Stringers Flawed By Design????

Hello iboaters! I am new to the forums , so please forgive me if this is a repeat topic. I have searched through several site forums, including this one, for specific information about stringer design, and although there is quite a bit of info on methods of replacing stringers, I'm not finding anything related to my idea or theory. The project is a 20' 9" 1990 Chris Craft 197 Concept Bowrider that I purchased for $300.00. The floor is shot and so is the wood in a lot, but not all, of the stringers. The boat was soaked and a lot of the foam was water-logged. The thing is this though; The stringers almost seem like they were designed with the knowledge that the wood was going to rot. Like they designed it that way. The glass around the stringers is very thick and very sold, and it doesn't flex even when I was prying against it with a crowbar to get the foam out. It also appears that there is a hole where glass was intentionally left off on the top of every intersection where the stringers meet, but the bilge stringers and the fuel tank compartment are completely glassed and painted. I have read some discussions where people have mentioned that companies use wood or foam as a form, but rely on the stregnth and thickness of the glass for the structural integrity. Has anyone heard of this practice, and could that be the case with my boat? My other idea, if I have to replace the wood in the stringers, is to cut the top off of the exsisting stringers and dig out all the rotten wood. Then laminate two pieces of fir to the right thickness, coat them with thickend resin and shove them down into the exsisting stringer forms. I can't imagine that method not generating due and proper integrity, and it seems like such a waste to cut out all that thick, rigid glass. Any thoughts on this process and the level of structural integrity it might or might not provide? Also, I was told that stringers on smaller boats do not have to be bedded. Is there any truth to that, and if so, what is the size limit for that requirement? Thanks for taking the time to read this long post. All feedback is well received and much appreciated.

Re: Stringers Flawed By Design????

a lot of companys used bayliners designs in the 90.s

including foam stringers.

these are generally engineered.

as you guessed, the foam is a form to glass over, and the glass is the stringer.....
(i have to be very careful here, a lot of the guys might think because there is glass on the stingers that they have engineered stringers.)

when is see a stringer that is fully thick with glass, about 3/8th of an inch....i know that the stringer was a glass stringer.....i just leave it...if the owner insists...i will open it up......but the water in the glass stringer is of little consequence...the glass is the stringer.

the only problem is that you will have to have something to screw your deck to....screwing into glass is not always a good option...pl and screws is ok......but just marginally.

as far as laminating two chunks of wood isn sticking them into the opened up glass stringer.....i would not.

a bond to the wood is almost impossible....and you have to bond to the glass to cover the channel.....that is 3 1708 sandwiches with csm in between.

i would leave the glass stringer alone.....and proceed with the foam rip out and replacement

Re: Stringers Flawed By Design????

Wood is an organic material and therefore deteriorates over time. So, yes the design itself has a limited life span. Boat companies use wood because of its workability. The voids in fiberglass coverage that you see are more likely workmanship issues. It seems to be prevalent. So, the rot starts where there are voids and then continues throughout the structure.

The stringers in and around the engine compartment are usually glassed in well, mostly for added strength. That alone does not keep the rot away. Lots of cases where a well glassed stringer ends up being hollow from rot.

If you replace a wood stringer with wood and isolate it properly with resin & fiberglass, you should expect 15-20 years of use. As a repair on a boat that is 15-20 years old, that is usually enough for the life of the boat.

I am dealing with a bulkhead and stringer rot situation myself, and it appears that I caught it in the early to mid stages. The repair will be a challenge due to the '2-piece' design of the deck & hull. I may use an approach that you described in not fully removing the fiberglass 'tabbing' that attaches to the hull. The challenge will be adhesion of the new stringer to the existing fiberglass tabs. So, lots of prep work and use of a strong adhesive resin, like maybe Vinyl ester instead of polyester.

In your case, chances are that you will have to remove most of the fiberglass covering and tabbing material anyway. So, what would be left really just marks the position of the stringer. If you have good access to the structure, you can do a better job of repair. So, make sure that you are not having to re-visit the structure again in 5 years.

As a side note, some of the boat companies are moving away from wood and going with a composite structure, as boats tend to have a longer life expectancy than 10-15 years. Southport boats is a good example, but I have also noticed that Formula (the brand that I have) is using composite structure on their larger boats. My understanding is that the composite structures are 'customer driven', which seems logical. If you are buying a bigger/expensive boat, you would not want to have to worry about structural issues in and around 'year 10' of ownership, which is probably around when you'd be looking to sell the boat.

