Trim Angle?

[PaulP]

OK, all you budding nautical engineers -

A lot has been written about trim angle and sailing a 12 "on her lines"

Measuring the bottom of the keel on a new (95 Std) EC12 hull, I find the angle to be approximately -2 degrees, pitched from front to rear. For this to sit level in the water, the deck would have to be bow high 2 degrees !

When they say sail on her lines, I understand this to mean the bottom of the keel is parallel to the waterline.

Yet articles and books point the deck angle to be between 1/2 to 1 degree up? What gives?

Am I interpreting this wrong? Help me to graduate to your level of nautical engineering

Thanks

Paul P

[Larry Ludwig]

It also means how your hull was trimmed from the mold... and <u>which </u>mold. There are different interpretations on the sheer of the hull before the deck is attached. This may be causing your deck to appear off. You were correct in the comparison of the keel to the waterline.

Then you get the fun part of ballasting, and to which line 42" to 43" and there are options and opinions here as well. I don't believe that there is any singular best way...only what you like and feel comfortable with. (i.e. what you believe to be fastest)

They are all different the same.

[Matthew Houghton]

The boat itself would have been designed with a certain waterline right? If this is the case, it wouldn't matter which mold (because they're all supposted to be the same right?)the boat came from.(?) What we need to do is find the correct trim angle and waterline associated with the drawings on the full size boat originally, right?

Also, I would not have thought that the base of the keel would have to be made parallel with the waterling. It seems to me that this is a design feature that does not necessarily need to be parallel but could have been tapered.

I am not trying to present these ideas as fact. I am not a designer but this is what I thought.

I am curious to see what the truth is.

Matt

[Larry Ludwig]

<blockquote id="quote"><font size="1" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote">For this to sit level in the water, the deck would have to be bow high 2 degrees !<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">

This is using the deck as a reference point... that is why I responded the way that I did. Yes, they are all supposed to be the same, no they are not all *exactly* the same.

Actually they can and do have some differences. That is what precipitated the `95 Hull program.

If you read the class rules it will describe to you the measurements that are regulated, the others are not. Freeboard for instance, is not. This is exactly why Rick West has instituted the new Hull Standard Program, and why it is needed now. I believe that "once upon a time" in Florida, hulls were checked using a half-hull mold that would confirm or deny the entire shape of the boat in one fitting.

Essentially the boats are all the same. The new molds that are coming out from RMD are going to produce the exact same boats that are produced now. (if you read between the lines here, it means that if you are waiting for the new molds thinking that you might get an advantage.... you will not)

The critical dimensions are defined and maintained therein. After that... they police themselves in the manner of... if you changed anything you could only detract from the boat, not improve upon it.

Making it heavier and carrying less ballast would be a good example. You can stay within the presribed weight limitations, but slow your boat down... not exactly what you want to do.

That is why heavy hulls around here become planters, target practice, I even set one off into the Gulf of Mexico with a note inside it. IF you find it... it is NOT Class legal.[xx(]

[kahle67]

"I even set one off into the Gulf of Mexico with a note inside it. IF you find it... it is NOT Class legal."


That's too funny! A message in a model.

[Larry Ludwig]

Sounds like a song title.... mess-age in a mod-del.....
heheheh I always liked that song...

[Chuck Luscomb]

Hi Paul,

I am going to stick my neck into this thread. The term "sailing on her lines" is a bit different to the term "Sitting on her lines".

Sailing on her lines is in fact a design term that refers to the boat trimed out and sailing on her designed water line for a given angle of heel. Not related at all to the relationship of the bottom of the keel to the actual water line. If the keel were an 1" deeper on the aft end you would have a pretty radical looking keel BUT she would still sit on nearly the same DWL.

The term Sitting on her lines means that when she is properly trimmed out, she will sit on her designed water line. For the EC12, she will have a water line of between 42" and 43" in fresh water (Less in salt water). Again no relationship to the angle of the keel bottom to the DWL.

A couple of good resources are "Principles of Yacht Design" and "Sailing Yacht Design".

Hope this helps,

Chuck Luscomb
1684

[Rick West]

This was all too funny! Thanks Chuck for cutting to the issue. Larry, thanks for understanding that there is no old and new just a change in the building program so that we all get the same.

Paul, I commend you on your measuring and you may be correct in the actually plane of the keel. I was told and have seen that it is not the keel but the waterline as I see in tests and it is known that I run a lower trim angle than most. I seek a level boat under power for the wind at that time. Because we cannot trim or ballast the boat to trim during the event, all that is left is the balance of the rig on the step and the sheeting of the sails. (Note that Rinehart's mast step holes are smaller apart than the rest of us at 3/8".) It is hard and what is it in the end...like Larry says...micro knots. And we all want them, right?

...94

[kermwood]

Can l just check some basic points here
whilst l can see that the water line is inportant to be legal for the class rules ie 42"-43".
Is it not the trim angle that Rick touched upon just as important to get right as the waterline?

Is the trim angle set in the tank totaly different from that on open water ie that when the boat starts moving forward this movement pushes the bows down and so alters trim angle?

So should be it set to account for this happening and would this in turn then alter the water line?

Or have l totaly lost the plot! Woody

[PaulP]

Kermwood,
You have it exactly right.

Rick,
On your Dummy Reflections, Page two, you refer to the boat "sailing on her lines". On another page, you refer try to fly an airplane at some angle other than the designed angle of attack and how it affects drag, lift and efficiency.

Larry,
Some of the hulls with a trimmed sheer line may have a different line but the hulls built by most include a molded sheer line so it comes out of the mold constant.

