Clyde_Wanderer
Well-Known Member
Was reading through an old for sale advert for my boat and noticed aspect ratio of 52% what is this value? and is it good or bad?
Just querious.
Thanks.
Just querious.
Thanks.
ASPECT RATIO
- Thread starter Clyde_Wanderer
- Start date
Aja
Well-Known Member
William_H
Well-Known Member
Aspect ratio is as I understand it the ratio of chrodr to length.
A boat can have a very tall mast with quite short chord sail ( short boom or foot of jib) givintg it a high aspect ratio.
The theory is that air leaks over the ends of an airfoil causing drag and loss of thrust. If the sail is large but the size of the top of the sail is small by comparison then losses are less.
You may be confused that the top is narrow cos it is a triangle even so the losses occur along the top edge even though that is the leach or back of the sail right down to the boom. In fact an eliptical top or semi circle appears to have the least drag hence you see racing yachts with an almost horizontal top of sail (large roach).
Likewise the spitfire fighter was famous for its eliptical wing tips.
Soeven though a tall sail gives more heeling force it is quite a lot more efficient especially in going to windward.
rudders and keels are described in the same way.
I have never seen an aspect ratio described by a number but presume that 52% is a ratio of average chord to sail height. You would have to calculate for the jib (largest) then average the two.
Perhaps someone else can tell us exactly what 52% apect ratio means. I don't know if it is good or bad.
I tend to go on the look of a sail plan. So gaff rig boats tend to be low aspect ratio while modern racing keel boats tend to be higher aspect ratio.
Just love the boat you have got. olewill
A boat can have a very tall mast with quite short chord sail ( short boom or foot of jib) givintg it a high aspect ratio.
The theory is that air leaks over the ends of an airfoil causing drag and loss of thrust. If the sail is large but the size of the top of the sail is small by comparison then losses are less.
You may be confused that the top is narrow cos it is a triangle even so the losses occur along the top edge even though that is the leach or back of the sail right down to the boom. In fact an eliptical top or semi circle appears to have the least drag hence you see racing yachts with an almost horizontal top of sail (large roach).
Likewise the spitfire fighter was famous for its eliptical wing tips.
Soeven though a tall sail gives more heeling force it is quite a lot more efficient especially in going to windward.
rudders and keels are described in the same way.
I have never seen an aspect ratio described by a number but presume that 52% is a ratio of average chord to sail height. You would have to calculate for the jib (largest) then average the two.
Perhaps someone else can tell us exactly what 52% apect ratio means. I don't know if it is good or bad.
I tend to go on the look of a sail plan. So gaff rig boats tend to be low aspect ratio while modern racing keel boats tend to be higher aspect ratio.
Just love the boat you have got. olewill
Lakesailor
Well-Known Member
In other diciplines an aspect ratio of 52% would give roughhly one dimension 2 times the other IE a TV screen 2 feet wide by 1 ft high, or visa versa.
Presumably an aspect ration on a sail plan refers to that.
But is it just the mainsail or the whole sail triangle? If it's just the main perhaps a sail with a 30ft luff and a 15 ft foot is a bit squat.
Presumably an aspect ration on a sail plan refers to that.
But is it just the mainsail or the whole sail triangle? If it's just the main perhaps a sail with a 30ft luff and a 15 ft foot is a bit squat.
gandy
Well-Known Member
For a wing it would be the ratio of span over mean chord. So for a 30' luff that would mean a foot of near to 30' as well, depending on the amount of roach.
I've never seen aspect ratio expressed as a percentage, either. Rather than 52% I'd expect the aspect ratio to listed as 1.92:1 or more normally just as 1.92 with the :1 implied.
I've never seen aspect ratio expressed as a percentage, either. Rather than 52% I'd expect the aspect ratio to listed as 1.92:1 or more normally just as 1.92 with the :1 implied.
boatmike
Well-Known Member
I think the term needs qualifying.
On cats it is used commonly to describe the ratio of beam to length.
Otherwise mast height, keel depth, what have you.
The term aspect ratio without qualification could theoretically apply to anything I believe....
On cats it is used commonly to describe the ratio of beam to length.
Otherwise mast height, keel depth, what have you.
The term aspect ratio without qualification could theoretically apply to anything I believe....
S
Skyva_2
Guest
Aspect ratio could be applied to any planform. A general purpose definition is (Span squared) / Area.
See http://www.grc.nasa.gov/WWW/K-12/airplane/geom.html
See http://www.grc.nasa.gov/WWW/K-12/airplane/geom.html
sighmoon
Well-Known Member
Course, all this is assuming the previous owner said what he meant.
I suspect that number's your ballast ratio. In fact I just googled it, and the ballast ratio of a hummingbird 30 is 52%...
I suspect that number's your ballast ratio. In fact I just googled it, and the ballast ratio of a hummingbird 30 is 52%...
Other threads that may be of interest
