[PSUBS-MAILIST] landing craft

[hank pronk via Personal_Submersibles]

Sean,I only use the word cavitation loosly, since I have no clue.  The water flow is very unrestricted as it is a pontoon vessel.  It could be ventilation.  But why does it work perfect when it is pushing against an immovable object, same trim, same water flow.Hank 

    On Wednesday, June 14, 2017 7:47 PM, Sean T. Stevenson via Personal_Submersibles <personal_submersibles at psubs.org> wrote:
 

 Are you sure that it's cavitation (spontaneous vapourization and subsequent bubble collapse on the low pressure face of the propellor blades), and not ventilation (surface air being sucked into the upstream flow ahead of the propellor)?Cavitation can be addressed by changing propellors - go to a lower pitch, or greater number of blades (increased disc area). If possible, fit a larger diameter prop and operate at lower rpm. Also check that the upstream flow path is not restricted in any way.Ventilation can be addressed by adding an anti-ventilation plate on the skeg, increasing the immersion depth of the prop, and checking for any adverse trim issues.Sean


On June 14, 2017 7:10:32 PM MDT, hank pronk via Personal_Submersibles <personal_submersibles at psubs.org> wrote:
Hi All,Got a problem to solve, my sub barge has a 30 hp outboard motor.  When I try to cruise fast it cavitates real bad.  When I push something that won't move like a dock, I can push at full throttle no problem.  I am planning to build a landing craft 36 feet long using the steel hull from my paddle wheeler.  I am building it to carry and launch Elementary.  My concern is, because it is a displacement hull and it will be slow,  will I have the same problem with cavitation  that the  barge has.  Do I need to use a jet instead?   I can't work on it for a year, but I want to  source all the parts, engine, drive etc etc.Hank
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