'73 MerriMack Under Deck Questions

[scottzfx]

Ok. I have searched, read, and re-read, but I am more confused now than ever. I have a '73 15 ft MerriMack fiberglass tri-hull. I knew there was a soft spot in the floor when I got her. Finally got around to cutting it out, which turned into me taking out the deck in the entire passenger area to finally get to good wood. Of course, you all know what I found, a lot of foam and "some" water. I have pulled all of the foam and checked the stringers. Believe it or not (I couldn't), they are good! Given this piece of luck, I have a few questions on which I would appreciate any guidance:

1. What do you recommend I use to fill the nail holes and minor (< 1/8") cuts I made in the stringers. They're not rotted, and I want to make sure they stay that way.

2. The stringers have no limber holes in them. Should I drill some? If so, how big and how do you seal them?

3. Since its a fiberglass boat, do I need to use the pour foam for structural rigidity? If I do, how does the water drain back to the bilge? I know a lot of you don't like the foam and given what I found, it seems to me it would be better to use some material that would allow the under deck area to breathe. As I said, I'm more confused now than ever.

Sorry for all the questions, but this is my first attempt at boat work. I've never glassed before, but have read as much as I can on here and even practiced on a couple of pieces. I know just enough to be dangerous. By the way, I have already coated the replacement pieces with resin to seal it. I'm using exterior grade 3/4" plywood. I poured the resin along the edges to really seal them up. Thanks to everyone who has made this place a great compilation of knowledge.

 

[scottzfx]

Re: '73 MerriMack Under Deck Questions

Ok, having gotten no input and doing a whole lot more reading here and elsewhere, I think I'm going to try this. I've ordered the pour foam from US Composites. I'm going to line the areas between the stringers with a plastic drop cloth and pour the foam to the the pieces to go between the stringers. I'll pull those pieces out and peel the plastic from them. For drainage, I'm going to route shallow channels in the pieces to let any water that does get in there run back and down to the bilge. I'll also round over the section against the bottom corner of the stringers to allow for free flow of water.

I think this will give the strength of the foam I need for a fiberglass boat, while allowing movement of any water to the bilge. I know a lot of people don't like the foam because it fills in. I'm hoping this will be a good compromise of the two. I'll also put a coat or two of epoxy resin on the pieces before I install them to seal them tight. This is a trailered boat, so all of this is probably way overkill.

I still have a question about limber holes. The current stringers have none. Since I am allowing for water to flow, I think I should put in at least two towards the back to let water on the high side get into the main channel to run back to the bilge. What is the best way to seal a limber hole when drilling into pre-existing stringers? They are fully enclosed in glass.

Any thoughts, suggestions, comments are more than appreciated.

 

[Bob_VT]

Re: '73 MerriMack Under Deck Questions

Seal holes with 3m 5200 or get some 2 part epoxy and use that.

If you drill limber holes I would seal them with 3m5200....... you could even use plastic tubing and use 3m5200 to seal them in..... any pet store will have clear hard plastic tubing about 1/2" diameter.

The foam really does not add any support unless it was designed that way such as in a whaler....... however, you should use it and you seem to have a grasp on it. You could also use blue board from lowes or home depot and just place that in....... or even pool noodles.

 

[mytquinn]

Re: '73 MerriMack Under Deck Questions

Ok, having gotten no input and doing a whole lot more reading here and elsewhere, I think I'm going to try this. I've ordered the pour foam from US Composites. I'm going to line the areas between the stringers with a plastic drop cloth and pour the foam to the the pieces to go between the stringers. I'll pull those pieces out and peel the plastic from them. For drainage, I'm going to route shallow channels in the pieces to let any water that does get in there run back and down to the bilge. I'll also round over the section against the bottom corner of the stringers to allow for free flow of water.

I think this will give the strength of the foam I need for a fiberglass boat, while allowing movement of any water to the bilge. I know a lot of people don't like the foam because it fills in. I'm hoping this will be a good compromise of the two. I'll also put a coat or two of epoxy resin on the pieces before I install them to seal them tight. This is a trailered boat, so all of this is probably way overkill.

This is how I plan on doing my next build as well. I was too far along on my current rebuild when I read Bobsglasstream's method. I think you are on the right track. I was just going to lay some pvc pipe or tubing in place under the plastic sheeting before I poured the foam. I suppose it's just as easy to carve the channels after. I would also epoxy the foam like you said. Just make sure the compartments shape is not such that it will lock the foam in place when poured. Bob also put some plastic on a board and then set it on top of the pour to make it nice and flat. Makes for less leveling after the pour.

Good luck,
Lets us know how it turns out.

Q

 

[scottzfx]

Re: '73 MerriMack Under Deck Questions

Once the foam, epoxy and glass gets here, I'll try to take some pics as I go and post them back here. Thakns for the info. This is my first boat and my first repair.

 

[scottzfx]

Re: '73 MerriMack Under Deck Questions

Got a question about the fiberglass cloth I have ordered. I'm second guessing myself. I went with a 7.5 oz cloth that I'm going to use with the epoxy resin. Is this a good weight cloth for flooring. Also, since I did not take out the entire floor (a 6 x 4 section in the main compartment) I will be tying back into the existing deck. This is what I'm thinking, use 4 inch strips over the cuts, then lay a section in the middle and build up from there until level with old deck then one more layer overlapping joints and blending into existing deck. Does this sound good?

As I said, this is my first attempt at anything like this, so I'm going to have lots of questions. I haven't seen much in the way of references to weights of cloth for the deck, but I see everyone here prefers epoxy to polyester. I ordered the medium set hardner to give a noob some time to work with it.

 

[scottzfx]

Re: '73 MerriMack Under Deck Questions

Nice, I left the cover off the boat today because it was supposed to be hot and sunny with no precip. I ended up working late and as I was leaving, the weather radio went off and we were under a severe storm watch. Great! I get home and the drain hole looks like a water faucet. As I was getting the cover back on, of course the rain stopped. I'm leaving it covered from here on out. Supposedly, the covers "breath". I need to get a house with a garage so I can actually enjoy my projects!

Any advice on cloth weight for the new deck section?

 

[mytquinn]

Re: '73 MerriMack Under Deck Questions

Bump...

Any advice on which deck cloth to use with epoxy?