Please allow to introduce myself....

New to this one, but not new to forums. I LOVE forums. People with a common cause from all over the world freely exchanging information. I am on boat forums, car forums, music forums, airplane forums....I even have a forum of my own, but it's rather quiet, and that's OK.

HERE you can read what I've gotten myself into......and what I discovered when I brought part of it in for some paint.....yeah right.

The good news is that there's light at the end of the tunnel. All the insides of the ama hulls are back up to snuff. (80% balsa replaced).

Now I am getting ready to put the plugs back in the deck and put the beams back on.

It's hard to see, but the hull to deck joint is sort of an inside/upside down shoe box lid which, aside from being loose in a few places aims the joint UP....yes that's where the water comes from.

I have decided that riveting the joint every 10" or so would greatly improve strenght. And, I need to beef up the deck which has a few soft spots (now dry but still soft).

The solution I've come up with is to use the existing deck as the bottom of a new laminate, fill up to the top of the joint with foam (1") (this will hide the rivets) and then glass over and around and down the lip for a nice waterproof, flush, strong deck and hull to deck joint. All of this with a minimum of weight gain and relatively little labor.

The question is...what foam to use. The divine stuff is rather $$. I had the unmedicated audacity to go to my local house of home improvement worship and get some "pink" (Extruded polystyrene, hey, the same stuff as the "divine" brand) and experiment. It plays with the epoxy nicely, takes fabric well, gets strong and does all the other things a core should do....and you can buy a 2x8" sheet for under $10. It will get painted and no one will know.....

Is there ANY (good) reason not to use this stuff?

 

Well I'm not sure why, but I don't seem to be welcome here. Sorry to have bothered this elite group.

 

Oscar
I have not quite come to grips with your problem. You have made it hard work to go through the detail you provided on the other links.

The balsa work you have done in the amas looks good. I am wondering why don't you use the same method on the deck.

Pink polystyrene foam is OK for stiffening things up providing the foam is never exposed to solvents like petroleum.

There are better but more expensive foams that have better properties for use in the marine environment.

If you attach some pictures to a post here you might get more comments.

As far as my understanding of your problem - The foam should not be exposed to point loading that breaks the bond. The foam should not be exposed to solvents that erode it. The foam should not be exposed to heat that will melt it. On this basis it will do the job. I use it inside sealed hulls as bulkheads without problems.

Polystyrene foam is used structurally for a variety of purposes in the form of sandwich panel. It is covered with thin sheets of aluminium or steel. Insurers do not like it because it burns really well.

Rick W

 

Attached shows a fire test on sandwich foam panel. The main concerns here is how quickly it flashes, the extent of fumes, rapid loss of strength and the heat intensity.

It is not the ideal material to place near/above any exposed heat source such as combustion heater or spirit/gas cooker.

Rick W

 

One more thing - the title of the thread does not get to the issue at all. Those who follow structural issues like this would not be given any idea by the title of the thread.

If you do not get more input here than start a thread titled like:
Trimaran structural core - which foam is best

Rick W

 

Hi Rick, thanks for responding. Good to confirm my suspicions one more time.

Roger the heat and the solvents. Neither will be an issue. Point taken on the thread title.

Re-doing the balsa on the deck is tough. First of all most of the work would have to be done with head and arms inside the hull, right in front of my face. Secondly the outer glass layer has numerous cracks in it and would still need at least grinding down and glassing over to make it waterproof again. And, again, the hull to deck joint is loose in quite a few places. Getting "in there" is almost impossible, I'd have to take the deck off, not something I want to do. With the proposed method I can rivet the flange every 10" or so and get some mechanical fastening going, then glass all around and "wrap it up tight."

Attached a picture of a now installed bulkhead, and of a piece of foam and fabric loosely laid down as I plan to install it on the deck. (Properly faired resined and glassed of course.)

Last, I've hear from quite a few surf board builders that happily work with the pink foam instead of the expensive blanks and say they have very good results. If it works for them it should work for me.

 

Eh Oscarvan,

Welcome to the forum. I see you're a jack of all trades when it comes to forums

Just because there wasn't an overwhelming response right from the start doesn't mean we don't see you. We're all buzy with our little 'problems' and besides half of us are sort of off our rockets... those into boat building anyway. So it's more a matter of we don't want to emabrras you or ourselves

That purple colour will make you fit right in with the rest of us lunies here. I also wanted to go purple but the wife forbode me. I see you call it pink. Mmmm... we guys have to get in touch with our female sides a bit more so it's probably not so bad

Anyway, Rick is one of the best...

Welcome again, and don't be shy with the pictures.

 

The bulkhead looks fine.

I do not like the idea of the foam being used on the deck. You will need quite a few layers of woven cloth to get the strength to avoid point loading from feet/shoes. At least 600gsm - preferably 800gsm. This will add a lot of weight. Water will find its way under the foam as well. You are going to have a very messy mating of the fabric to the hull.

I would regard a job like this as shoddy. Depends on how much value you place on the boat. If it is regarded as throw away then it might be acceptable to you.

