I got my Wavewalk S4 from capt Larry and love it. I am a former Navy SEAL and have ridden many hours in inflatable boats, so I appreciate the stability and comfort of my S4, and I volunteered to be a local demo agent for it. I rigged my Wavewalk for lobster fishing, and I am currently rigging it for diving.
Wavewalk S4 rigged for lobster fishing, with 4 HP Yamaha outboard motor
Another important trade-off that you should be aware of is related to propellers: High pitch propellers are designed to deliver more speed and less torque (thrust, push force), and they work best with lightweight boats such as the S4, while low pitch propellers are designed to move bigger and heavier boats at lower speeds, but they should not be used with lightweight boats such as the S4, since they might make the motor run at a too-high RPM.
Outboard motors manufacturers’ websites say that (quote) “UNDER NO CIRCUMSTANCES SHOULD YOU EVER USE A PROP WHICH WILL ALLOW YOUR OUTBOARD TO OPERATE ABOVE THE OUTBOARD’S RECOMMENDED MAXIMUM RPMs“. This means that you should avoid using propellers designed for use with very heavy boats, namely propellers in the low-pitch range.
Note that 20″ long (L) propeller shaft motors typically ship with propellers that are not necessarily optimal for very lightweight boats such as the S4. For example, the 6 HP 20” long (L) outboard from Tohatsu often comes with a medium range 8 pitch propeller, which is fine, but mounted on the S4, such a motor could drive the S4 12% faster if outfitted with a 9 pitch propeller.
Propeller pitch information is available on outboard manufacturers’ websites.
Since the S4 is a very lightweight boat, you should preferably outfit the outboard motor for it with the highest pitch propeller available for it.
Diameter – Don’t try to use a propeller from a small outboard with a bigger outboard, or vice versa.
Hydrofoils (“Fins”) for the outboard
A hydrofoil is an add-on device attached to the outboard motor’s propeller shaft (a.k.a. “leg”). The hydrofoil generates lift at the boat’s stern – The higher the speed the more lift. Hydrofoils can help correct various problems that a powerboat may have, but the S4 has no problems that require correction. This said, hydrofoils help keep the bow down and the stern higher, and a boat that travels this way, namely in a more level position, planes better than if its bow was higher and stern lower. Therefore, outfitting your S4’s outboard motor with a hydrofoil device can result in higher speed on flat water when driving in a solo mode, that is without a passenger in the front. The downside of using a hydrofoil is that when driving with a lowered bow in the ocean, the boat might generate more spray as it bumps into big waves, especially if there’s a passenger in the front. Bottom line: If you like driving solo at high speed on flat water, consider adding a hydrofoil, and if you need to drive in big waves with the hydrofoil on, trim the motor less aggressively by using its trim angle adjustment rod, or knob, especially if you have a passenger on board whose presence also works to lower the bow.
SMALL PORTABLE OUTBOARD MOTORS
For the S4, small size means a highly portable but under-powered outboard motor.
2 HP outboards
Outboard motors in this class weigh around 30 lbs, which makes them fully portable even for a user who’s not very strong. A 2 HP motor can propel an S4 skiff with one person on board at speeds up 8 mph, even in choppy water. This speed would decrease as the boat is required to carry more passengers on board. S4 owners who tested such motors with their S4 skiff reported that the boat felt under powered, which means that they felt like going faster, but the motor lacked the power required for this. For this reason 2 HP motors are not popular with S4 users. Another reason for their lack of popularity is the fact that being air cooled makes these small motors noisier than bigger, water cooled motors.
Propeller pitch – The Honda 2.3 HP comes with a 4.75 pitch propeller
MEDIUM SIZE PORTABLE OUTBOARD MOTORS
For the S4, a medium size outboard motor means powerful enough but still portable. Motors in this 3.5 HP to 6 HP range are the ones we recommend for most users.
