Composite Construction Method/ Difficulty

Hey everyone,

This is my first time posting here, but I have some experience in boatbuilding only smaller craft including strip-planked canoes etc. and am a decent woodworker. I’ve been wanting to build a sailboat for awhile now, but have been looking for the right plans. I have come down to two options which i am trying to decide between. Time/money differences aren’t absolutely vital for me, but I’d like to know the difference.

The first is this design: https://aacdesigngroup.wixsite.com/acdesigngroup/fast-75-en?lightbox=i1zg3
I love the lines and the overall design of the boat, plus the specs of it are just right for what I am planning on doing with it. The plans however and designer said it is a composite construction with Airex Aim and Composite Fibers. From my research it seems Airex aim is some sort of foam core? Also what composite would I use. The website has some pictures of the construction process which are somewhat vague; the composite seems to be multiple layers of plastic-like strips joined with some sort of bonding compound with support struts running along as well. Am I close at all?Can anyone explain the process to me and Pont me towards additional resources? Is it similar to stripplanking where you build you mold stations them lay the Airex over it then the composite? Simply put, Is this worth the extra time effort and cost. How much is the composite, airex, etc. Is the boat even accomplishable with relatively novice skills and no previous composite experience.

The other design is a 23 ft strip planked daysailer, nothing too out of the ordinary.

Thank you so much for your help.

 

It looks like cold molded to me.

 

Composite is a blanket statement and means made out of several materials. In this case we are talking about foam cored fiberglass reinforced plastic. It's similar to the wood cored composite canoes you are familiar with, only with foam instead of wood and thicker skins.
There are several methods to make the foam core conform to the compound curves of the hull, horizontal and vertical stripping, thermoforming, kerf cutting. The necessary support for the foam ranges from fully closed tooling to stringered molds to stations only. It all depends on foam thickness and chosen building method.
The pictures from your link seem to show a closed male plug (stations planked with thin ply) and foam stripping.
How much it costs is anybody's guess without a bill of materials and local market prices. You need to know surface area, type of foam (I am not familiar with any Airex product called "Aim"), foam thickness, total fiberglass (and carbon if present) weight and fabric types, and the intended resin (polyester, vinylester, epoxy).

The question of it beeing worth isn't for us to answer. The primary advantage of a foam core over a wood core is weight, the secondary is that foam won't rot wich usually leads to a higher resale value.
It's your decision if one of those seems worthwhile to you. Building in foam core on a male mold is entirely doable for the amateur. If you have built a strip canoe you have the basic skills, build a strongback, errect stations, install stringers or a mostly closed skin, fiberglassing the core. In its most basic form, stripping a mold with foam is no different from using wood.

 

In general terms, the lighter the weight; the more complex the build. I'll catch hell for it, but it is close to accurate.

Airex that I know is a honeycomb core with a veil on each side; perhaps with a resin blocker under the veil (or not). The airex probably gets partial lamination and then gets placed on the mould, so you need a table for laminating and this can benefit from vacuum. But the cost is time. Each panel is glassed and then bent over the form, generally. If not, the core is not rigid enough without lotsa ribbands and when you take it off the form; it will deform. After finishing the hull; you would glass the exterior in a male jig in situ. This process takes a lot of time if vac is used.

The other strip planked hull can be done quicker, with a few caveats. Strips cannot be laid one per day, nor can you lay them in one area at a time. Once strips are laid; hull is glassed (can be infused or vac bag if not too large or in steps). Boat is flipped and inside glassed.

Neither are super fast, but the Airex is more difficult and will take longer. I was not able to keep my vac table producing more than about 2 panels a week. Keep in mind some were 34' long, but we ended up at about 2 a week or so. My project ran about 48 months of vac work and somewhere around 200 total panels..so, you can also determine total panels and use 2 a week for a garage build. People may criticize this rate, but space and man hour limits production rates for custom builds.

 

I have to admit to being fascinated by fallguy's post,because I never knew that Airex were in the honeycomb business.I have used their foams for quite while and they are as good as any.There are other fine foams from concerns such as Corecell or Divinycell and they all need to be selected for their particular properties.The whole business of composite engineering requires knowledge of both materials and processes and is best applied knowing what a particular enquirer has the facilities to undertake.What isn't a good idea is to begin with a vitally important component.Much better to get some experience with things such as small hatches and different aspects of the laminating processes.It hurts a lot less to throw the small parts away.When you can confidently read a laminate specification and be certain that exactly that will be the outcome,its time for the bigger stuff.

 

well, if I have erred, so be it, I do not know what airex aim is

I only recall seeing an Airex honeycomb, and I could be mistaken on my recall. A datasheet would end any question.

but, if airex is a core; it would still need one side laminated to be set over a male mould and hold shape unless the flip is done or mould is BH, etc

Edit: It appears I have erred. I don't know why I thought Airex was a honeycomb..

 

Airex is a line of cores I think, or at least my c1 catalog has stuff of several densitys and compositions even a coosa like substitute.

I'd try and see if the outfit making the bigger boat design has a dingy plan.

Did the material transition 4 years ago, and wish I'd of started on a dingy of the same construction used on my 32 footer. Boats are boats and certain fundamentals don't change, but goodness gracious we learned a lot. Probably could have built a nice little run about from the dust made grinding down the mistakes and lessons learned.

Make a dingy. Call it cheap tuition, learn mistakes small then go big.

 

For the curious,here is a selection of cores.

Aluminum Honeycomb Core | All-Aluminum Custom Furniture | HyCOMB http://honeycombsolution.com/1-aluminum-honeycomb-core.html

Nomex Honeycomb Core | Honeycomb Sandwich Panel Supplier https://cacomposites.com/core-materials/nomex-honeycomb-core

1/2''Honeycomb Polypropylene 4'X8' Sheet https://www.rayplex.ca/1-2-honeycomb-4-x-8-pp-details.html

UK Distributor of the AIREX® and BALTEK® Range - Composite Core Materials - Trident Foams https://www.tridentfoams.co.uk/airex---baltek.html

They all have their place and a good composite engineer will know where that place is.

 

Another question, now I’m questioning doing the airex construction due to its unknowns, but still considering it. Do you think if I bought the plans for it then built the mold stations and strip planked it instead it would work? I know I’d gain some weight but at least I still get the ideal design.

 

No! Don't go away from the designer's build recommendations.

A core boat is generally lighter; so you build with strip and end up with unknowns on the waterline.

It would be foolish to build in a different core than the designer recommends. That said, he may be comfortable specifying the boat in strip; so ask.

 

It will work, but the weight increase is significant. By my estimate a WRC core will add ~165kg, and that's coming out of your payload allowance of 430kg. This means that you will have a two person boat and have to always watch the weight you bring on board. The designer could shave some of that added weight but even he can't work miracles, typical boatbuilding foam is 80kg/m3 and WRC is ~370kg/m3.
Contact the designer and solicit a study plan package, that's a materials list, some layup examples, etc. Also ask if he is ok with a core change, maybe he is willing to do some redesign.