Hull Shapes and Behaviour in Heavy Seas

[MartinR]

Originally Posted by NevisDog

Look again at the GZ curve published for the HR 57 cruiser then tell me it won't stay inverted. Size alone will (hopefully) keep that thing outa trouble, not its stability curve. Other similar designs were mentioned; maybe worth checking those out too if you think them good in heavy seas.

This is a side effect of the relatively large beam. One of the reasons I prefer narrower beam.

But, no, they will not stay inverted, but will take longer to right itself. Need a bigger wave to do so. GZ curves are interesting, but give just a piece of the puzzle. Many of the successful working boats from old times, like the fishing smacks and pilot cutters, had positive stability only to about 90 degrees. They kept the sea under all conditions. Definitely not cat A compliant, but the balanced design made them very seaworthy. Heavy rigging made for a high roll moment of inertia, not easy to roll these boats, even though there was no external ballast.

Also, higher stability does not necessarily mean that a boat is safer. Boats that loose their masts are at a very high risk to be rolled again, even though the stability is increased due to the weight loss above deck. But - at the same time the movement will be much quicker and the roll moment of inertia much reduced.

[NevisDog]

Originally Posted by MartinR

...But, no, they will not stay inverted, but will take longer to right itself. Need a bigger wave to do so...

Think about it - that's exactly the same as saying "they will not stay upright, but will take a little longer to invert." Longer to invert than a Cat A? Cat A is minimal, not as good as Cat A is terrible.

Compare its stability with Cat A - being big, it may just creep across the line; size may keep it safe, not stability.

[boatman61]

So.. Who's Category A are we talking about.. The EU one or does the US have one as well.
Not a lot of faith in the EU's CE: A, B, C, D.

[daletournier]

Originally Posted by Westsail-32

Tolerance people, tolerance.



I've been following this forum for quite a while and this is my first post.


CptPat was asked a direct question by the original poster in post number 252. He did his best, in an honest effort to answer that question, and then took the extraordinary step of including a disclaimer to fend off more attacks.


He was called "thick headed" etc. in this thread, among other insults, had his writing misquoted and misrepresented to fit a distorted image, and faced truculent demands for specificity when specific descriptions are impossible. And had experience used not as a source of wisdom but instead as a "mine's bigger than yours'" weapon. These uncivilized people have used every dirty rhetorical trick to attack this poster. He was even criticized for saying fin and full keeled boats behave differently in heavy seas. Really??? They are the same??? Seriously??? CptPat isn't the first person to believe the trend for greater speed can result in reduced stability and safety.


I'm dismayed at how the fangs came out and went for this poster's throat. And then by the audacity of accusing him of being non-civil. The pot is definitely calling the kettle black. These types of partisan attacks belong with childish politicians in Washington - not among civilized adults. I have no desire to jump into this maelstrom to post anything. I'd rather jump into a wood chipper.


I'll just go back to reading here. This is my first and last post.

Hi Westsail, I say again Capt pat is not getting attacked. He's making claims that simply aren't true, well not all at least. Eg, his view that the Adams 13 is not suitable for ocean cruising and needs 4 people to handled safely (or similar words) is simply not true. I met a couple last year that sailed across the Indian ocean and are currently in Tanzania, they sail a Adams 13. Jim has also told of Adams that he knows of sailing Bass straight.

If Pat or others are going to make statements like the above then others are going to point out that he's wrong, it's that simple.

Anyway I'm done, people are entitled to believe what they need to.

[MartinR]

Originally Posted by NevisDog

Think about it - that's exactly the same as saying "they will not stay upright, but will take a little longer to invert." Longer to invert than a Cat A? Cat A is minimal, not as good as Cat A is terrible.

Compare its stability with Cat A - being big, it may just creep across the line; size may keep it safe, not stability.

Yes, of course, bigger boats need less angle of positive stability than smaller boats. More force is required to overturn them. You will find that the area under the positive stability curve is quite large. Size is a part of the stability equation. Also, today there is a trend towards more beam and less ballast. If you would combine the wide beam with a high ballast ratio the boats would be very quick of motion, terrible in a cruising boat. All boats are compromises, and to just look at one part of the equation is only giving you part of the answer.

[MartinR]

Originally Posted by boatman61

So.. Who's Category A are we talking about.. The EU one or does the US have one as well.
Not a lot of faith in the EU's CE: A, B, C, D.

The "China Export" marking?

Who has faith in these? These are rules written by the EU boat industry to suit their purposes, mostly to keep the competition out of the market.

[boatman61]

Originally Posted by MartinR

The "China Export" marking?

Who has faith in these? These are rules written by the EU boat industry to suit their purposes, mostly to keep the competition out of the market.

Precisely.. Hence my question.. I had faith in the old Lloyds Standard but I am afraid I have as much faith in the boat industries self regulation as I have in icebergs not melting in a furnace.

[NevisDog]

Cat A is not self-regulation - it is law in the EU. It took many, many years to negotiate (of course). Boat industry fought it all the way but it was pushed on by just a couple of guys who recognised there was no way for you and me to assess whether stability of any boat design is good, bad, or mediocre, yet lives are lost when it's bad (yea the 79 Fastnet again ). It's a very comprehensive standard. Many designers consider it too low a standard but the big manufacturers held them to this MINIMAL standard. I say again, if a boat meets the Cat A standard that does not make it a great offshore boat - if it fails to meet the standard then it's a terrible boat for serious weather: run!

The HR 57 could not be sold in Europe unless it met this MINIMAL standard, therefore it must meet the standard. It would be truly astonishing if it exceeds the standard by much though. If we ever get to discussing behaviour in heavy seas then that boat would not come close to satisfying my ideals on stability, not even close. If you intend to potter around the Med then no problem, forget about stability and go for comfort.

