Ballast/Dsplacement Ratio

[cenej]

Hi,


I try to compare some sailboats of 34 feet in length:

First 34.7 (LOA 10,26m, LWL 8,73m, B 3,37m, Draft 2m, D 4,52t, Ballast 1,67t, SA 70,3m2),
Dehler 34 (LOA 10,51m, LWL 9,38m, B 3,49m, Draft 1,95m, D 5,11t, Ballast 1,85t, SA 75,4m2),
Dufour 34 (LOA 10,6m, LWL 9,13m, B 3,48m, Draft 1,9m, D 5,7t, Ballast 1,75t, SA 70,95m2),
Elan 340 (LOA 9,99m, LWL 9,39m, B 3,48m, Draft 2,1m, D 5t, Ballast 1,49t, SA 71,64m2),
X-34 (LOA 10,36m, LWL 9,09m, B 3,4m, Draft 1,9m, D 5,3t, Ballast 2,2t, SA 67,9m2).

I find out that they are pretty same, except that Elan has a bit smaller ballast/displacement ratio than the others.

As a novice here my question is: what are the drawbacks or advantages of such a small ratio and how ballast/displacement ratio affected yacht performance, quality of motion and last but not least Safety.

Any help will be appreciated.


Regards, Cene.

[Guillermo]

Hi Cene, welcome to these forums.

From: http://www.loca.ac/Technotes.aspx

"Ballast / Displacement Ratio

The ballast / displacement ratio is a measure of the stability of a boat's hull. Basically it describes how well a boat will stand up to its sails. Since ballast is placed below the boat's center of gravity, it is a more effective way to add stability than placing weight elsewhere. The ballast displacement ratio indicates how much of the weight of a boat is placed for maximum stability against capsizing. The ratio then is an indicator of a boat's stiffness and resistance to capsize.

Up to 90 degrees, weight stability increases with boat heel, thus providing increased stability at higher angles of heel. The higher the ratio and the deeper the draft, the more stable the boat and the less the likelihood of it turning turtle. The ratio is calculated by dividing the weight of the ballast by the displacement. It is therefore simply the percentage of the total displacement that is ballast.

Although a high ballast ratio makes for a more stable boat, one that is very high is said to make a boat extremely stiff, resulting in supposedly uncomfortable “quick motion.” The ratios vary from a low of 0.25 to a maximum of 0.50. The lower the value, the greater the tendency toward instability, the more tender the boat, and the less sail it can carry. While B/D ratio is one indicator of stability, centre of gravity, centre of buoyancy versus heel angle and total weight are necessary to get a complete picture. Within the Catalina fleet, the C-36 MkII leads the way with a B/D ratio of 0.47. The C-270 has the lowest B/D value at 0.32. The remainder of the fleet has B/D ratios ranging between 0.34 and 0.45. An alternate way to estimate stability is to divide the boat's roll period (in seconds) by the beam (in meters). Values less then 1 are "stiff". Values greater than 1.5 are considered "tender". "

Perhaps you could be interested in reading the seaworthiness and STIX and 'old ratios' threads (very long and passionated ones!) as you may find some info and opinions of interest there. You may also want to search botdesign.net forums for 'ballast displacement ratio' to find out more related posts.

Cheers.

[Brent Swain]

More beam lets you get away with a lower ballast ratio, but only initially. If it capsizes with a lot of beam and low ballast ratio , it will tend to stay capsized. A narower boat has less tendency to stay capsized, but will be initially less stable unless the ballast ration is increased.
The shape of your midship section can have a greater influence on self righting ability. For example a beach ball with a tiny amount of ballast on one side will be totally self righting whereas a raft witha 70 % ballast ratio will stay inverted indefinitly. Thus a midship section that resembles a beachball( High cabintop camber, trunk cabin instead of flush deck, moderate beam,etc) will have far more ultimate stability than a beamy flush decker, when inverted.
Brent

[Antonio Alcalá]

I entirely agree with Guillermo, but in my opinion there are two circumstances in addition.

1.- The size of the main sail. It´s directly relationed with the ballast, the higher ballast the bigger mainsail. Although this rule not always fulfilled by the naval architects. This is a very interesting point of the performance of the sailboat. Swan,X-Yachts, Grand Soleil usually follow the rule, sometimes Beneteau and Jeanneau, but not always. This is the only way for growing the sail performance in light winds and directely relationed with this comment..

