Model Trial Blog 3: Ship vs Box

Tim Lovett April 05 | Home | Menu

Hull Comparison


Naval architect Dr Allen Magnuson proposes a ship-like hull for Noah's Ark. Naval architect Jim King employs a symmetrical design with pointed bow and stern. Modeler and presenter Rod Walsh sticks to a the cuboid form - a virtual rectangular box.

But how do they compare in the water?


The Magnuson hull. Forecastle at the bow to catch wind, skeg (keel fin) and the stern to catch the water. See Allen Magnuson model.

The Cuboid hull. (Rod Walsh design without sidewall camber, or pure block as portrayed by Joe O'Connell)

Pointed Block (Similar to Jim King design in bow and stern but without deadrise)


Pool Waves

17 April 2005. Testing seal and gyro sensor in the Magnuson model.  The forecastle is held on with PVC tape. Plenty of water on the weatherdeck but the revised lid seal kept the water out this time. The cordless Gyromouse tracks roll and pitch motion, sending the data via an RF signal to a poolside laptop. Looks like we might be needing an antenna - the range was a bit limited - no doubt something to do with the steel hull (or maybe low batteries!).  

Robert Willson keeps the Ark away from the pool edge.


Weights

20 April 2005. Getting a bit nervous about throwing this thing in the sea. Better make sure the weights are tied down. Using 50 x 50mm steel bar (around 4.3kg each). The weights are mounted on threaded rod to allow vertical adjustment - and some chance at achieving the all important vertical position of the center of gravity. The frame can also be positioned longitudinally to tweak the pitch inertia, although I can't imagine getting quite that serious.


Sea Waves

21 April 2005. First (sort-of) ocean test; Botany Bay south of Sydney was running a nice 4-8 knot easterly wind with largest waves around 1ft (0.3m), a typical afternoon onshore breeze. The models are 1:76 scale using the short cubit, so these waves represent the occasional 76ft (23m) monsters.

Happily broadside. The cuboid hull in its favorite position, side-on to the waves. This hull never got out of this position and spent virtually 100% of the time rolling exactly in a beam sea. 

Broadside... despite forecastle and skeg. Not so strictly parallel to the waves as the cuboid hull, the ship-like hull form of the Magnuson Ark stayed within approximately 10 to 30 degrees off beam sea. 

There was clear indication that the 6:1 Length to Breadth ratio turned naturally broadside to the waves - this happened within 10-20 seconds with all the models. The forecastle added no perceptible improvement in avoiding the dreaded beam sea - at least not in these few trials. Of course, the forecastle was great for keeping the water off the weatherdeck when heading into the waves.

Allen Magnuson's hull, minus the forecastle.

The eye bolt at the stern is dragging a submerged plastic drink bottle as a drogue. A last minute attempt to swing the bow around using a buoyant bottle was a failure - the bottle simply hugged the lee side of the hull.

 

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