Water Ballast for small boats

[Toot]

Hey folks. My recent thread on a mini kiddie boat got me thinking.

Ballast is nice for boats as it lends additional stability, however, of course, it adds weight and on a smaller vessel that's intended to be hauled in and out of the water, the extra weight may not be terribly appreciated. So I got to thinking...

What if you designed a "system" below the waterline that would allow water to flow in to a compartment through a series of open holes? Perhaps a hollow and water-tight keel with a few holes in it would be the best example. The holes would, of course, add a little drag so it would be wholly infeasible for a racing vessel (besides, water isn't that heavy). However, for a craft where ease of haul-out is more important than cruising speed, could such a system be a viable option?

On, say, a 14 foot vessel, you could have a 1'x1'x12' box that would hold as much as 750 pounds of ballast and yet would add little or nothing to the haul-out weight. Ideally, you'd also be able to cap the water up in there while aboard so that in the event of a capsize, you'd retain the water to help you get the ship back upright. Maybe you could even just have a capped PVC pipe with a rounded nose hung a few inches below the keel.

I'm talking about small boats here, obviously- things that come in and out of the water every day. My objective, really, is to provide more stability while at a standstill so that the deck of a small boat can be more usable without a risk of capsizing- perhaps even enabling you to extend the deck of a small boat beyond the limits of the hull itself without resulting in a big splash.

Has this been done before? Is it absurd? What do you think?

[l_boyle]

Look at submarine... They uses water as ballast, it help them to dive. Luxury cruiser uses water as ballast in their hull..
If you could have a pump the quickly fill the chamber, as well draining it.. Well, why wouldn't it work? Remember this, water in water have no action... Therefore it's netural. But, as uprighting the craft it may stop at the surface of the lake, ocean or which ever you sail in... I would of experiment with a toy boat or something simliar before getting into bigger thing like your own boat.

[Toot]

Look at submarine... They uses water as ballast, it help them to dive. Luxury cruiser uses water as ballast in their hull..
If you could have a pump the quickly fill the chamber, as well draining it.. Well, why wouldn't it work? Remember this, water in water have no action... Therefore it's netural. But, as uprighting the craft it may stop at the surface of the lake, ocean or which ever you sail in... I would of experiment with a toy boat or something simliar before getting into bigger thing like your own boat.


Your reasoning is flawed and your examples are of expensive craft which are virtually the antithesis of what I am proposing.

Water-in-water has no buoyancy. However, it does have mass- so it takes work to move it and it resists rotational forces. Fill a 55 gallon drum with water, fasten it to the bottom of a canoe and tell me that wouldn't make the canoe more difficult to tip. This is the same effect as a hydrodynamic keel on a sail boat, except instead of being a dynamic application of force to an ever-changing portion of the water (drag), the water is self-contained, thereby working better at low speed or while standing still (but being less effective at speed- hence my caveat that this would be inapplicable to racing boats).

Just try lifting a 5 gallon bucket out of the water. It weighs a lot more than an empty bucket sitting on the beach! And if you are trying to lift it with a long stick, the closer the stick gets to horizontal, the harder it will be to lift the bucket (you've got a moment-arm there).

[Guillermo]

Macgregor 26 uses 1150 lbs of water ballast when sailing.
http://www.macgregor26.com/water_ballast/water_ballast.htm
(I don't like the boat, but that's another story)

[Toot]

Macgregor 26 uses 1150 lbs of water ballast when sailing.
http://www.macgregor26.com/water_ballast/water_ballast.htm
(I don't like the boat, but that's another story)

Wow! And I thought I was being creative again! :)

Cheers!

[safewalrus]

Guillermo you've done it again mate! Superb! :cool: the only thing is I think I'd like to bable to dump the water whilst standing still in the water - you may not always be able to 'steam' at five knots, would a two way valve on the bilge pump be sensible? pump either the bilge or the ballast? (or even shift it around the boat?) :confused: or am I being too complicated? I don't think so - your views would help! (not just Gilly's but yours as well Toot)

Mike

[Toot]

For low cost and simplicity, I think I would have the holes facing downward, with a small bit of tubing running up to the deck. With the tubing open, the air would vent and the ballast tank would fill with water. When you want to empty it, just hook up a bicycle pump and just keep pumping till you see some bubbles coming up to the surface. Once you've got it filled with air, just clamp off the hose and the air will stay there.

Of course, you can design a fancier and more complex system, but for my purposes, I'm trying to keep it simple.

[Guillermo]

...would a two way valve on the bilge pump be sensible? pump either the bilge or the ballast?...
Yes, why not? The only thing is you'd need a rather big bilge pump to be able to pump out ballast in a reasonable time.
Let's say you want to empty the thing in 10 minutes; you'd need a 51 lts/min (806 US gall/hour) pump for that.

[Toot]

Remember, it's not just about removing the water, you've also got to get air into there. Air will displace water, so I say pumping air will be easier than pumping water. Air weighs less. :)

[Guillermo]

When you want to empty it, just hook up a bicycle pump and just keep pumping till you see some bubbles coming up to the surface. Once you've got it filled with air, just clamp off the hose and the air will stay there...
I'm afraid it will take you a lot of time and sweat to do that, if the amount of water is bigger than a few litres! (just think about the air pumped at every stroke of a bicycle pump). An electric pump or a devoted hand bilge pump such as a Whale Gusher fits better to the job.

P.S. The Gusher 30 pumps out 117 lt/min (31 US gall): http://www.whalepumps.com/marine/product_list/7/48/

[safewalrus]

Remember, it's not just about removing the water, you've also got to get air into there. Air will displace water, so I say pumping air will be easier than pumping water. Air weighs less. :) ?

Still prefer the bilge pump rather than a 'bicycle pump' you wouldn't want your air vent too big would you? otherwise it could become a water vent with a decent head of water

Your bicycle pump would be a bit small! and from experience a good bilge pump with a large capacity is needed for any boat (never mind the jokes about frightened men with 2 gallon buckets!)

[Toot]

I'm afraid it will take you a lot of time and sweat to do that, if the amount of water is bigger than a few litres! (just think about the air volume in a bicycle wheel)

I suppose you are right. What about a "piston" that you can pull forward inside a long ballast tube.

Behind the piston will be an air tube running to the surface. As you pull the piston forward, air fills the aft portion of the tube and the water ahead of the piston is displaced.


Or a method of tilting the ballast tube upward to get air into one end, and the slowly lift it up above the waterline.

Or maybe make it an external ballast tank on a tether and make just slightly buoyant. Pull a release switch to send the ballast floating to the surface, then pull the tether line to bring it to the transom where you can empty it and bring it aboard. Then, before the next voyage, just affix it to the keel and you're ready to go again.

[Guillermo]

Have to leave now. Cheers, guys. :)

[safewalrus]

cheers Guillermo, catch you next weekend!

Toot mate it would appear your getting away from your first idea - keeping it simple - you don't want to spend too much on this SMALL boat do you?

Mike

[Crag Cay]

The original Avon Searider RIBS used water ballast to make them stable when stopped. The whole volume of the deep V hull below the deck would flood through two small holes near the bow. As you began to move forward again all the water would flow out of the larger hole in the lowest point of the transom.

