Long Island Marine Surveyor

Telephone 631 589-6154  Fax 631 563-3758

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Long Island Marine Surveyor 631-589-6154

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Underwater Machinery
Compression testing Boat Engines Boat Delamination Underwater Machinery Steering Station Boat Engines Boat Bilges Marine Fuel Systems Boat Fire Safety Safety equipment Electrical Oil Analysis

 

 

Underwater Machinery 

Underwater Machinery consists of propeller, struts, stern drive units, bushings, rudders and various other items necessary for the operation of a boat.  These always consist of metals that are corrosion resistive.  Aluminum, stainless steel bronze are extensively used.  Noble metals resist corrosion better that less noble metals  Stainless steel will resist corrosion better that aluminum.  Underwater machinery  must be inspected for collision damage and electrolysis damage and wear.  The type of underwater machinery varies from sail boat to jet ski as does the method of inspection.  

Propellers

Propellers are carefully machined, they rotate hundreds of times per minute and must be is good condition to give the best performance.  Inboard boats have propellers attached to propeller shafts that usually rotate in a cutlass bearing which consist of a bronze sleeve and a rubber lining.  (This is shown in the photo above). Stern drive units do not have a strut or cutlass bearing. (See photo below).

Propellers are inspected for the correct size.  The incorrect size propeller will impair the boats operation.  An incorrectly size propeller can result in poor performance, transmission and engine damage.  Propellers must be free of nicks, wear and electrolysis.  Struts must be securely fastened to the hull and free of leakage at the point of fastening.  Underwater machinery must be properly grounded to the vessels grounding system.  Cutlass bearings must hold the propeller shaft snug with out undo wear or play.  

The Aluminum casing of stern drive units must be free of electrolysis, it must be without collision damage and must pressure test to 15 psi.  Aluminum casing are most susceptible to electrolysis damage and must be protected by zinc.  Stern drive units are essentially boat transmissions that are submerged underwater during use.  The stern drive is filled with gear lube (oil) and must remain free of water or damage to the internal gears of this unit will occur.

This photo shows a stern drive with electrolysis damage on its lower skeg.

Sailboats

Careful attention must be paid to the keel, rudder & rudder linkage, in addition to the propeller strut and propeller shaft on sailboats.  The rudders on sailboats are sometimes delaminated.  Wear in not uncommon at the mechanical steering mechanisms of rudders.  Drop keels must be inspected for corrosion at their pivot pins.  A sailboats keel is most exposed to collision damage.  A collision of the forward section of the keel will produce extensive aft damage to the keel.

Problems associated with each of these units remains the same, collision damage, electrolysis, corrosion and wear.  

Key Benefits of a survey

bulletA stern drive unit replaced new can cost as much a $6000.  This can be an expensive item to replace.
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Since underwater machinery drive a vessel.  Loss of its use will surly ruin your day and probably cost much more that if the problem had been corrected prior to use.

bullet

With correctly running under water machinery you boat will last longer and run better.  Their are no gas stations on the water, many breakdowns result from problems with these parts.

 

 

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