Water Ballast for small boats

Discussion in 'Stability' started by Toot, Sep 24, 2006.

  1. Vega
    Joined: Apr 2005
    Posts: 1,606
    Likes: 26, Points: 58, Legacy Rep: 132
    Location: Portugal

    Vega Senior Member

    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.
     
  2. MikeJohns
    Joined: Aug 2004
    Posts: 3,173
    Likes: 198, Points: 63, Legacy Rep: 2054
    Location: Australia

    MikeJohns Senior Member

    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 .
     
  3. frosh
    Joined: Jan 2005
    Posts: 621
    Likes: 14, Points: 0, Legacy Rep: 44
    Location: AUSTRALIA

    frosh Senior Member

    I might have mis-understood the original premise.

    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.
     
  4. webbwash
    Joined: Oct 2004
    Posts: 35
    Likes: 0, Points: 6, Legacy Rep: 10
    Location: Lakewood, WA

    webbwash Junior Member

    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?
     
  5. Tanton Yachts
    Joined: Jul 2005
    Posts: 202
    Likes: 4, Points: 0, Legacy Rep: 73
    Location: Newport. RI. USA

    Tanton Yachts Yacht Designer

    Small water ballasted vessel.

    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.
     

    Attached Files:

  6. Vega
    Joined: Apr 2005
    Posts: 1,606
    Likes: 26, Points: 58, Legacy Rep: 132
    Location: Portugal

    Vega Senior Member

    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.
     
  7. frosh
    Joined: Jan 2005
    Posts: 621
    Likes: 14, Points: 0, Legacy Rep: 44
    Location: AUSTRALIA

    frosh Senior Member

    Maybe try a mini lead bulb.

    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.
     
  8. MikeJohns
    Joined: Aug 2004
    Posts: 3,173
    Likes: 198, Points: 63, Legacy Rep: 2054
    Location: Australia

    MikeJohns Senior Member

    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.
     

    Attached Files:

  9. Vega
    Joined: Apr 2005
    Posts: 1,606
    Likes: 26, Points: 58, Legacy Rep: 132
    Location: Portugal

    Vega Senior Member

    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="carl beyer"
     
  10. Vega
    Joined: Apr 2005
    Posts: 1,606
    Likes: 26, Points: 58, Legacy Rep: 132
    Location: Portugal

    Vega Senior Member

    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.
     
  11. Raggi_Thor
    Joined: Jan 2004
    Posts: 2,457
    Likes: 64, Points: 0, Legacy Rep: 711
    Location: Trondheim, NORWAY

    Raggi_Thor Nav.arch/Designer/Builder

    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?)
     
  12. Raggi_Thor
    Joined: Jan 2004
    Posts: 2,457
    Likes: 64, Points: 0, Legacy Rep: 711
    Location: Trondheim, NORWAY

    Raggi_Thor Nav.arch/Designer/Builder

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

    Attached Files:

  13. safewalrus
    Joined: Feb 2005
    Posts: 4,742
    Likes: 78, Points: 0, Legacy Rep: 659
    Location: Cornwall, England

    safewalrus Ancient Marriner

    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)!
     
  14. roy marine
    Joined: Sep 2006
    Posts: 4
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: Barrie, Canada

    roy marine New Member

    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.
     

  15. Guillermo
    Joined: Mar 2005
    Posts: 3,644
    Likes: 185, Points: 63, Legacy Rep: 2247
    Location: Pontevedra, Spain

    Guillermo Ingeniero Naval

    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:
     
Loading...
Forum posts represent the experience, opinion, and view of individual users. Boat Design Net does not necessarily endorse nor share the view of each individual post.
When making potentially dangerous or financial decisions, always employ and consult appropriate professionals. Your circumstances or experience may be different.