Jib Transfer Bench

Zeb Koch

Jib Transfer Bench

Feasibility Analysis

After doing an analysis of some of the components of the current jib transfer bench, it was determined that some things could be modified quite easily. First of all, the back traveler bar can be changed to a tubular shaft. During the design of the first system, it was determined through a MATLAB analysis of the loading of the system, that under the worst case scenario of loading (when the person is directly in the center of the bar, while going over a wave) the maximum overall loading of the bar would be approximately 140lbf. Using this information in ANSYS, it was determined that the 1 inch OD, 48inch long shaft would have a maximum stress of 13326psi and a deflection of 0.0572in in the center. After seeing the design in action, it was apparent that this solid shaft could probably be replaced by a tubular one. Keeping with the same material (hardened 440c stainless steel: yield stress=100,000psi and modulus of elasticity= 30,000,000psi) and switching to a tubular shaft with an ID of 0.6in (which is a common size), it was determined that the shaft would be able to withstand this loading. Please see the calculations below:

Courtesy of

The stress and deflection formulas are and where "I" is the new area moment of inertia.

So: and

Neither of these are significant increases, and are under the limits that we need for this project. The defection is what really drives this design though, because if too much deflection occurs, the pillow block that slides on the rail will be prone to binding, which is why a hardened material was chosen. Another material that is lighter/cheaper but still strong enough could also be looked into in future senior design projects.

In regards to the weight of the system, it would be nice if this could be reduced as much as possible. When we originally specified our weight target, we had it between 50 and 100 lbs (the lighter the better, obviously). When our system is fully completely, it looks as if it will be towards the higher end of this range (about 80lbs), and should be reduced going forward in the redesign. It would be good to have the weight of the device reduced to about 60lbs if possible. Please not that the strength of the design and functionality should not be compromised for weight reduction. The highest concentration of weight is coming from the steel pieces of the system because most of the rest is made of aluminum. Stainless steel was chosen for these parts in order to get the strength that was required. The steel pieces are the back traveler bar (for which the calculation above was done) and the pieces that make up the seat bracket. These two areas will be the most important components for possible weight reduction. As stated before, the back traveler bar can be reduced to a tube, which will eliminate approximately 4 lbs. The seat bracket needs to be looked into more as well, because it weighs about 24lbs. if the design for this was changed, it would greatly reduced the amount of weight.

After testing this system at Imagine RIT, when it was under load, it was seen that there was really no deflection in the back bar or the seat bracket. A lot of deflection in the system came from the bending of the wooden platform under the load and the corresponding moment that was created by the load. Also, there was deflection in the polymer bearings on the bottom sliding carriage. There could be another way to do this portion of the system as well, after seeing this system in action. Another track and corresponding carriage style might be able to replace the current design, which could help with binding and deflection. maybe switching to two circular shafts on the bottom ( instead of a square box tube supporting a special track, as it is done now) could be a good alternative. This could allow for buying several of the same components (same as the back traveler bar) instead of specially machining the box tubing to support the track. This could save money and machining time.

As the system stands today, it costs approximately $3,000 to make (not including machining labor or the engineering hours that were put into it). The high cost items were the purchase system components, the seat bracket components, the back traveler bar and corresponding pillow block (the component that slides on it), the hand hold system (which secures the system to hand holds in the frame of the boat), and the fasteners. In regards to the fasteners, there are many different thread types and sizes. A lot of this had to do with component geometry and some of the purchased parts (some required odd-sized fasteners and metric fasteners). If the number of different style fasteners could be reduced, it would greatly reduce the complexity of the design and definitely help in the assembly process because it got quite confusing at times. This reduction would also allow you to buy more fasteners in bulk sizes, reducing costs. These were also very expensive, especially on the larger bolts (~0.5") because all of the bolts were stainless steel to withstand corrosion, which drove up the price. Overall, if the system could be reduced to about $2,000-$2,200, that would be much more preferable. This amount would make it accessible to individuals or sailing centers that are able to get small grants to subsidize these systems and not have to pay so much "out of pocket."

Lastly, there is a big issue with manufacturability of the current system, which is the main goal of the redesign of this project. The components that took the longest time to machine were the parts that went into the support cup (which attached the legs to the bottom support bar), the support bar itself, the seat bracket, and the legs. The support cup in particular definitely be redesigned going forward with this system. There are too many custom pieces required to complete a pretty simple function. This would be perfect for a brainstorming area with many different possible ways to complete this function of the system. As of right now, they are too bulky and cumbersome, as well as taking way too long to manufacture. Another problem that might be a good place for redesign are the side brackets. They required a custom, complex design that had to be water-jetted in the Brinkman Lab. Most people do not have access to such a machine, so this part could be replaced by another part to attach the back traveler bar to the support bar. Overall, this project is perfect for a redo within senior design. This is a successful project that has a few major areas for improvement which need to be addressed: manufacturability (mainly reduced number custom-made parts and machining time), weight reduction, and cost reduction. It will be a challenging project, but a very rewarding one, just as the first project was. I would suggest maintaining the exact same team structure: 3 mechanical engineers and 1 industrial engineer, because that worked out very well the first time around. I would also suggest that at least one of the team members has some sort of sailing experience going into the project. The one person on our team who had experience was a great asset because he was able to help us determine the exact functions that our device had to perform, based on the function of the jib trimmer during competitive sailing.