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Old 08-11-2011, 23:20   #1
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Understanding the Ratios

So all the threads about "blue water" boats vs. "coastal cruisers" got me to looking at some of the ratios that are used to categorize different designs. Specifically, I wanted to compare the Pearson Triton (28.5') with the Pearson Vanguard (32'). As a "control" compare/contrast vessel, I went with the Bristol Channel Cutter (a known, heavy, well-respected, true "blue water" boat).

When people have asked for good "blue water" designs in the 30' range (and low budget), people seem quick to recommend the Pearson Triton, but they almost always dismiss the Vanguard as a "coastal cruiser". But their numbers (when plugged into the different ratios) are almost identical across the board. What gives?

Then I noticed that even though the Vanguard (and all those old CCA designs) are typically called "tender", the Ballast/Displacement ratios of both the Triton and the Vanguard are actually higher than that of the BCC which implies that they are "stiffer"/more resistant to heeling. How can that be?
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Old 09-11-2011, 02:00   #2
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Re: Understanding the Ratios

They are both also quite narrow which gives them less initial stability. That said, being initially tender doesn't rule them out as "blue water" in my mind.

I'm one of those that sails the open ocean in a racer cruiser design. I put more stock in a boat that sails well and is properly equipped and maintained for "blue water" duties then the pedigree of the design for that purpose.
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Old 09-11-2011, 11:56   #3
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Re: Understanding the Ratios

Mike is right. The ballast doesn't take effect until the boat is heeled over a bit, really doing nothing at 0 degrees of heel. The form stability of the design is what makes a boat initially tender or not. A boat with more beam for a given length always wins at form stability. The designs of the CCA era are all relatively narrow boats by today's standards.

To many "bluewater capable" means heavy and long keeled. To me it means a boat that is well built and sails well without vices and not needing 6 crew on the rail. A fin keeled boat with a spade rudder is bluewater capable if well designed and built.

Some of the other numbers such as displacement/length ratio mean even less as far as seaworthiness is concerned.
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Old 09-11-2011, 12:04   #4
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Re: Understanding the Ratios

Yeah, a narrow Folkboat for instance may have 50% or more ballast and round bilges. It heels immediately until it reaches a point that it gets "in the groove" well heeled. You're in for a wet ride!
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Old 09-11-2011, 12:43   #5
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Re: Understanding the Ratios

A boat with more ballast, at the same displacement, can be more tender - the ballast is not attached to a generic hull, is it.

Imagine two boats with the same amt of ballast but one is deep and narrow while the other is wide and flat. Now which one, with the SAME ballast will be stiffer.

Ballast =NOT= stiffness.

A catamaran has no ballast and yet is pretty stiff, isn't it.

When you learn about ratios, try to learn the broader concept: how they were invented, how they are used and what their limitations are.

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Old 09-11-2011, 12:50   #6
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Re: Understanding the Ratios

b

Initially the wide flat hull will be stiffer. The narrow deeper boat will have better ultimate stability. It better have a gimbaled stove as well.
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Old 09-11-2011, 13:03   #7
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Re: Understanding the Ratios

Also keep in mind that a lot of the ratios are calulated with the boat just sitting in the water and you have to think about how each boat changes as it heels etc.

And not that it matters in the current question, but a lot if the "ratios" don't carryover well into more modern designs.
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Old 09-11-2011, 13:15   #8
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Re: Understanding the Ratios

The ratio I dislike is the displacement/length ratio, which many believe deems a boat either light or heavy.

If you take a Alberg 35 for example it has a D/L ratio of 430, with a waterline of 24'. If the same boat had a 30' waterline with no other changes the D/L ratio would be about 223. This would lead many to think the 30' waterline version was lighter when it is actually heavier by the amount of structure used to increase the waterline length. I have allowed 200 lbs extra displacement at a guess for this in my calculations.

D/L ratio is valid for comparing boats of the same type, but not for an older CCA type design with a long waterline boat from this era.
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Old 09-11-2011, 13:23   #9
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Re: Understanding the Ratios

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Originally Posted by mitiempo View Post
b

Initially the wide flat hull will be stiffer. The narrow deeper boat will have better ultimate stability. It better have a gimbaled stove as well.
As you say. The narrow deep thing will also have less reverse stiffness ... ;-)

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Old 09-11-2011, 13:49   #10
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Re: Understanding the Ratios

