Hull repair

[Christopher]

What is the best method for fixing gashes, scrapes, nicks in the hull?  Every boat I look at seems to have scrapes, or even chunks gashed out of the hull, especially on the bottom of the keel.  Is this a costly or time-consuming repair or is it pretty much standard operation on a sailboat?  What materials are best for the repair?

How much would it cost at an average marine joint to have these repairs made with a new hull paint job?

[CharlieJ]

On a 32 footer I recently worked on thehull paint job ran 7,000 including paint.


The best material for repairing what ayou mention is thickened epoxy.

[Amgine]

In sculpture and boat building there are two base techniques - additive and subtractive. Invariably, the subtractive method requires a higher level of skill, and thus is more expensive.

Fibreglass is additive. It's about as hard to do as making mud pies, if a little more technical. On the other hand, when you're looking at aesthetics it can get a lot more complex.

When looking at scrapes and damage to the hull, you have to determine if it's basically an aesthetic issue, or if it is also structural. They have different solutions. If the scrape or damage does not penetrate the gelcoat, it's probably strictly aesthetic. If you see torn or damaged glass, or if you can see a discoloration of the resin surrounding the point of impact, or the shape of the hull is visibly deformed, you probably are looking at a structural issue. Both are easily repaired in fiberglass.

Depending on the extent of structural damage, these kinds of repairs are surprisingly easy to do. The basic rule is to remove damaged resin, and rebuild the layup as necessary. Often for dings and gouges in the keel it's just a light grind and fill with some soft body filler, fair it and paint it. I've seen structural repairs as large as a 16'x5' portion of the bottom and topsides rebuilt by amateurs over the course of a few weekends, but I don't think you're talking about anything that extensive.

Aesthetic repairs are, bluntly, more difficult. Gelcoat color is effectively impossible to match exactly. There's black magic done by some professionals which result in repairs which are undetectable. Often the amateur can do the basic work, and the pro comes in to do the aesthetics, but only after consulting before any work is begun. All gelcoat eventually will need to be painted or replaced. If you keep that in mind you might make the decision to move to paint which can cover a lot of sins in an older hull.

The best over-all repair material for fiberglass hulls is usually epoxy. Polyester resin is theoretically better, because that's what most frp boats are made with and it can be a single molecule when done right, but the reality is it won't bond as well, and isn't as strong. Polyester does not stick to later epoxy repairs, so once you start using epoxy you cannot turn back.

Unfortunately, there's no such thing as an average marine joint, and the range of possible hull paints makes pricing it equally difficult. Location has a huge effect. Call around to the yard and contractors in the area you would want to have the boat hauled; they should have ballpark figures for a topsides, bottom, and deck paint jobs.

[Christopher]

Thanks for the great information!

Being a complete newb to repairs and maintenance I've often been curious as to the exact composition of the hull.

I understand fiberglass as it's just cloth with resin applied, but what is the hull composed of inside to out?  What I mean is, when I stare at the hull from the inside of the cabin, am I looking at fiberglass or something else?  What comes between that sequentially from the inside to the bottom paint on the outside?  What is the gelcoat made of?

Thanks for the education :)

[ThistleCap]

As Charlie J said, epoxy is your product of choice for nearly all repairs.  It bonds well, has a longer pot life and working time, is waterproof, permanent, and can be adapted to nearly any job.  Epoxy formulations can be varied for laminating, gluing, made non-sagging for vertical or overhead jobs, adapted to fast or slow curing time, hot or cold temperatures, etc.  A wide range of additives alter it as well.  Micro-balloons or Q-cells make it easy to sand for fairing or small jobs.  Micro-fibers or random-cut fiberglass strands make it good for gluing and help fill voids between gluing surfaces.  Thixotropic agents or silica change its viscosity.  Filling agents help the epoxy fill gaps or create putties.  Epoxy is essential for some jobs, like polyester will not bond with metals, where epoxy will.
If auto body filler was what was meant by soft body filler, I'd steer clear of it IMHO.  It has no place in boat work.  It is too soft, weak, has poor adhesion, absorbs water, and its temporary nature makes another repair necessary down the road.   
If you get into structural repairs, you're entering a whole different field.  We can get into that if that's what you're looking at.

