Newer, Lighter or Older, Heavier

[hansdg53]

I would say if you intend to spend longer time on the boat, and you are not going to make extended voyages, get the most spacious boat your money can buy.

[Hiracer]

I've owned two sailboats. A 1982 medium displacement 33' (Wauquiez Gladiateur) and a 2001 heavy weight custom steel 36' (Ted Brewer Humoric derivation).

I will would never again think of cruising in anything other than a heavy displacement sailboat. In normal to blustery conditions, there is no comparison in terms of comfort. Motion comfort is one of the most underrated characteristics in boat performance, IMO. It is hard to understand without first hand experience cruising both ways.

Further, motion comfort one of the most expensive performance criteria to get, if purchasing new. All of the boats built to a price are lightweight. With a new boat, to a great extent, you pay by the pound.

Further, the older you get, the more important comfortable motion is, IMO. I'm 52, and I can see that already. At some age, motion comfort becomes a safety issue.

New or used, don't get a light boat if you intend to go cruising. It can be done light, sure, but it not adviseable--not by me at least.

I feel strongly about this because I've vacation cruised both ways, and the difference blindsided me when I purchased a heavy boat and didn't realize what I was getting until after I got it. Pleasant surprise and radically changed my outlook on sailboat displacement.

The only caveat I would like to add is that you need to get a decent SA/D ratio, no matter what, heavy or light. A boat that will not sail in light airs ain't much of a sailboat in my book. In fact, I think SA/D is even more important than D/L ratios.

Many will claim that a heavy boat will not sail in light air, and that's categorically not true. An undercanvassed boat will not sail in light air. Many heavy boats, unfortunately, are undercanvassed, so look out for that.

Finally observation: construction quality is important in an offshore boat. It's way easier to get quality construction in a heavy boat (although certainly no guarrantee) than it is in a lightweight boat. In fact, I would put construction quality as even more important than SA/D or D/L ratios.

[Paul L]

John,
You've obviously found what works well for you. I personally have not found a direct correlation between displacement and comfort. As Bob Perry likes to say, we are talking about levels of discomfort here. From y experience, waterline has more to do with comfort than weight. You mention age and wanting better motion comfort to help out the old aching body. That may be true, but then trying to get a decent SA/D means that you using much larger sails for the same length boat. Something that definitely gets harder as we age. Even in stronger winds, you will have up significantly more canvass on a heavy weight than a moderate weight boat and be dealing with the heavier loads.. You also said:
"It's way easier to get quality construction in a heavy boat (although certainly no guarrantee) than it is in a lightweight boat."
I'm not sure that is true if you also want B/D ratio that is also reasonable. Quality construction is expensive - light-weight or heavy weight.

Paul L

[Hiracer]

Paul,

My wife used to get seasick frequently on the old boat. Not once on the new one. The new one is only 3' longer.

I think total displacment, total beam, displacement/length, and B/D ratios all matter to motion comfort. A light but big boat, a la Dashew, can have good motion too if it's big enough (total displacement counts). But in my size category, it's largely a function of D/L and B/D ratios along with beam.

Comparing our two boats, they have similiar beams but the old boat ratios were 240 (IIRC) and .44, respectively while the new boat is more like 300 and .35. Taken together, those two ratios indicate radically different motions in a normal seaway. My wife's experience confirms this. Plus, I can feel it too. It's a night and day diffference.

The effect of a high B/D is not to be understimated. I think it is responsible for about half of the difference between our two boats. Our new one just doesn't have the snap roll.

For our boat size, sails have been a non-issue.

In Perry's most recent book he talks about how he came to design boats from a racing background, so he's laid his biases on the table. Ironically, he is known for his cruising designs, but his sailing background is racing.

His own boat is a 26' lightweight Swedish boat with outboard motor. I'm sure he gets bounced around a bit in that boat and has various degrees of discomfort in a normal seaway.

[Paul L]

John,
The seasick anecdotes are legendary. I'm not sure they say much about the actual motion. I am very susceptible to seasickness and need to watch my self carefully when offshore. (Although a lot less now that God has delivered Stugeron to me). I think those of us cursed with seasickness all have different sets of conditions that trigger it. For me a slow motion or getting cold, will do the most damage. To each his own.

Paul L

[Hiracer]

I have highlighted some of the motion numbers to give a little objectively to the discussion. Pretty large deltas.

