Fiberglass 101

[Hermit Scott]

The JB welded "through hull" was a glassed in threaded pipe. It was done by the factory like that, it has no mushroom head.(the factory didn't JBweld it, but they glassed in a pipe) They put it in at an angle to the hull. I cut it out with a grinder/sander to prepare to install a real through hull. However since the hole is angled it seems easier to just glass this hole up and redrill a hole straight through the hull. There is another through hull that was done the same way;it is the sink drain. I think that one needs to be moved to make it easier to get to and away from the muffler so I will have more room for the backing plate.
It looks like I will be able to use the holes from the other 3 through hulls, raw water feed, marine AC, head pump out. But these two holes will need to be glassed in or plugged up.

What is the best way to fill in the holes? Do I need to feather out the outside and then fill it in with layers of cloth or can I just fill in the hole somehow?

 

[sand sailor]

i would feather it inside lay in a couple layers of over sized mat then fill the rest on both sides with alternate layers and filler to finish it out

 

[jibes138]

Check out the West System instruction manuals

West has some outstanding instruction manuals that may be posted on their web site. I remember reading about this once. When you repair like this the area wants to spread the load over a large surface so you want the angle to be very shallow and on both sides of the hole. The final diameter of the repair will be something like 12 times larger than the original hole (or maybe it was the radius was twelve times larger). Regardless bigger is better. Make sure you do this right because you are trusting your vessel and maybe your life to it. As you fill in the repair you layer in glass and the large surface area spreads the load. Remember that fiberglass gets its' strength from the glass not the resin so the higher the glass to resin ratio the stronger assuming it is fully wet out and no resin starved areas.

 

[Bill Roosa]

Other options

This is not a structural fix so all you are looking for is good attachment if I read this correctly.

The sequence is drill, place mold in place, putty, remove mold, place and seal thru-hull.

Alternatively you can just putty over the hole and then drill.

I find that a single layer of saran wrap will keep your mold from sticking and eliminates a step.

Be sure the vertical surface of the old hole has a good 80 grit sandpaper finish so the putty can get a good grip.

 

[Maine Sail]

The general

The generally accepted safe practice for repairing holes below the waterline is to use a 12:1 inside and outside taper based on hull thickness.

See here: West System Hole Repair (pdf LINK)

 

[Ron20324]

Seems to me there has been a change in the train of though about the laminate buildup. Not sure where I saw it, but it has been more recent than the 2003 date on MS's PDF link. Opposite previous thinking, the thought was the biggest patch should go on first so it has the largest contact area with the hole-surrounding area. Then fill in to build up with increasingly smaller circles. Like I said, it's just my recollection, so don't shoot the messanger.

 

[Maine Sail]

Seems to me there has been a change in the train of though about the laminate buildup. Not sure where I saw it, but it has been more recent than the 2003 date on MS's PDF link. Opposite previous thinking, the thought was the biggest patch should go on first so it has the largest contact area with the hole-surrounding area. Then fill in to build up with increasingly smaller circles. Like I said, it's just my recollection, so don't shoot the messanger.

This is accurate data. West System shows it both ways in different pdf docs. I prefer the largest patch in the bevel first as to increase the primary bonding site and distribute the load better but I think either way will work so long as you use epoxy as polyesters secondary bonding characteristic are quite low when compared to epoxy. Laying in the biggest circle of cloth first is also much easier...

 

[Ron20324]

I think if you start with the small patch, when you add the next, bigger one, you almost can't help but to have a bit of void when the smaller patch ends. Epoxy fill, sure, but we want glass in there, not "glue".

 

[SamLust]

Holy carp!! I would not feel even a littil bit comfortable with what I saw in your picture.

Get the West System booklet on fiberglass repair. Read it till you understand it in and out. Use ONLY epoxy for the repairs. West is a known excelent product and many of us here have used it successfuly. Some of the other systems seem to offer a bit more versatility in mix choices.

A trick I use:

Cut out your glass patch discs in increasing diameters. Staple a piece of clear plastic material on your work surface. Wet out and stack up your patch pieces. Lay another piece of the same plastic over the patch. Roll out the excess epoxy so your patch has no excess resin. Lay the patch in to the already wet out spot. (I like to add a bit of thickener to the wet-out.) Lay another piece of the plastic over the patch and roll it into place. Blue tape the plastic in place. Peel the plastic off after curing is complete. You get a shiny surface almost free of voids. Less sanding and filling/fairing makes for a happier repair guy.

 

[RichH]

Seems to me there has been a change in the train of though about the laminate buildup. Not sure where I saw it, but it has been more recent than the 2003 date on MS's PDF link. Opposite previous thinking, the thought was the biggest patch should go on first so it has the largest contact area with the hole-surrounding area. Then fill in to build up with increasingly smaller circles. Like I said, it's just my recollection, so don't shoot the messanger.

Yup, this layup repair schedule will affect the 'least resin rich' patch - much stronger than putting 'circles' into the hole - as the 'ends' of the circles will be 'resin rich' therefore not as strong.

 

[kloudie1]

Hermit, Bill is correct. If you don’t want to do the whole tapered patch thing, you can plug the hole fair on the outside and cover the hole and plug inside with a glassed in patch or glass over with 3-4 layers.. The holes are “small” in relation to the panel and they have not been adding structural support because they are holes.. so it is not any less strong to simply plug patch the hole.. The issue might be keeping the plug patch from leaking in the future, but that can be done with a carefully applied epoxy glass-over. The holes are rounded, so you have no stress concentrators to worry with.. Either way is fine.. I know this will generate some discussion, but it is the same as cutting holes in the sides of pressure vessels to add connections.. If the hole is small, it does not require reinforcement.

