DIY structural foam (or honeycomb) panels 1

[curtis74]

I'm engineering a new boat floor for a customer's boat. He uses the boat very heavily and he's tired of replacing the flooring every few years and wants something a bit more permanent. I've discussed some FRP panels and some monocoque honeycomb skinned panels that would do well, but the cost of materials is rather prohibitive, as is supply when you're only buying two sheets. Here are some examples of things we found that might suit to give you an idea of where I'm going with this:

http://www.ayrescom.com/products/default.asp

(specifically the 2016 material)

http://www.fiberman.ca/structural_insulated_panels.cfm

Is there some way I can make some structural panels myself here at the shop? Concerns are weight, rigidity, and oil/gas resistance. The panels will be sealed from all edges, but if microfissures develop in anything down the road I don't want a the possible hydrocarbon introduction to eat the foam. For the same fissuring reason, I don't want the foam/honeycomb to absorb water. UV won't be much of a concern since we are going to coat the entire floor with Rhino liner.

 

[MikeHalloran]

If you don't want it to retain liquid, leave the bottom open.

I.e., use FRP bar grate to carry the load, and skin the top with thin stainless steel.



Mike Halloran
Pembroke Pines, FL, USA

 

[curtis74]

I like that idea a lot. My concern with the stainless is denting. It would only take a few times setting down the anchor to make the deck distort/conform to the bar grate.

... but maybe some FRP bar grate with FRP sheet bonded to it

This is grate... I mean great. My knowledge of materials is a bit behind.

 

[berkshire]

If you have the shop capability to make a foam cored FRP panel
fully linked PVC foam rather than Polyurethane foam has better resistance to water because it is a closed cell foam.It swells a bit in MEK but seems to do well in gasoline.These people sell small quantities.

http://www.fiberglasssupply.com/Product_Catalog/Core_Materials/core_materials.html

Pvc foam manufacturers are Diab and Airex.
I get the idea that this is a commercial fishing boat.
But I have no idea how big your panels need to be.
A disposable mold for floor panels can be made from melamine faced bathroom board.
B.E.

The good engineer does not need to memorize every formula; he just needs to know where he can find them when he needs them. Old professor

 

[curtis74]

It isn't quite a commercial fishing boat but its used as such from time to time. Its a 19' Baja that the customer is completely in love with. He fishes recreationally about 8 hours a day and the rest of the time its used as a utility/rescue/repair boat for a fishing lodge. In a pinch it also gets used as a rental boat so the possibility for intense use and abuse is pretty high.

I don't have the measurements in front of me, but the cabin floor (from bilge to helm) is about 8' long and the bowrider section is about 6' long. Width at the widest point is 4'-1" which is easily done with 4' material and 1/2" of filleting on each side.

Here is a photo of what it looks like right now (with the exception of the fact that the motor stringers have been completed.)

 

[curtis74]

Apologies... link troubles.

 

[MikeHalloran]

I'll assume you've already coupled the stringers with stiff torque boxes.


I think stiletto heels entered women's fashion in the 1960's, and immediately caused a problem with dents and even punctures in airliner floors. That problem has been solved. You might find usable exemplars in an aircraft junkyard.



Mike Halloran
Pembroke Pines, FL, USA

 

[curtis74]

Good call on the airline salvage...

The aft end of the stringers are doweled and epoxied to the transom. The front is currently tied together with a 3/4" plywood bulkhead as a temporary support until I finish designing the floor.

The original design was this way but it didn't suit me. I will be extending the floor the whole way back to the transom on either side of the motor stringers. The outsides of each of those stringers will be supported by a complete stressed-skin composite box

I did a super-quick, not to scale drawing of a general idea. Imagine those triangular supports continuing back on the left and right of the motor stringers, and the floor continuing as well.

 

[berkshire]

Depending on how much weight you are trying to save, sheets of 1/2" or 5/8" fir plywood covered on both sides with glassfiber cloth make fairly low cost floor panels, they are just not the lightest. Honeycomb panels are great if they are sealed,if they get perforated on top they will allow water to get in and if there is any frost around the panel will quietly come apart.

