balast ratio....

[Tranona]

Yes, I know, but mostly because charter boats are not sailing in heavy weather. Or not that heavy.
But no struggle at all, I have included link right at beginning on my posts - english investigation in capsize of Jeanneau at Biscay. With AVS = 109', btw.
Tis one: http://www.maib.gov.uk/cms_resources.cfm?file=/Ocean Madam.pdf many more probably can be found, as I have a book about accidents at sea somewhere, with details and investigation results. Interesting reading that was. Over 10 years ago.
As for current regulations - yes, I'm not current, may be wrong. Wouldn't be so sure though, seeing test of some boat.

Yes, there have been some cases - I can think of 3 in the last 25 years, of which 2 (including the one you cite) have been on delivery trips rather than on charter, and in situations that would have challenged any boat. In fact it was this case that was one of the examples used to justify the stability requirements in the RCD.

Stability is in the RYA syllabus for Yachtmaster and there is extensive material on the subject on the RYA site. It is also regularly covered in articles in the yachting press. Since 1998 builders have been required to publish a wide range of design data for their boats as part of compliance with the RCD. However compliance and enforcement is patchy, not helped by the fact that the standards are ambiguous in that they allow different methods of calculating stability which do not give consistent answers. As James Jermain pointed out magazines try to include the data in their tests but it is often difficult to extract it from builders.

In reality very few buyers consider such data in making their choice of boat, relying more on the integrity of designers and builders to produce a safe boat that suits their needs. Some would say this faith is misplaced, but equally it is difficult to find any reliable evidence that modern boats are inherently "un"safe.

 

[Sailfree]

When I got interested in big boats I started a spreadsheet with length, beam AVS, ballast ratio, weight, cost and so on.

What became apparent was that cheaper production boats were lighter and the price /kg was slightly less. A heavier total weight was often accompanied by a higher ballast ratio and a high price. After all its the weight of materials that we are buying. Generally lighter boats got going in light winds and heavy boats need a stronger wind for same passage time. There are always exceptions though and boat owners that delude themselves.

I considered the American stability factor (developed after the 79 fastnet) and the AVS as the two best indicators of stability.

On investigating X yachts (as a potential purchase) I initially was alarmed at the relevant light weight of the hull but on deeper investigation discovered that X yachts included the inner structural frame as part of the ballast while on a GRP boat all the reinforcement to take the rigging loads down to the hull are part of the boat weight and not the ballast weight.

So you see even the ballast ratio can be misleading until someone clarifys what ALL boat manufacturers consider ballast instead of what we perceive it to be!

Anyone know what Arcona include in their ballast figures as these are constructed similar to X boats.

I would add that an Ovni aluminium boat is a frequent choice and is a sucessful blue water boat yet IIRC its AVS is only 107 deg!! With its lifting keel and ballast inside the hull (not in the fin) my understading is that in bad weather you raise the centreboard and skid sideways ratherthan trip over a fixed deep fin.

To try to consider/compare various boats a fair amount of knowledge is really required if unreasonable comparisons are not to be made.

 

[grumpy_o_g]

Sorry, no intention to upset anyone or such...

Absolutely no need to apologise - you didn't offend anyone as you didn't specify any particular person. Your English is so good I assumed youwere an ex-pat.

 

[lw395]

....

I considered the American stability factor (developed after the 79 fastnet) and the AVS as the two best indicators of stability.

......

AVS is a grossly over-rated indicator of stability.
A log with a nail in it can have 179.9 degrees of AVS.
It's a measure of Instability when upside down in flat water, a mode not very relevant to yacht sailing.
Taking any one number in isolation does not help.

The few yachts that roll are generally rolled by waves, apart from the significant few where the keel falls off!
For a given size of wave, one of the biggest determinants as to whether it will roll a yacht is the size of the yacht.

 

[Rossynant]

AVS is a grossly over-rated indicator of stability.

Taking any one number in isolation does not help.

The few yachts that roll are generally rolled by waves, apart from the significant few where the keel falls off!
For a given size of wave, one of the biggest determinants as to whether it will roll a yacht is the size of the yacht.