It provided excellent stabilty when at rest and they were great for sitting out at sea and 'watching' (if that was what you were paid to do). But other manufactures, as well as many operators of the Seariders themselves, found you needed much less power to get onto the plane, if you didn't have to drain the V hull first.

You could also get up faster with a shallower V, so soon loads of competitors to the Searider appeared claiming 'more speed, better acceleration, with less power and cheaper' which is a hard marketing pitch to compete against. Especially when all you can really offer is 'better stabilty when stopped in extreme conditions'. But I appreciated it.

[Toot]

cheers Guillermo, catch you next weekend!

Toot mate it would appear your getting away from your first idea - keeping it simple - you don't want to spend too much on this SMALL boat do you?

Mike

Here's what I'm envisioning based upon Gilly's and your own inputs.

Take a large PVC pipe, capped at both ends. Add maybe 3 cups of slurry to it (to make it just a little bit buoyant), let it cure. Then fill it with water. It'll weigh a lot when full of water, but will just barely float.

Now imagine a clasp, like you have on the trunk of your car- it has two parts, one fixed, and one that is attached to a spring to keep it closed. Attach two or three of those to your keel.

Press the PVC tube sideways into the clasp and it shuts. Go boating around with a few hundred pounds of watery ballasted goodness.

When you want to remove the ballast, pull on a few small wires to open the clasp and the "ballast" will float on the surface- not a lot as it still weighs perhaps 55-60lbs/cu.ft., but it'll get to the surface. Now pull the rope attached to the ballast to bring it to the stern. Then unscrew one end of the PVC pipe and tilt it downwards and all the water will run out. Haul it on deck, and bring the boat ashore.

Total cost: PVC pipe, some .1" thick metal to make brackets, a couple of springs, some slurry, a few nuts&bolts, and a rope.

It'd be pretty cheap to make, but it's a complex little task. Perhaps a bilge pump would be the way to go afterall....? But anyway, even with the bilge pump setup, you'll still need an air vent line to get air inside. I'm thinking that to prevent backflow, you would have something like a plain check valve. Close the valve, and no water or air is going to run backwards. Open it up and you can start pumping the air in, or the water out- either way.




Crag- sounds like a perfectly good and simple system for a motor boat. Would be quite the challenge on a sailboat though, I would think. But your description of its benefits is exactly what I am imagining.

[Toot]

Ok, this is along the same lines. I admit it wouldn't be as functional and it wouldn't work once the keel is out of the water, so it would only be good for balancing the boat, not righting it.

What if you made something sort of like a drogue chute...... But instead of being tied to a line, it's attached to the hull... basically trap a bunch of water in a sack underneath the boat to keep it stable while standing still?

argh... there's the complexity problem again, I'm afraid. I can't envision a good way of retrieving the "chute" or getting it out of the water without getting very wet in the process.

[Toot]

Ok how bout this.... A little unconventional, but bear with me...

Twin keels with a space between them. At the aft portion of the boat, you have a tunnel between the keels which slopes downward toward the bow. Then you've got a hinged bracket with a collar at the pivot point for the pipe and you've got the locking bracket near the bow. The collar prevents the pipe from slipping into the water and the front locking bracket allows the pipe to attach solidly before launching the vessel.

This allows you to stand at the stern and lift the tube up into the boat, allowing the ballast to self-drain as you lift. Then, once the pipe is angled upward into the boat, you pull it up and aft, slowly drawing the pipe as you slide it out of the water.

[frosh]

Hi Toot, Do you recall the original stuff you used to put at the bottom of all your early postings on this forum. Here I will remind you. I thought that I could find it on some of first postings but they have all been changed to
"Are we off topic yet?"

Anyway you will remember it much better than me!

Something like --"I don't even know enough yet to understand if I have any knowledge about boats" Sorry but that is not exactly it.

The thread so far apart from your first posting has been about the methodology to get the water ballast in and out of the keel section as simply as possible.
Somehow it seems that you and most other respondees have already accepted that the original hypothesis will work, and it now just a matter to determine how to do it.

I must strongly disagree with the original premise and suggest we go right back to beginning and first try to determine if in fact there is something to gain by incorporating water ballast in the first place.

I have never tried it of course, and I am not a NA, but I have studied university level physics, amongst other things.

In my humble opinion the relative bulk (not weight) of the water being pulled through the sea, lake whatever is going to slow the boat down dramatically. Even worse, I dont believe it will really add to stability at all, just increase the inertia that will be needed to be overcome when the hull starts to heel.
Inertia is only an issue related to the speed that a body changes it's orientation. Sure, with the water keel, and a gust hits the boat it now will respond more slowly to heeling forces, but if crew weight in relation to sail area and moment of force between CLR and CE of sail is insufficient to keep the hull fairly flat in the water, there will be no improvement ultimately to this imbalance with a water filled keel no matter how big it is.

Don't take me word for it, and check with a NA, but I would be very surprised if he disagreed with my hypothesis. :o

[Toot]

Hi Toot, Do you recall the original stuff you used to put at the bottom of all your early postings on this forum. Here I will remind you. I thought that I could find it on some of first postings but they have all been changed to
"Are we off topic yet?"

The software does that automatically, it's not my own doing, I assure you. I'm guessing it just saves storage space if the computer only needs to "fill in the blank" with "x" rather than save all those words many times over. I changed it because people took that to mean I know nothing of anything whatsoever, and that became somewhat annoying, as I do have a knowledge of structures, aerodynamics, composites, and a touch of metals, but am defficient merely as pertaining to boats in particular. Some people failed to pick up the tongue-in-cheek nature of my statement. So I changed it. Screw it (but not with drywall screws, eh?)

The thread so far apart from your first posting has been about the methodology to get the water ballast in and out of the keel section as simply as possible.
Somehow it seems that you and most other respondees have already accepted that the original hypothesis will work, and it now just a matter to determine how to do it.

I must strongly disagree with the original premise and suggest we go right back to beginning and first try to determine if in fact there is something to gain by incorporating water ballast in the first place.

I have never tried it of course, and I am not a NA, but I have studied university level physics, amongst other things.

In my humble opinion the relative bulk (not weight) of the water being pulled through the sea, lake whatever is going to slow the boat down dramatically. Even worse, I dont believe it will really add to stability at all, just increase the inertia that will be needed to be overcome when the hull starts to heel.
Inertia is only an issue related to the speed that a body changes it's orientation. Sure, with the water keel, and a gust hits the boat it now will respond more slowly to heeling forces, but if crew weight in relation to sail area and moment of force between CLR and CE of sail is insufficient to keep the hull fairly flat in the water, there will be no improvement ultimately to this imbalance with a water filled keel no matter how big it is.

Don't take me word for it, and check with a NA, but I would be very surprised if he disagreed with my hypothesis. :o

Again, the first sentence of my first post explains that this is for a slow, safe, sailing boat that is intended for use by children and will spend considerable time standing still. I am not considering this for a long range cruiser of any sort. Neither efficiency, nor speed are of particular concern here. It goes back to the old idea of "everything has its use." It may not be right for 99% of the boats out there, but I'm questioning whether it might be good for a particular application.

