Help Me Build the Ultimate Kayak

Hi Everyone,

Apologies in advance for the long post.

I’ll start off by introducing myself. My name is Junior; I’m new here and this is my first post. I’m addicted to fishing and love the idea of small personal watercrafts. Yes, big boats are amazing. But there’s something special about being able to throw a kayak on top of the jeep, take it to a remote launch spot and launch it by myself, then still catch the same trophy fish as a 48’ sport fisher… no literally. I hauled in a 45lbs wahoo while trolling on my Malibu X-Factor kayak.

I use my kayak in the Caribbean where I do saltwater fishing. Because the sea is typically windy and has strong currents, I decided to rig my X-Factor kayak with a 2.5hp gas engine. I put a lot of thought and work into it and it came out pretty good. I’m able to go between 7mph and 8.5mph depending on weather conditions and the load that I carry. Initially I was going to build outriggers/stabilizers but I decided not to… I’ve only flipped twice lol. And it was in some serious surf that would flip almost any small to medium vessel. I had the engine serviced, and was back on the water in a couple days after both incidents. No damage to the kayak or the rigging. I have a video of all the modifications I did to the kayak somewhere on my old phone so I’ll try to find that and upload it so you get an idea.

Besides the 45-pound wahoo, I’ve caught kingfish between 10-20lbs, blackfin tuna, and tons of barracuda all while trolling diving plugs. The kayak is a beast.


After building that rig successfully, I want to push the limits on a motorized kayak. I want to cover more ground, go faster, and have a bigger and better suited rig for my fishing needs now.

I have an Old Town Predator XL MinnKota kayak, which is a much better rig that the X-Factor. I also have a 9.8hp Tohatsu 4stroke that weighs 85lbs. Now by itself, I know this will be too heavy to operate on the kayak without some serious modifications to the kayak. It’s not necessarily that the 85lbs is too heavy, it’s that an engine that size will have too much torque/power when in operation. It’s much more likely to flip, or for the back of the kayak to be underwater.

The 2.5hp Yamaha on the first kayak is approx. 40lbs. And many times when I would run it at WOT the back of the kayak would basically be underwater. I had a bilge pump in the back tankwell of the kayak that would be running constantly (during certain weather conditions) to pump out water that was flooding over the gunnels. (This wouldn’t happen on very calm days, but we have very few of those).

The new kayak is a bigger, beefier kayak with a higher weight capacity. It also sits higher out the water. So I know it can handle the 85lbs, it’s just to make something that will stabilize the kayak and also add some lift to the back half of the yak. My plan is to build some heavy-duty stabilizers for the kayak that will also act as mechanism to increase the weight capacity. Here’s my thoughts…


I want to build pontoon-style outriggers/stabilizers that will be about half the length of the kayak. I will mount them at the back half of the kayak as to not interfere too much with fishing and landing fish. What they will be made of is carbon fiber sleeve material, formed over builder’s tube. Not sure what everyone calls it, but I’m taking about that thick cardboard tube that is 8” in diameter that you use to make concrete posts in the ground. I was going to get a 6 foot section of that and slide the carbon sleeve over it and wet it out etc.. then add another layer or 2. I already have the carbon tube, just need the epoxy. The carbon is 12k carbon twill and I have enough to make 3 layers, but I was told 2 layers would be more than enough with that weight.


Since the builder’s tube is hollow, I have 8” of diameter of hollow space for 6’. What I planned to do was add a high pressure float to the inside of the tube. The float has the same 8” diameter and can be pumped up to 21psi. I figure this would give more flotation that just empty space (air) at atmospheric pressure. Does this reasoning make sense? Will it actually add more weight capacity and/or flotation to the overall kayak rig?


After I add the floats to the inside, I will use some sort of foam core to shape the “torpedo” ends of the stabilizers. Then I will wrap those in carbon fiber as well as the whole pontoon and make sure the whole thing is sealed.


Now of course this is the super simplified version of what I want. Before I get it all the details of how it’s all gonna go down, I want to get feedback on how accurate I am in thinking that the weight capacity will be increased. Do you all think the stabilizers, if mounted correctly, will work at high speed (15mph)? I know they will cause lots of drag, but that will be overcome by the motor. Do you think the high pressure floats and the whole outrigger system will keep the back of the kayak out of the water?


Also, the motor has a hydrofoil on it so it should help the kayak plane easier and keep the back of kayak lifted. That’s what they say at least..


Let’s hear your ideas. I’ve attached pics of how I think the stabilizers could/should look. The black part would obviously be the builders tube wrapped in carbon, and the yellow is depicting the parts that would have the foam core. The red line would be either stainless steel or aluminum tubing. Similar to the one they use on boats. I think either 3/4” or 7/8” tubing.