Yess. That's the point.
Writing here so much already I will ad simple example:

As maybe not everyone realizes the wave dynamics at first glance:
Breaking crest of a wave is a part of water that has no weight. 0. That's why it's falling off, or blown with the wind

Now take that drawing in the link on stability earlier cited on topic ( http://www.sailboat-cruising.com/gz-curves.html ) and easy to see that a boat is held upright by a moment of two forces - displacement and weight. Archimedes law, as said.
Important to remember (in case someone forgot ) that those are forces - they have a value and a direction which can change, any time, in any way. It is not the mass of boat (which is constant). The are equal in value and acting against - not always, but usually.
But then again - not necessarily in a way shown in this illustration...

Now imagine boat floating, whole of it, on wave crest - the one that has no weight itself (not a place here for wave theory, take my word). It's a situation of weightlessness same as in spaceship, or as in free-fall state; local accelerations being such that they act against gravitational acceleration.
Boat in such situation, that is lifted up on the wave big enough, is also weightless. So forces acting - displacement and weight - are equal to zero. In practice it's usually not as much absolute, but a greatest portion of weight is lost anyway.

So - according to picture in link, the theory there: static stability of the boat is lost, = 0. No forces to keep her upright. None.
And then she probably carries some storm sail, which will heel her...

This is simply put, or so I hope, quite easy to grasp idea. It's not the only, or even not the most frequent mechanism of capsize, nevertheless capsize on a crest is quite common and known for ages.

This idea, and the whole theory of ship stability in seaway, was presented by William Froude in 1861. In UK...
http://en.wikipedia.org/wiki/William_Froude
And since then stays put in every textbook on boats and Naval Architecture.

Maybe that is not on the topic of what ballast ratio is - but worthy to explain what ballast ratio is not
So may be of use to someone, and so I have put it here - a bit ashamed in fact to do so. Because this is school knowledge that I explain to teenagers...

 

[Sailfree]

AVS is a grossly over-rated indicator of stability.
A log with a nail in it can have 179.9 degrees of AVS.
It's a measure of Instability when upside down in flat water, a mode not very relevant to yacht sailing.
Taking any one number in isolation does not help.

The few yachts that roll are generally rolled by waves, apart from the significant few where the keel falls off!
For a given size of wave, one of the biggest determinants as to whether it will roll a yacht is the size of the yacht.

Agree its one factor. I believe it was Portsmouth university (Wolfstone Institute) that demonstrated that any boat will roll if hit beam on by a breaking wave 0.66 of it beam width. IIRC I read that in Coles Heavy Weather Sailing. The shape of the boat and its AVS determines how quickly it rights itself. However The AVS and the comparison of the areas of the graph both beneath and above the line does give a useful guide of a boats stiffness.

Rossynant - you may not appreciate how lacking in theoretical knowledge some UK sailors may be. My understanding is that qualifications are compulsary in most European countries but the UK government has left UK qualifications as being voluntary and the examination system left with the RYA. Its actually quite a good system but can leave a number that don't bother to study for the exams with little knowledge going to sea in either sailing boats or motorboats. Like everything in life you don't know what you don't know!!

A number insist that its their right under freedom of the sea and generally there is little problem but regulation is creeping in eg compulsary lifejackets in Ireland.

A small amount on stability is now included in the RYA course and I would hate it to be so theoretical as the hydaulics I had to study at university with metacentric heights etc surely that can be left to the yacht designers.

 

[BobPrell]

Rossynant, you are a breath of fresh air.

The only things I know about yachting in Poland is Roman Polanski's film Knife in the Water, and Radoslaw Werszko - his free stitch and glue sailboat plans.

In view of your contributions to this thread I would love to know more about your personal background, trade or calling and how and when you got your sailing experience.

Nothing that would let me steal your identity of course, though I don't think I could keep up the act for long.

cheers

 

[lw395]

Ballast ratio is a useful indicator, that's all.
A boat with a higher ballast ratio, or a deeper keel will generally be able to power to windward better in roughwater.
But having a high ballast ratio with low displacement and shallow draft is probably not going to be as effective as a heavy displacement moderate ballast ratio deep draft.
Although the light boat with 8 fat blokes on the rail will probably go quite well.

And of course, sometimes we get to sail downwind too, where stability comes from the speed of the hull through the water and its shape, as well as ballast.

 

[Rossynant]

Re: upending a Carter 30, if it's the same as the one I sailed on a couple of times that must have been a hell of sea and wind and you would need to be pretty over-canvassed too (I'm assuming you weren't in a Force 10 mid-Atlantic or something). I think there may have been a racing version though??