I fully realize that this offers little advantage while underway. However, as I said in a later post, I'm thinking that the moment-arm of the weight at the bottom of the boat may allow a small boat to better accept asymmetric loadings- perhaps even extend the deck beyond the hull to provide more usable space without the cost of a longer or wider hull. Again, this isn't for a cruiser. I'm fully aware that there are better ways of doing this as far as efficiency is concerned. However, in terms of ease of getting the hull in and out of the water, this seems to be a reasonable approach.

I am primarily questioning the effects of the water-ballast while standing still. On a small boat, obviously, standing far off to one side may cause a capsize. However, when you do that with a water-ballasted keel, as the boat rotates around its CoG (on the longitudinal axis), the water ballast and the person's weight form a moment arm, and so long as the moment arm for the water ballast is greater than that of the person, the boat ought to remain upright. This means it may be possible to extend the deck out farther without increasing the size of the hull. Now, of course, you'd ask, "Why would a smaller hull be beneficial? Why isn't efficiency while underway important?"

The answer is that this is intended to be a light boat that can easily be lifted in and out of the water, but can give another "fun" option to someone who wants more than a sail-trainer, but is not interested (or incapable of using) a larger, heavier boat. It's a niche market, for sure.

As to your suggestion that this is wholly impractical and without benefit, I point you to Guillermo's post that gives a specific example- the MacGregor 26 which uses a design based on the very same principles that I am discussing here. Further more, I point you to Crag Cay's post where he describes his personal experiences with a system which is not unlike the one I describe.

You are thinking very much like someone focused on speed, efficiency, and sailing performance. These three items are of only secondary importance for the application I am discussing. I see your point about inertial-attenuation as being the main thing here. I agree. And you may be right. Nevertheless, I do appreciate your input and am still thinking about it. Thanks!

[Guillermo]

...Even worse, I dont believe it will really add to stability at all, just increase the inertia that will be needed to be overcome when the hull starts to heel.
Inertia is only an issue related to the speed that a body changes it's orientation. Sure, with the water keel, and a gust hits the boat it now will respond more slowly to heeling forces, but if crew weight in relation to sail area and moment of force between CLR and CE of sail is insufficient to keep the hull fairly flat in the water, there will be no improvement ultimately to this imbalance with a water filled keel no matter how big it is.

Don't take me word for it, and check with a NA, but I would be very surprised if he disagreed with my hypothesis. :o
Well....I'm afraid static transversal stability has nothing to see with inertia, but with forms and vertical position of the CG. In fact when studying the static stability curve (the righting arms or GZ curve, or, to content Vega, the RM curve, whatever) we asume heeling is produced in slowly infinitesimal motions (So inertia is taken out of the game!).

In fact a fresh water tank in the bottom of the boat has the same effect on stability than the kind of ballast tank discussed in this thread. Empty it and the boat will be more tender; fill it and it will be stiffer.

Of course fresh or sea water, being not very dense, has less effect, for the same volume, than lead or iron, i.e., but for the same weight and CG position it has exactly the same. In a small boat some dozens or a few hundreds of kilos down at the bilges will have a definite effect on stability, absolutely, be them water, lead, or feathers. Of course they'll occupy different volumes, but asuming we can locate equal weighted iron pigs or feathers cushions having both the same VCG, both will have exactly the same effect on static transverse stability: If VCG is low enough they will increase it.

Of course inertia around a longitudinal axis also increases with the added mass, and, as you point, the effect of this in real life is to slow down roll movement at its beginning, and, on the other hand, increasing the amplitude of the roll angle at the end of the movement. This makes the total angle bigger than what strictly would have corresponded by what the GZ curve dictates. Movement is not infinitesimally low, and inertia plays it's role.

Cheers.

[Claus Riepe]

Frosh:
>>If this is so good why don't existing boats have it?
<<

It is there. Swallowboats are already having it in their new raid boats ( www.swallowboats.co.uk), the aluminum 'Innovaar Alife' has it since last year, and another dutch boat is getting ready to show it off at Sail Caledonia next spring. It is in full swing already.

Claus

[Crag Cay]

".......If this is so good why don't existing boats have it?...."

The emphasis there might be on 'so good'. Well, actually it's not that good. Anything with a density greater than water will be better as a given weight will sit lower in the boat.

HOWEVER, there is nothing as convenient as water if you want to have some ballast in your boat, but don't want to trailer it home at at end of the day. Way more convenient than rocks off the shore, which were the traditional method.

[Vega]

Water ballast is used in racing sailing boats and in some fast cruisers, but not on the keel. It is used where it increases more the RM (not at rest, but while sailing), on the upper side of the hull, on the opposite side of the heeling.

These boats have two water tanks, and the only one that is full is the one on the opposite side of heeling. It works the same way as the weight of all the crew that sits there when the boat is racing. Weight in that place can increase RM a lot.

The tanks can be emptied by gravity and they can partially fill by the pressure of the water created by the movement of the boat; a pump will finish the job.

Of course this is only good for travelling big distances.

[tom28571]

Craig,

There are some Swedish powerboats that use an auto water ballast system to gain stability when still or running slow. They have a longitudinal chamber in a double bottom along the inside of the keel. As the boat picks up speed the water exits thru the stern. Lighter weight for planing and greater stability at the dock.

Anything that weighs more than air low in a boat is ballast.

[Claus Riepe]

Crag Cay:
>>Well, actually it's not that good. <<

Vega:
>>Water ballast is used in racing sailing boats and in some fast cruisers, but not on the keel. It is used where it increases more the RM (not at rest, but while sailing), on the upper side of the hull, on the opposite side of the heeling. ...
Of course this is only good for travelling big distances.<<

Sorry guys, but you are quite misinformed.

Waterballast works absolutely brilliant in small boats.

I am NOT speaking about asymmetric waterballast here.
This is about keel-symmetric waterballast.
If done well, that is good for travelling short distances too.

Any more misconceptions? Let them come.

C.

[Crag Cay]

Yes I know. I think in another thread I wrote of my experiences in the 70's with the same system in the Avon Seariders.

My only point in this thread was to try and quantify exactly how good is 'that good' ? It was in response to a statement that said 'If water ballast is that good, why doesn't everyone use it?"

My suggestion is that there is nothing magical about water as a ballast material, EXCEPT you can move it easily in and out of a boat, move it around a boat and it will conform to any shape of available space.

However if you don't need those qualities, then there are loads of materials that make better fixed ballast.

[Raggi_Thor]

...Of course inertia around a longitudinal axis also increases with the added mass, and, as you point, the effect of this in real life is to slow down roll movement at its beginning, and, on the other hand, increasing the amplitude of the roll angle at the end of the movement. This makes the total angle bigger than what strictly would have corresponded by what the GZ curve dictates. Movement is not infinitesim ally low, and inertia plays it's role.
Cheers.

As a rule, concentrate ballast as much as possible longitudinally, close to the lcb/lcg, but spread it out transversely, out in the bilges. In most boats we want to minimize the longitudinal roll period to get over waves and maximize the transverse period for comfort.

[Raggi_Thor]

Craig,
There are some Swedish powerboats that use an auto water ballast system to gain stability when still or running slow. They have a longitudinal chamber in a double bottom along the inside of the keel. As the boat picks up speed the water exits thru the stern...

Jan Herman Linge is Norwegian :-)
he claimed to have a patent on this I think

[FAST FRED]

We tried water balast in our 33ft loa 28lwl 10.5 beam Motor Sailor.
The boat displaces 17000 lbs with 7000lbs in the keel.

3, 40 gal water tanks are on either side , the difference between carring the water on the "high" side ,low side empty is not noticable.

Perhaps with a boat with a far lower DL ratio the water would be more effective , but for a heavy offshore cruiser , hardly worth the extra pipe .

A great advantage tho is the ability to use the 2in Edison pump to empty the tanks easily when chlorene and flushing are needed.

FAST FRED

[Vega]

Fred, the height of the water ballast that you have used in your boat is so small that doesn't make any real differences. It is like sitting in the rail a very small children.

Compare for instance with the water ballast in the "Adrenalin", a fast cruiser designed by Dick Zaal :

Length: 43ft; displacement: 23,400lbs; beam: 4'.4"; Water Ballast 210 Gallons.

In this case, the water ballast effect is similar to the one of having, sitting in the rail opposite to the heeling, 10 adults.

Of course, the bigger beam will improve things, but anyway, the water ballast will make a very noticeable difference, if its height is significant.

[MikeJohns]

We have been using water ballast in ships for a very long time. It adds to both the dynamic and static stability. In full keeled yachts we put the tanks in the keel for good reason, and this is one good argument for a bigger keel on a cruising boat.

There is a common misconception that water ballast has no effect because its the same density as the water the hull is floating in. One of those seductively compelling but erroneous lines of reason .

[frosh]

Hi Guys, the original posting by Toot to whom I must also ask to forgive me for taking on a signature very close to his latest one, seemed to be worded in a way that caused me to misunderstand the waterfilled keel concept.
I immediately imagined a protruberance of a hollow nature at the centre line of the hull bottom actually shaped like a keel of a conventional keel boat. This hollow protuberance would then be allowed to fill with water to a certain level when the hull was in the water. Based on this assumption I could see no advantages at all and only negatives. From subsequent postings I think that the usual hull lines of a dinghy bottom are not distorted at all, and water is allowed to collect in the bottom area of the hull. This is quite a different scenario, and I don't see anything wrong with the concept now.

[webbwash]

Since we are talking of a 14 ft boat here and with minimal technology (handled by kids) the double bottom of the Avon RIB's makes good sense. The only negative is putting the transom with the open exit hole in the sand.

The concept works and as you increase your speed, you decrease the amount of ballast and this leads to greater speed and, what do kids want?, adventure and performance. What do their parents want? stability and ease of handling and SAFETY. (All this coming from someone who used to take the single bottom Penguins and the occassional Flying Tern for an underwater swim without proper flotation.)

Obviously a CB or a Dagger Board are required for lateral stability, but the numbers work in your favor and with the double bottom this will provide strength for the trunk and a dry inside drained out the transom.

Have fun in your Laser with a difference or is it a new style Blue Jay?

[Tanton Yachts]

When the boat is launched, the ballast valve (under the cockpit steps) is left closed to provide a minimum draft for shallow launching ramps. Once in deep enough water, the valve is opened to let in the 1000 pounds of water ballast and sink the boat to its normal operating draft. When the tank is full, the valve is closed, and off you go. Pulling the boat is likewise devoid of surprises; open the ballast valve before putting the boat on the trailer, and pull it out. Most of the water will drain right outon the ramp in a few minutes, and the small amount left can be emptied through a drain plug in the heel.

[Vega]

In full keeled yachts we put the tanks in the keel for good reason, and this is one good argument for a bigger keel on a cruising boat.

There is a common misconception that water ballast has no effect because its the same density as the water the hull is floating in. One of those seductively compelling but erroneous lines of reason .

When we talk of water ballast, that means water instead of another ballast.

A boat has to have water tanks and fuel tanks. They can not be considered as ballast and if they are considered as such, the boat can have a nasty behavior when sailing with almost empty tanks.

When talking about ballast in keels of cruiser sailing boats, I would chose lead every time, and of course I would locate fuel tanks, water tanks, batteries and engine, as low as possible, but that is another story.

About bigger keels on a cruising boat, what you gain in punting the water there, is not a match for what you gain with a big lead bulb on the bottom of the keel. Of course big keels are more resistant to grounding, and I will agree that can be a good reason to think about that when choosing a cruising boat.

[frosh]

If we imagine a laser with daggerboard, but with a daggerboard that can be winched up and allowed to drop under its own weight slowly. The bottom of the daggerboard has a small teardrop shaped lead bulb fixed to the bottom of perhaps 60lb. This would be far more efficient as a sail trainer than any water ballast system in regards to stability, and also have better performance in all conditions. The winching up system might need a tripod built over the daggerboard slot. and a block and tackle system.

[MikeJohns]

When we talk of water ballast, that means water instead of another ballast. ...............
When talking about ballast in keels of cruiser sailing boats, I would chose lead every time,

About bigger keels on a cruising boat, what you gain in punting the water there, is not a match for what you gain with a big lead bulb on the bottom of the keel.......
Vega

It was just a comment on Frosh's earlier post. Which he has now covered.

I agree, with what you say.

With a wider keel the issue is a bit more complex because that is carrying all the dense ballast (eg lead) so the keel displacement to overall keel mass ratio is very favourable, the free space therein is along for the ride and makes a very sensible place to put tankage.

For example here's a picture of one of those chine boats you find so pleasing to the eye :)

The attached vessel has 10 tonnes lead in that keel. In the remaining displaced space it carries 1 tonne fuel (integral), 1 tonne fresh water (separate tanks). A very useful space with a very low penalty as far as raising the COB. Large tankage on boats can adversely effect the transverse stability curve unless you can get them low. And as you say that massive girder makes the vessel very rigid and strong, and the well sloped LE on a long keel is the best collision insurance you can buy.

[Vega]

If we imagine a laser with daggerboard, but with a daggerboard that can be winched up and allowed to drop under its own weight slowly. The bottom of the daggerboard has a small teardrop shaped lead bulb fixed to the bottom of perhaps 60lb. ..

Not properly a laser, but take a look at this 6.6m sailboat, designed by Carl Beyer.

Look at the boat on the trailer, and in the end of the page, look at the keel;)

http://www.xpogroup.no/newweb/pdf/broschyr_norge1.pdf#search=%22carl%20beyer%22

[Vega]

With a wider keel the issue is a bit more complex because that is carrying all the dense ballast (eg lead) so the keel displacement to overall keel mass ratio is very favourable, the free space therein is along for the ride and makes a very sensible place to put tankage.

For example here's a picture of one of those chine boats you find so pleasing to the eye :)


Sorry if I have misunderstood you. About tankage in the keels, Carl Beyer, the Architect of the gorgeous little boat of the previous post, uses to put, at least the diesel tank in the keel, on several of his cruising boat designs, and they are not long keel boats. I would say generous fins.

I am particularly impressed with the tankage he managed to put in this small ocean going boat (fuel tank in the upper part of the keel, lead on the bottom):

http://www2.yachtworld.com/discovery/discovery_14.html


About that one of “here's a picture of one of those chine boats you find so pleasing to the eye”..I guess you are teasing me:D . Some months ago I have said that I didn’t like hulls with chines. I still prefer (a lot) a round bilge hull, or eventually a good radius chined hull (like those of Dudley Dix).

