Another swabb on deck, reporting for duty!

[Craig Weis]

Geeee Cap't. kchunk; thanks for the smack down. It's displacement. Displacement had not changed. Shape had not changed. Speed had not changed. Ability to resist a list had not changed. And sailing characteristics had not changed.
So let me ask all..

"Is the hole in the water made by the hull one iota different with 6" and 800 lb of lead in the keel? And 18" of air above?" mating to the hull.

Or...

"Is the hole in the water made by the hull different with 24" and 800 lb of concrete in the keel? And 0" of air above?" mating to the hull?

It would make a difference if the keel was longer. Then the ballast would be further away from the waterline. But it is not in these examples.

So I still think that the resistance to leaning over remains the same with or without a hollow keel or a full keel...as long as the bottom of the keel has the 800 lb in it. Just don't move the weight up or you'll get wet sooner.

skip.

[wordnut]

I'm just an English major but here's what I think: With the concrete you ARE moving the weight up. Your center of gravity is higher.  The thing to remember is the "lever" isn't just the keel, it's the entire height of the boat from the bottom of the keel to the top of the mast. The more wind in the tops of your sails, the more you want weight at the bottom of your keel.  As you move that weight up (toward the center of the lever), righting power is reduced. That's why concrete that spreads the weight all the way up to the sole of the boat is not as effective as lead at the extremity. If two Skips are on a teeter-totter and one moves toward the center, the other falls toward the ground. The one that moved has less leverage.

[Craig Weis]

Your too funny. skippies...

Oh, somebody's commit about the aeroplane and the center of gravity reminds me that in Jackson, Michigan a 727 jet cargo plane banking to get into the landing pattern splattered all over the woods because a heavy pallet broke loose and slammed fwd. It was a few miles from my house.

Yep move one skippy fwd and the other skippy falls to the ground. That is correct. Wordsmith...WORDSMITH!!

Ohhhh SNAP!! I got it. The key is that word fulcrum, which is the same point as waterline. Your bending the teeter tauter at the waterline. And this does not change between lead or cement. The moment of bend [folcrum] with a hollow lead tipped keel or a full solid keel remains the same as long as the waterline is constant...I think [?] this is why were having this problem. The word fulcrum. So lets make a model.

~Take two beer bottles and fill one with lead till about 2/3 is above water. Might be two inches of lead.
~Mark the waterline.
~Take the second beer bottle and fill it to the top with something that also pulls the bottle down to the same marked waterline.
~Glue on two balsa wood caps to both bottles.
~Glue on two balsa wood sticks to both caps. Standing straight up.
~Glue on a few foot of thread to the top-o-each stick.
~Float both bottles side by side up against a fixed yard stick laying down [floating] on the water's surface.
~Set the threads to pull at the same angle with your fingers.
~Pull both threads till each stick is 4" above the water.
~Let me know which bottle pulls hardest. [I honestly don't know]
~Let go the strings.
~See which bottle rights [rites?] fastest.
~See which bottle rocks back and forth and undulates the most times.

I don't know the answer. But I'd like to learn the answer.
My uneducated guess is both bottles will act the same.

Kind of remember that science class thing about a pound of lead and a pound of feathers dropped together and both hitting the ground at the same time [baring wind resistance] from the Tower of Pizza..

A sniper knows that his bullet leaving the muzzle at three foot horizontal to the ground will hit the ground exactly at the same time a bullet also at three foot above the ground falls off the shelf. Both bullets will hit at exactly the same time as the spent bullet. The only difference is the spent bullet will travel three miles in the same time as the bullet falling hits the ground. [assuming the ground is equally flat to the fallen bullet.]

skip.

[Salty19]

Yes, the waterline is the fulcrum.  The further weight is away from the fulcrum, the more leverage it has. 

I have this worked out in a spreadsheet and graph to show you. Also have computed the total righting force (at the masthead) in both scenarios.   I think you'll be shocked at the difference this makes.   Will post tonight, need to format them...

[nies]

All this sounds good, but waiting for Hutchins comments....Phil

[Craig Weis]

[OkieBob]

I received a response from Gerry Hutchins.

