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Old 21-04-2014, 11:13   #1
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bal./disp. ratio

Just learning here...
Whats the ideal bal./disp. % for blue water cruising??
Whats too little and whats too much?
I know the westsail 32 has 35%, and the Tartan 3400 has 55%!
Would that make is super stiff and uncomfortable? or would it be good?
So my question is if you were going to make a blue water passage or circumnavigate what would you want your bal./disp. % to be?

Thanks
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Old 21-04-2014, 11:36   #2
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Re: bal./disp. ratio

By itself it doesn't mean much if anything. A boat with the ballast hung close to the hull needs a lot more for the same righting moment as a boat with the ballast hung from a deep keel bulb.
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Old 21-04-2014, 11:51   #3
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Re: bal./disp. ratio

The amount of ballast will vary widely depending on the type and use of the yacht.

Here is a good article and general guide by Ted Brewer on this subject.
Good Old Boat - Is your boat stable? article
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Old 21-04-2014, 11:52   #4
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Re: bal./disp. ratio

OK thanks!
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Old 21-04-2014, 12:04   #5
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Re: bal./disp. ratio

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Originally Posted by youngson View Post

So my question is if you were going to make a blue water passage or circumnavigate what would you want your bal./disp. % to be?

Thanks
Check the data on this Contessa 32. Without going into a detailed explanation maybe just looking at the overall specs will help. (keel size, depth, length, boat lwl, mast ht, sail area, etc)

This small boat has sailed many a bluewater voyage and also has an angle of vanishing stability (AVS) of like 157. It will handle a knockdown quite well and some have rotated 360 degrees.

See story of Contessa 32 Assent in the Fastnet '79 race manned by 4 sailors 18-25 years of age.


CONTESSA 32 sailboat specifications and details on sailboatdata.com


Fastnet 79 - The winner's story | Yachting World

And John Kretschmer also sailed one around Cape Horn:

http://www.sailnet.com/forums/buying...ats-story.html

Jessica Watson circumnavigated on an S&S 34:

http://sailboatdata.com/viewrecord.asp?class_id=4458

These two boats have some similarities and both are extremely well built.
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Old 21-04-2014, 12:31   #6
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Re: bal./disp. ratio

Yah i really like them Contessas thanks!
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Old 21-04-2014, 13:12   #7
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Re: bal./disp. ratio

Theres a Sail Calculator called Carls Sail Calculator that may be of help.

I am hosting it for a bit so have a look and book mark it.

Sail Calculator Statistics of over 2,800 sail boats
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Old 21-04-2014, 13:22   #8
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Re: bal./disp. ratio

Not sure what it is but it seems like this boat is calling your name;
YOUNG SUN 35 sailboat specifications and details on sailboatdata.com

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Old 21-04-2014, 19:22   #9
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Re: bal./disp. ratio

The ballast is used to lower the boat CG.

There are other ways of lowering the CG namely lowering the ballast and the ballast CG: Bigger draft, bulbed keel, torpedo keel. Even when a lower draft is required lifting keels or ballasted swing keels can be used. The B/D ratio needed depend on these factors and only on boats with similar type of keels and the same draft the B/D ratio is relevant in what regards the boat CG.

A boat can have a considerably bigger B/D ratio and have a higher CG than another one with a all the above factors maximized. Instead of looking to the B/D ratio you should look to the AVS and to the stability curve instead.

Maybe this helps:

Interesting Sailboats: STABILITY - 1 : MISLEADING INFORMATION ABOUT STABILITY

Interesting Sailboats: STABILITY 1: MISLEADING BOATS - Hanse 345 / HR 342

...
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Old 22-04-2014, 00:34   #10
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Re: bal./disp. ratio

Quote:
Originally Posted by youngson View Post
Just learning here...
Whats the ideal bal./disp. % for blue water cruising??
Whats too little and whats too much?
I know the westsail 32 has 35%, and the Tartan 3400 has 55%!
Would that make is super stiff and uncomfortable? or would it be good?
So my question is if you were going to make a blue water passage or circumnavigate what would you want your bal./disp. % to be?

Thanks
Be careful what you read. Sailboat Data has a few mistakes in it. The Tartan 3400 has a ballast ratio of 32% for the fin keel, just over 33% for the beavertail, and just under 34% for the keel/centerboard model.
Tartan Model 3400 Sailboat Information | Tartan

Ballast ratio is but one factor of stability. Where the ballast is and what it is composed of have an effect as well. For example the Pogo 10.50 looks from the numbers to be under ballasted at 30%, but its ballast is in a bulb with a depth of over 9'. As far as material, lead is more concentrated for its weight than iron so all else being equal a boat with lead ballast will have more stability than the one with iron.

And then there is hull form.....
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Old 22-04-2014, 20:19   #11
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Re: bal./disp. ratio

thanks for the input everyone!
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Old 23-04-2014, 06:49   #12
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Re: bal./disp. ratio

As it was explained here, the ballast/displacement ratio is rather meaningless in abstraction of other factors influencing the stability.

If You really want to compare a stability factors for two given boats You need really to compare two sets of curves: G/Z curve and righting moment curve of one boat against respective curves for another boat.

Here and also here You can find explanations made easy
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Old 23-04-2014, 17:10   #13
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Re: bal./disp. ratio

Thanks ill check it out
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