In terms of mounting to the kayak, there are several threaded inserts built into the kayak for various reasons (seat, pad-eyes, etc). All of the threaded inserts are rotomolded into the kayak and have a thick “bump” of the plastic material that is on the backside of the inserts. I would use as many as these as possible, and then also use geartrac with backing plates in some areas. Check out the pics


In terms of mounting to the stabilizers, that would be a little more tricky since its carbon fiber and I’m building that part. I’d have to put some sort of backing plate on the builder’s tube and drill thru the carbon? Or some other way.. I’m open to options.


Hope I haven’t babbled too much. I look forward to you input

 

Here are the design ideas for the stabilizers

 

Have you considered a proa? Instead of two small outriggers, one bigger. With the outboard in between them, less likely to swamp. Also, try the little OB in the bigger rig. Might be enough power.

 

I understand your preference for portable boats, but can I suggest a main hull that is in two or three parts, and assembled at launching.
That way, you can still carry all the components, but you end up with a much, much better small craft.
a. Much faster with little extra power, and way less wash and drag under decent speed
b. Much better load carrying
c. Much better Directional stability

Then DogCavalry Proa concept, is also a great idea. With one small float on one side, its easy to bring upright after capsize, but way, way more stable in the first place, and much bigger deck area for those huge fish.
The added ability - when (not if) your motor is broken, you can rig a simple sail, and get a greater degree of safety.

 

"Since the builder’s tube is hollow, I have 8” of diameter of hollow space for 6’. What I planned to do was add a high pressure float to the inside of the tube. The float has the same 8” diameter and can be pumped up to 21psi. I figure this would give more flotation that just empty space (air) at atmospheric pressure. Does this reasoning make sense? Will it actually add more weight capacity and/or flotation to the overall kayak rig?"

The air inside the Outriggers has weight and it would be necessary to remove all the air (ie. have a vacuum) to make the Outriggers lighter and produce a tiny bit more buoyancy.. Anything that is pumped in under pressure (even helium) is just going to add more weight compared to a vacuum, the higher the pressure the greater the weight that has been added- and the Outriggers sink lower.

Someone can help you if you give a statement of requirements (SOR) list. Start with the most important aspects for the kayak at the of the top of the list, and go down in the order of importance. The professionals boat builders will be able to juggle things around as needed to give the best possible compromise, including as much from the list -as is practically possible.

As with most aspects of life, which also applies to boats: Someone can have anything they want, they just can't have everything they want.

Ps. My opinion only , The LIGHTEST way to move up significantly from the speed you already have is with a powered hydrofoil. Here's a link of a pedal one with added stability, would have to be modified for adding a motor.



Of course, hydrofoils come with their own issues..

 

Your kayaks hull is not designed for high speeds, as evidenced by the sinking stern at higher speeds.
A planing hull is what you’re looking for, the added pontoons will likely slow you down some, and throw spray all over.
Search on You Tube for Lite skiff, H Skiff, and many others that have already done their homework, and are producing some pretty impressive products that you could benefit from studying.

 

Modifying a non motorized hull to efficiently use a 10 hp outboard will be somewhere between difficult to impossible, better to start from scratch. I'd lean towards a scaled down panga, they are common along the Caribbean coast for a reason. It's an interesting design challenge, I think you would want a low freeboard hull with just a footwell with minimal accessories (do you really need a trolling motor?). Best wishes on the deal we need more simple boats, which are hard to do.

 

Thanks everyone for the replies.

I've never explored the proa design and here's why. The one section that's way out to one side will inhibit fishing on that side. An important feature is that I'm able to fish off both sides of the kayak.. this is necessary for trolling for tuna, wahoo, etc. That's why I thought of the 2 outriggers that are fairly close to the kayak to just add a little more stability.

I don't really need a lot more stability, as I know how to handle myself in the water. The 2 times I flipped the first rig was totally my fault. I knew I shouldn't have tried to go in the inlet with those waves breaking. Every other time I operate the kayak I have never felt like I was gonna flip. And I've been in 3 foot seas with it... literally meters away from giant sailboats and sportfishers. It really handles well.

 

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What idea do you have about this? Having a main hull that is in 2 or 3 parts? Do you mean stabilizers that are detachable basically? The thing about this is that I don't want to have to assemble anything when it's time to launch. Taking the kayak off the cartop, then loading all the fishing gear, then mounting the engine is already taking 30-40 minutes depending on how far from the water I get to park. Having to assemble something would take another 15-20mins.

 

That hydrofoil looks wayyy out of my realm.

Oh wow, I didn't actually think of that in terms of the air inside. I thought that the pressurized air would create more buoyancy than normal air, and even a vacuum. I know it would have more weight, but also more "flotation." The people that make the floats say they have 33lbs of lift each. And I could fit 2 of them in each stabilizer.

How would I create a vacuum in the pontoon?

I'll also come up with that SOR list, because it is important that I have the fishability of both sides of the kayak, and hopefully the ability to stand in calm(ish) water.

 

Maybe I may be overcomplicating it for this application with the 9.8hp, but I really wanted to go with that size engine. I also have the option to put a 6hp on it, but I did some reading and the 6hp has a single cylinder as opposed to the 2 cylinders of the 9.8hp. It is said that there is less vibration and noise with the bigger engine and it just runs smoother overall.

