Lazarette Cover

[Rick]

I'm replacing the lazarette cover on my A21. The old one is severely bowed and has several significant cracks. It also doesn't blend in very well after I painted the cockpit and deck! This will be my first fiberglass construction, although I've replaced a gelcoat floor in a small motorboat and done lots of epoxy tabbing, fairing and repair of cracks and holes in my 1972 A21.

Here's a picture of the old cover


I created a mold for the new cover.


I have 2 questions before I proceed. First, this seems like a project that could be constructed using cheaper polyester resin instead of epoxy. Do you think I need the strength of epoxy (and higher cost) for this? I've got 2 quarts of old (5-6 year old) polyester resin waiting for a project. However, does this old polyester resin deteriorate over time, so I should toss it and get some new stuff?

The next question is whether the following layup schedule will provide enough strength for this cover. It's dimensions are 45" x 24". I was planning to layer the following: cloth, mat, roving, mat, 3/8 marine ply, mat, roving, cloth. Do you think this is enough, too much or too little? I don't want it to be overly weak or heavy. The above layup schedule is based on my available fiberglass and using the polyester resin. Does that seem to be the proper sequence for both the polyester or epoxy resin?

[Case]

For brand new construction, I do think cheap polyester would do fine. After all, your boat is really made from polyester fiberglass and its fine! It is what I would do if making new stand alone items. If bonding to old fiberglass, I will always use epoxy. Issues with polyester often comes from bonding to fully cured fiberglass (meaning old fiberglass). If its new construction, there shouldn't be any bonding issues as long its done right.

Now, as for the age of the polyester, if the can is not opened, I think its probably okay. 5 years are a bit old but I'm pretty sure you can find 5 year old cans sitting in hardware stores waiting to be bought right now. So its probably not a big deal. Go ahead and use it!

- Case

[Tim]

Most resins have a pretty long shelf life. Catalysts (MEKP in this case) tend to have shorter shelf lives than their partner resins, so it's likely you'll need to buy more catalyst.

Polyester is OK for new construction like you're suggesting. However, since you're planning on including a plywood core in the new structure, consider that polyester is a poor bonding choice when bonding to wood. Epoxy would be a better bonding adhesive for the plywood core.

The laminate schedule you suggest is adequate. The plywood will be doing most of the structural work, and the fiberglass, while adding strength, serves more to sheathe and encapsulate the plywood in this instance than any significant strength addition, though the sandwich construction and fiberglass skins will add strength to the plywood.

[Rick]

Thanks guys. I really appreciate the quick, informative responses.

[tpl]

at 45" this is pretty long: have you considered laminating in some stiffening ribs on
the underside? They could be attached to yr 3/8" ply, then glassed over.

[Rick]

tpl,
Excellent idea. The old cover bowed up at each of the long ends, so some stiffening ribs should prolong its life. I completed the first few layers of glass and the plywood board, but then got greedy and tried to add another layer of glass too soon. I think it got too hot, because it hardened almost instantly, before I could completely flatten it out. I've got to grind a portion of it off. I plan to grind back to the plywood and add some ribs and then cover it with epoxy. Of course all this depends on the sun coming out sometime, since I'm working outdoors!