newbie with stringer question

[abandonedandabused]

Ok, I've been doing a lot of research before bringing my 91 Bass Cat Pantera II back to life. As far as bedding stringers. I've read a lot of forums that said bedding stringers is primarily for holding them in place and off the hull while glass can be applied. Not so much for a structural bond. Many recommend liquid nails or PL premium for bedding adhesive. Any thoughts or opinions? Now keep in mind that this will be my first attempt at fiberglass work, so be nice. I am a 20 year mechanic, cars, heavy machinery, and currently oil field. So I have mechanical know how, Just never fooled with fiberglass

 

[jbcurt00]

Re: newbie with stringer question

PL takes 72hrs+ to off gas before proceeding to the next step. Although I was once a firm believer in PL as a better choice, that is no longer the case. The cabosil, 1/4" chopped strand resin mix (often referred to as peanut butter (PB) because it's about the consistancy of actual peanut butter) is a much better choice. Any excess PB that's applied, can be smoothed into a fillet that needs to be done before glass can be applied anyway. W/ PB this could be accomplished as 1 slightly longer step in the process all in 1 work session VS the PL needing to be left for 72hrs to cure and kept from sagging, pooling or any portion of the stringer or hull that it's been applied to, moving until the cure is complete. If the hull or the stringer move enough to break the PL bond before it's cured, the PL will skim over & you'll be hard pressed to re-establish the adhesive bond.

Yes, the bedding holds the stringer up off the hull, but is also adds structural support to the hull & stringer.

The bedding also keeps the stringer from being in contact w/ the hull & spreads any load across a wider cross section then just the thickness of the stringer (in most cases that's 3/4"). So when pounding thru waves or wakes (it happens, even when you try to avoid it), any load on or flex of the hull has a wider surface to disperse the forces. Prevents hard points of contact that could cause checking & cracking of the gelcoat &/or fiberglass on the hull along the stringers. Kind of like a footer under a foundation wall. W/ a narrow (undersized) footer, the wall may stay unchanged for a long time. But apply some additional down force, freeze upheaval, or lateral forces & the wall MAY deflect &/or crack. We are trying to prevent that.

Read thru some of the other resto threads. This is a fairly common question. When you are ready to tear into the Pantera start a resto thread & try to keep all the questions & info about your project in 1 place. It will prove a valuable resource to you & others as you move thru the demo, grinding, setup & putback stages of your resto.

You can not post too many pix or ask too many questions BEFORE & during your resto.

Good luck w/ your project & welcome to the iboats dry dock.

 

[DeepBlue2010]

Re: newbie with stringer question

Running the risk of getting swamped with opposing replies, I will present a different opinion here and my reasons behind it.

Last year, I was trying to fill the voids between a bulkhead and the hull of my 22 with PB. I followed the mixing recipe on iBoats with slight variation which is that I catalyzed the resin first before mixing anything to it to ensure an even distribution of the catalyst. Then I added previously measured – I just made a sacrificial batch and reordered measurements of cabosil and glass that brings it to the consistency of PB - portions of the cabosil and glass and mixed with a drill attachment for few minutes and started using it. It held up will and got the job done fine.

Later in the project, I decided to tear down this bulkhead. When I started the process of taking it out, I noticed that the PB is shattering and breaking under the demolition forces. I went back and reviewed my mixing weights and I was convinced that this PB is a very resin rich compared to a good laminate or layup. At this time, I was following the common wisdom and planning to bed the stringers with PB as I saw many iBoaters do. But then I started thinking, what if this happened after the stringers are already in. The truth is, no one ever grinded or cut the glass to see what happens after a year or so of battling waves and wakes. If the PB under the stringers will look like the PB I collected in pieces from the demolished bulkhead, I would rather use PL and wait whatever time it needs to cure for the following reasons..

1. PL has a rubberized texture that absorbs and muffles the flexing of the hull.
2. It is not hard and brittle as PB and expected to stay in one piece for as long as we want it to.

PB still has its uses in my plans – when I finally get to resume work on the 22 – such as..

1. Creating Radius fillets to ease the sharp 90 degrees corners for the fiber glass.
2. Filling gaps and voids that will be fiber glassed over provided that these gaps/voids will have no forces applied on them while the boat is in use and the only reason to use the PB is to eliminate the possibility of air pocket that compromises the integrity of the laminate.

I don’t think I will be using PB to attach my transom wood to the transom either. I am still searching for a better way for that.

If you disagree with any of what I said so far, please discuss rationally not emotionally, I am not married to my opinion and welling to change it if it was to be proven wrong.

 

[jbcurt00]

Re: newbie with stringer question

Deep:
Your reasons for favoring PL are the same as mine were. But I firmly believe that PB is a better choice, for timing and prevention of delamination of the glass when laid over PL.

