Heeling Explained

[Don Guillette]

bentwing60: I know you didn't mean it as a slur and I didn't take it that way. It's been the truth over the years that I always leave the scientific explanations to others. I'm just not a scientific guy and Richh, joe from San Diego, Stu j, scott and others know that and that's why I'm glad they participate on the forum. They add that aspect and, in fact, that's what makes this forum unique.

To further illustrate my point, on page 5 of forward of my book I say "This book may not be for everyone. If you wanted a scientific presentation that includes intricate details, together with a complicated formulae for hull speed, wave lenght and displacement/lenght ratios plus endless verbiage, then this book is not for you. Sail trim is an acquired art and simple to learn and understand when it's presented in an easy-to-understand fashion".

 

[davenlynn]

Who cares? Heeling is fun!

 

[RichH]

I am not a mechanical engineer, but I have always assumed that the air foil effect happens with air which expands and therefore creat a lower pressure when flowing over the air foil.

With water being incompressible and stay as liquid until cavitation occurs, is the air foil affect still there?

Can some one please confirm or correct me on the basic assumptions for the Bernulli effect?

With the keel having a symmetrical shape on both sides, there is no uneven lift when vertical but may have a lift due to angle of attack when heeling. If so, the lift is actually in the same orientation as the heeling moment created by the sail.

The main drag has to come from the rudder though for doing all the work in offsetting weather helm.

Oliver.

Classical aerodynamics and gas dynamics holds that AT NEAR ATMOSPHERIC PRESSURE and at subsonic flow that gases are 'incompressible'. The actual compressibility at such conditions is so 'trivial' that when calculating or measuring such effect is that it is always 'ignored'.
Bernoulli Theorem is valid, but only is valid for fluids that have viscosity, AND the velocity and pressure observations MUST be 'adjusted' to include 'sensible' (measured by gages and instruments) AND/PLUS 'insensible' effects (cant be measured by instruments, etc. and must be 'calculated')

As regards symmetric keels, foils, etc. it really makes NO DIFFERENCE (ignoring efficiency) as long as a 'recirulation' flow 'around' the foil is started and maintained. .... this includes flat plates used as foils !!!!!!!
Remember also that a sail is only a 2 dimensional shape ... with essentially NO THICKNESS!!!

At the 'maximum' lift from the keel, etc., the rudder is used to hold the keel at that proper optimized angle of attack relative to the motion of the boat ... the rudder in doing so experiences 'more' drag when held at a 2-3° offset than when held 'straight' to obtain that 'slight' rudder pressure attitude. That slight induced 'helm pressure' through the rudder by the helmsman .... sets the proper attack angle of the heel to get 'maximum lift' from the keel.

The following 'article' will explain (for the layman and without all the supporting fluid dynamics mumbo-jumbo and intense math) how a foil/sail/wing gives 'lift'. Its valid (as a summary) for aerodynamic flow on sails, wings, keels, turbine and fan blades, propellers, etc. For the layman, it may take 'several readings' before comprehension and .... to arrive at the "I see" moment. The 'key' to this article is 'recirculating flow AROUND a foil' ... and of course 'viscosity of the fluid'.
http://www.arvelgentry.com/techs/origins_of_lift.pdf

;-)

 

[RichH]

Here's a measure of simplicity for all those who arent fluid dynamicists. This is the method that those 'dynamists' originally used to observe and collect one hell of a lot of data that led them to their conclusions, etc.:

Simply 'experiment' with what you have and what you know or perceive, record or remember the results that produce the 'best output' and then continually refine your method. This is called the 'empirical method' - and the results will be the exact same as the 'theoretical method'.
Start with such simplicity of what Don has in his Sail Trim guides, then attempt to master them ... this will save you about 5 years of 'experiments'.
Learn what "velocity made good - VMG" is all about .... the optimization of sailing angles; and, the 'adjustments to sail trim and shape' will become readily obvious if you continually 'test' by experiment of which trim or shape condition give you the optimum VMG, etc. A simple record/log of windspeed versus boat speed vs. VMG to a distant waypoint, sailing angles, how the tell-tales are flowing, how much 'helm pressure' even as a guess .... will all combine to increase your expertise, your FUN ... and your 'safety'.

Start with Don's Sail Trim Guides, and then 'figure it out' by yourself and the 'notes' you record in a small book, etc. will ultimately expedite your 'mastery' of sailing trim and sail shape, etc.
If you talk with and interact with all the LIONS of ultimate sailing, they mostly all started with such 'experiments' and 'data/record' keeping, they then excelled and became the absolute masters of the sport. They will all tell you that they all became 'happily addicted' to the absolute joy of 'understanding'.

;-)

 

[Don Guillette]

RichH: At my mini sail trim seminars -- the normal seminar is 3 hours long - which are 35 minutes long followed by a Q&A that can go on forever. I do the mini's for YC's and sailing clubs in AZ. All I discuss is draft depth, draft position, twist and angle of attack. The audience is anywhere from 35 to 50 and topped out at 165 sailors in Lake Havasu, Az a couple of years ago at a trailer sailor convention.

Here's my question for you: I tell them in one sentence that lift is provided by 3 things -- the sails, the keel and the rudder and they should induce about 3 to 5 degrees of rudder to take advantage of the lift from the rudder and don't heel the boat past 25 degrees so as to maintain lift from the keel. That's all I say and then I move on. How would you suggest I compose that one sentence? thank you.

 

[Stu Jackson]

Don, I think that's just perfect. If they don't ask detailed questions, then leave it a that. Most sailors want to sail, not do thermodynamics or physics. If they want more details, have 'em buy books (other than yours ).

 

[RichH]

Your single sentence is pretty much spot on ....

.... trim and balance so you induce only about 3 to 5 degrees of rudder to take advantage of the lift from the KEEL and don't heel the boat past 25 degrees so you dont slip/skid to leeward.

;-)

 

[anchorclanker]

I was reviewing this thread and a couple of things struck me --- it was all the great info but the other thing was where do you guys come up with the "handles (CB Jargon)" you use? I like normal names like Scott, RichH, Alan, StuJ, Robert Lang and Joe"from San Diego". I especially like the name Joe from San Diego because that's what I call him!!! .

I was wandering around and came back across this thread, and thought I would explain myself. My name is Paul, but I dont use it because, well, I guess because I like being more "private". Its why I dont do FB or Twitter or Classmates or any other of those deals. I'm not hiding, so much as I dont care to be "out there" in the world. As for the name Anchorclanker, its one of several ive used. But when it finally got my own sailboat and joined a forum, none of the old names (handles) made sense. I needed something "nautical".

Before I was born, my parents lived in San Fransisco and my Dad worked at NAS Alameda. He also drove Taxi around the bay area spoke about working and living there all my life and had a million stories. But one of the funniest terms he had was for guys he called "dry land anchor clankers". The reference was to Navy guys who had never been on a boat, never saw a boat, and who couldnt tell one end of a boat from the other. He never sailed, and hes gone now, but I think he would love it. He really loved boats and ships.

A side story, a guy on the FD that I know is a retired Navy Admiral. I dont know squat about the Navy I guess, but he claims he never stepped one foot aboard a Navy vessel during his career. I called him a dry land anchor clanker and he laughed so hard. Said he hadnt heard that term in ages, but agreed that thats what he was. I just dont understand how a Navy guy could make Admiral without knowing boat stuff.