Mk.II Floats - Week 3

by Web FishMay 10, 2014 @ 12:40pm

Final finish. An external coat of epoxy applied and finished to a polish. We are now ready for mounting on the vacuum base plate:


With combined weight of float model and ballast of 19.5 lb. we still have 2" of free board. In a catamaran configuration this gives us a target total weight of 40 lb:

Mk.II Floats - Week 2

by Web FishMay 6, 2014 @ 11:26am

More hand plane, sanding, filler, sanding. The float plug takes shape:


Mk.II Floats - Back to Square 1

by Web FishMay 2, 2014 @ 01:22pm

As we mentioned in our previous post, the new design called for increased displacement and lower weight. Going back to the early days of the project, the original plan was to have the float shells thermoformed / extruded from polycarbonate plastic. This plan proved to be too ambitious and was abandoned early in favor of fiberglass shells (and later on composite wood/foam/fiberglass construction). With the new weight target in place we decided it was worth revisiting the plastic shells idea. Instead of polycarbonate (which, even though very strong, turns out to be less than ideal for thermoforming) it was decided to stick with more traditional polystyrene or ABS floats. The two materials have similar properties with the ABS route adding extra flexibility to the structure (which might or might not be a desire-able feature). Both materials lend themselves very nicely to vacuum forming.

There are two major hurdles when going the vacuum forming route: the cost of the process makes it impractical to run really short series of pulls (we really only need 4 floats for now) and you need a solid (and strong!) plug (positive model). There isn't really much one can do about the former (other than run a larger batch and store the extra shells for future use ;) so we focused on the latter.

Week one results:


Building the floats - Step 6

by Web FishMar 19, 2013 @ 01:59pm


The fiberglass skin on the floats is now done. Ready for the final finish. Before we do that, we should put the frame on water to validate our math (and make sure Archimedes was right :)


Building the floats - Step 5

by Web FishMar 13, 2013 @ 08:30am


Fiberglass week at the shipyard. Floats should stay under 3.5 lb. each to to keep within the overall weight budget:

Building the floats - Step 4

by Web FishMar 9, 2013 @ 07:34am


Final layer of body filler on the floats. Sanding halfway done:

Building the floats - Step 3

by Web FishFeb 26, 2013 @ 10:37am


Time to put some "meat" on the bones of this fish. Polyurethane foam is light, sticky and easy to shape with basic tools:


Once the foam is set, its cut down to size and further shaped to produce the final float core:

Building the Floats - Step 2

by Web FishFeb 22, 2013 @ 07:55pm

The sun is finally out and we have three more float frames:

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:


Foamy Fish?

by Web FishDec 17, 2012 @ 12:27am


The hull mold is finally getting there:


After a lot of back-and-forth, the decision was made to go with foam hull core with fiberglass skin. On the hunt for the right self-expanding foam now - trying to find alternatives to Great Stuff.