PilotFish Mk.III - If at first (and second) you don't succeed...

by Web FishMar 24, 2015 @ 08:49pm

If at first you don't succeed, try, try, try again.

Another year - another PilotFish design. Since this is the second major reboot of the project, we should be getting very good at learning from our failures :)

What did we learn from Mk.II? Here is the short list:

  • Structural integrity is both paramount and difficult to achieve. Actually, this statement is only partially true. We can make things reasonably strong, but in the process they get quite heavy. Reliable mounting points on thin-walled structures are a challenge;
  • Weight is important. Really important. Mk.II floats got extended vertically twice to compensate for the ever growing total weight;
  • Free board is overrated. Well, not really. But in our case it doesn't seem to make a big difference - it only increases windage with little effect on everything else;
  • Ease of build. Spending 4 man-years building something that has a limited chance of survival doesn't sound fun. And now that the MicroTransat challenge is open to powered vessels, this is becoming important.

 

So what's next for Project PilotFish?

 

 A simpler, lighter, stronger and hopefully better Mk.III design:

 

 

As we all know, third time's the charm. Apart from that, this is what Mk.III has going for it:

  • Simpler tubular floats made from multi-layer plastic stock - light and strong with reasonable drag;
  • No need for risers and cross-members in the deck structure - light and simple;
  • Super-strong mounting points while still allowing full disassembly for maintenance / repairs;
  • Very low vertical profile driving down windage factor;
  • Natural compartmentalization of float volume;

And a few challenges which will need to be addressed during the build process:

  • Limited displacement / floatation. Adhering to the design weight budget is paramount;
  • Switching to a smaller size / lower power rating solar panels will put extra stress on the power budget;
  • Watertight mounting for rear and aft float sections;
  • Mounting / orientation of the GPS and satcom antennas with floats having limited freeboard;

 

Let the journey begin...

 

Building the Floats - Step 1

by Web FishFeb 21, 2013 @ 01:57pm

Bulting the floats: Part 1

After spending a good portion of the last month experimenting with various build techniques (composite skin with minimum glue-on frame, one-off float core cast from two-part polyurethane foam, even considering CNC machining of the foam cores) the decision was finally made to go with a structural cross-frame built of 1/8" plywood, polyurethane foam cast inside the frame cells and a fiberglass skin finish. This will give us almost 100% flotation preservation in the event of float breach (OK, it is probably less than 100% as the polyurethane foam will never be 100% closed cell and as such it will soak water in the event of a skin breach, but it's way better than a hollow float), manage-able cost and reasonably reproducible results (shape/weight) using simple tooling (we will need at least four of those floats). On the flip side, this is a bit more labor intensive than simple foam casting / machining, and the solid hulls mean that we'll have to fit the navionics bay and all batteries within the deck structure. Under other circumstances this would have been a less-than-desirable solution (high center of gravity) but considering our overall design (what is up today might actually be down tomorrow) this works ideally to contain the weight in a balanced way.

 

  • The float frame starts as 4 separate elements: upper deck, lower deck, upper keel, lower keel:

 

  • The upper deck with the upper keel section:

 

  • The lower deck attached to the upper keel section:

 

  • The lower keel section attached to the lower deck:

 

  • The extra cut outs (keeping the overall float frame structure under 18oz.):

 

  • The motor pod tunnel:

 

  • Finally, the deck frame mount points are bolted on / glued and float frame is ready for the foam treatment: