1970 Mirrocraft deck replacement. The foam under the deck?

TinBoats.net

Help Support TinBoats.net:

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.

Roadblock

Member
Joined
May 18, 2014
Messages
9
Reaction score
0
I've got a 1970 Mirrocraft Ski-N-Troll that the transom was completely rotted out of. Bought this boat with a Merc 50HP on an EZ Loader trailer for $750.00 knowing it needed a little work.

So I've got the transom out and everything is going good there. The deck was replaced at some point and pressure treated wood was used.

I also noticed it looks like I've got TONS of water under the deck being trapped by foam so I thought I'd get all of that taken care of while I've got the splashwell and part of the gunwalls ripped down.

So this foam stuff under the deck, I can't explain it but it has a very odd texture to it like its suppose to be like this, like it's suppose to hold water?

I pulled up a small section of wood under the splashwell area so I could get a better look.

What am I looking at here?

I'm worried that if I pull up all the wood and remove whatever this foam is the boat is not going to be as solid on the water as it is right now but at the same time I assume water isn't suppose to be in there? Right now two adult people can get up and walk around in the boat and it basically doesn't move in the water.

02e6889c-be8a-4f61-83e0-f08c5a4bb6b8_zps300f2b01.jpg


b6f25b53-cdee-4999-bb09-94c22e38d53b_zpsb75071e1.jpg
 
Removing that foam and the transom and the pressure treated decking will be the best 3 things you can do for that boat.

That foam is holding hundreds of pounds of water weight that's slowing down your boat, saturated foam also loses it's buoyancy and won't float your boat in an emergency.

That pressure treated decking has chemicals in it that corrode aluminum.

You can easily replace your foam with the rigid polystyrene sheet foam insulation (pink or blue), and it's much more water resistant than that old junk you have in your boat.
 
Wow dude your everywhere! :D

The only issue I see is that is seems like the foam is what is making the deck so solid. The plywood is directly sitting on it.

I pulled up a corner and broken it by mistake, looks like the boat was sprayed with some type of liner? The hull under the foam was DRY. I guess what I'm getting at is if I pull up the foam, it looks like I will have to build bracing for the deck wood.

Also is this foam the reason the boat is so stable in the water?

One last thing, once all of this is out of the boat, does it need to be sealed with anything?

Here was the corner I pulled up.

38cf46bf-1aa7-4aaf-92d8-890751b30f3d_zpsdd7626d3.jpg


4a9d9cc5-f962-48ac-a89d-c0dd2b73b5a1_zps75a72a58.jpg


eff82386-0838-4412-9256-f9ec2ae18598_zps7a0c96db.jpg
 
The foam doesn't add stability, that comes from the hull design.

The foam won't make your boat float higher in the water when the boat isn't swamped, but wet foam will make it sit lower because of the weight.

The foam does support your deck and adds a certain amount of structural stiffness to your boat.

You can skip the sheet foam and install new urethane foam like the old stuff in your boat so you can get the same benefits from it.

The foam is a 2 part expanding urethane foam that you mix up and pour, I suggest the 4 lb. density because it's more water resistant than the 2 lb. This is the best price on the internet I've found for it:
https://www.uscomposites.com/foam.html
They also have the best price on the 2 part epoxy resin.

This is an entertaining vid on the 2 part foam:
https://www.youtube.com/watch?v=zAIY0I5GGw4
 
I um, I'm feeling a little overwhelmed right now for sure!

I don't think "not" putting the foam back in is an option. I've got a good chunk of the foam out and I've yet to see a stinger or a brace. The bottom of the boat is really flimsy like the outer hull transom skin.

I can actually see where the hull is sitting on the rollers of the trailer because it's now pushing into the skin where the foam is gone, boats still on the trailer.

There is no framing that the wood sits on that I see either. There where 3 cross beams of just some thin wood that the original decking mounted to to hold all 3 sections together and then the foam was apparently sprayed into the hull threw some holes I guess.

The foam appears to be the structural rigidity of the boat.

I've got more out than this picture shows and like I said above, so far I've not found any bracing. There appears to be a TON of this foam in the boat. I've got an 8 inch deep hole huge up front and I've not hit the hull yet.

I definitely could have waited to do this until winter. Even if this was P/T wood it was not touching ANY aluminum and the foam was completely sealed. There is some type of spray in liner on the bottom of the boat. Look at the aluminum in the photo. It was 100% dry and clean. The liner was acting like a big pan that held in all of the wet foam and whatever else.

ed844afe-cb4d-4c17-9175-553aa8305038_zps902a06ac.jpg
 
OK major change of plans I think...

