Assembling 3-layer design.

2011-04-16 Build Session Report

Up to overall project info

Attendees: Adam, Clark, Ratha, Tobias.

Session photos

Goals

• Build two full modules of the 3-layer plywood design and join them in the water.
• Evaluate feasibility and identify remaining design gaps.

Testing flotation.

Results

The team reached consensus that the layered plywood design is adequately rigid and stable. One more prototyping session is needed to choose between two layers of 3/4" plywood vs. three layers of 1/2" plywood. The flotation is definitely adequate and we will go ahead with the lids as the attachment method.

Lessons learned:

• Organizer must ensure snacks and drinks are available for the crew and make sure we stay fueled and hyrated.
• My Subaru is really not supposed to carry 350 lbs on its roof. From this point on we may need to beg, borrow, or rent a truck.

Oof. Heavy.

Remaining problems to solve:

• The weight of the assembled module (150lb) is formidable. We needed 3 people to carry it, and even then it was a struggle. Handling 15 modules this way would be a difficult task.
• Getting a finished module into the water, especially without partially submerging it (which runs the risk of getting water into the flotation), was a challenge. We had some luck using 2x4s cantilevered out from the dock, but that may not work on a houseboat. Getting the platform out of the water shouldn't be so bad since we can deconstruct it and all the pieces basically float.
• The size of the finished module being larger than 4'x8' means it will be difficult to transport the platform. It means we pretty much have to move up from a pickup truck to a box truck.

Other findings:

• Due to friction, the 3-layer design could not be pulled together on the water as tightly as I was able to do it in my test (design drawing - photo). This meant there was more weakness in the joint than anticipated, even though the joint strength was still acceptable. Considering this, we may be able to use 2 layers in 3/4" plywood thickness instead of 3 layers of 1/2" plywood, which we can expect would be equally rigid and heavy, easier to assemble in the water, slightly cheaper ($40 vs. $45), and probably no weaker in the joint. We need to test this to ensure the joint really is adequate.
• We tested some double-stick foam tape as sealant. We found it did help as insurance against water in the flotation bins, but we disliked the one-time use aspect. Clark will research using old bicycle innertubes as gaskets. NB: The group has agreed that we do not want to use anything liquid such as silicone caulk sealant, because of (a) mess, and (b) decreased reusability.
• We tried eschewing the bin lids and attaching the bins directly to the plywood with wood screws. This was more resistant to taking on water, especially with the foam tape sealant, and so added peace of mind. However, consensus found that the additional trouble of wood-screwing the bins on at launch time (as opposed to snapping them on to pre-attached lids) would not be worth the additional benefit.