As promised to write about Carter 30 - sorry for delay, tried to find tech specs that I had somewhere.

Athough I have seen force 10 in North Atlantic, not on Carter. But some did.
As for the topic - yes, at least one Carter - and it was a racing version, but no compromises in stability or ballast - was lost rolled over at sea.
Boat was well known, well built, had highest safety certifications, including UK survey of RWYC just before. "Carmen" had earlier participated in OSTAR race, and at the moment was running in race Plymouth-Spain-Plymouth, somewhere about entering the Channel. I may find details if anyone interested.
IIRC: the boat, storming close-hauled, was rolled by 3 consecutive breakers. First one stopped her, next turned her side to; then helmsman payed off to take the third one from astern, but boat broached to it, and then capsized, making 360' turn. She righted herself immediately, but mast was broken and construction damage dome to the hull, like bulkhead broken and hull-deck joint leaking. Unable to deal with leaks and water dangerously high inside after 2 hours captain turned the beacon on, and they were saved (by Polish ship, btw) few hours later, abandoning the boat.
Damage might be attributed to racing rig being lighter, nevertheless aluminum masts are prone to breaking.


It is perhaps worth to explain further.
As "static stability" looses importance in such situations, what can prevent the boat from being rolled too far is mainly her moment of inertia. Inertia is actually a measure of resistance to being moved, in this instance to be rolled. (there is also a water damping provided by underwater area of hull - which resists sideways movement - for which old longkeelers have much to be recommended ).
A moment of inertia depends on the mass and distribution of it. Obviously a heavier boat will have more inertia, but distribution of this mass is more important. Not going into physics much, but formula is: I = m x r2
moment of inertia = mass x square of distance from roll axis, radius. (if I'm not messing this).
Now axis of roll would be in the hull, somewhere about waterline. Ballast, which is the topic here, is a great part of boat's mass but close to the axis. And distance (lever length) is the most important here as it's in square. So objects far away from hull center contribute most to the inertia. Easy to realize what is farthest - the rig.
Now rigs in modern boats often are made as light as possible, a lot of 'space age technology' goes into design so to get it lightweight. And interestingly - this is done to obtain better 'static stability'!
Well, with stability calculations there is the same aspect - "righting moment" being similar in principle as 'inertia moment', that is weight distribution plays the same role. Weight placed far from axis has more importance, the distance is in square power, formula looks same way as above. And rig is high up, so it's weight is heeling the boat, and ballast has to act against it; but ballast is close to axis and a lot of it is necessary to overcome rig weight. Making the rig just a little bit lighter allows designer to save quite a lot in ballast weight.
Not to wonder newer boats with high-tech materials for rigging, and so a rig weighting less, can have less ballast - thus lower 'ballast ratio' - for the same "stability criteria". And this weight saving is very important in design, because lighter boat is faster in light winds (absolute' must have' for racer), and also cheaper in production. Not everyone remember that boats cost by a pound of material to make - but the are sold by feet of length. Not easy to sell a smaller boat for higher price just because it's heavy and solid

So everyone now strives to get lighter, faster construction.
The problem often overlooked being: such boats have a lot lower moment of inertia...

 

[wotayottie]

Can somebody please explain in simple terms what balast ratio is and what ratio makes a boat safer? Many thanks.

In engineering terms it's a meaningless statistic and there is no level of it at which a boat is safer.

Imagine that you have hold of a 28lb weight. Is it easier to hold near your chest or at arms length? Near your chest of course since it makes less leverage there. Its the same with boat ballast.

People divide the weight of the boats ballast by the weight ot thye boat overall to give a ballast ratio. But that makes no note of where the ballast is. To be slightly silly, put that ballast at the top of the mast and it would be a real disadvantage. Put it 1 metre below the hull and it will be just half the use that it would be if 2 metres down. But whether its at 1 metre or 2 metres, the ballast ratio is the same.

And all this ignores form stability, that is the stiffness provided by the shape of the boat. Best example is a catamaran where the resistance to being capsized is way bigger than a mono of the same length because of form stability.

So when someone boasts to you that his boat has a 40% ballast ratio and therefore is better than a Benny with just 25%, ignore him . All he is showing is a lack of understanding.

