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Kayak Designing & Building

Thread Status: Hello , There was no answer in this thread for more than 60 days.
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Spearomania Desperata
Apr 10, 2004
Hello People

This thread will be dedicated to the definitive study of DIY Kayak building. All those with experience please contribute your knowledge.
In the meantime we shall begin with some outlines from Kayak Guru and Mcgyver of the Southern Hemisphere: Pablo.

Safe Diving

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To go spearing on a kayack you want:

-A fast and reliable boat to get safely and fast to your spot.
-Sit on the top design to ease the entry/exit of the water.
-A low profile to minimize windage
-Good fittings to hold all your stuff outside the boat.
-High load capacity with out affect too much the speed (not a 600lb BF!)
-A steering system to concentrate your arms on the paddling.
-A build in chilly bin to keep your fish fresh (I think he makes sense?).
-A day hatch to keep small items (safety stuff, radio, food & drink, papers, keys, tools...) under your hand.
-A dry hatch to keep more stuff.
-A flag.
-We may as well think about a sail!
-An optional tandem structure to go get big fish

Is a lot to ask...

For the design I think about a fish form water line to work on endurance instead speed (a surfsky is fast... but over a long run the fish form gets the hand), a 58-65 wide and 520 m long hull. This way still easy to get on top of a normal car and load close to 200 kg.

A fish form hull sits you slightly on the front of the kayak, leaving a huge space behind to build a holding system for the stuff and the inboard chilly bin.

He doesn't go to be a super maneuverable boat... but you don't need to run a slalom: go from point A to point B with your gear as fast and easy on your arms as you can. Instead is better to have a kayak that tracks straight (most of the kayaks have the stupid tendency to move they nose to the wind!!!).

To get the weight down, a 3 layer kevlar/s glass +renforts should do the trick.

The only specific tool you could need for the building is a band saw, but in any wood work shop they will strip the foam for the mold versus a few $$$. The rest is as low tech and DIY you can get on a normal garage.

the building stages:

-Get the materials and design sorted
- Build the male molds. ( wood 6*2 back bone, plywood ribs, foam and filler, paraffin cover)
-Apply the fiber skins.
-Get hull, deck and dry walls together (that's the only really tricky part).
-Design and place all the safety, fittings, steering system, sit....
-Painting (kevlar doesn't like UV)

To build a few of those, revert the male mold to female is wort the better finish you get, but is more work and $$$.

Lot's of work!!! still here?

I'm looking for someone in NZ with a real garage to build conjointly a couple of those spearing kayaks... my garage is too small!
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Amazon.com has many books on DIY boatbuilding and several of them have kayak plans that might be a good starting place. Has anyone explored this route of march?

p.s. this weekend I discovered that I can hold my breath for 3 minutes and slow my breathing down to an easy 2/min. Now if I can just figure out how to deal with allergies and sinus pain . . .

Excellent outline of the the features and stages. We are lucky to have an expert enthusiast as yourself available to explain such things.

My humble opinion is that we should elaborate on the 6 unities (stages of production) you mention separately for each stage.

Stage 1 Design & Materials

-Step 1 Design

So for starters Design . You recommend the "Fish Form" and mention measurements of 58-65 width and 520 m length. Man can you post some designs of the "Fish Form" for us hatching kayakers? I am not sure if what im imagining from your description is correct. So once we get the shape the external dimensions (length. width , height) should be...?

Step 2 Materials

We now have the design with our complete dimensions and are ready to go. What materials will I need and roughly in what quantities so I can start building?

(Following Stage 2 : Building the Molds)

Many thanks Pablo and please bear with my ignorant questions.

I think this thread has alot to offer and am recommending you for the Deeper Blue Medal of Honour :D.

Safe Diving

Hey Oldsarge

Congrats on the new PB.

This thread could be a book in the making!! Am newly introduced into kayaking and dont know too much on the subject but I think a kayak made to serve the spearos needs exclusively is yet to be made. Some have the building skills others have the imagination here in this thread theyll come together. Some ambitious ideas have been discussed http://forums.deeperblue.net/showthread.php?threadid=50229&perpage=15&pagenumber=2.

Lets see what happens...
You really want this kayak, doesn't you?

The design is a hard one, an I'm working as much I can on it. but two weeks minimum to have something usable. I need to optimize stability, wet area/drag and do a bit of virtual water tank.
All that is theory, and I hope the result would be up there. I work on the sailing industry where I develop new technologies... anything that floats on water is of professional interest for me.

