Superstructure Round 1

Again thanks to Christian for helping out. We've made great progress and the extra hands were very helpful. This time we assembled the stock cut into the first semblance of the superstructure of the craft.

The stock is an unlikely 1.5x1.5" redwood. (Home Depot's selection was less than ideal, but the redwood should work well, and looks quite nice.)

The planning sketches I drew up

To get started I put together a sketch. Here's the version we started with inside. After going out the expected 12" height of the fan was measured to be 10" and the outside radius was 26" so the cross members were extended by 2" and the verticals shortened by 2".
 
Here's the timelapse of our work.



And the result:

The superstructure placed on the hull. It's not exactly in place as the hull's upside down at the moment, the skirt strips are on the bottom.

There was one complication that the engine mount for the vertical shaft has 3 bolt holes on an recessed circular pattern. The pair of boards going across will not work. We will need to find a more complex solution.

Remainder of matching skirt strips created and superstructure rough cutting

With more help from Christian I've been making great progress. We successfully create all the remaining skirt strips matching pieces.

We made much faster progress by using a small template piece, pictured below. This allowed us to not worry about the lateral alignment and simply make sure it lined up along the length of the strip. All the matching strips are paired to match a particular strip on the hovercraft to match their specific idosyncracities. (aks hand drilling inaccuracies.)

An example of the template for marking the mating strips.

Here's the time-lapse of this stage.


You'll see at the end we also started cutting the stock for the superstructure.

Skirt Strip Matching Strips

Christian and I made the first two matching strips for the skirt attachments.

This involved cutting them to length, followed by carefully marking out and drilling the clearance holes. We first drilled with 3/16th, but due to imprecisions using hand tools we found 1/4" holes were much more likely to line up.

Here's the time-lapse of our work. 



Then end result looks pretty good. I'll need to get some more approximately 5/8" screws.  

The 5/8" screws next to the attached skirt.

The corner with both matching skirt strips in place.

Side Skirt Strips Attached

Thanks to the help of Christian and Michael the rest of the skirt attachment strips are attached to the perimeter of the craft.  With the strips now attached we officially have a top and bottom to the craft. (It's upside down at the moment.)

Here are a few pictures of the results of the strips on the bottom.

You'll see that the surface was pretty wavy and as much as we tried to staple and glue it down they still stood up a little.

I forgot to mention that we used masking tape on the backs of the t-nuts to prevent epoxy intrusion into the threads. 


Today we had the luxury of working on much flatter surfaces. Thanks to our previous efforts of sanding the sides smooth, and the areas not being big enough for the plywood to buckle. We also sanded a little bit and brushed off the dust for a better surface treatment.

For gluing on the side we used the masking tape again to attempt to keep the glue in place which worked quite well.

The tape before applying the epoxy.

As you can see we loosly taped the pieces in place. Then we ran tape all along the underside of the strip to keep the glue in place. It also made it really convenient for adding the epoxy, as we just had to take off the loose tape and it folded down for easy access with the brush. After which it could be folded back up and taped into place while being stapled.

Here's the timelapse from today.

Skirt strips applied

Today I was able to attach the skirt strips for the bottom of the vehicle. Thanks a lot to Christian for the help today!

We attached the strips to what will be the bottom of the boat where the inside edge of the skirt will attach. 

Here's the timelapse view of our work. 

The strips as prepared before. We applied epoxy to the strip and then used a staple gun to staple the strips to the hull. The staples will provide shear stiffness and help hold the strips down while gluing.

There were a few areas where we had issues keeping the strips down due to wavyness of the plywood. When stapling I tried to hold it down as well as possible but the staples weren't strong enough when there was a valley between two peaks of the waves. I added some of the buckets afterwards to try to help weigh down the problem areas.

The next step will be to do the sides. It's going to be a little tougher as it will be not on a horizontal surface. But the sides are much flatter so we won't need to worry about weighing it down or gaps forming. 

More skirt stirps

Having started on the skirt strips there were a bunch more to do. There's actually quite a bit of perimeter of the skirt. There needs to be both strips lining the outside along the side of the hull, as well as on the underside holding the skirt to the bottom of the hull.

My fabrication technique was relatively quick and the hole are probably +- 1/2" so the outside strips will likely need some slightly larger holes with washers. 

After the previous test run I was able to put together the rest of the strips I needed for the inside.

The next step will be to attach them all to the hull.

Skirt attachment strips

I've started working on a way to easily attach the skirts, with the ability to detach/reattach as well. My plan is to embed t-nuts in a strip of wood which is attached to the hull. On the outside a second strip can be screwed through to clamp the edge of skirt.

A t-nut from the back side

the t-nut from the front

For better seating I needed to counter drill the back so the strip will lie flat

The first skirt attachment strips

The t-nuts are 8-32 and are embedded in the back of 1.25x3/8" Everything is stainless steel for better longevity in and around water.

Unfortunately the GoPro does not do well when left powered down.. I tried to use it, even with the battery back pack. However it would not even turn on. After a few hours of charging there was no change. However a few days later i checked on it and it was fully charged and ready to go. I'll have to work on keeping it plugged in, or at least charging it the day before I want to use it.

Vulnerable Plywood

I'm not sure when this happened but after I flipped the hull over I noticed a small pebble (~ 1/2") embedded in the plywood. It must have been on the ground when the hovercraft was placed on the ground.  More evidence that I need to get some skid plates on the bottom asap.

The pebble embedded

The pebble popped out.

Plywood sides for lift fan cutout

I've added some plywood sides for the lift fan cutout. Reinforcing the strength of the hull for the extra stressed sections, and protecting the foam some more.

Round 1:

Round 2:

Due to a lack of clamps I had to do this in two shots. And each piece only got 3 clamps. I had to go back and do a little rework to reglue a few corners where the plywood warped or the underlying surface was slightly recessed and I needed more localized pressure.  Another improvement would have been to use 6" backing boards for applying the pressure to avoid the warping. However I didn't have any on hand so I just went ahead with the direct clamping.

Here's a photo of the touch up I did, after flipping it back over.

Gluing down a few extra corners.

Sanding down the corners

My gluing has left several rough edges where the plywood stuck out so I spent a while today taking those off with the belt sander. Here's my timelapse:


This took longer than I expected. One of the challenges was that I discovered that I was not getting the suction from vacuum, nor the impeller built into the sander. I discovered that although I had previously cleared the foam from the intake. There was still foam in the narrow passage between the back of the belt on it's way to the impeller. The passage is about as deep as the sander is wide. But it's only about half a cm tall. And the foam pieces clog that up pretty well. To discover and clear that clog I had to take apart the belted gearbox which drives the impeller and sander.

The sander partially dissassembled to clear the clogged exhaust vent. 

Sanding without the suction left a lot of dust:

At the end you can see me getting ready to add plywood to the sides of the lift fan cutout.