Page 48 – STABLE KAYAKS AND MICROSKIFFS MADE BY WAVEWALK

Updated October 22, 2024

1. BEST MOTOR FOR MY MICROSKIFF

The three primary factors to consider when choosing a motor for your microskiff are Power, Weight, and Propeller Pitch

Our choice is either a 6 HP outboard gas motor for max power and speed, or a 3.5 HP motor for min weight and max portability.
For all motor sizes, we recommend a new 4-cycle motor, and not a used 2-cycle motor.
In this range of portable outboards, the ratio of weight to power is around 10 lbs for 1 HP.
For a 6 HP motor, we recommend the Tohatsu and Mercury brands, because they enable outfitting their motors with an 8″ or a 9″ pitch propeller, which is higher than the other 6 HP outboard brands offer. The higher the pitch the higher the speed, and a low pitch propeller can create problems. Motors from these two brands also have the best Power to Weight ratio in this 6 HP class.
For a 3.5″ HP motor we recommend the 20″ Long shaft Tohatsu and Mercury, since they have the best Power to Weight ratio for this size.
The S4 works only with 20″ Long (L) propeller shaft motors.
Electric motors work for slow cruising and trolling in ponds, small lakes, and slow moving rivers, but not for moving water, long trips, and a fully loaded boat.
We strongly recommend outfitting your outboard motor with a U-jointed (articulated) tiller extension that will allow you to drive fully facing forward, and/or standing up, and from the middle of the cockpit instead of its rear, and thus optimize trim and maximize speed.
We recommend not to exceed the 6 HP for which the S4 is rated.

Note that some 6 HP outboard models come outfitted with an alternator that can produce the electric power that you need on board for lights, and for recharging the battery of a trolling motor.

Top Speed

An S4 Microskiff running a new 6 HP 4-cycle outboard motor outfitted with an 8″ pitch or 9″ pitch propeller, and driven from the middle of its cockpit with a long articulated tiller extension for best trim (no hydrofoil, no trim tab), should move you on flat water at speeds around 16 mph with just the driver on board, and providing this driver is not very heavy . BTW, adding these accessories won’t increase your speed.
Since the S4 is so lightweight, and 6 HP isn’t very powerful for an outboard motor, expect different results for drivers of different weight.

Power

How much power you need: How fast you want to go, in what kind of water, and how many passengers you’ll have on board
How important to you is the motor’s weight.

There is a trade-off between power (I.E. Speed) and weight (Portability), namely that the more powerful the motor, the heavier it is the harder it is to carry it.
In case of motors that exceed the 6 HP recommended max power, the additional weight would reduce portability, require additional trimming and outfitting work, and yield only little gains in speed.

In any case, your S4 must feature only a 20″ long shaft (L) outboard motor.
Do not use a 15″ short shaft (S), or a 25″ extra-long (XL) shaft motor.

Propeller Pitch

Another important tradeoff 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 (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 propel the S4 a little faster if outfitted with a 9″ pitch propeller.

Propeller pitch information is available on outboard manufacturers’ websites.

Since the S4 microskiff is a very lightweight boat, you should preferably outfit the outboard motor that powers it with the highest pitch propeller that’s available for it.
8″ pitch and 9″ pitch propellers work best with the S4.

Propeller Diameter

Don’t try to use a propeller from a small outboard with a bigger outboard, or vice versa.

Gear Ratio

Gear Ratio refers to the ratio between engine revolution (RPM) and propeller revolution. A higher gear ratio means that the motor revolves more times in order to generate one revolution of the propeller, which results in a higher torque. But high torque is beneficial for propelling heavy boats, and it is not very useful for propelling small and lightweight boats such as the the S4. In speed terms, S4 users would benefit more from motors with a lower gear ratio.

About Portable Outboard Motors

For your S4 microskiff, 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.

The typical Power to Weight ratio of for this range of motors is about 10/1, namely 10 lbs to 1 HP. For example, a 3.5 HP outboard should weigh about 40 lbs, and a 6 HP outboard around 60 lbs. If the motor you found has a Power to Weight ratio that’s very different from this, keep looking…

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 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 3.5 HP motors –
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 recommend the 7″ pitch propeller, unless you think 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 15 mph, and it can propel the boat at 10 mph with three adult passengers on board.
6 HP is the most popular motor size among S4 users.

