Adding Ballast to stiffen Boat

[jeffg]

Hi,
I don’t have an issue with the chockfast. As a matter of fact it is an excellent fill material and, as you said, it dose not shrink so it holds in place. My concern is that the weight of the chockfast is far less than concrete and pig iron. So, when they removed the cement and pig iron and filled the keel void with chockfast, they reduced the weight in the keel. I think is what is causing the “lively” behavior of the boat. My goal is to try to restore the weight lower on the keel to stiffen the boat.

[Henning]

Hi,


Some of the advice given in this thread reflects a certain confusion as to what your exact problem is, and I can't say I'm too sure of that myself. You say you want to stiffen the boat, yet you complain that she is too "lively", which is usually taken to mean that she reacts quickly to wave action. This in turn is usually due to a stiff gz curve and / or low moment of inertia.



To correct lively roll characteristics, bilge keels can work very well. What's your five degree roll period at rest?

[Benthic2]

Originally Posted by psneeld

probably cheaper to offer free beer to 10, 200 pound guys for an hour to come aboard.

And easier to move around too !!

[CanadianBoater]

Just a thought on this topic, maybe you can borrow or rent a bladder. Put it where you think you may want weight and pump it full of water. See how it reacts to the weight and then also drain it and move it fore or aft to find the sweet spot. No I don't have any experience with this or know if it would work, just throwing it out there.

[KiwiExplorer]

Hi jeff
I have a 35ft steel displacement launch. I know how lively they can be to to point that my wife did not want to come aboard anymore. I took another route and installed passive stabelizer wings. Underway i have a roll reduction of 95% and at anchore about 50% with the roll stopping much faster. Even when takeing a beam wake of over 1m i still dont spill a drop of my coffee on the saloon table. Before the stabelizers she shook and rolled intolarably. Everything flying everywhere. Now she is a dream, i dropped only half a knot in speed for the luxary of a smooth ride. I have also discovered that most of the time i only need 1 wing down. 2 down are only needed on off shore trips in 2 to 3m seas. I designed and built the stabelizers myself at a cost of around $3000. Best money spent on my boat

[Mako]

Kiwi, what exactly is a stabilizer wing?

[KiwiExplorer]

Hi
Its literally a fold down wing with a brace pole up againts the hull. Many comercial fishing trawlers use it here in NZ. I modled mine off a nieghbour in the boat yard with a few changes to suite my launch. Its basically a fold up steel wing on each side. Its princple works like a keel on a sailboat exept that they stick out the side generally at 45 degrees below horizontal hinged at the chine.

Google passive stabeliser wings ther is not much info out there but i never cruise without mine being deployed

[BluesII]

The following comes from an article published by Bray Yacht Design
Generally, when people think of stability and ways to increase it they think of adding ballast.
Generally, this will help - but not in all cases. If ballast reduces the freeboard to the degree
that the deck edge enters the water at a much lower angle of heel, then the overall stability
is drastically reduced. Again, it is the relationship between the hull form and the overall center
of weight that tells the story. Removing top weight from as high up as possible will have a
greater effect than adding ballast low down.
Also, ballast will not do much to increase initial stability (stability at very low angles of
heel). It’s real forté is at higher angles of heel. Once the heel angle starts to reach or exceed 45 degrees ballast comes into its own. Although this may provide real peace of mind, it does little to improve a day to day comfort situation.
Source: http://www.brayyachtdesign.bc.ca/Stability.pdf

[Benthic2]

Here's a short article about different types of stabilization if anyone is interested:

https://www.marineinsight.com/naval-...ation-systems/

[ben2go]

Originally Posted by Tad Roberts

The boat is hard-chined with a fairly flat bottom, it really wants to follow the face of the wave (snap-roll) . It sounds like the boat has excellent low angle stability, so it will take considerable force to change the motion. Adding 2000 lbs of ballast probably won't do much, but it will do something. By adding the ballast down low you will increase stability, and thus the motion will get faster.


Rolling chocks, bilge keels, bat wings, or stabilizers of some sort will significantly change the motion (damp out rolling), but any of them is a big project.



I would be very reluctant to reduce high-angle stability by adding weight up high, but that would slow the motion. It will take about 1500 lbs to sink your boat 1". I would try putting the lead inside on top of the chockfast, see if it does anything noticeable. The lead needs to be secured so that it will never move, ever!

How would you feel about sand bags being placed below deck? Do you think by moving them around, the motion could be better controlled, and then weight permanently installed in those areas?

[Nomad Willy]

jeffg,
HaHa that’s the opposite of the percieved problem I have.
Took out all the concrete and steel punchings and replaced w lead. Just the Laz though. But it’s still qite a difference I think. And I do appear to be stern heavy. Beats bow heavy by quite a margin though.

However most of the lead on top is birdshot so won’t be much of a problem getting it out. Does anybody think breathing the air in the laz would be a health problem? I’ll wear a paper mask but???

Perhaps I should give you my lead? haHa

Does this mean I have a “lead ass”?

Incase anybodies wondering ... my avatar pic shows the boat only about a week after we bought her. No lead then.

[Henning]

Sorry, you describe your problem succinctly enough, I just didn't read your post very well this morning. It is the time of long days at the yard and I was very tired.


Adding ballast to the keel would only serve to stiffen her further. You would ultimately get her to calm down if you just kept adding weight, because you would decrease the response to small wave inputs, but this would come at a prohibitive displacement increase.



Adding ballast high up to slow the roll is a terrible idea because it adversely impacts your stability curve at the extremes, which can leave you in a death trap.


Like I said, you should look into bilge keels. They're easy to engineer, cheap to experiment with and usually work pretty well. Wedge keels work better on hard chined vessels, but they're damage prone if improperly designed and increase your draft.


Willy, the soup created by decaying bird shot is horribly toxic, tread lightly.

[Blissboat]

"Less judgment than wit is more sail than ballast" - William Penn

(Been waiting quite a while for an excuse to bring that old quote out for an airing).

[BYNW]

I worked for a charter company in the BVI that had several Ponderosa 35 sundecks. I believe they were the same design or mold. the charter company added poured lead in the bilge to help with the 3-5' swells and 2-3' seas that were typical there. FYI

[Nomad Willy]

Henning,
You wrote;
“Willy, the soup created by decaying bird shot is horribly toxic, tread lightly.”
Isuspected as much. Thanks

[Al]

Originally Posted by cappy208

Maybe your expecting too much out of a little boat? Better weather awareness and laydays may be the easiest cure.

That too and in spades!!!!

Al-Ketchikan

[Comodave]

I would invest in a really good weather app and then use it. If you are out and it is too bad, change course. Heck, if you were in a sailboat, you would be changing course all the time...