[ThistleCap]

Fiberglass is translucent.  Gelcoat on the outside, especially if it's a dark color, and a sprayed on coating on the inside block the light.  Gelcoat is nothing more than pigmented resin.  In fact, if you ever sustain an impact that shows no penetration, but was hard enough to knock something loose on the inside, you can inspect the laminate by sanding those two surfaces off.  If you then shine a light through the laminate, you will be looking at something that looks like an x-ray.  Dark areas will represent delamination of the hull, or fractures, which must be cut out and relaminated to retain the integrity of the hull.  Between the two light-blockers are roving and mat, also called batten.  If the fiberglass strands in the roving are thinner and tightly woven, it's call fabric.  If they are larger and loosely woven, it's called woven roving.  Mat is millions of randomly cut fiberglass strands glued together similar to fiberglass insulation, but only 1/8" thick.  Neither is totally satisfactory for fiberglass construction.  One has high tensile strength but is brittle and has little flexibility.  The other is flexible, has bulk and builds thickness quickly, but has little tensile strength.  The solution is to combine the two in alternate layers, mat/roving/mat/roving until you get the desired thickness.  Finer fabric is used on either side of the laminate, since it yields a smoother surface, and woven roving is kept near the center of the laminate.  There may be as many as 20-30 laminates depending on the thickness of the materials used and the thickness of laminate sought.  The secret to strength comes in having the highest possible glass to resin ratio.  Resin is brittle and has little strength of its own, and is used just as a bonding agent.  Resin is applied and worked into the material until there is complete saturation.  Aerator rollers remove any trapped air bubbles,  and any remaining resin is removed or worked into the next layer of material.  There was a process of making hulls with a chopper gun, but it quickly fell out of favor.  Random strands of glass were mixed with resin as it was sprayed into a mold.  It allowed a quick build-up of material, but it never had the strength of hand-layed laminate.

[Christopher]

So looking at the hull from the outside, all you have is paint between your eyes and the gelcoat?

[Tim]

Here is a pic that might help.
The blue is the bottom coat paint, the whit is the gelcoat, and the brown are the layers of layup, in the case of my Ariel it was about 3/8" thick here.

[CharlieJ]

So looking at the hull from the outside, all you have is paint between your eyes and the gelcoat?

If the hull is painted, yes. If it's newer then all see is gelcoat

Forgive my short replies-I'm using a IPhone and two fingers-grin

[Christopher]

no worries!  I appreciate the information so much you guys.  Wife and I are taking a little trip this weekend to see some boats and I want to be able to make some informed decisions about the sort of work certain things will take...

[ThistleCap]

Okay, a couple things you might look for are crazing and core delamination.  These are two things you'll encounter in older boats.    Gelcoat is not flexible and can create hardspots.  So in areas where there is stress or where sharp corners occur, you can encounter crazing.  Crazing may indicate an area that might need reinforcing, or it may just indicate a junction between one area that's flexible and one area that isn't.  Examples of reinforement problems may be cockpit hatches.  You may find that the coaming under the seat or hatch doesn't support the hatch all the way around.  A history of the unsupported area flexing may lead to crazing.  It's nothing usually to fear as you can expect it's more cosmetic than structural, but may mean you'd want to do two things---support the hatch more uniformly, and route out the gelcoat along the craze lines, refil with an epoxy putty and sand smooth, and repaint.  No problem.  Crazing around chainplates that come through the deck may mean the chainplates need to be adjusted where they're attached to the bulkhead below to reduce the play that's allowing the deck to flex.  It may mean the previous owner didn't know how to properly tune the rig and was overtensioning.  In either case, the coverplate may need to be removed and recaulked, but after checking to make sure the chainplates are secure, again it's a matter of repairing the crazing.  This is usually not structural.  Core delamination, however, is a whole different issue.  It is structural and requires extensive repairs that translate into repairs that may exceed the value of the boat, or months of work on your own.  Look for spongyness in the deck, bubbles in the surface, especially around areas that allow water leaks---masts, hatches, deck hardware.  If you suspect something, tap it with the heavy screwdriver handle or phenolic mallet.  If it sound solid, good.  If it sound hollow, you have a problem.  Here' you're just looking to distinguish between solid repairable boats and lost causes.  In any event, look for recommendations for good local surveyors for an inspection of any boat you become serious about.  Ask for proof of certification through NAMS (National Associatiion of Marine Surveyors), SAMS (Society of Marine Surveyors), or ACMS (Assoc. of Certified Marine Surveyors).  
Also, go to page 4 of Boat Bits.  Adrift At Sea did a nice article on boat inspection trips.  Have fun.

