i am interested in installing some cabinets and shelves in my oday 34. The purpose is both to solve a moisture problem in the winter and also increase my storage. I am going to remove all of the carpet off the walls first. (I did see the comment and replies on the fabric on walls) Next I am going to install some "ribs" or bracing for the shelves and cabinets. I was going to glue these materials to the fiberglass sides using liquid nails or something similar. The question: Is there a possiblity that the ribs may pull away from the sides when the sides flex under heavy weather? I have noticed in the forward birth area that there is some flexing when under heavy sail. Should I be concerned with this?
- Status
- Not open for further replies.
D
david lewis
Stress concentrations
You raise an interesting question from a design standpoint. First of all I know some folks with a gulfstar 41 ketch and they removed all the fabric in the v-berth then they epoxied ribs to the side hull panels and then ripped some teak veneered plywood into strips and screwed them to the ribs. It came out looking like a professional job right from the factory. An excellent upgrade. As for mounting the cabinets I would just sand the surface to roughen it up then use epoxy to mount what you want with adequate clamps or devices to hold it while it cures. Changing the stiffness of the hull can have some effect in terms of moving the point of maximum stress, however you will be reducing the amount the hull flexes by the increased stiffness, so essentially the stress pattern will change but should be at a total lower level. As far as the epoxy breaking off due to the hull flexing let me put it this way, I build GRP propeller blades for aircraft. These props are about 12 feet in diameter and spin at 1200 RPM's. The testing these blades go through to simulate the worst stress imaginable on an aircraft you would not believe how much strain (deflection) they can take without breaking or delaminating. You should be OK but obviously not seeing a design or doing a real stress analysis this is just conjecture. If you are still concerned see a marine design firm. I have a 35 which is the same interior layout ...let me know how it comeS out!!! Do you already have the shelves along the sides of the v-berth? dave
You raise an interesting question from a design standpoint. First of all I know some folks with a gulfstar 41 ketch and they removed all the fabric in the v-berth then they epoxied ribs to the side hull panels and then ripped some teak veneered plywood into strips and screwed them to the ribs. It came out looking like a professional job right from the factory. An excellent upgrade. As for mounting the cabinets I would just sand the surface to roughen it up then use epoxy to mount what you want with adequate clamps or devices to hold it while it cures. Changing the stiffness of the hull can have some effect in terms of moving the point of maximum stress, however you will be reducing the amount the hull flexes by the increased stiffness, so essentially the stress pattern will change but should be at a total lower level. As far as the epoxy breaking off due to the hull flexing let me put it this way, I build GRP propeller blades for aircraft. These props are about 12 feet in diameter and spin at 1200 RPM's. The testing these blades go through to simulate the worst stress imaginable on an aircraft you would not believe how much strain (deflection) they can take without breaking or delaminating. You should be OK but obviously not seeing a design or doing a real stress analysis this is just conjecture. If you are still concerned see a marine design firm. I have a 35 which is the same interior layout ...let me know how it comeS out!!! Do you already have the shelves along the sides of the v-berth? dave
R
R.W.Landau
Hard spots.
Be careful not to create a hard spot in the hull. A retired Westinghouse engineer and his son started to build a 28" fiberglass seaworthy sailboat in their backyard seven years ago. Their slated launch is this spring. They built a frame, laid-up the hull, rolled it over, slid it down a 50' 30degree slope, set it on a cradle, built the deck and cockpit, finished the cabin with custom made cabinets, installed a Westerbeke deisel ( out of warranty now and never been started), and even built and fabricated much of the rigging and things like a brass throttle and shift( they didn't like the ones available). They used microballoon to bed the bulkheads and the ribs before glassing them in. This was to allow some flex. They tried to work cabinetry from bulkhead to bulkhead. They are installing 1/4"x (I beleive) 2" strips on the ribs as cabinet liners and backrests/hull liner. I don't know how well the liquid nails would hold up. I am a contractor. I know stuff works great on things like tub surrounds with all the temperature and moisture variables. I think the hard part would be holding the ribs in place until the glue sets up. I don't know if I would want to trust the liquid nails if I were going to do any heavy weather sailing. The Westinghouse engineer kerfed the backs of all his ribs so that they laid easily on the hull so that minimal stresses would be introduced. r.w.landau
Be careful not to create a hard spot in the hull. A retired Westinghouse engineer and his son started to build a 28" fiberglass seaworthy sailboat in their backyard seven years ago. Their slated launch is this spring. They built a frame, laid-up the hull, rolled it over, slid it down a 50' 30degree slope, set it on a cradle, built the deck and cockpit, finished the cabin with custom made cabinets, installed a Westerbeke deisel ( out of warranty now and never been started), and even built and fabricated much of the rigging and things like a brass throttle and shift( they didn't like the ones available). They used microballoon to bed the bulkheads and the ribs before glassing them in. This was to allow some flex. They tried to work cabinetry from bulkhead to bulkhead. They are installing 1/4"x (I beleive) 2" strips on the ribs as cabinet liners and backrests/hull liner. I don't know how well the liquid nails would hold up. I am a contractor. I know stuff works great on things like tub surrounds with all the temperature and moisture variables. I think the hard part would be holding the ribs in place until the glue sets up. I don't know if I would want to trust the liquid nails if I were going to do any heavy weather sailing. The Westinghouse engineer kerfed the backs of all his ribs so that they laid easily on the hull so that minimal stresses would be introduced. r.w.landau
J
Justin - O'day Owners' Web
Flex
I understand why the GRP prop blades can flex so much, and why the hull can flex, but I would think that since the cabinets are not flexible that hull flex would tend to pop them off the hull. Why doesn't this happen? I imagine it like gluing a cube, say a die, into the curve of a paper cup. If you then flex the cup the die is going to pop free from the cup. Thoughts? Justin - O'day Owners' Web
