Lynnwell
New member
Hi, we are looking at our first sailboat and how important is draft and ballast in regard to stability
Draft and ballast
- Thread starter Lynnwell
- Start date
Poignard
Well-known member
Very important.
If you want to study the theory there are books you could read, perhaps starting with Skene's "Elements of Yacht Design" or Chapelle's "Yacht Designing and Planning".
Elements of yacht design : Skene, Norman L. (Norman Locke), 1878-1932 : Free Download, Borrow, and Streaming : Internet Archive page 33
If you want to study the theory there are books you could read, perhaps starting with Skene's "Elements of Yacht Design" or Chapelle's "Yacht Designing and Planning".
Elements of yacht design : Skene, Norman L. (Norman Locke), 1878-1932 : Free Download, Borrow, and Streaming : Internet Archive page 33
mjcoon
Well-known member
You could imagine if your hull were cylindrical, like a hollowed log. Until it is hollowed it has no preferred way up. Hollowing gives the effect of some ballast, but probably not enough to counter the weight of a mast or sail with wind in it. Conversely a plank will float flat because it has "form stability"...
Lynnwell
New member
Yes I understand that ,but what is confusing me is that some yachts are sold giving there displacement and some are sold with there displacement given and there ballast. Does this mean that some dont have ballast.
Tranona
Well-known member
You need to look at the ballast ratio - that is the weight of ballast as a %age of displacement. You will find ratios of typically between 25% and 45% on cruising boats (although some older designs may be as high as 50%). On its own though it does not tell the whole story about stability. The two other main factors are "form" stability, that is the shape of the hull and draft which is an indicator of the depth of the ballast below the centre of gravity. Generally speaking the greater the form stability and the deeper the draft the lower ballast ratio for a given overall stability.
However even looking at those variables these are still rather simplistic. Stability can be seen in different ways. At a "normal" level it gives an idea of the ability to carry sail area (that is the power to drive the boat) and the degree of heel that a boat will tolerate under sail. The other way to look at stability is the angle of heel at which the boat may capsize and then its propensity to right itself. These are captured in the stability curve (particularly the AVS -angle of vanishing stability) in determining the RCD category for the boat - that is its ability to cope with weather captured by average wave height.
Designers juggle with these variables to find a balance that meets the objectives of the boat. So, a light performance boat is likely to have a lower ballast ratio, deeper draft, wider flatter hull (greater form stability) than a heavy cruising boat of similar size. In simple terms for a 35' size range you might see a performance boat with a 27% ballast ratio, deep bulb keel at 2.2m, beam 3.9m carried well aft and a long distance cruising boat with 36%, beam of 3.5m narrowing to the stern, deep canoe body and longer chord keel of 1.8m.
This is a very basic overview of the principles, but yacht design is a very complex subject - whole books are written about it as well as basis for arguments, sorry discussions at yacht club bars and yottie forums.
When looking for your first boat the key thing is to try and decide what you want the boat for as this will/should narrow down the types of boats that are suitable. For example if you are looking for a typical coastal family cruising boat then at the one end a boat that is deep, narrow with a high ballast ratio (stands up to a blow - people have sailed round the world in one of these) or a wide flat bottomed deep keel with big flexible rig - very tweeky, jumps on the plane in 11 knots of wind may not be for you. Most mainstream builders build mainstream boats for cruising, but seek to differentiate their boats to appeal to sub sets of the market and looking at the stats gives you an idea of where particular model is on the spectrum. I think its fair to say though that first time buyers tend to buy popular conservative design boats to get experience of what they like ready for the inevitable (if sailing grabs you and your family) second and third boat. This is why once you decide on your budget certain models automatically select themselves and allow you to focus your search.
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boomerangben
Well-known member
Tranona gives a great explanation and insight into complexities of stability.
In short, all sailing boats other than dinghies will have some form of ballast. Unless you are thinking of designing your own boat, I guess you are looking at boats built from designs of experienced naval architects, by competent builders, probably regulated in some way. Almost all boats on the market will have more than adequate ballast and stability for their intended use. I suspect that as you progress through the journey to boat ownership, you will move ballast and draft further from the top your list of needs.
The first question is what will you be using the boat for and next where will you be sailing. Draft might become a key consideration if you are wanting to sail in shallow or very tidal areas. Angle of vanishing stability to my mind (as a lapsed Naval Architect) is largely irrelevant to beginner and 90% or more of leisure sailors. It is only relevant to storm survival and even then is a measure of static (no wind, no waves) stability where a storm is anything but. The shape of the graph of stability is much more important in an academic sense, but see comment above about being properly designed and built. Some boats will be more "tippy" than others but as Tranona alludes to, ballast and stability are not the only factors.
I wouldn't worry about ballast and stability. If you want to learn to race, get a racing boat with a larger draft and lower ballast ratio (but be kind to yourselves, don't get too extreme too early). If you want to sail and explore nice places around the coast get a boat that feels right, if you want to go around the world, you'd possibly want to get a smaller boat first anyway.
