Ballast?

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RT Firefly

RT Firefly

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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.
 
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.
 
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.
 
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. :)
 
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.
 
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.
 
We have something like 7,000 in ballast.
 
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.
 
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?
 
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.
 
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.

"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"
Click to expand...
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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cardude01 said:
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?
Click to expand...

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.:D

Larry
M/V Boomarang
 
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Tad Roberts said:
This subject is a vast quagmire.....Really difficult to discuss in generalities.......
Click to expand...

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

Larry:hide:
 
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.
 
twistedtree said:
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.
Click to expand...

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.
 
Tad Roberts said:
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.
Click to expand...


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.
 
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.
 
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.
 
twistedtree said:
Your lecture isn't available to read by chance? It sounds interesting.
Click to expand...

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.....
 
Xsbank said:
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.
Click to expand...

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.
 
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.
 
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.
 
>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.
 
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.
 
LarryM said:
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.
Larry
M/V Boomarang
Click to expand...

It is not unheard of to add ballast high in the structure to slow roll period.
 
boatpoker said:
It is not unheard of to add ballast high in the structure to slow roll period.
Click to expand...

+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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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...

Jealous goat | Best Funny Gifs and Animated Gifs Updated Daily - Gif Bin

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.
 
RT Firefly said:
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.
Click to expand...


Oh come on. You don't think we can't figure out the vessel is a Cheoy Lee?
 
boatpoker said:
It is not unheard of to add ballast high in the structure to slow roll period.
Click to expand...

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.:thumb:

Larry
M/V Boomarang
 
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