"speed" vs "comfort"

[Joli]

Go to SA cruising. All the prints are there plus lots of posts.

Originally Posted by dcstrng

Ears perked up on that; can't stay in stealth mode... hopefully the conceptual outline will be available in time... ??

[44'cruisingcat]

Originally Posted by James S

44Cruisingcat

Great vid...you got some pretty serious surfing going on there.

I have to admit I'm a slow, heavy, very comfortable mono guy...but that really looks sweet.

I would have thought there would have been more pounding going on.

What happens when you quarter those following seas...is it still good?

Thanks again for the nice vid.....I could smell the sea.

Sorry to say, it's not my video or boat.

[44'cruisingcat]

Originally Posted by bob perry

I think I will poke the dog with a stick:

Cruising cats and speed?
How are you defining speed?
Upwind?
Downwind?
Or a combo of both the way real boats are used.
I've seen plenty of cruising cats that were pigs upwind. Pigs I tell you.
Here we are back at trying to define "performance".
And please try not to paint me as a multi hull hater. My most favorite sail of last year was on a Farrier 28. I love a good, fast multi hull boat. I started sailing cats in 1964, Cougar cat. I'm just saying that it is best not to paint all cats with the same brush. The same way it's not smart to paint all monos with the same brush. I have designed cats and tris. I like them. But, there is a world of difference between the good performing cats and what we see marketed as cruising cats today. Treat each boat individually and look at the range of performance numbers.

Game on

As you say, some cats don't sail upwind well at all. But then some mono's don't either. The boat in the video is a St Francis 55, and is one catamaran that will most certainly sail upwind. Obviously it wouldn't be as comfortable or as fast as the downwind ride, but then heeling at 30 degrees isn't comfortable for long either.

14 - 20 knots downwind in comfort is pretty good for a cruising boat IMHO.

[Joli]

14 to 20 on a reach? Yes for sure.

Up and down? Nope, won't do it.

Originally Posted by 44'cruisingcat

As you say, some cats don't sail upwind well at all. But then some mono's don't either. The boat in the video is a St Francis 55, and is one catamaran that will most certainly sail upwind. Obviously it wouldn't be as comfortable or as fast as the downwind ride, but then heeling at 30 degrees isn't comfortable for long either.

14 - 20 knots downwind in comfort is pretty good for a cruising boat IMHO.

[dcstrng]

Originally Posted by Joli

Go to SA cruising...

Thanks a bunch... but a tad too cryptic for this geriatric-ward refugee… don’t think I know the secret handshake…

[Joli]

Here ya go.

Linky Target market - Sailing Anarchy Forums

Originally Posted by dcstrng

Thanks a bunch... but a tad too cryptic for this geriatric-ward refugee… don’t think I know the secret handshake…

[Evan]

My Richard Woods cruising cat is 40' and is light. Only 1 head, "British double berths" (skinny berths in the hulls), nothing in the ends. Full load displacement is about 12,500 lbs, SA with 100% Fore triangle is about 675 sq. ft so SA/D = 20. D/L is about 119.

Sticky in light winds? Not really. I am always sailing in the Gulf Islands when the cruising monos are motoring (say true wind speed of 5 knots).

Windwardly challenged? You bet. At least with a blown out genoa, and a mast beam that sagged a lot, it was hard to get a straightish forestay. Tacking angle is 100° in flat water. But with a new tri radial genoa, a clean bottom, and a stiffer carbon mast beam, we shall see this summer. If I get 95° between tacks (as measured on GPS) I will be happy enough.

I am much much happier with it's motion at sea compared to our previous boat, a heavy disp. Stan Huntingford Fortune 30. That thing absorbed tons of stores, but was not fast. If you don't have a lot of cash, a small mono is a good solution, but it doesn't have to be quite so heavy

[dcstrng]

Originally Posted by Joli

Here ya go...

Appreciate it... thanks !

[bob perry]

Evan:
Compared to that Huntingford Fortune anything would be fast.

I firmly believe in judging each boat individually. You current cat sounds very interesting.

[Stephen Phillips]

Bob,

Please explain the meaning of "Motion Comfort" and "Capsize Ratio" as they are used in Carl's Sail Calculator http://image-ination.com/sailcalc.html .

Discussing these boats might refine the thread so some of us might have a better understanding of "comfort" and "stiffness": Carl lists the Alberg 35 MC @ 36.48, CR @ 1.63 and the J37 MC @ 21.51, CR 2.07. Also, the Baba 35 MC @ 41.4, CR 1.61 and the Tashiba 36 MC 36.28, CR 1.73. How do these numbers relate to your experience sailing these boats? I mean, do they adequately describe the motion of these boats? Is the J37 radically different from the other three boats, and are the other three boats similar regarding MC and CR?

