Fibreglass mat or fibreglass cloth?

Hi All,

I need to fix the front part of the boat, by cleaning everything and applying fresh layers here:



However I'm unsure if I should use fibreglass mat or fibreglass cloth? I read that fibreglass fabric (cloth) is best for structural repairs where strength is required, as this is the case here. But it may not give as smooth surface as the fibreglass mat?

Could you advise here?

 

Welcome to the forums.

So....Torn up as it is, with no other options, I'd use vacuum bagged mat (for omnidirectional strength and resin penetration into the cracks) with a skim layer of putty (to make it smooth) and glass cloth over that. YMMV.

 

That is an almighty mess and there is no telling how deep those remaining cracks could be.The bow roller needs to come off,and that may be quite a challenge,then the extent of any damage beneath it ought to be visible.Once you have determined the extent of the damage,and if you believe the effort is worthwhile,the approach recommended in post #2 could work if the structure has the integrity to allow a vacuum to be applied.If not,just adding mat a layer or two at a time until it is close enough to the desired shape to be sanded to the correct profile to allow adding gelcoat.You really ought to get beneath the damage and add a couple of plies or more to the underside and for reasons of practicality,I'd suggest mat there too,as it will be a horrible place to have to determine the shape of cloth and to make it conform to the surface.

 

Hi jehardiman, thanks for the reply!

Yes, I was thinking about 403 Microfibres from WEST SYSTEM (with epoxy rasin) to fill the wholes, etc.

And this is the confusing bit: a glass cloth (fabric), for example https://www.svb24.com/en/seatec-glass-fabric-200-g.html, or glass mat, for example https://www.svb24.com/en/seatec-glass-fiber-mat-300-g.html?

Hi wet feet, thanks a lot for the reply!

So you suggest instead a glass mat due to ease of application, even though this is a structural repair and glass cloth (fabric) should be more appropriate (as I read)?

I'll be fixing more internal part up until the roller as the boat is on water. I'll be moving her out to do an osmosis treatment and at that stage I can remove the roller and apply the layers from the other side.

 

Do you have a reason to believe that the original builder used cloth?I would doubt it,but if you can clearly see the regular pattern of strands that cloth has,then use cloth.Be aware that it doesn't drape well and will need tailoring to suit the shape.That roller needs to come off before you do anything else or you are likely to discover that your repair isn't extensive enough.The crack that runs forward needs to be investigated.It is also vital that you get inside the hull to inspect the damage there.If you are unlucky,it will mean an hour or two hanging upside down through the anchor hatch.Which will give you a few pointers about why cloth might not be the most workable option.Be thankful that a decent phone will allow good resolution images to be taken at arms length.Hanging there and laminating upside down is nobody's idea of fun,but it will need to be done.

I wouldn't use epoxy anywhere as the boat is much more likely to be laid up with polyester and you don't get a marvellous bond when laminating with polyester over epoxy.For rough shaping of the surface,I'd choose one of the repair pastes that has glass strands in polyester resin.The mat or cloth over that is where the strength comes from and you will be using the paste to allow the repair materials to follow an undistorted shape for better load paths.I will repeat,don't start the repair until the bow roller is off.If the roller is tapped into an embedded plate,take care to plug the holes with plasticene or similar and take measurements to re-locate the holes.

 

Sorry, but neither will suffice structurally. You need to remove the roller and then saw out the entire damaged area and carry it over to a bench. There you will fix up the surface of the piece and make a quickie mold for making the replacement. The mold doesn't have to be anything fancy here, just a plywood channel, painted with enamel, with a generous fillet and waxed or sprayed with mold release. Then go buy about 20 pounds of 1708 biax and a gallon of epoxy And lay the new one up solid to about 1/2 the thickness as the original. This gets fitted, the joints get bevelled back to a knife-edge at 10:1, and the new piece gets tabbed in. Tabbing starts with the widest pieces first and works to narrower strips as the bevel gets filled it. The tabbing will end up spilling out at least a foot past the part you made in all directions. The contour with a big belt sander, putty, prime and paint. It's probably a three day weekend sort of job. Keep checking that the roller plate will fit inside - ask me why I tell you this

 

Got it, thanks a lot for the advice.

No, I don't have any reason to think the original builder used cloth - I'm just trying to understand the difference, and it's clear now. I will use mat.

Regarding the roller, thanks for clarifying. The issue is that the boat is on the water and I'd need to get some advice on site if removing the bower is safe as I don't want to do any more damage and risk that I won't be able to put it back. I'll be only on site for a few days to prepare the boat before moving her to another country - a week of sail - and then I'll have more time to do it properly.

So as a temporary solution, I understand this is not ideal, but at least it'd provide some measure of security, I though that after cleaning all of this up, I'd apply a few layers up to that metal stand:


And then once I take her out of water, during the osmosis treatment when I remove all the layers, I'd be able then to take the roller off and apply the layers in the other direction to properly secure this area:



The outside surface would be much easier to repair once out of the water with the roller out:

 

@wet feet

The reasons you give for using poly are not really correct. He uses poly to use a similar gelcoat.

In order to properly fix this; the person doing the repair needs to understand if movement caused the failures first. And if so, the remedy is to add the correct type of glass to reduce such movement. But it sort of looks more beat up by an anchor than anything; perhaps save for the cracks near the bow roller, which means it is largely cosmetic.

If the area is flexing under loads, another possibility is you are not tying off the anchor to a proper cleat and this area is taking anchor loads which is a major error as the area was not designed for it. If that is the case, a bit of mat glass or 1708 underneath can help restore the integrity, but you must discontinue loading the area.

It is impossible to fix without removing the roller as the gelcoat is cracked under it.

 

My post crossed with your last. I see the bow roller area is meant to take loads. This changes everything.

It isn’t a couple days repair. The best you could do now is travel with the anchor off the roller. If that is not possible; perhaps you can reinforce the area with wood planking and screws. The repair is extensive and will take more than a few days to be made well.

If you can fin roll some mat glass or 1708 underneath it all; it may also be a temporary repair. If you grind away all the gelcoat or paint/dirt under and get to glass; that would be a more perm solution. 1708 has strength and would be preferred if available.

Phil Sweet’s option is probably best, but that ain’t 3 days of work; it’ll take most people about 2-4 weeks, although not sure how you blend back to the old gelcoat using epoxy.

 

Thanks a lot for the reply.

OK so we've got two observations:
1) bow roller area takes loads
2) cracks are probably due to an anchor
And
3) not a problem to travel with the anchor off the roller

Given this, is there even a sense of doing a temporary fix as I wrote earlier (without removing the roller) and wait until I take the boat out of water later this year? I was planning to grind away all the gelcoat anyway so then I'm able to fix it at the same time.

Is there a risk of postponing the temporary fix (= without removing the roller) given points 1-3 above? I'll have a very short season anyway, in total not more than 3 weeks of sail until the boat is removed from the water in August.

 

Thanks a lot for the detailed answer. I'll do some research and also watch some videos (I found https://www.youtube.com/@boatworkstoday and https://www.youtube.com/@SailLifeto of great resource) to understand what this all means and will make a plan, thanks!

 

In my opinion, removing the anchor underway and tying the bow roller to the boat in case it is really loose are the best temp solution. If you must anchor, the decision is based on how bad the area is flexing. If you are worried about a full failure; reinforce with wood somehow so you can anchor at nite, but still run anchor off.

 

Can you post a complete photo? It looks like the fitting also holds the forestay.

 

I’m just going to add one thing.
The reason Phil is largely and likely correct is it appears the fiberglass in the area is damaged structurally. This means it cannot be repaired; only bandaged or replaced. A bandage goes over the damaged area, but doesn’t fix it. That would be 1708 underneath. The downside to replacement is you must damage it somewhere else that is easier to repair if you cut it out.

Before you cut it out; make sure you choose wisely where to cut; perhaps Phil can help.

And if there is not a lot of movement; perhaps it can be repaired in place. The only way to know is to grind back all the gelcoat about 3” from all the areas where there are cracks and assess things and also to identify areas of flex to mitigate future repairs.

 

If there are mast loads here; disregard all my comments and ground it. I did not expect that to be the case.