Building a new deck

I own a 28 foot Bristol Channel Cutter. It is an early model built by Lex Whyte now living in Australia. The deck underlayment is 3/4" plywood and is rotting in a few places.

I am going to remove the existing deck (iroko) and the 3/4 inch plywood the deck is screwed down to and put down 3 layers of 1/2" plywood. Over the plywood I will put down 6oz glass. My question is what kind of plywood will work best. I assume it should be marine grade, but there are so many grades of marine plywood. I have also heard that Baltic Birch plywood works well.

Any guidance will be appreciated.

Thanks, Larry Heitman

 

Welcome to the forum.

First of all, why are you increasing the deck substrate thickness by 50%? This will do fine if you don't intend to put the hardwood over it again. The triple layer is a bit redundant, but will make a very stable, leak free and stiff deck. It might be cheaper to install two layers of 3/4" and certainly means less cutting and fitting. Again, this assumes the Iroko is being left ashore. If you do plan on applying a veneer or regular thickness hardwood deck again, consider two layers of 3/8" or 1/2" if you think you need more support.

6 ounce cloth will not offer much abrasion resistance and no additional strength or stiffness, just waterproofing. 2 layers of 6 ounce is better, but Xynole or Dynel are much better choices, having far superior abrasion resistance than 'glass cloth.

Plywood choices abound, as you've found. Baltic Birch is pretty heavy stuff. If properly encapsulated you can use APA 1-95 grades. These would be Marine AA or AB or regular "Exterior" grade. Avoid any label that says it's "Exposure 1" even if the word "Exterior" also appears. Only the "Exterior" grade is acceptable if using the construction grades from the local big box store. This stuff isn't very good, but 3 layers of it, all epoxied and fastened down over staggered seams will do fine if sheathed in fabric.

All outfits that carry plywood can special order the good stuff, though they'll often charge you hard for it, some will just tack it on their next order. BS-6566 grade plywood is considerably cheaper than the good stuff (BS-1088) and there are also the Hydrotech and Aquatech brands too. All of these are far better than the construction grades found a Lowe's/Depot. There are also places around the country that can ship it to you. Yeah, shipping fees are a pain in the butt, though if you're ordering a good amount of plywood, not much more per sheet, once it's all said and done.

 

Thanks for the quick replay re my Bristol Channel Cutter deck. The total thickness of the existing deck is 1 1/2". I thought that 3 layers of 1/2" would bend easier to conform to the shape of the deck. I don't want to use the Iroko for the new deck. This project is a bit over my head skill wise, but there are a few people here in Suttons Bay MI that can help if I get in over my head. Two layers of glass on top of the plywood makes a lot of sense, Thanks. Also I appreciate all the info on the plywood. Larry Heitman

 

I've been doing fiberglass over plywood decks for many years. Mostly on commercial boats. 2.0 RSM with epoxy resin will last 20 years on a commercial boat. Forever if maintained. The 2.0 absorbs more resin and makes a thicker coat. One layer is enough. Polyester resin is a waste of money. It doesn't stick to anything well, even itself. When redoing a deck made with poly, I can usually lift a corner and take off the whole fiberglass deck in a couple pulls. Epoxy usually has to be ground/sanded off.

 

Lepke, is quite correct, though I don't recommend CSM (RSM?) with epoxy, as it's just a resin sucking bitchh, that offers little benefit. Xynole and Dynel are better choices, if you want a resin rich substrate with good abrasion protection.

I too remember many jobs, of using a vise grip at one corner of a polyester covered deck and yanking all put a few hunks off in one shot. It sticks long enough for the boat to be out of warranty, that's about it.

 

Raplacing deck with plywood

Thanks Lepke and PAR for the information on my deck. I won't be starting the project til spring. My boat is in outside storage at this time. I will, by early may, have the boat inside for about a year and a half. I am also going to replace the bullwarks at this time also the stanchions too. The existing deck is 1 1/2" thick. I think I will replace the old deck with 3 layers of 1/2" ply rather than 2 layers of 3/4". The reason is that 1/2" ply will flex a bit easier. What do you think about this reasoning? Dynel sounds better and maybe easier than glass cloth for the top of the plywood. It also gives a canvas look.

