Another swabb on deck, reporting for duty!

[Salty19]

Skip if all the lead weight would be lower in the hull-quite a bit actually, creating a more efficient lever to counteract leaning force, the fulcrum (center of gravity) moves down towards the water.

Check out the link
http://www.engineeringtoolbox.com/levers-d_1304.html

Really the calculation for us is pretty difficult because the weight is distributed over a longer area of d1. We would look like the example near the bottom with many weights hanging from different lenghts along d1. 

That is provided the lead weight equals the concrete. She should sail flatter if the weight is distributed lower.

Physics aside, you are wise beyond your years...this would probably cause unwanted keel flexing issues.  Something to brace and support from oil canning seems critical in this area.

[Craig Weis]

"Junior, it ain't gonna happen."
"Skip if all the lead weight would be lower [HOW IS THE WEIGHT GOING TO BE LOWER?. THE KEEL IS THE SAME DEPTH] in the hull-quite a bit actually, creating a more efficient lever to counteract leaning force, the fulcrum (center of gravity) moves down towards the water."

[BOAT IS NOT GOING TO BE ANY HEAVIER, NOR KEEL ANY LONGER. NOR WEIGHT ANY FURTHER DOWN. NOW IT WOULD MAKE A DIFFERENCE IF THE WEIGHT WERE RAISED TO THE TOP OF THE KEEL WITH AN AIR SPACE UNDER, THEN THE BOAT WOULD BE MORE TENDER. MAY EVEN ROLL OVER.]

Only if you stick that keel further down into the water by making it longer, regardless of where within the keel the weight is, full height vs a little bit in the bottom assuming down. Keeping the weight the same.

The keel has not changed nor has the displacement within the water. It's still the same size hole in the water. You do know these boats will stand up by themselves on the grass, right?
skip.

[brackish]

The central axis of rotation does not change, nor does the displacement.  What actually changes in the suggested modification is the centroid of F1.  It moves out on the moment arm and is concentrated in a smaller area.  Forces can be point loaded or uniformly loaded on a moment arm or anything in between, but they all have a centroid of force, that point which is equidistant from the outside of a mass with a constant specific gravity.  If the force is long, like a keel the centroid is not a point it is a centerline, in most design cases parallel to the axis of rotation between F1 and F2.

The characteristic that can change with the moving of the centroid is motion comfort or tenderness with change of F2.  The reaction between F1 and F2 might be initially delayed and F1 might have a higher tendency to overcome quickly upon reduction of F2, returning to steady state in a more rapid manner. 

The ability of a Com-Pac to sit on its keel represents compressive strength of the design, maybe aided by the filled keel chamber.  The ability of the boat to have the ballast mass supported on the moment arm as it rotates represents tensile strength of the design, also possibly aided by the filled keel.

Not saying there is any inherent problem with the modification, may be better in some ways, just saying it does change things.  If I were going to void the keel I would consider glassing in some cross braces above the lead, or at least bounce the idea off Hutchins.

My$.02 worth and probably worth exactly that.

Frank 2

[nies]

Call Hutchins.....my 2 cents......Phil

[Salty19]

Skip the keel of course does not change lenghts. The *concentration* of ballast vertically is what changes.  In other words more weight further out on the lever, less weight closer to the fulcrum.   I'll put together some calculations to show you a real life example in a day or two.

[Craig Weis]

skip gives it up. Go ahead. Put the weight where ever you want to. Happy sailing.
skip.

[OkieBob]

a call to Hutchins will get all of us the right answer. If you don't want to call I would be happy to.....Phil

Phil, If you call them; I'd be curious to hear what they say.  I really suspect it was a cost analysis choice for them.  Not just the cost of the lead, but all the additional handling costs and liability exposure that goes with it.  The real downside would be if the concrete is providing needed support at the upper section of the keel.

For me, I live in a fairly windy area and suspect lowering the weight would create more force on the fulcrum when needed.  Plus the added space is an attractive bonus.  I've done an informal cost benefit analysis for myself, and it isn't worth the effort (since the weight is only being dropped about a foot).  This isn't a business decision for me though; it's part of the pimp-my-ride playground, similar to adding brass cleats.

Milt, After I free up some space, I intend to change the floor plan down there a little.  Probably to focus on the sleeping arrangements.  At the very least, I'll get that storage space above the upper the keel.

