Comfort Index what's yours?

onesea

onesea

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I was reading this months YM and saw the admittedly tongue in cheek comfort Indexes...

Well mine came out at:
Disp = 3901 kg Comfort index = 17.41784181
LWL = 27.25 ft
LOA = 34.75 ft
Beam = 11.42 ft

Go on what's yours?

They reckon the formula is:
Comfort Index = (Displacement) /(0.65*(0.7*LWL+0.3*LOA)xBeam^1.333).

Displacement in lbs all others in feet.

If you use eXcel (or other spreadsheet software) you should be able to cut and past formula and just replace values...
 
Displacement: 7280lb
LWL: 20'9"
LOA: 24'6"
Beam: 8'6"

Numbers are from an old PBO review; not sure I trust them 100% as I'm not convinced there's 4 foot of overhang to make up the difference between LWL and LOA. Anyway, taking them at face value:

(7280) /(0.65*(0.7*20.75+0.3*24.5)x8.5^1.333)

= 29.5 if I've done my maths right.

Is that good?

Pete
 
OK so here’s what I have for Paean. Not sure how accurate the displacement is but here goes:

Displacement = 6496 lbs
LWL = 19
LOA = 24.75
Beam = 8

I found the maths harder than I thought I would (must try harder!) but if I have this correct, I get 25.47
 
Vagabond 31

With a bit of extra keel weight over and above the standard:
Disp: 13200 lbs
LWL: 27.2'
LOA: 31'
Beam: 10'

CI according to Excel: 33.3

What does that mean? I don't get sea sick or what?

Actually I do every now and then - which is different from my old boat, an Aphrodite 101:

Disp: 6630
LWL: 26.2'
LOA: 32.6'
Beam: 7,87'

CI: 23.2

On this boat I never ever got sea sick. So maybe it is a reverse sea sickness index? :confused:
 
The boat I usually sail, a Polaris Drabant:

Displacement: 5776 lbs (of which keel 2976 lbs or 51.5%)
LWL: 21.3
LOA: 25.6
Beam: 7.9

Result: 25

I think it's usually quite stable. Possibly more than the formula implies, as the weight is down low, as lead at the bottom of the keel.
 
I also think the comfort index is inversely proportional to speed.
So my old Najad may be comfortable because it's heavy but it's never going to win around the cans.
You could probably modify the formulae to change some of the constants to reflect the height between the COG and COB. Similarly, hull shape.
 
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Rival 41C

Displacement 22046 lbs
LWL 32.67 ft
LOA 41 ft
Beam 12.25 ft

Comfort Index 34.2

As the article says its tongue in cheek; its subjective anyway, comfort.
 
PhillM said:
OK so here’s what I have for Paean. Not sure how accurate the displacement is but here goes:

Displacement = 6496 lbs
LWL = 19
LOA = 24.75
Beam = 8

I found the maths harder than I thought I would (must try harder!) but if I have this correct, I get 25.47
Click to expand...

Just realised I didnt use the ^1.333 bit - what's the ^ for?
 
Mine is errr... 5!

So it clearly doesn't work for multihulls.

On a recent crossing of the Celtic Sea in winds up to 30+ knots true, we slept well, were relaxed, cooked and ate well. When we got in, other yachts that had been doing the same passage (it was a race) were full of tales of woe and how ghastly the conditions had been. We'd hardly noticed them, so I would rate our comfort index as considerably higher that J-120s, Starlight 46s, Dehler 39s, MAxi 1300s etc.
 
I have my own formula.

4" Dunlopillo x [old fleece + fluffy slippers] x [bottle of wine + cheese & biscuits]= comfy.
 
Found this article about the Comfort Index on North American Sailor site.

Apparently it doesn't work for mulithulls and the meaning of the results according to the article...

"numbers below 20 indicate a lightweight racing boat; 20 to 30 indicates a coastal cruiser; 30 to 40 indicates a moderate bluewater cruising boat; 50 to 60 indicates a heavy bluewater boat; and over 60 indicates an extremely heavy bluewater boat. If evaluating a larger boat, say 45 feet or longer, expect your results to be skewed a bit higher on this scale; if the boat is quite small, say 25 feet or less, they will be skewed slightly downwards."
 
jamesjermain said:
To the power of.
Click to expand...

Umm now I get 74.58 !!

Not sure my brain is working today. I think I'll give up on the business finance plan and go sailing instead.

edit: I used "to the power of" in my business plan and now it tells me that next year I can buy an Island Packet and cruise round the world.
 
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