Water Ballast Analysis (From another thread)

[Sumner]

Center line water ballast is does add righting moment
as the boat is heeled, but it is a very ineffective form
of ballast. This is why the boats you see that use water
in the keel, as their primary ballast. have such diminutive
rigs and sail so poorly............

Really?? Are you lumping all water ballast boats together? Are you aware of the large differences between say the MacGregor 26 S & D vs. the newer X and M??

What is your definition of "sail so poorly"? Sorry for the question, but some of us with "water ballast" boats get tired of remarks made about them from people who don't know the difference between different models and make blanket statements about them.

I agree that it takes less weight at the bottom of a keel to provide the same righting moment as much more weight in the bottom of a water ballast boat. These boats are designed as lake and coastal boats and for some of us they do quite well at that and even sail as fast or faster then other boats of the same length and point into the wind better than a number of larger boats.

Sum

 

[RichBone]

I am baffled by the confusion. It all seems so simple to me. If you put 1000#s of water in the bottom of a boat fixed in place in a tank. Then the boat is harder to tip over. If you put 1000#s of lead the CG would be lower but the effect would be about the same. The boat would displace the same amount using either lead or water. Maybe it is because I used to teach high school physics. Maybe it is because I have read about boat design. But I suspect Druid is a troll pretending to not understand. http://www.marine-concepts.com/features.html#ballast Wow here is a great looking thin water sailboat. Twin water ballast tanks one on each side. This would seem like a great fishing boat for Florida.

May be this will slow down this post a little.

Last spring I sold my Sea Pearl 21 that I sailed on Lake Erie since 1990. It's modeled on a 1929 Herreshoff Carpenter. I found it a very seaworthy and comfortable sailing boat even without the water ballast. But with the water ballast on board it stiffened up considerably and I never felt unsafe in it. I could stand on the gunnel and not come close to getting my feet wet. It's a very good example of the capabilities of a long narrow rounded bilge design. The builder claimed that it was self righting at a 90 degree heel with the mast touching the water.

Rich

 

[COOL]

Really?? Are you lumping all water ballast boats together? Are you aware of the large differences between say the MacGregor 26 S & D vs. the newer X and M??

What is your definition of "sail so poorly"?

We can exclude the 'X' and 'M' models from the the discussion
as they are not truly sailboats, and I will concede your point that
the 'S'and 'D' models are not terrible sailboats. But I will contend
that the Venture 25, designed in 1973,will likely perform slightly better.
A conventionally ballasted boat, such as a vintage Cal 25,
will be much faster, although not nearly as trailerable.
Three people hiking on the rail of any of these boats will provide
more righting moment than 1200# of water in a keel tank.

 

[Sumner]

we Can Exclude The 'x' And 'm' Models From The The Discussion
As They Are Not Truly Sailboats, And I Will Concede Your Point That
The 's'and 'd' Models Are Not Terrible Sailboats. But I Will Contend
That The Venture 25, Designed In 1973,will Likely Perform Slightly Better.
A Conventionally Ballasted Boat, Such As A Vintage Cal 25,
Will Be Much Faster, Although Not Nearly As Trailerable.
Three People Hiking On The Rail Of Any Of These Boats Will Provide
More Righting Moment Than 1200# Of Water In A Keel Tank.

Ok I have nothing better to do.........

[FONT=verdana,bolditalic][FONT=verdana,bolditalic]united States Performance Handicap Racing Fleet[/FONT][/FONT]

High, Low, And Average Performance Handicaps Organized By Class/type

Boat.............................High .............Low............Average

cal 25-1 Ib.................... 222................ 225 ................222
Cal 25-1 Ob.................. 219................ 231 ................222
Cal 25-2 Ib.................... 216................ 228 ................222
Cal 25-2 Ob.................. 216 ................225 ................219​

Cal 25-2 Sd.................. 213 ................228 ................219

MACGREGOR 25.......... 225................ 246................ 231

MACGREGOR 26-S...... 210................ 258 ................222​

MACGREGOR 26-D...... 210................ 219 ................213

Thanks for moving our S from 'terrible' to 'not terrible' and I'll let the X and M guys tell you if they have a sailboat or not. I'm still amazed at the number of people that just have to bash MacGregors every time they get a chance. As you can tell I'll be outspoken when I see it happening. I read a lot of this before we got our Mac and I finally realize that most if not all of these people had never sailed on a Mac.

Now if you pass us it might be because we haven't even sailed a year yet and with all of the stuff I've done to the boat it almost falls under the catagory of a commercial vessle and should be given the right of way :cry:. Right now from what we've seen of other sailboats and read about other sailboats if we had all the money we wanted to spend on a sailboat for "our needs" we would keep this one. Yet I'm not bashing anyone else's sailboat and if we lived a different place or had the time to be aboard full time or close to it we would probably have a different boat.

Sum

Our Trips to Lake Powell, UT - Kootenay Lake, Canada - Priest Lake, ID

Our Mac Pages

Mac Links

 

[nofd843]

OK, I am a visual person... I got tired of reading, so if this has already been posted... then don't look at it.

http://www.youtube.com/watch?v=w00suzaDh_A

 

[COOL]

Sum,
Sorry to come across as bashing your boat,
it looks as though you have a great time with it
and use it for exactly the purpose it was intended for.
With a little optimisation any Mac, disregarding the
unmentionable models, can be made the perform
fairly well under sail. In my experience however, I have not
observed many Mac owners extracting much performance
from their boats. That is not to say they are not extracting
tremendous enjoyment from them.