My email:  Hi, I am refurbishing a '76 Com-Pac 16' and will be removing the concrete ballast.  I intend to replace most of the ballast weight with lead, either encapsulated in concrete or an epoxy.  By increasing the density of the ballast I will be reducing the volume, and will create additional storage space; possibly space in the upper keel.  My question is this, "Is the concrete in the upper section of the keel, providing critical structural support?" My second question is this, "Why was it necessary to add the two additional concrete ballasts on opposite sides of the bottom of the hull, above the keel?"  Did the builder initially plan to use the keel for ballast with a denser material, and then the plans were changed?  I'm confused why it wasn't just one big pour.  Respectfully, Bobby, a huge Com-Pac fan.

His reply:  Bobby – first, the concrete adds no structural support.  It is there only for the weight.  Second, I do not understand about the two additional concrete ballasts on the opposite side of the bottom of the hull.  We have never done anything but pour concrete directly into the keel.  As you say, it was just one big pour.  Perhaps you could send me a photo of it.  Gerry (G.L. Hutchins, Hutchins Co., Inc./Com-Pac Yachts).

My follow-up:  Gerry, First off, thanks for responding personally, and so fast.  I've atttached a photo and a link to a series of photo's from the source http://cpyoa.geekworkshosting.com/forum/index.php?topic=1168.0.  Please note, this is not my boat, but when I saw the photo's I decided I would have more room if I removed those extra two ballasts and replaced part of the keel with lead.  The pictures sure looks like a Com-Pac 16.  Do you think a previous owner could have added extra ballast?  Also, I rough measured my keel and it appears to be about 2 cubic feet; two cubic feet of concrete only weights 300 pounds.  Most Respectfully, Bobby.

I'm curious to hear what he thinks about the extra ballasts.  I'm also, surprised there was no structural intent; Skip's hammer scenario noted above makes since to me, but I'm no Einstein.

Now somebody please tell me how to move these posts to a more appropriate topic area (e.g. CP-16s or Boat Modifications), so adifferentdrummer can have his post back.

[Craig Weis]

Cool the O'man speaks.

I am also surprised to here that cement adds no structural intent [ ? intent ].

So apparently the fiberglass is only to act as a mold for the concreate which adds no structural support. In so many words.
So yea go ahead and figure out how to add 6" of lead and keep the top open for storage. I'm no Einstein either but this makes no seance to me.
You didn't ask about the weight lower business. Nor about how to pour lead into a fiberglass mold. Snicker, snicker.

"I'm curious to hear what he thinks about the extra ballasts.  Skip is also, surprised there was no structural intent; Skip's hammer scenario noted above makes since to me, but I'm no Einstein."

Nice to hear from Rich.

Now somebody please tell me how to move these posts to a more appropriate topic area (e.g. CP-16s or Boat Modifications), so adifferentdrummer can have his post back.

Sure open up the Com-Pac 16 main thread. Find the reply area you want to post these into and cut and paste. Come back here and highlite and click delete.
skip.  Like this highlight. edit-copy-place the cursor where you want this post to go. right click and right click paste.

[nies]

Skip, I know nothing about computers, as I am sure you guessed, but wouldn't it be easier to rename than move and start a new"....swabb on deck.....",you have noticed no more " CAPS " Skip, was not easy but figured a way to do it.......Phil

[kchunk]

To move the posts a moderator will have to do it. He can cleanly cut the off-topic posts and move them to a new thread in an appropriate forum.

Regarding pouring the lead. All it will take is lead shot and epoxy. No need to fire up the backyard foundry nor flame dry the inside of the mold. You guys do know that this has been done before (not on a Com-Pac) and discussed here? http://cpyoa.geekworkshosting.com/forum/index.php?topic=2314.msg12866#msg12866

Here's the link to the Montgomery 23 with lead keel: http://havasumontgomerys.piczo.com/?g=23004804&cr=1

--Greg

[adifferentdrummer]

OkieBob,

That was a very interesting reply from Gerry Hutchins, and I am also surprised. I thought Skip's hammer and straw analogies made perfectly good sense. Already, a couple of my questions have been answered. One note, though, I think the two additional concrete ballasts you referred to are actually pillows of poured polyurethane foam. I cut into these and removed a small portion when opening up my starboard berth for repair. I'm not sure what their intended purpose is, and I'm looking forward to finding out when Gerry writes back.

