Legend 35.5 - Crack under compression post
- Thread starter wilburleft
- Start date
Generally that's a bad sign.
First question, is it just a gelcoat crack or does the crack extend into the laminate?
Next, is the floor level, i.e., is it flat or does it sag?
How about other floors in the aft end of the keel sump, are they in good shape or is there evidence of damage?
Anything else look out of alignment or just not right where the various parts come together? Do doors open easily, drawers slide, etc.
First question, is it just a gelcoat crack or does the crack extend into the laminate?
Next, is the floor level, i.e., is it flat or does it sag?
How about other floors in the aft end of the keel sump, are they in good shape or is there evidence of damage?
Anything else look out of alignment or just not right where the various parts come together? Do doors open easily, drawers slide, etc.
Just out of curiosity, what is the age of the boat ?
Your photo shows a classical stress fracture of a beam with :
Without having a pic taken from much further back, we can't see exactly what we're dealing with but going at this completely blind, you're simplest solution solution would be :
Install a plate, somewhere between 1/4" to 3/4" thick under the compression post base and extend the plate along the top of the rib as long as possible. This will distribute the downward force of the mast as much as possible along the rib.
We can't say anything more definite than that not knowing what our constraints are. Lots of room to work in ? use 1/4" SS plate and reinforcement pieces. No room to work in ?, use a well painted 3/4" carbon steel plate with no externals. Remember that your mast is pretty well floating in air with the amount of material that hole has removed. Even worse, you couldn't design a worse location for the hole to remove the maximum amount of strength from that rib.
A few stress calcs are required before digging into this or otherwise it may all be for naught.
Your photo shows a classical stress fracture of a beam with :
Without having a pic taken from much further back, we can't see exactly what we're dealing with but going at this completely blind, you're simplest solution solution would be :
Install a plate, somewhere between 1/4" to 3/4" thick under the compression post base and extend the plate along the top of the rib as long as possible. This will distribute the downward force of the mast as much as possible along the rib.
We can't say anything more definite than that not knowing what our constraints are. Lots of room to work in ? use 1/4" SS plate and reinforcement pieces. No room to work in ?, use a well painted 3/4" carbon steel plate with no externals. Remember that your mast is pretty well floating in air with the amount of material that hole has removed. Even worse, you couldn't design a worse location for the hole to remove the maximum amount of strength from that rib.
A few stress calcs are required before digging into this or otherwise it may all be for naught.
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Hard to tell how deep it is. It’s deeper than the surface, but may not go all the way through.
It looks like there was a prior repair there. Also, the ledge just aft where the floor panel rests looks like it’s mashed down in that area. The vertical side of the cross beam and the ledge do not form a 90 degree angle. Posting a new pic that shows this. The aft face of the cross beam bulges out in the area of the crack.
All the floor panels are in good shape and fit fine, and the floors are all level. Doors close (front cabin doors don’t close perfectly), drawers in galley open and close just fine, cabinet doors close fine.
No sign of any issues up on deck at the base of the mast, and no sign of repairs.
In the first pic you see a hole in the aft side of the cross beam, not directly under the compression post where wires pass through from the keel bolt. I probed with a screw driver. Under the compression post it is solid. Other than that it seems mostly hollow.
Everything else on the boat seems fine. Just had it out on Friday in very light winds. 2nd time out, 1st time raising sails. All went well.
It looks like there was a prior repair there. Also, the ledge just aft where the floor panel rests looks like it’s mashed down in that area. The vertical side of the cross beam and the ledge do not form a 90 degree angle. Posting a new pic that shows this. The aft face of the cross beam bulges out in the area of the crack.
All the floor panels are in good shape and fit fine, and the floors are all level. Doors close (front cabin doors don’t close perfectly), drawers in galley open and close just fine, cabinet doors close fine.
No sign of any issues up on deck at the base of the mast, and no sign of repairs.
In the first pic you see a hole in the aft side of the cross beam, not directly under the compression post where wires pass through from the keel bolt. I probed with a screw driver. Under the compression post it is solid. Other than that it seems mostly hollow.
Everything else on the boat seems fine. Just had it out on Friday in very light winds. 2nd time out, 1st time raising sails. All went well.
It’s a 1995. I bought it from original owner in Miami one year ago. No survey….no, that was not a good choice ha ha.
Appreciate the feedback and ideas. Thank you!
Appreciate the feedback and ideas. Thank you!
I like the steel plate idea. It could span the floor, plus a few inches extra on each end to extend under the settees. Each end would have “ears” pointing down, embracing the beam. Run long bolts through the ears and the beam to hold it in place.
I’m no engineer or hull repair guy. But that might be easier, cheaper, and stronger than just re-glassing the crack area.
Wondering if compression post can be removed without lowering the mast. More forum searching is in my future. Thanks!
I’m no engineer or hull repair guy. But that might be easier, cheaper, and stronger than just re-glassing the crack area.
Wondering if compression post can be removed without lowering the mast. More forum searching is in my future. Thanks!
Trust me, in my experience if a crack goes all the way through on a steel box beam failure, it definitely goes all the way through on a FG box beam (aka. rib) and we're only talking the aft side of the rib. Can you get in to see the forward face of the rib ? Is it cracked as well ?
I have to wonder if you've already suffered a collapse of that rib. I can't see the top of the rib being fabricated at an angle (or a curve) the way the picture above shows.
