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Old 12-04-2014, 07:06 PM   #21
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suspicious of poured concrete in a wooden boat as I suspect it might hold moisture, as its porous, against the structure and accelerate rot. But that might be completely incorrect and I'm more than happy to be corrected.
It's a bit of a mystery. Shoreside construction practice says no wood in contact with cement unless treated with preservative. Yet, in boats, many very experienced people will testify that wood alongside cement in the bilge is actually preserved by being in contact with the cement. There appears to be something (Alkaline in cement) in the combination that discourages riot or even deterioration of the wood. I've seen it myself, oak frames that are falling to bits above the ballast line and perfect below it.
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Old 12-04-2014, 10:22 PM   #22
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I'm pretty sure my brain can't handle a 155 degree roll. And like Tad said the cockpits would probably fill with water before that angle and sink the boat anyway.

Thanks for all the interesting stability discussion.
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Old 12-04-2014, 10:35 PM   #23
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Ballast is also part of the whole weight distribution of a boat. In a way every piece of equipment is a form of ballast, every battery, water, fuel. For instance a 60' Nordhavn with displacement of 138,000 pounds has ballast of 8,500 pounds so around 6%. But the fuel, water and holding tanks have a capacity of over 23,000 pounds.
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Old 12-05-2014, 07:25 AM   #24
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>I'm not looking to get "knocked down" anytime soon however.<

Sailboats are the more likely to suffer a knock down.

On a power boat the fun begins with a beam sea with a large breaking wave that picks up the hull and tosses it on its side , or top.

Weather the house construction and windows can handle this is as large a concern as ballast .

Watch one of the TV shows for the fish boats in the Bearing Sea to get an idea of real!!! waves.
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Old 12-05-2014, 07:25 AM   #25
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I am interested to see what Tad says about tankage.

Unless you ballast with sea water as those tanks are emptied (which I doubt a yacht would do)...that is a balasting headache.

I believe the bigger they are, the bigger the designer's challenge.
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Old 12-05-2014, 10:27 AM   #26
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The Willard/Fales 30 has 4,000 lb. of ballast and an AVS (Angle of Vanishing Stability) of 122 degrees and a calculated STIX of 33. While these appear to be great numbers, the measured Roll Period is only a little over 3 seconds, which means that the motion can get pretty lively, or even violent at times. Offshore in 5'-8' beam seas and 20-25kt winds, it can roll through about 60 degrees. While the boat is absolutely safe, it can produce a very uncomfortable ride.
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It is not unheard of to add ballast high in the structure to slow roll period.
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Old 12-05-2014, 10:58 AM   #27
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It is not unheard of to add ballast high in the structure to slow roll period.
+1. Generally in stability, you want your righting arm to be within an ideal range. If too much weight is centered low down you end up with a stiff ship, and quick snappy rolls. In which case, you and all of your possessions will be pinballing around inside the cabin.

Stability is complicated. There are formulas to find out anything you need, but I've forgotten most of them. I generally leave that to the shipyard folks.
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Old 12-05-2014, 11:53 AM   #28
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Greetings,
All good points thus far which fit into my meager understanding of ballast and weight distribution. What generated the question in my mind was the amount of ballast that our boat was issued with. That's why I was looking for a general %age of what might be acceptable and what would be considered too much (as I mentioned to overcompensate for a bad design).
Mr. BB mentions 6%, minus, of course, fuel, provisions and goats...

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From what very little I've been able to find out via a copy of "supposed" specs, displacement is 49,200 lbs and ballast is 14,000 lbs which seems to me VERY excessive. Net registered tonnage is 31.07t. the last time she was on a travel lift, their scale was broken so I have no actual number for the weight. The manufacturer has been of no assistance as I was led to believe the records were either non-existent or subsequently lost...go figure.
So either I've got an atrociously designed vessel or the #'s are all wrong. I've also "heard" 4t ballast in the keel.
I'm not going to divulge the vessel (sorry, want to preserve my enigma-ism) so I apologize for the vagaries of my questions and the frustration generated. I'm not concerned with stability, simply curious.
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Old 12-05-2014, 12:08 PM   #29
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From what very little I've been able to find out via a copy of "supposed" specs, displacement is 49,200 lbs and ballast is 14,000 lbs which seems to me VERY excessive. Net registered tonnage is 31.07t. the last time she was on a travel lift, their scale was broken so I have no actual number for the weight. The manufacturer has been of no assistance as I was led to believe the records were either non-existent or subsequently lost...go figure.
So either I've got an atrociously designed vessel or the #'s are all wrong. I've also "heard" 4t ballast in the keel.

