Commercializing Conventional Cage and
Ring Type Propeller Guard Inventions

A Message To Conventional Cage and Ring Type Prop Guard Inventors

by Gary Polson – We often hear from inventors of conventional propeller guards (rings or cages) designed to protect people from being struck by propellers (NOT guards designed to protect the propeller) that are very similar to existing guards or guard patents. Sometimes we are contacted by their friends, by their family members, or even by people who have inherited the idea/patent from a deceased family member.

Their propeller guard is not yet widely on the market and most of them are wanting to sell the idea (license it) or find investors willing to put large sums of money into their projects. This page is addressed to these inventors.

NOTE – These comments are NOT addressed to those with conventional ring and cage type propeller guards already on the market. These inventors have already had first hand experience with the problems listed below. It is similarly NOT addressed to inventors of radically new ring and cage type propeller guards that have VERY significant advantages over the current field of ring and cage type propeller guards.

I wear another hat that regularly deals with independent inventors and have dealt with people trying to develop hundreds of mechanical inventions. You have to study the industry, determine the lay of the land, and see if any specific “rules” or barriers apply to commercializing new products in each industry.

The comments below are pretty harsh, brutal and frank, but that is the way it is in the marketplace.

Originally published in August 2010.


The conventional cage and ring type propeller guards market is fairly unique in that is has at least two major barriers to entry not present in most other industries.

  • Barrier 1 – The Industry Does NOT Want a Solution.
  • If you are with the industry and disagree with that statement (“The industry does not want a solution”), we would be happy to post your comments here inviting independent inventors to submit conventional ring and cage type propeller guards that meet your specific criteria and pass a specified series of tests, along with details of your technology prize (significant cash award) to be awarded to the first inventor to meet those requirements for a specific application. Please note that prize should be substantial since you claim not been able to solve the problem in over 30 years with much greater resources than those available to independent inventors.

    The industry does not want this problem solved. If you designed a conventional ring or cage type guard that prevents injuries without causing any other issues (handling issues, drag, increased fuel consumption, catches weeds, blunt trauma, fails and crushes into the drive causing drive damage, etc.) and does so while adding minimal cost to the boat, the industry would want you and your solution to go away.

    If your patented conventional ring or cage type guard actually solved the problem, created no additional issues and did so at minimal costs, and the industry admitted your guard worked, the industry would then have to:

    1. License your invention and start using it (they would have to pay you money which eats into their profits). Yes you might claim its safer and reduces long term liabilities but to most CEOs, long term is next month. CEO’s don’t care what happens in a few years, they will be probably gone by then anyway. Shareholders are holding stock for a few weeks or a month and clamoring for profits (they want the share price to go up so they can dump the stock). Many shareholders don’t care about long term liabilities.
    2. Explain in court how somebody on the street came up with this solution while the industry has diligently been working on the problem for over thirty years with all their resources and they were unable to find it.
    3. Possibly retrofit your guard to millions of boats in the field at their own expense, including installation costs.
    4. Eat crow after saying for decades that no conventional ring and cage type guards were safe above planing speeds.
    5. Give up some hefty profits from the sale of replacement propellers (guard would protect propeller from damage in many situations.)
    6. Some people would still be injured by your guard (even if they just dropped it on themselves while they were installing it). The industry would have to assume liability for those injuries or defend themselves against them.

    And don’t think you will sell the industry on the idea they could sell more boats now because they would be safer with your guard. The industry will tell you their boats are safe now and would be more dangerous with your guard.

    Also, do not think you will get far by claiming lower insurance premiums as a sales feature if the industry says your guard is dangerous.

    This is one situation in which if you build a better mousetrap, the industry will nail your door shut.

  • Barrier 2 – The Industry Will Object to the Use of Your Guard
  • If you are able to develop your conventional ring or cage type propeller guard to the point that it starts making some noise in the marketplace, or it is used as an exemplar (example of a safer approach) guard in a propeller injury case, the industry will publicly say your guard has a given list of problems. They will specifically oppose the use of your guard and say it is dangerous. That will make it difficult for you to sell or license your guard. They will also make it difficult for you to attract investors.

    The industry is not a bunch of criminals. It is totally within their prerogative to resist the use of guards for as long as they want to. Even if regulations required the use of guards, the industry could still be against their use. You need to understand that.


    In addition to the significant barriers above (the industry does not want a solution and the industry specifically objecting the use of your guard), this field has some challenges from the Laws of Physics.

  • Laws of Physics Challenge 1 – Some Ring Guards May Plane.
  • Ring guards typically have a thickness of less than 3/8 inch, length of distance around the prop blades of more than a three feet for a 14 inch prop, and a breadth of a few inches. If the ring of your guard (or other large flat surfaces) have much breadth to them, the industry will say your guard affects the handling of the boat in certain conditions, including taking off with the drive trimmed under. The boat wants to plane on the flat surface (the breadth of the ring). Planing on the ring tends to raise the stern and can create bow steering, especially with the drive trimmed full under. If you invented a ring guard, and your target boat population has top speeds in excess of about 15 mph, you better find a way to beat this problem if you want to sell it. Note we are not saying rings cannot be successful on planing boats. We are saying rings with large surface areas intended for use on planing boats are going to have problems getting past some handling issues raised by the industry, including planning on the ring, porpoising, steering torque, and laying over on one side of the hull.

  • Laws of Physics Challenge 2 – Additional Basic Physics and Hydrodynamics Are in Play.
  • While not unsurmountable, many independent inventors of conventional cage and ring type propeller guards fail to fully consider some of the basic physics and hydrodynamic issues surrounding propeller guards. They neglect things like drag (which also impacts top speeds, fuel consumption and emissions), corrosion, hydrodynamics, strength of materials, vibration, blunt trauma, fouling, striking debris, grounding (striking bottom), propeller streamlines, propeller cavitation, performance of the propeller in reverse, porpoising, boat laying to one side, steering torque, and other physical variables when designing their guard. You need to make sure your guard has no problems with the laws of physics, and optimally, you would like for your guard to employ the laws of physics to help it do its job better.


    In addition to the Barriers and Laws of Physics challenges above, the same basic rules apply to those trying to commercialize inventions in this industry as in most other industries. Barrier 1 (the industry does not want a solution) impacts some of the normal rules, so we reformulated them below. These rules have been put together from our years of experience and from the writings of many others.

  • Rule 1 – There Has to be a Market for Your Product.
  • Right now, the industry has pretty well blocked the use of guards. Drive manufacturers may void drive warranties if you install a propeller guard, plus the industry constantly speaks out against their use.

    Look at the firms currently producing cage and ring type guards. Most are small operations and few if any of them are “making a living” solely off their sales of cage and/or ring type guards. Most of them are doing something else to support themselves. Plus with the boating industry down strongly the last couple years due to the poor economy, things are even more challenging fro them.

    So the bottom line is, there are already a hand full of firms out there (see them on our Propeller Guard Manufacturers List) trying to capture what sales there are. It is a niche market. The market for your product is almost non-existent until the industry changes its position.

  • Rule 2 – You Have to Have Something to Sell.
  • Napkin sketches don’t cut it. If you are serious about it, you need field tested hardware. That is where you learn and make improvements, not napkin sketches. One video of your guard running over stuff is worth thousands of napkin sketches.

  • Rule 3 – No Spreadsheets Allowed.
  • Every inventor wants to run a spreadsheet showing there are “x” million boats of various sizes. Even if we only sell to just a few percent of those boaters we will sell tens of thousands of units a year. Yes and if you get just 1 percent of the soft drink business you will be a zillionaire. Spreadsheets don’t require you to prove you can get that few percent market share of all boats. Look at market shares of those currently in the market as a percentage of all boats on the water. Each builder of conventional guards and rings has a miniscule percentage of all boats. You are not going to get a few percentage points of all boats as long as the industry opposes the use of guards.

  • Rule 4 – You Have to Play the Hand You Were Dealt.
  • Many inventors of conventional propeller guards want to belly ache about how the industry wronged them, the industry has lied about this or that, the industry was unfair during their tests, the industry failed guards on purpose, the industry has set the bar too high, etc. That is just the way things are, inventors have to deal with it. Back in my younger days as a pool player, a pro once gave me some advice about unlevel surfaces on pool tables. He said do not be belly aching about the table roll, be the first player to learn the table and use it to your advantage. The same goes for propeller guard inventors. Quit wasting your time gripping about how the industry kept your product off the market, learn the table roll, and figure out how to use it to your advantage.

  • Rule 5 – Why Mine?
  • There are already several guards on the market, why would someone choose yours over the others? We provide an extensive list of objections raised against propeller guards and other propeller safety devices. Is your significantly better against the competition when compared against that list? If your invention is just a conventional ring or cage type guard its hard to imagine it somehow performing magnitudes better than those already on the market. If you invention is just slightly different from the existing guards, you can probably enter the market and try to sell them, but don’t expect to be immediately successful against well entrenched competitors.

  • Rule 6 – Think Before You Patent.
  • Before spending thousands of dollars in obtaining a U.S. patent, make sure you really have a market for your product and you can sell it for several times (think four to ten times ) what it costs to manufacture so you can make enough profit to feed your family, take care of the overhead, pay the distribution costs, advertise, and pay off the patent. That environment rarely exists today in conventional ring and cage type propeller guards, especially with the current low volumes.

    Also consider the success ratio. Most U.S. conventional propeller guard patents are in patent classes 440/71 and 440/72. As of 12 August 2010, there were 84 patents in 440/71 and 33 patents in 440/72. Please note some of these patents are just cross referenced into these class and subclasses, and some may be listed in both subclasses. The bottom line is there are something in the range of 100 U.S. patents, with just a handful of U.S. guard manufacturers in the business, and some of those manufacturers accounting for more than one patent. Plus some may be manufacturing non-patented guards. Without counting, we suspect over 90 percent of the guard patents assigned to independent U.S. inventors are not currently in production. Those are not good odds.

  • Rule 7 – Variety is NOT the Spice of Life.
  • Have you given any thought to tooling costs to produce your cage type or ring propeller guard? Have you noticed how many different frame sizes of outboards and stern drives are sold by each major manufacturer and how many different sizes of propellers are available with those drives? Plus did you happen to notice many drives currently in service in the field represent still more frame sizes combined with more propeller sizes. For broad application of your propeller guard, you will need to be able to adapt to dozens of frame sizes, each with several propeller sizes. You can think of it as 3D matrix with frame sizes on the vertical axis, prop sizes on the horizontal axis, and drive manufactures on the Z axis coming at you. That is a lot of tooling costs for jigs and fixtures if you are welding them up, and insane costs for casting molds or dies.

  • Rule 8 – Die Casting and Plastic Molds Require High Volumes.
  • Everybody wants to die cast or plastic injection mold their ring or cage type propeller guard to get nice cheap uniform parts. Guess what, they are nice cheap uniform parts if you can really sell the gazillion of them needed to pay back the tooling cost for EACH individual die needed for each individual combination discussed earlier (drive manufacture, frame size, prop size). In today’s market, you can not afford the tooling cost to die cast or plastic mold conventional ring and cage type propeller guards, at least not at startup volumes.

    Spend some time figuring out how many guards you would have to amortize tooling costs over for just a single die / mold for just one specific frame size and prop size combination. You will soon find yourself turning back to weldups, sand castings, and machining.

  • Rule 9 – Transaction Costs Can Kill Your Invention
  • OEM’s (drive manufacturers and boat builders) will not buy your guards. That reduces the possible size of your transactions (sales) from hundreds to as many as thousands of guards per order to one or two guards per order (sales to individual boaters) which unbelievably increases your transaction costs per guard (the costs of taking an order, writing up the order, creating invoices, packaging costs, cost of boxing the order, shipping costs, etc. on a per guard basis). It also increases your risk of not being paid (taking orders by credit card or from Joe in Nigeria) and forces much smaller production runs which also increases your costs per guard.

    You might elect to establish stocking dealers / distributors to achieve slightly larger economies of scale, but you are going to have to share a large piece of the pie with them, plus right now who wants to be a stocking distributor when:

    1. The industry is telling boaters not to buy their products.
    2. They would have to stock dozens of guards just to possibly have the one a customer might want.
    3. The industry might actually cut off the supply of parts they do sell (for example if drive manufacturers and boat builders could black list your dealers and not sell them other parts as a punishment for selling guards).

