How reliable an idicator is the ballast ratio of a boat?

[magicol]

I am still looking for my first yacht; thanks to everyone for the earlier advice. I have been pointed in the direction of a boat's ballast ratio to determine how seaworthy and comfortable it will be. With more boats ashore and the keels visible, my confusion is growing. Take two boats, a Moody 336 and a Beneteau 34; the traditionalists advise going for the Moody and their respective ballast ratios would confirm this. But ashore the Moody clearly has a tapered keel with the weight seemingly higher in the water whilst the Beneteau has a significant bulb nearly two meters below the water. I am no marine architect but should the ballast ratio not take the design of the keel into account? Or are there other factors involved? And in any case, am I right to be concerned as I am never going to take my boat on an ocean cruise.

 

[aluijten]

A very fair point. Ideally you should know the distance between the center of gravity and the waterline. But the AVS (angle of vanishing stability) is also a good indicator.
Today you see more and more bulb keels manufactured. The real hip boats even carry a torpedo-keel. The latter is (IMHO) not great for cruisers as it could catch a lot more underwater crap than you would find enjoyable.

 

[Wansworth]

The ballast ratio gives some idea of how the boat will behave.Too higher Br will make the boat stiff and quick to get back to upright whilst a low Br will allow the boat to be easier.and more comfortable.A cruiser might have say 36 per cent Br and an out right racer 50 per cent.Overtime what with loading stuff on and not taking stuff off and water absorption the Br will be pretty meaning less.

 

[VicS]

The ballast ratio gives some idea of how the boat will behave.Too higher Br will make the boat stiff and quick to get back to upright whilst a low Br will allow the boat to be easier.and more comfortable.A cruiser might have say 36 per cent Br and an out right racer 50 per cent.Overtime what with loading stuff on and not taking stuff off and water absorption the Br will be pretty meaning less.

havent you got this ass-about-face

 

[doug748]

I am still looking for my first yacht; thanks to everyone for the earlier advice. I have been pointed in the direction of a boat's ballast ratio to determine how seaworthy and comfortable it will be. With more boats ashore and the keels visible, my confusion is growing. Take two boats, a Moody 336 and a Beneteau 34; the traditionalists advise going for the Moody and their respective ballast ratios would confirm this. But ashore the Moody clearly has a tapered keel with the weight seemingly higher in the water whilst the Beneteau has a significant bulb nearly two meters below the water. I am no marine architect but should the ballast ratio not take the design of the keel into account? Or are there other factors involved? And in any case, am I right to be concerned as I am never going to take my boat on an ocean cruise.

A great many people would give their teeth and one testicle for either of the boats mentioned. It's not worth worrying about, buy the boat that catches your eye, in the best condition you can find.

Do as much sailing as you can first, so you have an idea what the abstracted figures mean on the water.

 

[Wansworth]

havent you got this ass-about-face

.a.err my cruising boat had 33 per cent Br......... whilst a racer has much more..I'll check in my yacht design tome....tomorrow

 

[anoccasionalyachtsman]

You may not be a marine architect, but you're certainly thinking like one! A heavy shoal draft keel may well have a higher CofG than a lighter bulbed keel, and if the differences are large enough the lighter bulb will be more effective. Short of doing all the calculations yourself, the best bet is to find the published stability curves and compare them.

 

[Tranona]

The ballast ratio is only a good indicator of how much of the boat's displacement is in the form of ballast. You have highlighted one of the reasons for high ballast ratios in older designs. Keels tended to be wide at the top and tapered down so to achieve the same righting moment they had to be heavier. As you say the big difference with newer designs is keels with the majority of the weight at the bottom and often overall deeper draft. The older keel shapes were influenced by the IOR which penalise stability so greater weight was needed to provide sail carrying capacity.

The other major change - but not so obvious when using a 336 as a comparison is the greater form stability of newer designs coming from wider beam and flatter bilges. So you can achieve similar stability curves with lower ballast ratios. It is rare to find, even in the most conservative, heavier displacement designs, ballast ratios over 40%. for example the latest HR designs have ratios of 39% or so compared with older designs that were in the mid 40s.

