Install a Spurs Line Cutter —By Jan Mundy Made by Spurs Marine Manufacturing in Ft. Lauderdale, Florida (Tel: 800/824-5372; Website: www.spursmarine.com; Email: spurs@spursmarine.com), Spurs consists of two separate cutting blade assemblies: the rotary cutter with two blades mounted 180° apart, and the stationary cutter, all mounted onto the propeller shaft. With each revolution of the prop, either forward or reverse, the rotating section spins, passing the stationary blade and slicing any fouling at the same time. We choose Spurs to install because it was the original line cutter, it’s made in the U.S., and after four years as eavesdropping neighbors at the U.S. Sailboat and Powerboat shows in Annapolis, Maryland, we had heard mostly positive feedback. The cutter mounts on most boats with solid, folding or variable pitch propellers. Sizing
A Shaft diameter B Propeller hub diameter C Space between prop and stern bearing or strut D Stern tube or strut hub diameter E Length of exposed taper F Height of cutter Selecting the proper cutter for your boat is determined by five measurements ( see Figure 1 ). Since it’s designed to mount on the straight part of the shaft, the critical dimension is the length of the exposed taper ( shown as “E” ) between the prop hub and the stern tube or strut hub. With the propeller installed, use calipers to determine where the shaft taper ends ( Figure 2 ). When installed on a tapered shaft, the device wears unevenly, reducing cutter life. Other important dimensions are the prop hub ( B ), and strut hub or stern tube ( D ) diameters. Drawing a line ( F ) between the two, the cutter should mount flush to this line, so just the blades extend past the strut-hub OD. There are a variety of combinations and shapes offered, both for wedge blocks and cutters. Though not complicated, measuring correctly will ensure a proper fit. On our demo shaft, the tapered portion of the shaft is under the prop hub ( Figure 3 ). Spurs can mount on the tapered portion, provided the exposed taper doesn’t extend more than 3mm (1/8") beyond the rotary cutter assembly ( Figure 4 ). Where the taper extends further aft, you’ll need to manufacture space, either by adding a custom spacer between the transmission and shaft coupling that slides the shaft back, or saw off a ring from the metal strut hub or stern tube (call Spurs for instructions). There are certain boats on which you cannot install a Spurs because of the exposed taper. Installation
Installation is not difficult, provided you take precise measurements and have the proper tools. The most demanding job is drilling and tapping the strut. Installation by a pro takes about two hours max. An amateur should allow an extra hour or two. The cutter is loosely assembled first, then all bolts tightened firmly. Though not mentioned in the instructions, it’s good practice to coat screws with a thread locker.
Photo tag: PJ14.tif, PJ15.tif, PJ16.tif, PJ17B.tif, PJ17.tif, PJ18.tif, and PJ19.tif (these are all in order and correspond to the number in the article - see PDF)
Position the two rotary cutters on the shaft as close to the propeller hub as possible, allowing for any exposed taper, as mentioned above. Insert the bolt in the hole where the two half castings join together on the even (unnotched) edge, and fasten loosely (1) . Insert the bolt into the hole on the notched half castings, known as the lip side, and torque the nut loosely (2) . Install the U-shaped bearings (3) , then insert the stationary cutters into the bearings, and tighten the screw (4) securely. Position the cutter against the prop hub, behind the leading edge of any blade. Tighten securely the bolt on the lip side (notched) side (5) . This automatically aligns the stationary cutter groove to the shaft bore. Tighten the other bolt on the rotary cutter. Next step is to mount the holding block on the portside of the strut for left-hand props, starboard side for right-hand props. Position the holding block on the strut so the cast line meets the tip of the wedge (6) . Be careful not too position the wedge beyond the line. It may appear that the wedge and holding block fit tightly together, but this is not correct. Drill three, 17/64” holes in the strut, the center one first. Tap it for a 5/16x18 bolt, insert a bolt and torque the nut loosely. Now drill the next hole and insert a bolt, and finally the last hole. Securely tighten all bolts (7) .
If you catch a steel cable, chain or anything that Spurs cannot cut, a built-in fail-safe feature prevents permanent damage. As the propeller turns, putting pressure on the cutters, this causes the two forward bolts on the holding block to shear, and the holding block drops down on the third bolt and disengages the cutter. There are some drawbacks to this design. Once the bolts shear, the boat is still held fast by the cable, which still must be disengaged, and likely means a tow and haulout to reinstall the holding block. Routine Maintenance To prolong cutter life, you’ll need to replace bearings and zincs regularly. During the annual haulout, check the zinc anode mounted on the wedge of the stationary cutter. This anode is the only protection this assembly has against corrosion. (The rotary cutter is protected by the shaft or prop nut zinc.) Spurs recommends retrofitting older models that are equipped with a wire that bonds the stationary blade to the boat with a zinc anode. Since the Kevlar-Teflon bearings are water lubricated, replacement times vary depending on water clarity. Sediment and silt act as abrasives, accelerating bearing wear. |
If you cruise on waterways shared with commercial
fishermen, and your boat is equipped with a Spurs or other shaft-mounted
line cutter, you were likely unaware of the dangers below. Without
a cutter installed, a crab pot line or fishing net could wrap
around the prop and shaft, continuing to wind itself tighter
and tighter, eventually bringing your boat to a dead stop. And
if running at high speeds, you risk damaging the prop, strut
or other underwater gear, and perhaps overload the engine, causing
transmission or clutch failure, even shaft breakage. Either way,
you’re stranded,
resulting in an unscheduled dive to c ut fouling lines, or worse,
a tow and costly haulout to affect repairs. 
The first step is
to thoroughly scrape and sand the shaft using emery paper.
Partially disassemble the cutter, loosening the stationary blade
screws just halfway to prevent losing the two small washers and
spacers. Remove screws on rotating cutter assembly. 
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