What do you think these ratios tell me about my boat?

[steve yates]

sail area/ displ.1. 20.1
Ballast/displ. 33.27%
Displ./length 112.38

Got them from the specs on sailboat data.com

 

[Tranona]

That it is a fairly light, lightly ballasted boat with a generous sail area. Typical of the type of boat you have.

SA/Displ is a measure of power to weight. Typical mid range cruisers are in the range of 14-16, racy over 20.

Ballast ratio is some indicator of stability, but actual stability is also influenced by hull shape, know as "form stability" - and broadly the beamier the boat the lower ballast ratio. So older style, narrow slack bilged boats may have a ratio in the high 40's but on modern hull shapes ratios in the 30's are common.

Displ/length is what it says - a measure of weight in relation to length of boat and is higher on narrow heavily ballasted boats.

There are trade offs with these measures, - for example, if it has a high disp/length ratio it may well require a high SA/Displ to power the weight. However the ratios are measured with "plain sail" so actual sail areas can be higher, for example by using a cruising chute to increase sail area in lighter conditions.

 

[Javelin]

Well roughly this is my interpretation.
SA/D -
14 or less = motorsailer
14 - 16 = heavy ocean cruiser
16 - 18 = cruiser
18 - 20 = cruiser/racer
20+ = racer

B/D the more the merrier.
Less than 30% is tender
30 - 40% average
40%+ stiff

D/L -
100 or less - ultra light racer
100 - 150 - light racer
150- 200 - cruiser racer
200 - 250 - light cruiser
250 - 300 - cruiser
300 + heavy cruiser

So it tells me you have something pretty light for its length.
Slightly under powered for a racer so typical cruiser racer territory.
She's a little bit tender so more of a coastal boat than off shore.

Oops - Tranona beat me to it.

 

[steve yates]

Thank you gentlemen, that's very useful. extrapolating from that, it might be a good idea to reef or roll away some Genoa earlish if my little Bradwell 18 shows a desire to sail on her side?
And that she would not be as seaworthy as a similar sized boat like a silhouette?

 

[bitbaltic]

This link seems quite useful:

http://www.yachtingmonthly.com/yacht-reviews/understand-boat-statistics-30154

Cheers

 

[Tranona]

You will find through experience when you need to reduce sail and whether you reef the main first or roll away a bit of jib. Around f4 is when you would expect the boat to feel overpowered and you would lose little speed by reducing sail and keeping the boat flatter.

 

[Fantasie 19]

Thank you gentlemen, that's very useful. extrapolating from that, it might be a good idea to reef or roll away some Genoa earlish if my little Bradwell 18 shows a desire to sail on her side?
And that she would not be as seaworthy as a similar sized boat like a silhouette?

I'm guessing you won't need the stats to know when to roll away some sail, you'll feel it, my last boat was light/tender (Bal./Disp.: 34.74%) and I usually planned on putting reefs in at F3, or I spent the entire afternoon fighting the tiller and sailing at an angle of 45' or more.. The current one was bought specifically because she was heavier in about the same length (Bal./Disp.: 44.08%) she carries sail for longer which is a good thing... :encouragement: