The Science of Soggy Decks

[minaret]

Originally Posted by MacG

There are modern methods of building but those are intended to reduce waste of resin and to keep resin/glass ratio within certain limits. Injection moulding and vacuumbagging helps but cannot prevent osmosis in the final end. Only the use of epoxies can do that but that makes a boat much more expensive because of some unpleasant habits of epoxy when drying out. Prepregs (epoxy) might overcome those technical issues but do not solve the financial ones.

All this concern on your part about osmosis doesn't really apply to cored decks. For osmosis to occur there needs to be a substantial pressure differential between the material substrate and it's working environment. This is almost never the case on a deck, with the rare exception of water trapped under a teak overlay or equivalent. I totally agree that cores of any type should never be used below the waterline due to the risk of water intrusion and delamination, but above the waterline it's a concern which just does not apply. Water intrusion in a cored deck occurs due to failed/poor bedding of hardware and voids/manufacturing flaws, which were shockingly common before the era of infusion and SCRIMP. Post infusion though, a foam cored deck is a perfectly viable construction technique and better than solid generally speaking. More strength and less weight is good. Sandwich construction will keep moving forward and continue to be the method of choice above the waterline.

[Cheechako]

Having seen a few decks and hulls cut open for repair, I dont agree that all fiberglass "imports water". All the ones I've seen have dry core outside the area where the leak started through a poorly bedded fitting or through hull etc. I suppose there is some "humidity" in there, but not wet core that I've seen... wet balsa is easy to analyze; if unsure if it's wet, just take a small chunk of balsa between your thumb and finger and squeeze, water comes right out of semi wet core...

[s/v Jedi]

T.P.I. in Newport, Rhode Island, has been using the SCRIMP process for ages. Our boat was build in 93-94 this way, with full balsa core and vinylester resin instead of polyester. Where fittings or fasteners go the core is tapered out to solid glass in that area. It is 100% and I guess all the biats they build are done the same way.

ciao!
Nick.

[justwaiting]

Originally Posted by minaret

Water intrusion in a cored deck occurs due to failed/poor bedding of hardware and voids/manufacturing flaws, which were shockingly common before the era of infusion and SCRIMP. Post infusion though, a foam cored deck is a perfectly viable construction technique and better than solid generally speaking. More strength and less weight is good. Sandwich construction will keep moving forward and continue to be the method of choice above the waterline.

Let me know if i am drifting the thread too much and i will start a new one

Retrofitting a form core
How bad would a balsa core need to be before you considered retrofitting with foam?
Would you retrofit the whole deck? ( i asume that you would)
Would you RF the foam by cutting the topskin off and if you did that would you try and reuse the skin bedded on resen or would you reglass and fair?
How would you deal with the areas where deck hardware is to be reinstalled?
Would you (and how) take the oportunity to fully bond the deck to the hull eleminating the hull joint?

thanks

[MacG]

The hollow tubes of the glass-strands are part of the osmosis problem. But I stop here before getting another 1000 pages of yes and no. Not every boat is a pitfall of osmosis but the fact that any polyester resin is not waterdamp tight remains, whatever you say.

[minaret]

Originally Posted by justwaiting

Let me know if i am drifting the thread too much and i will start a new one

Retrofitting a form core
How bad would a balsa core need to be before you considered retrofitting with foam?

Would depend on the boat. If it was built properly with infusion or similar, I would do spot repairs around failed bedding or other areas of water ingress. In an older boat without that type of construction (still 80% or more of the cored boats out there), I would not need much of an excuse to do it, if it was my boat, just on general principle. Any readings over 20% relative on the FRP scale would warrant recoring in my eyes.


Would you retrofit the whole deck? ( i asume that you would)

If it was my boat, absolutely. Unfortunately I have a very hard time convincing clients to do this. They almost always want to do a spot repair on what must be fixed now, and get out the door as cheap as possible. Many times over the years I have done a partial recoring, only to have the boat come back in to get the rest of the deck recored five years later or less. This means painting the whole deck twice instead of once usually, unless we are blending gelcoat. Often it means they pay twice as much as they would have if they had just sucked it up and done it all at once. Some boats I have done as many as three core jobs on, and they still don't have all the original core removed. Madness. But good job security for us.

Would you RF the foam by cutting the topskin off and if you did that would you try and reuse the skin bedded on resen or would you reglass and fair?

Nice relevant questions. This is a commonly disputed debate in the field. I am somewhere in the middle on this debate. The problem with reusung an outer skin is bonding it to your new core without any voids and while keeping it fair. The methods needed to do this without vacuum bagging defeat the purpose (ie, drilling holes for squeezeout and fastening fairing battens to the skin), so vacuum bagging is the only right answer for reusing a skin to me. This is enough of a process that I only do it in certain situations, usually when I'm trying to save a molded-in non-skid pattern because the owner likes it. Often I will do this by making the waterways a little wider and doing all glass work and fairing in the waterways after bagging the skin back on. It's a PITA and not appropriate for most applications IMHO. I think most yards who reuse an outer skin are not bagging or even using battens, there is no guarantee of no voids and often they end up with a high this way that cannot be faired out. I think it is a common half-assed repair done by many "pro" yards. When we bag a skin back down we set it in Core Bond for a poly job, it bags great. For many jobs I prefer to toss the original outer skin and simply reglass fresh. This means you don't have to glass a seam afterword, you are guaranteed a perfect bond to the core with no voids at all, you can use a superior resin with better laminate schedule for a stronger stiffer laminate that is more resistant to water, and you can fair the whole job perfectly before laying new skid and waterways. Much more efficient and proffesional.


How would you deal with the areas where deck hardware is to be reinstalled?

This is a common selling point in recoring jobs for us. We generally are replacing balsa or ply core with 5lb. rigid urethane. For areas which need extra stiffness and were built with ply core as a result, we use Coosa board to replace the ply. Stronger and totally synthetic, will never rot- Coosa Composites, LLC - Manufacture of high-density, fiberglass-reinforced polyurethane foam panels . In areas that need to be really strong and never compress, such as deck in way of winch mounts or windlass mounts, or under a deck stepped mast, we use either custom made flat stock to the required thickness or for the more high end stuff we use mil-spec G-10 flat stock. Solid block outs like this are ideal for through bolting. We often do them even for stanchion bases and smaller stuff, nothing beats an extra 3/4" of solid glass in these areas.



Would you (and how) take the oportunity to fully bond the deck to the hull eleminating the hull joint?


No. That is a job which is very rarely undertaken, because it usually means removing the entire interior. Usually only done when a boat is gutted for refit. There are so many different hull joints out there that each must be addressed individually. Some could be done from outside without removing any interior, but usually the way the flange overlaps prevents that.

thanks

Anytime, glad to try to help out. Nice questions! Sounds like you may be faced with some of these issues and have put some thought into it.

[justwaiting]

Originally Posted by minaret

This is enough of a process that I only do it in certain situations, usually when I'm trying to save a molded-in non-skid pattern because the owner likes it..

Thanks for you responce

Just following up the section quoted: given the non skid application that are now on the market do you think that there is any real advantage of molded in surfaces. If not which of the surface applications would you recomend to clients, or better still which would you use on your own boat?

[minaret]

Originally Posted by justwaiting

Thanks for you responce

Just following up the section quoted: given the non skid application that are now on the market do you think that there is any real advantage of molded in surfaces. If not which of the surface applications would you recomend to clients, or better still which would you use on your own boat?

AAARG! I wrote an epic response to this and it disappeared when I hit post. Here goes again-


I strongly dislike molded in non-skid surfaces. They are generally very difficult to repair to like new condition. I can fix almost any surface on a boat to like new condition, with the sole exception of molded-in skid. The only way I have found to make a perfect repair on it is prohibitively expensive. I pull a mold off a different section of deck and use it to build a color matched very thin fiberglass panel with the molded skid in it. Then I grind off the whole skid patch the repair was done in nice and fair. Then I cut the panel to the exact shape required and vacuum bag it down in color matched gelcoat, wet sand and buff the seam, and voila! a new molded in skid pad. This obviously costs thousands of dollars more than a simple skid repair.
I much prefer to use Griptex, by US paints, the makers of Awlgrip. AwlGrip GripTex Non Skid Additive It provides a nice aggressive grippiness to the foot, but is not too uncomfortable to walk on barefoot or lie on with bare skin. I like to use a mix of fine and coarse to acheive the desired effect. Griptex is designed to work with Awlgrip, but I have used it with many different products. It is superior to other particulate non-skids because the particles are not simply encapsulated in paint like sand would be, instead the paint actually soaks in to them on a microscopic level. This provides dramatically superior bond and durability. I prefer to use it with traditional Awlgrip, as this provides the hardest painted finish. I have applied using many methods, from rolling with stippled rollers or regular, to sprinkled with a sifter, to sprayed. A sprayed finish is by far the best, but requires an experienced or at least intelligent painter with special equipment. The ultimate skid finish is IMO Griptex fine/coarse sprayed in gelcoat. The gel soaks in to the griptex and makes a bomb proof skid finish that is easy to repair. This requires experience both to spray and acheive a perfect surface cure on the gel, which is obviously critical. I like PVA for this.
Anyway, enough for now, hope that helps to answer your questions.

[Nicholson58]

On a side note it looks like the builder used a combination of balsa and plywood on the deck. weird huh?[/QUOTE]


not so wierd. Ours are balsa filler with teak main framing.

[Nicholson58]

Minaret - have you tried making a silicone rubber mold of the non-skid taht you can impress into marine tex or other moldable epoxy (epoxy & microballoons) on a smooth repaired area? Roll the rubber from the middle gently and apply heavy enough loads on the edges to force the rubber to conform to the non-skid boundary. Wipe excess from the edge.

[minaret]

Originally Posted by Nicholson58

Minaret - have you tried making a silicone rubber mold of the non-skid taht you can impress into marine tex or other moldable epoxy (epoxy & microballoons) on a smooth repaired area? Roll the rubber from the middle gently and apply heavy enough loads on the edges to force the rubber to conform to the non-skid boundary. Wipe excess from the edge.

Many times. The product of choice in this department is called Flex-Mold. The pro technique is to use the Flex-Mold with color matched gelcoat to make the pattern so that you can wet sand the edges of the repair to blend it. I have been the go-to guy for molded skid around here for years, and spent a lot of time and effort playing with products like Flex-Mold and countless other techniques including going to the lengths of using jewelers files to hand carve a pattern. Nothing will give you a perfect result, except rebuilding the pad as I mentioned. I have pleased many owners who thought a repair was invisible, but I have never pleased myself using these techniques. Mind you, I am talking about yacht quality repairs here. If it doesn't look like it just came out of the mold it's not good enough for me. The technique I mentioned above was develepod by me after long years of trial and effort. I'm sure I'm not the only one who does it though. It just works, and in many cases is the only thing that does. Flex-Molding anything but diamond skid and making it invisible can be a nightmare.

http://www.gibcoflexmold.com/

http://www.masepoxies.com/public/ind...oductid=777755

[GordMay]

Originally Posted by minaret

... Faith in the moisture meter comes with experience, I have clients question the meter all the time. They are always wrong.

My faith (or skepticism) is placed in the operator and his ability to interpret the readings.

[Cheechako]

Originally Posted by s/v Jedi

T.P.I. in Newport, Rhode Island, has been using the SCRIMP process for ages. Our boat was build in 93-94 this way, with full balsa core and vinylester resin instead of polyester. Where fittings or fasteners go the core is tapered out to solid glass in that area. It is 100% and I guess all the biats they build are done the same way.

ciao!
Nick.

Yep, my 42 lagoon cat was built like that. zero blisters at 10 years anyway. hurray for TPI!

[unbusted67]

Anyone know where I can find foam core other than from Coosa? I am looking for a few different options.

The fact that we have a marine plywood shop a block away from us makes me think I might be doing this job with ply but want to check out my options.

On a totally different tangent: does having moisture in the decks make a boat unsafe? Does having the extra water weight up high destabilize the boat or are the affects negligible?

[minaret]

Originally Posted by unbusted67

Anyone know where I can find foam core other than from Coosa? I am looking for a few different options.

The fact that we have a marine plywood shop a block away from us makes me think I might be doing this job with ply but want to check out my options.

On a totally different tangent: does having moisture in the decks make a boat unsafe? Does having the extra water weight up high destabilize the boat or are the affects negligible?

I don't know much about suppliers on your coast. Here's where I get laminating materials and supplies- Fiberlay

They have a great website and ship fast. Excellent selection of first rate materials at good prices. Heres a link to the 5 lb. Airex I like to use in 3/4", they have it in every imaginable dimension including up to 2 1/2" thick and oversize sheets. Note the sheet dimensions carefully, they are small unless you get oversize. You can order by the sheet or by the case.


Fiberlay

Please don't go through all the work it takes to do this job only to stick ply back in your deck, you'll be doing it again in another ten years or so if you do. Or the next owner will. Foam and Coosa is actually very easy to work with, more so than ply, and will not rot. You can save a few bucks by using cheap ACX ply or pay more for marine grade, but the savings are a drop in the bucket compared to the cost of labor to do the job.


The effects on stability are definitely negligible. Structurally speaking it's a different story though. Your deck is a key part of the boats structure in many ways. Without it's normal stiffness the hull can start to flex severely and put much more stress than normal on the bulkheads, leading to bulkhead print through and failed tabbing. It is a serious stuctural issue.