    You could setup some catalog dealers (boaters come in and order one from their catalog, the dealer contacts you, you ship it to the dealer or to the customer, and your transaction costs are skyrocketing again.

    That leaves you with online sales or sales directly out of your shop. If you do not live near a very major boating area (hundreds of thousands of boats within 100 miles of your door, you are probably stuck with Internet sales as your marketing method (look at your competitors, that is what most of them are doing).

  • Rule 10 – Investors Want to Make Lots of Money, Not Listen to Your Story.
  • If you are looking for an infusion of cash, you need to be able to prove to the investors that they can make a lot of money. Right now that is just not possible. The industry has effectively blocked sales. The market is miniscule. It does not matter if you just invented the world’s best propeller guard or not, nobody in their right mind is going to invest in it till the logjam is broken.

    Plus most inventors are males that witnessed or read about a propeller accident in their area and began to think about ways of preventing them. They go on and on about how they were thinking about the problem, came up with their invention, and how it will save lives. That is all well and good if you are talking to the media doing a human interest story, but if you are talking to potential investors they could not care less. All they care about is making money. Quit spending time focusing on how you came up with your invention or how it can save lives and start focusing on how your invention can make investors rich. That may sound a bit harsh, but that is the way it is.

    You need to prove your guard can make them money by providing well documented realistic production cost figures (including tooling costs and overhead), distribution costs, advertising costs, along with proven sales forecasts (including tentative orders in your hands) and show them how profitable your operation can be. Note that is going to be very hard to due as long as the industry continues to block sales.

  • Rule 11 – Licensees Want to Make Money.
  • For exactly the same reasons listed in (10), nobody is going to license your idea unless it is a great one and you are giving it away. Somebody might be willing to invest the time and effort to do the paperwork to license it for free and sit on it hoping things change. Plus who are you going to license it to? The industry is adamant they don’t work. They will not license a guard from you. That leaves those outside the business of building drives and boats. Do you really think some body building farm equipment is going to pay you a lot of money and try to enter a down market in which the well established industry tries to drive their customers away?

    If you were able to interest a company in the marine accessories business, the industry could scare them away by threatening to blacklist them and not provide them with materials they may need or not purchasing their other profitable products from them.

  • Rule 12 – A U.S. Patent Gives You the Right to Manufacture and Sell in the United States.
  • A U.S. Patent does not automatically mean your invention is worth the paper your patent is printed on. Patents are often issued to companies manufacturing products in a given industry. For example, if Brunswick were issued a U.S. patent for a bilge pump they would have the rights to manufacture and sell that pump in the United States. They could make all of them they wanted and even more too. Patents are worth something when the device is unique, solves a problem better than the other solutions, and can be sold at a volume/price point creating significant profits for the manufacturer compared to the other solutions. “Me To” patents (those extremely similar to products already in an existing market) are sometimes issued to manufacturers wishing to enter a vibrant, profitable existing market with their own unique “brand” solution. Their “Me To” patent is really not much different than other devices already on the market, but they have the rights to build it and keep others from doing the same. These same manufactures would never consider applying for a “Me To” patent in a stagnant, non-profitable existing market. Why would they even want to enter such a market, much less patent something in it.

    Patents are sought to enter vibrant, growing, profitable markets, not stale ones. If you are trying to patent a “Me To” conventional ring or cage type propeller guard, you better be hoping one of the game changing scenarios below comes to pass pretty soon.

    Some people tell us their invention was patented in the 1980’s or 1990’s (meaning ten to twenty years ago). Guess what, if your idea has been patented for over a decade and no manufacturer has contacted you wanting to license it, chances are its not going to happen.

    Also you really need to closely study the claims of your patent. The claims are the most important part. Inventors should try to capture as broad of claims as possible so others will not be able to build something pretty close to them without infringing on your patent. This field is already littered with something near a hundred propeller guard patents. Many of them resembling conventional ring and cage type guards. There is very little room left. Your claims are probably very narrow which further reduces any licensing potential your idea may have had.