They are many plans out there for different purposes but I try to came up with my own "spearo desing". Up to you to choose the design you want. The boat building information is the same, and probably the shortest way to a functional DIY kayak.

I will post full CAD, 3D views and conventional plans.

I hope someone in NZ could be interested on the project. Good pictures should save lot's of my clumsy words.

At the moment I use as reference a couple of canoe kevlar building and boat building books, the advice of a race boat designer friend of mine, and a lot of internet information. I'm not a professional on the mater, and I'm interested on the opinion and input of as many people as possible to accomplish this project.

Next post about the materials...
You might try to come up with two different sets of materials. While I know that a lot of people have some skills in the synthetics and foam industries, I suspect that most of us will be more comfortable building with thin plywood strips in the manner of "cold molding". I know that I certainly would. Can it be built to carry two sea-hunters and their gear? Hmmm . . . I wonder if it might be suitable for sea-duck shooting, as well. There are so many camoflauge wetsuits on the market these days . . .
Tamdem... what a nice idea: but he becomes a big structure to design! I may try something...

A spear fishing kayak is better on a sit on the top configuration. I've never seen a wood strip design that enables this feature. A laminate glass kevlar is more apt to take the beating than a wood piece of art: you can drag it on the beach, bang it on the stones, drop your weight belt on it...

But if you have the skills to make a strip kayak you will find a laminate one easy and faster to build. Is as well a cold molding technique, but more follproff.
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hull & deck materials:

kevlar: is a tough fibber that enable to save weight (less layers of glass) and makes your kayak bulletproof (is the stuff they use on the bulletproof vest's)

the kevlar act on tension and the glass fiber on compression: the kevlar go to be on the inside of the hull, and the glass on the outside. you will need another layer to protect the laminate form rocks and other accidents... in total 2 layers + 1 on the bottom.

the hull is curve, the fabric is flat... because they are soft woven, the fabric can take a bit of a curve... but if you try to lay all the hull on one piece you go to end up with ugly crises to cut out! Better of to lay in longitudinal sections. I like the idea to have two halves on the kevlar (good structural reenforcing on the middle line) and tree sections on the glass (sides to the waterline and bottom twice.). This layout enable overlapping a middle reenforcing of kevlar and two softer on the water line to cope with encounters. Along the middle line you want to add on to your laminate another narrow layer of fiber glass. See the picture.

A sit on the top deck is complex, and some patching will be needed... all depend on your design!

for the kevlar you can use 8.9 kevlar 49, an for the glass some 5.6 s-glass (make sure is s-glass) will do nicely. for the middle reenforcing band you may go heavier...

When you cut this fabrics they have tendency to fray... can not do much about, just be careful. Once you have done one and you know the shapes you need to cut (make paper templates) you can draw them, run them though a zigzag sewing machine before cutting at the edge.

Kevlar is a beach to cut, you need sharp scissors or a knife with a new blade.

Carbon is lighter and have a higher modulus... but is brittle and hard to work with: I don't recommend it.

the separations between the compartments can be done with some of the foam you got for the mold and fiber glass cut outs.

You can either opt for epoxy or polyester resins. For a couple of hulls use epoxy... is easier to use and more stable under heat. But if you do more of them use polyester, even if he stinks, is not so bad for your health... Any resin for marine use is find. For both use a good mask to avoid the fumes, and avoid any direct contact with the skin. At least 4-5 gallons of it.

To add strength you want to fillet any hard angle you could get (separations, sit, fittings...) with a specific filler to give texture the resins.

kevlar doesn't like UV, you can either paint the hull with a polyester gelcoat or an epoxy paint. You can as well use colored epoxy additives on the outside layers, but keep the inside ones clear to see any bubble left.


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mold materials:

The base is the spine or backbone. he will ensure a straight work and a stable work: for each mold get 2 straight 6*2 (inches) wood beam. joint both together as a T (glue and nails).

You then need some plywood to cut out the "ribs" of your hull: you can keep that relatively thin... 3-4mm

Enough hight density insulation foam (not the white light one made of little balls, he will melt under contact with epoxy...) about 25mm thick (1 inch). he normally comes on 4*8 foot and you need at least 4 of them... easily more depending on your design.
This foam need to be cut in strips of about 40mm with the sides cut to convergent angles between 8 and 10 degrees: set the saw to +-8 degrees, and keep cutting turning over each time the sheet.

