What Do These Stability Figures Mean?

[Deleted member 36384]

Hi,

My Rival 41C has a 'Stability Category Allocation' which states that 'The above vessel is suitable for Stability Category : 1'. I assume this means 'Area Category 1 - Up to 150 miles from a safe haven' as defined in MGN 280(M), but maybe it doesn't and 'Stability Category 1' is something else, any comments on this?

The actual data is as follows: -

Listed under the title 'Stability Estimates'

RR1 131
RR2 125
RR3 118

FVA1 0.83
FVA2 0.96
FVA3 1.14

STOPS 1 44
STOPS2 50
STOPS3 59

Listed Under the Title 'Categories'

Wolfson 3
STOPS 1

The RYA issued the calculation and she also has a Commercial Coding Certificate for voyages up to 60 miles from a safe haven, also issued by the RYA.

What do the various numbers in the stability estimates mean?

Thanks,

BlowingOldBoots

 

[Avalon]

From the RYA Website, on the subject of coding.

The distance you are allowed to operate depends on the boats stability. The first stage of coding is to fill out an Application for Examination and an Application for Stability Category Allocation. These should be sent to the RYA. They are analysed and a Stability Category allocated. There are seven area categories:
Area Category 6 – To sea, within 3 miles from a nominated departure point(s) named in the certificate and never more than 3 miles from land, in favourable weather and daylight.
Area Category 5 –To sea, within 20 miles from a nominated departure point named in the certificate in favourable weather and daylight.
Area Category 4 – Up to 20 miles from a safe haven, infavourable weather and in daylight.
Area Category 3 – Up to 20 miles from a safe haven.
Area Category 2 – Up to 60 miles from a safe haven.
Area Category 1 – Up to 150 miles from a safe haven.
Area Category 0 – Unrestricted service.

The area reflected in the Allocated Stability Category is the maximum distance it can operate commercially. For instance, often a RIB will be lucky to get Cat 3, whilst a yacht may get Cat 0, but an owner may only choose to operate and equip the boat for Cat 2 waters.

So your boat is suitable for category 1, but presumably is equipped and coded for category 2.

I'm surprised a Rival is not Category 0 - although I don't know how they work these things out.

 

[Deleted member 36384]

.... I'm surprised a Rival is not Category 0 - although I don't know how they work these things out.

Thanks Avalon. She has no collision bulkheads or water tight areas which are required for Category 0. I think her STOPS numbers are high enough for Category 0 if all other measures were in place. I don't really know; interested in what the numbers mean in relation to the calculations.

I believe when she was measured in 2000 she had a generator in the engine space and a very large radar arch on her stern, both of which have been removed now. Perhaps they contributed to the calculation in some way.

 

[Deleted member 36384]

The original question was posted on PBO's forum here: -

http://www.ybw.com/forums/forumdisplay.php?13-Practical-Boat-Owner-s-Reader-to-Reader

Forumite 'andyp' stated: -

I will give it a try...



MGN437(M) at this link https://www.gov.uk/government/upload..._437_-_Gov.pdf provides UK guidance on stability requirements for vessels coded under the Small Commercial Vessel Code (SCV). Stability is covered in Annex 5 which repeats Section 11 of an earlier document.
ISO 12217-2 is the standard referred to and will result in a Stability Category Allocation which in your case is 1. This does not equate to an Area of Operation since Stability Category 1 vessels could be allocated Areas of Operation 0 through 5 depending on their Range of Stability.


In your case your vessel has been assessed as fit to operate in Cat 2 waters, up to 60 miles from a safe haven.


The STOPS numeral, which your vessel may have been assessed against, in the absence of any inclining test, was developed by the RYA. For operation in Cat 2 waters a STOPS number of 30 or above is required


To be coded for operation in Cat 0 or 1 waters a STOPS calculation is not sufficient and would need to be replaced by a stability curve or inclining test.


If coded, your vessel may have a Stability Information Booklet as part of her paperwork which should contain more detail.
I imagine the different Stability Estimate numbers refer to different load conditions although the RR and FVA are beyond my knowledge. I would guess RR refers to your Range of Stability in degrees. WOLFSON refers to an assessment technique developed by the Wolfson unit at Southampton University to model/measure stability.


And that is about all I know...!

Stability Category Application and Area Category Waters are not the same thing based on Andy's comments above. When I find out more I'll update the thread, or if anyone else has more information it would be appreciated.