Clean Machine Stringer Replacement

[fishnkid]

First off, Hello fellow Trojan owners!

We are about to begin a stringer replacement project.......I see a few of you may have done this and I would like any input you may have. What did you use for the stringers? 4x6?

Thanks.

[yorklyn]

I used 3/4 marine plywood, laminated two pieces together with thickened resin and stainless screws. That is what was origionally in my international.

[Paul]

I've done this job a few times and have had great success doing it as Todd described, laminating marine plywood together. Strips of plywood laminated together to give you the desired thickness are much stronger than a single solid piece of wood. Here's how I go about it. First, determine how much of the stringer needs to be removed and cut it out flush to the hull with a reciprocating saw. This will expose good stringer at each remaining end. (this is assuming that you are replacing only a section and not the entire stringer) Cut a notch half way up and horizontally about 12 inches long out of the remaining good stringer to create a lap joint to join the new stringer at each end. Using an angle grinder with a coarse disc, grind down the area where the new fiberglass will be to expose a good surface for resin to adhere to. Secondly, make a cardboard template of the new stringer including the lap joint ends and transfer it onto the plywood. If the required stringer is longer than the sheet of plywood, be sure to stagger the joints. Cut out as many pieces as required to achieve the desired stringer thickness. Laminate the pieces together using West System epoxy resin thickened with 406 Colloidal Silica and clamp them together for an overnight cure. (if engine mounts are to be located in the new stringer, I usually notch and epoxy in a piece of hardwood at these positions) Thirdly, use thickened epoxy to bed the stringer into place at the lap joints and at the hull. Its recommended that you leave a filleted edge along the hull edge. Lastly, use multi-layers of fiberglass roving and resin to cover and tab the stringer to the hull.

You can also find helpful information for doing this job at http://www.westsystem.com

Hope this helps

[Big D]

++1
I will add that glass mat does not like wrapping around outside 90 degree angles so round off the top edges of the stringer or the mat may separate from those surfaces.

I'm pretty anal about some things so here is some food for thought; epoxy is best to laminate the layers of plywood, however for this application vinylester or even polyester resin for the purposes of glassing everything will suffice, and is cheaper, and that's coming from a guy that is very pro epoxy! What I'm anal about is flexing when it comes to epoxying in a new section. Depending on how much of the stringer you replace, the concern is the old part of the stringer will flex completely different from an epoxied section, and flex it will. I've seen the old sections at these joints fail in boats that are run hard not only because the older part of the stringer is weaker to begin with, but also because it is fastened to a much more ridgid section of stringer that flexes at a completely different rate. The joint doesn't fail but the old section just before the joint does. Think of it as the same reason why some recommend not soldering wire connections because the failure point is where the flexible wire meets the soldered part which does not flex. This is something you should keep in mind and consider based on your type of boating and the conditions you usually boat in. The remedy is to replace the entire stringer from stern to bulkhead which is what I have always done save for one that was simply not practical. On that note; if you tie into the bulkhead, make sure it is structurally sound also......for what it's worth!

[yorklyn]

++1
I used epoxy to join the two pieces of plywood and polyester resin for the glass work for the same reason. if the prep is done properly you will get a sufficent bond to the old fiberglass. I used a router to round the top of the stringer. If you are only replacing a section , be certian the old stringer is completly dry and structally sound. The "Fiberglassite" has great materials and good info. you can get resin and fabric from them. Good Luck!

[Big D]

[/quote]

....if the prep is done properly you will get a sufficent bond to the old fiberglass....

Todd, the "bond" isn't the concern if using epoxy, it's the point of most fatigue due to the stresses of flexing that I was trying to point out.

......be certian the old stringer is completly dry and structally sound....

Very important point.

[yorklyn]

I was refering to the new polyester to old polyester bond. Alot of people say you cant get a good enough bond trying to use polyester resin for repairs. I went that route for two reasons
I wanted the hull to flex the same as the origional laminate.
Cost (we went through 15-20 gallons of polyester resin on my stringers. (I have since gone through 15-20 gallons of west system epoxy for patching and repairs, the west system hurt my wallet alot more! LOL!)

[Big D]

It may not hold true today but I remember "the three fives" epoxy analogy years ago; 5 times stronger, 5 times lighter, and 5 times more expensive!

[Big D]

....new polyester to old polyester bond. Alot of people say you cant get a good enough bond trying to use polyester resin for repairs.....

It's acceptable for a lot of applications. Again, depends on the application/use and the stresses involved. For most of what the average recreational boater with a cruiser does, it's just fine. Can you do better? One can always do better but is it really needed, practical, and worth it?

[fishnkid]

Thank you very much for your input! I will update with pics & progress soon. What oz Woven did you use? 32 with 2 or 3 layers?

Thanks, Eric

[yorklyn]

I used 2408 biaxial mat. it was good to work with and because of the thickness it expedited the layup schedule. It has a nicer finish that's smoother than the woven roving

[Lawman]

I used 3/4 marine plywood, laminated two pieces together with thickened resin and stainless screws. That is what was origionally in my international.

Exactly what I did. I used the WEST system.

[fishnkid]

Having issues getting the bathroom/shower fiberglass floor up......arrrggh! Any thoughts?

[cleanestmachine1]

HI there,

i have a 73 Clean Machine. unlike the photos in this thread....my engine beds are wood , and attached to the full length glass stringer. I suspected rot and so i pulled the holding tank last week. Sure enough the starboard bed was wet powder. my question is....does this wooden one run all the way back to the transom, or just to the aft bulkhead of the engine room?

[prowlersfish]

Your full length stringers as wood but glassed over . Not sure about the engine bed length . If the owner of my old clean machine is on his boat today I will look .