Cheap ballast

[corkonian1]

I have a mirror offshore with a shallow (2ft draft) keel.
As the volvo md1 (365 lbs) has been replaced by an outboard I thought of adding ballast by filling keel with concrete as is done in old wooden boats.
Any opinions, advice, do it, don't do it etc.
Pics here mirror offshore

 

[sarabande]

if you remove the engine and fill the stub keel with concrete you will be lowering the CofG. This will make the boat appear "stiffer", but may increase the loading ("wringing stress") on the joint between the keel and the hull, possibly beyond the design limits. On a relatively light yacht such as the MO, this lower CofG could make the boat uncomfortable ("snappier") in the roll mode. Pitch is unlikely to be affected, as moments of inertia in that plane are spread out.

Have you considered putting secure moveable ballast (lead / iron) where the engine was ? This will replace the engine with some mass roughly in the same place as the original design.

Are you proposing to sail with the outboard permanently stuck on the blunt end ?

 

[boatmike]

Concrete is a poor material to use as ballast. The density is not really very high. I agree with the other post as well in that the structure of the boat may well not be intended to take the stress. I would rather see a couple of steel ingots (painted first) glassed lightly in where the engine was if you think it's a problem.

 

[matelot]

A good honest Irish solution - concrete! /forums/images/graemlins/grin.gif

 

[graham]

Try asking a tyre fitting garage for old lead wheel balance weights.Probably get them for scrap value and you could experiment with them before perhaps casting them into a cement block .

 

[corkonian1]

Thanks for inputs.
Filling keel with concrete not a good idea as I suspected.Thats a scary word 'wringing'
The displacement is 2000lbs, the normal ballast is 380 lbs cast iron block buried in the keel.
Will the removal of the volvo the ,a 365 lbs weight , lying on pretty much top of the keel and maybe 2 ft high change the characteristics of the boat significantly layout

 

[PuffTheMagicDragon]

Please don't get lost in technobabble - you could easily hang your 160 kilos from one5mm bolt! Forget 'wringing' stresses in this case.

Look at it this way, when your boat is heeled, the forces that are pushing the boat over are acting through your windward shroud. The stub keel of your Mirror Offshore is much stronger than your shrouds.

Personally, though, I would prefer to use something that is denser than concrete; I would investigate the possibility of recycled lead (e.g., from old car batteries).

 

[pampas]

Sash weights !!