Lengthway trim

[Col_T]

So, there is movable ballast in the stern and, perhaps not surprisingly, shifting this to the bow causes the stern to lift and the bow to sink a little. Useful to remember when seriously grounded!

 

The question is, if all the existing movable ballast is in the stern, what happens if I add new ballast to the bow? Clearly the bow will sink a little, but will the stern also lift a little, or the whole boat sink a little with the bow sinker further, or what??

[howardang]

So, there is movable ballast in the stern and, perhaps not surprisingly, shifting this to the bow causes the stern to lift and the bow to sink a little. Useful to remember when seriously grounded!

The question is, if all the existing movable ballast is in the stern, what happens if I add new ballast to the bow? Clearly the bow will sink a little, but will the stern also lift a little, or the whole boat sink a little with the bow sinker further, or what??

Loading extra ballast will have two effects: it causes a bodily sinkage because of the extra weight and it also causes a change of trim, in your case an increase in draught forward, a decrease in the aft draught and a slight increase in total bodily sinkage.

 

Howard

Edited February 17, 2017 by howardang

[Tacet]

Broadly speaking, the back will come up as the front goes down - but the total displacement will increase with the weight, regardless.

 

I once saw a cruiser refloated by BWB at Llangollen. The evening before it had gone down relatively slowly, due to being flooded through/over the outboard transom, notwithstanding the combined ministrations of the Fire Brigade and numerous well-intended helpers. BWB stood two burly blokes on the bow, which levelled it up/lifted the stern whilst a relatively small pump did its work. No fuss.

[Wrinkley]

A practical example of what howardang explained in post #2 is when we were stuck on the cill on the Oxford we had to get four passers by to stand on the bow. This lifted the back end allowing us to slide into the lock. But must have increased the depth over all.

[system 4-50]

My experience is that the centre of "tip" of my narrowboat is much further back than I initially expected, maybe 1/3 to 1/4 of the boat length from the stern. In consequence a change in height at the bow is matched by a much small change in the opposite direction at the stern. But this is just my boat. HTH.

[Col_T]

Thanks to all for your replies, most useful.

 

The additional ballast in question is a pine chest of drawers; I first have to work out how to get that on board!

[Neil Smith]

The weight of that will have hardly any effect on your trim.

 

Neil