# False floor or core hull?



## Guest (Jun 26, 2018)

If you attempt to core it, use epoxy for the bonding advantages and agitate the area to be bonded real good with some 80grit. If you can, vacuum bag it too. If cog is an issue, I’d core it. If you like how it’s been working then some stringers and floor will do also.


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## trekker (Sep 19, 2015)

Whichever path you choose, use epoxy thickened with a filler. It will hold for 10 million years, Which is a really long time.


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## Fishcally Irresponsible (Jun 26, 2018)

Thickened epoxy will likely be the adhesive of choice this time around, and If I stick with the false floor, I'm going to add stringers. Previously, I had used thickened [with cabosil] VE resin without stringers, and I think the lack of stringers enabled the hull/floor to flex too much. Another option I'm considering for bonding the floor/stringers to the hull is 5200. Anyone have any thoughts or experience using it for this application?

Between the two--coosa false floor and divinycell core--which is likely to be the lighter option? I would love to attempt vacuum infusing, but realistically it just isn't in the cards right now.


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## Guest (Jun 27, 2018)

Ok, I bite. Do not use 5200 to bond your core! I’d go with 3/4” d-cell over coosa for your needs. Use the scored version. Support the hull very good with multiple runners under it! After aggitating with 80 grit, apply your thickened epoxy. ( I like to mix in some chopped fibers around 1/2-1” with my putty, it will help stop cracking of the putty) place d-cell into putty and weigh down with a whole lotta weight!!! Use any spoodge “squeeze out” to do some filleting/ rough fairing around the core to save waste. After cured, you can then remove weight, finish fillets/fairing, 1-2 layers biax over top and she’ll be stout!


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## Fishcally Irresponsible (Jun 26, 2018)

Boatbrains,

5200 was suggested [and an idea I was kicking around] if I stuck with the false floor/stringers, which is the direction I'm currently leaning. The process you describe is how I set the floor in last time, substitute VE resin for epoxy. Even though I used VE rather than epoxy, I have to think something went wrong in the curing process, or the boat was jarred before the bedding and filets had fully cured. 

Any idea as to how total weight would compare between 3/4" d-cell core and 1/2" coosa false floor+stringers? I already have the coosa, but if I can shed weight going the other route, that would make that decision much easier.


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## Guest (Jun 27, 2018)

I can’t say on the weight of the two off my head. If you have the coosa then by all means... use it.


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## weldandglass (Sep 29, 2009)

The coosa is much heavier. Coosa panels range in density from 15 to 26 lbs/ cu ft. I typically use 6 to 8 lb/cu ft divinycell for decks. The coosa has better mechanical properties but it's overkill for a deck, in my opinion and isn't a "light weight" core. I only use coosa in transoms, primarily because I can't get renicell reliably any more. 

15 lb/cu ft coosa in 1/2" thickness would weight .625 lbs/sq ft and 6 lb/cu ft divinycell would in 1/2" thickness would weight .25 lb/sq ft. You could use less glass with the coosa but I'd rather have a little more glass and a lighter core than a heavier core and less glass, as the glass skins are primarily what give a foam sandwich laminate its stiffness.


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## Fishcally Irresponsible (Jun 26, 2018)

weldandglass said:


> The coosa is much heavier. Coosa panels range in density from 15 to 26 lbs/ cu ft. I typically use 6 to 8 lb/cu ft divinycell for decks. The coosa has better mechanical properties but it's overkill for a deck, in my opinion and isn't a "light weight" core. I only use coosa in transoms, primarily because I can't get renicell reliably any more.
> 
> 15 lb/cu ft coosa in 1/2" thickness would weight .625 lbs/sq ft and 6 lb/cu ft divinycell would in 1/2" thickness would weight .25 lb/sq ft. You could use less glass with the coosa but I'd rather have a little more glass and a lighter core than a heavier core and less glass, as the glass skins are primarily what give a foam sandwich laminate its stiffness.


I'm sure I'll go back and forth over it right up until the point I pull the trigger, but I'm leaning towards reusing the coosa I already have and sticking with a false floor [and adding pvc as support/stringers]. 

The plan right now is to end up with something very similar to the layout in the image attached. I'll either use whatever scrap coosa I have left over or cut panels from the original benches/panels that I've removed for the rear bulkheads and the forward storage compartment. Despite going overboard on the coosa and use of 1708 previously, I'm trying to keep weight to a minimum.


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## DuckNut (Apr 3, 2009)

Fishcally Irresponsible said:


> and adding pvc as support/stringers


Want lightweight? Use the blue foam from HD. You are going to glass over it and the foam is light and easily shaped. The foam is only there to create the structure which you glass over.


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## Fishcally Irresponsible (Jun 26, 2018)

DuckNut said:


> Want lightweight? Use the blue foam from HD. You are going to glass over it and the foam is light and easily shaped. The foam is only there to create the structure which you glass over.


Part of the reasoning behind the false floor [other than a level floor] was the structural reinforcement/rigidity it adds to the hull. Is the blue HD foam going to have the same effect?


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## DuckNut (Apr 3, 2009)

Fishcally Irresponsible said:


> Part of the reasoning behind the false floor [other than a level floor] was the structural reinforcement/rigidity it adds to the hull. Is the blue HD foam going to have the same effect?


Not at all. BUT the glass that you lay it up with will. This is the same method they use for big boats. It is the glass that makes it rigid, not what is inside the stringer.

Here is a company that makes foam stringers. Same concept.
https://www.jamestowndistributors.com/userportal/document.do?docId=679


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## Guest (Jun 28, 2018)

Try nidacore! A 4x8x3/4 sheet with 2 layers 1708 on both sides weighs less that a sheet of 1/2” ply. I have a layup table and use it to layup my own panels and avoid excess resin but they are light


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## Fishcally Irresponsible (Jun 26, 2018)

DuckNut said:


> Not at all. BUT the glass that you lay it up with will. This is the same method they use for big boats. It is the glass that makes it rigid, not what is inside the stringer.
> 
> Here is a company that makes foam stringers. Same concept.
> https://www.jamestowndistributors.com/userportal/document.do?docId=679


DuckNut--are you suggesting I use the blue HD foam to make stringers or core the hull?

I hadn't considered it for stringers, but I had thought about using strips to stiffen and reinforce the sides. I think d-cell [or similar, high-density foams] would be more appropriately suited to coring and require less glass layup.


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## DuckNut (Apr 3, 2009)

Use the foam as if it were wood and build the grid layout as you would normally. The foam will be inside of a couple layers of 1208/1708 and the glass is what will give the hull the strength. 

The only thing is if you are using any of the ester resins they will melt the foam so you would need to use epoxy (which is far superior anyway) or you could use pieces of the foam you took out.

You can use steel, concrete, redwood, aluminum, etc. but you are over thinking it. The material such as the divinycell you reference is NOT what makes it strong, it is the glass.

Think of it like a paper machete balloon. You blow up the balloon and spread the paper concoction ove the balloon. Once you are done you poke a hole in the balloon and it pops but the structure is still intact. You cut a hole in it, fill it with candy, hang it by a string and let your kids beat the crap out of it until the candy falls out. You cannot make a paper machete balloon without the balloon as the forming structure and it provides zero structural integrity.

The balloon is not the piñata, the paper machete is. The foam is not the stringer, the glass is.


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## DuckNut (Apr 3, 2009)

I want to take a minute to warn you about something that happens to all new builders. I am going to pick on YOU but don't take it personally as you are not alone.

New builders want to use products like 1708 and put 2-3 layers down. What they don't realize is that one layer is super strong two layers is overkill for any gheenoe. Three layers is enough for a bay boat.

Because you don't understand how strong the products are you go way overboard and end up with a gheenoe hull that weighs 350lbs all the while you thought you were building it light because you used the latest and greatest lightweight composites.

There is an old saying in the boat world: light, strong or cheap, pick two.

You are working on a hull that is made to a thickness of less than the thickness of the 1708. One layer of 1708 that you use will be way stronger than the original hull. The 1708 is a structural product and chopped stand mat is not, but yet the entire hull is made from that non structural product.


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## Fishcally Irresponsible (Jun 26, 2018)

DuckNut said:


> Use the foam as if it were wood and build the grid layout as you would normally. The foam will be inside of a couple layers of 1208/1708 and the glass is what will give the hull the strength.
> 
> The only thing is if you are using any of the ester resins they will melt the foam so you would need to use epoxy (which is far superior anyway) or you could use pieces of the foam you took out.
> 
> ...


DuckNut--I appreciate the warning, but I won't be using 1708 on this particular project. My Gheenoe, while still a devoted fishing boat, is first and foremost a duck boat. The hull itself is a 2001, and I've been running a mud motor since 2007 (surface drive since 2010). Needless to say, she's had some bumps and bruises. 

Two years ago, after noticing a soft spot in my floor, I repaired some areas and reinforced the bottom of my boat with a layer of 1708. While 1708 may be a little heavy for a Gheenoe, mine probably doesn't get run like most Gheenoes, and I wanted the strength and rigidity. I was also tired of rolling my ankle and trying to balance a dove stool on an incline, so I opted to put in a false floor (1/2" coosa, laminated on each side with 1 layer of 1708) from the center bench, forward, and between the rear and center bench.

I got the itch earlier this summer to finally customize the boat exactly how I've always wanted--wide open layout, small front storage hatch, flat floor, etc. Since I was already cutting her up anyways, I thought I would pose the question regarding false floor/coring. 