[Cpt2Be]

Were you going Chris? Make sure we don't try to buy out from one another LOL!

Seriously though have a great time and enjoy your boat lust weekend

[Amgine]

Hull composition, from the inside heading out to the bottom paint:

The surface is usually paint or sprayed gelcoat. If it's not gelcoat, under the paint the layup will have been coated with finishing resin, which seals out oxygen and allows the final cure - quite literally allowing the hull to potentially be one huge boat-shaped molecule - if your boat was built in polyester resin. Under the finishing resin is the layup schedule; alternating layers of matt and cloth, with extra layers in stress regions, maybe foam or balsa core in some portions, and possibly some hard points molded in. The outer surface is gelcoat, which was sprayed into a glass-smooth mold on top of a thin layer of release wax. The wax was carefully cleaned off after your boat came out of the mold, a layer of bottom paint primer, coal-tar epoxy, or similar was then applied, and then the bottom paint layers.

Some boats, like my Cape Dory 25D, have a fiberglass liner. This is used to make a lot of the cabinetry in the boat, and hides the wiring and plumbing from showing inside, and makes the inside look nicely finished. It also gets in the way if you're trying to figure out where a deck leak is coming from, and hides the wiring and plumbing when you're trying to fix it/add something/remove something. It's really cheap fiberglass, with gelcoat only on the side facing you.

Of course, as a boat ages the gelcoat gets sun damaged and oxidized and eventually loses its shine. Owners will try pretty much anything to keep that shine, but eventually the hull will need paint or new gelcoat to get that wet look back.

Similarly, the bottom paint will probably need to be stripped back at some point, if it hasn't already been done, and everything from the barrier coat out needs to be reapplied. Blistering may require the bottom be peeled back a layer or two, the fibreglass layup thoroughly dried out, then the layer built back up using a more impervious resin such as vinylester or epoxy.

I've been very lucky and haven't had to do anything beyond simple maintenance to any of my boats. I belonged to a club where I got lots of opportunities to work with epoxy doing repairs, though. And lots of time on a paint brush, sander, grinder... It really is much easier to do than it may sound like.

[Christopher]

Here is a pic that might help.
The blue is the bottom coat paint, the whit is the gelcoat, and the brown are the layers of layup, in the case of my Ariel it was about 3/8" thick here.

This explains it perfectly.  Thanks!

One other thing I wanted to ask.. what is the giant hole in the hull I see in some boats?  This one was taken from a Commander


This is below the waterline and I would assume it would need to have a bung or seacock installed or something...  What is this for and what's supposed to plug that sucker?

[Christopher]

One other shot I have a question about --- Does this image look like the gouges went through the gelcoat?

[Tim]

The Ariel/Commanders have cockpit and deck drains that go through. They are not designed to have a seacocks. But like any hole below waterline they have a potential for leaking. Modifications by owners sometimes reroute the drains so they are not below waterline, something I am contemplating currently. CJ did his on Tehani documented somewhere here on the site.

From your picture it does not look like it is all the way through gelcoat but hard to tell. In either case it does not look significant.

[Christopher]

I recall on the Solings I used to sail that they had drains in the hull that you could pop out when moving.  These only worked when you were moving as the flow of water across the hull would pull the water out of the cockpit via these drains...

Is this the same intent for these?  I assume that these holes allow water to fill within the drain channel up to the water line then?  It doesn't seem that this drain would remove water quickly from the cockpit if overwhelmed...  but then again I'm no physicist..

[newt]

Now that everyone agrees on epoxy, let me say that I had my deck redone by a professional. There is no way I can tell that the deck is not new, and he used the original fiberglass type layup. I also cannot tell where he stopped and the old fiberglass starts....
But he was part of the team that build my boat originally...

[Tim]

Here is an "in process" photo of the deckwork I am in the middle of, filling in two holes with epoxy the PO put in.

Before



During



It will be awhile before the "after" shows up as there is a lot more to do before paint

:)

[s/v Faith]

Looks like you have made a good start of it Tim.

  Did you come across any cottage cheese core while you were at it?  Hope not.