What I am trying to do is quantify just exactly where is the designed waterline? By changing trim angle, it moves around. We know it has to be 42-43" But there are no marks or lines to establish a starting point. If you trim for 1degree, the waterline is at a certain point. If you trim to 0degree, it is at another point.

So I can get some of those "micro-knots", just where is the best spot to set the trim angle?

Yea, I know I could do better practicing my sailing than worrying about this, but I am always after the grail!

I tried to note to the math guru, Larry Robinson, but have not received a reply.

Anyone want to venture out on a limb and speculate on the best trim angle?

Paul (Looking for more speed in a new boat) Proefrock

[Larry Ludwig]

To find the best trim angle look under BEST.... baseball player, race car driver, best heavy weight boxer... hehehehe

If you win, congratulate the skipper... if you lose blame the boat.[xx(]

[Rick West]

Oh Boy, "the grail." This what we are supposed to do on hot early evenings on the veranda with our favorite beverage. Okay, here we go...

Remember the key word was "Dummy." It began in late 1998 with the reading of both manuals to understand this EC12 and the building of it. Upon reading Optmizing, Bill Cullen and I knew we were in for a long run. I will not get into it all but what we embarked on was a post graduate course and likely a thesis in the end. It was never scored, so what did we know. However, to condense this, Bill built an incredible transparent test tank to presision instrument standards and we produced the numbers on the Final Weigh In page on the building site.

Page 27 of Optimizing carries a statement that we could understand with relation to the lines of the keel and the waterline. The problem was, what waterline! The chapter, Trim Angle, was not the whole story but only a segment of balance, ballast plots, righting moments, inertia and the perceived force of the sail plan on all of this. This is when it became a course.

The waterline of the EC12 is that which you set it to be at any given time for conditions of sailing you determine to be. Legally, it must be between 42 and 43 inched by rule. By common since, it must be on its lines while under power and in the seas that it is.

It was our perception in the see through tank that the keel and the deck were parallel. We did not measure it nor thought there was a need. Maybe there is and maybe Paul is right but at the time the concepts of drag on a presented surface and the resulting laminar flow at and across the rudder were clear. (a high bow angle would present a larger surface to the oncoming water and a low angle would create turbulence across the rear of the keel and the rudder.)

Water, for general purposes, is level with the planet. Therefore, our quest was to make the keel and deck parallel to the surface of the water when the boat was underway and under power. You can't do that in a tank without it being in a wind tunnel as well. So, it was decided to use the tank for what it was designed, measuring.

Based on the theory that the boat should sail on its lines and using the multiple ballasting options a fully prepared boat for sailing was placed in the tank at the least weight that would produce a 42" waterline measurement. This would be where you would want to sail the boat in drifting conditions, zero to one. Then trim the boat to a positive angle but near zero. Likewise, the boat was ballasted close to the 43" waterline measurement and trimmed for 1 degree positive for heavier sailing conditions. Over the course of this, a weight and a location was chosen to be one. We were thinking of moving the trim weight for the conditions after testing but found it was not needed. it sits in one place today.

Optimizing is the total sum knowledge and presentation of the testing Lon and Larry Robinson did. Like any technical document it has to be viewed as a whole. It was the whole of it, through several charts and text the trim angle spread and the ballasting properties were determined from their recordings. The results of our efforts in the tank is presented on the building site and is still being used today in my building. How precise is it? I do not know. I only have my eye to judge the profile of the boat in the water in various conditions to support those efforts. When the boat is under power, in the planned wind, she is level with the planet for the weight and trim designed.

What I have found on the East Coast that the competitive sailors have used a shorter and higher single pour for a 42.5" measured waterline with one degree positive angle on the deck. When we all gather I take my proper place further down due to my lack of mental prowness in tactical matters not because my boat is slow.

Paul, the search for the "grail" can be fun. One rainy night in equatorial South America I sat under the wing of my plane with a local discussing the aspirations of higher goals (Latins do that a lot)and he said, "You must climb only part of a mountain to know it is a mountain." Maybe it is the heat.

Woody, you do have it right and I hope this supports it.

Larry, you are @%# disturber! [:)]

...94

[PaulP]

To all,
In the EC12 manuals, and associated software, Larry Robinson says they found a .4 degree variance and changed their base line to reflect this.

Any ideas on what this was? I am still trying to figure out my proper trim angle.

If I want my boat to sail at 1 degree, and with the new 95 std hull having a -2 degree difference between the keel and the deck, for this 1 degree trim, should the deck line be

at 1 degree (which would put the keel at -3 degrees)

or at 3 degrees (which would put the keel at +1 degree)

Come on, surely somebody stayed awake during their nautical engineering classes? If I had the email address for Bernoulli, I'd ask him.

Paul P [:p]

[MichaelJ2K]

Sailing on the lines.... Now that's an interesting concept. Having been involved in the International A Class, the waterline position and length was determined by freeboard measurements and draft. It was up to the skipper to sail and trim, sail and trim, sail and..... well, to make a long story short, measuring an A boat became such a chore that most skippers didn't bother to measure and submit a rating certificate. Shift the ballast and mast position until you find that magic combination of balance and speed. Because it was so demanding of the skipper have all his ducks in a row to get an approved certificate, the interest level hit -0.

BTW, a fast A boat will run rings around one of those J's any day of the week! [:D] Anyone for a grudge match? [;)]

[Larry Ludwig]

You got it pal, see you in 6-8 kts... I just murdered a brand new Bantock carbon "A" boat. Bring your lunch. (I Like roast beef)

I am running 6000 sq in of sail.... how about you?
[:D]