2015 wavemaker paddle replacement
Note: This documentation is very incomplete.
Issue: #22
The paddle and the submerged portion of the ram framework were sandblasted and recoated with epoxy fall 2011. When the work was done in 2011, funding limited the project to sand-blasting, undercoating and 2 layers of paint. In the intervening 3 years the coating at the waterline and below has failed at several points exposing the steel structures. At various points on the paddle, correlating to previous places where corrosion dug into the plate and struts, growth is beginning again. Since some of the pitting was at least hallway through the plate, I have no reason not to believe the surface of the paddle may now have holes. Therefore the limitations of this approach are now evident, adding another layer of triennial maintenance along with the beach material.
Based on observations on the hinge as it sits in the boneyard, it seems to bind, or catch at a certain position. For new paddle designs I intend to reuse the "foot" of the hinge, but review and modify and replace as necessary the bearing mechanism. I also intend to remove the foot from the paddle, have it blasted and powder coated (or otherwise coated) prior to re-installation.
As of July 8th, the paddle is removed from the tank. Post-removal inspection shows extensive corrosion and pitting to the point of numerous penetrations and layered patches flaking away at a simple touch. The paddle is now stored at the boneyard.
Additionally, the vertical I-beam supporting the bridge structure which anchors the ram exhibits significant corrosion. The current plan is to cut out the I-beam and run numerical models to determine if the structural component is necessary. Igor Tsukrov is providing consulting on this.
The wave and tow tank has undergone major cleaning and prepping this month. After lifting the flapper from the tank on July 8th, it was suggested by the contractor and determined by on site UNH personnel that the flapper cannot be replaced using the same equipment and techniques used to lift it out. The weight of the flapper was measured at 3,000 lbs. Estimates had it at less than half of that. Regardless, this motivates all interested parties to move in another direction when this component is replaced.
The vertical support member for the hydraulic ram bridge was removed. Said removal revealed cement pad installation problems requiring repair. The initial installation had the support member shimmed into place and a cofferdam built around the base for pouring of the cement platform. During the pour, cement did not fully infill below the support member, thus creating a pocket of water that ate away at the support beam. this will need to be repaired prior to replacement.
The hinge plate for the flapper is to be ground and painted 7/22/2014. This puts fill start to late afternoon 7/23/2014.
Draft fabrication drawings are complete for a composite paddle utilizing a welded, powder coated aluminum base for interfacing with the hinge and an all fiberglass paddle made from Strongwell's Extren Series 300. The drawings have gone out for quote to Strongwell for the FRP fabrication and Assembly, and Custom Welding for all Aluminum and Steel pieces. -Matt
New paddle design has gone through several iterations to include a review of: Structural FRP designs, Cored layed up fiberglass designs, Structural Aluminum designs, and blends of each. The old paddle was drawn in CAD for analysis comparison and dimension reference.
See the old paddle drawing for reference.
A design review will be called once an acceptable option is developed.
Aluminum sample of 6061 donated by Halo with their coating was put in the tank on 12/3/14 to gain insight on how coated aluminum withstands the tank chemistry.
The chosen concept should have the following characteristics:
- Cost: ❓
- Can last 30 (?) years without visible corrosion.
- Does not cause iron fertilization.
- Does not have a mass exceeding the original paddle mass (1200 kg).
- Material does not exceed 0.5 (?) times the yield stress in operation. See here for loading calculations.
- Material will not fail due to fatigue for at least 106 cycles.
- Maximum deflection under load: ❓
- Maximum deviation from flatness when static: ❓