Both sets of numbers provided by the same N. A.

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


* * *


Numbers for my custom steel boat, a Ted Brewer design:

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]

My previous boat had a calculated motion comfort of 36.48 (Alberg 35), my current boat has 21.51 (J/37) according to SailCalc. For me, there is no way I could say I got less seasick on the first over the latter. The latter is less tiring, but that is because it is an easier boat to sail.

Paul L

[Hiracer]

If I were to go lightweight, it would be a J-Boat. I like J-Boats. I know delivery captians who love J-Boats too.

[Paul L]

And if I were to go way North or way South, it would be steel or aluminum. As they say, horses for courses.

Paul L

[dcstrng]

<That may be true, but then trying to get a decent SA/D means that you using much larger sails for the same length boat…>

As arcane (or at least bothersome) as it may seem, I think a potential skipper should keep most of the “numbers” in mind… The numbers won’t (or at least shouldn’t) make the decision for you, but with a bit of experience of knowing one's own preferences, they will help get in the ball-park at least… Heavier disp/length ratio boats often have lower SA/D ratios – hence often a need for more light air sail options all other factors being equal (when is that ever true…?), conversely a lighter vessel may need to have tackle aboard that allows `em to gear-down a tad more…

One figure I watch is the comfort factor (can’t remember where I pilfered that; Brewer, Benford…?) and at least for me I like boats that score above 26-27 on the comfort ratio (usually with screen number comfortably under 1.90) although that is usually associated with boats with a disp/length noticeably above at least 250 which may not be everyone’s cup of tea… in any case, I’ve diddled a twiddled with a little spread sheet for some years that I run a quick check on a boat before falling in love with it… Like I said, it won’t make the decision for me, and surely doesn’t address quality issues, but at least I know at the outset whether I’m dealing with a sprinter or a distance runner and what that may mean up front…

And of course, the numbers provide a modicum of entertainment when window-shopping as well…

[GordMay]

Originally Posted by dcstrng

... One figure I watch is the comfort factor (can’t remember where I pilfered that; Brewer, Benford…?) and at least for me I like boats that score above 26-27 on the comfort ratio (usually with screen number comfortably under 1.90) although that is usually associated with boats with a disp/length noticeably above at least 250 which may not be everyone’s cup of tea…

Motion Comfort Ratio was developed by Boat Designer Ted Brewer.
The formula predicts the speed of the upward and downward motion of the boat as it encounters waves and swells. The faster the motion the more uncomfortable the passengers. Thus, the formula predicts the overall comfort of a boat when it is underway. Higher values denote a more comfortable ride. As the Displacement increases the motion comfort ratio will increase. As the length and beam increases the motion comfort ratio will decrease.

See “Ted Brewer Presents A Primer on Yacht Design”
http://www.tedbrewer.com/yachtdesign.html

[dcstrng]

<was developed by Boat Designer Ted Brewer….>

Gord, yer knowledge base is impressively encyclopedic as always… thanks for the link as well…

[Paul L]

You might have posted the start of Brewer's description of Motion Comfort formula:
"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."

If me, the number has not proven useful. As Brewer says also says:
"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."
Significant differences in Motion Comfort do not have any significant difference on me getting seasick. Different sea and weather conditions do (radically), but Motion Comfort 36 vs Motion Comfort 21 are irrelevant.

Paul L

[dcstrng]

<Significant differences in Motion Comfort do not have any significant difference on me getting seasick…>

Yep – that is precisely the limits on the “numbers…” Is a D/L of 300 heavy, medium or light –well, quite portly by J-Boat standards, but not so for others… is a SA/D of 22 preferable to, say, a 15, or even a 13, well, Hmmmm….. Is $250K expensive or not… for some, exorbitantly; others, definitely not… although in the abstract the “numbers” are modestly informative (or at least interesting, if not always illuminating…) at the end of the day it comes back to the crew… except in racing, where I have no clue, but am told no-numbers (admittedly somewhat different ones), no-race…

[Paul L]

Larry,
Sounds like you have a reasonable grasp on how you use the various ratios and when to use good judgment. Sometimes it sounds like people use the ratios to justify their own subjective decisions or support their prejudices. I find the Motion Comfort ratio and the Capsize Screening formulas to be less than useful.

Paul L