24' Fiberform - Rotten Stringers/Transom

[Ehdrian]

Good to hear your starting the project!

Thudpucker was right about the buddy... my friend Adam has put in almost half the hours I have into this boat for beer and free fishing. He has helped allot!

Tools... I made out fine with: Grinder with metal grinding disk, hammer chisel and screwdriver, Sander, Router, Skill Saw, Paint roller, Metal roller, Lots of mixing containers, Squeege, ratchet set and tape measure, ratchet set etc....

Removing the stringers.... A good idea is to grind the stringers out from the base and then lift them from the boat without wrecking them. This way you can use them as templates for the new stringers. Then take the grinder and smoothen the hull to the stringer channels (if there is any) so your fiberglassing is made easier. Also try and make sure you know where the stringer were - so you can put the new ones in later. The best way to brace the boat is to make a 'cradle' out of long 2x4s that 'hug' the bottom of the boat. I didn't do this though... I just put three extra stands along the bottom of the boat and one under the transom. These are in addition to the three already holding the boat up at the bow and chine. This braced the boat just fine for me, and now I'm finding that I'm building the boat more square than it was manufactured.

The transom... if you are going to rip it out from the inside and have access to the wood there..... Take a skill saw and cut from the bottom to the top of the transom about 6" apart and also from port to starboard, until you have a bunch of 6" squares cut. Then take a chisel and screwdriver and 'pop' the squares out until you have a thin film of old wood. At this point you can chisel out the thicker spots until all the old wood is about 1/8" thick or less, then grind it all off until you have bare fiberglass. Make sure and set the depth of the skill saw! And e careful not to grind through the hull anywhere! Remember that your trying to save the outer skin.

Fiberglass... I used the blue stuff, and I'm having issues with some of the layers, due to curing (not the resin's fault at all!). If your temperature is 30 degrees then you might want to only add 1% catalyst to your resin and fiberglass to a clean dry surface. Try cleaning the surface with acitone first and grind or sand a thin layer off of the surface. I had to learn through mistakes. I used 1705 Nytex 45 degree and 1705 Nytex 90 degree for the stringers. I put 4xlayers at the tips of the stringers and 4xlayers in the engine area and 2xlayers in the middle of the stringers. This 'Nytex' is mat and biaxle stiched together and costs about $17/yard by 50". I'm using mat, biaxel and woven roving for the baulkheads and decking.

Sofar on this 24' boat I have used:
20yds 1705 Nytex
10yds 18oz woven roving
10yds 1.5 oz mat
17gal resin (2-3 gal lost due to not knowing how fast this stuff can set in the heat lol)

I hope this helps you get your bearing on the project.

Cheers!

[frastorno]

Thx for the info Thudpucker, I’m sure about the rot resistance, balsam is used for under water structure of marina’s decks and they last forever I just don’t know about how the resin and fiber stick to it, so I’ll try to test it tomorrow on a little piece of balsam, fiber glassing it and see how it behaves. I have all the metal parts in different plastic boxes, all the wood I removed was rotten so I just throw it away .. still more to remove. The boat was modified from inboard to outboard, so no engine on the stringers. I Have thousand of pictures already
Ehdrian, thx for your direction on stringers and transom, let me see if I can recap that step by step:
• First I’ll ensure the hull is cleared out grinded and well cleaned with acetone.
• I’ll then shape the stringers properly and have some layers of resin on it to seal.
• I’ll then paste them to the hull with epoxy (that would be using some of those dual tube syringes mentioned before), and let it cure.
• I then start fiber glassing 4 layers (mat, biaxial, mat, biaxial ... woven and biaxial are the same right?), starting from the top of the stringers and then onto the rest of the stringers and hull. I don’t need to fiberglass the whole stinger at once, the important is that the 4 layers on each portion are added at the same time. Each time I start a new section over a cured one, I’ll have to ensure that the previous layer is grinded and acetone cleaned.
• The wood of the stringer will touch the wood of the transom and them both fiber glassed together
Is this all right? I should be able to clear the deck tomorrow, remove the transom the following week-end and start the above steps the next one .. can’t wait!

[TerryKing]

Originally Posted by thudpucker

The USDA forestry has tables on the qualities of Various woods.(snip)...Go to your public library, tell tell the counter person what you want. It'l save you some time.

Or, look here at the BoatDesign Wiki:
http://www.boatdesign.net/wiki/Mater...od_Handbook.22

The Wood Handbook is online....

[Ehdrian]

I didnt use epoxy anywere, although that stuff is a lot better than polyester, from what I hear.

I put 3M 5200 under the stringers - its similar to other sealants exept for its amazing ability to adhear to wood and resin... it also stays rubbery. This reduces hard spots in the hull - so when you hit a wave the hard shock is somewhat absorbed by the rubbery 5200 instead of the fiberglass, which can cause the hull to micro-fracture which lets in humidity under the stringers.

You could also put foam under them, or just leave a gap.... but I'm not sure how that works.

