RNI fuel requirements

[khayyam 92]

so.... you have to have an engine that can actually move the boat at a decent speed, and enough fuel to use said engine to get out of trouble. sounds onerous! 

[splat 56]

To reiterate I have no problem with achieving the requirements both under Cat 2 safety regs and RNI NOR. I understand perfectly whay the requirment are there. I remain somehwat conflicted as to the safety of carrying circa 120 plus litres of 91 octane petrol on board. This is my issue and ultimately is an economic question probably resulting in moving to a 4 stroke motor. Thanks again everyone.

[Black Panther 1,688]

Squire root of wl for me is a bit over 7kn.

3 2 times wl is about 50kn.

 

What am I doing wrong?

[Fish 0]

Squire root of wl for me is a bit over 7kn.

3 2 times wl is about 50kn.

 

What am I doing wrong?

Multiple your LWL (in meters) by 3.28. Then take the square root of that.

This will give the speed your engine needs to achieve to be powerful enough to comply with CAT 2.

 

Its not your hull speed, its substantially less.

 

PS, formula for hull speed, take the square root of your LWL (in feet), then multiple that by 1.34

 

Note the difference in units.

To convert feet to m, multiple by 0.3048

To go m to feet, divide by 0.3048

 

BP, I'd expect you hull speed to be a sh*t load more than 7 knts. My kauri log of wood is 7.7 knts...

[markm 30]

or for LWL of 14.5m, 6.9kts with hull speed 9.24 if that helps

[Black Panther 1,688]

Since my top speed is about 7.25 I guess I cant qualify.

[Jon 391]

What’s your waterline length BP

My boats WLL is 13.74m so 6.713kts is all I need to achieve ?

Even if I use overall hull length 15.32 it only works out at 7.08kts

[Fish 0]

Since my top speed is about 7.25 I guess I cant qualify.

BP is 19m LOA, so guessing a LWL of 16 m = 7.24 knts

or a LWL of 15 m = 7.0 knts.

 

If your top speed is 7.25 knts, you should be fine. Don't forget, this speed is in calm water (i.e. dead calm), and with a perfectly clean bum etc. Those conditions don't occur very often, esp not at the same time. I would have thought, for the purposes of complying with the CAT 2 requirement, some 'careful measurement' of your speed, and ensuring it is done in ideal conditions, would give you a fair bit more than what you say your top speed is.

[Fish 0]

Was it Paul Elvstrom who said,  "You haven't won, if by doing so you have lost the respect of your competitors"?

[Fish 0]

Umm, That make no sense to me, not an unusual occurrence.

Do they mean hull speed?

ie 1.34 x  square root/LWL in ft. (in flat watere)

 

Ok, got it, just leave off  1.34. In what conditions?

In 'smooth' conditions - quoted.

 

Multiply you LWL (in meters) by 3.28.

Then take the square root of that. 

Answer in knots.

Its loads less than the hull speed, probably requires half as much power as that needed to get close to hull speed with an engine.

[markm 30]

BP, last PHRF cert had Black Panther LWL at 14.5

[Jon 391]

BP, last PHRF cert had Black Panther LWL at 14.5

6.9kts BP

[Fish 0]

LWL, design or actual loaded? naff all difference anyway.

I guess some latitude here.

 

5.5knts @2800  is pretty achievable if my lwl is 30'.

Kiwi is down on the fixed blader.

1.34√30  no chance.

So to comply with the safety regs power requirement, for a 30 ft LWL, your speed to achieve is 5.48 knts.

Your hull speed is 7.34 knts.

 

BP, if your LWL is 14.5 m, then your speed to achieve is 6.9 knts. If you already say you can do 7.25, you are sorted.

 

Note, the required condition, as per the regs, is 'smooth' water...

Additionally, it is customary to assess top engine performance with all other things being perfect, i.e. no head wind at all, perfectly smooth bum, coldest day you can get (for denser air, more engine power) etc etc. There is a massive variance in top speed based on a bunch of variables. Even half a knot from an 'OK, doesn't need a clean hull' to a 'freshly cut and polished and only just re-launched hull'.

