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RNI fuel requirements


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Not necessarly diesel related but I note the existing smaller boats will have a mix of inboards and outboards. I have calculated our fuel requirement as rather onerous and arguably unsafe. What (how much)  is everyone else going to carry?

 

  1. Option one - Carry the specified fuel requirement
  2. Option Two - Buy a new motor and re-engineer well :(
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From memory fuel requirements are based on being able to motor x distance in flat water. (150nm?).

 

And 20L extra fuel.

 

Are you saying outboards use too much fuel to motor 150nm to be able to carry safely onboard?

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8hp 4stroke yamy, 2.5 litre per hour, 6 knots in virtually anything.

 

150 miles divided by 6 knots equals 25 hrs. 25hrs times 2.5litres equals 62.5litres to meet ruling.

 

Therefore 12litres in main tank and 50litres in portable containers. Not a problem for us.

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From memory fuel requirements are based on being able to motor x distance in flat water. (150nm?).

 

And 20L extra fuel.

 

Are you saying outboards use too much fuel to motor 150nm to be able to carry safely onboard?

No - but using Tohatsu 9.8 two stroke figures being  5.1L/Hr at WOT to achieve say 6 knots requires carrying a minimum of 127.5 Litres! Sure can ease back on throttle and do say 5.0 - 5.5  realistic) and probably save a heap of gas and meet requirement - still going to be considerably more than SMU. SMU are you running standard Yamaha 8 - 4 stroke prop or High Thrust?

 

Model M9.8l

Type     Two Stroke Maximum output HP (kw)   9.8 (7.2) Maximum operating range rpm   5000-6000 Fuel consumption at W.O.T L/Hr (gal/Hr)   5.1 (1.35) Number of cylinders      2 Bore x Stroke  mm (in)    50 x 43 (1.97 x 1.69) Displacement  cc (Cu in)    169 (10.31) Engine lubrication system      Premixed Fuel Starting system      Manual or Electric starter Spark plug     NGK BP7HS-10 or BPR7HS-10 Ignition timing  degree   ATDC2.5゜- BTDC26゜ Alternator output     Certain Model : 12V 80W 7A Engine oil      Genuine recommended 2stroke engine oil (TCW-3) Volume of engine oil tank  L (Gal)    - Fuel tank capacity  L (Gal)   12 (3.17) Speed control      Twist grip type or Remote control Gear reduction ratio      2.08 (13:27) Specifications and descriptions are subject to change without notice.         Standard and Optional Extras   Type  S / L / UL EFS / L   EPS / L Electric Starter  -  ●  ● Manual Starter  ●  ●  ● Engine Stop Switch Lanyard  ●  ●   Alternator  ○  ●  ● Rectifier  ○  ●  ● Oil Pre-Mixing  ●  ●  ● Transom  15 / 20 / 25  15 / 20  15 / 20 Propeller  ●  ●  ● Analog Tachometer  ○  ○  ○ Analog Trim Meter  -  -  - Remote Control Box  -   -   ● 12L Plastic Fuel Tank  ●   ●  ● Tool Kit  ●   ●  ● Emergency Starter Rope  ●   ●  ● Spare Spark Plugs  ●   ●  ● Owners Manual  ●   ●  ●   Standard    Optional           - Not Applica
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Currently running std yamy 4 stroke 3 bladed prop. Remember you don't have that extra weight in the stern compared to the 4 stroke. No rules on storage and moving petrol containers around as far as I know.

 

Have contemplated trading in for a 6hp 4stroke. Thirsty work goes well with that and in a Ross outboard well, it surely would be enough.

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From memory fuel requirements are based on being able to motor x distance in flat water. (150nm?).

 

And 20L extra fuel.

 

Are you saying outboards use too much fuel to motor 150nm to be able to carry safely onboard?

How many litres do you burn an hour Ken?

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SFA. Old engine seemed to burn about 2.5 - 3L an hour

Wow that’s a lot, we wouldn’t burn anymore the 2L an hour. I know this as we are currently working with a very small tank while our new one is fabricated.

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Actually, based on approx 40L for 120nm, I guess that 20 hours at 6 knots, your number seems more accurate. Not too interested in cutting it fine.  Any easy way to actually measure it?