In what order would you chose these boats to sail short handed from Nantucket to Bermuda? This might better exemplify a cruising boat less that 40' LOA.

If you were to design today the Baba 35 and the Tashiba36 with modern materials and with the same objectives that you had back then, what numbers would we see in Carl's Sail Calculator? Cutters again?. And, what would the transom look like?

[Hiracer]

Quoting from Ted Brewer's website, the originator of one of these numbers:



COMFORT RATIO (CR): This is a ratio that I dreamed up, tongue-in-cheek, as a measure of motion comfort but it has been widely accepted and, indeed, does provide a reasonable comparison between yachts of similar type. It is based on the fact that the faster the motion the more upsetting it is to the average person. Given a wave of X height, the speed of the upward motion depends on the displacement of the yacht and the amount of waterline area that is acted upon. Greater displacement, or lesser WL area, gives a slower motion and more comfort for any given sea state.

Beam does enter into it as as wider beam increases stability, increases WL area, and generates a faster reaction. The formula takes into account the displacement, the WL area, and adds a beam factor. The intention is to provide a means to compare the motion comfort of vessels of similar type and size, not to compare that of a Lightning class sloop with that of a husky 50 foot ketch.


The CR is : Displacement in pounds/ (.65 x (.7 LWL + .3 LOA) x B1.333). Ratios will vary from 5.0 for a light daysailer to the high 60s for a super heavy vessel, such as a Colin Archer ketch. Moderate and successful ocean cruisers, such as the Valiant 40 and Whitby 42, will fall into the low-middle 30s range.

Do consider, though, that a sailing yacht heeled by a good breeze will have a much steadier motion than one bobbing up and down in light airs on left over swells from yesterday's blow; also that the typical summertime coastal cruiser will rarely encounter the wind and seas that an ocean going yacht will meet. Nor will one human stomach keep down what another stomach will handle with relish, or with mustard and pickles for that matter! It is all relative.



CAPSIZE SCREENING FORMULA (CSF): Some years ago the technical committe of the Cruising Club of America came up with a simple formula to determine if a boat had blue water capability. The CSF compares beam with displacement since excess beam contributes to capsize and heavy displacement reduces capsize vulnerability. The formula is the maximum beam divided by the cube root of the displacement in cubic feet; B/Displ.333. The displacement in cubic feet can be found by dividing the displacement in pounds by 64, of course.

The boat is acceptable if the result of the calculation is 2.0 or less but, of course, the lower the better. For example, a 12 meter yacht of 60,000 lbs displacement and 12 foot beam will have a CSF Number of 1.23, so would be considered very safe from capsize. A contemporary light displacement yacht, such as a Beneteau 311 (7716 lbs, 10'7" beam) has a CSF number of 2.14. Based on the formula, while a fine coastal cruiser, such a yacht may not be the best choice for ocean passages.

Ted Brewer Yacht Design

I would not get too hung up on either of these numbers because they only approximate the information they are trying to convey. Both are overly simplistic.

[Hiracer]

Here is an example of the kind of information I like to see when comparing boats. It's hard to get, admittedly, but you can learn lots more.

Motion comfort ratio, heft ratio, roll period, and roll acceleration acc will collectively tell you lots more about how the boat will feel than just MCR alone. I was lucky to have a N.A. in Spain compute this for my boat before I purchased her, and later I found the same information for my old boat (a Wauquiez) so I could compare the sets of numbers to better understand what they mean.

Actually, he did the numbers before I purchased her, and again after closing when I realized that the actual input numbers for the boat did not correlate to what was conveyed to me by the broker. I have since discovered that, in my experience, faulty information from brokers is pretty much the rule.



INPUT
Lh = 11,13 m (36,52 Ft)
Lwl = 9,22 m (30,25 Ft)
Bmax = 3,51 m (11,52 Ft)
Bwl = 3,35 m (10,99 Ft)
Draught T = 1,85 m (6,07 Ft)
Body draught Tc = 0,76 m (2,49 Ft)
Disp = 9070 kg (20012 lbs) (medium load)
Ballast = 2810 kg (6200 lbs)
Sail area = 70,8 m2 (762,08 Ft2)
Mast height = 15,24 m (50,00 Ft)
Heeling Arm = 6,84 m (22,43 Ft) (Guess)
Power = 25 KW (34 HP)
Wetted Surface = 29,41 m2 (316,51 Ft2) (Guess)