[Salty19]

Salty, my cats are of a breed called Ragdoll. They are sweet kitties; not sure if they might be related to Balinese, but I think they did come originally from mixing Persian and Burmese. There are more pictures and info in my Katz album, or you can google 'ragdoll' and find a 'boatload' of information on this exceptional breed. I've got a bunch, and one has even set up camp under the winter cover on my boat. I think she wants to be a sailor, too.

Milt

Thanks for clarifying.   Looks like a beautiful cat to be proud of!  Enjoyed your pics...

[OkieBob]

Skip,

I like your strength analysis, and suspect you are right on the money regarding the hollow space.  I'll need to take that into account, and appreciate everybody's comments.  This brain tank probably just saved me from cracking my keel.

Thanks!!!!!

[OkieBob]

Phil, I sent Hutchins an email.  I'll let you know what I findout.  I bet Skip is right about the upper part of an empty keel being about as strong as the empty part of a straw.  That makes complete since, considering the abuse a keel takes.  Now I need to decide how to work through that.  But as everyone can see, the cost vs benefit is just not there.  Only a fool (like myself, and possibly some others) would bother messing with this.

I may not of mentioned it earlier, but I plan on encapsulating a combination of scrap lead and lead shot, most likely in concrete.  But now I will probably need to recalculate to ensure the concrete fills the keel.

How do I move this feedback to the proper area (e.g. boat modifications)?  It has gotten technical.  I've seen where people have moved posts, but I don't know how it is done.

[Craig Weis]

Cement is so easy. Why mess with lead. Or change the shape of the keel?

I worked in a department that made cement lined water booster heating tanks for Hatco Foodmachine Company.
And we dealt with cement turning to concreate over it's 88 year* drying process using Portland non-shrinking cement.
Which is actually cement that shrinks less then regular cement.  But it's not non-shrinking.

It's the cement used in highway bridges too. Four bags screened #60 sand and two bags Portland cement.
Mix it up dry in a huge covered mixer. That's about 600 lbs of dry. Dump all this into 5 gallon pails. Dump the 5 gal pail into the wet mixer.

Then smaller wet batches for about 8 pales per batch/ five gallon in a normal cement wet mixer.
A portion of a wet pale for each tank...so we were always making wet mix to dump and spin or pour in to the tanks.
Starting at 6:00 am usually everybody finished their tanks about 2:30 pm but we had to wait our ten hours before going home. So we hung out till 4:30. We made two 600# dry mixes a day.

This cement was used in the tanks so water would not rust out the inside of the 16ga sheet steel tanks from the inside. We rolled our own tin and punched the heating element holes first and machine welded the tops and bottoms to make a tubular tank.
A hundred other coatings were tried and this works best. No rot for 50+ years.

Pour in the cement, spin the tank making a side wall, pour in a bottom & pound down, pour in a top & pound down, paint the outside shells and send it to the next department for the electric heaters and controls. Six lines each made 88 tanks of three different sizes each day in a four~10 hour day. To make one tank was a four day process. Cement lined tanks were between 79 lb small to 147 lb large Imperials. We hand loaded our own tanks by hand to a monorail overhead conveyor for air dry paint.

Anyway, fill the keel void with cement, dump in the lead, insert the rented vibrator [a donkey dick in the trade] and shake out the air. Women love this job. The lead or pig iron will sink to the bottom of the cement, in the keel void and DISPLACING the cement. So scoop out this extra cement overflowing the top of the keel into the hull. That's about it.

If you think about it, the fiberglass keel could technically be peeled away exposing 100% of the cement and the damn boat would still float for years. The cement will not pass water. Don't panic if you find a little chip in the glass and see cement looking at you. So go ahead and mess with success if you want to.

* Portland Cement Company estimates that cement turning to concreate will not reach it's full hardness for 88 years.

I loved the stuff. skip.

[rwdsr]

I just got on tonight, but read you post for the first time the other night.  I've been wanting to come over and check out Douglas lake for a couple of years now.  Maybe we could get together for a sail when the weather gets warmer.  I've got a CP 16 1978 #592.  Haven't got it on the water yet, but looking for the day..............