Propeller pitch for 6 HP motors
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 works too, especially if you intend to have the boat fully loaded, so that it would weigh over 500 lbs in total.

We do not recommend the 6 HP Suzuki, because it comes with a 6.75″ pitch propeller and no propellers with a bigger pitch are available for it. The same is true for the Honda 5 HP.

The 6 HP Tohatsu and Mercury (and Evinrude) motors can be outfitted with a 9″ pitch propeller, which is why we recommend getting one of them for your S4. If you already own a 6 HP Yamaha, you could keep it, as long as you make sure it’s outfitted with the 8″ pitch propeller that fits it, which is biggest pitch offered for this model.

Integrated or External Fuel Tank?

Most small, portable outboard motors come with a integrated fuel tank. Typically, such tank can hold 1 quart (0.9 liter) of fuel. Since these small motors consume very little fuel, such small size tank can suffice for a short trip (30 minutes with a 6 HP motor) at full throttle, or for a longer trip at a slow speed, e.g. when trolling, or cruising.

An integrated fuel tank can be easily refilled from a small portable fuel tank: Just turn off the motor in case it is still on, turn around to face it, grab the fuel tank, open the cap on top of the motor, fill it in, screw the cap back in place, restart the motor, and keep driving. Such refueling takes less than a minute, and it can be performed even in choppy waters.

The inconvenience in using an integrated fuel tank is that you can run out of fuel without warning, in a situation when you’d prefer not to stop for refueling. The advantage of these tanks is that they have less problems, compared to external tanks that feed the motor through a fuel line, a pump, and a filter.

The big advantage of an external fuel tank used in combination with a small motor is that it allows you to run for many hours without caring about refueling.
For example: The 6 HP Tohatsu outboard can run at full throttle for about 30 minutes on the fuel that’s in its integrated fuel tank, or for a couple hours at low RPM. In comparison, a 3 gallon external fuel tank should suffice for 6.5 times more time than this.

The 3 gallon fuel tank that ships standard with the 6 HP Tohatsu fits perfectly at the bottom of the S4 hull, and since the density of gasoline is 3/4 that of water, the tank will simply float in case a lot of water gets into the hull.
Alternatively, using bungees, you can attach your external fuel tank on top of the saddle seat, either behind or in front of you.

OUTBOARD MOTOR BRANDS

After years of testing motors and getting input from our clients, we can say that Honda and Yamaha have good motors, but we recommend Tohatsu and Mercury motors, which are made by Tohatsu. The reasons for this include a better power to weight ratio, higher pitch propeller available, and the convenient location of the gear shift lever in the front of the motor, facing the driver.

UPGRADING A MOTOR’S HORSEPOWER

Some outboard motors can be upgraded to generate more horsepower. For example, from 3.5 HP to 5 HP.
Upgrade kits are inexpensive, and installing them isn’t very hard.

The advantage of such upgrade is financial, I.E. buy a lower cost motor and get the power of a higher price one, and sometimes a better power to weight ratio, namely buy a lightweight motor and get the power of a heavier one.
However, before you decide to buy a low HP outboard motor and outfit it with an upgrade kit, you’d better make sure that your motor can take a propeller with the diameter and pitch that the higher HP motor is suitable for. If this is not the case, you might find yourself with a very powerful motor that rotates a small diameter and low-pitch propeller ineffectively, and possibly even at speeds that are too high, which means exposing the motor to a risk of serious damage.

PROPANE OUTBOARDS

These outboard motors are cleaner than regular gas (fuel / benzine / petrol) outboards, and less prone to develop problems in their ignition and fuel systems. Their disadvantages in S4 terms is in the fact that typically, getting an extra bottle of propane takes more time than filling a fuel tank with gas from the pump.

4-Cycle or 2-Cycle motor?

In the US, outboard motors manufacturers are no longer allowed to sell 2-Cycle (2-Stroke) motors, but used 2-Stroke motors can still be found on the secondary market, typically on Craigslist.

Most used outboard motors are not in great shape, and they often require refurbishing, or at least a serious update. On top of this, since these motors have been used for years, and therefore all their sub-systems and components were subject to wear and tear, it is unlikely that they can still deliver the horsepower that they generated years ago, when they were brand new. The typical used 2-Stroke outboard is considerably weaker than what its HP sticker says.

So, unless you’re a good mechanic and you found a truly clean 2-Cycle outboard, your best bet is buying a brand new, or almost-new 4-Cycle outboard.