2.- The lower ballast, the bigger LWL in light winds, this is the point by that Beneteau applied in their ancient models different rules than in the newest. This is the point too by that some people think Beneteau designs are not for ocean passages ( really fast in light winds but not as much the the wind is strong and the sea too). And if we see designs like bavaria,beneteau, and anothers have a ballast relation of only 21%. They are fast i repeat in light winds but the problems come true above 20 knts.
On the other hand we have designs like Contest, Nauticat,Hallberg-Rassy very safety in strong conditions but very slow in lights winds. These kind of conditions are usual coming back from Bermuda to Europe in third week of June and this supposes more days of trip in a nordic design and not in a french design like 34' Beneteau.


But if you answer me about what would i do in my personal case i will not have any doubt: I have a 473 Beneteau ( Ballast 32%, MCR 26.5, STIX 51.5) very fast in light wind and very secure in strong wind but , pay attention, her weight is 14200 kgs at maximum load, this is an abism between a 34'.
And i recognize yoo, i love swan designs, i love Hallberg- Rassy, but they are so expensive for me...

Best winds

[Guillermo]

I have done some homework on such boats. I took the lighter (First 34.7) and the heavier (Dufour 34), took data from manufacturer's sites, measured here and guessed there (so please take numbers with due care), and I came to this:


FIRST 34.7

INPUTS
Loa = 10,35 m
Lh = 9,99 m
Lwl = 8,73 m
Bmax = 3,37 m
Bwl = 2,90 m
Draught T = 2,00 m
Body draught Tc = 0,53 m
Moulded depth H = 1,77 m
Disp = 4650 kg (lighship)
Ballast = 1375 kg
Sail area = 52,9 m2
Mast height = 15,8 m
Heeling Arm = 7,12 m
Power = 15,5 KW


OUTPUTS
Length/Beam Ratio (2Lwl + Lh)/3B = 2,72
Lwl/Bwl Ratio Lwl/Bwl = 3,01
Length/Draught Ratio Lh/T = 5,00
Beam/Draught Ratio Bmax/T = 1,69
WL beam/Body draught Bwl/Tc = 5,47
Ballast/Disp Ratio W/Disp = 0,30
Displacement/Length Ratio D/L = 194,94
Sail Area/Disp. Ratio SA/D = 19,30
Sail Area/Wetted surface SA/WS = 2,40
Power/ Disp. Ratio HP/D = 2,05 HP/ton
Hull speed HSPD = 7,17 Kn
Potential Maximum Speed PMS = 8,27 Kn
Velocity Ratio VR = 1,15
Best motoring speed (1.1) CSPD = 5,89 Kn
Capsize Safety Factor CSF = 2,04
Motion Comfort Ratio MCR = 21,45
Roll Period T = 2,50 Sec
Roll Acceleration Acc = 0,14 G's
Stability Index SI = 0,74
Angle of Vanishing Stability AVS = 118 º
Dellenbaugh Angle DA = 21,21 º (14 kn wind)
Wind pressure coefficient WPC = 1,00

Estimated STIX = 34,41


DUFOUR 34

INPUTS
Loa = 10,60 m
Lh = 10,28 m
Lwl = 9,13 m
Bmax = 3,48 m
Bwl = 2,99 m
Draught T = 1,90 m
Body draught Tc = 0,59 m
Moulded depth H = 1,80 m
Disp = 5700 kg (lighship)
Ballast = 1670 kg
Sail area = 50,52 m2
Mast height = 15,42 m
Heeling Arm = 6,93 m
Power = 13,8 KW