3.5 HP outboards
Outboard motors in this range weigh around 40 lbs, which makes them still portable, but less so than 2 HP motors. A 3.5 HP motor can propel an S4 skiff with one person on board at speeds up to 11 mph, even in choppy water, and it can propel the boat at 8 mph with three passengers on board in moving water. This size motor is popular among S4 and W700 users, as it offers a good trade-off between power and weight for people who must lift the motor or carry it by hand over long distances. These motors are also less expensive than bigger ones.
Propeller pitch – For their 3.5 HP motor, Tohatsu recommends either the 7 pitch (Plastic) or 6 pitch (aluminum) propellers, for lightweight boats such as the S4 (under 500 lbs). We say get the 7 pitch propeller, unless you think that you need the more durable aluminum propeller.
6 HP outboards
Outboard motors in this range weigh around 60 lbs, which makes them portable only over short distances, and not for everyone. A 6 HP motor can propel an S4 skiff with one person on board at 17 mph, and it can propel the boat at 12 mph with three passengers on board. 6 HP is the second most popular motor size among S4 users.
Propeller pitch For their 6 HP outboard used with lightweight boats up to 500 lbs (such as the S4), Tohatsu recommends their 9 pitch propeller. The 8 pitch propeller would work too, especially if you intend to have the boat fully loaded, so that it would weigh over 500 lbs in total.
BIGGER OUTBOARD MOTORS
8 HP to 10 HP outboard motors are too heavy to be carried by hand, and they may be too powerful for inexperienced drivers to use safely. However, some of them come with electric start instead on manual start, which is a nice feature. They also come with an alternator that can serve to power small electric devices on board.
8 HP outboards
Outboard motors in this class weigh between 65 and 80 lbs. At such weight, these motors can no longer be considered as portable, and the main reason to use them is the fact that are offered with electric ignition, which eliminates the need to start them by pulling a cord. People who like driving at high speed may prefer these motors to less powerful ones. The S4 outfitted with an 8 HP motor performs well in choppy water, but it could feel over powered for an inexperienced driver, which should avoid using such motors with their S4. Heavy users may benefit from driving with a U-jointed tiller extension, in order to move some weight forward from the stern towards the middle of the boat.
Note that these bigger motors don’t come with an integrated fuel tank, but this isn’t necessarily a problem, since external fuel tanks can fit inside the S4’s hulls.
9.8 HP and 9.9 HP outboards
We tested the S4 with a 9.8 HP Tohatsu and a 9.9 HP Yamaha outboard, and it worked well. Practically, this class of heavier and more powerful motors offers no advantage over smaller motors unless you’re a speed fan, and you’re also capable of driving small boats safely at such speeds. To those who want to take the risk of overpowering their S4 with such big motors, we recommend reinforcing the mounting plate.
This video shows an S4 powered by a 9.8 HP Tohatsu motor filmed from the deck of an S4 powered by a 5 HP Tohatsu motor:
Currently, the S4 is the world’s fastest designated kayak. The 17 mph kayak speed record was achieved by Captain Larry Jarboe, of Key Largo, Florida, in his S4 outfitted with a 9.8 HP Tohatsu outboard motor.
We recommend that inexperienced drivers avoid using high power motors with their S4. Instead, they should pick a motor within the 3.5 HP to 6 HP range.
OUTBOARD MOTOR BRANDS
After years of testing motors and getting input from our clients, we can recommend all Japanese brands, namely Honda, Suzuky, Tohatsu and Yamaha. Mercury is a Tohatsu brand, and the small, portable motors offered by Evinrude are made by Tohatsu. Motors from all these brands are good, and your decision about which motor to use with your S4 should be based on factors such as price, weight, features, availability, warranty, etc.
A kicker motor is a name given to any outboard gas motor used on a big boat for trolling, or as a spare motor, and for positioning and driving sailboats over short distances when sailing them is not possible. Being used on bigger boats, kickers often feature a 20″ long (L) shaft, which is the right size for the S4, but the propellers used with them are typically low-pitch models that are not optimal for lightweight boats such as the S4. If you buy a kicker, check its propeller, and if it’s not a model with the highest pitch that the manufacturer recommends for lightweight boats, replace it with such a propeller.
