Can someone explain boat weights?

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dewent

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Thinking of upgrading from my Bavaria to something more comfortable in rough conditions. I was of the opinion that perhaps a heavier boat of similar size might be kinder for SWMBO in a bit of a blow.

Can someone explain how to understand boat weights? Displacement and ballast, do you add them together for total weight?
 
dewent said:
Thinking of upgrading from my Bavaria to something more comfortable in rough conditions. I was of the opinion that perhaps a heavier boat of similar size might be kinder for SWMBO in a bit of a blow.

Can someone explain how to understand boat weights? Displacement and ballast, do you add them together for total weight?
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get a lead keel yacht, the weight is low down where its more effective ;)
 
Displacement is the total weight of the boat,The boat displaces x tones of seawater that weighs errr x.The ballast is part of the weight expressed as a % of total weight,A good seaworthy cruising boat may have about 35% ballast.Its a very complex business and not just weight,form also plays a part in seakindlyness.
 
But other things lead to a seakindly boat as well. The ballast could do to be low down, lots of ballast in the bilge rather than in the keel isn't as helpful. The hull shape and keel shape are important.
 
mogy said:
Displacement is the total weight of the boat,The boat displaces x tones of seawater that weighs errr x.The ballast is part of the weight expressed as a % of total weight,A good seaworthy cruising boat may have about 35% ballast.Its a very complex business and not just weight,form also plays a part in seakindlyness.
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Very true; it's unfortunate that the slimmer the boat the less it is likely to "slam" when going to windward in waves. Because the less interior volume it will have, and the less "form stability". This means it will need a higher ballast ratio to get the same "stiffness".

Catamarans (or trimarans) are the extreme in width!

Mike.
 
mogy said:
Displacement is the total weight of the boat,The boat displaces x tones of seawater that weighs errr x.The ballast is part of the weight expressed as a % of total weight,A good seaworthy cruising boat may have about 35% ballast.Its a very complex business and not just weight,form also plays a part in seakindlyness.
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The 35% is nonsense. A boat with 35% but in the bilges would be less stiff than one with 20% in a torpedo keel 6 ft down. But the percentages themselves are usually meaningless anyway - arguably anything that contributes to roll stiffness could be called ballast including the beer you have stored in the keel sump.
 
wotayottie said:
The 35% is nonsense. A boat with 35% but in the bilges would be less stiff than one with 20% in a torpedo keel 6 ft down. But the percentages themselves are usually meaningless anyway - arguably anything that contributes to roll stiffness could be called ballast including the beer you have stored in the keel sump.
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My 40 foot yacht designed by Alan Pape had 35% ballast ratio......trad cruising boat.Obviously thats the boat on the drawing board.Too much weight in the keel is not always a good thing unless its a racer
 
nigelmercier said:
What, no jibes about Bavaria keels? You lot are mellowing :)
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TBH, it was was probably unnecessary as the OP referred to the need for a more seakindly boat. :)

Anyway, looking at the good discussion above, particularly Bobc's comment about a bigger Bavaria with a lead keel, I wonder whether the issue is really about keels. As the self confessed owner of a genuine MAB, ie it really is manky, with overhanging bows etc, I suspect the experience of sailing a snub nosed shallow flat-bottomed boat with a bolt on keel is rather different from a Roberts 34 in my case, or a Rival, Contessa 32, Sadler 34 etc etc.

I'm not knocking Bavarias that have a lot of bangs for the buck, or any of the other AWBs - their comfort, stowage space and performance in light winds is incomparably better than ours, but I'm not sure that I'd take to all the slapping when the seas get up. It's all a compromise and down to personal preference - we lose LWL and cabin space but, for us, she looks aesthetically more appealing and stands well up to rough weather. Trouble is, that after the superior cabin comfort of a Bav or an AWB, it might be rather expensive and a bit tricky finding a suitable encapsulated keel boat with a similar level of comfort and modernity.
 
