Russel Island, Rocky Point Power Lines

[undercutter]

Lots of good info, thanks Alan.

We did in fact find someone to do the rig inspection on Monday thanks to StuM. He says he is within a stones throw of Manly however no one there had room for us so we will go to Raby bay. We can just fit in there even with all the dangly bits. Since he will have to go up the mast anyway we will take the opportunity to measure the actual air draught of the boat as I am only going by the drawings. We could also remove the windvane for a few extra inches.

We also have the Genset guy coming to do some warranty work on Monday as well.

This will also give us a chance to do some more investigating over the weekend and Monday.

[Factor]

Originally Posted by undercutter

We wanted to pass through the main channel heading south from Brisbane to the Gold Coast and noticed the the Overhead Power Lines near rocky point is shown as 66' min clearance at HAT on the charts. It also looks like there is lots of width in the channel with 1 pylon in the water and the easterly one just onshore. Our air draught is 23.5m.

Has anyone with similar height navigated this channel successfully passing under the power lines. Looks like if we pass close to either side of the channel at a low tide we would have no problem but would hate to have to turn back and go all the way around Moreton Island and back down the coast.

Presently at manly harbour waiting for some warranty work on our genset Monday.

Its 20 metres at HAT. Same in the Caniapa Passage, however in the Caniapa passage the lines curve up significantly on the Straddie Island side, and its the course I take with a tall masted boat. Just hug the straddie island bank, down side is you will need a good high tide to get over the shoals at Slipping sands, so the answer is IMHO, you should pretty easily fit through Caniapa, but leave Manly on a making tide which will carry you with it to Slipping sands aiming for the top of the tide and then the ebb will take you down to the coats, done the trip 6 times in the last two week.

[undercutter]

Originally Posted by Factor

Its 20 metres at HAT. Same in the Caniapa Passage, however in the Caniapa passage the lines curve up significantly on the Straddie Island side, and its the course I take with a tall masted boat. Just hug the straddie island bank, down side is you will need a good high tide to get over the shoals at Slipping sands, so the answer is IMHO, you should pretty easily fit through Caniapa, but leave Manly on a making tide which will carry you with it to Slipping sands aiming for the top of the tide and then the ebb will take you down to the coats, done the trip 6 times in the last two week.

What was the tallest boat you have taken through there?

[foufou]

What about heeling the boat with a dinghy with water in it hanging from the boom all the way out? I have seen pictures of such solutions looking very effective. f

[JPA Cate]

Good morning, undercutter,

You will also need to wait for higher water between Jacob's Well, and the south turn north of the measured mile.

Foufou had an interesting idea for you to consider as well. I wonder how much work it is worth to undercutter to heel the boat, and how much a dinghy full of water would heel his 56' boat? The arithmetic's beyond me, but if you were to try it, you could determine the angle of heel he could attain by that method, and work out how much that would decrease the air draught. It's a great idea to measure the air draught to be sure the drawing's are correct.

Undercutter, this is is getting to be fun! What's the next plan?

Cheers,

Ann

PS, Canaipa is not possible for us, both air draught and deep draught wise.

[buzzstar]

I have always thought the folk from the underside of the world were great risk takers who were very parsimonious with their expenditures of caution. Apparently I was incorrect, and those who might have viewed the passage as an opportunity with the potential for a free battery top off have moved to other places. All that good advice has shattered another myth.

[undercutter]

Originally Posted by Ann T. Cate

Good morning, undercutter,

You will also need to wait for higher water between Jacob's Well, and the south turn north of the measured mile.

Foufou had an interesting idea for you to consider as well. I wonder how much work it is worth to undercutter to heel the boat, and how much a dinghy full of water would heel his 56' boat? The arithmetic's beyond me, but if you were to try it, you could determine the angle of heel he could attain by that method, and work out how much that would decrease the air draught. It's a great idea to measure the air draught to be sure the drawing's are correct.

Undercutter, this is is getting to be fun! What's the next plan?

Cheers,

Ann

PS, Canaipa is not possible for us, both air draught and deep draught wise.

How high are you Ann and what is your draught. I thought we were about the same. If you won't go the Canaipa way then I shouldn't either.

I saw a video once of a guy going under a bridge using the technique described by Foufou. He didn't use a dinghy and the ballast was hung on a halyard with a control line to a winch to allow the weight to be hauled back in toward the boat. Worked like a charm and I think he almost had the gun''l rail in the water. I'll have to do some calculations to see how much heel we would need to reduce our height by 3m. Could be quite a bit.

My engine literature says that we can motor while heeled to 25 degrees and more if the heel is brought back to less than 25deg every 30 seconds so quite a bit.

The wife is giving me hell already.

[undercutter]

So if we are 23.5m air draught then we would have to swing a counter weight out 12.34m on the beam to obtain a maximum height of 20m. Anybody have the trig tables to determine the angle of heel????

I wonder how much weight we will need to heel our 34 tonnes that much???

