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Buoyancy Tests

by Caroline Smith

The only sure-fire way to find out to what degree a swamped shell will support its seated crew and remain manoeuvrable is to test it. In June 2002, a group of volunteers in Oxford tested a Janousek VIII and two stern-coxed IV+s. Results and links to videos of the tests can be found below. Elder Rowing of New Zealand also performed similar tests, and their results can be found lower down the page.

Volunteer Test Results in Oxford

On 24th June 2002 a group of volunteers in Oxford carried out some buoyancy tests on Janousek shells which have the underseat volume enclosed. These may not have been the most scientific, rigorous tests ever done. But please remember that after over a year of talk we are the only people who have even tried. The boats used were all Janouseks owned by Somerville College, Oxford and all just under 3 years old (purchased after the old OUBC boathouse burnt down in the summer of 1999). Crew weights are taken from the boat, and in all cases a cox is assumed to be 55kg. Janouseks are designed to be tolerant to within +/- 5kg of the given weight.

Click on the file size and type to view videos in a new window, or right click to download and watch later.

VIII+

Serial number 99765, no weight given on boat but assumed 80kg.

Cox weight 54kg, crew average 79.75kg.

Filled the boat with water by tipping it on its side, then topped it up with buckets. Eventually, because of the design of the stern/coxes seat, the water begins to escape behind the coxes seat, and pouring in more water doesn't make the boat sit any lower. At this point, the sax boards are about 1in above the water in the coxes seat, and the slide beds of the bow seat are barely underwater.

A few of the buoyancy compartments leaked a little bit, but the only constant stream of bubbles was from the magnetic switch under the stroke seat.

Loaded crew in one at a time. When all in, riggers were still above water, and we backed down away from the raft, then rowed back to it without much of a problem. It wasn't really steerable, but that could easily be dealt with by dropping rowers out or adding them in. Self-bailed once moving forwards.

Unloaded, then tipped boat on side to get most of water out. A few compartments had a bit of water in, and the stroke one had a good 4 inches in because of the leak where the wire goes through between the slides.

IV+ (80kg)

Cox weight 54kg, crew average 79.75kg

Bottom nuts a good couple of inches out of the water. Easily rowable. Loads of momentum- ran far and fast after easying! Same problem with the magnetic switch under stroke's seat leaking (lots of bubbles).

Cox weight 55kg, crew average 96.75kg

I wasn't in this one so I didn't notice how far the bottom nuts were off/below the water, but it was rowable without a problem.

IV+ (65kg)

Cox weight 54kg, crew average 66kg

Bottom nuts again a good couple of inches off the water. Easily rowable. Still same problem with leaky switch under strokes seat. Had to empty water out before next test.

Cox weight 54kg, crew average 79.75kg

Bottom nuts at water level. Still definitely rowable.

Cox weight 54kg, crew average 89.75kg

Middle stay of riggers underwater during recovery, but still rowable.

Cox weight 55kg, crew average 96.75kg

Bent like an old Burgashell, stern canvas almost underwater, but still supported crew and they rowed it around a bit. I believe that if we'd overloaded an eight by this much the joint in the middle would have given up.

Volunteer Test Results in Oxford

On the 4th of August 2002, Elder Rowing swamp tested two fours and two eights in controlled conditions in a public dive well. Short results were we were unable to get any of the boats to have the sax boards lower than 50mm above the water even with the heaviest crew we had, and with the lightest crews we were considerably higher. All of the young rowers involved were shown how to empty their boats and one crew was made to right and re enter their four. Finished off with a single built for 85kg loaded to 152kg of crew and with the cockpit full. still rowable and with lots of freeboard left! Good luck with getting the ARA to improve their requirements. The New Zealand Rowing Association has been very positive on bouyancy matters.



© Copyright 2001-2011 Leo Blockley Memorial Campaign. Website by Alex Taylor and Caroline Smith [ 661284 visitors ]