A multi chined hull, if well made, can be an option (if I can not have one of the others) but definitively I don’t like single chined hulls. The one you have posted doesn’t look too bad to me because it is a deep V hull, but when they are used in sailing boats with almost flat hulls, I find them quite ugly.

[Raggi_Thor]

I posted this in the wrong thread yesterday :-)

Water tunnels in planing motorboats work very well, when you stop the boat sinks down to it's chine and feels very stable.

Here's another little Swedish sailboat,
campus 650 and 630 from Fabola, design by Bernt Lindquist.

Tekniska specifikationer:

LOA: 6.60 m
Length of hull: 6.20 m
Bredd: 2.30 m
Draft: 0.25 - 1.20 m
Ballast in keel: 60 kg
Water ballast: ca 150 kg
Mastheight above water: 9 m
Main sail : 9.00 m2
Genua : 8.00 m2
Spinnaker: 22.00 m2Dry weight (on the trailer) : 455 Kg

www.fabav.se (only swedish?)

[Raggi_Thor]

It's a nice little boat, the Campus, and it fits on a standard trailer.

[safewalrus]

Phew! Its amasing what can happen in a week - so this guy asks the simple question " can I use water as a ballast in a small sailing boat design for basic sail training for youngsters?" a couple of others give him some ideas and they chuck it about a bit! K.I.S.S. system working well (after all he don't want to spend a fortune, when the kids learn to sail they'll be upgrading to bigger and better after all!

then appears all the experts with all sorts of bright ideas and clever numbers and other stuff - forget the the low cost K.I.S.S. idea now we're paying millions! Come on "stay with the beat baggy" as they sing about in the 'jungle book'. couple of good points true but hell it's taking a maul to crack a peanut ain't it? Anybody heard of "free Surface?" (apart from MikeJohns of course)!

[roy marine]

I saw a water ballast system incorporated into the keel of a 17 fiberglass runabout at the Toronto Boat Show about 10 years ago. The tunnel was open at the transom and could hold about 20 imp. gallons. Good idea however I only saw this boat one year.

[Guillermo]

Anybody heard of "free Surface?"
Mike, if you mean the physical thing, there's no free surface if tank is 100% full. Or am I understanding wrongly your question? :confused:

[Raggi_Thor]

I think he means we have to make sure the tank is full.

[safewalrus]

Guillermo/Raggi - you got it, either fill thwe tank up or keep it MT (empty) or you going to get all sorts of interesting things happen (I ain't talking about 'flume' tanks or other patented systems here - after all it was originally about a simple cheap system to gety a bit of ballast into the boat)

Gerrry cans (5 litre orange squash containers) fill em with water before you go and chuck it away as and when! bit like using bags of beach I guess save it can be reused, trouble is it fills the bottom of the boat up with containers, nowhere for your feet!

[mflapan]

I had an 'interesting' experience in a water ballasted trailer sailer that I would like to share with you.

The boat was being tested for 'boat of the year'.

The test started by operation under motor with the builder highlighting how fast the boat went (though she trimmed excessively).

We stopped and the builder advised that he was filling the ballast tanks in preparation for sailing by opening a valve. This was noteworthy in itself as there were warning notices on the boat stating that the boat should not be operated without the waterballast tank full. Is it possible that he had operated unballasted under motor to impress with the best possible speed?

I queried how he knew the tanks were full. He replyed "By waiting 5 minutes". I mentioned the potential for free surface to remain but he assured me that it was not a problem.

In gusty 20 knot conditions, we hoisted the main. I was down below at the time as the cockpit was full. I felt the boat heel more than I would have expected. To find out what was going on, I stuck my head out of the companion while standing on the stairs. As soon as the jib was set, she went over on her beam ends with the boom in the water. As she heeled, I stepped onto the galley bench and then the inside of the topsides. My colleagues in the cockpit did not fare as well with them clinging to whatever they could grab and one dropping into the water.

We let go the sheets and fortunately she rounded up and very slowly righted. After a rather long and awkward period of near silence as we motored back to the marina, I spoke with the builder. He believed that the cause had been the ballast tank not being completely filled.

I subsequently had further dealings with this boat and it is my belief that the water ballast was not the only reason for its stability problems. As is so often the case, there was a chain of causation.

However, it did highlight the potentially unforgiving nature of water ballast if not properly applied, especially on a vessel operated by persons who might not have an understanding of the risks involved.

Regards
Mori

[Claus Riepe]

Mori:
An interesting story, thank you for telling it. It is absolutely creditable, and it is awkward, especially for the builder and/or designer and the crew.

But it's not the end of waterballast in small boats, because that is an absolutely superb new technique, when designed and handled with appropriate care and skill. But that applies -or should apply- to small boating generally.

But you are right, waterballasting adds complexity, compared with fixed built-in ballast, there are several more grips to do, handles or levers to operate until things are set, but then it works just as well as fixed ballast.

And even better.
For one, because you of course have the freedom of choice, at any moment, to have ballast in, out or in again. With every different course, wind drop or increase you can always weighttrim your boat for best performance and/or safety. Fixed ballast does not give you that choice. You are boring safe -and slow- all the time.

But there is yet another very important reason for waterballast vs. fixed ballast, where waterballast actually adds safety over fixed ballast.
If you are familiar with the stability testing details of ISO 12217, you know the dilemma.: The RCD (ISO) appreciates stiff boats, but the stiffer a boat is under normal circumstances, the more difficult it will become to right it from complete inversion, which is also a point in the focus of the ISO.

The only perfect answer to the conflicting ISO requirements is actually .... waterballast.
That -alone- can both ascertain self-righting stability of the upright sailing boat, AND it can also de-stabilize the inverted boat so that it can be righted again easily, meaning with minimum crew.
I do not wish to go into the details here, naval architects should grasp the idea themselves very quickly, it adds quite another dimension to the possibilities of small boat design under the restrictions of ISO.
It is the way to go in the future.
I am quite sure your guy in Australia who did not get it right first time yet will require very little time to come out with a much improved -maybe even foolproof- solution.
He clearly made a bad mistake (free surface, sloshing ballast water), but he did not disprove waterballast in general.

Claus

[mflapan]

Dear Claus

Thank you for your reply to my posting.

Yes, water ballasting opens a lot of possibilities. My comments were not to stifle innovation. Rather, they were to highlight that water ballast arrangements need to be designed and operated with care taking into account the relevant risk factors that might include operators with limited knowledge and potentially very serious consequences if they are not used properly.

While on the subject of water ballast, I saw at the last Sydney Boat Show a number of aluminium recreational fishing boats from New Zealand of about 6 metres length that were fitted with a duct keel. The duct would be flooded when the vessel was at rest. The duct was arranged so that when underway, the water would drain from the duct. The concept was that when stationary (a common occurrence on a fishing vessel), the added weight of water would reduce motions and when underweigh (often incorrectly spelt underway), the boat would benefit from the reduced displacement. It sounded like a good idea, though I did not see it actually in action.

Has anyone had practical experience with boats having this confuration?