And, I don't mind a bit that this discussion is taking place here. I've been following it with great interest. I have puzzled over these questions ever since I started working on my boat and anxiously await the answers.

Thanks for getting it going with your simple statement, "I acquired some lead."

And thanks for contacting Hutchins.

Regards,
Milt

[Salty19]

Well, here she goes...Excel can be your friend if you let it...

CONCRETE BALLAST   Notes:  

Assumes 18 equal segments of the keel exist.  Each segment is equal to 1" (horizontally) of concrete ballast or air on a CP16      
Assumes due to  \_/ shape of keep, more mass exists at higher points in the keel if material is evenly distributed. +3.5% assumption for each inch      
above midpoint, 3.5% reduction below the midpoint      
Assumes the waterline is the fulcrum of the lever and bouyancy keeps the fulcrum fixed (for our sake here, I'm not going to add an inch when on board).      
Assumes top of concrete is 4" below the waterline.  Better information is needed for accuracy, it's just a guess having owned one comparing the cabin      
sole, which appeared to be the top of the concrete, to the waterline.  If someone can try to measure this, we can put in the real values.      
Inches from masthead to waterline (de in the formula is shown, but is not taken into account right now.  The reason is the effort of force      
Assumes height of mast is 21 feet AWL      

LEAD BALLAST   Notes:  Assumes the same hull is divided into 18 segments as above.  Each segment is equal to 1" horizontal slice   
Since lead weighs more and takes up less space, the top segments are air (no ballast).  Table below assumes all 450lbs of    
lead are within the lower 5" of the keel, per comment that 3/5 of a cubic foot of lead are needed vs. 3 cubic feet   
So this is approximately 3.3" of lead vs 18" of concrete, thus why there is zero F1 values in segments above 4 (I rounded way up)

Assumes all else is the same   







And graphs to see the trends...




Heres's the same with lead



Notice the 54% change in force applied to the masthead.  Big difference!

Edit, a keen eye may notice I forgot to decrease the lower weight and increase the higher weight (due to keel shape) on the lead chart. Applying a 2.5% "gradiente" only changes the total force of the keel leverage by .02lbs. (from 26.07 as shown to 26.09).So basically the same.

Another edit.  Take skips diagram and imagine 14 separate skips and weight on that lever at different lenghts along the teeter. .  The lenght is what compounds the force., each sucessive outer skip and weight adds more lever force than prior skips and weights.

So if the hull had zero lateral resistance, which is of course has a lot of, a 16.966lbs weight at the masthead will knock the boat over.

[nies]

wow, need exec summary......there is dumber then there is dumber, I am the latter, will the lead change the performance of the boat?........and in what way?..............Phil

[OkieBob]

Way to go Salty!!!  I caught less than half of that, but very impressive.

[Salty19]

Keep staring at it, it will sink in. 

The table represents what each inch of ballast material weighs as you go from waterline to bottom of keel.
Then it shows the data you need for the lever formula with correct data (with the exception of the distance from the waterline to top of concrete, which I guessed at.

I just followed the compound lever formula and made some good guesses and forced formulas to determine what each 1 inch "slice" of ballast weighs.   You have to think about this not as 1 piece of concrete or lead that is all weighted at 18" .  You have to think about it in terms that the weight is *distributed* across several layers.  As the weight moves away from the fulcrum (waterline), the ballast/lever force goes up.

Nies, not a matter of dumb and dumber.  It's called "Used Excel for the last 19 years and getting pretty good at".
Actually this was fairly easy if you know your way around the program.  Wait to you see the electrical use/charge calculator I'm working on where you can input your electrical load and charge capacity, how many hours a day they be in use, what guage your wiring is..then it tells you what amperage charging rate you need or what surplus/deficit your charging system has.

Exec Summary is the last sentence:  Notice the 54% change in force applied to the masthead.