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Old 12-04-2014, 06:52 AM   #1
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Ballast?

Greetings,
I think I understand the general principles for ballasting and locating ballast on a vessel (trim, ride modification, stability etc.) but is there such a thing as too much ballast, short of sinking, to compensate for a bad design? Is a high %age indicative of a bad design? How much ballast do manufacturers plan into a design? Does every vessel have or require ballast? Is there an "average" %age for our vessels?
I don't think any of us want a repeat of: Vasa (ship) - Wikipedia, the free encyclopedia
Thanks.
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Old 12-04-2014, 07:33 AM   #2
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ON sail boats , because if the great variations in load and owner use it is not uncommon to hold back about 5% of the keel weight as movable ballast.

On power boats ballast is uncommon unless it is a blue water boat (rare!) that is designed to handle a knock down.

Small amounts of trim ballast are OK , because some dummy installed or carries heavy items on one side.

Ballast must be secured , not just tossed in.

A boat should float on her designed water line in normal use, ballast to cure a rotten design or build problem , is a boat to scrap, not purchase.
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Old 12-04-2014, 07:41 AM   #3
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Wow....even for TF this is a lot of "maybes" unless you narrow it down to a fairly narrow range of designs.

Some generalities I have learned....

Lots of ballast in some types of sailboats if at the end of a long narrow keel may be great,
Yet any unnecessary ballast on a racing powerboat may be a really bad thing.

Too much ballast may make a boat more resistant to capsize and self righting, but uncomfortable in an average seaway. Better placement of less ballast may be better.

Some think that ballast should all be centered and low...yet I always thought that too light of ends/beam, there is no weight to slow rapid pitching and rolling.

Yes, ballast can help a bad design but only to a point and not in al cases.
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Old 12-04-2014, 08:51 AM   #4
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My boat has 5000 pounds of ballast in the keel somewhere. It's a factory converted sailboat, so I assume that's why the ballast is there, plus the boat is advertised to be "self righting".

I haven't had the boat long enough to test it in any rough water. If I ever go anywhere I'll post up on how the ballast works out. I'm not looking to get "knocked down" anytime soon however. :-)
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Old 12-04-2014, 09:21 AM   #5
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The Krogen 42 has 2,500 lbs of ballast with a range of positive stability at 85 degrees. I know of many full displacement vessels with ballast but not many semi-planning boats unless for the reasons FF mentioned.
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Old 12-04-2014, 09:32 AM   #6
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Our Taiwanese Tub Classic has cement ballast below the aft cabin but I am unsure how much. I always assumed it was due to the boat being nose heavy.
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Old 12-04-2014, 09:41 AM   #7
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We have something like 7,000 in ballast.
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Old 12-04-2014, 10:18 AM   #8
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Living near Knoxville TN area on the Twin lakes (Ft Loudon and Tellico lake), we have several major boat manufactures; it is common on and off the water to run into people who work at every level of the boat manufacturing industry. More than once I have been told that they build hull #1 put it in the water then move ballast around various places. When all looks and runs OK, then they glass in the ballast. It then becomes hidden ballast that is added in earlier in the manufacturing process on every boat in that series. The majority of the owners have no idea that the lead is glassed into their bilge.
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Old 12-04-2014, 10:29 AM   #9
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Just read this about the SP Cruiser, which is the sail version of my boat:

"Although not pitched as a bluewater passagemaker, the SP Cruiser has a reassuring stability index of 39 and a capsize righting moment of 155 degrees"

Do those numbers also apply to my non sail-rig configuration in some way? Seems like anything with a STIX value over 32 gets the boat a Class A rating?

How do these numbers compare to that Krogen 85 degree roll number?
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Old 12-04-2014, 12:07 PM   #10
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The Eagles hull keel is filled with cement level with the bilge floor. I have look into adding more balast but most of the thru hulls would have to be raised. A sister 58 up in British Columbia been in rough water and he said the bow could use more ballast as the bow comes out of the water. But with the bow flare the water is directed to the out side and not over the gunnel for a reasonable dry ride.