P.S. If you want a more meaningful statistic, look for the curve of righting moment

 

[TimBennet]

If you want a more meaningful statistic, look for the curve of righting moment

Or look at its STIX number if it has one, (or its SSSN if it was 'racy' enough to have had one calculated in days gone by) which incorporates the data from the curve of 'righting moments' together with all the other relevant factors.

The STIX number is not perfect by any means, but it does try to combine all the qualities that are considered desirable in a seaworthy yacht and represent the result as a single figure. Generally a value of 32 or over is the threshold for an 'ocean going yacht'.

One of the drawbacks is that it incorporates a 'minimum size quotient' that generally means that boats of average proportions are unlikely to score enough points unless they are a minimum of 9.5 metres LOA. Similarly, larger boats do disproportionately better, simply because they are bigger.

At the moment there is a thought that a minimum STIX should actually vary with boat size and that STIX = LOA(feet) is actually a better indicator. Therefore something like a Contessa 32 that just squeaks into the 'ocean going' category with a STIX of 32 would then be seen as comparable to a 38ft boat that at the moment has a more comfortable ocean going STIX of 38.

There also needs to be research to see if the relationship could be extended down the size scale so a long keeled 26 footer might be considered 'ocean going' if it reaches a STIX of 26 instead of the practically impossible target of 32. (Fisher 25 and Vancouver 27 manage this cut-off, but only because of their massive displacements).

The whole STIX methodology also only considered boats of convention form, ie fixed keel boats. As little research has been done on the storm survivability of lift keel boats like the OVNI, it can only be 'evaluated' as a keel boat, even though its storm tactic of lying with its keel completely retracted and hence offering no 'tripping hazard', is diametrically opposed to the modelling considered.

So as I said earlier, comparing ballast ratios only makes any sense if you are looking at two boats where everything else (length, displacement, freeboard, draft, hull shape, bilge 'firmness', cabin house profile) are identical. In the 60's when most boats were indeed of similar form, with the almost universal influence of the RORC/CCA rules, ballast ratio was typically around 43% and the consequences of a design deviating from this might have had easily predictable consequences, but now with so many variables to consider, the STIX is the best tool we have at the moment, despite its myriad shortcomings.

 

[mjcoon]

...
Not to mention I am practicing English language skills here

And to great effect; much appreciated education in sailing and Polish history!

So perhaps I can be permitted a hint re UK-English (ignoring USA, of course). We generally have verbs with "s", as in to advise (which sounds as if with a "z") and licensing, practising etc. Versus nouns with a "c" as in advice, licence etc.

Mike.

 

[Pleiades]

Tony, Joe and David.

Thread reminded me of the sad loss of the Oceanis Fairview 2 which capsized and remained inverted off the Needles in 97, drowning three of her crew.

Rest in peace guys.

Robin
Pleiades of Birdham
MXWQ5

 

[Sailfree]

Oh, yes, easy to mix up And some confusion too as I learned the language in US...

Don't let the exact english make you hesitate to post. Your English is clear enough to be understood and a different perspective from another country is always welcome. it stops the Forum being too insular.

 

[lw395]

Or look at its STIX number if it has one, (or its SSSN if it was 'racy' enough to have had one calculated in days gone by) which incorporates the data from the curve of 'righting moments' together with all the other relevant factors.

The STIX number is not perfect by any means, but it does try to combine all the qualities that are considered desirable in a seaworthy yacht and represent the result as a single figure. Generally a value of 32 or over is the threshold for an 'ocean going yacht'.

One of the drawbacks is that it incorporates a 'minimum size quotient' that generally means that boats of average proportions are unlikely to score enough points unless they are a minimum of 9.5 metres LOA. Similarly, larger boats do disproportionately better, simply because they are bigger.

At the moment there is a thought that a minimum STIX should actually vary with boat size and that STIX = LOA(feet) is actually a better indicator. Therefore something like a Contessa 32 that just squeaks into the 'ocean going' category with a STIX of 32 would then be seen as comparable to a 38ft boat that at the moment has a more comfortable ocean going STIX of 38.

There also needs to be research to see if the relationship could be extended down the size scale so a long keeled 26 footer might be considered 'ocean going' if it reaches a STIX of 26 instead of the practically impossible target of 32. (Fisher 25 and Vancouver 27 manage this cut-off, but only because of their massive displacements).