Two Motors Bass Boat Style

Some S4 owners outfit their boat with two motors – A powerful outboard gas engine at the stern, and a bow mounted stealthy electric trolling motor. This setup is typical to bass boats, skiffs, and Jon boats.

Wavewalk S4 portable microskiff powered by two motors: a 6 HP outboard gas engine and a front electric trolling motor:

Motorized S4 kayak skiff with outboard gas engine and front electric trolling motor — Photo courtesy of Mike Silva, MA

2. ACCESSORIES FOR YOUR MICROSKIFF

Highly recommended: U-Jointed (articulated) tiller extension

We recommend getting a long, U-jointed (articulated) tiller extension that will allow you to drive sitting and standing facing forward, at a bigger distance from the stern, so as to reduce the weight there, and lower the bow, namely improve the boat’s trim. Doing so would make the S4 more level, and improve its speed.

U-jointed tiller extension — U-jointed (articulated) till extension

Must-Have: Paddle(s)

You need to have at least one paddle on board, for launching, going, and beaching in very shallow water, as well as for maneuvering in tight places. A paddle is also critical in case you experience a problem with the motor, that is as an alternative mode of propulsion.
A canoe paddle is shorter and easier to store on board than a longer kayak paddle, and it would do the job over short distances.

Must-Have: Anchor

Yes, you need an anchor in order to prevent your microskiff from drifting when you have to start your motor in shallow water. This is especially true if you go in the ocean or in moving water, big lakes, etc.
A 5 lbs anchor would suffice for ponds and small lakes, but we recommend a heavier anchor (10 lbs) for more challenging conditions, namely fast rivers and the ocean.
Some anglers who fish in shallow water use a stakeout pole.

This short list does not summarize all you need to carry on board, and you must make sure that your S4 microskiff is properly outfitted and equipped to comply with your state and USCG regulations.

Worth Consideration: Alternator (electric power generator)

Some 6 HP gas outboard models come equipped with an alternator that can produce the electric power that you need on board for lights, and for recharging the battery of a trolling motor.
If your 6 HP outboard does not feature such a device and you’d like to outfit it with one, these are available as add-on kits.

3. ELECTRIC 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 at trolling speed. This type of usage requires high thrust (small pitch) propellers, and it’s also the reason why many trolling motors are rated in Thrust units (lbs) and not in horsepower (HP or KW) – Typically, when you buy such a motor, your primary interest is how big (heavy) a boat it can move, and not necessarily 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 almost meaningless.

Remember the laws of physics, and apply the formulae for Kilowatts to Horsepower conversion, which are –

- - - 1 KW = 1.34 HP
    - 1 HP = 0.745 KW

No amount of words and no marketing hype can overcome this reality.

Thrust vs Horsepower

There are formulae that can help you convert units of Thrust (measured in lbs) to units of Horsepower (HP), but they are somehow impractical, mostly because they require hard-to-find information about electric motors and the performance of their propellers.
Instead, we suggest using the following simplified, approximate, easy-to-use “rule of thumb” formulae, based on calculations made on a number of electric motor of different size, from different manufacturers:

Conversion of HP to lbs of Thrust

- - - 1 HP ≅ 70 lbs of thrust
    - 3.5 HP ≅ 245 lbs of thrust
    - 6 HP ≅ 420 lbs of thrust

Conversion of Lbs of Thrust to HP

- - - 1 lb of thrust ≅ 0.0142 HP
    - 10 lbs of thrust ≅ 0.142 HP
    - 100 lbs of thrust ≅ 1.42 HP

This formula works pretty well for typical electric motors, but it’s not necessarily accurate for a specific motor. The only thing you can be sure about is that the result won’t be very far from reality.

Generally speaking, even a superficial look at these figures would immediately reveal how weak common electric boat motors are, including those promoted as “electric outboards”, namely comparable to outboard gas motors.

Speaking in terms of dollars per HP, a 120 lbs thrust electric motor with enough batteries to supply it with power for a few hours is in fact weaker than an entry level 2.5 HP outboard gas engine that we recommend for the W720 kayak skiff, but deem too weak for the S4.
Furthermore, such electric propulsion package is also heavier and more expensive than a 6 HP outboard gas motor.

What Electric Motor Is Best?

