Does anyone know about this? They do not seem to have any structural function, and I would like to take them out. I would like to make the cabin one large space, and maybe extend the v-berth aft. Anyone understand the design thoughts here?
dmcm@pctech.net
CD25 Are the wood bulkheads structural?
Moderator: Jim Walsh
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Bruce Bett
Re: CD25 Are the wood bulkheads structural?
I think the questionis how structural are they? I had a problem with the aft bulkhead portside working loose (I know of another CD25 that had the same problem). My first thought was it's not structural don't worry about it. It is not fastened to the hull or deck but to the liner. Still they are right under the mast step, and between the chain plates. The boat does tend to flex at this point or the bulkheads wouldn't work loose. I would be very careful about removing them. The liners are very stiff at this point, and I guess the make contact with the hull and deck in several places. I'd want to talk to a marine architect before taking them out!
Bruce Bett
Sostenuto
CD25 #496
Bett@smtp.munet.edu
Bruce Bett
Sostenuto
CD25 #496
Douglas McMullin wrote: Does anyone know about this? They do not seem to have any structural function, and I would like to take them out. I would like to make the cabin one large space, and maybe extend the v-berth aft. Anyone understand the design thoughts here?
Bett@smtp.munet.edu
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TOM COONS
tRe: CD25 Are the wood bulkheads structural?
Douglas McMullin wrote: Does anyone know about this? They do not seem to have any structural function, and I would like to take them out. I would like to make the cabin one large space, and maybe extend the v-berth aft. Anyone understand the design thoughts here?
I wouldn't do it. If anything they need to be beefed up. Scroll down to the discussion on "Deck Cracks" of March 3rd and March 4, 1998. You've kind of answered the question about whether they are attached to the hull or not. In my view this is a weakness in the Cape Dory design and your plan is to further weaken it. In a seagoing boat you want lots of bulkheads. The more the better. If you want a boatshow boat suggest you get something designed to look good at the boat show, i.e., big picture windows,open spaces below. When you choose a Cape Dory, you've chosen a sea going boat designed by a premier boat builder, don't try to make it into a mobile home with sails. There's plenty of those around and a lot cheaper than a Cape Dory. Carl Alberg just turned in his grave! In my view a major mistake to weaken a boat Someday when it's blowing 70 knots, you're under bare poles making 8 knots pulling a drogue and the waves break into the cockpit as they have in my CD 31 you'll be thankful for every bulkhead you've got and say a prayer of thanks to Carl!
TacCambria@thegrid.net
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Douglas McMullin
Re: tRe: CD25 Are the wood bulkheads structural?
Thanks for the thoughts on CD25 bulkheads. I agree that structural reinforcement in that area would be a benefit. At the same time, what is there at present fills no purpose. I guess my real question is how (on this boat) would you remove the existing bulkheads and replace them with functional members that are a more efficient use of space. Most modern offshore boats designed today include no structural bulkheads. Water tight bulkheads yes, structural no. If a glass hull of this size requires the support of bulkheads to be strong, then there is a massive problem with design and the glass lay-up.
In the case of the 25, the only value the bulkheads can have is support for the mast, and some deck support. I would like to figure out a way to maintain mast & deck support while making better use of the space.
dmcm@pctech.net
In the case of the 25, the only value the bulkheads can have is support for the mast, and some deck support. I would like to figure out a way to maintain mast & deck support while making better use of the space.
dmcm@pctech.net
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TOM COONS
Re: tRe: CD25 Are the wood bulkheads structural?
Douglas McMullin wrote: Thanks for the thoughts on CD25 bulkheads. I agree that structural reinforcement in that area would be a benefit. At the same time, what is there at present fills no purpose. I guess my real question is how (on this boat) would you remove the existing bulkheads and replace them with functional members that are a more efficient use of space. Most modern offshore boats designed today include no structural bulkheads. Water tight bulkheads yes, structural no. If a glass hull of this size requires the support of bulkheads to be strong, then there is a massive problem with design and the glass lay-up.
In the case of the 25, the only value the bulkheads can have is support for the mast, and some deck support. I would like to figure out a way to maintain mast & deck support while making better use of the space.
