SPURS FACT SHEET (Addendum to Spurs Cutter Installation
Manual)
Spurs Shaft Mounted Line & Net Cutter Systems
The shaft mounted cutters are available for shaft
sizes from 3/4" thru 6-1/2", or 22mm-165mm, and will match propeller hub
diameters from 2"- 11".
Spurs cutter
systems have been protecting vessels from costly and damaging propeller
entanglement since 1982. Worldwide navigating has been made safer for Coast
Guards, Navy, commercial fishing and pleasure craft vessels of all types
with cutter systems installed. To date, over 100,000 vessels depend on
Spurs.
The cutting
ability depends on the size of the line or net that is encountered as
related to size of the cutter on the vessel - the larger the cutter, the
larger line or net that can be cut. Original development and design of the
cutters for various size crafts was predicated on the size of line normally
carried on the boat, i.e. dock line, anchor line, etc.. The very smallest
cutters obviously cannot cut a line larger than the cutter blades. The
cutter was not designed to cut steel cable, anchor chain or Kevlar
line; however, we have received reports to the contrary in situations where
sailboat guy wires were cut after a dismasting encounter, as well as some
anchor chains at various times. Note: After this type of encounter,
cutters should be sent to the Spurs factory for evaluation.
The rotating and
stationary cutter blades themselves are made from specially hardened
stainless steel, using three heat processes to develop a hardness of
approximately 45 Rockwell C. This is very hard, just under brittle, and the
cutters remain stable under saltwater with anode protection. The hardness
is extremely essential in severe cutting conditions, as from time to time
commercial fishermen will encounter hooks and toggles.
The holding
block
(an essential part of the cutter system) is made of 316L stainless steel and
is held on by bolts that are drilled and tapped into the strut, or stern
tube, which must be metal. Fiberglas will not provide adequate holding
power (see page 6 of installation guide). The holding block has four
purposes:
1) It
must be fastened into the metal of the strut or stern tube. Screws drilled
into fiberglass will pull out when a cut is made;
2) A
stop line is marked on the upper casting to position and center the
stationary cutter wedge, and this allows both forward and aft axial shaft
movement to be taken up when cruising while the cutting blades remain
.005-.010 apart. Excessive shaft end- play must be addressed to revise
installation procedures.
3) The
wedge, which is an integral part of the holding block, is activated when a
line or net is encountered, forcing the stationary cutter blade aft against
the rotary cutter blade, achieving an instant cut with each revolution while
the line is washed away.
4) Held
by (3) bolts that are designed to shear and disengage the cutter system if a
larger line, chain or cable, etc., is caught that cannot be cut. These
bolts are made of 304 or 18-8 stainless steel and, therefore, rated weaker
than the cutter blades hardened stainless steel. Disengaging the cutter at
this point protects the vessel's transmission, engine and running gear from
possible failure and prevents the cutters from locking up. The sheared
bolts must be removed in order to reinstall the block in the same position.
Many prudent
sailors drill and tap (2) sets of holes to make this an easy reinstallation
underwater. In some instances, a stainless steel clamp will hold the block
in place as a temporary measure until the proper reinstallation can be
completed. Many commercial fishermen, however, weld the block to the strut
or stern tube, intentionally avoiding the disengagement of the cutter
system. Their engines are large and, in most cases, can withstand the force
created when encountering steel cable, hooks, toggles, etc. The hardness of
hooks is aprox. 54 RC, which is harder than the cutter blades at 45 RC.
Sometimes the hooks are cut due to the propeller inertia, however, the
cutter blades suffer various nicks and gouges on the cutting edges and the
bearing of the cutter shows excessive wear.
When installing
block #4, 5 & 5A, drill upper or lower hole first, then mount the block.
Proceed to drill and tap the remaining two holes. If shims are used under
the blocks, position shim in place first and then drill.
Zinc anode
protection in saltwater environment.
A specially
fitted zinc anode is mounted to the hardened stainless steel stationary
cutter blade, and is provided with every cutter system from the factory.
Spare zincs are available from Spurs dealer network or direct from the
factory with same day shipment for orders placed by 3:00 pm EST. The zincs
are designed to protect only the stationary cutter blade in a
saltwater environment.
The stationary
blade is completely isolated from the vessel due to the fact that it is
surrounded by the (non-metallic) bearing and the (non-metallic) sound
dampening plugs. Electrolysis will attack the threads and screws that hold
the stationary blade and will eventually loosen over time. We chose
hardened stainless steel over the soft, but more stable, grade 316 stainless
for the cutter blades because there is an enormous cutting advantage.
Therefore, it is extremely important to keep the cutter zinc anode in place
and check it regularly. The rotary cutter blades are mounted on the shaft
of the vessel and will be protected by the shaft zincs.
We recommend the
use of Tef-Gel on all screws. Loc-Tite or equivalent is not recommended.
Reconditioning
and evaluation services are offered by Spurs factory - send the complete
cutters and holding blocks for examination. It is important to include your
name, address and phone number; we will notify you if parts are worn and
replacement is required.
          
 Marine Manufacturing
Inc.
201
SW 33rd Street Ft. Lauderdale, FL 33315 USA
E-mail: spurs@spursmarine.com
phone: (954) 463-2707
Fax: (954) 525-0239
spurs cutters are protected by USA and International patents
logo is a trademark of Spurs Marine Manufacturing Inc
Copyright ® All rights reserved.
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