TOPIC: HOW DO I FIX THIS HOLE IN MY BOAT

I'm restoring my thunderhawk jr and as I was sanding the hull today I ran across an area that looked pretty bad so I started grinding it out and look what I found. It was filled with bondo and a white plaster looking something. Let me tell you what my plan was and you tell me what you think I should do. I have bondo glass and resin and mat. I was going to build it up a little with mat and resin then finish it off with bondo glass. So now it's your turn, tell me the way it should be done.

pix2

pix3

It is really hard to tell from the photo exactly what is wrong there.

If it is a hole, like you say, I would reinforce on the inside with a layer of mat, or a couple layers of glass. Go well beyond the hole, like 8" or more, and be sure to sand down to fiberglass leaving no paint.

You can concentrate more on the cosmetic appearance on the outside once the structural problem is fixed on the inside. A layer of fine weave cloth, maybe 2. I just lay the resin on real thick and blend it in. If I'm going to paint, I don't usually need much filler.

boozer,

IF it was mine, i would lay a piece of fiberglass mat on the inside of the hull, soak it in epoxy resin & let it dry. then i would feather the holed area on the outside & lay a piece of "cut to fit" mat in place & soak that with epoxy & then fill the area with epoxy "peanut butter & fair out the area.
(fwiw, a similar technique is strong enough to join together 2 sheets of 4x8ft plywood edge to edge, so i'd guess that the "patch" would be as strong or stronger than the glass hull itself. i would expect this patching technique to last as long as the hull will.)

just my opinion, satx

Boozer those appear to be pretty good sized "holes" in the hull, that appear to have been repaired incorrectly in the past. IMHO (and with all due respect), since it's below the waterline and in an area possibly subjected to a lot of stress while underway, you would want to alternate layers of mat (CSM) and cloth to build some strength back into that area. The repair on the outside could be mainly cosmetic, but more structural from the inside.

There's a great pictorial that illustrates the proper technique in the Research/Restoration section here;
www.fiberglassics.com/research/111-fiberglass-repair-pictorial.html
Although your repair area isn't as large as the one in the pictorial, the same method would apply I would think.

The process is also explained in greater detail in the corresponding article "Fiberglassic Guide to: Boat Construction and Repair" found in that same section.
www.fiberglassics.com/research/80-fiberglass-history-part-one.html
It's quite a lengthy read but if you scroll down to very near the bottom, you will find the paragraphs pertaining to Small Repairs and then Larger Repairs. I had several areas in my project hull that I felt required the use of these methods, I treated the outside as described in small repairs then from the inside as described in large.

Just my two cents worth, there's always "more than one way to skin a cat".

It appears you have a larger complication. The hull in your boat appears to be a cored construction. If the core was wet just covering over it might lead to other problems. Can you post a picture of the inside of the boat in this area. Does that material feel solid or soft when you poke at it?

I agree with mark. On Mine that had an almost identical hole from someone throwing something into the boat. I put two layers of mat on the outside bigger than the hole by about three inchs. I have some of that Bondo glass and it looks and feels like Tigerhair brand. I then put a thin layer of it over that and feathered it out. A little glaze took care of the rest and it looks great. After I flipped the boat back over I squeezed some level to the inside of the boat. Next I put 5 layers of mat on the inside for strength. I did not document the repair. The repair was about 6 inchs forward of the transom and just up from the radius where the gray primer is. I ground the damaged fiberglass out. Leaving a slot.with slightly sloped sides. Even from the inside you can hardly tell it was repaired and on the outside you'd never know it was repaired. The hole was where the black mark is. It was done in edit. It is not there just to mark where it was.

Tomahawk wrote:

It appears you have a larger complication. The hull in your boat appears to be a cored construction. If the core was wet just covering over it might lead to other problems. Can you post a picture of the inside of the boat in this area. Does that material feel solid or soft when you poke at it?

Larson Thunderhawks are just a single layer of fiberglass. (FYI)
What worries me is that the puncture might be under the seat, which doubles as an air flotation chamber. Which means he can't get to the back side easily.

I just looked again this morning and I realized that i do not think the damage went through to the inside but I can not tell because the damaged area is located right where the rear seat base is molded in and the wood stringers look to be in good shape in the damaged area. So what I think I should do is cut the top part of the seat out (red area in the picture)so I can see if it goes through then I can fiberglass the seat back in place. Damaged area is under the blue arrow in the picture. Tell me what you more experienced boaters think about that. As alway thanks so much for the help because without sites like this and people like you guys, us rookies might never finish a project boat correctly.

Boozer,

Larson Thunderhawk models have a lapstrake bottom. When you look at the floor inside you don't see the lapstrakes, but the floor has a number of longitudinal humps in the fiberglass. See pic 1 After the mold has been shot with the chopper gun the pattern of the lapstrakes also shows on the inside. To make the floor more even and to add strength to the floor Larson installed thin flat cedar strips from front to rear in the lapstrake voids and then glassed over them. The strips are wedged shaped so they made the floor flat and and the glass over the top made them stronger, more like stringer than just a filler strip.
Then they added transverse oak stingers in three or four places in the hull and glassed over them. This along with the bulkheads of seats formed thin, but rigid floor.
So your floor is not a true cored floor as the strips are thin and separated from each other, but it is not a fiberglass sheet floor as the strips are part of the structure like a cored floor.
The usual problem with the Larson floor is that water standing inside the boat finally gets into the cedar strip pockets and if the boat is in freezing weather the ice will break the top of the glass area out. See pic 2
Larson also had a problem with the seat pockets leaking from the floor drain passing through the seats and the foam soaked and ice formed in the pockets and damage occurred to the cedar strips inside the seats.
With the pics available it hard to say whether yours is external damage or ice damage, but it does look like the damage occurred right at a strip area. You should check the dark area with the grind marks to see if it's wood.
If it is, my experience is that the cedar may be damp, but it does not rot. Let it dry, and IMO you should feather the hole all the way around as the links above show, and repair it with epoxy resin and 6 ounce cloth. If you use epoxy (it bonds stronger than polyester) stay away from standard CSM mat as the binder hinders wetting out.
As for inspecting the seat interior, that might be a good idea, if nothing else to check the condition of the foam and drain. If there is internal damage it will be fairly easy to repair. Pic 3 shows a seat completely cut out to replace foam. You could cut out just a square foot of seat area and cut out the foam down to the floor. If the foam is dry and there is no damage to the floor you have less to re glass.
That hole doesn't look too serious, especially if there is no internal damage.

Interesting Flying Fish. I never knew that was standard practice on the lapline, million bubble boats. I wonder if that helps explain the common flaw of cracking down the center, where there is no wood.

Boozer, if it were me, I would just cut a hole over the area to be repaired. Large enough to work through easily, but not the whole seat. I would cut the surface of the seat starting about an inch from the vertical part and about 3" from the side of the outer hull.

Todd

how do i know if i have epoxy or polyester resin. i can find any info on the can.

That can you have there is polyester resin, and it's "pre-waxed" meaning the wax for curing is already mixed in Boozer. (Commonly found in home repair stores around here.) It's okay for putting a final layer on top, but for multiple layers it's really much easier to use "layup resin" that has no wax in it. (You add wax to the final layer to promote curing.) To put anything over the pre-waxed resin you have to rough it up with a 36 grit flapper wheel on your grinder and wipe down clean with acetone between applications. (A lot of extra work!)

I would suggest finding a local fiberglass supplier, or using one of the tried and true folks many of us have ordered from. US Composites in FL is where I buy mine. (There's another outfit in MN a lot of folks use, the name escapes me right now.) NO problems with the quality, excellent customer support and service, and their pricing offsets the additional shipping expenses incurred. You can also go to your closest West Marine store, Jamestown Distributors, etc. to source from them. Not sure where you're located, but I really suggest establishing a relationship with a supplier familiar with marine applications. I'm sure some of the gang on the west coast can recommend somebody out there if that's the case.

Just my two cents......

I get my stuff here.

www.iasco-tesco.com/index.php?page=shop.browse&option=com_virtuemart&Itemid=2

type "fiberglass" in the search box

Todd