If the hull to deck joint is already questionable I would be removing the deck and do a proper fix on it similar to what you have done with the amas. It is much easier to work with it in the open. You will get a job you can take pride in because it is the way a quality professional would do it.

You really should start another thread. There are some fellows here who do this sort of stuff regularly who can give very good advice.

I do not like what you are proposing for the deck.

Rick W

 

The hull to deck joint is loose, but not everywhere. In most places it is still very much attached. I'm guessing 10-15% is compromised. Because of the light build I'm afraid I will not be able to get it off in one piece without destroying it, or even damaging the hull. I removed a shelf that was glued in with the same thickened polyester and was loose in many places. However where it held, it held very well and had to be ground away. I won't be able to grind between the hull and deck without destroying one or the other. Also, with the hull I had the outer layer to work with. Here the inner and the outer layer is cracked. I would have to build a new deck. As far as water finding it's way under, I was going to solidly resin and fill the foam to the existing deck. Is there a higher density foam that would be a better basis? Or, I could use balsa.

 

Oscar
How about starting a thread with a title meaningful to your problem. There are others who can give you alternate advice.

The issue is really not with the foam. It is with the method of fix proposed.

I would have a very good look at the joint with respect to separating before patching over something that is in poor condition. I do not like the idea of covering over problems. They tend to have a habit of reappearing.

One test you could do is to see what I mean about denting the foam if you do not cover it adequately. This will be the case with most foams. Once the surface is distorted the adhesion starts to break down. Make up test pieces with various layers of glass and see how thick you need to go to avoid compaction. End grain balsa is hard to better for lightweight deck.

Rick W

 

One problem you may not have thought about with the fix is that you will remove the ridge that provides a kick rail along the outside of the deck. This adds a measure of safety to prevent unintended swimming.

Rick

 

"...I have decided that riveting the joint every 10" or so would greatly improve strenght...."

How much strength and why, and what have you 'decided' is wrong with the original and why, what load cases (and where obtained) did you use to calculate the strength and hence layup requirements to satisfy the loads?

 

What's wrong with the original is that it is starting to come apart. As can be seen from the myriad of cracks in the deck the layup schedule was insufficient to begin with (a few mm at best). That's how the water got in and the 1/4" of balsa was compromised.

Based on my suppliers recommendations I plan on using a biaxial with a stitched-on mat which comes in at 25 US ounces/sq yard.....rough math about 700g/m which is right about in the 6-800 mentioned above. Total area of each deck is about 4-5 sqm so we're talking a few kg here, hardly a problem. Yes, finishing the edge will be some work. The hull is also getting a layer of cloth on the outside as it is beyond thin in a few places. So I will fill and fair until it all looks decent.

I did think about it. To the inside there is a tramp. Underway there is no reason to stand on the float. I will apply an anti skid paint. During docking one will have to mind. None of Farrier's designs have a toe rail.

I did the tests for the bulkheads and was satisfied with the results. I will do the same when the biaxial/mat arrives. Yes, I am considering balsa.

I understand, and in principle agree with the objection to "covering up the problem", and it is normally not my first solution. Here, I am dealing with a very light design to begin with, and I think the line of "cutting corners in the name of weight saving" was crossed. The design is from a reputable designer in Denmark (Quorning) but mine is one of 80 boats built under license in Canada in the 90's. That relationship did not last.

So, in my defense, instead of "covering up the problem" I would like to look at it as "integrating the existing into the solution". I will mechanically strengthen the joint before I cover it up. Also, the fact that it is exposed is part of the problem. We have freeze/thaw cycles here in winter. The boat was uncovered so far, and any water that got in the joint (remember it stands straight up) did it's destructive work. Now that I own it it is under cover when on the trailer.

 

"...What's wrong with the original is that it is starting to come apart.."

Ok, this is noted.

"..Based on my suppliers recommendations..", as nice as these guys may be, who is in charge of the design?

Since as noted above, to cover up is not the solution, in any form. You need to ascertain the reasons for the failure first before you consider any form of corrective action.

The only way to begin this is by knowing what you boat was designed to in terms of structural loadings. Without first doing this, it is all pure guess work and you're very likely to repeat the same mistakes as before.

 

As I said: Too light an outside glass layer which cracked under impact of stuff and the perils of racing and what have you, a joint standing straight up, water intrusion, and freeze thaw cycles.

As much respect as I have for math, physics and the designers that employ them, there IS some value in the "eyeball" of the builder. Men have been building boats successfully for centuries, but it has only been in recent history that engineering came into vogue. When I went to school the answer to the question 2x2=? on a slide rule was "approximately four". (that was a joke).

I have built buildings with my own two hands strictly based on experience and they are holding up quite nicely. If anything they are overbuilt. And while overbuilding is a crime in the bottom line driven modern world, it works for me.

Soooooo, if I eyeball something like this and say: "It was under built but we can fix it like this and that should work quite nicely" there is, based on my personal history of messing with boats for a half century, a reasonable chance that it will come out OK. It may even be a little over built, not a crime in my book.

Again, no disrespect to the engineer.