There is a limit as the roll will be to snappy and or the bow boat will be to slow coming out of the water flooding the deck boat. So there is a limit. Having a comfortable roll is not a bad thing or the boat should have more balest.
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Old 12-04-2014, 12:22 PM   #11
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This subject is a vast quagmire.....Really difficult to discuss in generalities.

Some ballast is common in production trawler type yachts. Generally the lower speed vessels will have more and higher speed (semi-displacement hulls) will have little or none. Again a really general statement would be that; "heavier displacement (slower with larger ballast amounts) boats will have a lower center of gravity, thus higher angles of vanishing stability (AVS), than un-ballasted semi-displacement boats."

Many boats of any type will have trim ballast here and there. Larger volume hulls (wider and deeper) will often carry large amounts of ballast, typically converted fishing boat hulls.

The amount of ballast can vary wildly and by itself says nothing about the boat. To my mind, if anything more than 10-12% of displacement weight is ballast, you're hauling too much dead weight ($ down the drain). More typical pleasure boat numbers would be 3-6% of displacement.

Quote:
"Although not pitched as a bluewater passagemaker, the SP Cruiser has a reassuring stability index of 39 and a capsize righting moment of 155 degrees"
It depends on your definition of reassuring. A Catagory "A" (Unlimited Offshore) rating (STIX above 32) places operational limits at "Significant wave height of 7 metres and wind force at up to Beaufort 10." Beaufort 10 is a whole gale, 48-55 knots of wind speed.

The stability index (STIX) number really is not applicable to a powerboat, it's a comparison number for sailboats. Your power version of this sailboat/motorsailer is modified with removal of the rig but no (?) reduction of ballast weight. Therefore those numbers (from the sailing version) are meaningless. Ask the manufacturer for new ones.

The second part of that statement makes no sense. A moment is a force, not an angle. It could be that they are trying to say she has an angle of vanishing stability (AVS) of 155 degrees. That's quite high, undoubtedly due to the volume of her big high deckhouse. But I bet it does not account for the aft and mid cockpit being full of water.

Also the A STIX number allows a minimum downflooding angle of 30 degrees. Meaning that water starts filling the boat (downflooding) at something over 30 degrees heel, making the 155 degrees AVS utterly silly. But it's good marketing......
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Old 12-04-2014, 12:32 PM   #12
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Quote:
Originally Posted by cardude01 View Post
Just read this about the SP Cruiser, which is the sail version of my boat:

"Although not pitched as a bluewater passagemaker, the SP Cruiser has a reassuring stability index of 39 and a capsize righting moment of 155 degrees"

Do those numbers also apply to my non sail-rig configuration in some way? Seems like anything with a STIX value over 32 gets the boat a Class A rating?

How do these numbers compare to that Krogen 85 degree roll number?
In the event of a knockdown, your boat would survive being rolled over to 155 degrees and still theoretically right itself. The Krogen could only recover from 85 degrees and so forth.

The trade off is that normally, the higher the capsize resistance of a monohull displacement vessel, the stiffer it becomes and roll period and motion comfort come into play. A large keel will increase hydrodynamic resistance, and the additional weight of the ballast adds to the vessel's displacement, all of which require somewhat more power.

In the case of your boat, I would think the deletion of a substantial sailing rig would have necessitated a corresponding reduction in ballast, but this is pure speculation on my part. I'm sure you could find this out in the manufacturers specs by comparing the power vs. sail versions. Simply removing the sailing rig, with no other modifications, would result in a very stiff boat, but without the dampening effect of the rig's weight aloft, the roll period might be shorter which could make the motion more noticeable in beam seas.

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. Obviously, this is a function of boat size, and any 30' boat is going to move a lot in those conditions. This is one time where size matters.

