erikgreen
Captain
- Joined
- Jan 8, 2007
- Messages
- 3,105
Hey guys - long winded typist here at it again 
I've put up a couple posts in my ongoing refit thread about what I found out when I tore apart my own work from a couple years ago. I thought I'd condense and focus on it for a post or two... it's been very educational to me.
I won't re-trace the history of my boat, that's been done in other threads, but I will state that I re-did the stringers, deck, and removed the interior about two years ago. I had always intended to put a nice new interior in, but I only got as far as the side wall carpet and nautolex flooring before the time crunch set in, and then it started to wear badly, until last summer when the nautolex peeled up.
So this winter I decided to re-core the transom and re-do a major portion of the interior and hull... new structure, new painted floor, etc.
In doing so I had to cut out and remove work I'd done two years ago, including:
Anyway, on to the lessons I learned.
1) PL Premium. I used this after I'd redone the stringers to glue the deck on. I used a Bateau.com building method for the deck, no screws... I attached cleats to the stringers, 2x2 white wood boards cut to length on the top edge of each to give me a gluing surface for the deck. After the PL cured I glued the deck sections on the same way. I then covered cracks and gaps with epoxy mixed with wood flour and glassed over the whole top surface with 8 oz glass. Tabbing at the deck edges was biax 1708 plus some 3210 scraps.
The PL premium did ok for holding the deck in place. It peeled up much like 3m 5200 where it was in large clumps, although the 5200 would have stuck better. Comparing it to the epoxy mix I used, it was night and day... the PL was less than half the strength of the epoxy (and I was glad of it since I was removing it).
Using epoxy for the deck would have made the deck more of a one piece structure with the hull.. something devoutly desired by me since it makes the whole boat dramatically stronger.
So I won't use PL for much of anything critical in future... it's too weak to form a structural bond where I could otherwise use epoxy, and for sealing I'll use 3m 5200. For bedding stringers (not doing that this time, mostly) I'll use plastic spacers for an air gap and fillets made of epoxy.
2) Thick glass mat and epoxy - I had gotten some biax/mat combination off ebay, in a 20 lb box. This stuff is a great deal and is basically boxed up scraps of stitched cloth, about 3210 weight. I used it in places to tab the deck to the hull, since I was low on money and it was handy. In some spots it worked ok, but in most places I didn't get it wet out well enough. There was epoxy on the bottom and over the top, but the fabric failed in the middle, between layers of fibers. Anywhere I used it on the bottom of the boat it did ok, probably because gravity helped the resin pool into the cloth. But in the future I'll use biax without mat or plain cloth when possible, so not only will I get good wet-out but I'll save resin over using the thick stuff. This cloth is still great for poly molding and wherever you need thick build-up fast, you just need to wet it out in a box before applying. I encourage anyone using thicker cloth or mat to test wet a piece and let it harden, then destroy it. Sometimes it looks wet out and it really isn't.
3) Overbuilding. I think most of us have done this at some point. If 1 layer of plywood is good, 2 must be much better... if 2 layers of mat are good, 3 layers of biax are better, etc. Note that this is generally a good idea where boats are concerned... extra strength doesn't hurt except when you go overboard and add a ton of weight, or when you add resin without adding glass, etc.
I found when I was removing my old motor mounts and deck that I had gone way, way overboard. Near the joints, the thickness of the fillets, two layers of 3/4" ply, and the glass exceeded 3 inches. This is on a 20 foot boat. To cut through a 10 inch linear section of that with a fresh blade on my sawzall took about 1 minute. Then I had to do it 6-7 more times to get the rest of the wood out.
Now, I know this is super strong and won't break, but it's also about 5 times heavier than it needed to be.. I could have given it almost the same strength with much less work and weight. Probably more important to my wallet, I could have used one quarter the epoxy I did. I think the whole section I removed took something like a half gallon of epoxy. I even found epoxy pooled in the bilge from when I'd put this in.
I believe by removing and re-doing the aft deck and transom I'm going to end up with a stronger boat (by reason of improved structure) that weighs about 300 lbs less in the stern. I'll save more weight by removing and replacing the cap. It should be interesting to see if I gain speed.
4) Grinding and prep work. This is very hard to overdo In the previous repair I'd ground until I was sick of it. I was working in my cold (mostly) garage, and grinding the hull and sides for stringer and deck replacement got really, really old. I think I spent 16-20 hours doing just grinding. As I've been removing the old deck and structural parts, I've found out that it really affected the strength of the work. Some areas where I ground less I can pull the glass off with one hand after I peel an edge up. Others where the grinding and prep were good I have to grind the glass off.
To give you an idea, I had ground the old glass until all loose fibers were off and the glass and resin looked solid, maybe with some discoloration. In other words, an average prep job.
Looking closer I see the discoloration was left over from the chopper gun glass that originally coated the sides of the boat. This glass was loosely attached, and when the epoxy and glass I put on peeled up, it broke the bond between the discolored stuff and the actual hull. In other places I pulled off apparently "clean" sections of glass to expose dry fibers beneath... the same layering from the chopper gun, just without discoloration.
So if you're not sure if you're done grinding, attach a piece of wood to your inner hull with epoxy. Let it harden, then pull it off. You'll probably see that you pulled off part of the inside surface of your hull, and how hard it was to do should tell you how much grinding is left.
5) Planning and measurement. I knew when I first finished the work I was doing that I hadn't gotten things quite square. This became apparent when I used the boat... it was solid, but water had a tendency to pool back at the transom on deck, and the boat wouldn't drain completely when tilted on the trailer.. there were a few low spots. Also the limber holes weren't fully open in places. The fuel tank hatch in the deck center was cut tapering, so the aft end was wider than the front. A 3/4" difference over a 6 foot length is enough to make it look strange.
So this time I'm going to spend the effort to measure from reference points and lines, to make sure that the deck is going to drain well, and that the hatch openings are even. I'm going to some effort to plan drainage, and I'll be building up certain areas of the hull bottom so they're high spots instead of low.
I encourage anyone who is doing a restore for the first time to take the time to do a sample layup... use some wood scraps and glass to make a mock stringer install, glass some plywood together at right angles, butt joint some and see how it looks.... then tear it all apart with saws and pry bars. Your restore work will be much improved knowing where you went wrong.
Erik
I've put up a couple posts in my ongoing refit thread about what I found out when I tore apart my own work from a couple years ago. I thought I'd condense and focus on it for a post or two... it's been very educational to me.
I won't re-trace the history of my boat, that's been done in other threads, but I will state that I re-did the stringers, deck, and removed the interior about two years ago. I had always intended to put a nice new interior in, but I only got as far as the side wall carpet and nautolex flooring before the time crunch set in, and then it started to wear badly, until last summer when the nautolex peeled up.
So this winter I decided to re-core the transom and re-do a major portion of the interior and hull... new structure, new painted floor, etc.
In doing so I had to cut out and remove work I'd done two years ago, including:
- Deck sections
- Stringer sections
- Motor mounts (re-cored 2 y.a.)
- transom glass (patches)
- transom shelf and hatches
- Side shelves to which interior panels attach
Anyway, on to the lessons I learned.
1) PL Premium. I used this after I'd redone the stringers to glue the deck on. I used a Bateau.com building method for the deck, no screws... I attached cleats to the stringers, 2x2 white wood boards cut to length on the top edge of each to give me a gluing surface for the deck. After the PL cured I glued the deck sections on the same way. I then covered cracks and gaps with epoxy mixed with wood flour and glassed over the whole top surface with 8 oz glass. Tabbing at the deck edges was biax 1708 plus some 3210 scraps.
The PL premium did ok for holding the deck in place. It peeled up much like 3m 5200 where it was in large clumps, although the 5200 would have stuck better. Comparing it to the epoxy mix I used, it was night and day... the PL was less than half the strength of the epoxy (and I was glad of it since I was removing it).
Using epoxy for the deck would have made the deck more of a one piece structure with the hull.. something devoutly desired by me since it makes the whole boat dramatically stronger.
So I won't use PL for much of anything critical in future... it's too weak to form a structural bond where I could otherwise use epoxy, and for sealing I'll use 3m 5200. For bedding stringers (not doing that this time, mostly) I'll use plastic spacers for an air gap and fillets made of epoxy.
