[PSUBS-MAILIST] landing craft

[hank pronk via Personal_Submersibles]

Steve,I did not try to lower because it is a weld job and the barge is in the water now.  But,,, when waves come down between the pontoons the water level is much higher momentarily, and there is no change.  If the lake is dead calm it is better, and I can speed up a bit more if I am gentle on throttle.  My buddy has the exact same problem with his pontoon raft and his motor is lower.  we thought it might be a prop issue because the prop is meant to be moving forward at the given rpm? hank 

    On Wednesday, June 14, 2017 7:23 PM, Stephen Fordyce via Personal_Submersibles <personal_submersibles at psubs.org> wrote:
 

 Hi Hank,I've done a fair amount of stuff with overloaded dive boats with outboards that size - enough to know that displacement speed + full throttle != cavitation (necessarily).
Have you tried lowering the engine deeper into the water?  And/or getting the "suction" area of it further away from the boat?
Failing that a different prop could be the next thing to investigate.
Cheers,Steve
On Thu, Jun 15, 2017 at 11:10 AM, 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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