Lets get right to the point. A number of people are saying that a number of models that are mass produced are good ocean boats. I just don't believe it for the following reasons:
The flat bottom with a narrow fin keel and dagger rudder make them jumpy in open seas. Even in calm seas the wide transom can make steering difficult.
The open design below decks can really hurt as you violently turned from side to side. I am not surprized at the broken bones that occur when these boats hit bad weather.
I have sailed Catalina/Benes/whatever on the ocean(s) Yes they will go from point A to B. They usually point well. But I find they are easily overpowered when the winds and the swells combine to make mischief. I would say because they are not designed for being out there in a storm, no matter what the ratios say. That is why reputation is important.
Call it crude, but I trust people and boats who have been there, done that and got home on their own.
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Old 09-11-2011, 14:06   #11
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Re: Understanding the Ratios

Is this thread going to become a production boat trashing one now?
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Old 09-11-2011, 16:38   #12
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Re: Understanding the Ratios

Not at all, what I am trying to point out is that seaworthyness is not in a brand, its not in a number, and its not even in a particular model. It is in the boat, and that is where we should be looking for answers. In fact, that is just half the answer. The other half of the answer is in you.
Case in point. I was part of a crew that sailed a 50ft production boat across the gulf stream with a northern blow happening. We would get jerked around so hard I thought I was going to get whiplash. The Captain was down below sleeping. Finally we heard some swearwords, and he lumbered up on deck. "Don't ya know how to sail" (all of his students had in depth sailing experience) he would growl as he took the helm. Instantly, the steep tall waves became no problem as he steered around them. "Do it like this!" we would all agree, and he would mutter something and go back down to sleep. As soon as he left the wheel, the boat would carve off the waves like a slingshot, and we would all be back to hanging on. I think I held my breath all the way to Alicetown.
Now- he could make that production boat behave like a BCC. I cannot. I can take a boat that is a know seafarer like the BCC and survive in a storm. It may have the same numbers as some production boats, and my observations may only be a small part in the total equation, but it is different, no doubt about it.
Not everyone want to cross oceans. Most people want to socialize at the dock or nearby. So the big companies, being very savvy to what people want, make their boats that way. What is wrong with that?? Is that criticizing them to say they are filling a need with a boat designed for that need?
What I am saying is- if we are going to compare boats, ratios may be useful, but track record is probably more important- because there are so many variables that go into a bluewater boat.
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Old 09-11-2011, 16:40   #13
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Re: Understanding the Ratios

Quote:
Originally Posted by s/v Beth View Post
Lets get right to the point.
Let's. ;-)

Quote:
A number of people are saying that a number of models that are mass produced are good ocean boats. I just don't believe it for the following reasons:
Even if half of the forum does so and if they claim this is true regarding half of the mass produced boats, then only 25% of the boats are suspect. Let's hope we fall into the remaining 75%.

Quote:
The flat bottom with a narrow fin keel and dagger rudder make them jumpy in open seas. Even in calm seas the wide transom can make steering difficult.
Flat bottom aft gives good ride off the wind, narrow foils are efficient. Look at an IMOCA or Mini or Class 40 boat riding the Southern Ocean swells at 15-20 knots - does it look like they are difficult to steer?

Quote:
The open design below decks can really hurt as you violently turned from side to side.
The open design is no longer there if you look at some modern boats where designers did the homework - the center of the boat contains most often some form of a settee etc that divides the space.

Quote:
I am not surprised at the broken bones that occur when these boats hit bad weather.
Perhaps if we measured the accident ratio it would be somewhere within the range off accidents on narrow deep hulls where crew tend to fall down the companionway and break their necks.

Quote:
But I find they are easily overpowered when the winds and the swells combine to make mischief.
A boat is overpowered when she carries too much sail or when the skipper cannot keep her under her sail. Blame the skipper, not the boat.

Quote:
I would say because they are not designed for being out there in a storm, no matter what the ratios say.
I do not think many boats are designed to be out there in the storm, except a lifeboat or a NOAA weather research vessel.

Quote:
That is why reputation is important.
But it should not be valued over the actual quality of the boat.

Quote:
Call it crude, but I trust people and boats who have been there, done that and got home on their own.
Now that's crude! Look at ARC lists - they are a huge percentage of mass produced boats. 99.9% of them make it on their own keels - both ways. They have been there, done that.

Now seriously, I agree with what you say and I was only trying to show that the same facts can be interpreted in many ways, none of them BETTER than any other.

Cheers,
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Old 09-11-2011, 16:44   #14
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Re: Understanding the Ratios

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Old 09-11-2011, 16:45   #15
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Re: Understanding the Ratios

I think we see eye to eye b. See my second post. I am not trying to offend the production boat crowd, just saying I am going to be out (have been out) in blows, and this is what I look at...
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