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Shallow Running Boats

by Mark Romanack   |  November 29th, 2004 0

Getting the most from mud motors and the boats they push.

A Go-Devil boat and motor on the go with the companies new blind attached.

The mud motor is an amazing invention. Thanks to its unique design, a mud motor is capable of navigating a duck boat laden with hunters, dogs and gear through the most unforgiving wetland. Bogs, marshes, sloughs and other duck magnets laced with logs, rocks, stumps, shallow water and heavy vegetation are no match for a boat equipped with a mud motor. Dubbed the four-wheel drive of marine motors, this title is well deserved. No other marine motor can compare when it comes to navigating shallow or hazard filled waters.

The beauty of mud motors lies in their simplicity. The typical unit consists of an air-cooled engine mounted to an elongated direct drive shaft and steel prop. The motor incorporates a simple bracket that bolts onto the transom of the boat and doubles as a pivot point for the motor. This bracket balances the weight of the motor and allows the long prop shaft to be lifted, lowered and turned with minimal effort. A mud motor features no transmission, offers only one gear ratio and no reverse. The moment the engine fires up, the prop starts turning. A simple throttle adjustment controls the prop speed.

Forward progress starts the second the prop is lowered into the water. To stop the operator, simply remove the prop from the water or turn off the engine. An elongated wedge-shaped skag is welded onto the prop shaft. Objects in the water hit the skag, allowing the prop shaft to lift up and over rocks, logs and other debris without the prop actually contacting the obstruction and being damaged.

Maintenance is equally simple on a mud motor. Change the oil and filter at least once a year. The drive shaft must be greased periodically with a few strokes from a standard grease gun. Clean or replace the air filter once a year and make sure the tank is filled with fresh gasoline. That’s it. The total amount of time it requires to maintain a mud motor is less than one hour per year!

The first mud motors were designed for flat bottom style aluminum boats. In recent years smaller mud motors suitable for a variety of modest duck skiffs have also become available.

PICKING A BOAT
Mud motors can power just about any small boat, pontoon or barge blind. Certain hull designs perform better than others, especially in very shallow water or when top end speed is important.

The wider the running surface of the boat, the better a mud motor is able to lift the hull on plane. Boats with wider bottoms also tend to draw less water, giving them an advantage in shallow water or when navigating waters with a lot of floating or emergent vegetation on the surface.

The long shaft design of mud motors makes them a little tricky to steer and maneuver, but the advantages of being able to run in shallow water and debris-filled muck far outweighs this minor disadvantage.

Flat bottom or modified V hull boats are the most commonly used hull designs with mud motors. Not only do these hull types perform well with a mud motor, they also provide the necessary space and weight capacity to haul large loads of decoys, hunters, dogs, boat blinds and other gear, safely.

Riveted hull designs are often used with mud motors. Unfortunately, riveted boats are not as strong and are less tolerant of abuse when compared to welded hull boats. Also, riveted boats create extra drag and friction as the water comes in contact with the overlapping sections of aluminum used to form the hull. Riveted hulls are made from thinner aluminum stock (.080 to .090 for riveted compared to .100 to .125 for welded boats). To compensate for the thinner hull material and to stiffen the hull, a pronounced keel and chime system is used on riveted boats. This construction increases the draft and sacrifices the boat’s ability to function in shallow water. Drag is also increased and the protruding keel and chimes easily catch on debris in the water further increasing potential performance problems.

A welded modified V aluminum boat’s hull is an excellent match for mud motors. Designed originally for bass fishing in shallow waters, these boats perform double duty as duck rigs in larger waters. Stronger and built using heavier gauge aluminum than riveted boats, the typical welded aluminum hull offers good performance features, plenty of space and cargo capacity plus low maintenance. These boats are also offered in a wide variety of lengths, widths and transom options to suit just about any duck hunting situation.

Just about every major manufacturer of aluminum boats offers a modified V hull design suitable for duck hunting. Wider models of modified V hulls perform best when used with mud motors. The typical 16-foot modified V features a bottom width of 48 inches. This bottom width is stable and provides satisfactory results with most mud motors. Boats that feature the slightly wider 54-inch bottom perform even better by drawing less water and displacing drag over a larger surface.

The performance difference of wider hulls can be significant. For the purpose of comparison picture two modified V boats powered with exactly the same mud motor. The first boat is a 16-foot model with a 48-inch bottom. The second boat is an 18 footer with a 54-inch bottom. Amazingly, the 18-foot boat will be faster, come on plane quicker, provide better weight distribution and run clean in shallower water despite the increased hull weight.

SPECIALTY HULLS
A few boats are being built especially for use with mud motors. Both Go-Devil and Mud Buddy offer welded aluminum boat designs built with performance and the serious duck hunter in mind. Compared to the average welded modified V hull the gauge of the aluminum on these specialty boats is thicker to better withstand impacts with stumps, rocks and other debris.

Another major feature is the slick bottom designs that create a hull free of keels and hard chimes. The absence of welded-on keels or chimes allows the boat to slide over objects in the water smoothly and permits the boat to come on plane quickly even in very shallow water. Also, the total draft of the boat is reduced making them the ultimate in shallow watercrafts.

The transom also includes another design feature unique to these boats. Instead of a standard transom that intersects the hull at a 90-degree angle, the bottom of the transom angles forward, meeting the hull about four inches forward of the flat portion of the transom. This unique feature allows the boat to be pushed backwards into grass or other cover with far less effort and helps to prevent the hull from hanging up on submerged stumps, rocks and other obstructions.