Lighter displacement boats tend to have ratios either side of 30% but as you have observed deeper bulbed or even T keels are the norm. One possible benefit of heavier keels is that the boats are often less lively in a seaway and therefore potentially more comfortable. However, this is as much to do with the shape of the underwater body and many modern designs have a comfortable motion despite the lighter weight keels.

So, as already suggested, choose a boat on its merits and suitability for the type of sailing you propose.

 

[ex-Gladys]

There's far more to comfort than BR... If you sail in heavy chop (Thames Estuary) a modern boat with flat sections forward will slam and stop, whereas a boat with finer sections may slice through better... All boats are a compromise...

 

[geem]

The ballast ratio gives some idea of how the boat will behave.Too higher Br will make the boat stiff and quick to get back to upright whilst a low Br will allow the boat to be easier.and more comfortable.A cruiser might have say 36 per cent Br and an out right racer 50 per cent.Overtime what with loading stuff on and not taking stuff off and water absorption the Br will be pretty meaning less.

its not a simple as that. My own yacht has a ballast ration of 41%. She also has a large rig and large sail area. The heavy lead keel allows us to carry lots of canvas so a yacht with high ballast ratio can carry more sail. This makes the yacht powerful. She can punch through seas in bumpy conditions with her weight and also has the power in her sails to drive her hard. It makes her comfortable, fast and powerful. You also need to consider the keel material. Lead is 30% heavier than iron so a lead keel can be smaller for the same ballast. A lead keel of the same weight and CofG can therefore be 30% smaller. our yacht has substantial masts. the weight aloft actually gives her a slow motion when combined with the 6 ton in the keel.

 

[KellysEye]

> Take two boats, a Moody 336 and a Beneteau 34

It depends what type of sailing you want to do. Ifyou sail inshore in fine weather then the Beneteau is fine. If you want to go over to France or elsewhere offshore the Moody would be better. To put it into context for long distance sailing we bought a heavy displacement long keel with cutaway forefoot steel ketch. It didn't heel much and we never got the toe rail in, it would immediately stand up after a strong gust, it doesn't broach, doesn't turn up to wind in a gust or surf. We have done all of of those in chartered Benenteaus but sailing in strong winds hence avoid them if buying the Beneteau.

 

[30boat]

Ballast ratio is a complicated thing.You can have a high BR with a high center of gravity ,the opposite and all sorts of permutations. A very deep center of gravity will make the boat's motion quick and unpleasant but will provide a high righting moment.
My Fulmar for instance has a 42% BR but a tapered iron keel.I believe this to be a reasonable compromise.When I was knocked over in a collision with a ship the mast went well underwater with the stb ports being completely immersed and the speed with which she came back upright was amazing.

 

[Neil]

Interesting, the Sadler 25 was designed to have greater form stability (as compared to the the Contessa 26), but yet still has a 47% BR. Combine the two attributes and it should give a stable boat indeed. When very hard pressed (both arms pulling the tiller), it still will round up gently when the grip on the rudder gives way. Compare that to a Ben 37.7 first which has to have the main dumped at the first sign of ardour.

 

[rob2]

All the posts so far have, in their way, pointed to the fact that the ballast ratio only tells you something about a boat's characteristics when considered against other factors. A boat with form stability can be made lighter and therefore faster with a lower BR, but runs the risk of slamming more in rough conditions. A boat with a narrow waterline and full keel needs a higher BR for its stanility, but is more directionally stable and will make to windward through a steep chop hardly noticing the wave (though the crew might ). In terms of righting moment a diagram of the curve puts all these factors together, though even that is not a complete picture.

A long-keeler will maintain steerage at almost any speed, but as the chord of the keel reduces with each more "modern" design the keel can stall at an increasing speed. Some pure racing designs have such a narrow chord to the keel with all the weight concentrated in the bulb that they are totally wayward at low speeds and a nightmare to manouevre. These trends are now showing in some models aimed at the cruiser market. I do't see this as a suitable attribute, but there will be younger, fitter crews who are not really cruising, but playing at racing (fully crewed) who will be delighted.

Statistics such as BR can give guidance when comparing similar designs, but to select a boat you can't beat sailing in a variety of design types to find what suits you and your style of sailing.

Rob.

P.S. Sail balance and rudder balance are a separate issue!

