Corecell Planking Doubt

Dear colleagues I will soon start the build of a oneoff boat which will be made with corecell core and bead planks and I have the following doubt or question: after the planks have been glued together which happened with planks nailed to the stations ... can we remove the nails in the absolute certainty that the planks which were glued together and fastened to the stations with the nails will hold its shape completely ???? or due to the planks being glued under tension when nails are removed ( for lamination to start) the planks will spring back slightly distorting the original shape ????

If this were the case how are the planks held against the stations after removing the nails before lamination ???

thanks in advance from Spain

 

When I said planking in my previous mail I meant Strip planking sorry for my english but it is not my mother language so I do my best.

 

Rather a nervous time when you release the planking from the forms.

I use wood strips. To help hold the planks down, I use a few blocks and screws from the underside. Each block has one screw going into the form and one screw going into the hull.

The other thing is that when I fill the screw holes, I inject some resin into the holes. This resin follows the hole thru the planking and into the form. Cast plastic nail of sort.

Between the two nothing seems to move.

 

She'll be right mate, as long as the job is done as per standard spec, the nails just rip out, no worries, the shape has already been set.

 

Once the strips have been glued together along their edges, they'll lay reasonably fair on the station molds. Some will have a good amount of twist, which will produce some "edge set" as you work that area, but they'll lay down once all the planks are on. Of course you'll use temporary fasteners (one of several methods) to convince the obnoxious ones to comply with your wises, but these get pulled before you lift the molds free. In most cases the hull will pretty much hold it's shape, but the sheer should be given some athwartship braces to keep it from "opening up" after the molds are pulled out.

 

I am surprised to see that some of you more experienced builders, say they the strips will stay keeping shape and contact like Landlubber while some others like Nero say it is a nervous moment.
The thing being that if the forms have been cut with CNC equipment to get all the precision available, they, "lying reasonably fair" like Par said might not be enough, in my modest opinion, the strips have to stay in full contact with the forms in order to keep the precion into which you have invested by cutting them in CNC cutting gear. so still afraid and looking for a solution ...

 

First up nervous comment was for you as a first time builder. I remember lifting the first hull up out of the forms.

Second up, I stated I am using wood strips not corecell for planking. The temporary blocks and "cast nails" are for areas where I am "concerned" about.

Before you pull the hull from the forms, the fiberglass or other fiber skin has to be laminated to it. This is the time when I add some hold down blocks. Some areas (at least on a complex hull shape), can lift up a bit (2 mm). Areas around the top of the mold can move in. Humidity and temperature can cause movement ... in wood. For corecell humidity these are not a concern.

If you will use your forms only once, then you could leave some of the nails. Set them a bit deeper. They could be pulled thru the foam from the other side after the hull is laminated. This will probably mess up your forms however.

Par has good advice.

Realize that strip planking is not a precision method. You will get a nice fair hull. It will be a few mm off from the computer design. Simply because the strips will facet the crossections. Then you will grind off these corners to smooth out the core for lamination. This doesn't mean you should go at it like a pallet builder.

Be thoughtfull in you actions and you will end up wit a great looking hull.

 

Hi back again,

Try not be too timid about it my friend, if you believe that CNC/CAD/CAM is going to be a perfect boat, then you are a little mistaken. In theory, yes, in practice, it is only as good as the builder anyhow.

A well set out mould, batten faired and layed in either strip planking or foam planking is refaired anyhow after it is put together before sheathing. Personally, I would not waste my money in computer creation, it is basically a very simple process that you are undertaking, you only see it as a big problem, try just looking at it as one step at a time, and all will be unfolded.

You can do bead planks in foam yourself with a cheap spindle moulder, or if the boat is only a little fella, say under 40 feet, then a 2hp inverted router on a nice table will do just the same job for 1/3rd the price.

Once the foam planks are on the frame, they are sanded fair, whether they are made by yourself or some other source, it is irrelevant, they will still be sanded fair, so there goes the supposedly wonderful computer manufacturing precision down the drain.

I have made world ocean racers, they really are not symetrical at all, we certainly try to do so, but the reality is, they are not. Even Americas Cup boats are not "perfect". Accept this as being the norm, and you will be happy.

Most importantly, understand it is just one step at a time and the boat will go nicely. Of course you must try to preserve the desired shape, outersheathing does a good job, but always try to keep inside forms in place for as long as you can, it is just common sense anyhow.

All the best mate.

 

Thank you, Nero and Landlubber for your input, I understand symetry and perfection in shapes do not exist, but I just want to make sure of only trowing away the smallest amount of precision I can, If I were making a male mold for a female mould building, I will definitely nail the strips and glue them to the forms and then for sure, when removing the nails, the strips will stay exactly where I nailed and glued them but since we want to build a one off and not a female mold ..... The idea of Nero of the injected resin in the nail holes looks fine, another idea I had is to sort of stitch the strips witha thin line trough some line of holes made in the forms near to where the strips will lie ... the stiching line can be left under the laminate and cut from the inside for the removal from the forms, anyway it has been nice to know that we all are facing ( or have faced) the same uncertaintys

 

Strip planking is an easy way to build round bilge hulls, but not particularly precise. So much so, strip scantlings usual incorporate an element of thickness removal, to accommodate the fairing process.

Modern strip planking methods are sheathed. Exterior veneers of wood or fabric set in epoxy are typical. Both of these require a substantial amount of fairing to get the sweet surface we all desire.

You'll note most table of offsets are dimensioned down to an 1/8". Even though your molds and strips may have a few thousands of an inch accurately in their machine cut dimensions, the net result is to the nearest 1/8". In other words, if you can lay a tape measure from rail to keel on each side and come within an 1/8", you're better then most.

I've seen several methods of "tacking" strips down to the molds, most have merit. I've found the best is a very thin brad, punched through a banding strap or small chunk of wood. Staples through banding strap is also good, but you have two holes per fastener. These small holes fill easily and are next to imposable to find once the sheathing goes on.

 

The boat I have in mind, is a center console of around 30 -32 feet with quite a flared bow which is the main area of my concern becuase there the curvature of the strips might make them try to spring back to a straight shape and maybe reducing the radius of the compound curvature and then deviating from the original design if it is only a couple of millimeters and the deviation is symetrical it will be OK but the fact of loosing contact with the forms when removing the nails for lamination definitely scares me.

But maybe it is my own nature of overcautioness what is the problem and surely Par and Landlubber are right and I will be OK, thanks to the new technologies and to the generosity of you all we novices can keep in contact with very experienced people like you all living in the US, where I live, in the Canary Islands Spain, the fishing is good, but here there is not a single boatbuilder so I would be on my own If it were not because of the possibility of counting with your generous advise.

I will also hire the services of a Naval Arquitecht probably Guillermo Gefaell for some calculations

 

picts for ideas

This the female form setup for my catamaran hull. It is half of the hull split down the middle. (not the best way to go about it)

Female forms are a very good idea. All the structure can be put inside of the boat before it becomes self supporting.

The first pict is my master template sheet. I use x,y coordinates and loft the profiles up to full scale. Since all the forms are spaced evenly, lines that are not equal distance from their neighbors have a problem. Thanks to TouchCAD, I had no problems with unfair shapes.

After the lines are drawn, I cut along one with a jig saw. Then I screw the template to the form sheet. Rough cut this and then use a router with a template bit.

Lots of fun.

 

To attach the foam core strips to the stations, one can use cheap hinges. Screw them from the back into the foam (the foam is strong enough to hold the screw) and screw it into the station as well.

great reading on the strip planking method with Core-Cell is the work of Andre Bilodeau. He has (had?) a website, but if you are not able to find it, give me a notice.

 

Thank you Herman for your collaboration, I have the André Bilodeau´s book and was surprised when I read the "hinge story", the hinges will certainly allow for some movement ( play) particularly if they are cheap, so I do not see Bilodeau´s point on using them, if keeping the strips in place is the purpose, why not use some small wood cubes with two holes at 90 degrees, one hole for screwing into the forms and other into the foam. Naturally where the edges of the forms are beveled the cubes should be moved a liitle bit away from the edges.

On the other hand, there are plenty of things in the bilodeau´s book which I find a bit strange and about his web site I have not been able to find it

So far the best idea I heard was from Nero, with the strips nailed to the forms make some little holes connecting the strips with the forms and inject some resin, but still this may cause small hard ponits wihich might make the fairing of the foam a bit difficult.

As I see it, the strips should be ( somehow) screwed from the inside ... after being temporarily nailed from outside

 

Screw the hinge in the foam, then pull on them in the inwards direction, and screw them tight to the station. use countersunk screws, and screw them such, that by fastening the hinge is pulled inwards just a little more.

However, I have plenty of customers that just nail the plank to the frame, then use some force to pull the station out later. The nails either get ripped out of the foam, or break (use plastic nails).

In any case, just fasten the strips that need it.

When using Andres T-shaped tool, not many planks need fastening.

About his sometimes strange solutions: I have met Andre several times. He is a great guy, just a bit strange. Can't find his website either. Such a shame.

Don't worry too much about hard spots due to small (plastic) nails or epoxy studs. You will be sanding with grit 40 or 60 at most, so that is not too much of a problem.