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Old 11-07-2017, 21:05   #1
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Best way. Manly to the boat works

I'm 23m high at best guess

14.8m X 7.6m and draw about 750mm to the bottom of outboard leg.

Do I have to go around and in through the Southport Bar or will I fit under the powerline?

I recall the powerline being much higher but have heard conflicting comments.
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Old 11-07-2017, 21:35   #2
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Re: Best way. Manly to the boat works

Nominal height is 20.3m If you hold right over to port going south, you will get a bit more - but I think that a guestimate of 23m would be really pushing your luck.

At 20m air draft, it looked bl**dy close to me the times I've gone under it.
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Old 11-07-2017, 22:10   #3
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Re: Best way. Manly to the boat works

Hi, Dave,

I just checked on C-Maps, and it is marked 20.3, like Stu said, at lowest point of sag. There is "some" margin for safety, but I doubt it is as much as 2.7 m.

The prudent thing would be to actually measure. You might be able to find a 30m tape measure on E bay. It would be a good deal to really know, so you could work it out. Get someone to help you go aloft. Oh, yeah, and if your VHF antenna is up there, remember to include it, too. Then, you could query the electrical people about the heights of the eastern tower and the western tower, and make the trip at spring lows, if the arithmetic works out right, and of course, go around if it doesn't.

Canaipa's out, at 20 m.
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Old 11-07-2017, 22:11   #4
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Re: Best way. Manly to the boat works

Thanks

A big problem if I don't make it. I'll plan to go around.
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Old 11-07-2017, 22:16   #5
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Re: Best way. Manly to the boat works

Now here's one of those times when a cat is a disadvantage... can't heel it over to reduce air draft!

Seriously, Dave, the penalties for not quite making it are severe, so you want to be damn sure that you have the numbers right. The clearance is rated at HAT, so going on a spring low will get you over a meter for sure. Moving over close to the tower will gain more (and you don't have to worry a bout running aground like we do), but I'd sure want some hard data about your height and the wire height at the tower. I have heard that folks with Van de Stadt Samoas have made it, and they are around 80 ft IIRC, but I could have that wrong.

Scary stuff... good luck!

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Old 11-07-2017, 22:19   #6
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Re: Best way. Manly to the boat works

I've allowed some safety in 23m but with an antenna I'd be there.

You would expect a fair amount of sag in the cable over that distance so it could make the height. I just don't want to be on the news as the boatie that blacked out Straddie for a week.

Not to mention its probably 11,000V.


P.S. 80' that's about 24.3m. I still think I'll chicken out but I might do a bit more work on my actual height as you say.


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Old 11-07-2017, 23:31   #7
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Re: Best way. Manly to the boat works

My cat has an Air draft is 23.5 meters plus VHF and 4G antenna and I draw 1.4 meters. Have been under and back at least 8 times this year.

I take the Western Chanel past Russel island going South, I aim at the Western Pylon in the water and when 3 to 4 meters away turn 90 degrees to Port as I go under. Photo from my vessel of sister ship as she goes under the lines. This shot is of vessel headed North. We have already gone under in front.



I will not tell you what is safe and what is not, this is just what I do.
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Old 12-07-2017, 05:17   #8
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Re: Best way. Manly to the boat works

Hi Paul

Is this what you do. Note the small dot is the tower.
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Old 12-07-2017, 14:33   #9
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Re: Best way. Manly to the boat works

Quote:
Originally Posted by Dave_S View Post
I've allowed some safety in 23m but with an antenna I'd be there.

You would expect a fair amount of sag in the cable over that distance so it could make the height. I just don't want to be on the news as the boatie that blacked out Straddie for a week.

Not to mention its probably 11,000V.


P.S. 80' that's about 24.3m. I still think I'll chicken out but I might do a bit more work on my actual height as you say.


Thanks
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The other consideration is temperature - the hotter the day, the more the lines expand, and the lower they droop.
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Old 12-07-2017, 14:34   #10
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Re: Best way. Manly to the boat works

Black dots are Pylons, red dotted line is cable and yellow line is North South track.

When headed South I pass green buoy "A" on my Port side and navigate directly at Western Tower. On this track there is enough water all the way to the tower. At Approx 3 to 4 meters from tower, I turn to Port to go under the lines.

It shoals very quickly directly North of the Tower so when coming from the South as soon as I am level with tower I turn directly towards green buoy "A".

Just to push the pucker factor up a notch, one time this year I arrived at the tower to find a small fishing boat anchored directly on my track towards the tower and just for good measure he had dropped some crab pots between the fishing boat and the tower. I do not think he appreciated 45 foot of catamaran weaving around him and his pots. Probably did not even realize the power lines where an issue to any one.

I try to arrive at low tide but have been through on up to 1.5 meters of tide. 1.3 meters in photo in previous post.

Until I had done it a few times it was always a scary proposition, but going through with the same boat as mine directly behind me has made me realize that there is plenty of clearance. It is very hard to judge the height from the mast to anything above you standing on the deck. Even going under a 60 meter tall bridge looks close from the deck.

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Old 12-07-2017, 14:44   #11
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Re: Best way. Manly to the boat works

Thanks Paul

I appreciate the effort you've gone to. I'll measure up my boat and give it a go.

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Old 12-07-2017, 15:58   #12
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Re: Best way. Manly to the boat works

Quote:
Originally Posted by Dave_S View Post
I've allowed some safety in 23m but with an antenna I'd be there.

You would expect a fair amount of sag in the cable over that distance so it could make the height. I just don't want to be on the news as the boatie that blacked out Straddie for a week.

Not to mention its probably 11,000V.


P.S. 80' that's about 24.3m. I still think I'll chicken out but I might do a bit more work on my actual height as you say.


Thanks
Dave
On the Safety front - do not forget that the power lines are NOT insulated! Bare conductors, high voltage and then having a masthead antenna etc attracts the energy like a lightening conductor. The clearances they state are the safe heights under all loads, times of high current draw on a hot day, lots of sag, lowest point etc etc. That does not mean it is safe to exceed the height if the loads are not all at the maximum, just that it is then YOUR risk.
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Old 12-07-2017, 18:39   #13
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Re: Best way. Manly to the boat works

You will have no problem if you stay over by the western pylon I have a 44ft cat with a app23 m air draft and have been under several times.
The Catenary sag is massive I was very wary 1st time under but there was plenty of clearance AT LEAST 10 M
I have also been under Canaipa channel cable and there is plenty of clearance there too
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Old 12-07-2017, 18:45   #14
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Re: Best way. Manly to the boat works

Hi.....I have taken various Perry 43 catamarans under the wires....nearest the western pylon.....no dramas.....
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Old 21-07-2017, 01:41   #15
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Re: Best way. Manly to the boat works

This thread was most timely for me.
We were at the Gold Coast and having little luck in finding if we could fit under the power lines or if we would have to sail around Moreton Island.
Golden Dream is a 50' sloop with an air draft of 21 metres.
Reading the advice and seeing the photos encouraged me to give it a try. We followed the course descibed towards the western pylon, and had an estimated 10 metres clearance under the wires (at a low tide of 0.4m).
Thanks for the guidance.
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