Using cement

[Manny]

Hi all,I have my mast down while repairing the step. I also had to remove the compression post. The sole has sagged approximately a quarter inch under the compression post (it sits above a stringer). Removing the post has removed most of the sag. From what I've seen in the archives, this is a common problem on this model. The side of the stringer I can see through the bilge has no evidence of cracks or anything. Anyway, since I do not feel comfortable cutting up the sole and fiberglass underneath (and the stringer) I'm thinking of jacking up the floor slightly through the bilge, drilling into the stringer under the post, and if it is hollow, filling with cement (concrete). I've tested some cement at home by mixing it thin enough to pour into the stringer and replicating the width and depth of the stringer, including a small pour hole, and it seems to be impressively strong. Anyone think this is a bad idea?

 

[palacegrand]

Seriously?

Manny, I don't mean to be offensive but you are joking right? Concrete?Not sure if I understand the construction layout 100% but here's a couple of really quick thoughts:- From what you describe, it seems to suggest that the "stringer" is hollow. If that's true, (hard to visualize it without some photo's) then how much space are you talking? And is it fiberglass, or wood, or ....?- I think you'd be far better off using some form of epoxy to fill this cavity as it will bond to the stringer and give you much greater strength & longevity. The concrete would only fill the space and not bond to the stringer.  *Epoxy may seem overwhelming at first glance, but in reality is pretty easy to work with. Heck if I can use it properly then anyone can! With all of my ongoing repairs, I've become a big fan of West System. - To my mind concrete does not belong in a modern boat. (Unless of course it's a some special mix meant for marine use and impervious to water etc etc etc. I'm also not sure how the concrete would react to the fiberglass when moist for a long period of time) How would it dry out/cure unless it's open to the air? How much shrinkage will there be as it cures?- Are you drilling into the stringer from the top or sides? You will likely need several holes to pour or squeeze the filler material into it.Anyway, post a photo if you can, that would help me to understand the layout.Cheers,CraigRanger 28

 

[Honeyman]

HOW about...

"boxing" the top of the stringer with aluminum plate, welded to form an upside-down U shape (flat at top and open at bottom). I would not use cement, as it will eventually absorb any water that gets in there. Hopefully, you will get other ideas from some who have done this repair.

 

[Landsend]

use hydraulic cement...

this woud be the best for the job.

 

[Ross]

This is a good example of how a little knowledge

can lead to some interesting conclusions. Portland cement IS hydralic cement! Meaning that it will harden under water. The use of concrete in this application will be appropriate IF the stringer is being distorted by the compression post load. Concrete is used for bridge piers in salt water areas for highway construction so on the inside of a boat it will last as long a granite.Manny, How long is the stringer? Will you be creating a "hard spot" that concentrates loads on a narrow line on the hull. Would you be better served by building the stringer up with resin and glasscloth from the outside in the manner of the suggested aluminum weldment? Is there a good way to connect the load from the compression post directly to the keel? I am not in favor of long term loads on bendable supports.

 

[Bill Roosa]

Beams and columns

The good newsconcrete will work fine provided you take into account the following:Are there lumber holes that need to be maintained?Can you get a top-to-bottom port-to-starboard fill of the stringer (you are trying to use it as a beam right?)?How much will the stringer "flex" and how will the flexure effect the concrete? Note concrete is not good in bending without steel reinforcement which is suspect would be difficult to install.The bad newsIf you use the concrete as a device to take the compression load from the mast on the stringer and transfer it to the hull why do you need the stringer in the first place. The stringer is designed (I would hope) to distribute the load out across the hull. A little flexure is normal and the parts have to flex to actually work. A 1/4" flexure at the stringer would seem to be a lot however. The stringer is actually acting like a beam and not a column. So if you "internally" support the stringer right under the mast load you will effectively be removing the stringer from the load bearing system and concentrating the load onto the hull in a small spot.Concrete is great when you can use it but this is a case where you need something that does what a beam does (Honyman's suggestion). You could construct a concrete beam but you would need some sort of steel in the tension (read hull) side to make it of any use. I would not recommend using epoxy to fill the inside of the stringer either as it will have the same effect of concentrating the load onto the hull.Make the stringer stronger by adding fiberglass or a metal structural ("C" or "L" or "I") element to preserve the builders design loading of the hull. It is possible when you load up the mast you could drive the bottom right through the hull with rather unpleasant results.

