I have an older (hull #14) CD 28 with significant separation between the aft deck and the hull flange at the point where the backstay is attached.
At the time I took possession of the boat the previous owner indicated to me that the separation had been there as long as he could remember. Meaning, he had been sailing the boat like that for some time. I have pictures of the boat 15-plus years ago and there is no sign of the separation in the old, undated, pictures.
The deck has lifted from the flange about 3/4 of an inch and the flange itself has been significantly deformed. Except for some minor deformation the deck itself looks solid and intact. The backing plate for the backstay hardware was non-existent, I picked the entire remains out with my fingers!!!
I have been looking at the joint for a long time and just started to get serious about making it right. This looks like a major rebuild of the deck/hull joint.
The thing I am trying to work out right now is the big picture on how to get the deck to 'lay down' back to it's original position and re-establish the deck/hull attachment integrity, specifically to handle the loads placed on it by the backstay. The fiberglass in the hull flange has risen significantly and in some places has fractured. I am cleaning up the joint right now, removing non-structural filler. There is debris within the joint which may be contributing to the deformation of the deck but it also appears that the backstay has lifted the fiberglass and the deck material has taken on a new "shape memory".
I'm going to go slow on this and right now i am just in exploratory mode. Comments welcome...
John
Backstay lifting deck at hull joint
Moderator: Jim Walsh
have other 28's had this problem?
In other words, is it:
a design flaw (repair w/ modifications -gusset?-)
a maintenance issue (simple repair)
just overtightened back/fore stays? (simple repair + adjustment)
a design flaw (repair w/ modifications -gusset?-)
a maintenance issue (simple repair)
just overtightened back/fore stays? (simple repair + adjustment)
Photos
Here are some pictures of the affected area.
The pictures are not the best. Most of them are too close or at strange angles. It's hard to take pictures inside a confined area.
[img]http://www.geocities.com/johnfconnolly2 ... CSzpPM.jpg[/img]
(Figure 1)
This view is on the center line looking aft. The idea of the tape measure is to show the lift, not the spacing. The spacing is OK. The lift is hard to see but it is about the thickness of the deck itself. The tape is basically level, with one end over and the other under. The two surfaces should be the same level.
[img]http://www.geocities.com/johnfconnolly2 ... JXXXPM.jpg[/img]
(Figure 2)
This view is looking through the engine instrument panel cutout, looking up. The void is, I think, where the backing plate was once located. Below the void is the mat covering the rebar that would have been attached to the backing plate.
The two holes for the backstay bolts are visible in the top/center of the picture.
[img]http://www.geocities.com/johnfconnolly2 ... JyOvPM.jpg[/img]
(Figure 3)
The intent of this picture was to show the lift. Not good perspective. The filler material has been removed across the lifted area. Where the filler is in place the deck is normal. It rises from this position to the high point at the backstay location.
[img]http://www.geocities.com/johnfconnolly2 ... zgtBPM.jpg[/img]
(Figure 4)
[img]http://www.geocities.com/johnfconnolly2 ... rV9fPM.jpg[/img]
(Figure 5)
Figures 4 & 5 show the hull flange. Figure 5 shows a section of broken flange. NOTE: I couldn't get behind the boat, without getting wet, so these pictures were taken from the cockpit and then inverted.
I will try to get some better pictures tomorrow.
John
The pictures are not the best. Most of them are too close or at strange angles. It's hard to take pictures inside a confined area.
[img]http://www.geocities.com/johnfconnolly2 ... CSzpPM.jpg[/img]
(Figure 1)
This view is on the center line looking aft. The idea of the tape measure is to show the lift, not the spacing. The spacing is OK. The lift is hard to see but it is about the thickness of the deck itself. The tape is basically level, with one end over and the other under. The two surfaces should be the same level.
[img]http://www.geocities.com/johnfconnolly2 ... JXXXPM.jpg[/img]
(Figure 2)
This view is looking through the engine instrument panel cutout, looking up. The void is, I think, where the backing plate was once located. Below the void is the mat covering the rebar that would have been attached to the backing plate.
The two holes for the backstay bolts are visible in the top/center of the picture.
[img]http://www.geocities.com/johnfconnolly2 ... JyOvPM.jpg[/img]
(Figure 3)
The intent of this picture was to show the lift. Not good perspective. The filler material has been removed across the lifted area. Where the filler is in place the deck is normal. It rises from this position to the high point at the backstay location.
[img]http://www.geocities.com/johnfconnolly2 ... zgtBPM.jpg[/img]
(Figure 4)
[img]http://www.geocities.com/johnfconnolly2 ... rV9fPM.jpg[/img]
(Figure 5)
Figures 4 & 5 show the hull flange. Figure 5 shows a section of broken flange. NOTE: I couldn't get behind the boat, without getting wet, so these pictures were taken from the cockpit and then inverted.
I will try to get some better pictures tomorrow.
John
-
Kurt
- Posts: 188
- Joined: Feb 8th, '05, 11:12
- Location: 27' Cape Dory (Alerion),
9' Dyer,
Grosse Pointe, Michigan
repair idea
After hearing the description of the problem and seeing the photos I would suggest the following. Place a heavy weight over the affected area and then wait through the winter months for the deck to return to it's original height. I would protect the deck with a piece of flexible plywood (1/4"?) over the affected area and then strategically build a pile of concrete blocks to exert a down ward pressure. You might even try unopened bags of concrete piled on one another.
Update
The lifting of the deck is only a symptom of the problem. Forcing the deck level won't actually accomplish much.
The 'shelf' or inner flange that the deck is supposed to sit on is completely deformed and needs to be removed and replaced. It is this shelf, which is part of the original hull, that is holding up the deck. Normally the deck is though bolted to this shelf as is the backstay backing plate system. The shelf is severely deformed and fractured in some places. You can see some of the fractures in the pictures. It has also become apparent that the cloth, as installed at the factory, was not completely saturated with resin. You can see this in the pictures as well. Just putting pressure on the deck won't fix the problem because there will be nothing to hold it down.
I think what happened is that over the years the backing plate for the backstay padeye, and the rebar bonded to the transom, corroded completely away transferring the backstay forces from the backing plate system to the deck. If the shelf wasn't missing so much resin it might have been strong enough to accept the transfer of forces from the deck to the shelf but the shelf was not up to the job and buckled when the backing plate system failed.
Right now it looks like the current plan is to cut the shelf away and tab in the deck. This will look a lot like the original shelf except with the original shelf the deck was through bolted to the shelf and with the new system it will be bonded.
Once the deck is tabbed in I will probably install a large backing plate for the backstay and transfer its load to another backing plate bonded to the transom. The intent is that the deck itself will take none of the load, while right now it is taking 100% of the load.
Thanks for the feed back, both public and private. I will keep the forum posted on the results.
John
The 'shelf' or inner flange that the deck is supposed to sit on is completely deformed and needs to be removed and replaced. It is this shelf, which is part of the original hull, that is holding up the deck. Normally the deck is though bolted to this shelf as is the backstay backing plate system. The shelf is severely deformed and fractured in some places. You can see some of the fractures in the pictures. It has also become apparent that the cloth, as installed at the factory, was not completely saturated with resin. You can see this in the pictures as well. Just putting pressure on the deck won't fix the problem because there will be nothing to hold it down.
I think what happened is that over the years the backing plate for the backstay padeye, and the rebar bonded to the transom, corroded completely away transferring the backstay forces from the backing plate system to the deck. If the shelf wasn't missing so much resin it might have been strong enough to accept the transfer of forces from the deck to the shelf but the shelf was not up to the job and buckled when the backing plate system failed.
Right now it looks like the current plan is to cut the shelf away and tab in the deck. This will look a lot like the original shelf except with the original shelf the deck was through bolted to the shelf and with the new system it will be bonded.
Once the deck is tabbed in I will probably install a large backing plate for the backstay and transfer its load to another backing plate bonded to the transom. The intent is that the deck itself will take none of the load, while right now it is taking 100% of the load.
Thanks for the feed back, both public and private. I will keep the forum posted on the results.
John
Last edited by johnc on Oct 29th, '08, 18:29, edited 1 time in total.
Backing plate
I thought a picture of the backing plate may be of interest.
[img]http://www.geocities.com/johnfconnolly2 ... GrQSPM.jpg[/img]
This was all that was left of the backing plate. The plate completely disintegrated. The only evidence of its existence was a small section still attached to the bolts and the electrical bonding wire.
[img]http://www.geocities.com/johnfconnolly2 ... GrQSPM.jpg[/img]
This was all that was left of the backing plate. The plate completely disintegrated. The only evidence of its existence was a small section still attached to the bolts and the electrical bonding wire.
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John Vigor
- Posts: 608
- Joined: Aug 27th, '06, 15:58
- Contact:
An idea to consider
John, this is an extraordinary failure. It's incredible that it got to this stage without being properly repaired.
But you might make life a lot easier for yourself by simply supporting the backstay with a good old-fashioned chainplate bolted through the transom and bent at the top to take the angle of the backstay. This is what many other boats have and is perfectly satisfactory.
Or two backstays, one to each quarter of the transom, if that works better. (Or one backstay split into two at the bottom.)
Then, the tricky repair of the inward-bending lip of the hull and the aft deck becomes merely a cosmetic job, not a structural challenge.
Cheers,
John Vigor
http://www.johnvigor.com
But you might make life a lot easier for yourself by simply supporting the backstay with a good old-fashioned chainplate bolted through the transom and bent at the top to take the angle of the backstay. This is what many other boats have and is perfectly satisfactory.
Or two backstays, one to each quarter of the transom, if that works better. (Or one backstay split into two at the bottom.)
Then, the tricky repair of the inward-bending lip of the hull and the aft deck becomes merely a cosmetic job, not a structural challenge.
Cheers,
John Vigor
http://www.johnvigor.com
Agree with Mr. Vigor
I agree with John Vigor. If I were to be in your position I would go with a split backstay attached to external chainplates on the transom, properly secured to grounded backing plates. I would then repair the joint and feel secure in the fact that my repair was merely cosmetic. By cosmetic I mean a seamanlike permanent repair, not a bandaid. BTW your photos and description are valuable and we all appreciate your contribution. Please keep us updated.
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fenixrises
- Posts: 450
- Joined: Feb 13th, '05, 08:01
- Location: SunShine S2 11c
- Contact:
Hi John,
You may find it helpful to cut an access hole in the verticle aft side of the footwell. Make it the size of a ready made access hatch cover and it will look like it was designed that way.
I would recommend this because if you use one central backstay chainplate the hull lamination should be beefed up with say three extra layers of f/g. Bi-axial is easy to use and is very strong with the mat already attached. Also use vinylester resin.
If you use twin plate the extra re-inforcement should not be needed. This is what I have done and it works fine.
Take care,
Fred
You may find it helpful to cut an access hole in the verticle aft side of the footwell. Make it the size of a ready made access hatch cover and it will look like it was designed that way.
I would recommend this because if you use one central backstay chainplate the hull lamination should be beefed up with say three extra layers of f/g. Bi-axial is easy to use and is very strong with the mat already attached. Also use vinylester resin.
If you use twin plate the extra re-inforcement should not be needed. This is what I have done and it works fine.
Take care,
Fred
You should always have an odd number of holes in your boat!
Backing plate "Thing"
Fred,
I was just checking out your web site and saw the "Thing".
If my boat ever had such a structure there is NO indication it ever existed. I can see where the backing plate itself used to be but there is no sign of the rebar. I knew that there had been rebar at some point but the description given to me would not have led me to image the three legged structure you had in your boat.
For those that are wondering what I am talking about, check out this link from FeNIX http://www.sbastro.com/FeNIX Interior Projects -> General Interior Pictures:
http://www.sbastro.com/FeNIX/images/Pro ... /Thing.jpg
Like they say, a picture is worth a thousand words!
John
I was just checking out your web site and saw the "Thing".
If my boat ever had such a structure there is NO indication it ever existed. I can see where the backing plate itself used to be but there is no sign of the rebar. I knew that there had been rebar at some point but the description given to me would not have led me to image the three legged structure you had in your boat.
For those that are wondering what I am talking about, check out this link from FeNIX http://www.sbastro.com/FeNIX Interior Projects -> General Interior Pictures:
http://www.sbastro.com/FeNIX/images/Pro ... /Thing.jpg
Like they say, a picture is worth a thousand words!
John
Last edited by johnc on Oct 30th, '08, 11:14, edited 1 time in total.
Starting point
For reference purposes I thought I would post a picture of the transom as it existed when I took over the project from the previous owner.
I think the comment was something along the lines: "It's not as bad as it looks, I've been sailing it like that for a long time."
[img]http://www.geocities.com/johnfconnolly2 ... kXBzAM.jpg[/img]
I think the comment was something along the lines: "It's not as bad as it looks, I've been sailing it like that for a long time."
[img]http://www.geocities.com/johnfconnolly2 ... kXBzAM.jpg[/img]
Another option
Hi All:
On the MkII there is a system which eliminates the problems of chain plates rusting, steel rebars embedded in fiberglass rusting, and this type of failure for stay anchorage. Since your into a major repair, it would make sense to look at this system as an option. The connection relies on a large fiberglass "box" for lack of a better term which is glassed to the hull and acts as the anchor point for a SS rod which ultimately connects to the stay anchor. This weekend I will take some pictures an post them. Its a bit hard to visualize as I have never seen it used on any other boat. This system seems to have been an innovation used only on the MKII. Its about as bullet proof as I can imagine. Other MkII owners can chime in here if they have had problems in this area.
I think you can bring the stern and deck back together with a system of those large rod clamps that are typically used by cabinet makers. They rely on a 3/4" pipe and can be as long as necessary. Then join the hull and deck with fiberglass tape in progressively wider layers.
Once you get the deck and stern married again. Adding a glass L similar to the detail in the MkII will give you a rust proof anchor point to hold the backstay down and at the same time some reinforcement to the hull deck joint.
As far as general backing plates go, the premade fiberglass sheets from Mcmaster Carr are about ideal.
Boyd
s/v Tern
CD 30 MkII
Fort Lauderdale, Fla.
On the MkII there is a system which eliminates the problems of chain plates rusting, steel rebars embedded in fiberglass rusting, and this type of failure for stay anchorage. Since your into a major repair, it would make sense to look at this system as an option. The connection relies on a large fiberglass "box" for lack of a better term which is glassed to the hull and acts as the anchor point for a SS rod which ultimately connects to the stay anchor. This weekend I will take some pictures an post them. Its a bit hard to visualize as I have never seen it used on any other boat. This system seems to have been an innovation used only on the MKII. Its about as bullet proof as I can imagine. Other MkII owners can chime in here if they have had problems in this area.
I think you can bring the stern and deck back together with a system of those large rod clamps that are typically used by cabinet makers. They rely on a 3/4" pipe and can be as long as necessary. Then join the hull and deck with fiberglass tape in progressively wider layers.
Once you get the deck and stern married again. Adding a glass L similar to the detail in the MkII will give you a rust proof anchor point to hold the backstay down and at the same time some reinforcement to the hull deck joint.
As far as general backing plates go, the premade fiberglass sheets from Mcmaster Carr are about ideal.
Boyd
s/v Tern
CD 30 MkII
Fort Lauderdale, Fla.
Alternative solutions
Boyd,
I would very much like to see a picture the structure you describe.
I have been thinking along the lines of the pre-made fiberglass sheets for the backing plates on the shrouds.
What I have been trying to work out is how to transfer the load from the horizontal backing plate to the vertical hull using non-corroding materials. Since there is a lot of room under the backstay padeye, what you describe would work great for the backstay. I'm not sure there would be enough room to use this solution on the shrouds but it may inspire an idea.
John
I would very much like to see a picture the structure you describe.
I have been thinking along the lines of the pre-made fiberglass sheets for the backing plates on the shrouds.
What I have been trying to work out is how to transfer the load from the horizontal backing plate to the vertical hull using non-corroding materials. Since there is a lot of room under the backstay padeye, what you describe would work great for the backstay. I'm not sure there would be enough room to use this solution on the shrouds but it may inspire an idea.
John
Film at 11:00
Hi John:
I will get you pictures ASAP.
I think you will be able to adapt the idea easily. It uses a SS rod from the underside of the deck to the fiberglass "box" to hold the deck down. The SS rod is threaded so you can adjust the tension to hold the system taut.
Instead of a "box" as CD did it, I see adding an L which would make a box with the deck and the hull as the other two sides. The access hole CD put in to install the rod is the only size controlling part of the design.
Boyd
s/v Tern
CD30 MkII
Fort Lauderdale, Fla.
I will get you pictures ASAP.
I think you will be able to adapt the idea easily. It uses a SS rod from the underside of the deck to the fiberglass "box" to hold the deck down. The SS rod is threaded so you can adjust the tension to hold the system taut.
Instead of a "box" as CD did it, I see adding an L which would make a box with the deck and the hull as the other two sides. The access hole CD put in to install the rod is the only size controlling part of the design.
Boyd
s/v Tern
CD30 MkII
Fort Lauderdale, Fla.