MUD MOTORS – SURFACE DRIVES
Most motors feature a surface drive, and they offer a huge advantage to people who want to drive in very shallow water, mud, water with many underwater obstacles, and water with plenty of vegetation. Mud motors are bulkier and heavier than regular outboard motors of similar power.
3 HP motors
A 3 HP long tail mud motor weighs about 40 lbs, and as such it’s portable. It works well both in flat water and streams, although not very fast ones. The S4 can definitely use much more powerful motors.
6.5 HP motors
A 6.5 HP mud motor weighs around 80 lbs, and it’s not portable. The reasons you’d want to use such a motor instead of a regular outboard of similar power are if you need to go in very shallow water (skinny water) and mud, and if you fish or hunt in water with plenty of vegetation and underwater obstacles. The S4 performs very well with a such a mud motor. We do not recommend using less powerful mud motors because typically, these motors require more power than regular outboard motors do.
Electric outboard motors
Typically, electric trolling motors are not powerful, and they are designed to propel heavier boats than the S4 (e.g. bass boat, skiff, Jon boat) at a very low speed, namely trolling speed. This type of application requires high thrust (small pitch) propellers, and it’s also the reason why trolling motors are rated in thrust units (lbs) and not in horsepower (HP or KW) – When you buy such a motor, your primary interest is how big (heavy) a boat it can move, and not at what speed.
Some electric trolling motors are described by their manufacturers as “outboard motors”, namely comparable in performance to small outboard gas engines. If you’re interested in such electric motors, we recommend comparing apples to apples namely power units to power units, and not power to thrust, which is meaningless. Remember the laws of physics, and apply the formulae for Kilowatts to Horsepower conversion, which are:
This article is an attempt to answer some questions that Wavewalk skiff owners ask in the process of choosing an outboard motor for it –
Short shaft or long shaft?
We definitely recommend using outboards that feature a long (20″) propeller shaft, and for multiple reasons, which are discussed in this article entitled Outboard motor propeller shaft length for Wavewalk fishing kayaks and boats » We recommend not to be tempted by the availability and lower price of 15″ short shaft outboard motors, because such motors don’t fit the W700, and using one would never produce optimal results, even for a highly skilled individual with a lot of experience in boat outfitting.
Here is a list of long (L) 20″ shaft outboard motors currently available in the 2 to 6 horsepower range, and their HP rating:
Water cooled motors are quieter but heavier than comparable air cooled motors. The only motor featuring on the above list that’s not water cooled is the Honda 2.3 HP. It is very lightweight, and works very well, but being air cooled makes it considerably noisier.
Note: Outboard motor manufacturers recommend flushing the motor’s cooling system with fresh water after every trip in saltwater. It’s possible to flush an outboard with a garden hose outfitted with a special adapter.
4-Cycle or 2-Cycle engine?
Nearly all new small motors on the market are 4-Cycle (4-stroke) and not 2-Cycle (2-stroke). The advantage of the 4-Cycle system is twofold –
The motor runs on regular fuel, and there is no need to mix it with oil.
A 4-Cycle motor is cleaner, namely it emits far less stinky fumes than 2-cycle motors do.
Some experts argue that for the same displacement of its combustion chamber (cc, volume, size), a 2-Cycle engine in more powerful than 4-Cycle one, but we think that convenience and fresh air are more important.
electric or gas?
Many Wavewalk owners outfit their W500 and W700 with electric motors in the 30 to 50 lbs thrust range, and some go as far as 70 lbs thrust. They use their electric kayaks and skiffs for assisted paddling, recreation, touring, trolling, fishing, snorkeling, etc., but we prefer not to include electric motors in our list of “real” outboard motors for two reasons, which are:
Power – Although some small electric motors are offered as “outboard motors”, just looking at their basic, objective power rating makes us think that they are too weak. Kilowatts to Horsepower conversion: 1 KW = 1.34 HP, and 1 HP = 0.745 KW. Consequently, an electric motor can work well on flat water and at a moderate speed, but not necessarily in adverse conditions, namely strong current, strong wind, etc.
