Motorboat Ballast

[Fire99]

Hi All,

I've recently been discussing the ballast thats been added to my Freeman 30 over the years.

Can anyone tell me why do people add weight (ballast) to boats?
My boat recently had new engines in her which are lighter so i could understand someone adding some weight to balance the boat with the lighter engines but she was ballasted even with the old engines..
Someone did point out to me that boats are not normally designed to have ballast from new so why??
any ideas??

thanks,

Nick


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[trev]

Some boats are 'stiff' and some are 'tender' - its all to do with a stability component called metacentric height which induces the righting lever. This is what brings the boat back upright after she has been displaced by an outside force.
In some boats this is too small for comfort (tender) and the boat behaves in a somewhat sloppy/sluggish manner and may roll excessively. Its therefore neccessary to add ballast low down to increase the GM (Geometric Metacentre) and induce a larger righting lever.- in effect lower the centre of gravity.
If a vessel is 'stiff' the righting lever is too large and the boat rolls violently (quickly) and it may be necessary to add weight higher to decrease the GM.
Here endeth the first (stabilty) lesson.

<hr width=100% size=1>Trev

 

[Fire99]

Cheers Trev for the information...

So oh great metacentric, how would i know if my Freeman 30 would need ballast or not? (the 20 thousand dollar question)

Thanks again,

Nick


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[byron]

<font color=blue>In no uncertain terms...Your Freeman does not need ballast The only craft that could possibly do with a little ballast are the Dutch Steel ones that have Singer Sewing Machine as an engine, even they can get away with it as long as staying inland.

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[Fire99]

Cheers Byron...
I think i get the message ... Ahh the fabulous Singer Sewing Machine... If we all run out of oil, we may see Sunseekers with Triple Surface Drive Singers.. Always handy for making that jumper out of season..

On a serious note though.. Why on earth do people load these boats with Ballast then? Believe it or not i've got about 5 actual weights and half a Train wheel..plus the bagged shingle that was added when the previous owner put lighter engines in. Thats gonna be one serious slim fast diet for my Newly acquired Freeman..

cheers,

Nick


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[mike_kolling]

Nick

Now do you believe me?

Cheers

Mike

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[trev]

See how she sits in the water - does she 'look right'? Then see how easily it is to get her rolling and how quickly she stops, Is it comfortable? Perhaps compare the degree of roll and the period with a similar vessel or maybe the manufacturers can give you some stability info. I think Sheridan Marine on the Thames (Moulsford?) may be able to help for Freeman stuff.
It really shouldn't be a critical issue for a standard motor cruiser, most are on the 'stiff side', with plenty of reserve stability. Unless the engine change you mentioned was dramatic she should be OK. Perhaps all you need is a bit of weight shifting for trim?

<hr width=100% size=1>Trev

 

[byron]

<font color=blue>Who knows why the previous owner did it. People get bees in their bonnet and do things, maybe he thought it was a freighter and was travelling without cargo /forums/images/icons/wink.gif Look on your own boat to see the builder's 'bee in his bonnet' you will find that the drinks locker has an octagonal holder among the round ones. This was because the builder wanted everyone to drink the same brand of gin as he did, consequently every Freeman built has this.


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[Fire99]

Cheers Byron...
Either that or he wanted the first Freeman Submarine...

thanks,

Nick


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[duncan]

are you per chance implying that gin, in octagonal bottles, is appropriate ballast ?......./forums/images/icons/smile.gif

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[Fire99]

Cheers Trev,

I'll drag it all out and have a look, see if she looks like a cork..

thanks,

Nick


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[aztec]

duncan, ask byron about rum bottles. esp those plastic one's. i believe that they're designed to fit in any available locker.

can't remember the name.... can't remember much actually. /forums/images/icons/wink.gif

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[longjohnsilver]

When I bought my boat I found over half a ton of lead shot all neatly wrapped in plastic in the stern. Saw no point in it so took it all off. I agree with Byron, if the boat needed ballast trhe builders would have altered the design or increased the weight.

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[duncan]

Re:so I heard...(nm)

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[Fire99]

Blimey,

Some people love to fill their boats with weight..
If its heavier would a boat have less tendency to drift on say a canal..
Maybe people put weight on it to lower the air draught or something..
just a guess..

I'll be trying mine without at the soonest possibility..
Ive only owned her for 5 days..

cheers,

Nick


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