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Discussion Starter #1
Hi.

How significant is the displacement/ballast ratio? For example, a 36% vs 44% ratio; would that make a huge and noticeable difference in the boat's cruising capabilities?

Thanks.
 

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Farr 11.6 (Farr 38)
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In and of itself, the displacement to ballast ratio only gives you one small portion of the story. It really is not all that useful without knowing the vertical center of gravity of that ballast, and the beam of the boat. For example, a deep draft boat with a smaller D/Bal say, around 33% but which employed a high density in a bulb, would inherrently be more stable than a shallow draft boat with a much higher ballast ratio but in the form of a low density ballast carried in the bilge or an encapsulation envelope.

Similarly, a very narrow boat with a very high ballast ratio carried very low, might not have as much stability as a more moderate beam boat with the same ballast ratio or even with a lower ballast ratio.

In other words, boats act as a system. While a boat's statistics and ratios may provide helpful information, they cannot provide a comprehensive picture of the behavior of the boat as a whole. For that reason, modern designs which are often lighter and have smaller ballast rations than more traditional designs may in fact have significantly higher stability (relative to their displacement and drag) across a broad range of heel angles.

Jeff
 

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This is one number out of many. Is everything else completely identical between the two boats? That is pretty unlikely.

If the additional weight is at the very end of the keel, perhaps in the form of a bulb, it could make the 44% boat stiffer. If it is evenly distributed throughout the keel it could be less noticeable.

Chances are that the lower B/D boat has a wider beam and a hull form that provides more form stability, so the builder was able to get away with less ballast.
 

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Ballast displacement ratio is an important indicator regarding boat stability but one that is pretty meaningless if you don't see the whole picture. It is an indicator regarding a way of lowering the CG of a boat but the CG can be also lowered by a superior draft, or a more efficient keel, a bulbed one, being the most efficient a torpedo keel. it can also b lowered even more if the ballast is lead instead of iron.

if you compare for instance American production cruising boats with European ones you will see that American ones will tend to have a superior BD ratio but that does not mean that the CG is lower since European boats have normally a bigger draft and more efficient keels, including torpedo ones.

Lowering the CG is also a way of increasing the stiffness of the boat (power) but not the only one. That can also be made through increasing beam. Normally narrower boats need a bigger BD ratio regarding beamier boats to have the same positive stability and power. However, regarding beamy boats you have always to keep a CG lower enough to allow the boat a good stability at 90 degrees and a good AVS (reserve stability) even if that low center of gravity is not needed to have the power to sail the boat.
 

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Discussion Starter #5
Thanks for the responses; a bit advanced than my current understanding of boats, but I am learning as I go.
 

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Farr 11.6 (Farr 38)
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Neither appear to be particularly good designs. Both appear to be somewhat dated, light duty, coastal cruisers. Neither would fall into a category of a comfortable cruiser. Unless they were extremely inexpensive for some reason, there are much nicer boats out there in their general size and normal price range.
 

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Discussion Starter #8
These are in the 3.5-5K range.

There is a J24 for sale - but different purpose boat, is it not?
 

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What will be of interest to you also is DWL displacement to water line ratio .
But by itself, even that only tells you a small piece of the story. Take two equal length, beam, and weight boats but one with a short waterline and the other with a longer waterline. The D/L of the long waterline boat would perhaps suggest it is less suitable as a distance cruiser, yet that would not at all be the case.

Jeff
 

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whats better a tractor or a moped?

different stuff all together...

look at general stats and if possible reviews by owners and stuff you can find from clubs and such

ive had boats mostly with high ballast to displacement rations even one that had 51% Ill let you guess which one that was...

in the end all boats have other attributes and deifficiencies that make them what they are

cheers
 
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Comfort is a relative term, but between the two, I'd give the nod to the Sonic.
 

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Does the data point to one boat being a better, more comfortable cruiser?
Cruising is a vague term. For some people that might mean short day sails where the goal is relaxation. For others it could be going around the world non-stop. For most they mean something in between, single or multiweek coastal trips in protected waters.

How do you intend to use the boat?
 

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As many have mentioned, the numbers only tell a portion of the story, if any at all. Better to talk with owners and others with real world cruising experience aboard the boats you're interested in. I love using numbers, ratio, etc. to compare boats but there's really no substitute for firsthand experience.
 

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Jeff you lost me in that last sentence .
That last sentence probably would have been clearer if it has said, "The smaller D/L of the longer waterline boat would perhaps suggest that it is a lighter boat and therefore as viewed by traditional standards,[/I] less suitable as a distance cruiser. In fact, because the longer waterline boat would typically have a better motion, better carrying capacity, often more stability, and more preformance, the longer waterline boat would typically be the better cruising boat.