In short, all sailing boats other than dinghies will have some form of ballast. Unless you are thinking of designing your own boat, I guess you are looking at boats built from designs of experienced naval architects, by competent builders, probably regulated in some way. Almost all boats on the market will have more than adequate ballast and stability for their intended use. I suspect that as you progress through the journey to boat ownership, you will move ballast and draft further from the top your list of needs.
The first question is what will you be using the boat for and next where will you be sailing. Draft might become a key consideration if you are wanting to sail in shallow or very tidal areas. Angle of vanishing stability to my mind (as a lapsed Naval Architect) is largely irrelevant to beginner and 90% or more of leisure sailors. It is only relevant to storm survival and even then is a measure of static (no wind, no waves) stability where a storm is anything but. The shape of the graph of stability is much more important in an academic sense, but see comment above about being properly designed and built. Some boats will be more "tippy" than others but as Tranona alludes to, ballast and stability are not the only factors.
I wouldn't worry about ballast and stability. If you want to learn to race, get a racing boat with a larger draft and lower ballast ratio (but be kind to yourselves, don't get too extreme too early). If you want to sail and explore nice places around the coast get a boat that feels right, if you want to go around the world, you'd possibly want to get a smaller boat first anyway.
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doug748
Well-known member
It's often just convenience, they don't have the figures to hand or the inclination to find them.
Sailboatdata is pretty good. Just Google the boat you want eg: Moody 30 sailboatdata and it will lead you to the appropriate page with the details you want.
Yachtsnet also have an excellent archive page:
Archive boat data from Yachtsnet Ltd. online UK yacht brokers - yacht brokerage and boat sales
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jwilson
Well-known member
What are you expecting in terms of stability? Are you concerned about how much a boat normally heels under sail, or are you actually concerned about ultimate stability - the ability to self-right from inversion
For example many narrower beam older boats with high ballast figures - often 40-50% or more - heel a lot before setlling down to sail quite happily and fast well heeled over. These are often boats that if in really extreme weather - something you are most unlikely to go out sailing in - are the safest as they will usually recover rapidly even from a complete inversion.
By contrast many beamier modern cruising boats have quite low ballast ratios - typically 25-30% - but sail best fairly flat and are very difficult to get to heel much. Their stability comes from hull shape more than ballast. If however they do get inverted they may stay that way for a very long time.
Lynnwell
New member
Yes I'd quite like one that doesn't tip over thanks.
Boathook
Well-known member
Get a catamaran. They don't tip much but when they do tip too much they become stable again!
On a more serious note what type of sailing and areas do you want to sail in as already asked, and what is your experience ?
Tranona
Well-known member
Well, any ballasted keel yacht will give you that - they are self righting. However if you mean you prefer one that sails more upright (does not heel too much) then I am afraid just knowing the ballast ratio or even the stability curve will not be a reliable differentiator, for the reasons I explained earlier.
As others have said if you want helpful advice (if indeed you are looking for advice) in identifying suitable boats then saying what your intended use is, roughly what sort of size boat and budget will get sensible (although at time contradictory as there is never one ideal solution) advice.
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Lynnwell
New member
Looking about 30 ish foot, sail on the east coast, where I live is around the wash. I've never had a yacht for my first job was on a trawler and 3 years skippering a 50 footer
ProMariner
Active member
Is a subject that can fill many books, and even some of the guys who write the books have limited practical understanding.
Just make sure any boat you are thinking about sailing has Recreational Craft Directive (RCD) approval, and is rated for the kind of use you have planned. This means when it was designed and built, it passed basic stability and seaworthiness tests.
Also, like many trawlers, it may have been safe when it left the yard, but it has since been modified with items high up, that make it unsafe. There is a good reason not to have every toy you would wish, as fitting radar, davits, bimini, stern arch, etc etc etc could turn a good boat into a bad one.
As a rough rule of thumb, keeping the mast pointing up to the sky is the goal, but very few yachts seem to lose intact stability in use, it's not something you really have to think about when you leave the berth. As long as you have a waterproof well stowed and not overloaded boat under you, you should feel comfortable that the boat should be able to both resist and recover from a 90 degree knockdown.
The RYA publishes many good books covering subjects like stability, worth a read.
Just make sure any boat you are thinking about sailing has Recreational Craft Directive (RCD) approval, and is rated for the kind of use you have planned. This means when it was designed and built, it passed basic stability and seaworthiness tests.
Also, like many trawlers, it may have been safe when it left the yard, but it has since been modified with items high up, that make it unsafe. There is a good reason not to have every toy you would wish, as fitting radar, davits, bimini, stern arch, etc etc etc could turn a good boat into a bad one.