  • Rule 13 – Whether Your Conventional Ring or Cage Type Propeller Guard Works or Not is Absolutely Immaterial.
  • It does not matter if your guard is works perfectly and has absolutely no problems, OR if your guard is a piece of junk, either way the industry is going to object to it. They will probably actually object to it louder if it works perfectly. Either way, you are going to have most of the same problems listed in the rules above. The quicker you understand that, the better off you will be.


    What Would it Take to Change the Boating Industry’s Position?

    Are you discouraged yet? We did not set out to discourage propeller guard inventors, but many need a dose of reality. The reality is this business is on hard times right now and no amount of inventing is going to change that till the industry changes its tune.

    Yes that could happen, but that is what many people have been thinking for a while and it has not happened yet. For things to change, it has to be in the financial best interest of the boating industry. We only see it happening if one of or more of the following game changing scenarios come to pass:

    1. The industry develops some totally new, profitable approach that was not available earlier so they do not have to explain why they did not use it previously. The problem with this scenario is currently the industry is spending all their time and energy proving why guards don’t work, they are not really spending any time working on new approaches.
    2. An independent inventor comes up with a totally new, profitable approach, not available earlier that the industry does not have to explain why they did not use previously. The problem with this scenario can be seen in the reception the industry gave the Australian Safety Propeller at the U.S. Coast Guard Propeller Injury Mitigation Meeting. The industry tries to derail any possible solution, radical or not.
    3. The industry starts loosing large multi-million dollar awards in high profile prop guard cases. That could scare them into change, but with Brochtrup being the only recent win, it could be a while or never. Especially considering the industry has a well rehearsed legal team and deeper pockets than victims (or victims lawyers taking cases on contingency).
    4. The U.S. Coast Guard could mandate the use of guards in certain applications. The problem with this scenario is propeller safety advocates have been calling for regulations for decades, but the industry always defeats the proposals.
    5. The U.S. Congress could act on its own to require the use of guards in certain applications. The problem with this scenario is Congress is currently too focused on the economy, the war, health care, unrest in the Middle East, and getting themselves re-elected to worry about propeller guards.
    6. Somebody else starts using them first. For example several groups are starting to use guards on small boats in Australia, especially those used by or around youth. Plus the Australian Environmental Safety Propeller is getting a lot of attention there. Those movements could spread to here.
    7. A major celebrity or political figure gets maimed by a propeller and spearheads (and bankrolls) a national effort to overcome the industry’s resistance to guards by showing them being built, tested, and working to save lives (think Christopher Reeve being struck by a prop instead of falling from a horse. Imagine him on Oprah in his wheel chair talking about propeller guards saving lives and how everybody needs to call to change by writing their congressman at the link Oprah provides.).
    8. An independent inventor or small business with a zillion dollars develops an economical functioning guard with no problems, tests it extensively, then spends millions of dollars manufacturing and marketing their guard directly to boaters, probably using a major celebrity that has some outdoor ties as a spokesperson (somebody like John Denver in the old days). The problem with this scenario is it requires the inventor to have almost limitless funds at their disposal. I have been involved with hundreds of inventors for over thirty years and have only encountered one with pockets that deep.
    9. The Government could cut a special deal with the boating industry (or a major player) limiting its current and future liabilities for accidents from existing boats without guards (or other propeller safety devices) in exchange for putting propeller safety devices on new boats. The U.S. Government cut a somewhat similar deal with the firearms industry a decade ago (President Clinton’s March 2000 agreement with Smith & Wesson).
    10. A major stockholder takes an activist position. We do not see this happening because it would have to happen at the drive level (if a boat company chose to start using guards, the drive companies could refuse to sell them drives). Drive companies are huge operations that are sometimes part of even larger operations and conglomerates. It would require a lot of money to acquire a significant stock position (although when Brunswick stock tanked in recent years there were some times it might have been doable). Plus most stockholders are onboard for quick profits, not for activist positions. We are not aware of any major stockholders taking environmental activist positions in these or similar companies (emissions related positions) which would seem more likely to happen than a propeller safety activist position.
    11. Widespread regulations requiring prop guards in manatee areas.
    12. A significant new player enters the drive industry, probably from outside the U.S., and offers a guard or other propeller safety devices as optional equipment with its drive. As a new entrant, they would not face the historical baggage carried by current manufacturers (years of saying it was impossible, potential liability for past accidents because they did not start using the safety devices earlier, possibly being forced to pay retrofit costs for units already in the field, etc.)
    13. Same product for a different purpose – if the industry were to start calling propeller guards “rope guards” and begin installing them to prevent ropes from becoming caught in the propeller they might be able to escape some of the historical baggage surrounding the issue.
    14. Widespread leadership turnover in the industry. The “new regime” could be more sympathetic to the need for propeller safety devices. With leadership already turning over multiple times at many firms since the early 1970’s when the call for the use of guards began make noise, its hard to envision this happening.