OUTPUTS
Length/Beam Ratio (2Lwl + Lh)/3B = 2,73
Lwl/Bwl Ratio Lwl/Bwl = 3,05
Length/Draught Ratio Lh/T = 5,41
Beam/Draught Ratio Bmax/T = 1,83
WL beam/Body draught Bwl/Tc = 5,07
Ballast/Disp Ratio W/Disp = 0,29
Displacement/Length Ratio D/L = 208,90
Sail Area/Disp. Ratio SA/D = 16,09
Sail Area/Wetted surface SA/WS = 2,09
Power/ Disp. Ratio HP/D = 1,49 HP/ton
Hull speed HSPD = 7,33 Kn
Potential Maximum Speed PMS = 7,91 Kn
Velocity Ratio VR = 1,08
Best motoring speed (1.1) CSPD = 6,02 Kn
Capsize Safety Factor CSF = 1,97
Motion Comfort Ratio MCR = 24,21
Roll Period T = 2,78 Sec
Roll Acceleration Acc = 0,12 G's
Stability Index SI = 0,80
Angle of Vanishing Stability AVS = 118 º
Dellenbaugh Angle DA = 18,68 º (14 kn wind)
Wind pressure coefficient WPC = 1,13

Estimated STIX: 35,26


As I'm working on a STIX estimator, I'd greatly appreciate whatever info on the real values for them. Thanks in advance.

Cheers.

[Antonio Alcalá]

Very interesting numbers. Would you mind calculating on the HR 31 and 34?, it would be great to compare them and both with the 34.7 and the 34 Dufour.
All of them are class A , but wich of them are really safety for crossing the North Pacific.

Best winds

[Guillermo]

You make me work too much, Antonio!

Here some numbers for the HR 34. As always take them with care.
HALLBER RASSY 34

INPUTS
Loa = 10,28 m
Lh = 10,28 m
Lwl = 8,73 m
Bmax = 3,42 m
Bwl = 3,08 m
Draught T = 1,85 m
Body draught Tc = 0,67 m
Moulded depth H = 1,48 m
Disp = 5300 kg (lightship)
Ballast = 2100 kg
Sail area = 55 m2
Mast height = 15,01 m
Heeling Arm = 6,74 m
Power = 21 KW


OUTPUTS
Length/Beam Ratio (2Lwl + Lh)/3B = 2,70
Lwl/Bwl Ratio Lwl/Bwl = 2,84
Length/Draught Ratio Lh/T = 5,56
Beam/Draught Ratio Bmax/T = 1,85
WL beam/Body draught Bwl/Tc = 4,59
Ballast/Disp Ratio W/Disp = 0,40
Displacement/Length Ratio D/L = 222,18
Sail Area/Disp. Ratio SA/D = 18,39
Sail Area/Wetted surface SA/WS = 2,30
Power/ Disp. Ratio HP/D = 2,44 HP/ton
Hull speed HSPD = 7,17 Kn
Potential Maximum Speed PMS = 8,11 Kn
Velocity Ratio VR = 1,13
Best motoring speed (1.1) CSPD = 5,89 Kn
Capsize Safety Factor CSF = 1,98
Motion Comfort Ratio MCR = 23,74
Roll Period T = 2,74 Sec
Roll Acceleration Acc = 0,12 G's
Stability Index SI = 0,80
Angle of Vanishing Stability AVS = 124 º
Dellenbaugh Angle DA = 19,53 º (14 kn wind)
Wind pressure coefficient WPC = 1,08

Estimated STIX 39,82

As always: Whatever correction and better info on the real thing will be greatly appreciated.

Cheers.

[Guillermo]

And now the Wauquiez Gladiateur, with a higher Ballast/Displacement ratio:

WAUQUIEZ GLADIATEUR

INPUTS
Lh = 9,99 m
Lwl = 8,30 m
Bmax = 3,35 m
Bwl = 3,20 m
Draught T = 1,80 m
Body draught Tc = 0,60 m
Moulded depth H = 1,72 m
Disp = 5000 kg
Ballast = 2200 kg
Sail area = 48,36 m2
Mast height = 14,89 m
Heeling Arm = 6,68 m
Power = 18,4 KW


