Infusion Q&A

Yes you could place the vacuum line in line with the cutaway edge and the feeds along the hull center lines. You can have two issues by doing so, one I mentioned above out-gassing and the other will be the balsa deck be air tight.
Assuming neither one is a problem to you then all you need to do is to break up the vacuum line into segments, have 100mm gaps so that as the shorter sections get infused you shut the vacuum off to these so that you do not waste resin. When the entire job is complete you reopen all the vacuum lines.

I would do it reversed, feed in the middle and vacuum lines along the hull centers.
Simple parallel feed if the resin viscosity, gel time, mesh speed is OK for the spanned distance. If not then a fish bone distribution added to the center feed.

But because of my concerns with the balsa seal I would infuse each hull side first then the balsa deck.
Also another refinement I would make is remove about 300mm from the stations at the bilge so that you can achieve an overlap of your laminates along the bilge center line rather than of to one side. I mentioned this before.

 

Couple more things to think about.
The downside to infused thin laminates is that the resin content will be approximately half that of hand laminating so the laminates will be more fragile. They will get bruised more easily.
You also don't have bulkheads or shelves in the hulls, the very small amount of bridging you get along the vacuum and feed lines can lead to distortion of the hull shape.

 

Ah, these are old pictures, Andrew. Bulkheads are already in. I just used them to show the hull shape and missing section.

I was thinking the same thing about the balsa. I am wondering if I'll be able to get a seal on the balsa edge. I just bogged it up a little bit today to see if I can seal it off. Still may not work. Anyone ever infuse endgrain balsa blocks before?

I'll be doing my outside keel layup once the boat is out of the mold (after the topsides infusion). It will take longer, but I already have too many things that can be removed on my mold. I am trying to keep it at least a little bit accurate.

Now, you mention doing a suction down at the hull center lines and a feed at the top?

I was always told that infusing "downhill" is the wrong way to do it because you can get racetracking much easier. I was always told to use gravity to your advantage by working against it and filling the infusion area from the bottom up.

Have you done otherwise with your build?

I'm not infusing any thin laminates here. Just the 34oz triaxial I was using for hand layup, plus any local reinforcements (rub strip) from the plans.

 

1150g triax is a thin laminate, 1.4mm if hand laminated and 0.9mm infused.

 

Infusing end grain balsa should pose no problems. Just keep in mind 2 things:

-1. Chamfer the edges, or use triangular shaped balsa to prevent race tracking.

-2. Balsa can contain a considerable amount of moisture. When reaching some 20-30 mbar (abs) the water will boil off, this takes time. You will see the vacuum keeps stable at between 20 and 30 mbar, then suddenly it drops again. This is where the moisture is gone. This can take hours in humid conditions.

 

ive been speaking with a well known designer/boat builder about infusing with balsa cores... he said that he had been speaking with core material suppliers/manufacturers and that it was impossible to acheive a lightweight sandwich structure by infusion processes despite using the special pre-coated balsa cores to reduce resin absorption.

Can anyone confirm this or better still, does anyone know how much resin the pre-coated, grooved and perforated balsa core materials soak up under infusion? What about compared to no grooves/perforations/grid scoring and how does this compare with the PVC foam core materials?

 

Lightweight is a relative term.
When infusing plain foam I allow 200-300gsm of resin for each side depending on grade.
For uncoated 150kg balsa 600gsm each side.
Resin to fill perforations and grooves will be the same for both cores provided they are of the same dimensions.

 

thanks andrew, wow that uncoated balsa really soaks it up doesnt it? for a 10-12mm core thickness that almost doubles the core weight... food for thought...

Does anyone have any resin absorption figures on the precoated balsa cores?

 

I can also add something there. I've done balsa by hand and infusion now.

The key is to prep the balsa no matter what you do. Give it a "hot coat" of epoxy if you are hand laminating or just bog it in if you are infusing.

If you bog your balsa in, for a very minimal weight penalty, you can effectively seal off the core and infuse over that.

I might add there is really *no* weight penalty since you save all the epoxy filling up the core between the balsa blocks. Bog is lighter than neat epoxy.

 

yes i knew about bogging the core in when hand laminating, but if your using an infusion core that is perforated and grooved, then you cant do this without filling up the holes.... this means you cant infuse both sides of the sandwich in one shot, you must do single surface infusions only...

 

Yes, that is correct. Sorry. I didn't realize you were infusing both sides at once.

You have balsa that is perforated and grooved? I have never seen that in the States.

On my build, I am using the lowest cost quality core (plain sheets of Corecell). I am unable to infuse both sides at once, but it's not so bad doing one at a time.

 

I once saw a fella who scored his own foam cores. He had a section of drill rod setup with a bunch of old saw blades & collars at regular intervals. This sat on a frame made of 2x4's above a table and was powered by a half inch electric drill. He just slid the foam through the blades.

I think it's one of the Aussie catamaran builders but for the life of me I can't remember which one.

 

Joining

Regarding infused parts. I like the fact that there is an optimised homogony about the parts and that the quality of the resin spread is good. What about joints? Given that the parts are fine, are there recommended ways and methods of making joints to go with the infusion theme. Is there a method for say a T joint, a right angle joint and a butt joint. I understand that the specific joint will be designed with a lam schedule or tape specification but from the technique viewpoint is there some information to share here??

Regards
Mick

 

Are you about to infuse the joint, or are you asking about joining infused panels using hand laminating techniques?

Or do you want to infuse all of it together? (inner skin, core, outer skin, bulkheads, stringers, etc)

 

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Hi Herman. The question is when you have infused parts and you want to join them can you/do you infuse the joints you make or just hand laminate the joints. The reason I ask the question is that the infused parts will have a certain set of characteristics like resin ratio, thickness, fairness etc. Is it sensible or not really that important to keep consistancy of the manufacturing technique when it comes to the joints. Or is it purely a question of estethics.

Regards
Mick