 

[Bob V]

Mac 26 alumnus

These days I am fortunate to sail a boat with plush accomadations and a big hunk of lead underneath but I started out on a Mac 26 D and I will testify to the fact that it is a great little boat. I can't comment on the new ones because I have never sailed one but it looks to me like they should have stuck with the earlier models.

The first time I saw the Mac, from the seat of my kayak, I thought it looked huge. I got a tour from the owner and saw that there were decent bunks and a porta-potty and a stove. It was love at first sight. I know first hand that the water ballast system works great as I have made many crossing of the Strait of Juan de Fuca and some of them were on really snotty days. I broached hard on a spinnaker run in Haro Strait. It looked bad enough that another boat came over to see if we needed a rescue. No thanks we just need to get our shredded spinnaker down and then everything will be fine.

I still get nostalgic when I see an older model Mac out on the water and I see them all around the Salish Sea not just on lakes.

 

[George H260]

I would love to have someone tell me what is wrong with Rod Brandon's analysis of how water ballast works.

George
h260.com

 

[Sumner]

Sum,
Sorry to come across as bashing your boat,
it looks as though you have a great time with it
and use it for exactly the purpose it was intended for.
..

I appreciate that and as far as I'm concerned it is history now ,

Sum

 

[Paul Brinkley]

George H260, there is nothing wrong with Brandon's analysis. There are apparently those who, for whatever reason, WANT it to be wrong.... The arguments against it are based on faulty physics. -Paul

 

[dvideohd]

there is the pratical side....

if you are out on a lake in the shallows.... it's nice to have something that you can pull a centerboard up - or have a swing keel (nicer) if you hit a stump or rock. This part is not about ballast....

but if you get stuck on the mud - or the tide goes out - or something else... it is nice if you can BLOW the ballast and get off the hangup... Can't say that this would happen much - but I read stories from gunk holers and read maps of Texas Lakes...

--jr

 

[Quoddy]

Ballast theory

It’s interesting how the scientific fact we know to be true today can be challenged by arguments that once may have been considered plausible but have since been shown to be incorrect. The belief that, water ballast, can’t work so the “theory” of it needs to be reexamined, doesn’t even have carbon wealth or dinosaur religion driving the attempted to prove established knowledge false.

Water used as weight for internal ballast has been well established for many years. Many boats have internal ballast as part of the ballast or as all of it. Put a bottle of rum in the bilge where it won’t move, until you move it, that's ballast.

 

[George H260]

I understand the confusion by the uninitiated. Maybe it's better to just accept it as one of the mysteries of life and go with the flow. The fact that it works is well established; spending your time trying to understand the engineering and physics involved might be better spent in other more productive pursuits.

 

[cephius (Dave)]

Druid,
If I follow your logic, water placed below the water line has no righting action, then any weight (including led) placed below the water line has no righting action. The rules for led and water are the same. Weight is weight.

I also debate your statement that it is air in your hull that creates buoyancy. It is the shape of the hull and the total weight pressing down against the water density and pressure that determines buoyancy. Trapped air, like trapped water, will have an effect, not just the empty space in your cabin.

Please don't take this as a harsh criticism, just a part of the lively debate. Thousands of us use this technology safely. It seems to work. (Maybe there is magic in the world after all )

 

[philwsailz]

 

[Paul Brinkley]

On with the show...

Enjoying the show, Philwsailz? Life is interesting. -Paul

 

[tommays]

Everything does weigh less underwater so a drum of lead would be tough to move BUT a drum of water pretty easy

Inside the boat 100# is 100#

 

[Patrick17430]

OK... This is beginning to sound alot like the chicken or the egg story. I spend alot of money, time and energy attempting to keep water out of the boat. I personally don't get a warm & happy feeling when I contemplate a water ballast boat. I remember the time I came home to find my wife was filling the radiator on her corvette through the filler cap on the valve cover. Do you see where im going with this ?

 

[philwsailz]

I for one did some studies just last April, (rather early in the month as I recall). I had access to a water-ballasted boat, the Lirpa 1, and was pondering the relative merits of "enhanced" water ballast so I pondered the possibilities of using both gelatin and cornstarch to enhance the effects of water in the ballast taks. I determined through careful speculation that too much dissoved gelatin would have a negative effect, at least for trailerables in cold climates. On the plus side though, I realized there was a protein source I could eat in the event of being stranded.

The cornstarch had its own set of peculiarities, in particular, in very high concentrations, a water and cornstarch mix will behave as a liquid at rest, but instantly act as a solid upon agitation. This intrigued me as I felt there must be some way to capitalize upon the instantaneous altered state of the solution in a dynamic manner. Alas, to date, that experiment only proved to be beneficial while in the galley attempting to thicken some broth into gravy.

I may continue my experiments come the first of April, and I will let you know if I manage to realize any breakthroughs....

 

[Roger Long]

On the plus side though, I realized there was a protein source I could eat in the event of being stranded.

I've been told that the perfect survival food is cooking oil because it requires no additional water for digestion. Just think how far you could go in a Mac 26 with the tanks filled with olive oil and how low your cholesterol would be when you got there