Ballast Tube Facts

[stuart]

As a person who is building their own plate alloy boat I have a deep appreciation for the guys that do this full time. I have also dealt with in length a naval Architect and engineer who designed the boat in conjunction with my self and my requirements. To say this was a learning curve is understating the fact, it’s a headache trying to remember half of what the naval architect has explained to me as to why I cant have something with out some thing else and so on. Hence why you pay good dollars for a good architect, you simply get what you pay for.

I would like to ask those who maybe in the know as to what their thoughts are on the ballast tubes and there benefits and disadvantages on small alloy boats, say from 5.5 to 8mtrs? I asked my naval architect about designing these into my current boat and said that you wouldn’t get any more than 10% extra stability with the ballast tubes. I then asked myself as to why people use and promote them. 10% is obviously better than 0% gain but why can’t boats be better designed so you don’t need ballast tubes? I don’t mean for this post to start any sort of arguments, it’s a question have been asking myself and others for quite some time. Every person seems to have differing ideas but no one has given me hard facts or data showing the key benefits of this design on smaller plate boats, do any such figers exist by plate alloy builders who use this design? This is not meant to be argumentative in any way shape or form.

Stu

[cbs]

Can you define exactly what you mean by ballast tubes? Any links to those that promote them?

[wessel]

STu

If I understand you correctly, then you are referring to the tubes that fill up with water when the boat is at rest. While under way, the ballast tube will auto drain and aid bouancy.

The reasoning behind it is along the lines of additional keel weight when at rest. This will assist in stabilizing the boat =>more weight on the keel the less tendency the boat has to "rock".
This is the first time that I have heard a figure being added to the efficiency of this design though. Them boys with thick glasses and big calculators hey

A 10% gain on anything is something that should not be sneezed at I would have thought. But then, would you really add a figure like that to your advertising campaign and charge extra dollars for this marvelous design feature and get away with it?

Probably not if you knew the facts.

In your case, I think it would be a balance between what is needed, what is practical and is it worth the additional construction hassles it would create?

Good luck with the boat by the way.

Wessel

[just_cruisin]

I take it you are refering to the same sort of ballast tubes as used in the 'maxi series' of Fisher boats (fill up with water when at rest, empty once moving).

The tubes being full of water bring the centre of gravity of the boat lower to the water (favourable for stabilty) also adding to the boats displacement (also favourable stabilty). When the boat begins to move, ballast tubes empty, allowing easy plaining, good fuel economy etc....

[just_cruisin]

Wessel u beat me to it !
hahaha

[Mr__Bean]

I reckon stuff the boffins, just ask Col if it makes much difference.

My guess is yes, but only once you get to a certain deadrise.

- Darren

[cbs]

If somebody give me an idea of the tube size typically seen on a 6-7m boat (say the fisher) (x-section and length) I'll get out my calculator and thick glasses and give a real answer.

[stuart]

cbs,

That's what I'm looking for mate, tests and data so I can see for for my self this design is what its cracked up to be. I have heard many say that it makes the boat site down on the chines better, I say design a boat that does it on its own.

Stu

[just_cruisin]

Stuart,

All hull designs have their trade offs. 'Compromise' is a word that i like to use when looking at a boat, as there is not one hull out there that does everything u want.
Companies over the years have come up with all sorts of wacky ideas to achieve this so called 'do it all' boat. I'm yet to hear of one!

[HarryO]

Hi guys...

The architects almost right here, tho.

When they design the boat originally, they determine the
"VEE" of the hull while taking into consideration the weight
of the vessel, and the beam at the waterline chines.

If the desired VEE is too deep for the weight, the boat won't
float at the waterline chine, and will list from side to side,
depending on the movement of weight onboard.

To rectify this, they can use ballast tubes to lower the boat
onto its chines.

To fit these tubes to a vessel that is designed already to
float at its chines will only sink it lower, hence making it more
unstable.

Harry

[cbs]

I ran a couple of number on a boat I have details on.

It's a centre console design of less than 7 metres. Loaded displacement of 1.5t. The vessel has positive freeboard with an intact watertight deck. Deadrise angle at the transom is around 12 deg. The vessel rests with the chines immersed in the loaded condition.

I calculated the effect of adding a non buoyant compartment 200mm wide, 100mm deep on the centreline at the keel. Length was nominally chosen to be 4m. Effectively, this has added 65 kg in ballast when taking into account the shape of the hull.

Flooding of this void completely effectively increased the energy required to heel the vessel to 30 deg (the area under the righting arm curve) by 1.6%. Initial stability (GM) actually reduced by 1.6% (coincidence this is the same number) due to the increased displacement.

The above criteria are pretty simple, and only part of the entire stabilty picture, but give some indication of the magnitude of any effect. these numbers only apply to this particular vessel, and will change somewhat for other boats, In any case, I think the effect would be greater on deep V vessels that tend to rest with there chines very near the waterline.

There is a lot of garbage out there when it to comes to information being presented on vessel stability of small boats from manufacturers. I see claims on a semi regular basis that a new model has better than ever stability, and yet the hull looks the same, the arrangement is similar and the weight is similar. Fact is, the initial stability of a hull is primarily dictated by displacement, distribution of displacement (VCG, LCG) and waterplane area and shape (ie length and beam). Everything else is just the fine details.


You guys are going to have to believe me on the calculations, I have a fancy program that does it for me...


<puts down goggle glasses, calculator and goes to bed.....>

[stuart]

It's elementary dear Watson. So cbs, what does all this mean, Is it good bad or indifferent?
Stu

[Mr__Bean]

CBS,

What about a plate ally that runs up around 23 degrees deadrise?

Hardly any point at 12 degrees and already down on the chines.

Some of these are running serious ballast tanks.

- Darren

[sid_fishes]

that is some serious ballast mr bean------- so guys is this a serious go at fisher boats?many plate boat builders use naval guys for there work and like most architects go to bed with an idea and wake up with a mess[ this is common as i have to work with them day in day out]cols boats work ther is no doubt about that[ otherwise there would be more up for sale ] no boat will be the same as the next just like rods , builders .......... so stuart how did this all come around.......... and have u flipped it over yet ,,try making a roisttere stands and attach them to the hull. but if you need a hnd to flip it ,it will cost ya but its all good mate

[cbs]

Stu,

for the example I gave, its a lot of work for very little gain, On a light deep V boat, there would be some merit.

Perhaps, stu, you could give me the deadrise angle of your boat, and size of tube that could be put into it, and I'll take another punch at it. Gotta get the paying jobs out of the way first though (of which there is plenty on the desk (and floor) right now)

Or you could ask your guy to do the exercise.

cbs


sid, why lump all na's into the no hoper basket, bit of a generalisation there don't ya think.