MapisM
Well-Known Member
Unless I'm missing something, the analogy is actually still valid.
If the force exerted by the water would always be perpendicular to the earth rather than to the water surface, boats wouldn't pitch, I reckon...?
The reason why the cork floats stationary is that its own mass is extremely low compared to its volume, hence it doesn't slide downwards because the gravitational force is not sufficient to contrast the drag.
And probably, if measured scientifically, it actually does slide downward whenever the water surface is not flat, albeit very slightly. Of course, the net effect of some very slight movements in one direction when "climbing" the wave will be compensated by the same movements in the opposite direction when going downhill, hence resulting in a stationary position of the cork.
In a boat equipped with electronically controlled engines, it's very simple to see that the work required is indeed affected by the ups and downs, though it takes some peculiar sea conditions (long oceanic sea swells) to make it very evident. If you cruise through such swells at a constant RPM, without touching the throttles, you will see the engines load slightly increasing/decreasing when going up/down hill. The engine ECU takes care of that automatically, as soon as it senses a change in the prop demand.
The only condition when the load wouldn't change is when already running at WOT and (with a properly sized prop) at 100% load. In those conditions, the higher work required would translate in a lower STW, rather than a higher load/fuel burn. But unless the STW is measured by an extremely accurate instrument, surely the load variation reflects better this kind of effect.
The reason why I said that the consumption is probably more affected by the overall longer distance cruised, rather than by the ups and downs, is that I assumed the higher load/fuel burn uphill to be roughly compensated by the lower load/fuel burn downhill. But this is just a rough guess, of course.
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If the gauge works then it will be probably be a kinked pipe or even split/air leak. They're quite simple in principle so shouldn't be difficult to fix if gauge itself is working... If the fix is simple, you'll have the luxury of both STW and SOG.
), but things that don't work bug the hell out of me and it would be a permanent niggle when on the boat! (Probably my equivalent to fender OCD)
That said it get's us out there and it's cheap - so will do for now... 