Range of travel – A gallon (3.8 liter) of fuel costs a few dollars, and it’s enough for a typical small outboard motor to run for 4 hours at a high RPM, or an entire day at a lower RPM. You can refuel a small outboard’s built-in fuel tank when you’re on board your Wavewalk®. You can take several gallons of fuel with you on a long camping trip, and you can buy more fuel almost everywhere, while recharging an electric motor’s battery can take half a day. Therefore, gas outboard motors offer a reliable and convenient solution whose price / performance ratio is unbeatable by any electric motor available today.
All small outboard motors listed above are considered to be Portable. However, between the 29 lbs of the 2.3 HP Honda and the 59 lbs of the 6 HP motors there is a considerable difference, if you need to carry the motor by hand over a distance.
The shallow water position
Most of the small outboard motors listed here offer to lock their propeller shaft in an intermediary position between the vertical (down) and horizontal (up) positions. In this intermediary, slanted position, the propeller drafts less than in the vertical position, and this allows for driving the boat at a moderate speed in very shallow (‘skinny’) water. Therefore, if you’re looking to fish in skinny water, we recommend that you look for this feature.
gear shift lever
Most outboard motors on our list feature a gear shift level, and this is a good thing, because the alternative is a centrifugal clutch that lacks an absolute neutral position. The absence of a full neutral gear can make starting the motor a little tricky, if you’re a beginner. Our preference goes to the outboard motors that feature the gear shift lever at the front, rather than on their side. The frontal position makes it easier for the driver to access the lever whether the motors points left or right, and even if the driver is facing forward.
built-in fuel tank
All the above listed outboard motors come with a built-in (integrated) fuel tank, and this is a convenient feature considering the alternative is to have a fuel line run from a separate tank to the engine. When you operate such a small craft as a Wavewalk, simplicity becomes increasingly important.
The propellers that come standard with these outboard motors fit Wavewalk’s kayaks and portable skiffs. Typically, these motors propel much heavier boats, which is why the propeller’s diameter and pitch which determine output in terms of speed and torque are of no real consequence to the owner of a Wavewalk under normal conditions.
price and brand
All the brands listed above are known to produce quality motors, and in fact some of them produce motors for others. For example, Mercury is a Tohatsu brand. This is to say that we see no reason to pay more for a particular name brand, and we recommend to consider only the motor’s technical attributes, and its price.
HP rating – can i overpower my skiff?
6 HP is the absolute maximum for which the W700 is rated, and this is only for its RIB model. Overpowering your Wavewalk can be hazardous, and if you use the wrong motor mount you’d be calling for trouble. This said, if you happen to own a 20″ shaft 5 HP motor and your W700 is rated for a 4.5 HP motor, you can keep your motor, and you won’t necessarily have to get a new one. Similarly, if your W700 is rated for up to 4.5 HP and you found a nice 4 HP that you like, you’d be fine with it.
If you choose to make a DIY mount for an electric trolling motor, chances are that you’ll succeed, since these motors are so weak that they’re not likely to cause trouble. But this is not the case with the gas outboard motors in the range that features on the above list. There are several issues to overcome with motor mounts, and the motor’s weight is the least of them. The main problem is that operating at the end of a 20″ lever, the motor’s propeller generates a great amount of torque, especially at high speed, in rough water and when making sharp turns at high speed. This torque can twist and crack a 4×2 timber, and pull out nails and screws from their place. After having seen motor mounts get broken by outboard motors ranging from 6 to 3.5 HP that were mounted on them, we strongly recommend not to build a DIY motor mount for these motors, and to use only the motor mounts that Wavewalk recommends.
Some of the more powerful outboard motors listed here can be outfitted with an alternator and an AC to DC converter. Note that such accessories cost hundreds of dollars. The electric current produced by this system can be used to power lights on board, or to charge a trolling motor’s battery. Such setups are common in bigger boats (e.g. bass boats) that feature much more powerful motors. Although some Wavewalk owners have outfitted their W700 with two motors (a powerful one for driving and a small one for trolling), we don’t know of anyone who’s outfitted their outboard motor with an electric current generation system.
