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Thrust in Electric Trolling Motors for Fishing Kayaks

Thrust is a unit of measurement that manufacturers of electric trolling motors for fishing kayaks and other boats use to describe propulsion capability. Thrust is measured in units of weight. In the USA it’s usually pounds (lb.).

This can be confusing, since we often tend to think of propulsion in motion terms, or in horsepower (HP).

Before going further, we’d better clarify what weight and thrust have in common:

Thrust of an electric trolling motor for a fishing kayak

This (rather crude) illustration shows a small boat on the water.  The boat is equipped with an electric trolling motor and propeller unit whose measurable output is 36 lb.  The boat is attached by a line to a 36 lb weight that’s pulling it backward.  Since the motor unit can provide 36 lb of thrust it will keep the boat in place: It would be strong enough to counterweight the 36 lb weight, but not strong enough to get the boat to move forward.

Once the battery gets weaker and/or the propeller entangled in seaweed the thrust achieved will diminish and the 36 lb weight will drag the boat backwards.

Similarly, if we lifted the propeller out the water it would still thrust the boat forward, but much less so, since it would be pushing against air that’s hundreds of times less dense than the water this propeller was designed to work in… In this case the 36 lb weight would easily win this tug of war.

Note that this simple model describes thrust without using speed terms.

There is no simple formula that can help you convert thrust to horsepower or vice versa, although the terms are closely related to each other when motorized boats are concerned.

In our case Thrust is the directional force resulting from the rotation of a propeller at a certain speed. Different propellers rotating at the same speed will generate different thrust. The same propeller will usually generate more thrust at a higher rotation speed (RPM).

Horsepower is a unit of measurement for power (it’s quite obvious isn’t it?…), which is the ability to do work. Power is described by weight lifted over a distance during a certain time.

1 HP is equal to the power needed to lift the weight of 550 lb over a vertical distance of 1 ft – in 1 second.

Just by looking at these numbers we can sense that not every human is capable of producing 1 HP – not even for a short period of time.  Most of us can produce much less than 1 HP over long periods of time, such as when paddling, biking etc.  Estimates vary from 0.2 to 0.4 HP, but that doesn’t mean much for us as individuals.

So, going back to our illustration, if we had a 1 HP gas engine on top of the dam, and that engine was attached with a pulley to the line holding the 36 lb weight, we would be able to lift that weight up at a staggering speed of over 15 ft per second (550:36 = 15….).

Apples to apples: How can we compare the 1 HP gas engine to our 36 lb electric trolling motor?

We need comparable, that is mutually convertible units of measurement. In this case it’s HP and Watt.  To convert Watts (W) to a horsepower rating (HP) simply multiply the Watts by 0.00134

In other words, a 750 W electric motor (1:00134 = 746…) produces the equivalent of 1 HP.

In boating terms, Thrust would be the result of applying this power to move a boat through the water by connecting the engine to a suitable propeller and letting it move water… In order for such a comparison to make some practical sense we need to assume certain things about RPM, type and condition of propeller, boat size, boat speed etc… It’s really not that easy.

More specifically, when it comes to electric motors for kayaks you shouldn’t be tempted to get a strong motor that would consume your battery power too fast.  If such a thing happens you’ll have to paddle your kayak back with a heavy battery and motor on board…

Read more about motorizing fishing kayaks >>

How to Avoid and Repair Scratches in Your Kayak

Going with your kayak over oyster beds, shells, sharp rocks, broken glass, metal debris and even concrete ramps can get its hull scratched. In most cases such scratches are negligible, and you need not pay attention to them. However, if you want to avoid getting your kayak scratched you’d better watch out for signs of such potential hazards in the water – especially if you’re fishing or paddling in shallow water. Needless to mention is the fact that fishing and paddling from a higher position than ordinary kayaks offer you can help a lot in detecting potential problems in the water ahead of time, that is before hitting them. This is yet another advantage the W Kayak offers you, and W Kayak paddlers and fishermen indeed stand up in their boats from time to time to look at the water around them.