 

[Scott]

Manny, how will that solve your problem?

It seems that what you have is a gap between the bottom of your sole and the top of your stringer. I don't think that adding concrete to the inside of your stringer (whether it is hollow or if you create holes) is going to do anything worthwhile. If you are thinking that you will cap the stringer with concrete, I think you are making a mistake. One quarter inch of thinly mixed mortar will crumble under load too easily.Ross is right that P.C. concrete will cure under water and that it is used for piers and abutments in hostile and marine environments. Not to criticize Ross, because he is largely correct , that is not the entire story. Concrete is not particularly strong and does not bond particularly well in relationship to other products (and it comes nowhere close to granite in this regard), but it is very cheap in mass quantities which are needed for the applications Ross mentions and though spalling is always a problem (particularly when it is used with iron rebars which is just about always because the rebars are needed to improve strenth) concrete needs to be improved with chemical additives (and sealants in some applications) and the mix always has to be designed for the application before its use will be successful. A poorly designed concrete mix will readily fail. In your case, I doubt that you would be able to create a mix that won't crumble under load. Also, concrete does absorb water and if it is wet during winter lay-up. The absorbed water will not dry out (even if it appears dry on the surface) and the moisture will freeze and cause the material to crumble.Therefore, I think your solution would be a poor one because you would be messing up a perfectly good stringer (if your assessment is correct) and not adequately filling the gap. I think the epoxy solution or the aluminum plate solution would be far better in this case. I will be interested to hear how you go about fixing the sag because I noticed a very slight compression of the bulkhead under my mast when I tensioned the shrouds earlier this summer (the door to the forward berth wouldn't latch properly). When I removed the mast, the door latches properly again. I have a deck stepped mast and there is no compression post (but there is a wood support that buttresses the fiberglass bulkhead that encircles the interior like a ring).

 

[Scott]

concrete?

Stringers are subjected to much stress and flexing. While concrete is certainly strong, it has no strength under the type of flexing to which it will be sujected. IMHO

 

[Ross]

Scott, There in lies the reason that I asked

More questions than I gave answers. Manny must evaluate the problem and determine the best remedy. This is not a new boat and this probably was not a problem when the boat was new.My mast compression column is supported by a locust block bedded on the keel. I am rather nonplused to learn that designers would attempt to support the load from the mast on a beam and not on a reinforced foundation built into the hull.I would not choose concrete as a material for this repair if it were my place to choose. Resin and fiberglass cloth can be used to reinforce the stringer and if I went that way I would be over generous with my material. Nothing too strong ever broke.If only the cabin sole is bending then a bit of added height on the stringer will solve that. But I am concerned that this gap represents a distortion from years of stress. (fiberglass will bend)So my approach would be to look for ways to reinforce this critical area and distribute the force more uniformly to the hull.

 

[Alex]

Stainless Steel

Manny,If there is 1/4 inch of space why not glass in an inverted U-shape stainless steel channel under the compression post? SS is much stronger and ductile than aluminium. Of the same thickness Aluminium fatique easier than SS. The goal is to distribute the load not to transmit the load. If you just transmit the load to the keel, the keel has to transmit it somewhere else. In this case will just pull the keel bolts out.You can get the local metal supermarket guy or welding shop to fabricate one for you. As far as strength goes, hollow is stronger and lighter than solid. Just look at I-beams and formula car frames.My 2 cents.

 

[Manny]

Heat!

I initially thought about using epoxy, but I was concerned that the enormous amount of heat generated would damage the hull & stringer. I talked to some old timers at marina and they also were concerned about the heat. From what I can see the stringer is only about 2 or 2 1/2 feet long. At its highest point it is about four inches high, and about two inches wide. The stringer seems to just provide a level surface for the floor/sole. It does not rise up the inside of the hull. There is a limber hole but there is a glassed tube in it. I don't think I'll have a problem filling most if not all of the area. All I need to do is to prevent the post from crushing the stringer. I know the hull is extremely thick in the area but is not directly over the keel. It is offset to the centerline.Thanks for all the responsesBy the way, aren't some boats made of cement?

 

[Ross]

By the way, aren't some boats made of cement?

Yeah! But you wouldn't want one.