OUTPUT
Length/Beam Ratio L/B = 2,81
Lwl/Bwl Ratio Lwl/Bwl = 2,75
Length/Draught Ratio Lh/T = 6,02
Beam/Draught Ratio Bmax/T = 1,9
WL beam/Body draught Bmx/Tc = 4,41
Ballast/Disp Ratio W/Disp = 0,31
Displacement/Length Ratio D/L = 322,77
Sail Area/Disp. Ratio SA/D = 16,54
Sail Area/Wetted surface SA/WS = 2,41
SA (metric)/ Power (Imp.) SA/HP = 2,08
Power/ Disp. Ratio HP/D = 1,70 HP/ton
Hull speed HSPD = 7,37 Kn
Potential Maximum Speed PMS = 7,92 Kn
Velocity Ratio VR = 1,08
Best motoring speed (1.1) CSPD = 6,05 Kn
Capsize Safety Factor CSF = 1,7
Motion Comfort Ratio MCR = 36,85
Heft Ratio HF = 1,29
Roll Period T = 4,1 Sec
Roll Acceleration Acc = 0,05 G's
Stability Index SI = 1,17
Angle of Vanishing Stability AVS = 122 º

[Paul L]

Originally Posted by Stephen Phillips

Bob,

...I mean, do they adequately describe the motion of these boats? Is the J37 radically different from the other three boats, and are the other three boats similar regarding MC and CR?
...

No, they do not adequately describe the motion of the boats. I just don't put any credence in the MC number. To start with, look at Ted Brewer's tongue-in-cheek comment. Secondly, I have a lot of experience on two of the boats you mention above, one with MC of 36 and the other 21. I happened to be pretty susceptible to seasickness -- mainly controlled by God's gift Stugeron. The higher MC on the Alberg 35 does nothing to tell you how it pitches in a seaway with its long overhangs. The lower MC in on the J/37 tells you nothing about how much stiffer the boat is and how much less sail needs to be carried to keep it moving well in rough conditions. In rough conditions, I am less likely to get seasick on the stiffer platform. Either way, no small boat is comfortable in rough conditions.

As far as CSR goes, I can't say that I have a lot of experinace with boats doing full rolls -- i.e zero experiance. Taking the boats you listed, the CS does not tell you anything about the VCG of the boats. So the fact that the loaded J/37 might have a lower CG than a loaded Baba 35 is just not part of the equation. Again the definition of the CSF starts with the commnet "simple formula".

If you look at Hiracer's comments below, you see a mass of data computed on his boat. Ceratainly more than what most of us can actually decipher usefully. In the end boats that are not extreme in their design and are well built do just fine on short-handed ocean passages -- and that takes in a lot of boats.

Paul L

[Jim Cate]

[quote=Hiracer;249067]Quoting from Ted Brewer's website, the originator of one of these numbers:



COMFORT RATIO (CR): Given a wave of X height, the speed of the upward motion depends on the displacement of the yacht and the amount of waterline area that is acted upon. Greater displacement, or lesser WL area, gives a slower motion and more comfort for any given sea state.

I reckon that Mr. Brewer's comments here are correct, but he doesn't point out that the slow vertical acceleration also means that the boat is going to have a greater chance of getting green water on deck. So, the price of a more comfortable ride may be a wet bum! Each sailor must choose which is more important to him...

I do like the idea of doing some numerical analysis of a prospective boat, but as mentioned, getting accurate input data is very difficult, and interpretation of the output is not all that easy... but it is sure better that guesswork!

Cheers,

Jim and Ann s/v Insatiable II lying Gladstone Qld, Oz

[bob perry]

Stephen:
I am going to upset a lot of people here but what's new?
I don't use either formulae.
To begin with Ted "invented" that mtoion/comfort formula as a joke. He'll tell you
And as for an accurate picture of a boat's stability profile being reduce to a simple ratio of displacement and beam that is equally as much of a joke. I DO understand the theory behind this formula but it is far too simplistic to be of any value to me other than a quick, surface check. In other words If I came up with a number well under 2.00 I might look into it further to see what was going on.

Let me be presumptuous, please:
If you had cornered Beethoven and asked him to describe how he used the Sonata form for his symphonies his answer would have probably been "What form?"

Applying all these simplistic formula to designs is for people who have no ability or little ability to see the design in total. I look at pretty much all the formulae but I don't let a design live and die by any one of them. You know the story about the guy who had the pie plate with the hole in the middle and he wa asked to look a an elephant thru that whole and then asked to describe what he saw. That's the way the formulae work. They give you little glimpses into the character of the boat. What they don;t do is to tie the entire picture together. That's what guys like me do. I cannot type. I cannot spell. I can envision an entire new yacht design, sailing along, in 20 knots apparent, wind on the beam, everything paid for and an 80 degree day.

The day they can come up wth a formula that describes that let me know.
In the meanwhile I will continue to work with the fragmented formulae that I have worked with for the past 41 years and do my best to have them make sense.
For me a full stability study is far better than a simplictic "capsize screenijg formula" and only common sense and experience will tell you how a boat will ride at sea.

Keep in mind, we are not talking about "comfort".
We are talking about degrees of "discomfort".

Give me five minutes to stack the sand bags up in front of the office.