March 20, 2009

The team is happy to report that the canoe was successfully removed from the form and is still in tact!  We were a little worried that some of the prestressing tendons would  pop out of the walls since this is the first year our canoe is 0.4" thick and there is no thickened gunwale.  Overall, the inside of the canoe turned out how we expected; each year, reinforcement is showing and the team patches over it.  The outside of the canoe still needs a lot of work to obtain the desired shape.  See the photos below, and check out more pictures by clicking HERE.

Overall, construction is progressing nicely, but there is still a lot of work to do before the competition!  Currently, the team is spending their spring break patching and sanding the canoe.  We are also testing stains, ordering the sealer, and working on the final product display.  The team has not started the cross-section yet (better hurry up guys!), and we are assembling the engineers notebook.  Overall, things are on track to finish the canoe by April 6 (giving the sealer about a week to cure before transporting it to the competition).  Good luck to everyone in the upcoming weeks!

Patching the holes from the grade screws

Removing the form

The inside after the form was removed

Another shot of the reinforcement on the inside

Patching over the exposed reinforcement

February 20, 2009

The team successfully poured the 2009 concrete canoe about two weeks ago!  They were able to fix the prestressing cables and reattach the springs before casting the canoe.  However, the cables that were replaced in the gunwale (the area with the highest stress) were not secured to the reinforcing as well as the other tendons.  So one of our concerns is that the tendons may pull out of the canoe when we pull it off the form two weeks from now.  Of course, we will cross that bridge when we come to it.  Overall, pour day went very well, although it was a little slow this year.  It took the team nearly twelve hours to finish placing concrete on the form.  One major hurdle was that the location of the top of the gunwale was not CNCed into the form; instead, the form was made too tall with a line drawn to indicate the top of the guwale.  This was a problem because the concrete sloughed off the form and pieces of wood were used to keep the concrete in place (see picture below).

For now, the team is diligently watering the canoe and they even started patching and sanding.  Unfortunately, our quality control was not as good on the concrete placement this year, and we have many low spots in the canoe between the grade screws.  It shouldn't be too much trouble to fix, but the construction team has a lot of patching and sanding ahead of them.  The rest of the team is working hard to finish the design paper, select graphics, begin the table display, and have stencils made for the letters on the side of the canoe.  Only 54 days until the competition, and the clock is ticking!

Placing concrete on the form.  Note the wood block used to keep the concrete in place.

Placing concrete on the bow of the canoe

The first patch coat on the canoe...it's pretty bulky

February 5, 2009

Due to some technical problems, we did not pour the canoe last weekend.   As usual, the canoe team spent all night on Saturday in the lab, tying reinforcement.  At 10pm, they just started the first layer of reinforcement.  By Sunday morning, the reinforcement was almost finished, but a tendon snapped just before they began mixing concrete.  Luckily, the tendon was held in place by the reinforcing ties, so no one was injured (always a major concern when applying 300 lb of tension to a cable).  Because of this, the team made an executive decision to postpone the pour until this Saturday (February 7th).  This way, they could finish tying the reinforcement, reattach the tendon, and be sure that there are no more problems with the prestressing.

The question you may ask is, "Why did the tendon snap?"  The breakage was unprovoked and quite unusual.  But the team saw another tendon snap on Saturday night before they started tying reinforcement.  We assembled some data and came up with some ideas.  The first thing they checked was the cable tensile strength.  About ten load tests revealed that the cable does not break until loaded with 400-500 lb.  But the team had only placed 300 lb of force on the tendons.  The next step was to investigate how the team measured this "applied load".  As usual, the team calculated the load using a spring and measuring a displacement. One problem was that each spring was not tested to determine a spring constant.  When the springs were tested, the team determined that the initial force (the force required to actually displace the spring) varied between 30 and 70 lb.  Since the construction team didn't take this into account when stressing the tendons, they had placed more than 300 lb on each tendon.  In some cases, it could have been 370 lb.  This was the main reason the tendon broke.  In addition, the team hypothesized that the individual tendon strands may be spliced throughout the wire, giving the tendon a lower tensile strength at certain locations.  Even though has not been proven, it is another possible reason the tendon could have snapped.

This week, the team released the tension in all of the tendons and tested the springs to determine the initial force for each one.  Then, the springs were reattached and the tendons were tensioned again to achieve a force of exactly 300 lb in each one.  Hopefully, this will prevent tendon breakage in the future.  Now, the team is set to cast the canoe on Saturday.  The delay is not too significant and the team is very relieved that it did not occur after the canoe was cast.  To see more photos of this year's mold and reinforcement, CLICK HERE.

Cutting the Ribs

The tool we used to cut the ribs into the mold

The first set of tendons

The first layer of reinforcement

Tying the carbon fiber to the tendons

There are about 250 grade screws in this year's mold

January 28, 2009

Over the past week, the construction team finished assembling the mold.  After the sections of mold were taped together, the form was coated in two layers of a mold/plug primer called Duratec.  They waited 24 hours between coatings to allow each layer to dry.  The surface was sanded and wet sanded with very fine sand paper (to ensure that they didn't sand through into the foam).  Afterwards, the team cast two fiberglass canoes for paddling practice.  Four layers of wax were applied to ensure that the fiberglass would release from the surface.  After the first canoe was pulled off the mold, the form was re-waxed.  Both canoes were removed from the form without damaging it.  The fiberglass boats look excellent and will be ready for practice this weekend.  One interesting note about this year's mold is that it is not equipped with a removable keyway as in previous years.  Instead, a 3" piece was sliced off the end of one of the sections.  The slice was reattached and wil be removed first after the concrete cures.  The team hopes that this will be sufficient to easily remove the form from the concrete.

In the next four days, the construction team is challenged with placing all of the reinforcement on the mold before the scheduled concrete pour on Sunday, February 1.  One problem is that the team forgot to add an extra section to the steel table, so the table is not long enough to anchor the tendons.  They will either have to remove the form (and risk breaking the mold), or weld on steel extensions for the anchor points.  We'll see what they come up with in the limited amount of time.

Sanding the Duratec on the mold

Fiberglassing the practice canoe

The first practice canoe

January 14, 2009

We finally got the form CNCed and construction is back on track.  The team rented a Ryder truck and drove to Southern California to have the foam cut to the correct shape.  This year, the team ordered the most dense foam possible (no kidding...it feels like wood when you touch it).  They don't have to prep the mold as much before placing concrete on it, meaning less error in the hull shape.  Also, a fiberglass canoe can be constructed directly on the mold without any coating or sanding (note that fiberglass resin eats through conventional polystyrene).

Before they drove to California, the team mapped out the approximate hull shape on the foam and trimmed the edges with a chanisaw.  They also cut the foam into sections so that it would fit in the truck.  Four sections were CNCed seperately and reassembled when they got home.  The mold looks fantastic and fits together perfectly.  Let's just hope that the CNC company didn't make any mistakes and that the canoe will be the correct shape.  Let's also hope that they compensated for the hull thickness properly and that the canoe will not be too large.

Tracing the shape of the canoe on the foam

Cutting the excess off the foam with a chainsaw

Half way done

A screen shot of the CNC program

The CNC in progress

The final product.  Wrapped in celophane and ready to come back to Nevada.

December 13, 2008

It turns out that the company that will CNC the foam free of charge is in Orange County, CA.  For everyone who is not familiar with the western United States, Orange County is a mere 494 miles away from Reno.  Thus, the latest challenge is getting the foam to and from the vendor by the end of the year.  You may wonder how we are going to do this.  If you have any suggestions, please let us know.

December 6, 2008

The foam for the form finally arrived last week (after a huge shipping delay).  The construction team will have the foam cut using a CNC machine this year, to more accuratley replicate the specified hull shape.  A company in Reno was set to do the work this month, but they are too busy and they can't get it done until March (which obviously won't work).  We recently found another company in California who claims they can cut the foam soon.  We'll keep you updated on the status of the form.

October 24, 2008

The construction process is slowly starting at Nevada.  The team ordered a very large block of high density foam and we are preparing to CNC a male mold for the first time this year.   Meanwhile, the construction team has been cleaning up the lab and preparing the steel table for this year's mold.  Check back for photos and an update on the mold.