Thanks again for the information

 

Just cannot imagine why a 28' fairly narrow boat would require 1 1/2"s of ply? If the deck beams are anything close to typical, you would be fine with 5/8' of good quality ply and a stout layer of glass and epoxy. That extra 3/4' of ply you would be carrying around adds up to a lot of extra stores or water or sailing qualities.

 

new deck for my BCC

Thanks DGreenwood for your quick reply. My boat is under wraps now til April because of the weather in Michigan. I have removed one piece of the iroco deck. It is 3/4" inch. I think the bad plywood below it is also 3/4" in thickness. It might be l/2 though. If the cabin side is resting on top of the deck then I will have to make the new plywood layer either 3/4 of possibly 1/2 inch thick. There is also some very nice trim pieces around the cockpit and forward hatch that I would like to keep. I definitely agree that a total of 1 1/2" is too much plus more expense and extra labor. If the cabin side is resting on the deck. I could add a thin shim piece under the cabin which would allow for a thinner deck. A total of 1" plus a layer of Dynal would be best for many reasons.

Thanks

 

I haven't started my new deck project as yet, but am considering using 5200 between the two layers of 1/2" marine ply instead of epoxy. It sounds like it should work well and also easier to apply. Any thoughts on this. Larry

 

If the plywood is only rotting in a few places, why not repair it instead of replacing the whole deck? If you know the project is a bit over your head skillwise, you'll have to hire it done at an enormous cost and wait for a year or two to use the boat.

 

REPLY TO SAM SAM: The deck is iroco strips over plywood. The deck was built when the boat was new in 1980. There are other areas that are just beginning to go bad also. My plan is to remove the entire deck, covering boards, bulwark and bulwark stanchions, basically everything except the house. I know it is an ambitious project, but I am looking forward to doing it. There are local (Suttons Bay, MI) boat builders that I know who will help when I have problems. I think it will take me a year or year and a half to finish. My son has a nice folkboat that will be ready to sail that I can use. I still have questions about the project such as how to bond the two layers of 1/2" plywood together. I got a price from a well qualified, local ship carpenter which was approx $15,000 to $17,000 to do the entire job most of which was labor at $40.00 per hour. The boat is a very nice 28' Bristol Channel Cutter so it is well worth the effort to fix her. Thanks Larry

 

Question. I have to remove my tabernacle on my Bristol Channel Cutter. It extends about three feet below the deck and is eight foot tall overall. There is a timber between the tabernacle that supports the deck stepped mast. The tabernacle that is two pieces is sandwiched on both sides of this below deck mast support. The tabernacle is now stuck to the mast support. I have removed 4 long bolts the held tabernacle tight against the mast support. The problem now is trying to get the two pieces of the 8 foot long tabernacle separated from the mast support. I don't think they are glued together. They may have been varnished before they were bolted together, though. Over the 35 or so years the varnish could act as a gluing agent, I guess. Removing the tabernacle will make my total deck replacement a lot easier and also make a better finished deck. Any ideas on how to make this problem easier to solve will be appreciated. I don't want to get so aggressive, say with a Sawsall, that will ding up the appearance of the interior. But like they say, If you want to make an omelette, you have to break some eggs.

Sorry for the long, and I am sure confusing, explanation of my problem.

Larry

 

I could be anything holding it together, but fresh varnish is very likely. With a squeeze bottle, try to work some solvent into the gaps, pushing a stiff putty knife in, wedging open what's available. Work slow and steady, from top to bottom, so gravity can help.

If it's been a long time since the mast was removed, you might need to consider a block of wood and a deadblow, to "convince" it to free up, possibly needing to drive a putty knife and/or wedge, into the gap. I think one of those plastic wedges available from the big box stores will ultimately get the job done. Again, start at the top and see how much will wedge open, squirt some solvent in, spank it with a block of wood and a deadblow and move the wedge down, as the parts separate.

 

Thanks PAR - The solvent is worth a try along with wedges. That was going to be my next thing to try. I have heard of people using a hot wire and sliding it through two pieces of wood that have be joined with 5200. This might work, but sounds a bit tricky.

Larry

 

A hot wire isn't going to offer much for you. I use a hot knife on polyurethanes (3M-5200, etc.), but varnish doesn't melt like polyurethanes do. You'll just burn you way through. At this point, if the wedges and solvents don't work, you have to repair some surface damage anyway, so consider a multi tool, instead of a reciprocating saw.