I sailed on a friend's 39' Colin Archer gaff ketch on a passage down channel.
Her displacement was 19 tonnes (!), and she only really got going under full working sail once the wind got up to about a F 5-6.
And then she would tramp along happily on a beam reach (even a close'ish reach, but definitely not close hauled) doing 6 - 7 knots (with a clean bottom).
We could all sit around the saloon table very comfortably for dinner in these conditions, and nothing would be flying about.
 
Bajansailor said:
I sailed on a friend's 39' Colin Archer gaff ketch on a passage down channel.
Her displacement was 19 tonnes (!), and she only really got going under full working sail once the wind got up to about a F 5-6.
And then she would tramp along happily on a beam reach (even a close'ish reach, but definitely not close hauled) doing 6 - 7 knots (with a clean bottom).
We could all sit around the saloon table very comfortably for dinner in these conditions, and nothing would be flying about.
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My boat was like that,,way too comfortable below sothe crew quite happy to avoid deck work!-------it had 14 tonne disp and 35% ballast ratio,not too hot to windward !
 
Low ballast ratios were the norm in older style boats, partly because of the difficulty of building a structure strong enough to carry the weight. Rigs were generally low aspect and well spread out, as was ballast. High ballast ratios became popular as rigs became bigger and taller, but hull shapes still had low form stability. GRP construction that made it much easier to have lots of ballast (though not always well placed). Some 1970s/80s IOR boats are good examples of high ballast ratios that don't necessarily have high stability.

The Brewer index already quoted is an attempt to quantify comfort at sea. It penalises beam and rewards displacement. There was an article in YM recently giving exmples of the index in use.
 
Thinking of upgrading from my Bavaria to something more comfortable in rough conditions. I was of the opinion that perhaps a heavier boat of similar size might be kinder for SWMBO in a bit of a blow.
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For a given shape of boat, higher displacement reacts less to the action of waves, and motion will be less violent.

Long and narrow shapes usually have high pitching inertia, so pitch less going to windward. But may well be a lot wetter on deck as a result.

More laterally stable boats (however the stablity is created, by beam, by ballast or by shifting weight) will heel less in a given wind strength and direction. Of course, this can also be achieved by reducing sail.

In a beam sea, tall sails reduce the rolling more than short rigs, and shape stability rolls more than ballast stability

When sailing downwind (trade wind strengths), strong shape stability (catamaran's are best) reduce that tiring rolling.

All round, bigger boats are more comfy. But price goes up as a cube of the LOA.
 
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Older shapes are like a wine glass and often have long keels but they lean quickly and with a greater angle of lean than modern boats. Older and "quality" boats tend to be heavier with a higher % of ballast ratio BUT they need a stronger wind to get going.

Newer boats tend to have a vertical bow (longer water line length) flatter bow section (faster but can slam when beating) and wider stern. They sail more upright due to the wider hull giving an upward thrust as they lean (form stability). Boats have evolved this way in response to the majority of customers demands for cheapness, speed and internal space and volume.

If I was to cross an ocean with unpredictable weather I would want an older or heavier displacement but the majority of boats doing the ARC (Atlantic Rally crossing) are now new design boats. For the sailing I do with fairly accurate weather forcasts for up to a week ahead a modern, lighter, faster boat is my preference.

All boats are compromises but unfortunately these threads often produce more prejudices than information on the choice of compromises. This one so far is good!
 
> I was of the opinion that perhaps a heavier boat of similar size might be kinder for SWMBO in a bit of a blow.

Rivals and Bowmans are sea kindly boats, look up their ballast ratio and you will get a good idea of the type of boat to buy.
 
Some thoughts on cruising boats here:
http://www.saltyjohn.co.uk/resources/Defining the cruising boat.pdf

All boats are a compromise and you have to think really carefully about your intended use. No point having a heavy displacement, narrow, cramped, bulletproof boat if you aren't intending to take on the higher latitudes. A lighter displacement boat with large, airy interior is a much nicer place to hang out if you're coastal cruising.
 
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