 

[dunedin]

Magicol - your assessment and thinking looks sound. Ballast ratio part of the story, but keel type and shape also important, as you had deduced.

Be aware that some "traditionalists" may be knowledgeable - others are just biased opinions of folks who think old is good and new is bad. They probably still drive Morris Marinas

 

[Birdseye]

I am still looking for my first yacht; thanks to everyone for the earlier advice. I have been pointed in the direction of a boat's ballast ratio to determine how seaworthy and comfortable it will be. With more boats ashore and the keels visible, my confusion is growing. Take two boats, a Moody 336 and a Beneteau 34; the traditionalists advise going for the Moody and their respective ballast ratios would confirm this. But ashore the Moody clearly has a tapered keel with the weight seemingly higher in the water whilst the Beneteau has a significant bulb nearly two meters below the water. I am no marine architect but should the ballast ratio not take the design of the keel into account? Or are there other factors involved? And in any case, am I right to be concerned as I am never going to take my boat on an ocean cruise.

Its a far more complicated subject than just an issue of ballast ratio or even righting moment which is the factor you are highlighting with the comparison you make. The US coastguard did a detailed tank study of stability and the issue they highlighted was that of energy transfer from the waves rather than just the heeling moment from wund pressure on sails. So things like freeboard come into the equation. As does the vessel weight - better a 15 tonne Bav than a 10 tonne HR. And then there is the issue of keel depth and grip on the water - lot to be said for a drop keel or even a bilge compared to a deep fin.

Forget the ocean cruise bit. Apart from anything else bad weather in the open sea can often be less dangerous than in shallow water over a bar for example.

Instead focus on the very low level of deaths in sailing. You are far safer on your boat than you ever will be in your car in traffic.

I had a Moody 336. Never really got on with it but that was personal taste. In other respects it was a damn good boat, a decent sea boat and not at all bad round the cans.

 

[geem]

Magicol - your assessment and thinking looks sound. Ballast ratio part of the story, but keel type and shape also important, as you had deduced.

Be aware that some "traditionalists" may be knowledgeable - others are just biased opinions of folks who think old is good and new is bad. They probably still drive Morris Marinas

There are good new boats and bad new boats. There are good old boats and bad old boats. Age is not the issue. Boat construction has not moved on dramatically in 30 years but weather forecasting and the way people use their boats has. Boats have got bigger as people demand greater accommodation. The accommodation influences the design of many modern boats such that I would choose a similar sized older boat for ocean crossings as they were conceived in an era when getting two double aft cabins in the stern wasn't the priority. It's personal choice and it's my choice. It doesn't make it right for everybody.

 

[doug748]

There are good new boats and bad new boats. There are good old boats and bad old boats. Age is not the issue. Boat construction has not moved on dramatically in 30 years but weather forecasting and the way people use their boats has. ...

They all have their strengths, as you say.

The OP seems to have dropped off the radar, shame, it is always interesting to follow up boat buying decisions.

 

[magicol]

Thank you everyone. This thread has been really helpful. I think I have learnt that any one factor in a boat's makeup is unlikely to tell the whole story. For me, I don't want a project; I want to spend my retirement sailing not maintaining the boat. I also need some comfort for my crew, that is my wife, and I would like something that as a former dinghy sailor will provide reasonable performance. I think, inevitably and on balance, these factors (and not forgetting cost) will direct me to one of the modern production boats. The search continues and I will, of course, post the outcome however long this takes! Thanks again, everyone.

 

[ex-Gladys]

Thank you everyone. This thread has been really helpful. I think I have learnt that any one factor in a boat's makeup is unlikely to tell the whole story. For me, I don't want a project; I want to spend my retirement sailing not maintaining the boat. I also need some comfort for my crew, that is my wife, and I would like something that as a former dinghy sailor will provide reasonable performance. I think, inevitably and on balance, these factors (and not forgetting cost) will direct me to one of the modern production boats. The search continues and I will, of course, post the outcome however long this takes! Thanks again, everyone.

Don't think that having a "modern production boat" will enable you to sail any more than with a more seasoned boat... Any boat purchased will need to be personalised to meet your requirements, poor fitting out may need rectification beyond warranty term....