 

[jibes138]

Holes in Fiberglass

Scott noted that the holes in his boat were not round because the pipes had been bonded in during layup at some odd angle. If a new through hull is installed in the same location then there will be plenty of strength from the backing plate that will be bonded to the interior for the through hull and if it (the seacockl) is screwed in place the way best practices dictate it should be a pretty strong area. I doubt that stress concentrations will be an issue since fiberglass is good for fatigue anyway as the fibers tend to stop crack propagation. Of more concern would be delamination of the repair so proper techniques, cleanliness, and use of high quality materials will be important.

 

[sandpiper10471]

The reason for starting with the largest piece of laminate and working on down in sizes is that when the grinder/sander goes on for finishing and fairing you will be cutting through the highest layers. If the largest piece was put in first, you still have continuous strands of glass bonding all the way around the hole. If the smallest were in first, you might have discontinuous strands bridging the opening, losing strength. Also, as stated earlier, you get a bigger, better bond of old to new.

 

[Ross]

Does any one know of a case where someone has done some distructive testing in this regard? I know that the wide tapers originated with polyester/fiberglass repairs as a result of trial and error. I rather doubt that a repair made by either the largest piece first or last could be knocked out of place like dumping a muffin out of a well greased pan. I always use polyester resin and alternate layers of cloth and chopped strand mat. The contact area with CSM is much greater than with woven cloth. However you can't use most CSM with epoxy.

 

[Bill Roosa]

Don't know about distructive testing but...

I did this exact same repair on my Catalina 30 in 2001. Glassed in iron pipe as a thru-hull worried me but they had not leaked in 20 years the boat had been in the water. I took out the iron pipe, sanded/cut down the fiberglass "volcano" till it was flat then installed a proper thru-hull with backing plate. I did this on 3 thru-hulls and they have not leaked since according to the present owner.

 

[RichH]

I always use polyester resin and alternate layers of cloth and chopped strand mat. .

Matting (CSM) is only a 'cushion' layer to avoid print-through from roving or heavy cloth during subsequent/later curing of the structure, ... it has relatively little strength. Only in 'box-beam', etc. construction where the stress is carried on mostly 'outside' fibers of the structure would the use of CSM as a 'filler' be sound practice. The purpose of CSM is a cosmetic 'foundation' or base for gel.

 

[Ross]

Matting (CSM) is only a 'cushion' layer to avoid print-through from roving or heavy cloth during subsequent/later curing of the structure, ... it has relatively little strength. Only in 'box-beam', etc. construction where the stress is carried on mostly 'outside' fibers of the structure would the use of CSM as a 'filler' be sound practice. The purpose of CSM is a cosmetic 'foundation' or base for gel.

Alan Vaitsis disagrees with you. As do these people. http://www.ericgreeneassociates.com/images/Repair_of_Composite_Boat_Damage.pdf

 

[r.w.landau]

Got a picture of the outside of this thru-hull.

I am thinking why glass it over and create a worry point if it can be corrected by redrilling a real thruhull and sealing it or even using an oversized thru-hull and reducing it to your needs. The existing internal glassing can be ground parallel to the hull.
The hull is probably no thicker than 1/2" there. redrilling would be easy fill around and up sizing with a reducer would be less of a threat to me than a patched hole an another one drilled elsewhere.
I would sure rather use that hole than add a new one!
r.w.landau

 

[JerryA]

Glassing 101

I agree with Ron and Maine Sail on layup if you are going to fill these holes. R.W. makes a good point though. Why not fill these holes with appropriate sized thru-hulls? Of course you can see the situation much better than the rest of us. I've not done much glass work on boats (only once on my 13 footer), but I've done several repairs on Corvettes and made some of my own custom pieces, and Ron's & Maine's layup does work well and will last a long time. You may see some settling after a year as it fully cures.

JerryA

 

[Hermit Scott]

Landau, The through hull that is at an angle is a 1/2" pipe. I am installing a 3/4" through hull. I will try to drill that through first to see if I can go through the same hole. But the one for the sink drain is in a bad location because I can't get enough room for a backing plate with out ripping out the muffler pad that is glassed in. That one will have to be filled. I have vinyl ester to do the repairs. I have no doubts that it will suffice.
I will use 24 oz. roving with an outter layer of light woven. And if anyone thinks CSM is weak try taking a hammer to 1/4" or 1/2" CSM fiberglass, like an old water pressure tank, with no woven in it and you will change your mind on it's strength. I wouldn't build a whole hull out of it but again I would have no doubt with it plugging a hole; CSM and regular old polyester resin. There is polyester resin still stuck to my shop floor after 25 years after someone building a hover craft there. I didn't know what it was when I first got here but it has steel dragged across it all the time and it is still there in one piece.
That would be a great experiment to do with different types of resin, epoxy and fiberglass. I could probably get into the material engineering lab to destroy some fiberglass samples on a tensile strength test machine. We ripped apart different types of metals and plastics, fiberglass would do fine in it. When I do the fiberglass on my boat I will mold some samples that will be a standard size that will fit in the machine.
It would be difficult to replicate the enviornment of the hull of a boat in a lab easily though. I won't even try but I will try to keep all things equal for each sample.