OUTPUTS
Length/Beam Ratio (2Lwl + Lh)/3B = 2,65
Lwl/Bwl Ratio Lwl/Bwl = 2,59
Length/Draught Ratio Lh/T = 5,55
Beam/Draught Ratio Bmax/T = 1,86
WL beam/Body draught Bwl/Tc = 5,33
Ballast/Disp Ratio W/Disp = 0,44
Displacement/Length Ratio D/L = 243,90
Sail Area/Disp. Ratio SA/D = 16,81
Sail Area/Wetted surface SA/WS = 2,12
Power/ Disp. Ratio HP/D = 2,27 HP/ton
Hull speed HSPD = 6,99 Kn
Potential Maximum Speed PMS = 7,68 Kn
Velocity Ratio VR = 1,10
Best motoring speed (1.1) CSPD = 5,74 Kn
Capsize Safety Factor CSF = 1,98
Motion Comfort Ratio MCR = 24,04
Roll Period T = 2,76 Sec
Roll Acceleration Acc = 0,11 G's
Stability Index SI = 0,82
Angle of Vanishing Stability AVS = 125 º
Dellenbaugh Angle DA = 16,86 º (14 kn wind)
Wind pressure coefficient WPC = 1,25

Estimated STIX 41,89

Cheers.

[Antonio Alcalá]

Interesting, very interesting data from the numbers done by you according to STIX. Therefore we have a Hallberg-Rassy ( Unlimited Oceanics Voyages) with no more than STIX 40, but in A class:Mmmmm. Non good MCR, Non good Roll period, Non good Roll acceleration....ejem, ejem, there´s a mistake we could supose, but, no this is not a mistake , it´s the real life. Nordic designs!!! they are prepared for all sea conditions....then already we see that no.

Let´s remember

Typical Sailboat for ocean passages:

MCR> 30
CSF <2 ( the better the lower)
T > 4 sec

Do you know how much does it cost?

180.000 Euros

Now i bring your attention, because i gonna ask Guillermo for a new calculation: Puma 34 and First 345.

They are simply best in their size for the Atlantic Cross E-W and W-E. And their costs aren´t more than 60.000 Euros. Let´s see the differences between them and the HR!

Best winds and forgive me Guillermo ( We have to cheer the people up)

[Guillermo]

Those STIX numbers are not trustable, as they are a rough estimative using a not yet duly tested method. Anyhow A category begins in 32, so 40 is not so bad (although Rolf Eliasson is of the opinion this last figure should have been the one chosen instead of 32).

Also, MCR in the lower 30's+ is generally asumed as desirable for a 40 footer, but not for a 34 footer which can have a lower number. Enter in Carl's calculator and list 33-35 footers with CDF under 2 and MCR betwwen 24 and 34, let's say.

I wouldn't say nordic designs (nor the other) are not prepared for all sea conditions. Remember those numbers are only clues and also what Ted Brewer (father of the MCR) wrote:

"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."

I'll try to find out data for the Puma 34 and First 345, but it'll take some time.

Cheers.

[Antonio Alcalá]

I really like this forum!!!!

[Guillermo]

Originally Posted by Guillermo

.... Enter in Carl's calculator and list 33-35 footers with CDF under 2 and MCR betwwen 24 and 34, let's say...

Here you are:

Allmand 35 Pilothouse (1981), LOA=34.75, Motion Comfort=28.06, Capsize Ratio=1.89
Aloha 34 [198*], LOA=34, Motion Comfort=27.18, Capsize Ratio=1.89
Aloha 34 [Shoal], LOA=34, Motion Comfort=28.18, Capsize Ratio=1.87
Bandholm 35, LOA=34.84, Motion Comfort=27.96, Capsize Ratio=1.86
Bavaria 35, LOA=34.3, Motion Comfort=26.26, Capsize Ratio=1.9
Beneteau First 345, LOA=34.61, Motion Comfort=28.4, Capsize Ratio=1.87
Bolger Berengaria, LOA=33.46, Motion Comfort=31.49, Capsize Ratio=1.52
Brewer Morgane Le Fay, LOA=33.04, Motion Comfort=28.84, Capsize Ratio=1.83
Bristol 33, LOA=33.5, Motion Comfort=28.3, Capsize Ratio=1.82
Bristol 33.3, LOA=33.3, Motion Comfort=31, Capsize Ratio=1.84
Bristol 34, LOA=34.25, Motion Comfort=27.2, Capsize Ratio=1.85
Bristol 35, LOA=33.7, Motion Comfort=32.34, Capsize Ratio=1.75
Bristol 35 Centerboard, LOA=34.667, Motion Comfort=33.03, Capsize Ratio=1.72
C&C 33mk1 1986, LOA=33.77, Motion Comfort=24.75, Capsize Ratio=1.93
Cal 34, LOA=33.3, Motion Comfort=24.06, Capsize Ratio=1.89
Caliber 33, LOA=34.39, Motion Comfort=25.85, Capsize Ratio=1.91
Coast 34, LOA=34.66, Motion Comfort=30.88, Capsize Ratio=1.84
Columbia 34, LOA=33.6, Motion Comfort=29.36, Capsize Ratio=1.75
Compromis 34 ( C Yacht 10.40) (NL), LOA=34.12, Motion Comfort=24.82, Capsize Ratio=1.98
Coronado 34, LOA=34, Motion Comfort=31.34, Capsize Ratio=1.66
Coronado 34 (1968), LOA=34, Motion Comfort=33.39, Capsize Ratio=1.66
Crealock 34, LOA=34.08, Motion Comfort=33.74, Capsize Ratio=1.68
Ericson 34, LOA=34.12, Motion Comfort=25.57, Capsize Ratio=1.93
Ericson 35 II, LOA=34.48, Motion Comfort=29.14, Capsize Ratio=1.77
Ericson 36C, LOA=34.5, Motion Comfort=28.2, Capsize Ratio=1.91
Fortune 30, LOA=33.5, Motion Comfort=26.09, Capsize Ratio=1.95
Freedom 35, LOA=34.87, Motion Comfort=25.98, Capsize Ratio=1.96
Grampian 2-34, LOA=33.75, Motion Comfort=28.83, Capsize Ratio=1.75
Hallberg Rassy 352, LOA=34.75, Motion Comfort=30.23, Capsize Ratio=1.81
Hallberg Rassy Mistral, LOA=33.32, Motion Comfort=32.03, Capsize Ratio=1.73
Hallberg Rassy Rasmus 35, LOA=34.5, Motion Comfort=29.2, Capsize Ratio=1.74
Island Packet 32, LOA=34.44, Motion Comfort=26.95, Capsize Ratio=1.97
Island Packet 320, LOA=33.25, Motion Comfort=26.93, Capsize Ratio=1.97
Jeanneau Espace 900, LOA=34, Motion Comfort=24.62, Capsize Ratio=1.98
Mason 33, LOA=33.75, Motion Comfort=32.24, Capsize Ratio=1.8
Morgan 33, LOA=33.3, Motion Comfort=32.46, Capsize Ratio=1.68
Morgan 35, LOA=34.05, Motion Comfort=25.92, Capsize Ratio=1.88
Morris 34, LOA=33.75, Motion Comfort=27.15, Capsize Ratio=1.85
Nauticat 35, LOA=34.9, Motion Comfort=31.91, Capsize Ratio=1.78
Northsea 34 Pilothouse, LOA=34, Motion Comfort=26.8, Capsize Ratio=1.87
Pacific Seacraft 34, LOA=34.1, Motion Comfort=32.95, Capsize Ratio=1.69
Pearson 10M, LOA=33.05, Motion Comfort=26.43, Capsize Ratio=1.9
Pearson 35 Yawl, LOA=34.95, Motion Comfort=33.18, Capsize Ratio=1.7
Ranger 33, LOA=34.14, Motion Comfort=28.04, Capsize Ratio=1.75
Rival 34, LOA=34, Motion Comfort=32.25, Capsize Ratio=1.69
Sabre 34, LOA=33.67, Motion Comfort=27.49, Capsize Ratio=1.85
Sabre 34 MK I, LOA=33.667, Motion Comfort=26.79, Capsize Ratio=1.87
Sadler 34, LOA=34.75, Motion Comfort=27.08, Capsize Ratio=1.84
Sea Sprite 34, LOA=34.08, Motion Comfort=32.9, Capsize Ratio=1.76
Seacracker 33, LOA=33.32, Motion Comfort=26.97, Capsize Ratio=1.75
Southerly 101, LOA=33.75, Motion Comfort=24.89, Capsize Ratio=1.91
Sunbeam 34, LOA=34.78, Motion Comfort=24.19, Capsize Ratio=1.86
Tanzer 10.5, LOA=33.4, Motion Comfort=26.06, Capsize Ratio=1.96
Tartan 34c, LOA=34.21, Motion Comfort=28.13, Capsize Ratio=1.82
Tartan 34c E=13, LOA=34.21, Motion Comfort=28.13, Capsize Ratio=1.82
Temptress 34, LOA=34.5, Motion Comfort=25.89, Capsize Ratio=1.85
Terrapin 34, LOA=33.37, Motion Comfort=29.01, Capsize Ratio=1.71
Vancouver 34 Pilot, LOA=34.25, Motion Comfort=31.73, Capsize Ratio=1.74
Watkins 33, LOA=33.08, Motion Comfort=28.13, Capsize Ratio=1.82
Westerly Discus, LOA=33.25, Motion Comfort=31.72, Capsize Ratio=1.78
Westerly Storm 33' Cruiser, LOA=33.2, Motion Comfort=25.21, Capsize Ratio=2



