Tag Archive: 5 hp outboard

5-hp outboard for fishing kayak

How much HP for my S4 skiff’s outboard motor?

This article summarizes research performed by Captain Larry Jarboe, as well as inputs from Wavewalk dealers and S4 clients. Its purpose is to answer a frequently asked question (FAQ) from prospecting clients, which is “What outboard motor should I choose for my S4?”

The answer is that the outboard motor you should choose for your S4 depends on two factors, which are

  1. How much power you need
  2. How important is the motor’s weight for you

And there is a trade-off between power and weight, namely that the more powerful the motor, the heavier it is, and the harder it could be to carry it.
In any case, the motor should be a 20″ log shaft (L) model, and not a 15″ short shaft (S) model.

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 powered 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 them noisier than water cooled motors.

3.5 HP outboards

Outboard motors in this class 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 14 mph, even in choppy water, and it can propel the boat at 12 mph with three passengers on board in  moving water. This size motor is the most 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.

6 HP outboards

Outboard motors in this class weigh around 60 lbs, which makes them portable only for very short distances, and not for everyone. A 6 HP motor can propel an S4 skiff with one person on board at speeds up 18 mph, and it can propel the boat at 14 mph with three passengers on board. 6 HP motors are the second most popular motors among S4 users.

8 HP outboards

Outboard motors in this class weigh around 80 lbs. At such weight, these motors can no longer be considered as portable, and the only reason to use them is the fact that they are offered with electric ignition, which eliminates the need to start them by pulling a cord. 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 to the middle of the boat.

6.5 HP mud motors

Mud motors are bulkier and heavier than regular outboard 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

Some electric trolling motors are described by their manufacturer as “outboard motors”, namely comparable in power to small outboard gas engines. If you consider such electric motors, we recommend remembering the laws of physics, and applying the formulae for Kilowatts to Horsepower conversion, which are:

  • 1 KW = 1.34 HP
  • 1 HP = 0.745 KW

 

 

 

 

 

 

Three boats, six hulls, one outboard motor, four divers, and one captain & guide

By Captain Larry Jarboe

Florida Fishing Kayaks

 

 

 

A Wavewalk 700 attached on each side of an S4 powered by a 5 HP outboard motor.

 

 


 

Larry offers guided fishing and diving trips in the Key Largo and the areas that surround it »

More fishing adventures with Capn’ Larry »

Wavewalk S4 on diving trip

By Captain Larry Jarboe

Florida Fishing Kayaks

 

Motorizing in the open sea and paddling in the no motor zone.

 

 

 

 


Larry also offers guided fishing and diving trips in the Key Largo and the areas that surround it »

 

More fishing adventures with Capn’ Larry »

Wavewalk S4 first sea trial on windy day, with 5 HP outboard motor, Key Largo. Video and review

By Captain Larry Jarboe

Florida Fishing Kayaks

Some thoughts about the Wavewalk S4

 

Beautiful lines!  It may be the Cadillac of kayaks but it looks like a seagoing Corvette.  Is it a high performance motor yak or a portable runabout?
Super stable.  Because it looks so seaworthy, most other powerboats do not slow up when passing port to port.  No problem.  The S4 slides through wakes easily without leaving planing mode.
It seems to run a little faster than the W700 with the same motor.  I believe the wider hulls act like a pair of skis to help the boat skim across the water.  Handling tiller, camera, and a GPS at one time is beyond my skill set.
Tracking through turns while planing is wonderful.  The boat’s stern does not slide like many skiffs do.
The S4 is so easy to spin your body to face the outboard motor because the hulls are so wide.  You can keep your feet inside the vessel.
Also, the S4 is the perfect vessel for folks who are tired of maintaining their leaky inflatable tenders.  Or, people who want a lifeboat that can be used for shade or transport, too.
I still think the W700 is the boat that does it all, but the S4 is the boat that does it all, and more!

The video shows 15-20 knot wind close chop.  No problem.  Try paddling against this.

Larry J.

 

P.S. – This boat could make a run from South Florida to Bimini.  But, for the time being, I will be staying in waters managed by our Country.

 

 

 

Wavewalk S4 in gray with 5 HP Nissan (Tohatsu) outboard motor. Photo shot on the mother ship.


Larry also offers guided fishing and diving trips in the Key Largo and the areas that surround it »

 

More fishing adventures with Capn’ Larry »

Testing 15″ short (S) shaft outboard motor performance with Wavewalk kayaks and boats

This article summarizes the research that Captain Larry Jarboe, of Florida Fishing Kayaks and Boats in Key Largo, Florida did on this subject, and we are very grateful to him for this exceptional contribution.

Background –

 

Larry’s main goal in conducting this series of experiments that lasted for several weeks was to find the “sweet spot” for 15″ (S) outboards, namely a setup that would enable him to successfully outfit W500 and W700 boats with such motors, which are typically cheaper and easier to come by than 20″ (L) motors.
His secondary goal in running these extensive tests was to check the performance of Wavewalk’s TMM 700 HD motor mount, and see if we could improve it.

