Table of Contents
This page contains all of the information the team used/generated in the detailed design phase. The set of Detailed Drawings can be accessed here.
Jib Transfer Bench Overview
The P14031 team has worked in MSD I to design a Jib Transfer Bench that is lighter cheaper and easier to assemble than the Previous Jib Transfer Bench designed in 2012. The detailed design can be seen below:
The Jib Transfer Bench allows the user to sit in the chair and swing between port and starboard in the Sonar sailboat, in order to trim the jib lines.
The swinging motion of the chair can be seen below:
In order to develop and model the design, the team used the following:
- Dimensions of Sonar Sailboats obtained by the team at Shumway Marine
- Model of the Sonar Sailboat in Solidworks built by Matt Brunelle (SolidWorks File of empty Sonar is available for download here)
- McMaster Carr PVC component CAD drawings
Based on feedback from the systems level design review, the team has changed the movement method from a linear track to a cantilevered arm.
The team calculated the necessary load capacity for various size bearings:
Assumptions in calculations:
- Ball Bearings
- Desired Life of 13,000 Cycles
- 1.5 Factor of Safety
- 8 bolt hole pattern
The bearing selected is:
- manufactured by VXB (Part# Kit11283)
- 500mm outer diameter (486.2mm (19") bolt hole diameter)
- 12mm thickness
- 6 mounting points on the inner race and 6 mounting points on the outer race
- 550lb capacity
- VXB Bearing Selected (Part# Kit11283)
Bearing Feasibility Calculations & Test
For the VXB Kit11283 bearing selected, the following are the calculated forces and life:
Assumptions in load capacity calculations:
- Ball Bearings (a=3)
- Cyclic Loading
- 17 week sailing season
- 5 device uses per week
- 30 transfers between port and starboard per use
In order to verify our theoretical calculations, we wanted to test the bearing to make sure it would not break apart under the load it will see in the boat. In order to do this, we wanted to exert considerable force on one race to see if it would break away from the other race.
The bearing is rated to withstand 550 lbs for 1,000,000 cycles. We need it to withstand more force (1330 lbs), but for far fewer cycles (15,000). Based on the way bearing life is calculated, this bearing should be more than suitable for our purpose.
As a general math check, however, we still wanted some sort of physical test. To do this, we placed the bearing on the floor, turned a slate table upside down, and had all four team-members stand atop the table (putting the combined weight well above 550 lbs). Then we spun the bearing. Spinning appeared and sounded smooth throughout the testing, and no damage occurred.
The bearing is sandwiched between the baseboard and a circular base on which the cantilevered arm is secured:
Each of the bases will be cut from Marine-grade Plywood. The following is a summary of the marine grade plywood components used in the design:
This will require one 4' x 8' sheet of 1/2" thick marine grade plywood
Cantilevered Arm Design
Design OptionsThe following is the system design for the cantilevered arm:
The team chose to use PVC for the arm for the following reasons:
- Lightweight (Engineering Req # 4)
- Low Cost (Customer Req # 12)
- Piers Park uses PVC for various assistive devices already; thus, the user may feel more comfortable with the device and not as intimidated
Since the devices at Piers Park are stored outdoors, the team looked at the effects of cold on PVC's properties. According to the PVC Pipe Association Technical Brief, the PVC used in the transfer device should not be negatively affected when stored in cold temperatures. As temperature decreases below 73 degrees F (the temperature at which standard PVC specifications are given), tensile strength and modulus of elasticity increase, which increases its ability to withstand external loads. Impact strength does decrease, however.
For storage purposes, neither of these things matter, as the chair will not be loaded during the winter months. We have not found any evidence that exposure to cold temperatures have any lasting effect on PVC. Therefore, we feel confident that the PVC will not sustain any long-term negative effects due to exposure to winter temperatures.
Moving forward the team analyzed multiple PVC cantilevered arm designs. (The team referenced Charlotte Pipe PVC Manual while analyzing the designs)
The team has chosen design #9 from the table above:
- With an impulse load this design deflects 1.52in
- This deflection will cause the chair support to hit the top of the bench. The max stress under this load is 12350psi, this high and will break the assembly (the impulse pressure was 15.43psi on a half plate)
- THE USER CANNOT "PLOP” VERTICALLY ONTO THE SEAT (The analysis was done from a height of 6 inches)
The ANSYS Analysis of varying forces PDF outlines the models of user motions other than sitting straight down on the PVC arm. From these models we know that the schedule 40 will be able to withstand the user's common motions.
The selected arm design is assembled from various pieces of PVC piping:
Feasibility of Assembly
The red colored pieces are the straight PVC sections, the joints have been turned translucent. The straight sections will be inserted into the joints as shown in the first image, then all of the pieces will be pressed together simultaneously resulting in the second image.
Though the device will likely not become filled with water, the team has included grooves in the top base plate for drainage. In the event that water gets into the PVC arm assembly, the water can flow into the flanges and out of the device via these grooves:
Accessibility of Screws
Since there are layered bases, there was concern with the accessibility of screws. That said, we have incorporated access holes into the bases to ensure all screws are accessible. There are 5 total access points:
Securing Device in Sonar
The team has been referring to the Sonar Deck as the highlighted section of the Sonar below:
In order to complete feasibility analysis, a model of the Sonar deck was built in ANSYS:
Concerns with the ANSYS Model:
- Some material properties of the roving and CSM are based on the best information available to the team, but are not 100% accurate
- The actual composite lay-up is unknown - how many layers of roving and CSM are actually used and their thicknesses
The team has constructed the model with the best information available to us. The design has a factor of safety and the team is confident that the proposed design will work, despite some inaccuracies in the ANSYS model.
