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  #1  
Old 11-23-2010, 09:31 PM
Charly Charly is offline
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Choosing a deck core

Hello all. I am fast approaching the deck stage of my build, (Kurt Hughes daycharter 36 cat), and really could use some advice. I am only vaguely familiar with the arguments for or against balsa, but I know even less about the available foam core choices. The designer has expressed a preference for balsa core on the decks, with foam around the edges, because foam is easier to contour and fair into the topsides. Sounds good to me, but what kind of foam? The plans specify 3/4 inch core, minimum 150psi.

Decks are constructed as follows: 4mm ply, 3/4" core bagged on, with two layers of 20 0z triax layed up atop that.

I would appreciate any ideas or opinions, working tips, and favorite suppliers. Cost is a factor, but the relatively small area probably means price differences would be manageable.

Ps is "pro balsa" just a trade name, or is it different from other end grain balsa?

Thanks!
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  #2  
Old 11-24-2010, 09:21 AM
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Herman Herman is offline
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I am not fond of balsa as a core, and people know that. Every drill hole and other waterwat NEEDS to be properly sealed, for the whole life of the boat. Not only by you, but also by people that you hire to modify things, and by future owners. If not, the balsa will rot, and you will regret.

Boat decks are funny things: there are probably the rare piece of composite construction that sees so many modification after initial production, with people drilling holes in it.

Strengthwise, there is nothing wrong with balsa. (uh oh, the Core-Cell fans will kill me now... )

If you want balsa, you can make your edge strips from PVC foam, check the datasheet for the density you need. Probably 100 kg/m3 or so.

The other option is to do the whole deck in PVC foam.

Pro Balsa is a trading name, what you are after is "end grain balsa" which is the stuff that has the grain perpendicular to the sheet.

There are producers that give some options for their balsa, like grooves, holes, scrim, etc. That is just dependent on your processing. Holes would be nice, if you plan to vacuum things down, although you could do without.
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  #3  
Old 11-24-2010, 10:46 AM
mark775
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But foam unzips like too tight of pants on a fat person and balsa stays laminated. All foam is open cell with water and a few freeze/thaw cycles. I don't understand the need for foam around the edges - can you post a drawing of what your designer is talking about?
As an example, I know you are not going to build your deck this robust but I built the deck for my boat 20 years ago out of two layers of 1" balsa (because the original foam deck failed and was weighing the boat down with water. It was simply not strong enough to be the deck of a workboat). It has a span of eight feet (bulkhead under at eight feet) by twelve feet completely unsupported except by the perimeter. It has had flailing 200 kilo halibut, four wheelers dropped by a crane operator, 21,000 lbs. of water in a tank the size of the entire deck (of course that bulkhead is under at eight feet), 8,000 lbs. of fish, spilled barbeque coals, explosives, and has never had one idiot drill a hole in it. Plywood can make a strong deck, too. BUT FOAM? Foam is foam - good for areas that don't get holes drilled in them and don't need to be strong. I've got it on interior panels in my boat and for insulation - although I wish I had rock wool for that instead.
Let me go a bit further into foam, while I'm getting ramped up... If a panel is going to be protected by enough glass from the bumps and bangs of life, it will be lighter to make it from plywood. If it doesn't need to survive a gaff point or beaching to offload fourwheelers, foam can also make a good, light panel. Once you put foam into real life, and are not interested in just surviving for a few races, Eggo waffles would make a better core.
There are adherants to both camps, I know, and I am likely to start a firestorm with this but I am in the camp of Real World and have seen what a new foam boat does when the steering gear fails on the maiden voyage and it piles onto the harbor entrance rocks at just three knots - it delaminates. Fancy vacuum bagged, latest, best material, fast, light, expensive, glorious...and delaminated. Brand spanking new. Save the foam for lightweight cabins and such. Don't build the rest of the boat from it.
I would never build the bottom of a hull from balsa but I know a 65' Kelly that is entirely balsa cored.
Choosing a deck core-lu-lu-belle-boat.jpg

It once erred and piled onto some rocks. It holed the hull under the stem, which had to take an emergency repair and both rudders punched up through the hull in the lazarette. The boat had to get towed home. The rudder holes self sealed and only a few gallons of water entered the boat there. This happened in 1979 and the boat is still happily making money.
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Old 11-24-2010, 10:54 AM
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Herman Herman is offline
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Can you specify your "foam". PVC and SAN foams are closed cell. However, PU foam is a completely different ballgame, and this foam should be used only for insulation properties. (diy fridges, etc)

Also, good workmanship is in my experience more vital than the actual materials being used. and unfortunately not every yard realises that.

I feel that your reaction will only spoil another thread (like so many here), which will be of no use to the topic starter.
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  #5  
Old 11-24-2010, 11:09 AM
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I'm sorry, Herman but balsa is a superior deck material. As stated above, ANY foam is open cell once water gets involved with a few freeze/thaw cycles. "I feel that your reaction will only spoil another thread" Would you have me delete my post because some don't agree...including the designer of the the original poster's boat?
"...good workmanship is in my experience more vital than the actual materials being used." - agreed...and not drilling holes in a core
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Old 11-24-2010, 11:20 AM
charlyII charlyII is offline
 
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Thanks guys!

Herman, I have been under the impression that foam decks still need to have balsa or similar underneath deck hardware etc, in addition to the backing plates, because of balsa's superior sheer strength? Is this correct? If so, in my case I probably should just do the whole thing in balsa (edges excepted), becuse I don't know exactly where I will be putting things, especially stanchions. Easier to do that than to have to rout out and insert a different material every time I want to add something. OR, Is it OK to just put a hole in a foam deck for something that will have a load on it, with only a backing plate for reinforcement? (hope that makes sense)

But, also, It seems that foam at the edges would be a good choice, since unseen fissures from side impact might allow water in to stealthily cause rot in a balsa core.

Hey Mark, I definitely want a stout deck. This boat may eventually be chartered, and it will definitely be fished, and carry all manner of traffic- bicycles, dingys, dive gear etc.

The sheer gets a nice radius. Evidently it is much easier to machine a fair radius in the deck material if it is foam, because (I am told) end grain balsa is fussy to grind or plane. The foam strip would be narrow enough not to interfere with anything else going through the deck, ie, cleats. stanchions etc.

Has anyone purchased from Jamestown distributors, or fiberglass supply? any other recommendations?
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Old 11-24-2010, 11:53 AM
mark775
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Jamestown, yes. They are a stand-up outfit. The other, I don't know.
No, don't drill through the balsa, nor use it for backing. You need solid laminate wherever there is going to be something mounted. No core, ever, should have a hole drilled in it without proper measures. One way is to gnarl out the core around it and seal with epoxy. A better way is to plan in advance and take the laminate down to solid glass wherever there will be a penetration.
Your designer is right about the balsa - it grinds well but will choke you something fierce and maybe bring on lifelong health problems. Because of the varying densities of lower grades of balsa, it may not be as easy to grind evenly (it is razor-cut into end-grain squares and you can buy it density and weight matched but cheaper stuff could be inconsistent). It does not leave fuzz on the ground piece. I don't follow the radius thing there. I would consider taking the laminate down to solid glass at the edges. I know it is difficult to plan exactly where stanchion bases will lie so that's another reason to take the edges to solid laminate (maybe 7" or so) - more work initially but MUCH better for stanchion bolt penetrations later. If the builder can do it this way, it is one of the areas you will always appreciate.
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Old 11-24-2010, 11:54 AM
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Herman Herman is offline
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Quote:
Originally Posted by mark775 View Post
I'm sorry, Herman but balsa is a superior deck material. As stated above, ANY foam is open cell once water gets involved with a few freeze/thaw cycles. "I feel that your reaction will only spoil another thread" Would you have me delete my post because some don't agree...including the designer of the the original poster's boat?
"...good workmanship is in my experience more vital than the actual materials being used." - agreed...and not drilling holes in a core
Do you have sources for your opinions?

Do you feel you are helping the topic starter?

I never said I did not agree, just that it would not be my first choice, and also told why. I tried to help the TS.

Drilling holes in a core or even a laminate, and leaving them exposed, never is a good idea. Everyone knows, and hardly anyone cares...
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Old 11-24-2010, 12:02 PM
mark775
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It's not about you, Herman. Drop it. My sources are MY personal experiences with foam, to close the matter.
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  #10  
Old 11-24-2010, 12:09 PM
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Herman Herman is offline
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Quote:
Originally Posted by charlyII View Post
Thanks guys!

Herman, I have been under the impression that foam decks still need to have balsa or similar underneath deck hardware etc, in addition to the backing plates, because of balsa's superior sheer strength? Is this correct?
No, it is the high compression strength that you are after in these situations. However, best is to plan ahead and make the laminate single skinned in these areas. A block of high density foam (240 kg/m3) can get you going for certain fittings, or drill the hole oversize, fill with epoxy, then drill the right size hole. This will also seal the edges nicely.
If you follow this procedure strictly, you can get away with using balsa. Put a note in the boat log saying: "Balsa deck, seal and pot drill holes"

Quote:

If so, in my case I probably should just do the whole thing in balsa (edges excepted), becuse I don't know exactly where I will be putting things, especially stanchions. Easier to do that than to have to rout out and insert a different material every time I want to add something. OR, Is it OK to just put a hole in a foam deck for something that will have a load on it, with only a backing plate for reinforcement? (hope that makes sense)
The compression strength of foam implies that a backing plate should be fairly large. For stanchions, I really would like single skin laminate under it. They are live-saving gadgets.