I'm not going to divulge the vessel (sorry, want to preserve my enigma-ism) so I apologize for the vagaries of my questions and the frustration generated. I'm not concerned with stability, simply curious.

Oh come on. You don't think we can't figure out the vessel is a Cheoy Lee?
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Old 12-05-2014, 12:12 PM   #30
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It is not unheard of to add ballast high in the structure to slow roll period.
Yes, I had entertained that very idea, but at this point, relocating ballast would just be too much of a project to undertake.

The Willard/Fales 30s were available in a number of configurations, one of which was a motorsailer. It had a full sailing rig and it would be interesting to compare the measured roll period of the motorsailer vs. the trawler versions. I have found references to anywhere from 3.0 to 3.5 seconds in the owner's groups.

For now though, I'll just adjust my course and 'roll' with it.

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Old 12-05-2014, 12:31 PM   #31
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From what very little I've been able to find out via a copy of "supposed" specs, displacement is 49,200 lbs and ballast is 14,000 lbs which seems to me VERY excessive. Net registered tonnage is 31.07t. the last time she was on a travel lift, their scale was broken so I have no actual number for the weight.
The register tonnage (gross or net) has nothing to do with weight, rather a measurement of volume.
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Old 12-05-2014, 12:34 PM   #32
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Stability is complicated. There are formulas to find out anything you need, but I've forgotten most of them. I generally leave that to the shipyard folks.
.

Agreed, everything on a boat is complicated from s/l ratios to prop pitch.
The formulas are merely a starting point. I know of a number of boats that do what they are supposed to do really well but are way outside the formulaic norms.
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Old 12-05-2014, 01:07 PM   #33
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displacement is 49,200 lbs and ballast is 14,000 lbs which seems to me VERY excessive. Net registered tonnage is 31.07t.
So either I've got an atrociously designed vessel or the #'s are all wrong. I've also "heard" 4t ballast in the keel.
That does seem like a lot. I think my whole boat weighs about 16k lbs... haha. Is she a beamy vessel?
Also, here's some apples to compare to your banana: The ship I work on has a light ship displacement of about 7,000 net tons, and we carry about 7,000 net tons of ballast. When we aren't carrying cargo, that is.

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The register tonnage (gross or net) has nothing to do with weight, rather a measurement of volume.
Yes. The weight of the vessel would be it's Deadweight tonnage, or Displacement.
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Old 12-05-2014, 02:56 PM   #34
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The contents of tanks must be considered when doing a stability study of any vessel. Usual pleasure boat practice is to publish just one figure for displacement of the ship, usually this is "Half-Load" condition. So it's with half fuel, water, sewage, stores, crew, and owner's items aboard. Commercial vessel practice is to publish at least two displacement figures, one at "Lightship", (just the bare boat with no liquids, stores, or crew aboard) and the other at "Full Load" condition, with all tanks full and full crew and stores plus any cargo aboard.

Stability studies will consider a range of loading, from Lightship to Full Load, and the critical one will be the "Worst Case", when stability is least. Usually this will be "Arrival" condition. This is when the ship returns to port after a voyage. Her tanks are only 10% full, but she carries full crew and some stores, and full cargo.

Establishing the real displacement of any boat is tricky, published figures are always incorrect, at least to some degree. I often find boats that weight 20-30% more than the published numbers. Boat's also gain weight with age. Travellift weights are notoriously incorrect, I don't know why.

Stability is not intuitive. No one can say anything definitive about some boat's stability without doing an involved/time consuming/expensive study. Do not believe any of the "computer...instant...gibberish", that's just gigo bs and has nothing to do with the real world. Wishful thinking does not make it so.

An artificially low center of gravity is the usual culprit in mistaken ideas about stability. Another factor is incorrect displacement. Unless I've done my own inclining experiment (to establish real VCG) and measured the actual boat afloat in water I've measured the density of, I regard all stability figures with considerable suspicion. Especially when people start throwing around numbers like 155 degrees.

With tanks close to empty the usual pleasure power craft will run out of stability (AVS or angle of vanishing stability) at 70-80 degrees heel. Except in very rare unusual circumstances, that seems to work out just fine.
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Old 12-05-2014, 03:08 PM   #35
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Unless I've done my own inclining experiment (to establish real VCG) and measured the actual boat afloat in water I've measured the density of, I regard all stability figures with considerable suspicion. Especially when people start throwing around numbers like 155 degrees.