I will ask if you overlaid the PB 'bedding' (it was between the bulkhead & hull, not unlike the bedding under a stringer, correct?) w/ a correctly sized fillet (too big can be as bad or worse than too small)

and covered it all up an appropriate # of overlapping tabs of fiberglass


I will admit that there is no way to accurately gauge why some projects had delamination of the glass from both the stringer & the PL bedding (and in at least 1 instance the PL fillets) even when they waited 72hrs. Maybe they didn't wait that long. Perhaps their prep of the PL after it cured was insufficient to allow adhesion of the poly resin to the PL. Environmental temps & humidity affect the way PL cures. Perhaps it skimmed over because it was hot out, but not hot enough to speed the complete cure, and once skimmed over it needed additional time to full cure beyond the normal 72hrs. I don't know, but scan thru a few hundred resto threads. There are far more reporting problems using PL then using PB. Significantly more.

But I strongly urge everyone to be diligent & look for other sources (here & elsewhere) and educate themselves about all facets of boat rehab. Then make the best decision they can based on lots of info, their time frame, work space, skill level & budget. What works for 1 backyard boat builder, sometimes isn't possible for another.

 

[Woodonglass]

Re: newbie with stringer question

DB2010, I'd be very interested in knowing your exact mixing ratio and ingredients mixture. I have never had that issue with PB and I have had experience with tearing apart a boat with previously applied PB repairs and found it to be in the same structural state as when it was applied. My Recipe is... 1 qt resin approx 1 1/2 qts cabosil, 1/4 cup 1/4" chopped milled fibers. Catalyzed @ 1%. MEKP mixed into resin prior to adding cabosil. Milled fibers added last. 25 mins. working time @ 80? temps. I find this to work well and if you make a ball out of it and let it harden you can beat it with an hammer and it won't break. Not sure why you had this experience. With PL if you are not exceptionally clean with your work, your Poly resin and glass will have difficulty adhering to any areas where the PL residue has been. But as you say, If you don't mind waiting for it to come to a full cure, and if you are careful in applying it, it is a viable bedding material. For me, PB, is just a Faster, easier, and to me, Better method of doing it. Heck, back in the day, they didn't use anything to bed the stringers and the boats still worked. Anything we do is better most times than what the factory did.

 

[jc55]

Re: newbie with stringer question

My transom on the '68 was PB'ed in at the factory under the tabbing. I used a sharp wood chisel and hammer and it did indeed shatter like glass. I removed most of it in this manner before the grinding process. I am kind of taken aback by the materials used in boat restoration to be quite honest. PL Premium specifically says it is not intended for water immersion. Boats with center stringers are indeed immersed. You cannot use a boat "normally" without having water intrusion below decks. (I bedded my stringers with PL with the intention of setting them only before tabbing)

More power to Titebond users but this is another material that I wouldn't trust. I want that 2 part chemical reaction. In the end, all of these materials work as a system, none of them particularly independent of the other. You'd never detect a Titebond failure with tabbing and 4 honking outboard bolts clamping it together

 

[jbcurt00]

Re: newbie with stringer question

My transom on the '68 was PB'ed in at the factory under the tabbing. I used a sharp wood chisel and hammer and it did indeed shatter like glass. I removed most of it in this manner before the grinding process.

Are you sure that was PB as we define it w/ cabosil & 1/4" chopped fibers? The last person that posted chunks of PB they were shattering w/ a hammer during demo looked to be big blobs of just resin, no filler so no strength. Perhaps not even polyester resin, but some other sort of phenolic resin.

 

[jc55]

Re: newbie with stringer question

That's a good point JB. I don't recall there being fibers in these areas at all. It had a green crystalized appearance.

 

[jbcurt00]

Re: newbie with stringer question

That's a good point JB. I don't recall there being fibers in these areas at all. It had a green crystalized appearance.

Although it was a brand new boat when the factory installed the transom, it probably wasn't perfectly flat, but it was flatish.

Now that we've torn into them & hit them w/ a hammer & chisel and a grinder it's even less flat. We're designing the best possible process for rookies to do once, on 1 boat. Possibly another, but certainly not a bunch. For one of the most critical areas of the hull, the transom (I/O or OB). Allowing for a mistake or 2, possibly a void or 2, I'd rather go stronger and not need it if someone does a perfect install.

The factory globbed the resin on the transom skin & plywood and mashed them together, flat on flat. Hence the run off often seen. Admittedly they probably did marginal job of not slinging resin everywhere, but man it's often puddled & pooled everywhere :faint2:

We need to account for minor imperfections, dips & kerfs in the transom skin. There's also been a little of the existing fiberglass transom skin removed during the grinding & prep steps, so a little extra strength in the PB is a good thing.

IMHO ^^^

 

[abandonedandabused]

Re: newbie with stringer question

Thanks for all the info guys. I got a little time before I start this project, so I'm sure it's not the last you've heard from me.

 

[DeepBlue2010]

Re: newbie with stringer question

WoG,

My mixing ratios were pretty much what you mentioned but I did catalyzed @ 1.5%. I used 1 quart of Vinyl Ester resin. The technical specs for this resin says that the density (on average) is 1.8 grams/cc (cubic centimeters)
1 Quart = 946.5 cc
Then 1 Quart = (946.5*1.8) = 1703.7 g
If we follow the general rule for wetting out CSM which is 1.5 to 2 times the weight of the CSM in resin
Source : http://www.fiberglasssite.com/servlet/the-68/Fiberglass-Information,-and-How/Detail
This means that we need 1703.7/1.5 = 1135.8 g
Or
1703.7/2 = 851.85 g

So, we need between (852g ? 1136g) of milled CSM to have a mix that is not resin rich. The question now is how much a ? of a cup of a ? milled CSM would weight?