 

[Scott]

Ross, I noted ...

in your first post that you were not advocating the use of concrete . I agree with you that from the description it is hard to know if the stringer is actually in solid condition or not. It could be that it is still solid but has taken a set over the years that has created the quarter inch gap. I suppose the set could have been created by over-tensioning the shrouds for a long period of time.Manny doesn't describe whether or not the post bears directly on the sole and the sole rests on the stringer. If this is the case, and the stringer is solid, then why not simply shim the bottom of the post between the post and the sole or the top of the post between the post and the headliner underneath the mast? Some sort of spacer for the post could be fabricated or bought much more easily than working on the stringer underneath the sole.It seems to me that a re-fabrication of the stringer underneath the sole would be a difficult job at best and we don't even know if it is necessary. If the stringer is not solid, then he would be better off removing the sole and replacing the stringer with the correct fit.

 

[Scott]

Maybe this is a dumb suggestion ...

You noticed this quarter inch gap after the mast was removed? This doesn't sound like an awful lot. Could it be possible that there should be a gap when you release the pressure? You say that the floor is level when it is pressed against the stringer or when there is a gap (under load is the floor level)?I am not questioning that you have some compression failure in the roof, but could it be that there should be some compression anticipated when the mast is stepped and the shrouds tensioned?

 

[Ross]

I have been presuming that Manny has removed the

sole. The problem with a sagging support for the column is that you also get a sagging deck . In the case of my boat the support under the column had rotted so I had to refit the works. Bietzpadlin has a full keel with internal lead ballast glassed into place.Manny's stringer probably is just supported on the ends. If it were a wooden boat this stringer would be called a floor and would have tied the frames together. With the sole removed he could lay-up glass and resin to build up the top and overlay the sides to strengthen the stringer, extending the glass on to the hull to spread the load.

 

[Scott]

Ross ...

he says in his post that he doesn't want to remove the sole. I also now note that he says that the sole sagged before removing the compression post but does not sag now that the post is removed. This seems to indicate that either the stringer has failed, which means it should be re-built, or is solid but has taken a set. If it is set, then I think he could shim the post and live with a very slight sag in the floor (how would you notice a quarter inch?).IF the stringer is solid and has not taken a set (meaning the floor is level when the sole is pressed tight against the stringer, I suggest that there is some compression in the flex of the roof that should be anticipated. Since I am not a naval architect, I would not know if this is a valid design condition.

 

[Ross]

Scott, you are quite right. i missed the line

about the sole still being in place. Perhaps if he has access to that stringer from the bilge he can just drive a cedar shingle into place as a shim and be done with it.

 

[Scott]

Manny, that looks like a very nice interior!

I can see why it is important to get the job done right. I can't really see what is going on with surfaces, but it sounds like your stringer has taken a set that is also causing some warpage of the floor. It seems like the approach of topping off the upper surface of the stringer is the best option.I would try to do that by not compromising the integrity of the stringer IF the stringer looks like it is in otherwise good condition.I would definitely not shim the top of the stringer with concrete. I have a hard time imagining that a quarter inch of thickened epoxy could cause damaging heat. I bet the folks here on this site or at West Marine could offer some opinion on that.I don't know why a stainless steel or aluminum shim couldn't be used between the stringer and the sole as well, probably far more simply. Shimming the post between the sole and the post does not appear to be the way to go because the small warpage in the floor is noticeable because of the bilge cover.

 

[Manny]

Ross -

I like your idea regarding the cedar shingle!!!! I'm not sure if it would work though, I think the fiberglass portion of the sole is either bonded or screwed to the stringer (bummer). When the bilge cover is removed the edges of the sole are screwed into the stringers.It had been mentioned that maybe the shrouds and stays were too tight and I have a sneaking suspicion that they were. After checking other sailboats and what I've read on this site, mine seemed a bit tighter than most which probably contributed to the sag.BTW, I know that the cement idea maybe seem silly to some people, but I was just trying to think outside the box for the repair. Due to my comfort level with this sort of repair, availability of boat bucks, and time constraints, I was trying to find a good and simple solution. I wanted to put this out there to a large group of people to see if it is a viable idea. Sometimes the simplest solutions are the best (especially the cedar shingle idea!!!!)Thanks to all

 

[Manny]

Scott -

Thanks for the compliment on the interior. You should have seen it when we bought it, it was pretty bad. It was also fairly odiferous!! The boat was such a fantastic deal, even with all it's little problems, that it was worth it.One thing that I may have not conveyed properly is that I was thinking of filling the stringer with cement, not just shimming the top. A quarter inch of cement would definitely self destruct before I even got the boat back in the water!Manny