I don't know whether that explains that last sentence well enough. In essense, if the two boats had the same length, weight, beam, deck plan and draft, and same general weight distribution, as the waterline length grew, there would be better pitch dampening, large capacity per submersion inch, and a shallower canoe body reducing the roll angle, and increasing dampening, stability and foil performance. Generally, a longer water line boat is thought to be more seaworthy as well.

But the L/D of the of shorter waterline boat would make the shorter waterline boat seem to be heavier displacement and would make some people think that the shortline boat was a better cruiser when that would not the case.

Jeff
 
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But the L/D of the of shorter waterline boat would make the shorter waterline boat seem to be heavier displacement and would make some people think that the shortline boat was a better cruiser when that would not the case.
Do you think it would be useful to calculate a Displacement / Length Overall ratio? Would that tell you more about the feel of a boat than the standard D/L?
 

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I don't think that using the Length on Deck would tell you all that much either, since that would ignore the waterline length which is a key dimension in determining all kinds of behavior.

My point about the conventional way of looking at L/D is that the actual L/D of the boat can be misleading if only viewed as a single value on its own. Given the wide range of boats shapes that are out there, the L/D of any given boat needs to be filtered by looking at other factors such as the relationship of length on deck to length on the waterline, beam, draft, ballast ratio and so on. Its only when you look at the overall picture that you can understand the meaning of any particular L/D.
 

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Jeff- Modern designs seem to stress form stability and construction to minimize weight. I understand weight is the enemy of speed. I had thought increasing form stability had the risk of:
increasing wetted surface so increasing parasitic drag and therefore decreasing performance in light air resulting in increased motoring.
increasing beam and frontal surface so running risk of decreased performance to windward. Also slamming in a seaway when wind before the beam.
increasing risk of not self righting or doing so slowly so increasing risk of down flooding if turned turtle.
I understand performance down wind will be enhanced and "stiffness" as well. I also understand the boat will be lighter requiring less ballast. All this translates to a possibly faster boat if diligently sailed and attended to but cruising does not always involve that level of alertness. We sometimes need to attend to other contingencies or just don't have the mind set due to sickness or fatigue. I think ( possibly wrongly) a boat highly dependent on form stability is less forgiving of our frailties. I think they are like unballasted dinghies but in an ocean setting. Also my limited experience to date is these boats float on the water not in the water so in most circumstances especially short chop on top of swells the ride is less pleasant. I would be interested in your take on this. Is there a divergence in design with some customs and one offs holding to "traditional" design of a relatively heavy boat of modest beam and "cutting edge" design furthering weight cutting and maximum beam. Most folks are not racing. They are interested in cruising safely and comfortably be it coastal day hops, multiple days of watch and watch or passage making.
 

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I dont get into discussions like this anymore cause I never understood the new vs old argument

fiberglass still has some decades left to see what happens to it after say a century

what I think will happen is they will get soft and craze and become to flexible and you will just have to stop sailing them aggresively

in any case about ballast to displacement ratios without getting to technical it comes down to this

more ballast per displacement means that theoretically yo will be able to carry full sails longer, meaning the boat will like and perform better in string winds

if the keel is long and deep this means good tracking and stability

if the keel is short and fin like but still has a big ballast comparatively speaking this also means it will carry sail longer but the issue here is stress at such a small area in one point of the hull

this is why you see a lot or some better put fin keels with bulbs plopping off the flat racing bottoms on some maxi boats and surfing sleds, the reason is that the bolts stress a small area and unless hugeley supported inside or they point strees too much

anywhoo cca boats and the like had relatively small ballast percentages when considering they were cutaway forefoots or medium full keelers or shallow full keelers

tritons vanguards and rhodes and most albergs of that time hovered around 38-40%

compare that say to a nordic folkboat with full deep keel and they would be considered tender

I had a folkboat with 51% ballast ratio...that thing could be hammered into 30 knot winds...full sails or spill the main and it tracked like a train yet was nimble and very fast...

it also benefited from an extrenally bolted keel..and was rounded...and had a beatiful rudder...well balanced etc

lastly when one considers ballast displacement ratios its always wise to look at mast height and sail area as well...

cause as we all know the keel balances the mast...so if you have a too short and stubby mast with very little sail area and have a massive amount of ballast say around 45 percent and above your boat is going to need A LOT of wind t move and even then will have bad sailing qualities

what I love about cca boats is that they are dinghy like tender the first 15 degrees or so then they stay put at 20 degress and feel awesome...they also improve waterline length thanks to a rule design...and they are seakindly

anyone who argues that is just arguing for arguments sake

take a j24 and then take a pearson triton or smaller electra if you will

if you can tell me with a straight face that the electra or triton does not have better sea motion or stabilty then I applaud you cause the reality is they are apples and oranges even though ballast ratios are similar...

not to mention keel and rudder design as well as underbody design

again this is not technical just an opinion from somebody that loves BOTH types of boats...
 
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