These are things you mentioned in your original post

If you are intending to put that pourfoam back in later,run a perforated drain tube at the lowest point to a sump drain. The stuff absorbs 2% of its own weight in water in a 24 hour period and over time will become a water sodden mess if water is allowed to stand on it.
B.E.

The good engineer does not need to memorize every formula; he just needs to know where he can find them when he needs them. Old professor

 

[curtis74]

My problem with plywood is that (in his application) it only lasts a few years. Dropping an anchor on the floor or the flexing of a pedestal seat causes fissures and cracks to develop, and then its just a matter of time until its a rotten mess.

I refuse to put foam back in. I've never pulled dry foam out of a boat floor. I never understood why some engineer at the factory thought it would be a good idea. I'm hoping to come up with a composite material that I can use to make this framework and flooring that can be epoxied in place to supplement hull rigidity, and at least lasts long enough to warrant the additional labor involved when replacing it down the road. I'm trying to make a floor that basically can't be damaged by other than physically destructive means.

We have effectively removed nearly all the wood from this boat and replaced it with other materials that won't rot. The floor is the last thing and then we should have a basically rot-free boat.

It would also be nice to be known as "THE shop" that does this kind of custom work, so its not just one boat that I'm trying to throw together. I wouldn't mind finding a material and developing a process so I can do this on other boats.

 

[Compositepro]

Plywood is your best choice, but you must use marine grade which uses waterproof adhesive. Glassing both sides of the plywood will make it much stronger and more waterproof.

Rubber mats over the floor will do a lot to prevent damage.

 

[MikeHalloran]

Re plywood, even marine grade, "more waterproof" is not "waterproof".


Mike Halloran
Pembroke Pines, FL, USA

 

[curtis74]

Looks like FRP bar grate might not be any weight savings, but it sure seems like a pretty permanent fix. I found some distributors that have a pre-bonded 1/8" laminate on top. I'm just waiting to hear back from them re: spans and weight capacity.

 

[berkshire]

The pour foam started to get used in the late 1970's to meet coastguard requirements that powerboats manufactured after that time have enough reserve flotation to keep the motor or on an outboard, the power head, out of the water, if the boat got swamped.
It was customary to put it under the floor and up under the gunwhales ( gunnels).
B.E.

The good engineer does not need to memorize every formula; he just needs to know where he can find them when he needs them. Old professor

 

[Hansmeister]

Have you considered using pre-cured G-10 sheets bonded to balsa core? You would still need to seal the edges, but I suspect that the right shape (pre-cured) or bent on a brake would work.

All you would be doing now is bonding the pieces together.

 

[curtis74]

Hansmeister... yes I've thought about using plywood or balsa that is skinned with something to prevent the impact and flex damage, but the likelyhood of water ingress to the wood substrate is still pretty high. So far there have been enough promising FRP and other synthetic materials that anything involving a rottable substrate have been more or less ignored.

If I exhaust all other options I'll go back to considering wood substrates.

 

[MikeHalloran]

You could gain a little terminal flotation by using arrays of pultruded or shop-made FRP rectangular tubing, with the ends closed, bonded to FRP sheet. I don't know if it would meet USCG requirements, but it would give you hole spacing and penetration options that bar grate doesn't.



Mike Halloran
Pembroke Pines, FL, USA

 

[berkshire]

If you are against wood. Look at Diab H80 PVC foam , its not cheap but it is dense enough to stand damage from above without delaminating. A lay up of 1/8" on top and 1/16" of glass or Kevlar will give you an indestructable floor.
Pre butter the foam with a mixture of resin and Glass micro spheres for better adhesion of the faces.
B.E.

The good engineer does not need to memorize every formula; he just needs to know where he can find them when he needs them. Old professor

 

[berkshire]

Too soon on the submit button.
I meant to say 1/8" on the top face,and 1/16" on the bottom face.
B.E.

The good engineer does not need to memorize every formula; he just needs to know where he can find them when he needs them. Old professor

 

[curtis74]

Berkshire... that sounds like a nice plan. Do you happen to know how it does with hydrocarbons (e.g. fuel/oil)?