 

Interestingly this power requirement applies for CAT 3 as well as 1 and 2. I've never been asked about it in a CAT 3 inspection, but then we've always comfortably achieved it, so probably wasn't a relevant issue.

[Kaihe Atamai 2]

Regarding RNI fuel, engine size, location etc, I recommend changing the petrol 9.8 Tohatsu 2HP outboard out for a diesel 45hp Yanmar inboard; also requires adding a few displacement tons...

 

Speaking of which - what are the thoughts on splitting a 'spare' fuel line and tank into the diesel?

 

Current thought is:

 

- Y splitter (or 3-way valve?), between fuel filter and engine

- spare line has a shut off valve and input filter on it

- spare line long enough to run into a tank 2m away

- spare 20L tank either a jerry can or a re-purposed outboard tank

- spare 20L stored in lazarette

 

Atamai will be carrying plenty of spare - given we primarily charge with the diesel; also, hot showers, cold drinks, etc.

[Clipper 358]

Bryon, both Gale and Krakatoa plumbed in separate tote tanks with valves etc before RNZ. Come take a look one day. If i had a fuel issue the plan was to flick a few valves and carry on with new supply.

[Jon 391]

All of the above can work and boats did for the RNZ

Just remember that most modern diesels return large amounts of fuel back to the tank so you need a twin line. Because if your switching to your 20ltr backup because your main tank has been contaminated with seawater, bug or just shaken up the years of crud or you have split a tank or line and filled your bilge.

If you don’t have a return line to your temporary tank/ jerrycan then half or more could end up being lost back into your contaminated main tank.

Exception to the above was the Yanmar 30? In Katana which didn’t have a return line, so only single line required

[Kaihe Atamai 2]

Right, modified plan:

 

- Visit Ken

- Thank Jon

 

- Input line runs from spare tank to 3-way valve on existing input between fuel filter and engine

- Return line runs from 3-way valve on existing return to spare tank

- input and return lines of sufficient ID, and 2m long (in case of a need to use external cans)

- spare input line has input filter on it

- spare tank a 20+L tote tank

- spare tank stored below, ready to switch into

 

I presume one should be mindful that the return will be contaminated for a time before the engine recovers, so might have to switch the return to the spare tank only after priming the new fuel and getting it running steadily on the spare input...

 

thanks gents - B

 

All of the above can work and boats did for the RNZ
Just remember that most modern diesels return large amounts of fuel back to the tank so you need a twin line. Because if your switching to your 20ltr backup because your main tank has been contaminated with seawater, bug or just shaken up the years of crud or you have split a tank or line and filled your bilge.
If you don’t have a return line to your temporary tank/ jerrycan then half or more could end up being lost back into your contaminated main tank.
Exception to the above was the Yanmar 30? In Katana which didn’t have a return line, so only single line required

[raz88 97]

I presume one should be mindful that the return will be contaminated for a time before the engine recovers, so might have to switch the return to the spare tank only after priming the new fuel and getting it running steadily on the spare input...

 

 

Wouldn't worry too much about that. Anything that's made it through to the return line will have been through your (probably multiple) fuel filters.

- if your problem is crud from tank 1 then it's likely to cause you blocked filters rather than contaminated fuel getting right through and into the return line. This being the case it's worth considering that dealing with a fuel contamination issue is maybe also going to require a secondary filter change at time of switch over.

- if water or similar which has made it through your filters then the volume in a return line is likely to be sufficiently diluted on introduction to your spare tank to not cause an issue.

- if above point is a concern to you consider moving switchover valve to enable shorter pipe run?

 

My experience has been that it's surprising how much fuel goes back down the return line. I'd be concerned that in delaying the switch over while trying to flush it you'd be losing precious litres of fuel which if switching to backup in an emergency you might need.

[Fish 0]

If you want to get fussy about it, consider installing a second water trap / fuel filter, in parallel to you main, with valving to shut one off and open the other, if one gets blocked.

Means you don't need to change a filter if there is an issue, and you really really need the engine at short notice.

This isn't specific to RNI, but more about redundancy on yachts that go further than most.