Realistically, I won't be going very fast very often. Only when conditions are good or when running from spot to spot. Mostly I'll be trolling under 10mph or bottom fishing where I'm stationary. I feel like I could honestly get away with using the 6hp and not even need stabilizers at all. (Which I'm starting to think more seriously about doing). My main reason for wanting the stabilizers was for the extra weight of the 9.8hp engine, and also so I can stand up and throw a cast net fairly comfortably from the kayak.

I haven't been able to stand on my first kayak and definitely can't throw a cast net from it. This is a downfall that I want to overcome because sometimes you just need the live bait. The Old Town kayak I now have is more geared towards standing and has a 2-position seating system whereas the first kayak was just a molded in bucket seat. Albeit, because it was so low to the water, the center of gravity was low, which made it feel so stable.


For those of you saying to just get a rig designed to plane, that's not an option. I already have this kayak and I got it on an amazing deal from someone. Buying a new Lite Skiff isn't in my budget right now.

Also the getting a small panga or similar boat that they use in the Caribbean isn't what I want. Besides cost, those don't have even a quarter of the features of my kayak. The beauty of the kayak is being able to lift it by myself, be able to work on it by myself (since it's plastic), and launch it from almost anywhere. You cant do that with a fiberglass panga. The kayak has the ultimate rig-ability. That big hole in the middle is where a huge console goes that I will turn into a livewell (its a big removable storage console). The front hatch opens up to the inside of the kayak as well as that rectangular hatch in the middle (under where the seat would go). Then in the back tankwell you have the option to make an 8" circular hatch that will open to the back part of the kayak. So I can run wires, put in bilge pumps, install backing plates, and all the other electronics anywhere in the hull and still have a very clean and orderly deck. The options are endless in adding GearTrac accessories which can be mounted on any of the flat "gunnel" surfaces. I'll also have a bow mounted trolling motor, and likely dual garmin units and of course some lithium batteries. And all of this will be within the back tankwell or the hull of the kayak. You can't get this level of DIY customization for any other boat except a kayak.

I know this kayak is made to plane, but that doesn't mean it can't plane. If I didn't carry anything on the first kayak it would get up on plane... when I was fully loaded it was just at the cusp of planning.

So I know it may not be ideal, but it's definitely possible. Here are 2 video to get an idea of what's possible:

1. Guy with 9.8hp 4 stroke Tohatsu on a Jonny Bass 100. This is a 10' bass boat/kayak hybrid looking thing. I know it has a different shape than my kayak and looks more like a planning hull...but that thing is much smaller than my kayak. Note that he has stabilizers, but they don't actually touch the water when he's running.

2. Guy with 4hp on a fishing kayak (Feel Free Lure 13.5) going 20mph!!! The water is glass flat but still. That's impressive. No stabilizers, or anything.

 

Given your stated constraints, it might be possible to add shaped foam wedges under the back sides of your kayak to create a planing surface.
Glue them to the hull?
Thermoweld plastic sheet to the hull?
I think that the speeds you’re seeing now are being accomplished by the efforts of the foil plate on the motor.
Maybe a larger plate?

 

I thought about that. Building up the back part of the kayak with foam then covering it with fiberglass or carbon.

Would the glass or carbon adhere to the plastic well enough? Also, how much extra boat would I need to add. Here's a pic for reference. I thought I'd have to do something like this to add a lot of displacement to the back part of the kayak which would add more weight capacity and buoyancy. Essentially, the motor would still be mounted to the plastic part of the kayak and the extra added on stuff would just be for balance/displacement/planing etc.

I think it would be hard to determine where to begin adding material, as the kayak has a natural curve both front to back and side to side.

 

I'll make it easy for you, sell the Predator and use the money to buy something else.
The Predator was specifically designed to achieve hull speed with 1/2 of a horsepower, there's nothing you can do to make it go faster short of modifying the underwater hull shape. More horses will just make it dig a hole in the water. Since this is a rotomolded boat the only way to do modifications is by welding. Even with flame treatment epoxy or other adhesives won't stick well enough t glue something to it.

 

PC: it's the volume of the outside (airtight) rigid shell of the pontoon weighing maybe say 2 lb?, that provides 33 lb of upward flotation Force. If the air is removed using a vacuum pump, using a special valve, the pontoon might only weigh say 1.9 lb instead, so now that means a total of 33.1 lb of force upward instead of 33 lb because of the lower weight. If more gas or say air is added under pressure to the same fixed volume sealed pontoon, the weight of pontoon shell might increase to say 2.2 lb because of the additional air (more wt. if an interior bladder is used) which means only 32.8 lb of upward flotation force would be available instead of 33 lb. It doesn't work that way with something that stretches like a balloon ( no outside rigid shell) pontoon, because adding pressure makes the balloon increase in volume, and if the balloon increases to twice its volume when pressured up, it will have about twice the 33 lb or 66 lb of upward Force.

Hope this helps. Kind of complicated to explain..