You might want to lay a straight edge along the top of the rib and see how much it's deflected. You might also want to slack off on your shrouds and stays to see how much the compression post rises, unless rib does not want to return to its original shape.
This will not be a band aid repair but properly done, the rib can definitely be returned to 100% of its original strength "without the hole."
I was going to say "take your time and don't rush it as winter is already here" until I checked your avitar and saw that you're in Miami. It's ALWAYS summer down there. I can't remember when I last saw the sun here and there's already snow on the trees a few block up from our place. Pretty soon we'll be back to this :
Can't see how you can avoid dropping mast as the comp. post is going to have to be shortened by the thickness of the plate.
Take your time with this one. You may be able to find a similar problem on the archives here or on another sailboat site. Best of luck.
Tomorrow I’ll try to remove the floor panel in front of the rib to check for any cracks.
Not sure if the rib is supposed to be flat for the span of the floor. I can see it starts a gentle curve up before going under the settees, the curves up more sharply under the settees.
The hole in the rib might have to stay, for routing the thick insulated wires from the keel bolt. Must be for grounding? Will look into it.
Not sure if the rib is supposed to be flat for the span of the floor. I can see it starts a gentle curve up before going under the settees, the curves up more sharply under the settees.
The hole in the rib might have to stay, for routing the thick insulated wires from the keel bolt. Must be for grounding? Will look into it.
Just noticed this thought.
"Once bitted, twice shy." It was a hole in the rib which started all this trouble in the first place. There is no tendency of this new plate to want to slide from side to side as it will be held tightly in place by the screws going through the (1)comp. post plate, (2) through the newly installed long plate and (3) into the top of the FG rib.
It stays. The new long plate compensates for the loss of material.
I’ve driven through BC en route to/from Alaska. That’s a beautiful photo. Thanks for your input.
Vancouver, the most beautiful city in the world, on both days it doesn't rain.
Good morning people,
I lifted the forward floor panel to view the front side of the rib. No visible cracks, but it looks mashed under the post, just like the aft side of the rib.
Still leaning towards the steel plate fix. Not really confident that a fiberglass repair alone wouldn’t fail again. I never worked fiberglass. But it seems it would have to be precisely designed and executed. That means putting a lot of trust in the person doing the work, if I can find someone with experience in this repair.
I’d prefer not to engage an engineer. But I would very much value an engineer’s opinion. Not striving for perfection, just need a “go/no go” call on the steel plate proposal.
In this new photo you can see the rib is bowed, probably mostly by design but exaggerated by the mashing at the post. There’s a 1 1/8 inch gap between the rib and the straight edge in the center.
Metalsdepot dot com sells cut to size 1/4 inch 304 stainless steel plate. I think that’s a good thickness that will be strong enough support while still giving a little bit of flex.
I admit I know nothing about engineering or related material properties. But I think the question is: would this do the trick. What’s wrong with this solution?
I lifted the forward floor panel to view the front side of the rib. No visible cracks, but it looks mashed under the post, just like the aft side of the rib.
Still leaning towards the steel plate fix. Not really confident that a fiberglass repair alone wouldn’t fail again. I never worked fiberglass. But it seems it would have to be precisely designed and executed. That means putting a lot of trust in the person doing the work, if I can find someone with experience in this repair.
I’d prefer not to engage an engineer. But I would very much value an engineer’s opinion. Not striving for perfection, just need a “go/no go” call on the steel plate proposal.
In this new photo you can see the rib is bowed, probably mostly by design but exaggerated by the mashing at the post. There’s a 1 1/8 inch gap between the rib and the straight edge in the center.
Metalsdepot dot com sells cut to size 1/4 inch 304 stainless steel plate. I think that’s a good thickness that will be strong enough support while still giving a little bit of flex.
I admit I know nothing about engineering or related material properties. But I think the question is: would this do the trick. What’s wrong with this solution?
The floor the beam is sitting on should be level. Measure the height of the beam at either end and the middle. If the beam is designed to have a curved top the curve is probably symmetrical, thus the the height of the beam should vary evenly +/- a little because it is fiberglass.
The curve is fairly symmetrical. But the floor isn’t flat. It also bows down towards the center.
Measuring from the longitudinal stringers at the base of the settees, that the rib joins, to the center of the post, there’s a 1/4 inch difference. If the hull structure is symmetrical, then the base of the post is out of position by @ 1/8 inch.
Measuring from the longitudinal stringers at the base of the settees, that the rib joins, to the center of the post, there’s a 1/4 inch difference. If the hull structure is symmetrical, then the base of the post is out of position by @ 1/8 inch.
One of the many investigations you want to explore before you start cutting.
You want the least amount of flex possible to avoid further damage to the rib.
A quick calculation allowing for the following :
1. 1/4" thick X 6" wide X 48" long (width and length are estimates only)
2. Material is 304 SS.
3. Maximum expected mast loading = 1,500 lbs. (Pure speculation. Can anyone supply a better figure ?)
4. Allowable deflection = 1/8"
5. Allowable load support of the existing rib is zero as it may already be compromised.
................. No, this would DEFINITELY not do the trick unless additional reinforcement is considered ie. the flat plate becomes an inverted "U" channel.
You didn't do any calculations
. Mind you, I couldn't do any better using my calculations as I have no idea what the expected max. vertical loading on the mast would be, along with a few other unknowns.