[JPA Cate]

Originally Posted by undercutter

How high are you Ann and what is your draught. I thought we were about the same. If you won't go the Canaipa way then I shouldn't either.

I saw a video once of a guy going under a bridge using the technique described by Foufou. He didn't use a dinghy and the ballast was hung on a halyard with a control line to a winch to allow the weight to be hauled back in toward the boat. Worked like a charm and I think he almost had the gun''l rail in the water. I'll have to do some calculations to see how much heel we would need to reduce our height by 3m. Could be quite a bit.

My engine literature says that we can motor while heeled to 25 degrees and more if the heel is brought back to less than 25deg every 30 seconds so quite a bit.

The wife is giving me hell already.

High, undercutter,

Our air draught is between 20 and 20.5, says Jim, and our water draft is 2.2 m. Jim said he does not know for sure that we couldn't get through Canaipa, but our issue isn't the air draft, it is depth at the drying shoal and timing. It is more accurate to say of us that we won't try go through there, to us the risk of grounding and ruining the bottom paint makes it not worthwhile. A skipper decision, not a fact that we couldn't. You draw less than we do, and have a taller mast.

We have been dragged along with about a 30 deg. heel to get over a shallow spot. But not with the powerline problem, and didn't much care for it; however, it can be done, and with success.

By the way, Jim told me something I had not known about those power lines, and that is that it does not actually require contact with a 100kv line for it to arc to you, only that your VHF antenna be close enough to it, and that varies with heat and humidity, and atmospheric pressure. Cute, eh?

One of the things Jim used to ask me all the time, was "What could possibly go wrong?" When I consider that, it is also important to question how likely is catastrophic failure, and how the risk can be minimized enough to make it worth one's while to take it. There are some nice spots in there--where I identified my first Brahminy kite, but it is not the worlds most beautiful cruising ground, either, if you choose to go around, it's too bad to miss it, but not the end of the world, imho.

Finally, he said that he thinks you could make it. That the safety factor put into the clearance has to take into account the HAT and the highest temp days, and he thinks it may be over 3 m. It would be really great if you could dig up that info somewhere. Have you Googled it?

Ann

[buzzstar]

The mention of water in the dinghy in one of the posts reminded me of the photo I found at the following. How big are your balls? Tall mast & low bridge - I am absolutely certain an identical discussion (about bridges, not wires) took place on CF and a similar photo was included with replies. It is real, all that you need is some simple trig based on total height above the water to top of mast and anything else, the height of the wires, and the angle needed to provide the necessary clearance (with a margin for safety). Despite the occasional comment to the contrary, water depth has no direct impact on this method, although water to wire distance certainly does as it is directly related to tide height, which does affect water depth.

[Jim Cate]

Despite the occasional comment to the contrary, water depth has no direct impact on this method, although water to wire distance certainly does as it is directly related to tide height, which does affect water depth.

Brian, in the general sense this is correct, however in this case water depth plays a part. Y ou see, the deepest part of the channel lies beneath the lowest part of the wires catenary, and the water depths are marginal for deep draft yachts. The wire heights near the towers are significantly greater, but the depths are not charted in detail there. Some detailed sounding from a dinghy would answer that question, but the location is quite some distance from the OP's current location, and his reluctance to do an exploratory trip is understandable.

So, the heeling method of air draft reduction is appealing! Were it me, i'd want to do some careful experimentation before setting out towards the wires. One technique that might be easy would be to attach a line at the masthead with a weight at the bottom, and the line being the rated height of the wires in length. Then start heeling the boat with that line swinging free out over the water. When the weight touches the water, the masthead is low enough to clear the wires. This "gauge" could be carried while doing the transit to reassure him that he was safe. (But it would be a tight pucker string time for me anyhow!!).

cheers,

Jim

[Smooth Cruiser]

You should be fine. Stick right over to the east pylon as you go south - as soon as you clear the wires turn back towards the centre of the channel to avoid the spit that extends into the marked channel between the pylon and the next green beacon south.

My airdraft is 22.5m and I have been through at all states of tide and had a spotter once in a tinnie say that I still had a few metres clearance.

[undercutter]

Originally Posted by Smooth Cruiser

You should be fine. Stick right over to the east pylon as you go south - as soon as you clear the wires turn back towards the centre of the channel to avoid the spit that extends into the marked channel between the pylon and the next green beacon south.

My airdraft is 22.5m and I have been through at all states of tide and had a spotter once in a tinnie say that I still had a few metres clearance.

Better and better, what is your water draught Smooth Cruiser?

[buzzstar]

Originally Posted by Jim Cate

Brian, in the general sense this is correct, however in this case water depth plays a part. Y ou see, the deepest part of the channel lies beneath the lowest part of the wires catenary, and the water depths are marginal for deep draft yachts.

The angle of the dangle (also known as catenary) should be determinable either by observation or contact with owner and or operator of the power lines. If they were installed some years ago, observation may be best since they stretch. Calculations are still simple (fairly simple) math.

[Smooth Cruiser]

0.8m - but there is good water near the pylon.

(I have a catamaran.)