ANSYS was used to model the loads on the boat deck. The following image outlines the load positions on the Sonar Deck:
The balsa (layer 2) has the lowest ultimate strength of all the Sonar deck layers. That is why the team selected the balsa layer for stress analysis. The ultimate strength of the balsa layer is 2,000psi. The resulting stresses from the securing device are less than 450psi. The ANSYS model shows the stresses are located:
The device sandwiches the deck of the boat between the lower base and two clamp bars. These clamp bars are made of one inch aluminum square-tube and rubberized stand-offs. The stand-offs are rubberized to prevent damage to the boat. These bars will be inserted through the bilge opening and secured to bolt that hang down from the base. Also, the newer Sonar design has two supports positioned under the deck. The securing mechanism has been positioned to accommodate these supports in the newer Sonars; however, will still work with the older model Sonars.
- Securing Mechanism - View from under Sonar Deck
- Securing Mechanism - View from under Sonar Deck (shows that the angle stock is secured to the bottom base plate)
- Securing Mechanism - Cross Section View
To use this device, we propose to utilize the natural force of gravity as the main assist method to transfer the user from one side of the boat to the other.
In the normal course of action, the user of the jib transfer chair will start on the high side of the boat. When communication comes from the skipper that he is about to perform a tack (a maneuver that switches the side on which the boat is heeled) the jib transfer seat user will disengage the locking mechanism and will allow gravity to swing him around and down to the low side of the boat. The locking mechanism will automatically lock the chair in place. Immediately after this, the skipper can start the tack. At completion of the tack, the jib trimmer, without any additional movement, will be seated on the high side of the boat, providing counterbalance to the boat’s heel and being able to trim the jib.
Team Paradise Sailing, out of Florida, has a device that moves the user between port and starboard using gravity. This Paradise Sailing YouTube video depicts the process quite well.
The following calculations show us the speed the user will reach as they get to the other side of the Sonar:
This information helps us define the worst case loading and to design a mechanism to slow the user down as the reach the other side. This information was then used to design the braking system, explained in the next section
As the upper base plate rotates (when the user switches sides) the brake mechanism will automatically engage. The mechanism works by dragging a rubberized component along the lower base plate creating friction. Once the user is on the desired side of the boat the brake will lock in place preventing the user from moving. The user can disengage the device by pulling a cord, this will allow them to rotate to the other side. When the cord is released the brake will automatically engage again.
- Braking System - Released Position
- Braking System - Locked Position
The selected spring to use has a k-value of 157 lbs/in. Although this is below even the best calculated value for spring constant, k, we are confident that this spring will provide enough slowing force to allow the pin to lock into place relatively gently.
Force to disengage the lock
With the current spring the force required to disengage the locking mechanism is 37.5 lbs, which is quite large for a person who has one sided weakness. We have designed a block and tackle system to reduce the force required to 9.4 lbs.
Wearing on the base plate
At the start of spring semester team will conduct a test to see what depth the braking system will “dig” into the base. To do this we can put a piece of plywood into a lathe and run a screw head into the wood. Knowing the run time and speed we can calculate the number of cycles.
The max depth of a groove that would allow our device to function properly is 0.25”. We can extrapolate the data to find how many use cycles it will take to “dig” a groove this deep.
The team is planning on using a liquid rubber sealant coating on the bases to increase the coefficient of friction. This will increase the number of cycles the device can be used without wearing a groove. Also, the rubber can be reapplied occasionally to prevent the grooving.
Reinforcing the locking hole
If a bushing was to be used in the holes, and there was a groove in the base, the locking mechanism would get not be able to get into the locking position; it would instead hit the “lip” of the bushing. For this reason we are not reinforcing the holes.
The seat will be secured to the top of the cantilevered arm design:
The team has designed the Jib Transfer Chair in a way that a variety of seats could be used on the device. The following table outlines some options that the team considered:
The team was also given a chair from the RIT Facilities Group to consider for use:
Comments on RIT Facilities Chair:
(+) Mounting points known
(+) Ridged seat will allow user to settle into the seat
(+) No cost to project team
(-) Black Color will get hot in the sun
(-) No padding and will be difficult to secure a cushion to
Chair Selection Final:
- Picnic Time Ventura Portable Reclining Seat (~$55.00)
- RIT Facilities Chair ($0.00)
Jib Transfer Bench Design and the Engineering Metrics
In order to show that the team has been considering the Customer and Engineering Requirements throughout the design process, we have estimated the values for some of the Engineering Metrics that will be used to evaluate the ultimate success of the end product:
Bill of Material (BOM)
Test PlansThe Test Plan has been updated to reflect changes in the design since the systems level design review and preliminary detailed design review.
Risk AssessmentBased on the design changes from the previous presentation, the Risk Assessment has been updated.
MSD II Schedule
A Preliminary MSD II Schedule outlining the major deliverables the team will have in Spring semester for MSD II.
MSD II Project Phases
- Subsystem Level Prep/Build
- Build/ Test: Subsystem Level
- Build/Test/Integrate: Subsystem & System Level
- Build/Test/Integrate: System Level
- Verification & Validation
- Project Closeout
Design ReviewsSubsystems Design Review Presentation