2) Thick glass mat and epoxy - I had gotten some biax/mat combination off ebay, in a 20 lb box. This stuff is a great deal and is basically boxed up scraps of stitched cloth, about 3210 weight. I used it in places to tab the deck to the hull, since I was low on money and it was handy. In some spots it worked ok, but in most places I didn't get it wet out well enough. There was epoxy on the bottom and over the top, but the fabric failed in the middle, between layers of fibers. Anywhere I used it on the bottom of the boat it did ok, probably because gravity helped the resin pool into the cloth. But in the future I'll use biax without mat or plain cloth when possible, so not only will I get good wet-out but I'll save resin over using the thick stuff. This cloth is still great for poly molding and wherever you need thick build-up fast, you just need to wet it out in a box before applying. I encourage anyone using thicker cloth or mat to test wet a piece and let it harden, then destroy it. Sometimes it looks wet out and it really isn't.
3) Overbuilding. I think most of us have done this at some point. If 1 layer of plywood is good, 2 must be much better... if 2 layers of mat are good, 3 layers of biax are better, etc. Note that this is generally a good idea where boats are concerned... extra strength doesn't hurt except when you go overboard and add a ton of weight, or when you add resin without adding glass, etc.
I found when I was removing my old motor mounts and deck that I had gone way, way overboard. Near the joints, the thickness of the fillets, two layers of 3/4" ply, and the glass exceeded 3 inches. This is on a 20 foot boat. To cut through a 10 inch linear section of that with a fresh blade on my sawzall took about 1 minute. Then I had to do it 6-7 more times to get the rest of the wood out.
Now, I know this is super strong and won't break, but it's also about 5 times heavier than it needed to be.. I could have given it almost the same strength with much less work and weight. Probably more important to my wallet, I could have used one quarter the epoxy I did. I think the whole section I removed took something like a half gallon of epoxy. I even found epoxy pooled in the bilge from when I'd put this in.
I believe by removing and re-doing the aft deck and transom I'm going to end up with a stronger boat (by reason of improved structure) that weighs about 300 lbs less in the stern. I'll save more weight by removing and replacing the cap. It should be interesting to see if I gain speed.
4) Grinding and prep work. This is very hard to overdo
In the previous repair I'd ground until I was sick of it. I was working in my cold (mostly) garage, and grinding the hull and sides for stringer and deck replacement got really, really old. I think I spent 16-20 hours doing just grinding. As I've been removing the old deck and structural parts, I've found out that it really affected the strength of the work. Some areas where I ground less I can pull the glass off with one hand after I peel an edge up. Others where the grinding and prep were good I have to grind the glass off. To give you an idea, I had ground the old glass until all loose fibers were off and the glass and resin looked solid, maybe with some discoloration. In other words, an average prep job.
Looking closer I see the discoloration was left over from the chopper gun glass that originally coated the sides of the boat. This glass was loosely attached, and when the epoxy and glass I put on peeled up, it broke the bond between the discolored stuff and the actual hull. In other places I pulled off apparently "clean" sections of glass to expose dry fibers beneath... the same layering from the chopper gun, just without discoloration.
So if you're not sure if you're done grinding, attach a piece of wood to your inner hull with epoxy. Let it harden, then pull it off. You'll probably see that you pulled off part of the inside surface of your hull, and how hard it was to do should tell you how much grinding is left.
5) Planning and measurement. I knew when I first finished the work I was doing that I hadn't gotten things quite square. This became apparent when I used the boat... it was solid, but water had a tendency to pool back at the transom on deck, and the boat wouldn't drain completely when tilted on the trailer.. there were a few low spots. Also the limber holes weren't fully open in places. The fuel tank hatch in the deck center was cut tapering, so the aft end was wider than the front. A 3/4" difference over a 6 foot length is enough to make it look strange.
So this time I'm going to spend the effort to measure from reference points and lines, to make sure that the deck is going to drain well, and that the hatch openings are even. I'm going to some effort to plan drainage, and I'll be building up certain areas of the hull bottom so they're high spots instead of low.
I encourage anyone who is doing a restore for the first time to take the time to do a sample layup... use some wood scraps and glass to make a mock stringer install, glass some plywood together at right angles, butt joint some and see how it looks.... then tear it all apart with saws and pry bars. Your restore work will be much improved knowing where you went wrong.
Erik
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