A filler to fill the gaps between the foam strips. you can use either a specific polyester resin or simply some wall filler, gips or anything like. The best will set in a few min, but leave you 10-15 min to smooth the shape: ask your local DIY shop.
Plenty of that easily 15- 20kg.

If you use a wall compound you will need to smooth and close the pores to avoid the use of too much release wax. Paraffin seem to be the universal choice... And once apply a hair dryer will leave the surface smooth... smooth! 4-5 pounds of it, maybe more!

Mold relax wax, about a pound of it. they should have that with the resin.

You will need thin wood strips to hep to hold together the ribs forming the shape. They are removed when the foam hold everithing in place.

hot glue sticks to hold the foam on the ribs. Some use contact glue, but even if is faster you will found it harder to use.

you will need a bit of wood to build a basic structure to hold the mold hight and work conformable. make it strong... the mold can get heavy!


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Hmmmm. So building up a laminated kevlar/glass hull is much the same as plywood? Interesting. I await further developments.

There are a couple of SOT (sit on the top) plywood kayaks arround... you can buy the plans online.

They use the stitch and glue tech... easy and cheap to build.


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another one...


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Fantastic presentation. I understand completely on design and materials now. I am definitely oriented towards the glass fiber and kevlar than plywood. Now for the next question: How do you go about building the molds?
You mention about the 6*2 T-structure base which you build around could you perhaps provide detail in the steps of building the male molds?

Eagerly awating next post

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Now that first one looks right up my alley, Pablo. Where do I order the plans (he said, panting and drooling all over the keyboard)? That looks just like what I need to paddle out to the kelp beds a mile or two offshore . . . assuming that I can fix this allergy thing so that I can actually use it. (And if not, there's always possiblilty of surface fishing out of it!) Bring on the barbeque!
how to translate the plans.

No mater how you obtain your plans, they represent your inversion on money and time: better of to spend a reasonable amount of time interpreting them!

The two main ways I´ve seen plans is as a scale drawing or a table of numbers. Both represent the same information: the geometric definition (x,y) of two series of stations (the ribs) one to the bow(front) and the other to stern (back), the curves for bow and stern, the separation between stations, the water line information, the waterline height, Sometimes you can have another info, like deck plans (important on SOT´s), strong back position, or specific placements for the sit or other accessories.

The main technique to report the plans by numbers is to reference a plan (draw a central axe y and a x to each side on a sheet of strong paper), report the points defined for each station and then joint them with a smooth curve.
Draw the strong back reference and the floating line.
draw the bow and stern curves.

You can purchase your kayak as a pre cut kit of stations, or for the stitch and glue plywood ones get everything cut and just need to assemble...

Lately you can get DXF or a plot file (HPGL, PLT....) that are relative easy to get print or plot somewhere. I´m lucky on this one: I´ve got a 5*12m plotter cutter at work...

Your hull is translate in stations, plus bow and stern. All this pieces assembled along the strong back (the "T" 6*2 beam) will give a good idea of the final shape of your mold. If the plan is not intended to build a mold (for a laminate boat), if not you will need deduce the thickness of the mold form the stations...

The plan only give you halve the section of the hull at each station. Cut he plan by the y axis (the vertical middle line), and then cut around the outside curves. Report each on the 4mm plywood and turn over to get the final view of your station. cut then next one down and restart the process. On the plan you will have a drawing for the bow and stern pieces... do the same, but this time they are not symmetric.

the waterline image (comes with a scale) go to give you the data bout the strong back length (normally boat length minus the end pieces) and the placement of each station on it.


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This is a picture of the frame for a strip build kayak.. not the same but gives a good idea of how to proceed.


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Thanks Pablo

Very technical analysis. I need sometime to understand all the information completely and how to move to application from interpreting the design.
Ill post my questions in a couple of days (theyll be few!!!) as workload is insane at the moment.

Safe Diving and my Respects to NewZealand



That is a great idea using foam to build a stip planker !!!

I have been thinking of doing something like this for some time as my sea-kayak has a very small cockpit and 8 inch hatches...not really spear friendly.

What I would like to build for spearing is something like this.


very stable, space, sail, paddle or even small outboard !
Hey, welcomed...

Nice pictures... Yes the boat don't seem ideal for spear fishing.

Stay tuned, this thread should collect enough info to easily build something more suited.

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