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Old 16-07-2011, 23:17   #1
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Botany Bay to Thursday Island QLD

Hi All

I am thinking of doing a trip from Sydney to Thursday Island and back. A total of 4000 NM.

At the moment this is in the infantacy stage of planning. Thus that is why I am after your opinon.

The boat is a 31' Mariner with twin 255HP Mercruiser petrol engines. There would be only three of us on board and be travelling at approx 8 knots. At this speed my fuel burn is approx 40 lts per hour. My fuel load is approx 580 Lts water tank is 240Lts

I was planning on staying close to the coast , about 5 or 6 NM off shore and travelling only in daylight hours.

The boat would be anti fouled ,serviced all hoses replaced with braided hoses and new belts all round.

Is this boat too small for this sort of trip? I have read many a thread on this forum of long distance trips in all sorts of boat that's what's given me the idea.

What do you guys think?
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Old 16-07-2011, 23:36   #2
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Re: Botany Bay to Thursday Island QLD

31' too small? The Leyland Brothers circumnavigated Australia in a 14' tinny! Just factor in breakdowns and watch the weather and you should be fine.
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Old 17-07-2011, 00:20   #3
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Re: Botany Bay to Thursday Island QLD

Sounds like a great trip FB31, my wife & I cruised to Whitsundays & return in a 33' sailing cat some years ago doing day hops, your Mariner should do the journey well although a lot more thirsty than ours, maybe check the consumption at dispacement speeds running on a single engine too. All the best from Jeff.
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Old 17-07-2011, 00:31   #4
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Re: Botany Bay to Thursday Island QLD

Quote:
Originally Posted by Flybridge 31 View Post
Hi All

A total of 4000 NM.
approx 8 knots.
At this speed my fuel burn is approx 40 lts per hour.
580 Lts tankage
Have I got this right?

4000nm/8knots =500hours of motoring
500 hours @ 40lph = 20,000 litres @ $1.80/l on the water
Thats $36,000 worth of fuel
580litres tankage/40lph =14.5 hours @ 8 knots = 116nm range

Have you thought about how you will get a tank of petrol in these remote locations every 116nm?

Perhaps you would be better off fitting a small diesel that gives you 8 knots and used a lot less fuel, or buying the right boat for the trip.
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Old 17-07-2011, 01:37   #5
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Weather and fuel consumption...

You don't say how long you are planning on this trip taking.

Your biggest problem would be the weather, particularly along the NSW coast where it may be necessary to wait several weeks for a good weather window.

With two 255hp petrol engines I would have thought that your most efficient and reliable speed would be well in excess of 8 knots.

You'll need to do some time trials to establish your optimum power settings. With the amount of fuel that you would burn some fancy fuel measuring hardware and software could pay for itself many times over.

A quick search suggests that your top speed may be around the 20 knot mark but your best cruising speed could be a fair bit less than this. You'll need to do your own navigation, but as an example, if the distance between ports is 100nm your trip time may be measured in hours, rather than days. It could be possible to do some legs using the sometimes calmer morning weather, starting early and having lunch at your destination.

It may be possible to reduce the fuel usage by removing as much of the top hamper as possible.

When I was checking your top speed I found the Prop Scan website. They claimed increased efficiency and speed if they reset and balanced the propellers.

And finally I strongly urge that you wear lifejackets at all times offshore, preferably those with inbuilt harnesses so that you can be tethered.
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Old 17-07-2011, 02:02   #6
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Re: Botany Bay to Thursday Island QLD

I think a mariner would do fine if it is the offshore model. BUT the fuel and access to fuel would be an issue and the mathematics says this would be very expensive.

Fly up and charter a yacht and enjoy or you need to accept that is what it will cost?
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Old 17-07-2011, 05:03   #7
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Re: Botany Bay to Thursday Island QLD

Wow some people have way to much money to burn sorry if this offends but most on this site are sailors who avoid running engines and are for ever trying to save dollars.
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Old 17-07-2011, 05:31   #8
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Re: Botany Bay to Thursday Island QLD

Three guys, a quick run every day, time for fishing every day, night at the pub and off again in the am. New place every night most of the time. Only $30K - great time - go for it.
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Old 17-07-2011, 06:42   #9
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Re: Botany Bay to Thursday Island QLD

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Three guys, a quick run every day, time for fishing every day, night at the pub and off again in the am. New place every night most of the time. Only $30K - great time - go for it.
If you look at a map of Australia you will see it'll never happen, not with 116nm range.
So many of the fuel stops are so much further apart than that.
For example Yeppoon to Mackay 167 Nautical miles of high current area
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Old 17-07-2011, 07:32   #10
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Re: Botany Bay to Thursday Island QLD

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Originally Posted by cat man do View Post
Have I got this right?

4000nm/8knots =500hours of motoring
500 hours @ 40lph = 20,000 litres @ $1.80/l on the water
Thats $36,000 worth of fuel
580litres tankage/40lph =14.5 hours @ 8 knots = 116nm range

Have you thought about how you will get a tank of petrol in these remote locations every 116nm?

Perhaps you would be better off fitting a small diesel that gives you 8 knots and used a lot less fuel, or buying the right boat for the trip.
$1.80/L ?Fuel at Seisa was $2.43 a litre, lucky we only needed 20 litres.
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