Doug: Thanks for emailing me directly with details. You've got more experience than I have and I think are thinking correctly. As soon as I get this egg off my face I'm taking back what I said about mobile homes with sails. Your notion of replacing the bulkhead with something better is I think what we should all be doing or at least adding to the bulkhead. How about a stout beam that goes hull to hull supported with tension rods near the mast?
TacCambria@thegrid.net
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Matt Cawthorne
Re: They usually are
Doug,
I own a CD36 not a CD25 so I can't comment directly on that model, but bulkheads are usually important structural members. Don't be in a rush to remove any. The mast and rigging dump lots of loads into the hull and deck in that area. One of the jobs of the bulhkead is to resolve through tension,compression and shear in a flat plate what the hull would otherwise have to withstand in bending. A flat plate can handle loads in-plane much better than what is essentially a thin ring under bending loads.
Make yourself a model of this section of the boat. Take a cardboard oatmeal container and cut out the ends. Push on the side and see how easily the container deforms. Now put a snug fitting cardboard disk in the middle. Take a hot glue gun and put a ring of glue inside the tube near the disk on each side so that it will not pop out of position, but do not glue the disk directly to the tube. Now when you press on the side you will see just how much stiffer the structure is from being loaded the way the rigging loads the hull. It is even stiffer and stronger when the disk is glued in.
Some may try and tell you that a bulkhead was put in to compartmentalize a hull, but those bulkheads are contributing to the strength and stiffness, whether they were intended for that purpose or not.
If this is a democracy my vote is to leave the bulkhead there.
Matt
mcawthor@bellatlantic.net
I own a CD36 not a CD25 so I can't comment directly on that model, but bulkheads are usually important structural members. Don't be in a rush to remove any. The mast and rigging dump lots of loads into the hull and deck in that area. One of the jobs of the bulhkead is to resolve through tension,compression and shear in a flat plate what the hull would otherwise have to withstand in bending. A flat plate can handle loads in-plane much better than what is essentially a thin ring under bending loads.
Make yourself a model of this section of the boat. Take a cardboard oatmeal container and cut out the ends. Push on the side and see how easily the container deforms. Now put a snug fitting cardboard disk in the middle. Take a hot glue gun and put a ring of glue inside the tube near the disk on each side so that it will not pop out of position, but do not glue the disk directly to the tube. Now when you press on the side you will see just how much stiffer the structure is from being loaded the way the rigging loads the hull. It is even stiffer and stronger when the disk is glued in.
Some may try and tell you that a bulkhead was put in to compartmentalize a hull, but those bulkheads are contributing to the strength and stiffness, whether they were intended for that purpose or not.
If this is a democracy my vote is to leave the bulkhead there.
Matt
mcawthor@bellatlantic.net
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Douglas McMullin
Re: tRe: CD25 Are the wood bulkheads structural?
Doug: Thanks for emailing me directly with details. You've got more experience than I have and I think are thinking correctly. As soon as I get this egg off my face I'm taking back what I said about mobile homes with sails. Your notion of replacing the bulkhead with something better is I think what we should all be doing or at least adding to the bulkhead. How about a stout beam that goes hull to hull supported with tension rods near the mast?
I think the response that I got was on the money... I went back and looked at my original question and realized what a dolt I sounded like! Next time I will put more thought into the question before posting.
Thanks, Doug...
dmcm@pctech.net
I think the response that I got was on the money... I went back and looked at my original question and realized what a dolt I sounded like! Next time I will put more thought into the question before posting.
Thanks, Doug...
dmcm@pctech.net
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Jerry Hammernik
Re: CD25 Are the wood bulkheads structural?
Interesting discussion on this point. Let me offer some thoughts from my experience. I've owned Dauntless, my 25, for 20 years. When the boat was 6 years old I thought I noticed some flex in the area in question. I contacted the factory and they said yes this was a potential problem area. Now here's the interesting part. They called me up a few months later and said they had a crew out from the factory doing warranty work. They asked if I could have my boat in a slip and have the mast down. I said OK and two guys from the factory showed up with a kit that they proceeded to install. They removed the plywood on the berths in the main cabin and attached pieces to the bulkhead there and aft of the icebox. They also removed the teak trim on the bulkhead below the mast and installed new pieces which were carefully fitted to transfer loads from the mast down to the hull. They put everything back together and apologized for the inconvenience. I was dumbfounded, who ever heard of a factory doing warranty work on a 6 year old boat? They even left me a bunch of fiberglass cloth and a bucket of stainless screws and bolts that they didn't want to ship back. Off they went to the airport and I reset the spar. I've never seen a problem since! I have seen other 25's with some definite signs of movement in the area under the mast. My view is that the bulkhead is real important to the structure of the boat. Some of the other replies have done a much better job of explaining the whys than I could, but my view is that they are correct. I sure wish we hadn't lost a manufacturer that cared about its boats as much as Cape Dory did. I can't imagine another company spending that kind of effort for a boat so far out of warranty. Hope this info is of some help. Jerry
dauntles@execpc.com
dauntles@execpc.com
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Ron Rosenbrock
Re: CD25 Are the wood bulkheads structural?
Doug,
I just finished making repairs to the aft port side bulkhead on my 1976 CD 25. The bed liner that supports this bulkhead is very weak(and thin) and would not support the flex of the deck and compression of the mast. This caused the bed pan to sink (just aft of where the original head was.) and the bulkhead to fall into the center line of the boat offering no support at all. Needless to say this caused quite a few stress cracks on deck and on the interior of the boat.
My fix was to remove the port side plywood settee cover and insert a piece of 3/4 ac plywood under the existing bulkead, cut to the shape of the hull. This rests on oak shims which in turn rest on 6"x6" wood squares to spread the load and eliminate hot spots on the exterior of the hull. I than glassed the extended bulkhead to the hull and the existing bulkhead. The oak shims enabled me to get the bulkhead up tight to the overhead. In order to insert the new bulkhead I had to cut away a fair amount of the bed pan under the settee and open a 4"x8" hole under where the old head used to be. I guess a better way would have been to cut a whole new bulhead that extended to the hull.
I am not sure if this will work, as I am not a professional, but it appears strong and is certainly stronger than the original construction. I will be stepping the mast and launching the boat next week. I guess time will tell.
Another problem I had was that the bulkhead under the bridgedeck did not extend all the way up the the deck. This has caused the deck around the companionway to spread so the drop boards no longer fit tightly. I again used plywood, with the ends coated with expoxy, to extend up from the original bulkheads to the deck.I used bottle jacks to raise the deck slightly, installed the pieces and than lowered the deck back in position. I expoxied and bolted them in. This has added greatly to the strength of the cockpit area.
I hope this can be of help to you
drosenbrock@earthlink.net
I just finished making repairs to the aft port side bulkhead on my 1976 CD 25. The bed liner that supports this bulkhead is very weak(and thin) and would not support the flex of the deck and compression of the mast. This caused the bed pan to sink (just aft of where the original head was.) and the bulkhead to fall into the center line of the boat offering no support at all. Needless to say this caused quite a few stress cracks on deck and on the interior of the boat.
My fix was to remove the port side plywood settee cover and insert a piece of 3/4 ac plywood under the existing bulkead, cut to the shape of the hull. This rests on oak shims which in turn rest on 6"x6" wood squares to spread the load and eliminate hot spots on the exterior of the hull. I than glassed the extended bulkhead to the hull and the existing bulkhead. The oak shims enabled me to get the bulkhead up tight to the overhead. In order to insert the new bulkhead I had to cut away a fair amount of the bed pan under the settee and open a 4"x8" hole under where the old head used to be. I guess a better way would have been to cut a whole new bulhead that extended to the hull.
I am not sure if this will work, as I am not a professional, but it appears strong and is certainly stronger than the original construction. I will be stepping the mast and launching the boat next week. I guess time will tell.
Another problem I had was that the bulkhead under the bridgedeck did not extend all the way up the the deck. This has caused the deck around the companionway to spread so the drop boards no longer fit tightly. I again used plywood, with the ends coated with expoxy, to extend up from the original bulkheads to the deck.I used bottle jacks to raise the deck slightly, installed the pieces and than lowered the deck back in position. I expoxied and bolted them in. This has added greatly to the strength of the cockpit area.
I hope this can be of help to you
Douglas McMullin wrote: Does anyone know about this? They do not seem to have any structural function, and I would like to take them out. I would like to make the cabin one large space, and maybe extend the v-berth aft. Anyone understand the design thoughts here?
drosenbrock@earthlink.net