Larry is a passionate fisherman, mechanic, and seaman. He works as a commercial fisherman and fishing guide, and he is Wavewalk’s distributor in Southern Florida.
For the past fifty years, Larry has been involved in using, building, refurbishing and testing motors in various land and water vehicles, including electric racing cars, regular cars and trucks, a wide range of small watercraft, and big diesel engines in stern-drive commercial fishing boats, such as he still operates in Key Largo.

Means and Method –

 

In his tests Larry used five portable outboard gas motors that he had refurbished and tuned himself. Some of the motors had 15″ short shafts, and the others had 20″ long ones, and their horsepower rating ranged from 2 HP to 5 HP. He also tested a couple of electric trolling motors.

Larry conducted his experiments systematically – Being a handyman as well as a mechanic, he built a series of transom motors mounts that enabled him to mount outboard motors of both sizes in various places at the boats’ stern.
In his tests, he changed the height of the mounting plate, and/or its distance from the cockpit’s rear end.

Results –

 

There is no “sweet spot” for mounting a 15″ short (S) shaft motor on a Wavewalk, and any configuration involving the use of such size motor would inevitably result in sub-optimal performance compared to the use of a 20″ long (L) shaft outboard motor of the same power.

The main problems that Larry found with 15″ short (S) shaft outboard were the following:

Ventilation

 

Outboard manufacturers recommend mounting outboard motors with their anti ventilation plate (sometimes called “anti-cavitation” plate) immersed a couple of inches below the boat’s lowest point, which by definition is always immersed. This inevitably means that the anti ventilation plate is several inches below the surface. If the propeller rotates with its blades too close to the surface, it sucks air from the surface, and instead of rotating in water it rotates in a mixture of water and air bubbles. As a result, the propeller loses efficiency and power.

  1. At higher speed – Larry found that with 15″ short (S) motors, ventilation started to occur at about 5 mph, when the boat was transitioning from a displacement mode into a semi-planing mode, and its hulls were slightly raised, thus pulling the propeller upward and too close to the surface. The higher the speed the more extensive the ventilation and power loss. No ventilation occurs with 20″ long (L) shafts, even at speeds higher than 12 knots (13 mph), when the boat is in a full planing mode.
  2. When making sharp turns – Larry found that the 15″ short (S) motors’ propellers sucked air from the surface while he was making sharp turns. This happened since the boats tilted on their side, and the propellers got too close to the surface. In this case, ventilation resulted in loss of power as well as loss of control, to some extent, which made turning more difficult. Such problem did not occur with 20″ long (L) shaft motor, which performed flawlessly in sharp turns at high speed.

Splashing and discomfort

Splashing – In order to avoid ventilation, it is possible to mount 15″ short (S) shaft outboards at a lower level, with its propeller immersed more deeply. This can be done when a specially designed motor mount is placed several inches behind the cockpit’s rear end. However, at such position, the lower part of the motor mount’s vertical mounting plate is too low and too close to the surface of the water, and it will come in contact with the water. In such cases, the result is spray splashing over the motor’s head and into the cockpit’s rear end. No such problems occur with 20″ long (L) shaft outboard motors when mounted correctly on a standard Wavewalk motor mount.

Discomfort – When the 15″ short (S) outboard is mounted several inches behind the cockpit’s rear end, it is harder for the user to reach the motor and its controls (e.g. choke knob, starter grip), and it is harder for them to steer. This is not the case with 20″ long (L) motors that are mounted at the rear of the cockpit.

Bottom line

 

There is no “sweet spot” setup that allows for mounting a 15″ short (S) shaft outboard on a Wavewalk (500 or 700) without it incurring serious drop in performance. The way to motorize a Wavewalk is to follow the recommendations of outboard manufacturers about mounting their motors, as well as Wavewalk’s recommendations that fully coincide with them, namely to use only 20″ long (L) outboard motors with Wavewalk’s kayaks and boats.

 

A sweet spot, sort of…

 

When Larry checked 15″ short shaft, weak electric motors, he found that the ventilation problem at higher speed didn’t occur, because such motors lack the power to propel a kayak at speeds that are high enough to make it reach a semi-planing mode, or have the propeller suck in air from the surface. Knowing about such a sub-optimal performance envelope, the user already expects sub-optimal performance. This said, this rule is not ironclad, and ventilation may still occur in case the boat makes a sharp turn.even when it is propelled by such weak 15″ short electric motors, and while going at low speeds.

This is to say that Wavewalk recommends not to use short shaft motors even in the case of weak electric trolling motors.

In sum, the only propeller shaft size that we recommend for all types of motors is 20″ long (L)

 

More reading:  How to measure an outboard motor’s propeller shaft length? »