    So the immediate future for conventional ring and cage type propeller guards looks pretty bleak unless you are the inventor with very deep pockets (tens of millions of dollars to invest in your invention).


    What to Do Til The Industry Changes its Position

    Meanwhile you have invented a conventional cage or ring type propeller guard and are wondering what to do with it. Our suggestion is to think about rules above and decide if you still want to proceed, recognizing further development will require spending hundreds of hours and thousands of dollars. If you elect to proceed, we suggest you:

    1. Learn as much as you can about the whole swirl surrounding propeller accidents by spending a few weeks studying materials available at the Propeller Guard Information Center.
    2. Develop and run a prototype of your propeller guard. Much can be learned in the prototype stage.
    3. Contact us and we will be happy to make some basic comments about your design and point out some things you might especially want to consider.
    4. Follow the general processes listed on our Invention Commercialization Process: Marketing an Invention page.
    5. Be alert for other opportunities that might allow you to enter the propeller safety market in its current state (develop some other device or approach that can be profitably made and sold in today’s market). You could get established in the industry and bring your conventional cage or ring guard out later if things change.

    Some propeller safety segments have a much brighter outlook than conventional propeller guards. For example, there is plenty of room for electronic and mechanical interventions such as detecting people in the water near the propeller, wireless lanyards, swim gate and swim ladder interlocks, detecting and preventing the Circle of Death (unmanned spinning boats), improved downed skier/tuber/wake boarder visibility devices, trim cylinder cushions (provide some cushion when the guard strikes someone to reduce the potential for blunt trauma injuries), Safety Propellers (like the Australian Environmental Safety Propeller), safety interlocks, applications of drag reduction technologies and methods to propeller guards, virtual lanyards for passengers, propeller devices to reduce pontoon boat propeller injuries from those dangling their feet off the bow when underway (methods of preventing them from sitting there if the industry is not going to adopt the use of guards), safety devices for new emerging on water activities, deployable guards (guard just pops out right before impact), applying some of the unique properties of water to propeller safety devices, etc. many of these approaches and other emerging technologies are discussed on our <2011 Propeller Safety Technologies page.

    Plus there is still room for improvement in “swing up”, “flapper” ring or cage type guards in which part or all the guard raises from the water at higher speeds to reduce drag and the potential for blunt trauma injuries. See the Navigator 3PO guard as an example and Balius’s guard (U.S. Patent 3,889,624).

    Plus, we suspect there is still plenty of room for more innovative methods of attaching a guard, drag reduction, alternative uses of a guard, methods of constructing guards for many different applications from just a few parts (similar to “will fit” propeller hubs), and other innovations.

    If I was trying to invent a propeller safety device that had some chance of getting to the market and making a few dollars along the way, I would be focusing in an area other than “Me To” conventional ring and cage type propeller guards.

    This problem has been around a long time and will still take some some very serious work to solve in some applications. Don’t be making wild claims before you have put some work and effort into your device AND tested it. For as Carl Sagan, the astronomer once said, “Extraordinary Claims Require Extraordinary Evidence.”

    PLEASE NOTE – if the industry ever changes its position and openly starts utilizing propeller guards on new drives and boats, a whole new set of rules would apply, and this page would need a major rewrite.

    We salute your efforts to try to make boating safer and wish you the best in developing your invention. In closing, please remember we provide new product development services as Polson Enterprises, and have one of the largest libraries of recreational boat propeller safety information in the world.


    Feedback and Comments

    If you have any questions or comments about our suggestions for inventors of conventional ring or cage type propeller guards, please contact us.

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