As a rough rule of thumb, keeping the mast pointing up to the sky is the goal, but very few yachts seem to lose intact stability in use, it's not something you really have to think about when you leave the berth. As long as you have a waterproof well stowed and not overloaded boat under you, you should feel comfortable that the boat should be able to both resist and recover from a 90 degree knockdown.
The RYA publishes many good books covering subjects like stability, worth a read.
boomerangben
Well-known member
You have a fascinating dilemma I think and maybe you are thinking about shallow water, small draft and adequate stability? I have sailed across the Wash only once in a 16’ dinghy (Wayfarer) from Boston to Thornham Creek to the east of Hunstanton. It was 35 years ago but remember the sand banks!
I suppose the first thing would be where are you planning to keep the boat and what is the minimum water depth. You could go for a bilge keel boat with twin ballasted keels so you get similar righting moment with shallower draft than the fin (single) keel alternate. They can dry out without falling over but might not sail quite as well although that’s debated at length for some types of boat. There’s also lift keel yachts like the Southerly range amongst others whose ballast is part in the keel, part in a big steel plate making the part of the hull around the keel.
Again all are self righting. The amount it tips depends on the amount of wind and the amount of sail you have up, one of which you can control the other is what weather forecasts are for. I apologise if all the above is sucking eggs so ignore if appropriate ?
I think a good strong engine might be on the wish list too?
I suppose the first thing would be where are you planning to keep the boat and what is the minimum water depth. You could go for a bilge keel boat with twin ballasted keels so you get similar righting moment with shallower draft than the fin (single) keel alternate. They can dry out without falling over but might not sail quite as well although that’s debated at length for some types of boat. There’s also lift keel yachts like the Southerly range amongst others whose ballast is part in the keel, part in a big steel plate making the part of the hull around the keel.
Again all are self righting. The amount it tips depends on the amount of wind and the amount of sail you have up, one of which you can control the other is what weather forecasts are for. I apologise if all the above is sucking eggs so ignore if appropriate ?
I think a good strong engine might be on the wish list too?
Laminar Flow
Well-known member
Tranona summed it up nicely and as he and others have pointed out: stability is a complex matter.
Used in their prescribed context, most boats currently available are safe enough.
It pays to remember that wind (alone) does not capsize a boat, waves do. A thirty footer could potentially capsize in a ten foot breaking sea.
In this respect size does matter.
The two factors that are most likely to contribute to a capsize are light weight and great beam, even if the latter, at first glance, may seem counterintuitive.
Used in their prescribed context, most boats currently available are safe enough.
It pays to remember that wind (alone) does not capsize a boat, waves do. A thirty footer could potentially capsize in a ten foot breaking sea.
In this respect size does matter.
The two factors that are most likely to contribute to a capsize are light weight and great beam, even if the latter, at first glance, may seem counterintuitive.
jimi
Well-known member
Maybe I'm biased but Sailboatdata classes the Moody S38 as a coastal cruiser and reckons its slower than my old Beneteau 331. I'm not convinced by either analysis!!
My suspicion is that stability figures make people worried when in reality they are only relevant in extreme conditions which few people ever face.
Tranona
Well-known member
Look at what sort of boats other people use in your area. as already suggested shallower draft boats, probably twin keel may be better to maximise your time afloat and use a drying mooring.
Making an assumption that your budget is between £12-25k then the obvious choices will come from 4 or 5 of the bigger UK builders from the 1980s, most of which offered the choice of fin or twin keels. Examples are Moody (27, 28, 29, 30) Westerly (Merlin, Griffin, Konsort) Sadler (29, 32) Hunter (27, 30, 31) Jaguar 27. These are available in some numbers, although you may have to travel to actually view and buy one. Below that budget there are many more makes and models from the 1970s.
When buying in this price/age range the priority is condition, condition, condition. None of these are "bad" designs but given their age they are unlikely to be in perfect condition so look to spend anything up to 20% on repairs and upgrade. Pay particular attention to engines, sails and rigs as replacements of these cost an amount that is disproportional to the value of the boat. Fortunately many will have a replacement engine, but a new suit of sails will cost £4-5k. Many people selling in this sector of the market are doing so because they can see expense looming, and/or are retiring so may not have spent much on the boat in recent years.
Look at as many boats as you can to get a feel for what you like and don't like, particularly down below as this has a big influence on buyers' choice, particularly if family are involved.
Lynnwell
New member
Thanks for all your help, much appreciated
doug748
Well-known member
The figures can be wrong, maybe guessed or just mangled in the mists of time, I agree, it always pays to double check.
Sail areas are frequently hugely misleading because, traditionally, the genoa area was measured as equalling the fore triangle area. Manufacturers, understandably, would quote the true area including overlap. Similar with mainsail roach, it's often unclear which convention is being used.
As you say, stability figures are part of the whole and of narrow value on their own but they do tell you something about a boat's ability to stand up to her canvas.
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