Tuesday, January 31, 2023

Finalized kayak design. Work begins.

Calculating the length of a mathematically derived sheer curve.  If I used a programmable calculator, I could do these calculations in one step, but I routinely use a simple TI-36X which I bought years ago.  So, I need to do the calculations in a stepwise fashion.  It is a calculation I only use once per boat design, not worth spending too many resources on.

This equation for curve length was derived by calculus integration of the mathematical curve equation.  All my college engineering studies were not completely wasted.



 I am completely committed to the 170" long by 27.5" wide kayak design.  I have the keel plank roughed out and the bow and stern stem pieces also "roughed out".  These pieces are only in approximate shape and will be trimmed and detailed more later.  Next item will be a start on the ten frames.  Incorporating one inch of rocker at the bow and stern created some complication.  How will I ensure that the keel plank is held in the required position without using a building strongback?  

Part of that can be done by the type of support provided beyond simply sawhorses.  Additionally, I have completed calculations for the overall length of the sheer and its intersection with each frame.  With a double-ended hull and each frame fixed at the keel plus port & starboard sheer locations, all frames can only assume one position.  The entire frame will form a single "girder", at least in theory.

I have already drawn out the full-size patterns.  Not hard to do when the largest frame is less than 30" wide and 15" high.  The frames do not change when their spacing is altered.  

The deck beams are laminated from thin 'cut-off' scraps I have been saving for a few years.  I built a curved ladder to clamp the strips into a conforming curve.


Bow and stern pieces created from 2"X4" scraps.  At this point they are only roughed out.  I need to cut channels for the sheer and chine strips.  I used a half thickness lap and Titebond III to join the two pieces.

All the frame pieces have been cut to shape. but that is only a beginning.  I will be using a half lap when I start bonding the parts together.  With sixty pieces to fit, it will be a lot of fine cutting.


The six parts for frame #5 (of ten) positioned on the full-size paper template.  When more are ready, I will bond them with epoxy.  Then they will be trimmed and notched for the longitudinal strips.

A preliminary look at how the frames line up on the plank keel.  All pieces shown here are still unfinished, but it is motivational to see that the parts will fit together.  The keel is presently 0.5" thick; I plan to plane that down to 0.4".  I usually do that outside because it creates so much wood dust; however, we still have snow outside my shop door.  I have other details to keep busy with for a while.

Finally, the ten frames, two stems, two sheer strakes, and keel are sufficiently complete that assembly can begin.  I placed a straight 2X4 across two sawhorses and placed the keel centered atop that.  Then I clamped the central section of the keel to the 2X4.  Next, I placed a sawhorse under each end of the keel and added a few scrap wood pieces of the proper thickness to provide the desired rocker in the ends.  Next, each frame was bonded and clamped in its proper place, spaced at 15" centers.

Port and starboard sheer strakes had been created, cut to proper length, and each intersection with a frame had been marked according to the calculated curved length of the curve.  The calculation is amazingly accurate, hundredths of an inch, but my shop accuracy is only about 1/16".  With both strakes joining at the stem ends of the double-ended hull, there is less chance of distortion.  Unfortunately, after removing all the clamps, I see that frames #3 & 8 are about 1/4" out of alignment at sheer height.

With each frame fixed in place by the keel and port & starboard strakes (3 points define a plane), it was only a matter of having sufficient clamps to maintain that position until the epoxy hardened.  No fasteners have been required thus far.  This provides the basic framework for the entire hull.  I will add another strake at the turn of the bilge and outline the cockpit; then it will be time to start planking.

The only strongback needed has been a straight 2X4 (6-8 feet long) and some sawhorses.  Accurate measurements along the curved sheer strake made the difference.

I have plenty of clamps of all sorts.

After the clamps have been removed.  Starting to outline the cockpit.  Next, I will flip it over and add a stringer at the major chine.

Kayak frame with more details added. A cardboard pattern is clamped on the lower right.  That area is developable, thus, could be sheathed with a single plywood sheet, but that is not the alternative I have chosen.  This pattern simply gives me a better idea of how the planking should be laid out.


Stringer added.  Then it is time to fair all the frames and the stems, then create a shelf on the plank keel edge to support the garboard.  I use an angle grinder for fairing; the stems take some serious wood removal to get the proper taper.  For the edge of the plank keel, I use a router.  This time I used a full-size router, its weight made it easier to control; not as easily deflected by variations in the wood grain.  Near the ends of the keel, you are changing the angle and following a curve; thus, you need freehand control without a guide.

The intersection of the plank keel and the stem.  The edge of the plank keel has been routed to support an edge of the garboard plank, and the stem has been beveled to support the plank ends.

I have purchased some planks of knotty alder for the sheathing.  Why knotty alder?  1) It was cheap. 2) It was high quality; it looked somewhat like select alder. 3) After I rip it into 1/4" planks, I can scarf out any significant defects and knots. But we are taking a break before I get started on that next step.

Two months later and the break is over.  I have ripped the knotty alder into 0.2" thick planks, cut out the significant knots and other defects, and then scarfed the resulting pieces into 15 (so far) 15-foot-long planks.  With planks only 1.5" wide and my chop saw set at a 7-degree angle, it was easy to get consistent, smoothly beveled scarfs.  The knots were frequent enough that most of my 15-foot planks have multiple scarfs.  

Progress.  Planked up to the major chine.  These planks have been straight and full length.  The next planks will be more complicated, either tapered or curved.

As I create a new design, I am always asking myself what could be done differently.  When I look at this hull design (and after sitting in it), I feel like the deck should be 2.5" lower.  There is more foot space present than needed.  A lower deck would enhance paddling.  Also, the hull could easily be 10% shorter.  The changes would reduce weight and windage.  I do not want to reduce stability; this is not meant to be an advanced paddlers design.

The present hull will permit more stowage and allow a more relaxed seating position.  Every tradeoff is a compromise.

Getting close to completing sheathing the hull.  Then I will turn it over, lightly sand, then go over the hull with a flowable epoxy paste to fill seams and provide a smooth surface.  I'll let that cure while doing some finishing to the interior.  Then I will do final sanding on the exterior and start on the deck.





   

posted by Wayne @ 7:23 PM

0 Comments:

Post a Comment

<< Home