Quote:

But, also, It seems that foam at the edges would be a good choice, since unseen fissures from side impact might allow water in to stealthily cause rot in a balsa core.
Difficult to say, not knowing the exact structure. Side impact should not spoil your deck. by the way, there are also "balsa edge fillet strips" from some manufacturers.

Quote:

Hey Mark, I definitely want a stout deck. This boat may eventually be chartered, and it will definitely be fished, and carry all manner of traffic- bicycles, dingys, dive gear etc.
Totally off topic here, but consider a rubbery anti-skid. I really like the Sicomin / Map Yachting stuff for this, which is used on many fishing and diving boats in this region.

Quote:

The sheer gets a nice radius. Evidently it is much easier to machine a fair radius in the deck material if it is foam, because (I am told) end grain balsa is fussy to grind or plane. The foam strip would be narrow enough not to interfere with anything else going through the deck, ie, cleats. stanchions etc.
Sharp tools will do the job. Make sure you get the detailing right, after routing. It does need some glass and epoxy over it, probably some more than the other places, as it might see more abrasion.
Quote:

Has anyone purchased from Jamestown distributors, or fiberglass supply? any other recommendations?
Sorry, cannot help. I am in Europe.
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  #11  
Old 11-24-2010, 12:23 PM
charlyII charlyII is offline
 
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Thank you both very much for your help. And, please continue to dissent-- I learn a lot when folks disagree. :-)

I am off to grandmas house for a day, but will have some follow up questions, I am sure
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  #12  
Old 11-24-2010, 01:10 PM
mark775
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Good luck with your build!
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  #13  
Old 11-24-2010, 02:49 PM
Steve W Steve W is online now
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I agree 100% with Herman on this subject based on dozens of recoring jobs over 35 years of boatbuilding and repairs. Every time this topic comes up there is always someone who has a bad experience with foam but has no idea what type of foam he is talking about. The truth is foam is available in many different types and densities and every single problem i have ever seen can be traced to the builder making the wrong choice, usually in density.It is more difficult to engineer a foam cored panel than a balsa panel simply because of so many choices.I have never seen a foam panel where the glas has delamed from the foam,i have seen a Choate 40 where the scoring of the klegecell cored hull was not fully filled with resin allowing water that found its way into the core to travel all over the place,apart from being a nuciance it caused no delamination and no freeze problems(water in a balsa deck also wont freeze and blow things apart until it has rotted away enough to allow enough volume of solid water,this does happen with balsa,not with foam) Another issue people often claim with foam is that it fails in shear in a highly loaded panel,yes it can if the wrong density foam was used. Some years ago almost all the Whitbread 60s suffered from this so they specified a minimum density for the cores and problem solved. I am looking as i type at a 6" x 14" piece of foam cored cabin sole that i cut out of a 1977 sailboat that had sat on the hard with a foot or so of water over the sole through a winter,i cut this out to access the hull to instal a transducer.When i cut it out the jigsaw was spitting water in my face,the core was full of water because this was in the head where your feet would be if you were on the can and there had been a row of teak strips screwed down with no caulk and they had used scored foam(left over from the hull i suppose) As i look at this panel now it is completly dry and in perfect structual condition,interestingly this boat is the only boat i have ever seen with actual osmosis in the furniture.The cockpit sole also had the teak slats screwed down and was also wet but no delam.These would be structually unsound had they been balsa cored. Dont get me wrong, i am not anti balsa and i regularly use it but as Herman pointed out it is not at all tolerant of bad or even average building procedures and doesnt suffer ignorant boatowners well,used properly it is excellent.Over the years of recoring boats i have come to look appreciate builders who sprung the extra bucks for foam.
Steve.
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Old 11-24-2010, 05:29 PM
War Whoop War Whoop is offline
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I have never had a problem with Corecell nor have ever seen any,in my opinion it is the finest core material one can use.
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Old 11-24-2010, 06:03 PM
War Whoop War Whoop is offline
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Here impact testing:

http://www.youtube.com/watch?v=DRzyw0Jo8Zg



Bagged Corecell deck Bag pulled and ready for cleanup and rolling the corners ,you can see the adhesive in the perforations,I do work with this material everyday :







Finished deck:



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