Best regards
Mori

[Crag Cay]

Has anyone had practical experience with boats having this confuration?
This was a feature of all the Avon Searider RIBs from about the mid 1970's onward. I think it was one of the first features built into the RIB concept being developed at Atlantic College in the 60's.

It certainly improved 'at rest stability', but drastically increased the power needed to get the boat onto the plane.

[Claus Riepe]

This was a feature of all the Avon Searider RIBs from about the mid 1970's onward. I think it was one of the first features built into the RIB concept being developed at Atlantic College in the 60's.

It certainly improved 'at rest stability', but drastically increased the power needed to get the boat onto the plane.

Well, not quite true. Such a waterballast system does not increase the power needed to get the boat onto the plane, that is a bit simplistic. In reality, the boat can plane with the same power, but it cannot do so within seconds, as it first must shed the ballast water. That can be done through a self-bailing device which starts to suck from around 5 knots upwards through the suction created by the speed of the hull through the water.
Meaning, once the boat starts to move above 5knots, the ballast water load continually decreases, and parallel to this the power required to plane the boat is reduced. After a few seconds -or a minute- more the boat reaches the same planing speed as the unballasted boat, and with the same installed power.

Claus

[Crag Cay]

Well maybe, but as a professional user of these boats back then, I stand by my original statement. In reality, the load carrying of these boats was quite restricted and always required more power to get the same load on the plane than the identical boats that had the water ballast system glassed off. It's no coincidence that this system did not find universal adoption either across all of Avon's RIB range or with other manufacturers. Its specific advantages came at a price.

[ancient kayaker]

Toot's objective is to improve stability in a small boat at standstill so the deck is more usable without a risk of capsizing by using water ballast.

If water ballast is added the CoG is lowered but so is the freeboard. The ballast must be in the lowest part of the hull or pendulum stability is impaired; when the hull rolls enough to bring part of that ballast above water the rolling resistance stiffens rapidly; however for a a typically shaped boat (i.e., not a raft) the people on the deck have already slid overboard.

At more moderate roll angles stability increases slightly due to the increased waterline beam as the hull, er, sinks. That assumes no tumblehome of course. However, a safer and easier method is to attach pool noodles a few inches above the water line to improve stability, or add floats on outriggers. I don't recommend sailing in this condition however.

In the real world of course water ballast is added inside the hull but as a mind experiment you can think of adding water either inside or outside the hull. Add it inside and the boat drops in the water as above. Add it outside and nothing much happens apart from changing the lines until the ballast breaks the surface.

Water-ballast has some advantages on hulls that are designed from the outset as such, but this isn't something you can retrofit.

[benmww]

I'm guessing this stability came from the high polar moments from the ballast tanks on opposite sides.
did this system work to an equivilant extent when beam on in a sea way?
also what was the ballast/displacment ratio of this system?

[Claus Riepe]

Ancient Kayaker,
You have made the two key points:
1. The water ballast really kicks in most efficient -apart from it's passive effect from the hull lying deeper in the water- as soon and as much of it breaks over the outside water surface as the boat heels.
and
2. For that, the boat really would have to be designed for Waterballast from the outset.

Meaning, the waterballast should be distributed as near to the outside as possible, as close to the outside water level when on even keel, and not be sloshing to lee.

When done like that, it really does miracles to the stability, my current boat is proof.

Claus

[ancient kayaker]

Thanks for the confirmation Claus. I was theorizing and have no experience of (deliberately) admitting water into a boat. I would guess that boats that use water ballast are shallow draft and beamy, unless the ballast is movable. I think it would be useful in a catamaran, unless one wanted to get the weather hull out of the water to reduce skin drag.

[BOATMIK]

Hi All,

The great New Zealand designer Jim Young has a number of cabin trailer yachts that are designed for home building that use water ballast.

The system is gravity run and simple.

Put the boat in the water - wait for the water level to appear in a plastic tube that is attached to the ballast tank - then turn a valve to keep it there.

Before the boat is put on the trailer the valve is opened and the water pours out as it is winched aboard.

His boats sail well enough to burn off quite a few of the high tech trailer sailors.

He also designs innovative and very quick high tech and medium tech trailer sailors.

But the beauty if his water ballast system is that it is so simple and has been used successfully for around 30 years in hundreds of boats

Michael Storer

[Claus Riepe]

... I would guess that boats that use water ballast are shallow draft and beamy....
Yes, that is the point, and that is why waterballast has a special relevance for small boats. It only temporarily kicks in as righting ballast when being lifted above the water surface in a heeling boat, it 'vanishes' as righting ballast when under water, then it is just mass.
I myself had difficulties understanding this mechanism. What explains it is the 'potential energy' model: Every mass lifted from and above the surface represents 'potential' energy, which you can harvest from as it sinks back.
Somewhat topheavy stuff this 'energy theory' explanation, I admit, the beauty is how simple it works in reality and practice.

...
The system is gravity run and simple.

Put the boat in the water - wait for the water level to appear in a plastic tube that is attached to the ballast tank - then turn a valve to keep it there.


In my boat, a Swallowboats 'Searaider', as it's both a rowing and sailing racer, the use of waterballast is temporary and arbitrary. In addition to a slower gravity feeding you can quickly scoop the ballast water in through opening a reverse-positioned self-bailer, and you can sail it out again through opening three correctly positioned ones. This system works very quickly, through the scooping effect when taking the water in. Which is important, as the boat goes through moments of reduced heeled stability while the ballast tank is only part-filled, so the ballast water can slosh about and especially to lee. Therefore it is vital the filling -or emptying- process takes as little time as possible.

Can't wait to use it again as soon as spring -hopefully- arrives back here again.

A Happy New Year and good sailing to all in 2007!

Claus

[BOATMIK]

Howdy Claus,

There is perhaps one more thing to grasp. The change doesn't occur when the ballast water is lifted above the level of the body of water outside.

ANY rise in the boat's centre of gravity as a whole is what makes the difference.

And using water or any other ballast to reduce the height of the centre of gravity means that heeling makes the centre go up.

If the water ballast is used to move the centre of gravity up high - like at the top of the mast - then as the boat heels the centre of gravity moves down so it makes it easier to heel the boat.

So the water ballast is usually there to lower the centre of gravity!

Best regards

Michael Storer

[SuperPiper]

Claus' argument made sense at first. Here is the mental analogy I created to understand Michael's reasoning:

A perfectly cylindrical jar floating on its side would roll and not stop in any particular orientation. But, tape a condom full of water to the inside and the jar would always stop same-side-up even though the condom was still BELOW the waterline.

And, American beer is like sex in a sailboat: f&#$@ing near water.

[Claus Riepe]

Michael, Superpiper:
Nothing wrong with what you say. And analogies do help to grasp the mechanism.

I quite like that 'condom in a jar' analogy, which I feel would be the appropriate model for keel hulls.
For shallow but beamy dinghy-like boats, I think a 'condom in an open shoebox' is a better analogy. Now, the choice would be to put one big water filled condom onto the longitudinal centerline, or two half-filled ones on either sides, would the two different arrangements stabilize the box differently? Or will both arrangements have exactly the same righting effect?