I was not expecting to have to use 2-part foam right now. Also looks like there was a protective layer of something sprayed in the boat before the foam was poured in.

So a gallon of something like Gluvit is about $120~130.00 dollars, and I'm guessing this foam is 8lb or 16lb based on the descriptions of the different weights of foam because I can take a swing at it with a 3LBS hammer and it bounces off. I can stand directly on the foam, jump and it doesn't break or crack.

Hell, I could use the boat without deck boards, the foam is that solid.

So I'm going to buy some cheap non-P/T plywood and make a temp deck, right over foam like it came from the factory. Not even going to fill in the area I pulled the foam out of. May get a can of 3M spray in rubber liner and spray the seams and exposed aluminum bottom area where I remove the foam but I think due to the metal rail area on the edge, well here is how it appears the boat was built:

They sprayed in whatever the protective liner was. You can see the stuff on the outside of the foam pictures I posted.

They then laid deck boards in 3 sections, connected together with wood strips.

They then poured the foam threw some opening in the wood?

I emailed Mirrorcraft to verify but anyway I think because of the metal ledge long each side of the boat that the wood sits on, plus the remaining foam I will be OK to use the boat the way it is for this season.

Then I'm going to finish my transom rebuild, get my boat bolted and riveted back up and call it good.

Then when it gets cold (I live in Michigan) end of the year I can pull my temp deck out, pull the foam out and re-seal the boat and lay new Marine grade plywood in my heated garage while the snow comes down! Then when spring hits (will have taxes back by then) I can pour foam threw some access holes I'll put in the wood while I'm re-decking.

I think the aluminum will be OK to get wet for ONE season. I will only have the boat in water maybe twice a month til it's cold.

I highly doubt its going to get any corrosion by then.

Thoughts?
 
*UPDATE*

I just received two emails from the folks at Mirrorcraft. They have confirmed that the foam HAS to be there, this boat was designed with the foam being the structural support. They said the bottom of the boat will not hold up without it and will change shape and could cave in and also it would be dangerous at any high speeds. They have no idea what weight foam was used but that Owen's Corning made it.

They made the argument that the way the boat was designed, the way the liner was sprayed, the water wouldn't really matter too much as it would never touch the hull of the boat. The boat was still pretty dang fast.

Based on how strong the foam is, It's gotta be the 8LB or 16LB I'm guessing based on product description.

Well dang...

OK well what about this. Is there a product I could use to seal the area back up that I've broken out that might bond to the old foam if I let it get under the foam? I can lift up on the foam a a little. Then I can lay some cheap exterior plywood and pour a small amount of 8 or 16 pound foam to just by by this year and then I can deal with it in the winter after fishing season it over?
 
The 4 lb. density is all you need, it's rated for structural support and it probably what you have in there now... it may even be 2 lb. in there now.

Don't worry about the foam bonding, it sticks to everything.

I know removing and replacing the foam seems like a daunting task right now, but it's really not that bad. Using a pointed garden shovel will speed up removal, and you'll be able to break out large chunks.

You want to pour foam during warm weather, 75*F minimum working temp for the maximum expansion rate.

Back up with the camera and lets see what you have in the boat.
 
I am no expert but just from reading what you said about how you can see the rollers bulging through the hull, I would make sure when you do re-pour the foam it that your boat is not on the trailer with the rollers. The way I see it is that anything that is allowing the hull to flex in after you remove the hull, when you re-pour, your foam will take that shape. Then when you put the boat in the water you may find out that there will now be a void between the hull and foam cause the foam is in the shape of the hull when it was on the trailer but when in the water the hull might flex back to original contours leaving the void. Or if the foam adheres and is strong enough to hold the hull to the shape it was in on the trailer when you put the boat in the water you will notice that when viewing from underneath it might dip in a little where the rollers were seated, thus causing problems with the hulls performance. So my suggestion is when you pour the foam make sure that the hull is either in a cradle made to your hulls shape or somehow suspended above the trailer or whatever you have the hull on when doing the work so it will be in the proper shape. This is just my opinion.
 
[url=https://www.tinboats.net/forum/viewtopic.php?p=352755#p352755 said:
Linhardt » Today, 10:38[/url]"]I am no expert but just from reading what you said about how you can see the rollers bulging through the hull, I would make sure when you do re-pour the foam it that your boat is not on the trailer with the rollers. The way I see it is that anything that is allowing the hull to flex in after you remove the hull, when you re-pour, your foam will take that shape. Then when you put the boat in the water you may find out that there will now be a void between the hull and foam cause the foam is in the shape of the hull when it was on the trailer but when in the water the hull might flex back to original contours leaving the void. Or if the foam adheres and is strong enough to hold the hull to the shape it was in on the trailer when you put the boat in the water you will notice that when viewing from underneath it might dip in a little where the rollers were seated, thus causing problems with the hulls performance. So my suggestion is when you pour the foam make sure that the hull is either in a cradle made to your hulls shape or somehow suspended above the trailer or whatever you have the hull on when doing the work so it will be in the proper shape. This is just my opinion.

I completely agree.

The fiberglass guys make cradles for their boats all the time when they're working on them:
https://forums.iboats.com/boat-restoration-building-hull-repair/boat-hull-cradle-help-584635.html

... but I think the cheapest method would be to hang it in the garage from the floor/ceiling joists. 6 "C" clamps, 6 ratchet straps (truck tie downs), and 6 utility hooks and you'd be in business.

Pouring foam is a lot like pouring concrete, except foam is a whole lot lighter and easier to work with.

If it was my boat, I personally would install deck framing and then pour the foam. The framing would add more strength and give you something to attach the decking more securely to instead of just having it laying on the foam or anchored at the perimeter only.

I can draw you up some plans for hanging the boat and the deck framing if you're interested.
 
OK I want to revisit this project with the foam.

OK so I've been having a back and forth with the VP of Mirrocraft and someone that designs their boats.

Kinda feels like I messed up starting to rip up the foam because as I've learned, the foam is the structural support for the boat.

Also, apparently, it's designed to get wet per Mirrocraft. The setup on this boat is really goofy compared to boats I grew up on.

So there is a pan molded into the back end of the boat, in the foam where the bilge pump sits. Once water reaches a certain level, the water spilled into the pan and then the bilge pump can send it out.

The foam basically sits in a tray of some type of epoxy bases boat liner so even if the foam is full up with water, it never actually touches the alumium of the boat.

Problem is, I've broken the layer of whatever the sealer is.

I started ripping up the foam right after I had the boat out, and the transom area leaked so no surprise the boat took on water. The foam was wet so I thought it was water logged.

Today the foam seems to be COMPLETELY dry. I took some foam core samples from various parts of the boat and there is no water down in the foam now.

Sigh...

OK so rather than to rip up all the rest of the foam and reseal/reline the boat is there a way I can just reseal the area where I ripped up the foam so that it bonds to the current layer and then re-foam just that area.

I know I can re-foam because I've found several videos from makers of the 2-part pour foams saying if you have an area of rotted or damaged foam you can cut it out and then re-pour into that area and it will bond to the existing foam.

My concern is being able to reseal the boat.

Is it doable? What products would accomplish this? I'm really not against pulling all of the foam and resealing the boat with something like Gluvit and then laying new deck and pouring foam BUT I would like to wait until this winter to tear out all of the foam and then prep the boat so I an pour in the spring.

Thoughts?
 
Even if the water is contained in the foam inside the liner separate from the hull the water is still in your boat making it quite a bit heavier. I would gut out all the foam and just re pour new foam. After it sets it will have the same structural effect as the original soggy foam. As for sealing the hull underneath the foam you could use steel flex or gluvit.
Where I live in Florida boating season never ends but if the boat will be sitting idle for the winter you could do it then but working with foam and epoxy paint in cold weather lengthens dry time and slows down foam expansion
 
You need to go all the way to the hull when taking a sample, water seeks it's own level and wiilseep down until it finds more water to join with.

Water weight in floatation foam can be a huge factor in performance and safety.

You can reseal your boat where you've broken the liner with gluvit or coat-it, they're both epoxy based products made for this application.

You can repour your foam where you've removed it without problem.

With that being said, I'd like to point out that summer is the best time for boat restoration. Epoxy products, foam, paint, and adhesives work much better in warm working conditions... the job will go quicker, have less problems, and your materials will be less likely to fail... but it's your boat and you can build it any way and at any time you want.

... but then again, if you're less likely to try to rush through the job and more likely to take your time and do the job right in the winter, then winter will probably be your best choice.

I know what the whole problem for this boat work is for you.... you think there are fish out there in the soft/open water that need to be caught and if you don't catch them someone else will, but fish and fishing are highly overrated... you believe that s*it don'tcha? :fishing: :wink: :LOL2: 8)
 

Latest posts

Top