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Rotten Stringers

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Old 06-04-2017, 09:57 AM
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Default Rotten Stringers

I'm new here but I have some knowledge. I build boats in the 40 -70ft range and the molds. I keep reading about rotten stringers. What ever you do, do not cut them out. The stringers are installed while the boat is still in the mold. The stringers will keep the bottom design from changing. When you remove the stringers from the hull outside of the mold, the bottom will definitely flex. The bottom shape can change and the new stringers will keep that change. Many stringers are built hallow and then foam filled. The foam is for noise reduction and has no structural strength. The way I would repair it would be to grind the stringers and floor with a 24 or 36 grit paper.You need to grind 12 inches on either side of the stringer. This is the most important part. Vacuum the dust, blow it out and wipe it with acetone. The next step is 3 layers of fiberglass. You can use a 1708, 1808, a 24 or even a 36. I would use a combination of 1708 and 1808. You glass one side of the stringer and then the other side. The over lap is on the top of the stringer. The purpose of the overlap on top is that it creates an I-beam effect. The first layer is 3 inches from the stringer. The second layer is 6 inches from the stringer. The third is 9. The third layer can be one piece that goes over the whole stringer. On some boats we will put carbon fiber on toop of the stringer and down 3 inches on the sides' Be sure to grind between layers. I would not use vinyl ester resin. Its all I use but its very difficult to grind and gums up the paper quickly. Use a ortho iso blend. It will work better for you. Also use a 925 mekp. it works better also. I hope this helps someone.
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Old 06-21-2017, 05:02 PM
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So do leave the rotten wood in the boat. I am not seeing how to replace the stringers if you do not remove them.
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Old 06-21-2017, 06:02 PM
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What he is saying is the stringer isn't the real structure. The glass in the shape of the stringer is. And he has us doubling up the thickness of the glass. Not sure if I agree ir not, but I am pretty sure the stringers in my hatteras have no wood in them at all.
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Old 06-21-2017, 06:10 PM
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I need a little more information. Keep in mind that many stringers are built hollow. Is this a performance boat and the stringers are rotted where the engines are bolted to the stringers. Or actually any other IO boat. In these areas where the engines are 800 to 1800 hp we use a very high density composite material and fiberglass over it. In other areas we use a very soft foam core material. Tell me what your situation is and I'll come up with a doable solution that you can do yourself. Do not cut them out. There are other solutions.
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Old 06-21-2017, 06:37 PM
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The interior composite of the stringer does not make any difference. The only place it makes a difference are where the engines are mounted. This is primarily due to compression, weight and torque. I'm getting ready to do a 30 ft cat project where I'm removing the deck , cockpit, everything to take it down to a bare hull. I will absolutely not remove the stringers. I know all the problems that it would create and the tremendous amount of work it would take to fix it. All of this is my opinion of what I would do. Other people will have their opinions. I build all the fiberglass parts and assemble them on 4 million dollar boats. What do they do.
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Old 06-24-2017, 02:53 AM
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Quote:
Originally Posted by dereknkathy View Post
What he is saying is the stringer isn't the real structure. The glass in the shape of the stringer is. And he has us doubling up the thickness of the glass. Not sure if I agree ir not, but I am pretty sure the stringers in my hatteras have no wood in them at all.
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Why remove a rotted stringer if it's just a form for the fiberglass laid over it which is the actual structural piece? Fiberglass doesn't rot, wouldn't it still be providing support as designed?
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Old 06-24-2017, 07:11 AM
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Originally Posted by Tractionless View Post
Why remove a rotted stringer if it's just a form for the fiberglass laid over it which is the actual structural piece? Fiberglass doesn't rot, wouldn't it still be providing support as designed?
Because when the appropriate core is used fr the stringers and the laminate properly adhered, it makes it act like the fiberglass is much thicker than in actually is. So you get greater strength with less weight.
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Old 06-24-2017, 07:24 AM
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I have heard of people opening up the top of the stringer, leaving the glass either side of the wood intact. Then removing the rotted wood. I take it you feel this would be preferable to removing glass and stringer right down to the hull? And is there any option better than sliding new back into gap and gassing it back closed? I assume filling with resin and chopped strands would be a little heavy? Maybe something like gas tank foam? And what would one do to the engine mount section?
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Old 06-24-2017, 09:21 PM
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What about just properly supporting the boat with straight 2 x10's under the boat at the point where the stringers are located.
This might actually remove some hook of rocker in the bottom.
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Old 06-25-2017, 09:02 AM
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I have had the same argument about boats not being properly supported and than having their stringers cut out and new ones glassed in while sitting on bunks on a trailer.

the boat needs to be supported at the keel bow to stern and lightly blocked at the Chines..

ideally you block and laser level the boat off before you cut the stringers out Than inspect the bottom with a long straight edge before you do any cutting also.

i had repaired a old parasail boat That needed new stringers in years ago that had such a huge hook in it from it sitting wrong on a trailer with rotten stringers that I did the following.

I took two 12 foot 2by 12s mated with doubled up blocks of 2by4. I made up a pair of these and placed them under the boat exactly where the stringers go inside with the braces wide enough that I could run screws through washers and into the 2by 12s below thus pulling the big hook out of the bottom.but still have room to place my stringer in.

i than mixed up a few batches of thickened epoxy and bedded the new stringers down in it.

left it to dry for a day than pulled all the screws out and did the usual lamination process for installing stringers.

EasyPeasy way to make sure the bottom is straight.

i agree with the poster. I think there is a lot of old boats out there with new stringers that are hooked or twisted.

if the deck is off when your do the repair it further exaggerates the possibility of the boat being twisted as now you have a big wet noodle .

When I redo the stringers in my 19 Baron I'm just going to cut the top 1/2 inch cap off and eat the old stringer out with a electric chain saw.

Cut new stringers and butter them up with big batch of thickened epoxy with a slow hardner and push them in the slot and clamp them.

cap them with a couple layers of 1708 and vinyl ester and call it done.

no hours of grinding out good glass only to replace it.
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