Looking at this model, I feel the righting effect would be quite the same.
-I fear I just disproved my own theory. Hat off to you!

Anyway, the key thing remains we all agree that waterballast works in small boats.

Claus

[BOATMIK]

Michael, Superpiper:
Looking at this model, I feel the righting effect would be quite the same.
-I fear I just disproved my own theory. Hat off to you!

Hats off to you Claus, you disproved your own theory in record time!!! :-)

Stability comes from the relationship of two centres.

The centre of gravity and the centre of buoyancy.

The centre of gravity doesn't move much on conventional yachts.

The centre of buoyancy moves around considerably depending on the heel of the boat and other factors that make the hull change its disposition to the water.

If you take ballast and split it port and starboard without changing its height you haven't changed the centre of gravity so the stability will be the same.

The thing that will change is the period of roll of the boat. It might rock from side to side a little bit slower with ballast arranged on each side rather than at the same height in the centre.

Michael Storer

[Raggi_Thor]

Isn't it tempting to make a water tank able to move from side to side?

:-)

[BOATMIK]

Ha Raggi,

I think you have a big idea here.

But I think it would be awkward and difficult to move.

But we can use the natural properties of water to resolve the problem!

IF it was frozen it could simply be slid almost frictionlessly from side to side.

The refrigeration machinery might require running the motor continuously which would have been against the spirit of sailing once, but that seems to be OK in these days of canting keel yachts.

:-)

Michael

[Raggi_Thor]

Salt water?
:-)

I think I will give it a try, two sliding water tanks, stored under the sitting bench on each side of the cabin when they are in "neutral" position, dragged cloely together up to the windward side when beating...

[BOATMIK]

Hi Raggi,

Well if you don't use the engine for freezing the blocks (though I think it would save building/buying two tanks) maybe you can use it for moving them?

:-0

Michael

[LP]

Use a scupper on the leaward side below waterline to use the hydrodynamic pressure created by forward movement to fill the windward ballast tank. Then have a simple kick mechanism that opens a drain in the leaward tank while closing off the drain in the windward side. With a little ingenuity(sic), a person could maybe develope a siphon drain system that makes the entire system passive.

[Raggi_Thor]

yes, nice :-)
How much of the dynamic pressure can be used?
Do you have any numbers from self bailers?

Dynamic pressure (from speed) = static pressure (from height potential):
1/2 x Rho x V^2 = Rho g h
V squared = 2 x height x g (g~9.81, we use 10)
or H = (V^2) / (2

Say your speed is 1m/s after a tack (2 knots?),
then the dynamic pressure in the scupper equals (1/20)m or 50mm (two inches).
At 2m/s you can lift the water 200mm (8 inches).

Now that's theory, does it work in practice?

[LP]

Just throwing ideas out there. Overactive imagination thing.

Maybe my old worn out Force 5 could become the test platform. How do I get the tanks in without carving the thing up. Thinking out loud here. Tire innertubes might work. They're pliable. Just stuff them in under the rails. Might work to other means too. The windward tube would fill while the leaward would collapse. You don't have to worry about what to do with the air in a rigid tank. Two scuppers per side. One for pressure and one for suction. Pressure for windward ballast and suction for the leaward anti-ballast(drainage). As your speed increases on the tack, pressure and suction would also increase.

How much head pressure do you get at 6 kts? . . . 7 & 8 kts?

Actually, a test bed on an existing hull would be pretty inexpensive proposition. Too bad it's fricking winter here.

[BOATMIK]

The most widespread and successful method of water ballast is that used by New Zealander Jim Young to reduce the trailer weight of some trailer sailers of quite reasonable performance and ability.

Probably a few hundred boats launched.

The tanks fill when you put the boat in the water and empties when the boat is removed from the water.

I believe there is a valve to keep the water in or out as required so hydrodynamic effects or gravity effects don't empty the tank at the wrong time.

MIK

[LP]

I was looking at doing a waterballast trailer sailor and came up with a system that sounds very similar to the one you are talking about. The only addition I might have had was to incorporate a 12 volt air pump to assist in removing the water prior to trailering. Make it float higher for loading on to the trailer, but otherwise, very similar.

http://boatdesign.net/forums/showthread.php?t=8190&highlight=trailer+sailer

Sounds like some one took the their idea to task and came up with a viable solution. Is there a website to go to?

[ancient kayaker]

Just to return to the 'condom in a jar' analogy, if you tape the condom on the outside of the jar it has no effect unless it is out of the water. That was the point I was trying to make in my "mind experiment" earlier. Much the same thing happen in a water ballasted boat that's swamped. The mind experiment was intended to show the importance of the hull shape to the success of the water ballast strategy. It will not work on every boat.

Wish I'd thought of the condom analogy, but I've led a sheltered life ...

[SuperPiper]

A.K.:

You are from Alliston. I am from Peterborough. But, this response is being posted from a hotel room at the base of Mt Ste. Anne. Not a flake of snow in Ontario.

We should be sailing.

[LP]

Another concept or property of water that needs to be dealt with is the fact that it is a fluid and has very low moment of inertia properties about the areas that are concentric with centers of rotation. (Roughly, the center of gravity of the vessel) As an example, take a full 2-litre bottle of pop with(no condoms though please) and spin it with the cap. Almost no resistance to motion. Put the same bottle on it's side and spin it on it's side. Now the areas (volumes) at the ends develope moments and there is a significant increase in resistance to motion. Freezing the bottle now will increase it's moment of inertia even further, though I'm not suggesting a refrigerated ballast tank.

Should a person want to use a water ballast system, the chamber(s)s need to located at a distance from expected centers of rotation (bilge tanks) or the chamber(s) need to be sufficiently baffled that accelerations/rotational forces experiences by the vessel are tranfered to the water ballast. This will increase the MOI of the ballast and increase resistance to roll (and/or pitch) of said vessel. The point being to reduce eddy currents to a bare minimum within the ballast tank to make it respond more like a solid than a liquid.

In the example given earlier where sailboat went over on its beam ends, I could speculate that a lack of internal baffling in the ballast tank could cause the lack of initial resistance to rolling moments. Encountering an unexpected gust could send the boat over on her ear very easily because once the water mass(ballast) is in motion, it will try to stay in motion and aggravate the condition.

[ancient kayaker]

Hey SuperPiper of P'boro; what's stopping you sailing? I only just got back from the lake! I was paddling not sailing as the sailing stuff is lying in an untidy heap I didn't feel like sorting thru. I enjoyed improving my best in-the-water date, previously Nov 30.

No sign of any fish although the water was crystal clear but lots of breathing holes in the sand so there's something down there. I was treated with distain by a family of over-wintering geese who seem to be raising a second 2006 family; obviously they knew this was going to be a mild winter. The local heron no longer allows me within 50 yds because I surprised her during the Summer and caused her to attempt to fly thro rather than around a tree. Kayaks are quiet! Pity, she was becoming quite used to my green plastic UFO (undesirable floating object).

No nasty remarks about the plastic from those who know me please, I'm not about to push my flimsy wood canoe thru ice even if it is only a half-inch thick.

There were some walkers in the distance so I executed a flashy turn and cranked on the speed. Clearly impressed them; sound carries well over the water. I thought I heard an admiring comment or two but the only thing I heard for sure was "Stupid idiot".

