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Can my propeller be repaired? |
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In most cases, aluminum, stainless
steel, and bronze or nibril propellers can be repaired. Curled blade
edges, missing pieces of the blade edge, and bent blades can all be
straightened and filled. The central hub in aluminum and stainless steel
propellers can be replaced. Usually, if more than 1/3 of a blade is
missing or the metal of center hub of the propeller is damaged, the
propeller cannot be repaired. In addition, aluminium propellers that
have been repaired multiple times may not be able to be repaired due to
metal fatigue. |
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How are propellers repaired or
reconditioned? |
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There are really several phases to
reconditioning a boat propeller. The first step is to verify and correct
any pitch problems. This is accomplished by placing the propeller in
a special jig and aligning the blades with a pitch block using heat
and hammers. Once the pitch is set, the propeller is sandblasted to
remove any corrosion, old paint, or any other residue. After
sandblasting, any broken areas are cleaned up by grinding away areas that
won't hold new metal. The missing pieces of the blade are welded
back with the appropriate metal. In the next step the blades
are ground back to the original equipment manufacturers shape.
Following the grinding the propeller is tested for balance and adjusted by
removing small amounts of metal. The propeller is then cupped, if
necessary, then finished by polishing or painting. Once completed,
the propeller is checked one last time for balance and corrected if
necessary. |
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What is pitch? |
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The pitch of a propellers determines how
far a propeller will travel in water in one rotation. A 19" pitch would
travel 19 inches in one full rotation. Of course the pitch value of a
propeller is theoretical in nature and does not account for slippage and
other environmental issues within the operating arena. |
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What is cupping? |
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Cupping consist of changing the shape of
the blades at the trailing edge. Slightly curling the edge toward the
direction of rotation. Cupping a propeller effectively increases the
pitch of a propeller. The cup gives the propeller more grip in
the water and will bring the boat to plane quicker This puts more
strain on the engine, thus the effective increase in pitch. |
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What is a hub? or why can't I go
anywhere? |
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The hub part of the propeller is the
part that makes contact with the propeller shaft. Most outboard and
inboard/outboard props these days are splined. That is, they have
gear teeth that meshes with the propeller shaft. There are different
numbers of gear teeth depending on the make and model of the engine.
The two most common have 13 or 15 tooth splines. There are two
different kinds of these hub systems, the rubber hub and the exchangeable
hub. The rubber hub is composed of a splined shaft surrounded by
vulcanized rubber. The hub is pressed into the propeller hub cavity
using a hydraulic press, funnel, and hub driver. This is not a field
serviceable hub system. If you "spin" a hub you must have it
professionally replaced. The second kind of hub system is the
exchangeable hub system. Originally invented by Mercury and known as
the flo-torq hub system, this hub system has become more common. It
is a field serviceable hub system consisting of a specialized thrust
washer, a urethane drive sleeve, and a shaft adapter. The urethane
drive sleeve replaces the rubber in the pressed in rubber hub system and
works on geometry rather than friction. In both cases, the rubber
hub or exchangeable hub system the rubber or the drive sleeve are failure
points. Should the propeller strike something in the rotational
plane (e.g. tree stump, rocks, gravel, rebar, etc.), the rubber or the
drive sleeve are designed to release to protect the lower unit propeller
shaft, carrier bearing, drive shaft, etc. The release or failure of
the rubber hub or drive sleeve is know as a spun hub. |
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