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Salt vs Fresh water

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ABYON
Deckhand

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Canada
11 Posts

Initially Posted - 08/29/2007 : 19:34:29

This is my fifth season with my 2003 water-ballasted 250. For the first time, I trailered the boat 700 miles east from Ottawa to the Canadian maritimes to give the boat a taste of salt water. It was an amazing experience.

It just didn't feel like the same boat. In wind speeds that usually have me hurrying to reduce sail, I was able to keep flying at hull speed while the boat remained well-mannered at all times. On the lake I sail here at home, a well developed force 4 with its accompanying waves is quite a sporting experience. On salt water it was a cakewalk. The experience left a big smile on my face as well as on everyone else's on board. It also convinced me of the seaworthiness of these 25-footers.

I'm attributing all of this to the increased buoyancy of salt water and the corresponding increase of weight in the ballast tank. Or, am I just imagining things?

On another topic, the IDA Sailor kick-up rudder I installed a couple of years back performed flawlessly including the time I ran into a bit of trouble in skinny water. The only injury was the nylon breakaway bolt.

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delliottg
Former Mainsheet C250 Tech Editor

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USA
4479 Posts

Response Posted - 08/30/2007 : 09:03:17

I don't own a WB, but did the math for fun. Using 1200 lbs of freshwater weight as the benchmark, the extra density of seawater would have added about 32 extra pounds of weight.

Freshwater = 1000 kg/m^3
Saltwater = 1027 kg/m^3
1kg = 2.2 lbs

1200 lbs / 2.2kg/lb = 544.3kg
(1027 kg/m^3 / 1000 kg/m^3) x 544.3kg = 559kg
2.2lbs/kg x 559kg = <b>1232lbs</b>
<i>(I rounded all the above figures so if you work the math yourself you'll get somewhat different answers. When calculating it, I used the built in conversion factors on my HP 48 calculator).</i>

However, the [url="http://www.windows.ucar.edu/tour/link=/earth/Water/density.html"]density of seawater[/url] varies with temperature & pressure, so if the water was particularly cold, it would have been more dense, hence heavier.

I don't have figures for the displacement of our boats, so I can't figure [url="http://en.wikipedia.org/wiki/Buoyancy"]buoyancy[/url], at least not yet.

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Dave Bristle
Master Marine Consultant

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Djibouti
10005 Posts

Response Posted - 08/30/2007 : 10:13:28

Could it be that the waves were longer-period due to longer fetch and deeper water? Also, sea breezes tend to be much steadier than breezes across land--just ask any coastal sailor about the difference between on-shore sea breezes and off-shore winds--the latter, coming across the land, are generally more gusty and unpredictable.

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The Officers, Staff and members of this site only provide information based upon the concept that anyone utilizing this information does so at their own risk and holds harmless all contributors to this site.