Hi, I am trying to get a rough estimate of the weight of a keel in a sailing yacht. Is it correct to get an initial value by taking the weight of the keel as a percentage between 35% and 45% of the total displacement?
Thank you
Thank you
weight of a keel related to displacement
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The Ballast/Displacement ratio is one indicator of stability, but the center of gravity, center of buoyancy Vs heel angle, and total weight are needed for a complete picture. Values range from a low of 25% to a maximum of 50%. The template value of 40% indicates more emphasis on gravity controlled stability rather than form stability.
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Like so many questions... it depends.
Ballast ratios between 40-50% were pretty common in the 70s and 80s.. as designs evolved, form stability went up, winged and T keels came along and many designs rely less on pure weight for ballast. Many modern boats will be in the 30% range, but still be relatively 'stiff'.
On the other end of the scale the old 12M America's Cup class may have been approaching or exceeding 70% ballast ratios...
So... what boat(s) are we talking about?
Ballast ratios between 40-50% were pretty common in the 70s and 80s.. as designs evolved, form stability went up, winged and T keels came along and many designs rely less on pure weight for ballast. Many modern boats will be in the 30% range, but still be relatively 'stiff'.
On the other end of the scale the old 12M America's Cup class may have been approaching or exceeding 70% ballast ratios...
So... what boat(s) are we talking about?
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Can't you just put in the boat your looking at on the query line? It should come up with a/the model! from there you would be able to get your info no? Also try sailboat data. It is usually a fairly accurate sight! If your trying to learn how to figure out your self, disregard previous!
Thank you for your replies.
This is not an existing ship. I am a student and I am carrying out some calculations so everything is on paper only. The boat I am considering is a 30metres long cruising sailing vessel with an approximate displacement of 150tonnes. Basically I would like to know what percentage of the total displacement is given to the keel (and possibly the mast).
This is not an existing ship. I am a student and I am carrying out some calculations so everything is on paper only. The boat I am considering is a 30metres long cruising sailing vessel with an approximate displacement of 150tonnes. Basically I would like to know what percentage of the total displacement is given to the keel (and possibly the mast).
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Modern design? Boats this big rarely have 40% of their weight in keel. More like 20 to 30%.
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First and foremost, you have to differentiate between the weight of the KEEL and the weight of the BALLAST. There are plenty of boats where the KEEL weighs a much smaller percentage of the total displacement than the figures mentioned above. For an example, take a look at this boat...
PEARSON 40 sailboat specifications and details on sailboatdata.com
It has almost no keel other than the centerboard. The ballast is carried low in the hull. The keel is also weighted, but the majority of the ballast is NOT in the keel. In fact, other than the centerboard, there really is no keel. Or, another way of saying it is that the centerboard IS the keel. And the centerboard is not (relatively speaking) all that heavy.
As for the mast, that is always going to be a very small percentage of the total displacement.
Frankly, I have to wonder what it is that you are trying to do, and/or how you think you can use the information that you have asked for.
PEARSON 40 sailboat specifications and details on sailboatdata.com
It has almost no keel other than the centerboard. The ballast is carried low in the hull. The keel is also weighted, but the majority of the ballast is NOT in the keel. In fact, other than the centerboard, there really is no keel. Or, another way of saying it is that the centerboard IS the keel. And the centerboard is not (relatively speaking) all that heavy.
As for the mast, that is always going to be a very small percentage of the total displacement.
Frankly, I have to wonder what it is that you are trying to do, and/or how you think you can use the information that you have asked for.
Sounds like your boat is massively overweight. A modern 30m sailboats is more likely to fall in the 100ton range. With about 25% in the keel. But a boat this size almost certainly has a bulb, so bulb size is going to be largely determined by draft, and draft is going to be determined largely by the owners cruising preferences.
For a detailed look at a modern 30m boat Feature Superyacht: 30m Sailing yacht Antares III by Yachting Developments ? Luxury Yacht Charter & Superyacht News
For a detailed look at a modern 30m boat Feature Superyacht: 30m Sailing yacht Antares III by Yachting Developments ? Luxury Yacht Charter & Superyacht News
Keepin mind the 99 tons is lightship weight. Just in fuel she will ship an additional 9 tons and water is an additional ton. Outfitted weight could be substantially higher.From Stumble's link.. A 28% ballast ratio on a modern 100+footer. Looks like Kriss nailed it!
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bob perry's book goes into detail over how the ratios interact
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