IF YOU INTEND TO USE YOUR BOAT IN SALTWATER, MAKE SURE THAT THE ELECTRIC MOTOR YOU BUY IS RATED FOR SALTWATER

Trolling

For continuous, low speed electric propulsion, namely Trolling, we recommend using electric trolling motors that deliver between 40-55 lbs of thrust, powered by a 12 Volt battery, or a pair of batteries, preferably marine lithium-ion batteries, which are more expensive but lighter than lead-acid batteries.

Cruising

As for high speed electric propulsion… there is simply no such electric motor. Even if you use super expensive electric motors labeled “Electric Outboard” that are rated by their manufacturers at 3 HP or 3.5 HP, you’d barely eke out a 6 mph speed, and at such speed your battery will run out of power in a short time. Bottom line: it’s a non-starter.

Can onboard solar panels power a microskiff’s electric motor?

No. Not even on a sunny day. To generate the electric power needed to continuously move a small microskiff at an acceptable speed, you’d have to install on it solar panels that are bigger than what it could safely carry.

Electric motors are further discussed in the “Electric Trolling Motor or Outboard Gas Engine” section of the article about Motor Kayaks »

4. SURFACE DRIVES (Mud Motors)

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 mud 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 mud 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.

Note that since mud motors work differently from regular outboard motors for which the S4 motor mount was designed, it is particularly important to reinforce the motor mount if you use such a motor.

5. SMALLER OUTBOARD MOTORS

For the S4 microskiff, using an outboard smaller than the minimum 3.5 HP recommended would mean a more portable boat with a downside that it could be under powered –

2.5 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 2.5 HP motor can propel an S4 skiff with one person on board at speeds up to 8 mph. This speed would decrease as the boat is required to carry more passengers. S4 microskiff owners who tested such motors reported that the boat felt under powered, which means that they wanted to go faster, but the motor lacked the power required for this. For this reason 2.5 HP motors are not popular with S4 users. Another reason for their lack of popularity is the fact that air cooled small outboard models are noisier than bigger, water cooled motors.

2.5 HP motor brands and suitable models

Honda 2.3 HP L-Type / The lightest in this class, thanks to the fact that it’s air cooled, which also makes it noisier
Suzuki 2.5 HP 20″ shaft / water cooled and not too heavy
Yamaha 2.5 HP 20″ shaft / water cooled and the heaviest in this class

6. MOTORS BIGGER THAN 6 HP

The S4 is rated for a maximum 6 HP outboard motor, and we do not recommend using more powerful motors, for various reasons –

How faster would my S4 microskiff go with a ∼10 HP outboard motor compared to a 6 HP motor?

Not much faster, actually –
Let’s compare the Tohatsu 6 HP with the Tohatsu 9.8 HP: Both outboard motors have a similar Gear Ratio (2.15:1 and 2.08:1), similar max RPM (5,000 – 6,000), and similar max propeller pitch (9″ and 9.5″). The 6 HP motor weighs 60 lbs and the 9.8 HP motor weighs 85 lbs. There is no reason to assume that propeller slip would be very different, and it’s typically 10%.
Running these numbers in a an online Boat Prop Calculator would return these (theoretical) results:

For the 6 HP with a 9″ pitch prop at 5,500 RPM : 19.6 mph
For the 9.8 HP with a 9.5″ pitch prop at 5,500 RPM : 21.4 mph

Note that actual, real-world boat speed is likely to be lower than these figures due mostly to water conditions and the driver’s weight, which for an average US male is 200 lbs, a figure that equals the combined weight of the boat plus the motor.
The theoretical speed difference between the two motors is about 10%, but the stronger motor has a better chance of yielding results that are closer to its max potential than the weaker motor does, since the latter is more likely to be affected by adverse conditions.

Are the extra 4 HP worth it in the case of the S4 microskiff?

Not necessarily –
The extra power would be useful only if you need the motor to propel a much bigger and heavier boat than the S4 microskiff, for which a 6 HP motor with a 9″ pitch propeller is the optimal configuration for max performance.

If you decide to outfit your S4 with a motor that’s more powerful and heavier than the max recommended 6 HP motor, you will have to reinforce the boat’s transom motor mount, namely the molded-in plastic structure that holds the vertical wooden mounting plate, or risk damage and even accidents.

More reading: Motor Power Rating For Canoes, Kayaks, and Small Boats

Do you have any questions for us about this article?