Propeller Guards: Objections

List of Objections Raised Against Prop Guards

Many objections have been raised to the use of conventional cage / screen and ring type propeller guards as well as some of the related accessories said to help prevent or reduce propeller injuries Some of these objections have been raised by groups opposing the use propeller guards. These objections may or may not have merit depending upon a specific vessel, the specific guard, what the boat is used for, and its operating environment. Objections raised include:

  • Restrict Performance
    • Lower top speed
    • Decrease acceleration
    • Increase drag
    • Reduce reverse thrust
  • Disturb flow in front to the propeller, decreasing its efficiency
  • Guards themselves entrap people, injuries become more severe
  • Increase zone of danger (Guards increase cross sectional area for impact)
  • Create unstable handling conditions
  • Reduced maneuverability at low speeds
  • Reduced maneuverability at high speeds
  • Poor handling
  • Durability problems
  • Increased steering loads
  • Poor steering in reverse
  • Increase fuel consumption
  • Not as dependable as a bare propeller
  • Not as efficient as a bare propeller (takes more horsepower for same performance)
  • Guard cost, installation, and operational cost add to cost of ownership of a boat
  • Increased maintenance
  • Not aesthetically pleasing – detract from “appearance” of the boat
  • Detract from the appearance of the drive
  • Deeper draft (ducts stick down lower than the prop itself)
  • More surface area exposed to corrosion and marine slime problems
  • Some may be noisy
  • Are too expensive
  • Cavitation problems
  • Ventilation problems
  • Guards interfere with use of “ear muffs” (clips to run fresh water through the drive after use)
  • Guards interfere with access to the drive or propeller for maintenance
  • Easily foul with floating weeds / plant growth / seaweeds, especially in reverse
  • Easily foul with debris
  • Foul with ski ropes
  • Foul with fishing nets
  • Fouling could result in stranding of the vessel
  • Although guards may provide some level of protection from fouling with fishing lines or lobster lines, once a prop does becomes fouled with a line, the line may be more difficult to remove with the guard in place
  • The cage itself may become fouled with fishing lines or lobster lines
  • “Off throttle” steering performance
  • Increased stopping times and increased stopping distances
  • Increased turning times
  • When someone falls out they can be injured falling into the direct stream of water from water jets, including body orifices.
  • Engine emissions are increased due to the additional drag (engine has to work harder and creates more emissions)
  • Propeller guards/ prop guards added in the field may require purchase of a new propeller to keep the engine RPM in proper range (RPMs may be too low) or to improve efficiency.
  • Propeller guards / prop guards may decrease WOT (Wide Open Throttle) RPM below allowable limits and void the engine warranty.
  • Commercial boats, fishing charters, and others running a fixed route may require additional routine maintenance and overhauls because the engine must run longer to cover the same distance (lower top speeds take longer to run the route, get out to the fish, etc).
  • Rescue boats with guards may take longer to arrive at the scene, and longer to transport the injured to shore.
  • Why worry about protecting from a propeller strike if it occurs after they have already been struck by the lower unit (gear case, skeg, etc) at high speed before the propeller strike occurs.
  • Are not commercially available without the above problems
  • Many people just respond, “They are not technically feasible”.
  • Some sensor approaches require the person to wear a sensor (it only protects people with something on them)
  • Does not protect people from all the situations in our typical propeller injury scenarios list.
  • Just like motorcycle helmets, some people may want freedom of choice (no helmet and no prop guard)
  • Some suggest boat and drive manufacturers fight against their use to maintain highly profitable sales of replacement propellers (guards could protect propellers and reduce sales of replacement props).
  • If boat and drive manufacturers were to adopt them now, they might be forced to retrofit them onto units already in the field (very costly for the manufacturers).
  • If boat and drive manufacturers were to now say propeller guards worked, they could be liable to past accidents because they did not use them then.
