Advice on how to patch a hole in the hull needed please

Hi there, I'm new to the forum and equally new to boat restoration or in my case, repair. I really need some advice on what the best method is on fixing this hole I have in the boats hull. I have no great experience in any kind of woodworking, and I don't have every type of snazzy powertools at hand.

The boat is a 16' sailing dinghy, performance-wise somewhere between a 470 and FD. Unfortunatly she's been lying dry for the past 6 years and what looked like a patched up repair in rotten wood has finally fell apart.

Money and knowledge/skill being an issue, there's no way for me to remove the 2 or 3 affected plywood planks and replace them so I'm going to have to patch it. My question is how the heck to go about this. I'm considering cutting a rectangular hole and fitting 6mm sipo-mahogany marine ply. The outside of the hull looks like it's covered with 2mm gelcoat, and I'd like to get both the inside and outside flush with the surrounding wood.

Here are a couple of pictures, I appreciate any advice. Thanks alot

 

This looks like it probably isn't worth saving even if you had the money to spend, skills, and motivation. Maybe just ditch the hull and salvage any useful stuff for another future boat.

 

All may not be lost. (Emphasis on "may") It looks like someone took the cheap and easy way out last time.

Frosh has a point if the area shown is typical of the hull; in other words, if the rot has spread very far. The only way to know is to check. A flat blade screwdriver is often the best tool for this. Press the blade tip into the wood all over the boat. Use some force. The object is not to make depressions all over the boat, but to identify soft areas. With moderate pressure the blade will sink in to rotted wood, but only a tiny bit, if at all, in sound wood.

Assuming the damage has not spread too far and the boat is repairable, I suggest you go with replacing planks rather than trying to put in a plywood plug. I could be wrong, but the area is too big for a plug, in my opinion. The plywood square would not flex and work as the hull planks do, and the resulting stress might lead to leaks or further damage. There are many good posts and articles here and on other sites for wood sail boats; lots of info to explain how to replace planks. Like most things, with the proper instructions you should find the process doable. I wish you luck!

 

I think if the damage is isolated, you can do one of a few different repairs. It appears to be a light weight plywood bottom and also appears to have some goo, of some sort, along the stringers where they meet the bottom planks.

Cut away the damaged area, until you're back to good wood. From the outside (yep, you'll have to flip her over) grind a very generous scarf (bevel) around the perimeter of the freshly squared up hole (a square hole makes installing a patch much easier). This bevel should be several times the thickness of the planking. Don't cheat on the amount of bevel, it provides strength and ties the new to the old planking. Now an equivalent piece of plywood can be cut with mirroring edges to the bevels you cut. Make a reasonably precise fit, but it doesn't have to be perfect, just so it will lie flush with some assistance from braces, sand bags, etc. Glue this piece in place with thickened epoxy, fill imperfections, sand fair and paint.

This is overly simplified, but there are many previous posts, addressing a repair of this type, also using epoxy, making scarf joints and other methods of installing a patch. You will probably have to do similar repairs in other locations, so use the search tool at the top of the page and begin your research.

As a foot note, most small, performance oriented sailboats are lightly built, generally, the lighter the faster. This means good performance on the water, but not an especially long life for the boat without careful upkeep. This being the case, you must access if the boat is too badly neglected to warrant effort and money to get her going again. All wooden boats have a common flaw, they do not tolerate neglect for very long. Much less so then other materials. Being a beginner, you may have difficulty making this assessment. Bring over a boat carpenter and have him look her over, then make difficult but honest decisions about her future. Good Luck . . .

 

Thanks alot for the advice everyone. Apart from this "limited" 12" x 6" hole the hull is other sound so to be honest that's a stroke of luck. There's some superficial damage to the deck like peeling varnish and a bit of bad ply but thats not too much of an issue.

I'll be buffing up on how to do decent scarf jointing then

 

Alan, a close look at the photo, reveals the bottom to be plywood and that "batten" is a stringer. This suggests a conically developed bottom, but a couple of athwartship stripes make me wonder if it's a molded boat. There just isn't enough hull shape visible from the photo to judge. If it's molded, the repair will be a little more difficult, maybe requiring a couple of layers of planking rather then a single. In either case, the edge scarfs will hold the patch fine and the stringer will support operational loads. I don't recommend removing anything more then necessary, especially if the stringers have been glued down, fasteners puttied/bunged and other structural elements are glued and seem sound.

More photos, so we can see the hull shape and identify the construction method would be helpful, Oldgold.

 

Yes. I just looked closer, and you're right. I deleted the whole thing a minute ago, before reading your comment after. Wait for more photos and info.

Alan

 

Here are some more pictures. Unfortunately the rot is worse than I first thought. It looks like the previous owner has removed some rot along the stringers and filled with epoxy before. Now the moister has rotted the wood around the epoxy.

I was only planning to sail the boat 2-3 years but what was initially a 1 sq. foot patch now looks more like 4-6 sq. feet.

At this stage, for the cost of a half-decent repair I could buy another hull without rot and if need be replace the fittings.

Rot going from the drainer to the outer stringer


in close up


the cockpit


The gelcoat hull coating, another big job getting that kind of finish over the patch.

 

Condolences. The sails, hardware, spars, and rigging must be okay. A new hull could be built by strip method. In a small sailboat, using cedar strip/epoxy, the hull isn't that time consuming nor expensive as all the rest, and you do have what is probably an excellent pattern. If you set the boat up in a cradle right side up and make station molds every couple of feet under it (meeting the hull outside), you could do a female mold strip job to produce an identical hull, saving the need for plans and tedious set-up.
That way you KNOW what you've got--- and it will last for a very long time.
Building inside rather than outside the molds means sheathing with epoxy inside before outside. The advantage is that the outer surface will fair far more easily because the strips do not react to sanding pressure (being stiffened by the inner sheathing). $500-$700 would probably cover the materials, and 80 hours of labor. The hull could be varnished as well. A classic reborn.

Of course, this all requires some general abilities, space, time, and desire. To me, it seems a shame to toss out a boat because of some rot. I know how much time is involved in making spars, rudders, tillers, centerboards, attaching fittings, etc., not to mention how expensive all that stuff is nowadays, especially sails, rope, wire, wood, and so forth. It would be far easier, I'm sure, for you to buy a fiberglass boat ready to go for $1000. It wouldn't be as light nor as pretty, but maybe you are looking to just get in the water.
However, next winter, you might just want to try your hand at building. I just wanted to mention that alternative.

Alan