Ballast

[sfh]

I have a 130 gallon diesel tank and 100 gallon water tank, both are sat well below the centre of gravity in the bilge, what are your thoughts with regard to ballast, will the boat handle better in heavy weather with full tanks

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[Moose]

Probably, I mean Possibly, Oh, I don't know?

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Moose

 

[tr7v8]

I'd assume it would depend on hull shape, displacement and semi dis would probably be better withnthem full whereas to get stability in a planning hull you'll need the ability to plane and also low polar moment, eg empty tanks. Although empty tanks in a small boat which are low and wide may suffer slosh effect, probably only answer is suck it and see.

Jim
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[byron]

<font color=blue>Your boat is from the drawing board of a qualified designer. Such things as weight distribution have already been calculated into the design. You have no need to worry about such things as ballast. The only noticeable difference you will notice with say an empty water tank and a half full fuel tank is a slight increase in top speed. Carrying any extra weight would just be a useless exercise serving no purpose other than being detrimental on performance.


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[duncan]

whilst I agree with the principle of what you say byron surely most recreational craft (especially) are built to a compromise and it is possible that, at the extremes it is designed to operate, it will do so 'better' in certain states.
In flat calm perfect conditions a planning boat will normally benefit from near empty tanks for maximum performance, and for it's ability to fully plan at lower speeds as well. At the other end of the spectrum plugging into a headsea it will (may) 'perform better' - in this case comfort issues come to the fore - with full tanks.
There are also the situations where the manufacturer uses th same hull for different configurations - shaft or outdrive engines, open or hard top, even flybridge - where again your own particular model can be within acceptable limits for the designer but not ideal!

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[hlb]

But not altogether sure what you do when you've got all this information.

So you set off from Pool to go to Guernsey, get half way and discover weight distribution is not optimum. Go back to Pool for more fuel. Repeat operation.

<hr width=100% size=1> <font color=blue> Haydn

 

[byron]

<font color=blue>Exactly Haydn, in your own inimitable fashion you have summed it up. The boat is designed to operate over a spectrum of circumstances with high tolerances.

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[duncan]

always assuming you have choices of course....and for most boats and a major trip that won't be the case. But, for example, if I was setting out from Poole to Yarmouth and there was a settled SE 4, I would take on another 200kg of fuel if I had the room whilst if it was flat calm I wouldn't.
If I was going to Weymouth of course greed would rule and I would aim to arrive empty so that I could fill up cheap, and put up with a bumpier passage!

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[duncan]

Re:accepted but....

how does ballast trim differ from outdrive trim or trim tab trim. Most boats that have no TT would move a person even to 'level off' if the conditions required.
I contend that tanks are movable ballast and as such are a trim element...........

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[byron]

Re:accepted but....

<font color=blue>sigh! Because on a motor boat one does not have the facility to move the ballast at will to the most appropriate spot to gain any benefit. Its just a dead weight you are lugging around.


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[hlb]

Re:accepted but....

It might be OK to move a person about. Or even chuck him overboard to gain speed. But the thought of moving a ton or more of fuel into the front bedroom and back again to gain better trim. Then throwing it over the side when conditions changed, I find a bit alarming............../forums/images/icons/smile.gif

<hr width=100% size=1> <font color=blue> Haydn

 

[duncan]

truce.....(nm)

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[grant]

Re:accepted but....

Hi Byron, I have a question for you, I recently purchased a United Sailing Yacht (22' loa x 8' beam) and plan to add a pilot house to it, have already removed the mast and plan to use the boat as a displacement hull cruiser with a 10 hp motor. It has a keel bolted thru the hull that measures about 14 inches deep and 40 inches long with a swing keel inside. I want to remove the keel to reduce the draft, keel up about 30 inches, no keel should be about half that or 15 inches. I am sure I should have some kind of ballast but not sure how to go about it. Any ideas (other than I am crazy).
Thanks, Grant

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[byron]

Re:accepted but....

Sorry Mate, anything to do with engineering of any description and I am the last person to ask. My forte is Navigational. Maritime Law. Flags and older motor boats. I get a spanner and people who know me run screaming.

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[grant]

Re:accepted but....

Anybody have an idea about how to solve my problem?

<hr width=100% size=1>grant

 

[hlb]

Re:accepted but....

Have you got a problem??

Most boats dont have balast.

<hr width=100% size=1> <font color=blue>No one can force me to come here.<font color=red> I'm a volunteer!!.<font color=blue>

Haydn

 

[jfm]

ballasting

Grant:
1. Remove keel
2. Fix holes (probly put new ss bolts in the holes, grp over)
3. Weigh keel
4. Put concrete in boat as ballast, same weight as keel that you removed.

NB this is all rough and ready, depends on boat details. Also ballast must be well fastened in place, else in a storm it can come adrift with dire consequences. If you want flexibility, set the concrete on polythene sheet so it matches hull curves but can be lifted out. Use shuttering board to divide the concrete into sections and meebe create recess space for bilge pump etc. Cast bolts into concrete to fasten it to hull stringers. Concrete is very cheap.

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[grant]

Re: ballasting

thanks for all ot the good ideas, I am a bit puzzled. I removed all 5 nuts from the SS bolts holding the keel and it refuses to drop! I am sure there is some kind of sealant between hull and keel, but would think the weight of the keel would pull it free. Am I missing some other fasteners, none seem obvious.

<hr width=100% size=1>grant