There's a surprising amount of ice around considering the recent mild temperatures.

To add a few words to the thread subject: riding a kayak up on an ice floe does nothing good to its stability so freezing the water ballast doesn't help unless it's firmly attached to the boat. I read somewhere that ice-breakers ride up on top of the ice to break it by weight but it didn't work for me. Ice breakers are a shade heavier than 240 lb. Well, we learn by trying.

A Happy New Year afloat to all!

[im412]

i found this traditional style "kattumaran" that uses water ballast

http://mahasagarboats.com/kattumaran.htm

http://mahasagarboats.com/kat3.jpg

http://mahasagarboats.com/kat2.jpg



It incorporates a unique water ballast system whereby once launched, just by turning some valves, the craft ballasts itself with the right weight in the right place to provide all the stability required. Back from the fishing trip, the craft is hauled a couple of metres out of water and the ballast tanks opened to let gravity drain out the water ballast and restore the craft to its original weight for easy hauling the rest of the way up the beach.

[Claus Riepe]

Waterballast in small boats at its best.:

The new BayRaider is completed and capsize tested for CE /RCD.

See some videos on Youtube, linked through

http://www.swallowboats.co.uk/content/view/127/

C.

[RonW]

Here is a excellent little 14 foot rough water , water ballasted boat, designed by a pro.
http://www.selway-fisher.com/Mcup16.htm#SHETLAND

[Guillermo]

Another interesting feature of water ballasts is that they are useful to categorize motorboats under combined categories C and B within the RCD scope. You can get a light boat (so fast) for C category and a heavier boat for B category. It allows the designer to fulfill both requirements for some types of boats.

[Pericles]

How about pumping out the water from the keel with compressed air from a scuba diving set or a cylinder of compressed air mounted on the boat trailer, or finally a paint sprayer compressor. It's pointless carrying the weight of batteries and a high capacity bilge pump, when you are only going to use them whilst retrieving the boat onto the trailer. C'mon guys. Think it out. Lateral thinking eh?

Pericles

[Claus Riepe]

How about pumping out the water from the keel with compressed air from a scuba diving set or a cylinder of compressed air mounted on the boat trailer, or finally a paint sprayer compressor. It's pointless carrying the weight of batteries and a high capacity bilge pump, when you are only going to use them whilst retrieving the boat onto the trailer. C'mon guys. Think it out. Lateral thinking eh?

Pericles

That has been thought out. The air pressure would be very difficult to control, and could quite easily burst the structure, the surface areas of a large tank are so big.

Swallowboats did some lateral thinking too: The ballast tank can be filled and be emptied 'on the fly' using self-bailers, and/or through using a standard bailing pump.

C.

[Guillermo]

Yes, airing a tank under pressure is dangerous. On top of that you have to carry the weight of the air cylinders, compressor or whatever, while still needing the batteries for other services.

[Pericles]

I have to disagree on two points Claus and Guillermo. Scuba diving regulators are extremely accurate in metering air flow to the mouth piece, plus they perform this task whilst operating at varying depths. Quality control is absolute. Controlling the top pressure on the water inside the keel, which is tall and thin, rather than a ballast tank, would mean a far safer situation. 15 lb per square inch would be sufficient, bearing in mind that the boat is still in the water and the outside pressure is equal to the inside pressure. As soon as air starts to bubble up, turn off the valve and haul the boat out.

I also wrote that the compressed air is only required to pump out the ballast water when retrieving the sailboat onto its trailer. Therefore the pump apparatus stays with the trailer and does not accompany the boat to sea.

Pericles

[Claus Riepe]

Pericles,
you will know that Scuba regulators need regular professional service to reliably work properly, once a year is the usual interval.

But then, why would one need to airpressure-pump water out during retrieving? Before all else, I would let gravity do the job.

C.

[Pericles]

Remember, the boat is in the water with the water ballast still in the keel. Pump out the water with the compressed air. The boat is lighter to retrieve. So what, if the regulator needs servicing once a year? As it happens, as the regulator is not going to be used underwater, it probably won't require so much servicing.

Anyway, this is just an idea. It just needs refinement.

Pericles

[Claus Riepe]

... this is just an idea. It just needs refinement.
Pericles

Well you may wish to refine it so. We have long discarded it.
C.

[Pericles]

Nope,

Not interested in wind driven craft.

Sorry about that.

Pericles

[ancient kayaker]

In most cases the water should flood the tank(s) without need for pumping following or during launch, and can drain out while the boat is being raised from the water. The lifting weight need not be much more than the empty weight of the boat to get the water to exit under gravity. Pumping out before lifting will get you reduced draft but not much reduced weight, since you would hardly remove the boat completely before opening the drain cocks since that would put unnecessary strain on the structure.

Unless you need to reduce draft, why use a pump to raise the boat, when you can use something with serious power like a hoist or tow truck?

[Claus Riepe]

We actually have gone air-pumping. Found a big manual airpump with 5 ltrs. volume per full stroke, and with safety over-pressure indicator.

We use it when the wind drops in mid-race. The crew then pumps a little air pressure into the tank in order to help the selfbailers drain out the water quicker.
Also, when the boat has come home into the marina with full ballast tank, the airpump works more efficiently than the water bailing pump to get the tank completely dry.
C.

[bigshrimpin]

Here's an interesting Patent from 1970 from Carl Mosley (SeaCraft).



Patent number 3503358 (http://www.wellcraftv20.com/forum_pic_dump/3503358.pdf)

[Claus Riepe]

Yes, interesting. Waterballast for stability, and at the same time used to improve trim during acceleration and deceleration, in a fairly simple way.
Has the system ever been used in a commercial craft?
C.

[rotfix]

wakeboarders use ballast similar to what i'm reading here. there's also a company with a patented system in production...calabria...patent # 6234099

they have a bladder under the deck and inlets on the transom which are under water when at rest. open the inlets to flood the bladder. get the boat on plane and the inlets are out of water, open to drain. i'm not sure if there's an over-flow line too.

another variation i've seen is to use the vent as the control as was mentioned earlier in this thread. this was done with a baldder above deck. if i remember, a scupper was on the bottom of the hull to force water into the bladder at speed. the vent was opened to evacuate the air. close the vent to hold the water. at rest, open the vent and the bladder empties.

these are somewhat different though since the first requires planing speed and the second requires a bladder or tank on deck. hope this wasn't posted already, i did a quick scan.

[rwatson]

Toot -
Good to see your mind is in top creative health to come up with a good idea, but .. its already 'standard fare'
The Macgregor system works fine with no pumps and doesnt need forward facing holes or any of that stuff (speaking as an ex owner).
Yachts have been using perfectly adequate water ballast for years now, its all been done. Pumping rates are not a problem.
Anything under 30 ft ( down to 2 feet) is no big engineering feet - it works, its straightforard, its not even news.

But here is a twist for you - how about a flexible 'bladder' inside the water ballast container to hold fresh water for the crew. As the fresh water gets used, it is replaced with salt to maintain the ballast.

Keep those creative juices flowing.

[doug kay]

It sounds a good idea and it's something I considered for my Ground Effect catamaran but the extra weight you add to make the container defeats the purpose.