Why an outboard motor?
Skiffs, Jon boats and other small boats sometime come with other motors, among which are air drives or air motors (large diameter propellers) for running marshes and flats, jet drives (similar to personal watercraft, a.k.a. jet-ski), long shaft mud motors for going in shallow water and over obstacles, and outboard motors that run on propane.
While each of these motors offers certain special advantages, and we’d love to see the W700 outfitted with any of them, as well as with other propulsion systems ranging from sails to oars, and even pedal drives… we think the common small outboards such as we listed here offer the optimal mix of price, performance, reliability, versatility, ease of use, and ease of maintenance – Just think how common are boat dealerships and repair shops that service these motors… And if you know how to use your outboard motor and you take care of it, it’s truly a wonderful thing that you’d enjoy for years, and possibly even decades.
Wavewalk will no longer support the installation of any outboard motor whose propeller shaft is shorter than the standard 20″ long (L) on its W500 fishing kayaks and W700 portable boats.
How to measure an outboard motor shaft’s length?
An outboard motor’s propeller’s shaft length is measured from the top inner side of the motor’s clamp bracket to the horizontal anti-ventilation plate located above its propeller. Read more about how to measure this length precisely »
The outboard motor industry has determined four standard lengths for outboard motor shafts, which are:
15″ (S) “Short”
20″ (L) “Long”
25″ (XL) Extra Long
30″ (XXL) Extra Extra Long
For both the Wavewalk 500, 700 and 4 series, the length we recommend is 20″ (L).
What’s wrong with short shaft outboard motors?
Depending on the type and quality of the motor mount’s installation, the use of shorter shaft motor (electric or gas) can result in any of the following problems:
Motor mount’s mounting plate too high – Strong vibrations and loss of power due to ventilation that occurs when the propeller rotates at high speed too close to the surface, and its top part goes through a mixture of water and air bubbles coming from the surface.
Motor mount’s mounting plate is too low – The motor mount’s mounting plate’s lower side scoops water and generates excessive spray, some of which can find its way to the back of the cockpit, and some to the top part of the motor.
Motor mount too far behind the cockpit – Access to the motor’s controls is not easy, including for starting it, shifting gears, using the choke button, and refilling gas. Driving is harder too. The driver is forced to drive from the cockpits rear end, instead of driving from the middle of the cockpit.
Motor mount’s mounting plate too low, and mounting plate too close to the cockpit – The motor’s top part is prevented from tilting downward in case the lower part of the propeller hits bottom or a submerged object and gets pushed upward automatically, in order to avoid damage. If this basic safety function is disabled, the propeller is exposed to severe damage, and so is the propeller shaft.
For the above stated reasons, Wavewalk does not recommend using any motor, electric or gas powered, whose propeller shaft is shorter than the 20″ (L) standard length.
Why does Wavewalk restrict its support now?
In the past, Wavewalk supported owners’ efforts to outfit their W500 kayaks with short-shaft motors. This policy stemmed from the fact that long-shaft motors in the 2-3 HP range are harder to find than short shaft ones, and we don’t recommend more powerful motors for the W500 series. Installations of short shaft motors on Wavewalk kayaks and boats worked, but they were sub-optimal, since there is practically no way for a 15″ setup to match the performance and convenience that a 20″ outboard offers when properly mounted on a Wavewalk.
Last year we came out with the W700 series that’s compatible with several 20″ (L) outboard motors up to 6 HP, which is to say that since then, Wavewalk owners benefit from a much wider choice of outboard motor models.
Currently, the only outboard motor under 3 HP that we recommend is the lightweight, air-cooled 2.3 HP 20″ (L) 4-Cycle Honda. Several outboard brands offer water-cooled, long shaft (L) motors in the 3.5-6 HP range, and our preference goes to Tohatsu, since these outboards (also sold under the Mercury brand) feature a gear shift lever in the front side of the motor, where it faces the user, which makes them easier to use. Other 20″ (L) quality portable motors in the 3.5-6 HP range are offered by Yamaha, Honda, Suzuki, Evinrude (6HP only), etc.