Jouy-en-Josas,  September 27, 1999

franc.gif (1644 octets)

The draft of a boat

-A short draft is easier for mooring.
-A long draft makes the boat safer, faster.

It is necessary to find for every user the best balance, but every solution has its limits.

Increase the draft :

Decrease the volume of the ballast near the hull the boat is more stable reaching
Lower the centre of gravity
Give a better center board area tacking the boat hauls up better

Decrease the draft,

the qualities of the boat decrease gradually and degrade brutally   when the wind increases, heeling is coming and the waves increase. According to the size of the boat and with certain force of wind and  waves, the boat becomes incompetent to haul up  , to handle ; it becomes dangerous.
It is imperative not  to build or to buy boats under a draft minimum.

Examples :

Fig 1 : hauling up is function of the draft
Fig 2 : draft is function of the type of boat and of the size

 

Fig1pe. gif (10857 octets) Fig2pe. gif (10706 octets)

Fig   1 and 2                    


It is more simple to have a fixed ballast, but there is a limit below which we must not cut down the draft .

To escape the fixed ballast and decrease the draft , there are other solutions :

The ballasted centreboarder
A centre of gravity is kept enough low with  weight of  ballast increased.
Performances are still acceptable because of  the drift

But using and maintenance of  the boat are more delicate.

The lifting keel boat
a low centre of gravity and a good drift area

- a keel like a centreboard allows well to absorb the shocks.
- a lifting keel gives a centre of gravity very low.

These two solutions are even more difficult to build and to maintain than the ballasted centreboarder and the keel boat..

Double keel
Util now, the performances.of these boats are not very good
At present, we try  to improve and to confirm this type of appendixes.

 

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