Ballast ratio help please

NUTMEG

NUTMEG

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www.theblindsailor.co.uk
My CW 28' ketch has a ballast ratio of 33.3% and a white sail area of 400 sq ft. The ballast ratio of all the other CW's is higher, in the case of the CW25 a lot higher at 49.6%. The 28's sail area is also higher then all the CW's apart from the CW34 which carries 500sq ft. but is of course a lot bigger.

So am I right in thinking the 28 is going to be a bit more tender under sail but should be the best sailor of the marque?

In laymans terms for the hard of thinking what practical effect does ballast ratio have? Is it simply that higher figures mean she will stand up to her sails better and/or does it have an influence on her ability to recover from the unlikely effect of a knock down? The 28 has two tons of ballast in her hull plus a thumping great VP as well as two fuel tanks carried very low down.

What I really want to know I suppose is is she a good sea boat for theoretical off shore passage making, I am thinking east coast to Iceland at some indetermined point in the future. We all need dreams after all.

Steve
 
Ballast ratio is only one part of the whole stiffness/self righting question.
A keel boat initially has stiffness provided by the shape of the hull particularly the chines area and the total weight. (form stability) So a deep vee shaped hull might have little stiffnes initially despite a heavy keel. A catmaran on the other hand has no keel weight but has a huge stiffness due to wide spaced hulls. Equating somewhat to a hard chined monohull.
In other words intially the boat tries to lift itself up onto the chine area of floatation while the total mass tries to set the boat down again flat on the bottom.
(the chine being the part of the hull where the vertical sides turn to hoizontal bottom. A hard chine is like some power boats where there is an almost rightangled turn.)
Nowe if the boat tips over further than around 45 degrees the mass of the keel starts to try to right the boat like a pendulum. At 90 degrees heel the form stability has no effect but the mass of the keel (centre of gravity of the boat) has maximnum effect. Here the ballast ratio gives some indication of self righting ability but this till depends on the centre of gravity of the ballast ie high or low.
So nothing is simple. Your boat could be stiff or tender ,good at slef righting or not. The ballast ration will not tell you. Only sailing/racing it will tell. good luck olewill
 
I think that you can only get a meaningful assessment if you have figures of how high is the CE, how deep is the ballast and how beamy the boat is.

My 32-ft boat has two tons of lead at the very bottom of a fin that draws 1,80 metres. Just the genoa alone is 35square metres. She is nowhere near tender.
 
S19 - are you sure of that figure ?

http://sailboatdata.com/viewrecord.asp?class_id=6843

gives a shade under 40% which is more in keeping with the CW family.


A large ballast ratio (ignoring form stability) means that the boat will be stiffer and stand up the wind more than a low ballast ratio. However, high BR affects the roll characteristics, and will be 'snappier' in returning from a roll (again ignoring form stability).

I see no reason why your CW should not take you safely to Iceland - albeit a bit slowly. It was my plan to return to my ancestral home in 2008 in my 34, but SWMBO's illness sadly put an end to that.


Keep the dream going :)



EDIT BIG OOPS ! That URL is for the 23. I'll look up the 28.


EDIT2. Can't find anything just now. Sorry. Have you checked with Mike on Caer Urfa ?
 
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PuffTheMagicDragon said:
I think that you can only get a meaningful assessment if you have figures of how high is the CE, how deep is the ballast and how beamy the boat is..
Click to expand...

I couldn't agree more as a lot of fin keelers carry most of their ballast up in the hull where it doesn't have much effect. In contrast a long keeled yacht can have the ballast well below where it has the most effect.
 
coopec said:
I couldn't agree more as a lot of fin keelers carry most of their ballast up in the hull where it doesn't have much effect. In contrast a long keeled yacht can have the ballast well below where it has the most effect.
Click to expand...

:confused: Most of the boats designed in the last 20 years or so carry the ballast as a 'bulb' at the bottom of the keel. For example as below;

xp%2033_demoboat-0006.jpg
 
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Have you checked with Mike on Caer Urfa ?[/QUOTE]

Thanks for taking the trouble looking up figures. The data I have is from Mikes book on Colvic Watsons.
Just,seems odd that the 28 carries more canvas yet has the lowest ballast ratio. Clearly something I do not understand.

Thanks for all the replys chaps. Perhaps the 28 has a different hull shape. She did look surprisingly sleek when we dried her out for a scrub. Not as tubby as I had imagined.
 
Brent Goose said:
:confused: Most of the boats designed in the last 20 years or so carry the ballast as a 'bulb' at the bottom of the keel. For example as below;



Sorry!! I thought the CW28 was an old design cruising boat (certainly not designed in the last 20 years anyway). Now I am confused:confused:
Click to expand...
 
We had a ketch and because the sail plan is split the main mast is lower than an equivalent size sloop thus the heeling is less. The boat was a heavy displacement and never got the toe rail in the water.
 
Brent Goose said:
Indeed, my understanding of post #5 was that many fin keeled boats had thier ballast high up in the keel when compared with long keeled equiverlents which I didn't think was generally the case any more.
Click to expand...