The whole STIX methodology also only considered boats of convention form, ie fixed keel boats. As little research has been done on the storm survivability of lift keel boats like the OVNI, it can only be 'evaluated' as a keel boat, even though its storm tactic of lying with its keel completely retracted and hence offering no 'tripping hazard', is diametrically opposed to the modelling considered.

So as I said earlier, comparing ballast ratios only makes any sense if you are looking at two boats where everything else (length, displacement, freeboard, draft, hull shape, bilge 'firmness', cabin house profile) are identical. In the 60's when most boats were indeed of similar form, with the almost universal influence of the RORC/CCA rules, ballast ratio was typically around 43% and the consequences of a design deviating from this might have had easily predictable consequences, but now with so many variables to consider, the STIX is the best tool we have at the moment, despite its myriad shortcomings.

There is more to safety than being the right way up though.
The Fisher 25 might have a high STIX, but it would not be my first choice for beating off a lee shore on a very rough day. But then again it is toward the M end of the motor-sailer spectrum. Good boats though.

 

[Rossynant]

No way small boat could get away from a lee shore in really stormy conditions, especially when on shoal water. This is the problem. I wrote somewhere about racing, but powerfull old kind, 50 foot yawl, 15 tons... We could get some progress in 10 B, 11 was setting us back. Power against the breakers is necessary. I'd prefer strong engine in such situation. No idea if Fisher for this, but have chosen something similar for me.
And strong construction. The yawl mentioned is wooden; had her bow crushed in once, both sides, with all ribs and 3 bulkheads broken. From falling off wave on shoal water, about Helgoland. 9 B. Near shave with death that was. And this is strong kind, sister ship made around in forties, first Whitbread Race. Including a capsize on the way

Polish racer, big class, was in this Fastnet '79, sailing normally all the time, no problems and among the leaders, until the bows started to fall apart. She was strongly built, normal construction, meeting construction rules.

As for STIX - just a thought: "Design category A - wind speed up to 10 B". Now wait a minute... What?

http://www.ircrating.org/images/stories/pdf/STIX2009.pdf

 

[lw395]

No way small boat could get away from a lee shore in really stormy conditions, especially when on shoal water. This is the problem......

Yes, that's true, but I find some comfort in sailing boats that can cope with more adverse conditions than others of a similar size.
A deep fin boat with a decent ballast ratio will probably sail to windward very effectively in F7, given the right sails.
A shallow boat with low ballast ratio might struggle.
I have no wish to push the limits of the yachts I sail though!

In real storms I hope to be choosing 'which pub?', not 'which yacht?'.

 

[onesea]

Yes, that's true, but I find some comfort in sailing boats that can cope with more adverse conditions than others of a similar size.
A deep fin boat with a decent ballast ratio will probably sail to windward very effectively in F7, given the right sails.
A shallow boat with low ballast ratio might struggle.
I have no wish to push the limits of the yachts I sail though!

In real storms I hope to be choosing 'which pub?', not 'which yacht?'.

If you want fast sailing you want as little as possible below with the weight as deep as sensible.

If you want to easy sailing you want long and as deep as sensible.

IMHO on a sailing boat you cannot go wrong with more draft, until you want to go some where shallow
We have gone for fast to get us to the pub ASAP if forecast goes to ****. Given planning as you say we want to choose which pub

 

[laffinskip]

Having read these comments with interest,I have to say that in mid atlantic
heading for the azores,with a force 9 for 3 days & nights,I thanked God that I was in a long keel boat with a substantial amount of ballast.Plus of course full water & fuel tanks combined with a heavy perkins 4236 62 hp engine,all of which are well below the waterline.
Meant that she rode the seas comfortably,by the 3rd day the waves were up to about 30 ft + & we had no worries about strength of keels in relation to the boat etc.
Theory is very enlightening but it has to be mixed with a modicum of commonsense as well.The saucer shaped boats are "Im sure" great for racing around the cans,but in anything of a sea give me a medium to heavy displacement boat anytime.
If I want to enjoy the trip (however slowly) I sail.
If I want to get there quickly I fly.

 

[Sailfree]

Laffinskip

and the boat for 99.9% of the UK sailing population that will never sailthe Atlantic is ......??