I understand why the GRP prop blades can flex so much, and why the hull can flex, but I would think that since the cabinets are not flexible that hull flex would tend to pop them off the hull. Why doesn't this happen? I imagine it like gluing a cube, say a die, into the curve of a paper cup. If you then flex the cup the die is going to pop free from the cup. Thoughts? Justin - O'day Owners' Web
D
david lewis
flexibility
justin, a very simplistic example is a cantelever beam. let's say you have a sheet of grp imbedded in a concrete wall. you press down on the free end and it bends based on the amount of applied force. now imbed the same sheet twice as deep into the wall and apply the same load to the free end. The deflection will be less because of the change in stiffness of the structure and the reduced bending moment about the wall. using this logic on the boat you have a large expanse of GRP with a load applied in the center of the area with it supported all around the edges. This will cause it to deflect like a dish (obviously an exageration because of the boat shape but just for an example). Now adding the rigid cabenetry to the side opposite the applied load and what you have done is change the location of the support on the edges. the remaining sheet of unsupported GRP is now a smaller area and the center of area is in a different location. In your example I think you are assuming the hull flexing will be the same and thus the joint will fail. Instead you have changed the whole structure and the resulting material deflection patterns will be significantly different. If you have any access to a CAD system with a finite element analysis program you can build a simple model to help you visualize what is going on. The actual boat is a very complex shape and support structure so a sophisticated computer modelling capability is required and finite element analysis would be very elaborate. This kind of analysis is usually backed up with strain gaging under actual conditions to verify the assumptions used in the computer model and correlate the results. RW makes a great comment about hard spots in the structure and you can end up causing a stress riser that can potentially lead to a failure. Using the beam example the point of maximum stress is right at the wall. Now the designer planned for this and allowed for a safety factor and designed the joint for the conditions, now you move the point of maximum stress to a different position with a different joint geometry and a different cross section of material and the whole structure need to be reanalyzed to make sure a serious problem doesn't develop. At the very least make sure edges are nicely radiused to allow the stress lines to flow nicely across the corner.
justin, a very simplistic example is a cantelever beam. let's say you have a sheet of grp imbedded in a concrete wall. you press down on the free end and it bends based on the amount of applied force. now imbed the same sheet twice as deep into the wall and apply the same load to the free end. The deflection will be less because of the change in stiffness of the structure and the reduced bending moment about the wall. using this logic on the boat you have a large expanse of GRP with a load applied in the center of the area with it supported all around the edges. This will cause it to deflect like a dish (obviously an exageration because of the boat shape but just for an example). Now adding the rigid cabenetry to the side opposite the applied load and what you have done is change the location of the support on the edges. the remaining sheet of unsupported GRP is now a smaller area and the center of area is in a different location. In your example I think you are assuming the hull flexing will be the same and thus the joint will fail. Instead you have changed the whole structure and the resulting material deflection patterns will be significantly different. If you have any access to a CAD system with a finite element analysis program you can build a simple model to help you visualize what is going on. The actual boat is a very complex shape and support structure so a sophisticated computer modelling capability is required and finite element analysis would be very elaborate. This kind of analysis is usually backed up with strain gaging under actual conditions to verify the assumptions used in the computer model and correlate the results. RW makes a great comment about hard spots in the structure and you can end up causing a stress riser that can potentially lead to a failure. Using the beam example the point of maximum stress is right at the wall. Now the designer planned for this and allowed for a safety factor and designed the joint for the conditions, now you move the point of maximum stress to a different position with a different joint geometry and a different cross section of material and the whole structure need to be reanalyzed to make sure a serious problem doesn't develop. At the very least make sure edges are nicely radiused to allow the stress lines to flow nicely across the corner.
D
Don Evans
Work With Your Existing Interior Supports
Use the existing stringers (I assume you have them?), as tie in points for attachment of shelving and cupboards. Be creative. These stringers (1"X3"s on my boat) are glassed to the inside hull already, and can take small screws and glue once the carpeting is pulled back. Add additional support blocks to these stringers for shelving. If possible, extend them from bulkhead to bulkhead for additional end support. Realistically your not going to support hundreds of pounds. You can see some evidence of what I have done in my salon conversion pix, by adding additional teak shelving and compartments. I have also added a teak shelf at the head of the V-berth, up against the chain locker, an area not utilized well. Its a good project, well worth the effort. Don
Use the existing stringers (I assume you have them?), as tie in points for attachment of shelving and cupboards. Be creative. These stringers (1"X3"s on my boat) are glassed to the inside hull already, and can take small screws and glue once the carpeting is pulled back. Add additional support blocks to these stringers for shelving. If possible, extend them from bulkhead to bulkhead for additional end support. Realistically your not going to support hundreds of pounds. You can see some evidence of what I have done in my salon conversion pix, by adding additional teak shelving and compartments. I have also added a teak shelf at the head of the V-berth, up against the chain locker, an area not utilized well. Its a good project, well worth the effort. Don
- Status
- Not open for further replies.