Performance Factors

Ahh now i see what you mean

Originally posted by Chew my RS Originally posted by Guest#260 Interesting, but I am not sure how much I care about the relative performance of a class to another ... what I care about is: 1) is the boat fun to sail 2) is it good for class racing 3) are the people nice to hang out with .... True enough, but that's not really answering the original question about weight, length, sail area etc.  Anyway, many of us are unwilling or unable to travel the country to get some fleet racing.  So you may as well sail whatever tickles your fancy in the local handicap fleet. Not sure how to do a 'double quote', but in response to Smight's comments: N12s are light by most standards - 78kg all up.  Okay, that's more than a Cherub, but still...  Anyway, to clarify my point, a 12ft boat can't have a high maximum displacement speed (some times called hull speed).  Max displacement speed is physically related to boat length, so a 12ft boat can not be as fast a 14ft boat of equally good design.  However, light air performance is also determined by wetted surface area, and 12s are pretty good from that point.

I guess my point is that whilst these issues are of interest the most fun comes from quality fleet racing.

BTW the N12 is 78kgs for the hull, mast & c/b ... I'd guess a sailing weight of about 85kgs.

Originally posted by Chew my RS   A 12ft boat can never be fast in displacement mode, no matter how well designed.

I would argue that a national 12 (a 12ft boat) is fast in displacement mode especially light wind sailing. They are well known for there speed in light winds although i don't think this is because of weight because they are relatively heavy for a 12ft boat and the sails arn't particularly large.  

You could write a thesis on this question!  Ian Hannay has written an excellent AYRS publication called Rig theory which goes into this in some detail.  In  a nutshell:  length, weight and stability are the three primary parameters that affect boat performance.  Rig height, foil depth and sail area are the secondary parameters and detailed design such as hull lines and sail profile are the tertiorary factors.   All other things being equal (which they never are) long, light boats will be quickest across a range of conditions and courses.  Stability is obviously vital to harness power - an extra trapeze will allow you to carry bigger sails.  More sail area lets you reach your top speed in less wind, but doesn't actually give you a higher top speed.  Rig height and foil depth are key to efficiency, minimising induced drag, and allowing you point higher.  So, for any boat of given length, weight, stability, rig height, foil depth and sail area there is a theoretical maximum perofrmance that can be achieved.  Compromises in hull shape, sail planforms, rudder sections, mast sections etc prevent this maximum being achieved.

Compare the Dart 18 and the Cherub.  The Cherub has better foil sections, (arguably) a more sophisticated rig, better attention to detail, deeper foils, more sail area and is lighter.  And yet, becasue the Dart wins on 2 out of 3 primary factors (longer and more stable), it is quicker (on average, according to PY).  Its longer length and more stable platform give it  higher potential speed.  The excess weight and simple design mean it probably only reaches 60% of its potential, compared to the Cherub reaching maybe 80% of its. but the longer, more stable boat starts with more potential.  Cherubs of course sail extremely well when planing, but simple physics prevents it sailing fast when not planing.  A 12ft boat can never be fast in displacement mode, no matter how well designed.

As another example, my NS14 is the same length as a Merlin Rocket, and both are hiking boats with similar stability (the MR is a little wider, but in broad terms they are similar).  The Merlin has bigger sails and a spinnaker, so you might think it was faster.  However, because the NS14 is 5 stone lighter and has less drag it is probably quicker.  I look forward to finding out over the next few weeks!

I'm finding this thread interesting and basically underlining what I know
from windsurf world.

Waterline length is important in displacement sailing.

Rocker and or step to a planing flat important for boats that have the
option of high crew righting moment via trapeze or trapeze and racks.

A "rounded" hull important for light wind performance where a flat hull
will stick.

So the perfect shape would be rounded hull running into a stepped
planing area.

On a smaller scale, exactly the difference between the RS 500 and the
Laser or V3000 and the RS 400.

Boats I've now come to have some detailed competitive experience of.

The 400 is a very rounded yet wide hull that can shed wetted area by
heeling in light air, the 500 a little bit of both and the 3000 a fairly flat
bottomed hull that sticks a bit in a drifter yet really comes unstuck and
planes upwind in a breeze, something we're missing at the moment in
the 500 (though this may be a crew skill problem)and probably couldn't
happen on a 400.

As to weight, more important imo to boats that rely on being on the
plane, than say volume of displacement area in displacement style hulls,
at least this is the case in the sailboard world.

As a casual observer and really only recently keen newcomer to the sit
down world, the biggest single factor imo of late is the sometimes over
canvassing that has come about with the era of the skiff.

It seems to me to limit the higher performers to inland and or estuary
venues particularly in strong winds, I may be wrong, but that's how it
appears from where I'm now sitting.