  • Structural integrity of propeller guards – Some prop guards may vibrate off, crack or break under higher horsepower loads (larger motors) or after periods of running at full speed. When they fail, they may also damage the propeller or the drive itself, including the internal gears/shafts. Wires of cage type guards have broken welds in the past. They may cause severe vibrations when wires, rods, or welds break.
  • Device may require modification, adjustment or “tuning” for the specific drive, boat and boating activity. This modification, adjustment or “tuning” may be difficult and doing it improperly may make the craft unsafe.
  • If the device reduces performance (speed, acceleration, fuel consumption) of the vessel and is installed by the boat builder, the builder may install a larger engine to get the performance of the boat back near where it was without the device. If the boat owner wishes to eliminate the reduction in performance, the owner may remove the device at which time the boat may become overpowered and unsafe. Plus installation of the larger engine itself mentioned earlier results in increased weight and drag on the vessel. In some situations this could result in the need for a trailer with additional capacity and/or a larger tow vehicle.
  • Presence of safety devices may give boat operators or those in the water a false sense of security and result in them exposing themselves to additional dangers/risks of being struck they would not have without the
    device (such as operating the drive in proximity to swimmers). These operations may result in injuries.
  • Marine drives come in many types (outboard, inboard, stern drives, water jets, etc) in several different horsepower classes. They are used on dozens of types of recreational boats (bass boats, runabouts, saltwater fishing boats, pontoon boats, deckboats, houseboats, ski boats, wakeboard boat, etc) and used for dozens of applications (fishing, skiing, diving, wake boarding, high performance, river running, etc). No one single propeller guard method / design covers more than a few elements of the large matrix of drive type X horsepower X boat type X application. Plus those building the drive may not know what type of boat it goes in and those selling the boat may not know what it will be used for. This could make it hard for manufacturers to select the proper guard approach for your drive and boat. A 2002 U.S. Coast Guard article put it like this, ” There is currently no one size fits all solution…” or as a U.S. Coast Guard Boating Safety Circular 81 put it “None of the devices has the high degree of practicality in a wide range of operating environments (trash, weeds, shallow water, damage tolerance, etc.) as that established by an unguarded propeller. For planing vessels, the study concluded that some improvement in low-speed human protection can be achieved at the expense of decreased performance, decreased high-speed protection and some decrease in practicality. The cost benefit ratio for using the tested devices on planing vessels is sensitive to both vessel type and operating environment.
  • The large number of drive types, drive sizes, propellers, and applications (mentioned above) lead to a large number of models of cage type guards. Finding the right one is almost like going to the shoe store and looking through their catalog of all possible shoes. This creates design, manufacturing, inventory, distribution, and prescription/selection issues.
  • We found an incident of a surf rescue boat propeller guard fouling several times on jellyfish during a major jellyfish outbreak in New Zealand. They had to actually take the guard off to operate.
  • Propellers are well known for entangling with ropes, anchors, fishing lines, nets, etc. Some propeller guards / prop guards provide some protection against this entanglement (entanglements occur less frequently), but when/if they do occur the entanglements are more severe and require more time/effort and possible removal of the guard to untangle them from the propeller / guard.
  • Limited selection of propeller guards / prop guards. Some devices are patented and demand for guards (sales) is limited. This results in a relatively small set of off the shelf propeller guards for a specific boat and situation.
  • Lack of widespread use makes for limited profitability of firms in the business, leading to lack of long term suppliers. It is somewhat of the which came first, the chicken or the egg problem (demand or supply).