[NevisDog]

Originally Posted by MartinR

Yes, of course, bigger boats need less angle of positive stability than smaller boats. ..

More correct to say bigger boats will need bigger waves before stability becomes critical. In equivalent sea conditions, it doesn't matter if you are testing a tiny scale model or a super-tanker, the effect of waves runs exactly to scale.

[boatman61]

Originally Posted by NevisDog

Cat A is not self-regulation - it is law in the EU. It took many, many years to negotiate (of course). Boat industry fought it all the way but it was pushed on by just a couple of guys who recognised there was no way for you and me to assess whether stability of any boat design is good, bad, or mediocre, yet lives are lost when it's bad (yea the 79 Fastnet again ). It's a very comprehensive standard. Many designers consider it too low a standard but the big manufacturers held them to this MINIMAL standard. I say again, if a boat meets the Cat A standard that does not make it a great offshore boat - if it fails to meet the standard then it's a terrible boat for serious weather: run!

The HR 57 could not be sold in Europe unless it met this MINIMAL standard, therefore it must meet the standard. It would be truly astonishing if it exceeds the standard by much though. If we ever get to discussing behaviour in heavy seas then that boat would not come close to satisfying my ideals on stability, not even close. If you intend to potter around the Med then no problem, forget about stability and go for comfort.

I know its law but I believe it is not regulated by Brussels, rather an association of designers and surveyors who as you say.. set the minimal standard they consider acceptable.
And lets face it.. they rely on the builders like Bene etc for their bread and butter.. its like a surveyor based in the BVI's surveying a boat Moorings is selling.. short of catastrophic failure its going to pass the survey..

But hey..!!! I'm a cynic..

[Pizzazz]

Could I suggest to people who feel passionately about this topic to read a book by Peter Bruce called Heavy Weather Sailing or at least the second chapter, called Stability of yachts in large breaking waves. The book is highly regarded by people in the field. It will save a lot of flame posts.

The author of the Stability Chapter is Andrew Claughton and he examines in detail all major race and other disasters to date. There are interviews with the skippers of the racing boats and good stories on what worked, what did not and what could be better going forward. Some of the points being made:

- All boats capsize (i.e. 360 roll) in breaking waves on the beam exceeding 60% of hull length. Best defense is to avoid waves on the beam via active sailing but this is impractical as crew fatigue sets in (although some racing crews managed).

- Best way to avoid capsize in breaking wave conditions is to actively sail the boat but eventually even the best crews get tired and start making mistakes.

- Full keel vs. fin keel. Neither design shows discernible superiority but traditional full keel (due to narrower beam and larger coach roof) recovers faster from a knock down. The key issue, however, is ease of control and this depends not so much on the area of the keel but on the hull shape and sailing characteristics. [We are talking about running before large waves here]. Traditional designs surf readily despite their weight and are easy to control due to the balanced ends. Modern designs are harder to control because the wave lifts the stern and buries the bow and turns the boat sideways. However, modern designs, if sailed actively can accelerate faster as the wave lifts the stern and this increases the buoyancy in the bow via dynamic lift. This is something full keelers cannot do.

- It seems that the best way to reduce the chance of a knock-down is to deploy a drogue to slow down the boat in breaking waves 35% to 55% of LOA.

The third chapter, by Peter Bruce compares designs over the years with references to 1979 Fastnet, 1984 Vasco da Gama, 1987 races, 1991 Japan-Guam Race, 1993 Sydney-Hobart, 1998 Sydney-Hobart, 2014 South Atlantic races.

My point is not (nor I should) to summarize the book but just to suggest a great source on the topic. Spend a couple of hours reading the book.

SV Pizzazz

[Paul L]

Originally Posted by Pizzazz

.....Traditional designs surf readily despite their weight and are easy to control due to the balanced ends. Modern designs are harder to control because the wave lifts the stern and buries the bow and turns the boat sideways. However, modern designs, if sailed actively can accelerate faster as the wave lifts the stern and this increases the buoyancy in the bow via dynamic lift. This is something full keelers cannot do.
......

Not arguing, just commenting.
This hasn't been my experience. I guess it depends a bit by what you (they) mean by traditional designs. I have owned and cruised offshore 3 boats. An Alberg 35, a J/37 and an Outbound 44. Most on CF would consider an Alberg 35 as a traditional design. Its a CCA era boat with good looking long overhangs and short LWL. It was by far the hardest to control sailing in heavy downwind conditions. The J was easy but you had to deal with the acceleration. The Outbound is quick but doesn't have the acceleration of the J. Bigger, heavier making it easier. No way would I consider the Alberg as an easy to control boat in heavy downwind conditions.

[NevisDog]

Originally Posted by boatman61

...But hey..!!! I'm a cynic..

Yea, you are.

Blood sweat and tears went into that standard, years of pushing and haggling. Sure it's a minimum - falling below Cat A is about as low as a boat could get - but the designers for Bene and others darned well ensure they meet the standard. That Bene that capsized and sank crossing Biscay showed them just how critical stability really is for safety when their designs head offshore and it cuts up rough, and that wasn't even a severe storm either

[Lost Horizons]

So much drama in 22 pages of heated discussion of stability and not a mention of STIX? Why? Or have I missed it?

[NevisDog]

AVS and STIX combined make up Cat A - Americans don't seem to want to recognise Cat A much so I guess they'd be even less enthused over STIX. Feel free to offer pearls of wisdom though - just don't expect much enthusiasm.