Doug Demming is the owner of Fish Point Lodge on the shores of Saginaw Bay in Michigan and one of the region’s most respected waterfowl guides. Demming has owned and used several of the popular duck boats and mud motors available.

This mud motor rig is powering through a stand of cattails with ease. Mud motors don't generally provide the forward thrust of an outboard motor, but they are more than powerful enough to push heavy boats loaded with guns, dogs, decoys and other gear.

Saginaw Bay is one of those hunting destinations where a mud motor is an essential piece of gear. Declining water levels in the Great Lakes have left the prime duck marshes of Saginaw Bay with only inches of water. Depending on which way and how hard the wind is blowing, the water levels can fluctuate dramatically in a matter of minutes.

“I currently operate eight boats equipped with mud motors and it’s hard to imagine hunting without them,” says Demming. “The shallow water performance is what sold me on my first mud motor. Over the years I’ve owned several different brands and I’m also impressed how well each has held up to the abuse they get. My original mud motor is a Go-Devil with a Briggs and Stratton powerhead that’s 10 years old and still going strong.”

Demming has considerable experience with a variety of boat types including deep V, modified V and riveted flat-bottom boats. In recent years he has converted his fleet of duck hunting boats over to hulls designed especially for use with mud motors.

“Go-Devil was the first company to build a boat especially for use with mud motors,” explains Demming. “The smooth bottom and rounded chimes allows these boats to plane out in very shallow water while carrying an amazing amount of gear and hunters. I favor the 20-foot models, but have had good success with boats as small as 16 feet.”

Demming’s experience suggests that mud motors perform best on boats at least 16 feet in length. Smaller boats tend to have problems with weight distribution. “I’ve found that a 20hp mud motor is the ideal match for 16-foot boats,” explains Demming. “Boats from 17 to 18 feet in length perform well with 24hp motors. Larger boats require 27hp or larger motors to get the best performance.”

16- OR 20-INCH TRANSOM
Most duck boats are produced in either 16-inch (short shaft) or 20-inch (long shaft) transom heights. The majority of mud motors are designed to be matched with a 16-inch transom, which helps keep the angle of the prop shaft more in line with the boat. This allows more vertical travel on the prop shaft and a little more control over the boat.

Boats with a 20-inch transom can also be used in connection with mud motors. Often the manufacturer can make adjustments to the mud motor bracket, mounting hardware or shaft length to compensate for the taller transom.

PROPS
The props designed for mud motors are two-blade designs made of hardened steel. Different size props are produced for the various horsepower motors available. It’s best to consult each individual manufacturer when matching prop sizes to various motors. Unfortunately, there is not a one-size-fits-all prop for mud motors. Most of these props cost around $200 each. Damaged props can be rebuilt depending upon the amount and type of damage.

“For my money the Tiger Prop produced by Mud Buddy takes the most abuse,” says Demming. “The steel used in these props is harder than most. For my purposes running in sand, gravel and rock, they last about twice as long as other props I’ve tried.”

Demming typically wears out about 10 props per year with his hunting fleet. The average duck hunter is likely to get several years service before the prop needs repair or replacement. Just as a side note, Go-Devil produces a special tool that makes it easy to remove and replace damaged props. Without this tool, removing a badly damaged prop can be quite frustrating.

ENGINE BRANDS
Most of the major manufacturers of mud motors offer their products featuring two or more different brands of powerheads. Kohler, Briggs & Stratton, Honda, Vanguard, Yamaha and even Harley Davidson are among the engines used to power mud motors. Most of these motors are air cooled, but a few of the larger models feature liquid-cooled engines. Provided they receive the proper maintenance and care, all the major brands of motors will provide years of trustworthy service. Prices vary, but the differences in performance and durability vary little among the major brands.

SPECIAL MOTOR ACCESSORIES
A motor that includes a manual rope start as a back up is a good feature to have on any mud motor. Most mud motors are electric start, but should the battery go dead, this manual starting option could save the day. Some motors come standard with a manual start and some require the consumer to order this as an option.

A heavy-duty (1,000 CCA) marine battery is the best power source for any duck boat equipped with a mud motor. The extra cold cranking amps will come in handy not only for starting, but also for powering a spot light, running lights, bilge pump, VHF radio and other accessories.

Twin-engine mud motors provide more power and are becoming popular for use on larger boats. These engines may be a handful for the average hunter and in most cases unnecessary. Speed and power should not be the primary concern when selecting a mud motor. It’s best to select a boat and motor combination that is balanced and will function well together.

Boats with narrow hulls are especially tricky to operate with a mud motor. These boats are naturally on the tippy side and narrow boats do not function well in wind and waves. Narrow bottom boats are designed for use in protected waters.

A T-handle or some sort of grab handle is essential when operating any mud motor. Normally these are mounted in the center of the boat floor at a position that the operator can comfortably hang on with one hand, while operating the mud motor with the other hand. Also, any time the boat is under power all occupants should wear a life preserver, and the kill switch must always be in place.

Most mud motor manufacturers recommend changing the oil once a year or after 100 hours of service. Changing the oil more often than recommended is a good practice with mud motors as with any combustion engine. If your motor is worked especially hard, plan on changing the oil and filter every 50 hours. Stick with 30-weight oil for the majority of the season and switch to a 5W-30 oil if operating the motor in extremely cold weather.

Fortunately, oil and filter changes, cleaning or replacing the air filter and lubricating the drive shaft only takes a few minutes. The care a mud motor requires in return for the convenience and work it provides is exceptional. Each of the major brands has their individual cost and performance features that set them apart. With that said, every mud motor out there is a good value and an excellent investment.

 

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