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Old 12-04-2014, 12:45 PM   #13
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[QUOTE=Tad Roberts;288545]This subject is a vast quagmire.....Really difficult to discuss in generalities. QUOTE]

Tad, thanks for hanging around, to right the ship so to speak.
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Old 12-04-2014, 01:08 PM   #14
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This subject is a vast quagmire.....Really difficult to discuss in generalities.......
Ahem . . . Yes, exactly what Tad said!

After re-reading my prior post, I am reminded of two famous quotes:

"Better to remain silent and be thought a fool than to speak out and remove all doubt." - Abraham Lincoln

"Even a fool, when he holds his peace, is counted wise: and he that shuts his lips is esteemed a man of understanding." - Solomon 17:28

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Old 12-04-2014, 01:25 PM   #15
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At a minimum its important to distinguish between ballast that is part of the boat's stability design, and ballast that's installed to trim a finished boat. We have something like 10,000 lbs of ballast that's part of the boat's stability design, and probably 800 lbs of trim ballast. The boat weighs about 130,000 lbs, so those are pretty small percentages.
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Old 12-04-2014, 02:09 PM   #16
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At a minimum its important to distinguish between ballast that is part of the boat's stability design, and ballast that's installed to trim a finished boat. We have something like 10,000 lbs of ballast that's part of the boat's stability design, and probably 800 lbs of trim ballast. The boat weighs about 130,000 lbs, so those are pretty small percentages.
I don't quite see it that way.

Oh how I wish there was an easy way to talk about stability, but there isn't. There are just too many factors and too many variables for a simple discussion. I have a basic stability lecture that I've given a few times, it takes about 6 hours of me talking. I'd love to have people understand but mostly I get blank looks and "gee that's really complex" comments.

Back to tt's comments,

Every bit of your boat, including the kitchen sink, makes up the boat's "stability design". For instance, your flying bridge hardtop and mast both add to the boat's stability (greater displacement = greater stability), and detract from the boat's stability (by raising the center of gravity).

If your trim ballast is in the bilge, it's probably lowering the center of gravity and thus adding to stability.
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Old 12-04-2014, 02:31 PM   #17
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Every bit of your boat, including the kitchen sink, makes up the boat's "stability design". For instance, your flying bridge hardtop and mast both add to the boat's stability (greater displacement = greater stability), and detract from the boat's stability (by raising the center of gravity).

If your trim ballast is in the bilge, it's probably lowering the center of gravity and thus adding to stability.

I'm no expert on this, but didn't mean to imply that other things don't impact stability. Everything becomes part of the calculation to some extent or another. My point was just that some ballast gets designed in specifically to impact stability. That's it's role in life. Where trim ballast, though it also affects stability, has a primary purpose of trimming the boat. If placed wisely it can augment stability, and if placed poorly it could detract.

Your lecture isn't available to read by chance? It sounds interesting.
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Old 12-04-2014, 04:08 PM   #18
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Grand Banks boats are fairly popular, some people on this site own some, I even had one once. Guess what is in the keel of many of them?

Sorry FF, but your opinion of ballast is generally just a rant.

My only objection to ballast in a boat is if the boat is wood hulled, I can see an issue with having to move the ballast out when an inevitable plank replacement is necessary, and I always was 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.

Many ex-work-boats, now not working, have ballast installed to compensate for reduced loads, such as ex-fish boats.
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Old 12-04-2014, 04:40 PM   #19
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The ballast I was referring to in my post was I guess trim ballast. I remember in a boating magazine a few years back a story about a trawler that was bow high and the dealer installed 300 feet of anchor chain.
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Old 12-04-2014, 06:58 PM   #20
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Quote:
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Your lecture isn't available to read by chance? It sounds interesting.
No sorry, it's a really good idea though, I'll work on that. In the past I've tuned the lecture to the audience; commercial fishermen, yachtsmen, small boat sailors, and the Workboat Accociation all get something a bit different because their situations and concerns are different. Again trying to minimize the generalities.....
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