Most likely, I'll wind up reusing/adding to the existing false floor. I'll probably opt for epoxy over VE resin this time, and I may add stringers (or fill the entire void with foam) for additional rigidity and to replace the flotation I've stripped. Any glassing I do will be with CSM or 6oz cloth.


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## yobata (Jul 14, 2015)

Fishcally Irresponsible said:


> DuckNut--I appreciate the warning, but I won't be using 1708 on this particular project. My Gheenoe, while still a devoted fishing boat, is first and foremost a duck boat. The hull itself is a 2001, and I've been running a mud motor since 2007 (surface drive since 2010). Needless to say, she's had some bumps and bruises.
> 
> Two years ago, after noticing a soft spot in my floor, I repaired some areas and reinforced the bottom of my boat with a layer of 1708. While 1708 may be a little heavy for a Gheenoe, mine probably doesn't get run like most Gheenoes, and I wanted the strength and rigidity. I was also tired of rolling my ankle and trying to balance a dove stool on an incline, so I opted to put in a false floor (1/2" coosa, laminated on each side with 1 layer of 1708) from the center bench, forward, and between the rear and center bench.
> 
> ...


If you are going to use epoxy, there is no need for csm. You can use the 6oz cloth, and if you need to tab something in use 6" wide 12oz biax tape


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## Guest (Jun 29, 2018)

DuckNut said:


> Use the foam as if it were wood and build the grid layout as you would normally. The foam will be inside of a couple layers of 1208/1708 and the glass is what will give the hull the strength.
> 
> The only thing is if you are using any of the ester resins they will melt the foam so you would need to use epoxy (which is far superior anyway) or you could use pieces of the foam you took out.
> 
> ...


I use a lot of 12&1708 material, I am no amateur. I use it for puncture resistance. I think the biggest mistake amateurs make is using too much resin and soaking everything. Can’t say how many puddles I’ve ground out of boats. I lay up nida core and most foam board with 1-2 layers 1708 each side “depending on end use” on my table. I then use the panel like most use wood and cut to fit then fillet and glass in.


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## DuckNut (Apr 3, 2009)

Boatbrains said:


> I use a lot of 12&1708 material, I am no amateurs I use it for puncture resistance. I think the biggest mistake amateurs make is using too much resin and soaking everything. Can’t say how many puddles I’ve ground out of boats. I lay up nida core and most foam board with 1-2 layers 1708 each side “depending on end use” on my table. I then use the panel like most use wood and cut to fit then fillet and glass in.


You are exactly right. So you know exactly what I was warning about. Most amateurs will turn a 4lb sheet of foam into a log weighing more than a sheet of plywood.


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## Fishcally Irresponsible (Jun 26, 2018)

Is VE resin [mixed with cabosil] suitable for bedding and filets? If I go this route, what layup schedule do I need to use to tab in my floor panels?

OR--am I going to be that much better off in the long run going with epoxy + 12oz biax tape/6oz cloth? I'm assuming this would be the "lighter" of the two options.


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## Guest (Jun 29, 2018)

Given that this is the second round for you on this, I’d go epoxy! Epoxy’s bond strength is far superior.


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## trekker (Sep 19, 2015)

If you are gonna use cabosil on your fillets, make'em cute. Not fun sanding that stuff.


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## Fishcally Irresponsible (Jun 26, 2018)

Still haven't pulled the trigger on ordering materials, but for the most part, the deconstruction phase is complete. After grinding out the previously laid false floor, it was immediately evident why those panels had separated from the hull in places--in my haste to get the floors in prior to teal season [I was in law school and had 1 weekend to make the 8hr trek home to complete the project], I forgot to rough up the hull at the points of contact/adhesion. Stupid oversight, but I was already cutting out the center box and rear bench--slightly more "re-work" in exchange for a valuable lesson learned.

Epoxy is going to be the resin of choice, and the plan (as of now) is to extend the false floor (1/2" coosa) almost the full length of the boat, filling the void with 2lb foam. I go back and forth over the addition of stringers, but my fear is that the foam will eventually shrink, and I'll lose the benefit of that compression strength.

In terms of the flooring panels themselves, the previously installed floor was laminated top and bottom with 1708. Since the csm component isn't necessary given the epoxy, in addition to using a different material on the new panels, I'm considering removing the 1708 from the existing panels. Assuming stringers are added, what would be the "lightest" material suitable for the floors? 

I've also considered leaving the 1708 on the panel bottoms for compression strength and glassing in the topside with 6oz cloth. Any thoughts or suggestions on how best to glass in the floor?


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## DuckNut (Apr 3, 2009)

Glue the cost directly to the floor and cover every bit of it bow to stern. Then cover that with two lawyers of 10 oz cloth.

Skip all of the other hard work. It is a duck boat and is not suppose to have a great fit/finish. It it did it would take away the juju.


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