Brent I can see what you are getting at now. I was thinking of the vintage yachts. I can go along with bulb ballast but I think swing keels and water ballast was the wrong way to go .
 
Yes but will my CW capsize from a knockdown or bounce up again (assuming doors and hatches are shut) and should she be considered an offshore cruiser or a solid coastal boat? Just how capable a sea boat is she?

Stev
 
Brent Goose said:
Indeed, my understanding of post #5 was that many fin keeled boats had thier ballast high up in the keel when compared with long keeled equiverlents which I didn't think was generally the case any more.
Click to expand...

Usually the other way around but, like all catch-all statements, has more exceptions to the rule than followers.
For example my fin keeler has the centroid of all its 40% ballast 1.78m below the WL.
 
Sophie19 said:
Yes but will my CW capsize from a knockdown or bounce up again (assuming doors and hatches are shut) and should she be considered an offshore cruiser or a solid coastal boat? Just how capable a sea boat is she?

Stev
Click to expand...
To get an good answer you have some options
Find the staibility (GZ) curve for your boat
Calculate the above

Do a stability test like this
http://www.dandwboatworks.com/2007_0605_094926AA.JPG
 
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Someone will be along with some practical knowledge of the type, soon. Meanwhile.

These boats, developed from rugged inshore types, are not renowned for going over even as unballasted hulls, in motor boat form. In the event of a knockdown the huge buoyancy of the pilot house would ensure it came right up, provided it was not breached. This is the rub. Pilot house side doors and opening ports are the key reason why some exceptional and monumental boats find themselves with Cat B status:

http://www.nauticat.com/yachts/nauticat_331

Interesting to note that the ballast ratio in this example is below yours.

So on a jaunt to Iceland keep your door shut :-), Also I would think about poor weather tactics. Yotty stuff may not apply, it may be as well to think about fishing boat practice. Do they call it drudging? steaming slowly at 45 deg to the weather?

I found this quite interesting:

http://www.maritimenz.govt.nz/Publi...ing-safety/Vessel-Stability-Guidelines-A4.pdf
 
Doug748, thanks for that, very interesting reading. But all that talk of broaching and capsize is unnerving the missus!

Capsizing the boat just to see what happens might raise a few eyebrows in the yard, doubt very much that we could find a way of doing so anyway. Search as I may, I can find no published data or gz curves for these boats.
 
Sophie19 said:
Yes but will my CW capsize from a knockdown or bounce up again (assuming doors and hatches are shut) and should she be considered an offshore cruiser or a solid coastal boat? Just how capable a sea boat is she?

Stev
Click to expand...


Hi Steve

First lets clear up a few points also bearing in mind I personally have sailed quite a few CW 28'-6" and they certainly are no less a seaworthy CW then any of the others in the range.

The displacement of all Colvic Watsons can vary very much from boat to boat due to the weight of the internal fit out and particularly the engine weight due to the size/type fitted, also if the boat has a 'keel shoe' and heavy skeg construction this can make a huge difference.

Sails and sail area can again make a huge difference to the boats performance and handling, most CW 28'-6" are 'ketch rigged' and sail very well albeit I personally prefered to sail without the mizzen up,(but sure do when weather is poor) however I have also sailed a CW 28'-6" 'sloop rigged' and due to the Genoa and extra long boom fitted would run rings around the Ketch rigged boats in regards to knots achieved.

Coming back to the ballast ratio of 33.3% first you should remember there is/was a Mk 1 and a Mk II CW 28'-6" and the Mk 1 are heavier than the Mk II due to 'usually' an all wood wheelhouse construction and sometimes wood bulwarks and almost all have big heavy 4 cylinder engines.

Also I would not read to much into 33.3% and I have yet to find a CW 28'-6" weighing 6 tons and are more like 7 to 8 tons, I find most CW 25'-6" weigh more like up towards 6 ton rather than 4 ton and my own CW 23'-6" I know for sure weighs 4.8 tons.

Another thing that changes the ballast ratio was the 'type of ballast',some early CW's have cast iron/concrete ballast of 65/35% proportions. some are all shot, others pig iron one I inspected even had some railway lines fitted in it and most have encapsulated ballast !!

As for a knockdown few boats are unsinkable, but I have had my own CW go over in poor weather due to the fact I made the dreaded mistake of having too much sail up and did not reef soon enough, she went over so much water was coming in through the coachroof side windows an experience I do not wish to repeat! so again I would have no fears to their seakeeping capabilities and in poor weather a Colvic Watson is one boat I sure want to be in.

Have no fear to your boats capabilities and they certainly are an offshore motor sailer and they are a great boat and sail very well in all weather.

Hope this might help

Regards
Mike
 
Thanks Mike, and everyone else for your comprehensive replies. I mentioned Iceland, and that has and remains one of my ambitions. In truth however, this thread was prompted by SWMBO who feels that a trip under engine in a dead calm up the Blackwater would be stressing the boat beyond design limits. and risking certain foundering with loss of all crew.

I thought if I could find a definitive measure of Rhoda Roses seaworthiness I might go some small way towards putting wife's mind at rest. Worth a try.

Cheers

Steve
 
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