With tanks close to empty the usual pleasure power craft will run out of stability (AVS or angle of vanishing stability) at 70-80 degrees heel. Except in very rare unusual circumstances, that seems to work out just fine.
I've always wondered about how initial stability is actually measured.
The most I've ever seen was less than 40 degrees, and that was plenty scary. I can't imagine 70 or 80. You'd be walking on the bulkheads.
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Old 12-05-2014, 03:11 PM   #36
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Greetings,
All good points thus far which fit into my meager understanding of ballast and weight distribution. What generated the question in my mind was the amount of ballast that our boat was issued with. That's why I was looking for a general %age of what might be acceptable and what would be considered too much (as I mentioned to overcompensate for a bad design).
Mr. BB mentions 6%, minus, of course, fuel, provisions and goats...

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From what very little I've been able to find out via a copy of "supposed" specs, displacement is 49,200 lbs and ballast is 14,000 lbs which seems to me VERY excessive. Net registered tonnage is 31.07t. the last time she was on a travel lift, their scale was broken so I have no actual number for the weight. The manufacturer has been of no assistance as I was led to believe the records were either non-existent or subsequently lost...go figure.
So either I've got an atrociously designed vessel or the #'s are all wrong. I've also "heard" 4t ballast in the keel.
I'm not going to divulge the vessel (sorry, want to preserve my enigma-ism) so I apologize for the vagaries of my questions and the frustration generated. I'm not concerned with stability, simply curious.
Honestly, I would not be a bit concerned unless there is some obvious problem. Like...is the main deck underwater while underway? That might mean too much ballast. Does the boat throw things in a cross sea? (I've seen this, stuff thrown across the cabin) She might have too much stability.

You can take measurements and estimate the density of your ballast to arrive at an approximate weight. But that really won't change anything. If she floats at a reasonable waterline and is reasonably comfortable on the voyages you undertake, why be concerned? True, if there is 14,000 pounds of ballast aboard, it's costing you a few bucks more each hour to move it. But backing off the throttle a hair will save more than the ballast adds, with the benefit of spending more time at sea.....
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Old 12-05-2014, 03:15 PM   #37
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Stability is not intuitive. No one can say anything definitive about some boat's stability without doing an involved/time consuming/expensive study. Do not believe any of the "computer...instant...gibberish", that's just gigo bs and has nothing to do with the real world. Wishful thinking does not make it so.
In the Nov-Dec issue of PassageMaker on about page 106, there is an ad showing a Motor Yacht being dropped in the water upside down and it self righted. Kind of wondering why they went through the expense of doing such a test. I suspect boat wasn't fully finished. Not sure what they were trying prove with the ad but they must think they can get some kind of competitive advantage by doing so. Maybe, they did it to justify their catch phrase: "We turned the motor yacht world upside down".
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Old 12-05-2014, 04:08 PM   #38
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In the Nov-Dec issue of PassageMaker on about page 106, there is an ad showing a Motor Yacht being dropped in the water upside down and it self righted. Kind of wondering why they went through the expense of doing such a test. I suspect boat wasn't fully finished. Not sure what they were trying prove with the ad but they must think they can get some kind of competitive advantage by doing so. Maybe, they did it to justify their catch phrase: "We turned the motor yacht world upside down".
Elling is gearing their ad program on the buoyancy and tests and the ability of the boat to right itself. Having talked to someone who attended the big test and having seen video, it's pretty impressive and it's gotten them press. I compare it to the Boston Whaler "unsinkable". They weren't the only boat that wouldn't sink, but sure had an ad program that worked. Obviously we're not going to be dropping boats upside down. However, the Elling's are very unique and do have tremendous buoyancy and stability and provide a great ride in many conditions. Perhaps more impressive to me was the protection against the water and the ability to restart everything.

Now does this make it the best boat on the market? No. Most buoyant? I have no idea. But it gets attention for a very well designed and built boat. And doing all this in front of press, no censoring of the video, was a bold move and showed their confidence. I tried to look and not be impressed, but couldn't. Go to elling360.com and look at the tests and I think you will find it most interesting.
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Old 12-05-2014, 05:08 PM   #39
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As by my design, we have 4300 lbs of ballast. I increased the size of our fuel tanks, and the designer recommended adding 1200 lbs more of ballast. I've not done that yet.

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Old 12-05-2014, 06:42 PM   #40
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Hard to see how this might translate from racing sailboats to trawlers, but, the former can have water tanks either side which can be filled on the weather side to counteract heeling, and canting keels where the keel is hinged at attachment to the hull and can be swung to the weather side for similar effect.
Failure of pumps or power systems does not bear thinking about.
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