When it comes to repairing scratches in polyethylene kayaks the methods are similar and depend on how deep the scratch is.

For superficial scratches we don’t recommend any treatment, but if you insist on doing something you can just flame the scratch using a hand-held, propane blow torch. You should apply the flame over the scratch slowly and cautiously until it disappears or diminishes considerably, while being careful not to overheat the area so as not to cause a local deformation. In any case, flaming alters the color of the polyethylene to a darker hue.

hand held blow torch for repairing kayaks

 

For deep scratches or ‘grooves’ it’s better to heat the end of a metal spoon and apply the hot tip gently and cautiously along the scratch, thus ‘welding’ the surface. Here too, you need to be careful not to overheat the area you’re working on since this would cause the polyethylene to deform. You’d need to protect your hand that’s holding the spoon with a thick glove since metal conducts heat and you might get your fingers burnt.

Keep the work area free of any flammable materials and make sure you’re not accidentally directing the flame at yourself or at other people. Don’t allow children or pets nearby.

If you’re not experienced in working with a propane blow torch you may want to reconsider such a project because it can be dangerous.

As for cracks in a polyethylene kayak, those are rare, and they must be properly fixed. Just flaming or welding won’t be enough to fix a crack, and you’d need to patch it – preferably with an internal patch that you’ll weld over the entire area. This is necessary since even if welded the hull in the cracked area will be weaker than in other places, and it could reopen while you’re paddling your kayak or fishing from it – with dire consequences. If the crack appears above waterline you can reinforce the patch with rivets, but we recommend not to use rivets when making repairs below waterline because we think that drilling holes in the hull below waterline is simple too risky in the long run.

Paddling Over Submerged Obstacles in Shallow Water

Whether you’re on a paddling or fishing trip in shallow water, you don’t want to have to turn back, or worse – get stuck somewhere because of underwater obstacles. Such obstacles may be rocks, tree roots, fallen branches and fallen trees that prevent you from reaching your destination, be it an interesting place to tour or a promising spot to fish in.

If you have to turn back the W solution is either to paddle backwards, or turn the boat, or turn yourself inside the cockpit and face the direction from which you came from: The W kayak is fully symmetrical front and back and it feels the same paddling forward and backward.

Another strategy you can try is poling with your paddle (preferably the Wavewalk PSP), or going over the submerged obstacle – whether it’s top part is underwater or even a few inches above water:
You position yourself at the back of the cockpit, thus raising your Wavewalk kayak’s bow. Then you paddle forward full speed and try to get the boat to go as forward as possible over the barrier. If you succeeded in getting the middle of the boat pas the obstacle you’re almost there, and you’ll have to move swiftly to the front part of the cockpit and thus make your Wavewalk kayak tilt forward and go over the obstacle.
It may not be as easy as it sounds, but practice makes perfect, and in this case it’s fun too.
It’s also great to know that you’ve gone where no other canoe or kayak could go…
This video shows how it’s done:

Seal Launching your kayak – Sometime It’s Necessary, and It Can Be Fun

Seal launching your kayak can be a good solution if you don’t want to spend too much time looking for a better spot to start your paddling or fishing trip from. You can do it just for fun too.
The kayaker or kayak angler who’s planning to venture into seal launching should cover the front part of the cockpit, at least for the launch.
We advise you to start learning to seal launch on a moderately steep slope, and slide over a shorter distance… You can seal launch from a dock or a deck too.

Also, before you become proficient in seal launching, and when you’re just learning the technique, remember the rule ‘Stuff Happens’, so leaving your cellphone, camera, GPS and fishing gear on shore might be a prudent thing to do.

Have fun!

The following demo video was created by Roxanne Davis, a kayak angler from Connecticut, when she fished from a Wavewalk 500. These days Rox fishes mostly from a motorized W700 –