Bob

[kchunk]

Skip, don't be so quick to confuse fact with your opinion. Your opinions are just that...opinions. Obviously you don't like the idea of replacing the concrete in the keel with lead and that's fine. You're entitled to your opinion. However, the fact is replacing concrete with a smaller volume of lead of equal mass will change the vertical center of gravity. Think of it in terms of an aircraft. An aircraft has a given usefull load. For this instance, let's just call the load "ballast". The aircraft will fly just fine if you load this ballast taking into consideration the aircraft's center of gravity. Load it all in the back and you've just move the CG too far aft and the plane will not fly...for long. You didn't change the length of the fuselage or the amount of ballast, just redistributed it. The same applies for our keels. Load all the ballast in one (vertical) end and you've changed the CG, not the displacement nor the length of the keel, just the CG.

Now for my opinion...this would be a positive change. A lower vertical center of gravity will make the boat stiffer, allow you to trim the sails a little more while lessening the amount of heel, or will allow more power to the hull from the sails for a given degree of heel. A big change? Again, in my opinion, not enough to warrant the cost or effort involved. As most of us know, once you've approached hull speed, the amount of power required to move the boat just a little faster is an exponential relationship. However, if one did decide to go this route, will the keel break off? Certainly not (once again...opinion). Assuming the keel layup is the same as the hull, the additional torque or moment acting on where the keel becomes the hull would be increased, but, in my opinion, not enough to cause the fiberglass to fail. The highest stress will be at the fillet where the keel transitions to the hull. The torque arm at this point is what...12" or 18", whatever the length of the keel is. Moving a bit of ballast within an arm this short shouldn't be too dramatic an increase in moment (...I think). Will Hutchins give something like this their "OK"? Why would they? Increase their liability for no realized benefit...I don't think so.

Here's where you insert some inappropriate comment about opinions being like certain body parts.

Oh, and if you do chip the keel enough to see cement looking at you, the fact is you've got a problem. I agree, don't panic, but you've certainly got a problem that needs fixed.

--Greg

[adifferentdrummer]

This has been some very interesting and useful information and opinion from the collective consciousness of CPYOA, and thanks to all for the input. I expected the subject would get a rise, but I didn't expect such a tidal wave of comment. Perhaps, as OkieBob suggested, we could move these posts to 'Boat Modifications' or some other more appropriate heading, for future reference.

One further observation I would like to offer: when working on a water problem on my 16 (water trapped under starboard berth), upon cutting a hole in the berth and ripping out some water-soaked, de-laminated plywood (that 4" strip that supports the edge of the berth along the foot-well), I noticed that the concrete ballast appeared to be poured in two stages; first the keel was poured full to the top, then a second pour creating a roughly 2 inch thick slab of cement on top of the keel pour which seems to be for the purpose of creating a level surface for the foot-well pan. The fiberglass foot-well pan was formed on top of this slab and run up the plywood stiffeners that support the outer edges of the berths. I have a pretty clear picture of this at http://picasaweb.google.com/adifferentdrummer/Hatches. judging from the extent of the water damage under this berth, I believe it was a long term problem and not something that occurred over just the one season that I have sailed the boat.

I don't expect to ever have a need to disturb the concrete ballast, as it appears to be solid and in excellent shape on hull #635. I just find what others have done and are doing, or are planning to do to their boats, very interesting, and helpful in understanding and planning my own modification projects and repairs, and hope that some of what I have encountered working on #635 might be of help to some others.

I will also be looking forward to hearing what Hutchins has to say on the matter.

Thanks to All,
Milt

[adifferentdrummer]

I just got on tonight, but read you post for the first time the other night.  I've been wanting to come over and check out Douglas lake for a couple of years now.  Maybe we could get together for a sail when the weather gets warmer.  I've got a CP 16 1978 #592.  Haven't got it on the water yet, but looking for the day..............

Bob

Ahoy, Bob, and Welcome Aboard!

I just got on here a few weeks ago myself. I was hoping I might meet some other CP16 owners who live in the East Tennessee area. How far are you from Douglas, and what other lakes in the area are you close to? I want to sail on all of them next season.

I think it would be great fun to get our little sister ships out on the water together. As much of a head-turner as one CP16 is, we'll be giving folks whiplash! They'll be thinking they are seeing double! Imagine if we could get 3 or 4, or maybe even a half dozen or more together.

Do you have any pictures of your boat posted? I'd love to check her out. Is she in good shape and ready to sail? I guess you've noticed my Picasa link at the bottom of my posts. I've got loads of pictures of my repairs and mods on there as well as many from my outings on Douglas this past season.

Great to hear from you, Bob, and do keep in touch. We'll definitely have to get our little ladies together some time.

Milt