[powderpro]

I'm wanting to use Nida-Core as much as possible in the new boat that we will be building because of the weight savings and other beneficial properties. There are some areas in the boat that we will still be using plywood, like the back work deck where a large drum will be bolted, but I would like to use Nida-Core wherever we can. My father has built/finished 20+ fiberglass boats and has always used plywood for decks, floors, walls, bulkheads, etc. Since Nida-Core is a "new" thing to us, I need to know the ins and outs of how Nida-Core works versus plywood. Do you use it just like plywood? Is 1/2" thick Nida-Core equivalent to or can it be used in place of 1/2" marine plywood? Nida-Core seems to come in different versions, which version or product is most equivalent to plywood? I've heard/read that you can't bolt through Nida-Core unless you back fill the area you will be bolting through? Is this true? Any help or advice is appreciated from those of you who have knowledge of this product. Thanks,

Brian

 

[CaptPaul]

There is a difference between using a lightweight core and plywood. Plywood is a structural material that separates the two layers of fiberglass, which also should contribute some strength, along w/ their waterproofing properties. Lightweight cores serve to turn the fiberglass layers into a two-axis I-beam type of structure. The two layers of fiberglass contribute strength, as the top and bottom plates of an I-beam, and the core material serves as a separation web to magnify the unified strength of the two skins. The thicker the core, the more it will magnify the strength of the two skin layers. Plywood also serves to separate, and therefore magnify the skins, but also offers additional strength through it's own laminations.

If you do fasten through cored materials, you do need to close out the core, or replace the core w/ a compression-resistant material, such as plywood. Even plywood has drawbacks, since if there is water intrusion, it will rot and fail. Plywood cores should be over-drilled for the fastener, then back-filled w/ an epoxy filler, and re-drilled to acept the fastener. This will insure that there can be no water intrusion into the core. W/ composite cores, whether you worry about water intrusion and rot or not, you have to understand that the core will probably fail under the compression load of a bolt, which it is not designed to withstand. Furhther, wherever deck gear will laod the surface of a cored material, the core needs to be substituted w/ pywood or closed out to solid glass. Otherwise, the core will crush and loose adhesion to the skins, failing internally and offering no strength beyond that of the surface skin.

Paul

 

[GoodChance]

Brian -

When rebuilding my Duffy, I had the same internal debate that you are now facing. I sought the davice of many people who were more familiar with nidacore and coosa board than I am in order to make a sound decision. I also spoke to people familiar with the downeast boats and the potential benefits of a lightweight (but costly) material like nidacore to a relatively slow boat design.

In the end, I chose to use fir plywood in all areas where compression forces were anticipated (like decks) because plywood is a more durable material than nidacore. I used nida core for my canopy because of the very, very light weight of this material, plus I didn't want any "beams" in my main cabin and nidacore could span 10ft and hold a radius without using beams.

For the bulkheads, I again used plywood because it is easy to use, cheap, and reliable when finished correctly (by this I mean, I coated all surfaces with epoxy, including the end grains, BEFORE assembly. I wanted to make sure that no water could get in anywhere. Plus, the bulkeads and cabin walls are really quite small pieces of material. The NET weight savings by chosing nidacore over plywood in these SMALL pieces would have not been all than great after the project was completed (My finished Duffy would have weighed maybe 500-1000lbs less if I had used nidacore in the bulkheads, cabin walls and cabinetry vs plywood. Really not that big of an advantage when considering that a Duffy is a 13 to 14,000lb and the design is inherently NOT a fast boat anyway.

My advice - Use plywood as much as possible, save money, complete the project MUCH faster and put the savings by NOT buying nidacore into fuel.

Chris

 

[powderpro]

Chris- Thanks for your helpful response. I'm leaning towards using Nida-core as much as I reasonably can in the cabin area. Cabin tops, front bulkhead, bathroom walls, lower bunks, cabinets, seats, etc. If I could save 400-500 pounds over plywood in those areas, it would be worth it to me. But I'm going to have to sit down and really figure out if I can even save that much weight over say 3/8 or 1/2 plywood. My local hardwood supplier is having a "sale" on their 3/8 and 1/2 marine fir plywood. The 3/8" was $39.00 and the 1/2" was $44.00 per 4'x8' sheet. Sound like a good price to you? What's a sheet of Nidacore run? $100+?

I'm pretty sure I'll be using plywood for the rear work deck, for the reasons you listed (stronger, takes more abuse). I'm putting 500hp in this boat, so using Nidacore throughout to save 1500 pound isn't likely going to make it much faster. Thanks again, more responses are appreciated.

Brian

This post edited by powderpro 01:25 PM 07/19/2008

 

[claw1]

On those choppy days , those rolley , punky , grey stinky days , the heavier the boat {within reason} , the nicer the ride . I'd go with at least plywood for the deck and probably the whole job. The one place I would consider a core, would be the fore deck,the area between the wheelhouse and the bow . Good luck with your choices .

 

[GoodChance]

Brian -

You can purchase nidacore in 2 basic forms - just the raw nidacore sheets and the finished material. Raw nidacore is just the honeycomb material with a "fabric-like" material on both sides taht allows the application of polyester (or epoxy) resins. This is a very flexible material and is what you will need when trying to bend or camber the nidacore when making your roofs. The 2" sheet (thick) is the most popular for making roofs. It comes in a 4x7 sheet and it locally costs me about $120/sheet but then you have to apply a layer of biaxial and polyester resin to each side of the nidacore. Then finish cloth. It's a lot of work but the only way to go if you want a camber. For your square walls, or you can buy the finished nidacore and it'll cost you about $250/sheet (as I recall, this comes in a 4x8 sheet). I never purchased any finished sheets because of the cost and MY PERCEIVED benefit of this material for bulkheads and interior walls. I just don't see the cost benefit of nidacore in any areas other than the roofs of the trunk cabin and the main cabin. Sure, it's nice to have a "rot-proof" cabin, but just take the time to sael everything really well and plywood will offer you many benefits over nidacore.


For your calculations, my nidacore (2" thick with 2 layers of 1708 biaxial on the topside and 1 layer of 1708 on the bottom) weighs just over 2 lbs/sq foot over a 10x12ft area. This is a huge weight savings for the main cabin roof and it is super rigid allowing for no roof beams. This is the main advantage of nidacore in my opinion (super rigid).
Chris

 

[encaa5]

Powderpro,

I bought a bare Harris 36 hull in 1977 and used 5/8' plywood for bulkheads, bunks, and 3/4 " for deck in aalon, because it was the only material available and I didn't know any better.

I ripped it all out 13 years ago and replaced everything with finished 3/4" nidacore for bulkheads, and 1 1/2" for main cabin deck and bunks.

My bow water line dropped 6" forward, boat picked up 1 1/2 knots and boat salon is quiter. Nidacore will take more time to finish because you have may have to route and seal the ends and anywhere you want to compress it with hardware.

Add extra weight in fuel. At least you can have the option of light vs heavy. Lighter boat will require less power and therefore less fuel to get same speed.

 

[RayboMarine]

fuel aint getting any cheaper, for new construction the labor and costs are not that much. Would I rip up a perfectly good old boat to use the stuff? Not unless it was already rotting out or getting a total restoration.

Do it now because later on when your looking at the finished boat it will be too late to change it.