And now if we ask for MCR > 34 and CSF<2, we get:

Alberg 35 Sloop, LOA=34.75, Motion Comfort=36.48, Capsize Ratio=1.63
Allied Seabreeze Yawl, LOA=34.5, Motion Comfort=34.61, Capsize Ratio=1.72
Baba 35, LOA=34.9, Motion Comfort=41.94, Capsize Ratio=1.61
Brewer Sunshine, LOA=34.98, Motion Comfort=46.05, Capsize Ratio=1.57
Brolga 33, LOA=33.1, Motion Comfort=37.36, Capsize Ratio=1.63
CT 34, LOA=33.25, Motion Comfort=37.68, Capsize Ratio=1.63
Cape George 34, LOA=33.96, Motion Comfort=44.69, Capsize Ratio=1.51
Colvin Saugeen Witch, LOA=34.33, Motion Comfort=35.29, Capsize Ratio=1.63
Contest 34, LOA=34, Motion Comfort=34.37, Capsize Ratio=1.75
Fantasia 35 MK II, LOA=34.5, Motion Comfort=50.99, Capsize Ratio=1.53
Fuji 35, LOA=34.57, Motion Comfort=40.74, Capsize Ratio=1.58
Herreshoff Santee, LOA=34.73, Motion Comfort=47.97, Capsize Ratio=1.43
Jason 35, LOA=34.16, Motion Comfort=35.03, Capsize Ratio=1.75
Knutson 35, LOA=34.91, Motion Comfort=35.74, Capsize Ratio=1.66
Lord Nelson 33, LOA=33.91, Motion Comfort=35.55, Capsize Ratio=1.75
Mariner 35, LOA=34.6, Motion Comfort=42.3, Capsize Ratio=1.57
Nauticat 331, LOA=33.14, Motion Comfort=35.36, Capsize Ratio=1.73
Panda 34, LOA=33.92, Motion Comfort=34.87, Capsize Ratio=1.72
Rafiki 35, LOA=34.75, Motion Comfort=36.69, Capsize Ratio=1.69
Sea Trader, LOA=34.5, Motion Comfort=35.59, Capsize Ratio=1.67
Seafarer 34, LOA=34, Motion Comfort=37.08, Capsize Ratio=1.64
True North 34, LOA=33.13, Motion Comfort=45.92, Capsize Ratio=1.55


These last happen to have all of them the CSF equal or under 1.75 (No HR's here! )

Cheers.

[Antonio Alcalá]

Yeah, i know that url but i really be interested in learning more ( STIX) only about 345 and puma 34. Did you know every year a spanish man cross the Atlantic to West and after to East "solo" in a First 285?

Best winds, Guillermo

[Guillermo]

It's being difficult to find reliable info on the Puma 34. Selling ads only state very few and most of the time contradictory data. I've found also this sites:
http://www.tinet.org/~jponsg/
http://es.msnusers.com/CLUBPUMA
But they have also very little info on the Puma 34.
Trustable info on the First 345 is also hard to find. Even Carl's calculator seems to have wrong numbers for her.
I need profile plans for both boats.
Can you help with gathering of data?

Cheers.

[Antonio Alcalá]

I haven´t more than you. I work out with this 2 webs. Incredible trip of our Alfonso Bonet, incredible...The 345 must be in the web of beneteau or maybe not.

Waiting your interesting numbers

Best winds