Cheers

[frastorno]

Was reading from the wiki article that TerryKing posted, btw, thx! Excelent info there!.. but no mention of the "balsamo" wood!
"3M 5200: A rubbery, polyurethane sealant in various colors with adhesive properties sometimes used as a glue. Fails as a glue under water saturation without high clamping pressure, and without the proper strength testing I couldn’t do here, it’s not recommended as a stand-alone marine glue. Repairable with epoxy."
I also read other postings saing that the stringer should be solidly attached to the hull as a sole body, is it your a "test" or someone reccomended to proceed that way? BTW, I finally found a bigger 2 tubes epoxy that cure in 2 hrs (the little syrings I mentioned were curing in 5 mins!.. hard to place a stringer in that timeframe!!).. it's from Loctite, the name is Epoxy-Mill.. anybody ear that?

[Ehdrian]

This is an example of where I got some info on 5200:
http://www.vintageraceboatshop.com/E...gProject-1.htm

This is an example of where I got info on hard spots... if you do not shape your stringer perfectly to the shape of your hull, you may need a 'padding' under the stringer, at least. So I tried to do both, myself:
http://www.yachtsurvey.com/HullFailP2.htm

Cheers

[marshmat]

5200 has its uses, yes, and it's good stuff when used as intended. But at eighteen bucks per caulking-gun cartridge, there's gotta be a cheaper alternative.... or are the local stores just in cahoots with their rip-offs?
Loctite stuff is generally very good and very expensive. I haven't used that particular one though.

[frastorno]

Good news! The fiberglass perfectly adhere to the “balsamo” wood and I found a shop that sells the epoxy here in Panama (thx to TerriKing!), I read the article about the “soft bounding” of the stringers and I’m now a bit confused, it seems that there are different opinions about it: strong and rigid bounding with epoxy or soft with some elastic glue .. Marshmat, what’s your opinion about that.. I also posted this question in another thread: (Wood to use replacing keel stringer)

[Ehdrian]

Hmmm, I'm far from being expert and have no practical experience with this. If someone says you can hard bond to hull, then go at'er. I'm sure you would need to make sure you have the stringer perfectly grafted to the hull first. IMO

[marshmat]

Strictly from a first-principles engineering standpoint (I've never done the repair you are doing), you should match the product E*I (elastic modulus times area moment of inertia) among each discrete component of the combined structure. In layman's terms, each individual element should require roughly the same force to bend roughly the same amount- ie, it's all the same stiffness. Having one soft element combined with one hard element causes most if not all of the stresses to become concentrated at the weakest point of the harder/stiffer element, which will thus fail prematurely.
In a wood/glass stringer, you achieve this effect by giving the low-modulus part (the wood) a very large area moment of inertia (its large cross-section), while the high-modulus part (the fibreglass composite) has a smaller moment of inertia. In the ideal case, forces are thus spread throughout the structure. Using an excessively soft component would concentrate the stresses into the thin tab of fibreglass at the joint, rather than spreading them out along the entire stringer bed.

[TerryKing]

The original construction on any boats I've seen is intended to make the stringer and hull basically one fairly rigid piece.

There IS a problem with getting a good fit, and not having gaps between the Stringer and hull. I have used fiber filler with West Epoxy for a strong joint. Others have said that they put a strip of glass matt or roving (thickly woven figreglass cloth) between the stringer and hull to hold epoxy and conform. That sounds OK, especially if the fit has gaps of up to 1/16 or so.

Maybe the combination of a matt and thickened Epoxy would be good in a case where the fit is none too good.

In terms not as exact as Marshmat's, it should end up as one solid unit...

[Ehdrian]

And there you have it!

[frastorno]

Ehdrian, I hope I’m not jeopardizing your faith in your boat basement .. I’m sorry I had to dig in !
This is my plan so far then: I already have the balsam stringers, the Epoxy , cloth and mat. I’ll clean the bottom of the hull as much as I can, acetone first, grinder after. I’ll shape the stringers to adhere as much as possible to the hull and paint it with at least 2 coats of epoxy. I’ll order some fiber filler to add to the epoxy (does any filler works or needs to be fiber? They only have graphite filler from west marine at the moment, anything else should be ordered from US and that would take at least 2 weeks) and will paste the stringer with that. I’ll then fiberglass everything with epoxy, (which fiber should I use, cloth only or mat first?).. Sounds good?

[Ehdrian]

Not at all!

I had a fiberglass professional scope out my work so far, and he said that I could lay my work bare to a marine survey and not have any issues or second thoughts.

But it was nice to hear from him that polyester is good enough for a boat and that epoxy isn't a god sent to us from 'boat heaven'. I also saved $3,000 on the project by just not using it. So, so far I have no regrets.

[frastorno]

3K$? now I'm getting worried.. how many gallons will I need for 3 stringers and the transom? Also an aprox would be good just to recalc my budget .

I have half boat cleared now (decided to do 1 side at a time to avoid deformation of the hull), I only need to sand the hull and clear with acetone.

I cut a pice of the internal fiber of the transom and the wood behind is totally rotten as supposed. so I'll have to replace that also. How should I proceed, do I need first place the transom or the stringers? How did you do that Ehdrian?

Can I use a good strong and water resistant wood instead of plywood for the transom?