Comments on the List of Objections to Propeller Guards

The real or perceived animosity to the use of propeller guards by drive manufacturers and boat builders has at one time or another been attributed by some to:

  • Their fear of losing the lucrative business of selling propellers (if guards keep propellers from being “dinged” or damaged, they will sell far fewer propellers).
  • They are more concerned about the bottom line than the safety of their customers.
  • They would have to eat the statements they have said for so many years that guards were no good, did not exist, etc.
  • They are trying to pass responsibility down the chain:
    • Drive manufacturers say one type of guard wont work in all applications and we do not know what kind of boat this drive is going to wind up on, so we cant put a prop guard on it. That is a bit difficult to believe when it comes from Brunswick that is putting it own drives on its own boats)
    • Boat Builders say we do not know how or where the customer is going to use the boat so we do not know if it needs a propeller guard or not or what type of guard it needs.
    • Boat Dealers say they do not have the research capabilities to figure out what type of guard you need, they do not want to accept responsibility for it, put a prop guard on yourself if you want one, but it may violate your warranty.

There is considerable inertia resisting any change in accepting propeller guards. Some of this inertia exists due to:

  • Prior to December 2002, Federal Pre-emption was seen as a reason not to use prop guards (prior to the U.S. Supreme Court ruling on Sprietsma v. Mercury Marine, lower courts had said since the U.S. Coast Guard did not require guards, states could not require propeller guards.) This was actually an incentive to do nothing. It was the only safe square on the checkerboard for them. (See reasons below)
    • If they started to use propeller guards, it would signal their previous products were dangerous. (not good for them in pending or future court cases)
    • If they started using them and chose/elected or were forced to retrofit units in the field, who would bear the huge costs for retrofit/ recall (drive manufacturer, boat builder, dealer, owner)? None want to bear the cost or any portion of it.
    • Even with the use of prop guards, a few people will still be hurt now and then. Companies would still be sued by those struck by prop guards, injured installing them, injured by propeller guards installed improperly, etc.
  • Now in a Post 2002 world, the industry may be trying to hang on to their old ways for as long as possible.
  • They may be hanging on hoping for an alternative that does not make them look bad (something like the Virtual Lifeline tags from MariTech). Drive manufacturers could say these did not exist in the past so we did not make bad decisions then. Guards are still bad, but this new technology solves the problem, plus we can sell it at a good markup and our props will still get dinged up when they hit something, keeping our highly profitable aftermarket prop business intact. Its the best of both worlds.
  • In today’s economic environment (early 2011) drive manufacturers and boat builders are continuing to fighting for their very survival in these tough economic times with a very strong downturn in sales, lack of available capital, lack of loans for potential buyers, high fuel costs, decreased home values (potential boat owners cant take out a second mortgage on their home) and other issues, propeller safety is not on the table. Companies are slashing and burning trying to keep from sinking themselves and feel they have no time to spend on issues of this nature.

Closing Comments:

  • Before those objecting to guards say the list of objections above is insurmountable due to its pure length alone (number of objections that have been raised), please notice that if you mentally select a type of boat, a general use for that boat, and general type of guard, many of the objections listed above vanish, or do not come into play.
  • Some say boater safety education and warnings fix the problem and no guards are needed.

Cross Sectional Area, Impact and Water Density Issues:

Water is much more dense than air. A person struck by an object in water suffers a much greater impact than being struck by the same object at the same speed in air. One U.S. Coast Guard report says being struck by an object in water at 1 mile per hour is equivalent to being struck by the same object in air at 29 miles per hour. A 1989 NSBAC report indicates 80 percent of “struck by boat or propeller” accidents occur above 10 miles per hour. The use of cages, guards or deflectors usually increases the cross sectional area of the drive which could strike more people. For example, the boating industry has said that cage type guards can increase the cross sectional area (danger zone) by 40 to 100 percent.

There are plenty of challenges as to the exactness of the three numerical statements just discussed and re-listed below:

  • Being struck at 1 mph in water being equivalent to being struck at 29 mph in air
  • 80 percent of propeller strikes happen above 10 mph
  • Cage guards increase cross sectional area by 40 to 100 percent

However, the basic issues do exist (impacts are more severe in water, some people are struck at higher speeds, cage guards do increase cross sectional area) and need to be considered by those designing and applying propeller guards.