Re: [Electric Boats] RE: Harbor Test 2013

 

"Displacement is technically the weight of water that the boat displaces when floating... equal to the actual weight of the boat. (Archimede's law) Anything that weighs more than it displaces will sink.. (a chunk of lead, for instance)

The ballast is the portion of the overall weight that is in pure ballast form (a bolt on keel, or ballast loaded into a hull cavity) Ballast ratio is a general term that implies how tender or 'stiff' a boat may be. Ballast ratios generally range from .25 to .50 in production boats, running around .3 - .35 or less in more modern designs, whereas boats built 20 - 30 years ago often had ballast ratios in the .45-.50 range."

yes indeed, ballast should be included in the total weight of the boat when sizing the E-Prop System. One never knows where a boat may end up, having enough thrust is a matter of safety. However, every Skipper will do as they see fit.

-----Original Message-----
From: cirejay <cirejay@hotmail.com>
To: electricboats <electricboats@yahoogroups.com>
Sent: Fri, Dec 6, 2013 7:39 am
Subject: Re: [Electric Boats] RE: Harbor Test 2013

 

I don't think so.  One measures/calculates displacement based upon displacement of the boat, not displacement minus or plus ballast. 

 

Specifications are generally based upon the  design displacement and not as built.  It's not uncommon to see as built being heavier than as designed; add to that the 'stuff' one brings onboard you get a considerably heavier boat.

 

I realize that this is an electric boat group and not a sailboat group but the fact that a boat may be considerably heavier than as designed has some repercussion related to the sizing of the propulsion unit, be it sails, ICE, or electric.

 

As a side note, I always ask the lift operator to give the reading when my boat is hauled and have found that they often are not terribly accurate and that the operator will tell you such if you get into a discussion.  Their concern is only that they are not beyond the lift& #39;s capability.

 

eric SV Meander

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