to 'borrow' it?

The boat is a 1981 Catalina 38 (see www.catalina38.org )for specs.

 

[cameronke]

Your mast will need to be 35 degrees off vertical Mark

Swinging keel?

Regards
Cameron

 

[AndrewB]

Just under 35 degrees. Impossible. That's the trouble with the ICW, the bridges are supposed to allow 64' of clearance, but work on them frequently makes it significantly less. In some areas tides will give you a couple of extra feet, but it still won't be enough.

I tried this trick once in a sailing dinghy under Bursledon bridge. At a crucial moment a motorboat roared past, the wake knocking me upright and wedging the mast firmly under the bridge. Nothing for it but to get out and capsize the dinghy by yanking hard on a halliard - freezing in March before the days of wetsuits.

 

[Evadne]

... and sod's law would tell you that even if you managed to get her close hauled under full canvas plus spinnaker in a F7, that there would be a sudden lull just as you passed under the bridge.... Please remember to post the pictures here if you decide to try it!!

 

[tcm]

Arcosine of Florida

hum, i wonder how this migt be done?

a) awaiting a full gale, overcanvassing and fingers crossed.

b) with a crane, lift and put deep into the hold of a deep draught ship

c) take the mast down

d) something else?

 

[Lizzie_B]

There is actually a company at said bridge that exists to get over height boats through with use of weighted water barrels!!!

 

[Lizzie_B]

How do you work it out? Is there a formula? The actual charted airdraft of the bridge is 49 feet at highest water level. What would it be for 48 feet?

 

[jimi]

Think it is sine(angle of heel) = airdraft/mast height

 

[cameronke]

Hi Mark

I am sitting here with a CAD (computer aided design) sysem so just did it graphically

But the formula is basic trigonometry,
Angle from vertical = cos(^-1)(adjacent{height of bridge}/ hypotenuse{height of mast}

=cos(^-1)(46/56)
=cos(^-1)0.821
=34.772 degrees

For 48 feet
=cos(^-1)(48/56)
31 deggrees off vertical

regards
Cameron

 

[AlexL]

it is

Inverse Cosine (Bridge Height / Boat Air Draft)

 

[tcm]

Sohcahtoa

wrong! aintcha seen a boat called this, hm?

sine of heel = opposite/hypotenuse where hyp. =mast height and opp=distance the mast leans out

cosine of heel = adjecent/hyp= airdraft/mast height

tangent of heel = opposite/adjacent= leanout/airdraft

So write it out a hundred times.

 

[Lizzie_B]

Ok. Thanks.Is there anyone interested in freebie sailing in US, May to June time? Not under said bridge!!!!

 

[Lizzie_B]

Yes the ICW also has problems with maintaining the ruling depths of 12 and 10 feet. Some places it's down to 3 or 4 feet. However, this particular bridge is on the Okeechobee Waterway. I think I'll have see how many water barrels it takes to tilt the boat 35 degrees and how much weight on deck. If not, it's down to Key West, round the outside of the Florida Keys and up the East Coast to Miami. At least in places I get a 2knot lift from the current!

 

[jimi]

Re: Sohcahtoa

aaaarg i had my angle of heel = (*90-angle of heel) .. doh

 

[Salty John]

I think you have a problem! The Indiantown Marina heeling service will only get a mast height of 53 feet through the bridge. Also, there are some power lines at 55 feet. If you have the shoal draft Catalina 38 you can get to, and through, Moser channel at Vaca Key, 65 feet clearance. I've taken 6 feet on that route but it is a bit nerve wracking. Otherwise, it's the long way round. Good luck!

 

[Lizzie_B]

As luck would have it, I have a custom designed keel and bulb that draws 6 feet. Would be very interested in detailed breakdown of your route, as at the moment, until my charts arrive, I am having to work from government pilot books.

 

[Stingo]

What happens if you have a catamaran?

 

[tcm]

Re: rules for catamarans..

ah with a catamran, the normal rules of mathematics are totally changed! Yes indeedy, black is white, ugly is pretty, front to back and sides to middle.

 

[Salty John]

Heading south you will have rounded Cape Romano and if you were bound for Key West you would be on a heading of approx 187mag. At about 25.40N you should head more easterly, about 150mag, for a waypoint just east of Bullard Bank. I used 24.50N, 81.10W. There is a fl r 4s on this small bank and you will pass to the west of it. Next waypoint, about 4 miles due south, is the fl r 6s on the west edge of Red Bay Bank. From there you can head straight for Moser Channel, about 4 miles. I believe it is at 24.42.5, 81.10.5, but check it. The channel itself is about 15' deep from a quarter mile out and on the south side there are marks to keep you in the deep water - a red and green which you go between and then two reds to be left to port. By now you are in 20' and can turn west for the entrance to Boot Key Harbour on Vaca Key. Have a beer for me at Docksides. You shouldn't see less than 8' at mean low water anywhere on the route, and about 2' more at mean high water. You might want to check locally if there has been any significant shoaling of this area in the last few years. If you decide to go to Key West, remember you have to go all the way west to 81.54 before turning SE into Northwest Channel.

 

[Lizzie_B]

Moser channel sounds good to me. What's best jumping off point from Mainland, I am working my way down from St Pete.
Any recommendations for ports of call on the way down?
What sort of distance/time from Mainland to Boot Key Harbour?
What would you recommend as best route to Miami from there, and again with approx distance and time.