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Island time is bigger and heavier than most commenting here. If its interesting to anyone, we use around 2.7 l/hr at 6 knots, and 0.9 l/hr at around 4.8 knots. This is a diesel inboard, but it gives you an idea of how speed sensitive fuel use is. Max use is about 9.2 l/hr at WOT, about 8 knots

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Easy way is to fill it to the top, motor for 150nm (or 15nm or even 5) and top up tank again

 

Just remember that you will use fuel to charge your batteries and unless you are going to walk to the service station at Mangonui, Wellington and Napier round up your requirement to make a full 20ltr, then strap it to your mast base or similar

Also remember that the electrical output of an outboard is crap a low revs so if this is your primary form of charging you will need to give it plenty of revs (at least half but maybe full) test this with a clamp meter, not may boats will run on less than 50amps per day, nav lights,vhf, chartplotter, satph or ssb, phone, stereo, icemaker etc. You can run your battery down a little during the leg and at Mangonui you would need to take your battery ashore to top it up, hopefully Wellington and Napier you will be close enough to a power point, however you don’t what to be finding your way into any harbour on a rainy night with your battery flat and no chart plotter and your phone on 2% battery

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Island time is bigger and heavier than most commenting here. If its interesting to anyone, we use around 2.7 l/hr at 6 knots, and 0.9 l/hr at around 4.8 knots. This is a diesel inboard, but it gives you an idea of how speed sensitive fuel use is. Max use is about 9.2 l/hr at WOT, about 8 knots

Interesting IT

Ma’ara at 50’ and 20t uses 2.7ltrs at 6kts giving us a range of Fiji with a couple of hundred nm to spare

However at 7kts we are 5l/h and WOT possibly over 20

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Actually, based on approx 40L for 120nm, I guess that 20 hours at 6 knots, your number seems more accurate. Not too interested in cutting it fine. Any easy way to actually measure it?

 

We will be carrying 80 litres in main tank and the extra 20 litres. That should give us plenty of reserve.

 

Just get a 5L jerry can and run your engine from that and time it. Pick a nice winters day to go for a motor with the family.

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Why 150nm in flat water?

Man I would think that bad nasty in trouble Lee shore stuff would be more important?

Has the 150nm in flat water been reverse engineered from bad weather?

Let's say ya get hit by a nasty and half way down west coast with a big onshore 24hrs flat out would be more like it and would really be of more importance and if its blowing 50 and ya motoring into it how far do ya go vs flat water.

Would some smaller boats be able to motor into really big breeze?..and that goes for some bigger boats to. Not digging at relatively small boats I just think it should be an important thing to think about.

What factors make up the fuel criteria.

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Why 150nm in flat water?

Man I would think that bad nasty in trouble Lee shore stuff would be more important?

Has the 150nm in flat water been reverse engineered from bad weather?

Let's say ya get hit by a nasty and half way down west coast with a big onshore 24hrs flat out would be more like it and would really be of more importance and if its blowing 50 and ya motoring into it how far do ya go vs flat water.

Would some smaller boats be able to motor into really big breeze?..and that goes for some bigger boats to. Not digging at relatively small boats I just think it should be an important thing to think about.

What factors make up the fuel criteria.

I would have thought, if you were in a sailing race, you'd need to be able to sail off a lee shore, or something.

 

But the motoring distance sounds like a reasonable estimate of how far you may need to motor, if, for example, you lost your rig and after it was all cleared away and tidied up, you needed to motor to the nearest port.

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We will be carrying 80 litres in main tank and the extra 20 litres. That should give us plenty of reserve.

 

Just get a 5L jerry can and run your engine from that and time it. Pick a nice winters day to go for a motor with the family.

If doing this don't forget to plumb the return line into the small tank you're using. Don't ask how I know this...

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Yes reverse engineering

Easier to get competitors to calculate flat water than the variables of bad weather

This is a minimum not a target, you won’t need it until you do, then you will wish you had more.

 

Another thing to consider is anchors

The number of times I hear of yachts that take there cruising anchor and replace it with a racing one, they say they don’t feel comfortable anchoring with the family using the racing anchor, it it meets the code they will say. Wtf, same thing if you need to anchor on a lee shore, do you want to be in 10m of water (boat length of chain and 60m warp) 50kts with an anchor you don’t really trust ?

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Happen anyway? It sure will as who in their right mind would carry a sh*t load of high explosive on a boat that has no use for it and no safe storage for it 

Quiet right KM, it is definitely time we got rid of flares.

I always knew you'd come around to my way of thinking.

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