Performance Factors

As someone who finds this thread interesting but has no idea half the time what your all talking about… what makes some boats perform apparently punch above their weight. For example to my uneducated eyes boats like the 400 and 29er always seem to perform much better than a cursory glance at their size and shape would suggest.

 

Ian

One of the things that militates against longer boats is maintenance. I don't know what the typical standard single garage size is, but my IC fits in neither my garage nor my parents. This is a bit of an issue if you need to do some work. This was of course much more of an issue in the days of wooden boats which needed varnishing every year.

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.

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!

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.