Anyway, good luck with it. I'll be posting the progress on my structural repairs FWIW.

Re: Stringers Flawed By Design????

If you have good thick glass on the sides of the stringers you could dig out the wood and pour seacast or nida bond in the forms.... A bit pricey but may work in your application.

oops your thoughts on casting the stringers??

Re: Stringers Flawed By Design????

There is no way to tell what the thought process was on the original design, but leaving gaps in the glass, or unsealed areas is not something they would have as a design feature, more like an oversight or sloppy workmanship. Many boats suffer from this sort of thing.

The stringers may, or may not, be strong enough without wood in them, you would need to talk with the engineer that spec'd the laminate schedule, that is if there was an engineer that came up with the amount of glass needed. I say this because for a very long time few engineers were involved in boat design, people just built them and if it seemed strong enough that is what they used. CC was one of the better builders, so it's possible they did have an engineer involved at that time. The next thing that comes into play is if the people on the shop floor building the boat actually followed the instructions put in place to build it. With the workforce turnover in glass shops and lax supervision it's not uncommon for the design to be modified or not followed at all due to poor training or neglect.

Can you just glass the tops back on….yes, you could do it that way. The bond between the new wood and old stringer may not be that good though, the inside surface of the old stringer would been to be prepped correctly for it to bond well to the new wood. On many boats the glass over the old stringer is in such poor condition it doesn’t pay to try and save it.

Most stringers on small boats aren’t bedded in anything when new, they are just set right down on the hull. You should be able tell whether yours were bedded in something when you take it apart.

Re: Stringers Flawed By Design????

When I first read this, it was making no sense. I then discovered that the OP's question had been moved to the restoration thread, and all we had here were responses to his original post. Not sure how/why only part of this thread was moved, but here's the link to the OP's question.

http://forums.iboats.com/showthread.php?t=538000

Re: Stringers Flawed By Design????

floatfan said:

When I first read this, it was making no sense. I then discovered that the OP's question had been moved to the restoration thread, and all we had here were responses to his original post. Not sure how/why only part of this thread was moved, but here's the link to the OP's question.

Click to expand...

Not sure what happened either, but I put it all back together again.

Re: Stringers Flawed By Design????

Looks like it's all right now, Thanks Don

Re: Stringers Flawed By Design????

ondarvr said:

There is no way to tell what the thought process was on the original design, but leaving gaps in the glass, or unsealed areas is not something they would have as a design feature, more like an oversight or sloppy workmanship. Many boats suffer from this sort of thing.

The stringers may, or may not, be strong enough without wood in them, you would need to talk with the engineer that spec'd the laminate schedule, that is if there was an engineer that came up with the amount of glass needed. I say this because for a very long time few engineers were involved in boat design, people just built them and if it seemed strong enough that is what they used. CC was one of the better builders, so it's possible they did have an engineer involved at that time. The next thing that comes into play is if the people on the shop floor building the boat actually followed the instructions put in place to build it. With the workforce turnover in glass shops and lax supervision it's not uncommon for the design to be modified or not followed at all due to poor training or neglect.

Can you just glass the tops back on?.yes, you could do it that way. The bond between the new wood and old stringer may not be that good though, the inside surface of the old stringer would been to be prepped correctly for it to bond well to the new wood. On many boats the glass over the old stringer is in such poor condition it doesn?t pay to try and save it.

Most stringers on small boats aren?t bedded in anything when new, they are just set right down on the hull. You should be able tell whether yours were bedded in something when you take it apart.

Click to expand...

OKay, I thank all of you for your insight and suggestions. It seems as though there are several possibilities and methods for fixing the stringers. I am not sure what the intent was with my boat and it's stringer design. I know that the stringer and bulkhead system is relatively small and there are no stringers that run the entire legnth of the boat. The two main stringers stop at the fuel compartment and then two smaller stringers on either side of those that go from about mid-way of the hull back to the transom. When I say the glass is really thick and heavy, I mean thick and heavy. I have attached a couple photos to maybe help with the insight. I have looked into the Seacast, but that stuff is very pricey. Is there anything equally as good for a little less? Also, wouldnt wiping the inside walls of the exsisting stringer forms with MEK ( not MEKP) help to ensure a good bond between new wood and resin with the old glass? I just have a hard time understanding why, if the wood is so important, that it wouldn't be sealed. I mean, the wood is always the weakest link where laminating is concerned, right? The real integrity is in the stiffness of the glass, isn't it? I'm just trying to make sense of something that probably doen't make any sense regardless. Why put wood in a boat if you're not going to waterproof it? So my options are, cut the stringers out and grind them down and replace all new, cut the tops off and dig out the rotten wood and replace with Seacst or equivalent, try to bond new wood to the exsisting stringer forms and cap them with 1708, or leave them alone and take my chances on the integrity of the glass? Hmmff.... very interesting set of choices.

Re: Stringers Flawed By Design????

thanks for the pics....

those are not engineered stringers.

they are just wood stringers that were wrapped in woven giving them a really thick appearance.

i would cut them out and re string the boat

Re: Stringers Flawed By Design????

It looks like they sanded down the high spots on the stringers so the floor would lay flat, this exposed the wood.

"Why would they put wood in a boat and not seal it?" That is a question that has been asked frequently, and there are many possible answers. They don't care, didn't think about it, it was supposed to be sealed but nobody did it, the workers were in a hurry, they didn't think it was important, it will last 20+ years without being sealed so it's not a concern....you can pick one of these or make up your own reason, but it doesn't matter much...it is what it is.

A solvent wipe won't do much to improve the bond, you will have bits of wood and fully cured resin left on the inside of the stringers, for a good bond the surface should be sanded and clean.

Re: Stringers Flawed By Design????

oops! said:

thanks for the pics....

those are not engineered stringers.

they are just wood stringers that were wrapped in woven giving them a really thick appearance.

i would cut them out and re string the boat

Click to expand...

Well, that's a real bummer. I was really hoping it would be possible to leave them in, but I definitely want to do it right. So is there any magic trick to getting the stringers the right height and true? It seems like shaping the bottom of the wood to match the hull would be a trial and error deal. Maybe cardboard templates? Any advice on that topic will be GREATLY appreciated. This is my first boat project, but I worked at Searay PD&E plant for several years, until they began listing pretty badly, so I do have some knowledge of boat building. One area that I have absolutely no clue in, is getting the boat off the trailer and onto a craddle so that it's stable and level. Also, when I replace the stringers, should I replace all of them first and then fit in the bulkheads, or should it all be slotted and put together like a pedistal? Thanks for all the advice guys. These forums and your variety of expertise are a Godsend and a staple for us DIY people. Thanks again.

Re: Stringers Flawed By Design????

hi bud.......wanna have some fun?

read the link in my sig.....at least the first 16 pages.....everything you will need to know about stringers and transoms, and how to install them.

as well....if you click the how to links at the top of the forum....there is great stuff there....most out of the hull extension thread.
in the links up top is also some videos by frisco boater.....really good stuff..

as far as the trailer thing......that is easy as well...

just do a search on the subject.....there is lots of threads.
if you can find any, pm me and i will type out a formal post for you.

cheers
oops

Re: Stringers Flawed By Design????

oops! said:

hi bud.......wanna have some fun?

read the link in my sig.....at least the first 16 pages.....everything you will need to know about stringers and transoms, and how to install them....

as far as the trailer thing......that is easy as well...

just do a search on the subject.....there is lots of threads.
if you can find any, pm me and i will type out a formal post for you.

cheers
oops

Click to expand...

Hi Oops. I must say, that is one heck of a project. Thanks for sharing all of that info. I didn't make it to the end...yet, but I trust all ended well? I went over the stringer parts several times and the transom build. I gained a lot of insight and practical knowledge just from the pics and instructions, but I am just a bit unclear about a few details and the way some of them apply to my boat specifically. I do apologize if this is 101 for you, but I am taking your advice and completely replacing all of the stringers. I love this boat and her sleek lines, so I want to do it right this time, not next time. However, I am on a limited budget, so I have to be pretty thrifty. I have a few pics of my bow and transom area attached, and if it's not too much trouble, I would like to get your opinion on a couple of things.

First, I wasn't quite clear in my understanding of what part of the hull you traced to get the outline for the bottom of the stringer. I want to assume it was the bottom "V", but I want to make certain before I envoke Murphy (smile). And, is that outline carried over to all hull length stringers, or is each position done individually?

In the picture of my bow, where the stringers end, I would like to add some deck support. Is that reasonable, and if so, would I angle the supports from the end of the main stringers toward the center, or add two straight pieces equal distances (but narrower) from the center of the forward bulkhead?

With the engine mounting blocks, how do you account for the glass over the blocks where hieght is concerned? Is there a tollerance (+/-) to play with or is it pretty much a dead-on thing? Just curious.

In the pics of my transom and aft area, it looks like it's a combination of fiberglass form and wood inserts that were glassed over. I drilled test holes in all the stringers, enginge mount block and the transom, and all of it came out wet, if any came out at all. In your opinion, based on what you can see from the pics, can I replace the transom wood without pulling the cap? I absolutely have no means to pull it or store once it was off. Would you say that I have a full wood transom or does it look molded with some wood bonded to the glass for outdrive support?

I truly do appreciate your knowledge and willingness to take time out to inform and guide those of us who dare to take that leap. I doubt I will put as much "overkill" as you due to budget limitations, but I definitely want it to be done right so that it will last. This is my first boat that won't tip over if you stand up too quick (smile), so I am very excited and motivated about taking on the project. I will eventually get to the end of your Searay build as I'm sure there is lot's more to learn. Thanks again, Oops, for everything you contribute.

Re: Stringers Flawed By Design????

ok.....where do i start....lol

ok...its difficult to see with the pics as the motor is in the way.....there is a chance your actual transom is just a small 2 foot wide piece of ply behind the motor...
btw.....that is an omc...it now stands for obsolete motor company.

you have to pull the motor out of the boat to do the transom.

once you pull it......then we can see if you can do it with out pulling the cap.....chances are real good that you can....but it will be cramped work....
(most i/o/s you dont have to pull the cap.

ill continue after i get off work...! be back soon

Re: Stringers Flawed By Design????

oops! said:

ok...its difficult to see with the pics as the motor is in the way.....there is a chance your actual transom is just a small 2 foot wide piece of ply behind the motor...
btw.....that is an omc...it now stands for obsolete motor company.

you have to pull the motor out of the boat to do the transom.

once you pull it......then we can see if you can do it with out pulling the cap.....chances are real good that you can....but it will be cramped work....
(most i/o/s you dont have to pull the cap.

ill continue after i get off work...! be back soon

Click to expand...

Yeah, the motor is the next thing out. I actually started tearing it down today, and I have noticed the small fortune required for many of the replacement parts for the OMC's. Personally, I have seen quite a few boats on craigslist from 6 to 9 hundred that have the whole motor and outdrive. I was considering one for parts. Mine still turns over and has good compression when I kicked the starter over, so I'm hoping I can overhaul it.

I know it's kind of hard to tell in the photos what my transom looks like, but I think you are right about not taking the cap off. I think it's just an inlaid piece of wood. It's kind of shaped like a wide arrow head. The bottom of the wood takes the shape of the hull like a regular transom, but because of the built-in/molded swim platform, the wood doesn't go up as far. I don't know. It looks like I could cut around the edge of the wood and pop it out, much like I did around the edge of the floor. As soon as I get the engine out I will take more pics for clarification. I should have it out within the next week or so. Thanks again for all of your expertise and advice, and willingness to share it. I don't think I could do it without these forums or the insight and knowledge of people like you. Kudos!

Re: Stringers Flawed By Design????

Wouls be nice to find a rotten boat with a good Merc in it for a few hundred bucks.... repower with that

Re: Stringers Flawed By Design????

That would be nice, Rick, but I heard it's a real pain to change out the OMC's for a different power source. Do you know anything about it? I'm not sure if I have the means to get the alignment right on a swap like that either. I did ponder the idea of selling the parts off my engine and using the money for a new power source, but I think I need to do some deep investigating before I make any plans in that regard. What would be the Merc equivalent to an OMC 4.3L anyway?

Re: Stringers Flawed By Design????

Never done one myself.... the 4.3L Merc I would say.

Re: Stringers Flawed By Design????

Yeah, makes sense. I have a discussion going on with Rogersjetboat454 in the OMC forums as well, and he seems to have some great insight about the whole operation. As he suggested, I will more than likely just tear it down and see if it's rebuildable. Thanks for the input, Rick.