Bedding Stringers

[rbt]

In replacing the stringers in my 17ft Aquasport I am considering bedding them in 5200 rather than epoxy. The stringers are modified 2x10's treated with CPES and are going back into the original fiberglass sheaths. The sides and top of the stringers will be coated with modified epoxy and the top fiberglass cap installed. I read quite a bit about epoxy hard spots so I thought 5200 may be a better choice for the contact between hull and stringer.

[jimslade]

It would be a waste of money. Set the wood just above the bottom. If you want to make sure that you are not contacting the bottom you could use a strip of foam to set your stringers in.

[rbt]

Jim,
thanks for the reply, but I do want to secure the stringers to the hull bottom. I thought 5200 might be a little more flexible than epoxy.
Thank you

[JR-Shine]

but I do want to secure the stringers to the hull bottom.

I’m curious why you would not want your stringers secured to the hull

[rbt]

You must have misread this, I do want to secure the stringers to the hull bottom, just thought 5200 would be a little more flexible than epoxy, and possibly a less costly solution. Although at $15.00 a cartridge, it is closing the gap on epoxy. Thanks for the interest.

[JR-Shine]

I am willing to bet it would be cheaper (and a lot stronger) to glass them down with epoxy and biax ;)

[jimslade]

You dont want the stringers to touch the bottom of the boat because you will setup a stress point on the bottom that will cause all sorts of structural issues.

[JR-Shine]

You dont want the stringers to touch the bottom of the boat because you will setup a stress point on the bottom that will cause all sorts of structural issues.

The ideal way to do it is to rest have the stringers rest on a foam trapezoid - the glass the whole thing down

In this picture, you will see two stringers (already glassed on top of foam trapezoids), and a bulkhead which is sitting on the foam trapezoids waiting for glass


http://209.190.4.227/gallery/albums/userpics/12155/normal_stringer1.jpg

[rbt]

Interesting, they float on the foam, but are trapped in the fiberglass shell. Originally mine were set on a type of hardened filler, and I assumed they had released because of moisture intrusion. Stringers are never hard fastened to the hull bottom? Thank you both for the replies.

[JR-Shine]

The stringers were probably bedded down in Plexus or some adhesive – that’s the way production boat building works. The reason they do it this way is cost – its quick and saves labor, not because it’s the best way.

What you see above (while not pretty work) is a better way to install stringers. There are no hard spots, the load coming from the hull is spread out evenly through the fiberglass skin (multiple layers of biaxial cloth) to the stringers.

There is nothing secret or ground breaking here.

[rbt]

Good information, thank you.

[basstardo]

Good information! :)

[IHTFP]

JR Shine,

Where can you get the foam trapeziods? Are they made exclusively for boatbuilding. Also, when installing stringers in a deep V bottom, does the technique change any?

Thanks

[SamSam]

JR Shine,

Where can you get the foam trapeziods? Are they made exclusively for boatbuilding. Also, when installing stringers in a deep V bottom, does the technique change any?

Thanks
You just cut them yourself out of foam that won't be dissolved or affected by the resin system you are using. They are not structural but only serve as a form for the fiberglass tabbing and help smooth the 90 degree transition and distribute the stresses between the bulkhead and the hull. Sam

[eyes]

Got a question regarding to bedding the stringers.
I know Jimsdale wrote not to place the stringers touching the bottom, understood. But what do you use for filling between the stringers and hull befor you glass them?

[jimslade]

Set the stringers on foam just off the bottom. See jrshines link , 7 prev. posts.

[eyes]

Thanks Jimslade.
I saw the pic but didn't pay much attention to the details.
I'm currently replacing my stringers on a 17' 6" Flare Boat i just bought (See thread "Flare Boats?" for pics). I already mailed Russ for details on making them. I was thinking on making the in fiberglass filled with foam, wich i told him, but i want to finish the boat soon, so i decided to stick to ply sealed and covered with fiberglass. I will try to post pics later on the developement. Might need some gelcoat or paint advice later on.
Thanks again all. This is a very helpful site and a lot of good people.

[eyes]

Just decided to get back with foam filled stringers. I've just posted a pic of the stringer mold i'm going to use. (see "Flare boats?")

[JR-Shine]

The picture above is my flats boat. The stringers (blue arrows) are foam H100 1" Divinycell with several layers of heavy Biaxial cloth, they rest on a "pad" of foam, then they are glass to the hull with 2 offest layer of 12 oz. Biaxial 45/45 tape 6" wide.

The red arrows are pointing to a bulkhead which is resting on a foam pad, but it has not been glassed in yet.

If I were you , I would use ply for the stringers tabbed in with Biax tape and epoxy.

Joel
boatbuildercentral.com

[eyes]

Thanks for the info, but why do you suggest doing my stringers in ply?
As i've seen manufacturer are eliminating wood on fiberglass boats.
That's why i've decided to switch to fiberglass filled with foam. I've been posting pics at another thread i've started ("Flare Boats?").