I just measured it right now and it weights about 30 grams.

As you can see, this is only 3% of what is required (on average) for this mix to be balanced.

If anyone thinks my calculations are not acurate, please let me know.

 

[sphelps]

Re: newbie with stringer question

I donno .. I just use the by guess and by golly method . Hasn't failed me yet !

 

[jbcurt00]

Re: newbie with stringer question

Yikes, DB, that's like math & it's too late for that tonight. Maybe tomorrow after a cup of coffee :faint2:

 

[abandonedandabused]

Re: newbie with stringer question

Has anybody used "Hull and Deck Putty" by 3M for bedding? From the sounds of it, it is premixed PB. And could this work for fillets also?

 

[Woodonglass]

Re: newbie with stringer question

WoG,

My mixing ratios were pretty much what you mentioned but I did catalyzed @ 1.5%. I used 1 quart of Vinyl Ester resin. The technical specs for this resin says that the density (on average) is 1.8 grams/cc (cubic centimeters)
1 Quart = 946.5 cc
Then 1 Quart = (946.5*1.8) = 1703.7 g
If we follow the general rule for wetting out CSM which is 1.5 to 2 times the weight of the CSM in resin
Source : http://www.fiberglasssite.com/servlet/the-68/Fiberglass-Information,-and-How/Detail
This means that we need 1703.7/1.5 = 1135.8 g
Or
1703.7/2 = 851.85 g

So, we need between (852g – 1136g) of milled CSM to have a mix that is not resin rich. The question now is how much a ? of a cup of a ? milled CSM would weight?

I just measured it right now and it weights about 30 grams.

As you can see, this is only 3% of what is required (on average) for this mix to be balanced.

If anyone thinks my calculations are not acurate, please let me know.

I didn't note any cabosil in your formula, did you use any?? It's a critical binder in the mix/ratio as well.

 

[DeepBlue2010]

Re: newbie with stringer question

Yes, I did. I added just enough to change the consistancy of the resin so it is not saging and until it has the viscosity of PB. My research is leading me to believe that Cabosil will not add any strenght to the resin and it is just a viscosity modifying agent. Is this not right?

 

[DeepBlue2010]

Re: newbie with stringer question

Has anybody used "Hull and Deck Putty" by 3M for bedding? From the sounds of it, it is premixed PB. And could this work for fillets also?

I did not. Once I found a bedding compound in a tube - pretty much like 4200 & 5200 - in my marine supply store but I can't remember if it is 3M product. I am planning on testing this soon.

My understanding is that the bedding compund - no mattter what it is - is not supposed to provide any structural support to the stringers. Stringers strenght is a factor of how well they are fiberglassed to the hull. The bedding is to provide a "soft bed" under them that prevent them from touching the hull to avoid hard spots. Based on this understanding and based on the characteristics I observed for PB, I am more inclined to use a soft rubberized material rather than PB.
Here is another thought, suppose that everything I said about PB is not true and it is actually as hard and solid as the stringers wood itself, isn’t that violates the very purpose we are using it for which is to provide a gap between the hull and the stringers to avoid hard spots?!

In other words, if the PB is that hard and solid, it will act like a hard and solid continuation material between the wood and the hull. In this case, I am not sure how it will help avoiding any hard spots! Just a thought.

 

[sphelps]

Re: newbie with stringer question

If I am thinking this right the bedding being whatever . Is to distribute the support to the hull evenly without spots that are harder than the spot next to it . If that makes sense . :facepalm: That way the hull will not flex between the hard spots . Just think say your rolling onto trailer and you hit a soft spot . the hard spot next to it may crack the gell around it . Could that be the thinking . The force of water pounding down the stringers at wot may crack the gell at the hard spot .
Or I could be way off base ..

 

[DeepBlue2010]

Re: newbie with stringer question

This is not my understanding SP. The hull will flex no matter what you do. My understanding of a hard spot is that when the hull flexes and it hits a hard wood, the hard wood prevents the hull from flexing freely. As a result, it cracks.

 

[Daniel1947]

Re: newbie with stringer question

:hurt: :hurt: My head hurts from all this. I am always amazed at the amount of information that reveals itself from one subscribers question. While I have absolutely no idea of who is right or wrong, or what is the "best" way to bed stringers, I do have one question that seems to be unanswered. Does anyone know of any boater that has bedded stringers one way or the other, and ended up with problems/cracking from so called hard spots. Seems that many knowledgable boaters have done it both ways. I am not an expert by any means, however I am going to be restoring mine shortly, and would like to use the proper proceedures and materials. My experience as a mechanic has taught me not to mix certain chemicals when rebuilding engines. Don't use blue silicone on intake because gas will deteriortate it, etc. Using a product such as PL, imho, would be introducing a product not fully compatable to the poly resin and cloth. Looking forward to more discussion gentlemen.....:fencing: