Exhaust Outlet?

[scot]

I know that polyester should be used to fabricate the surge fitting due to temp, but can epoxy be used at the stern as the primary bond on a fiberglass thru-hull?

Thanks

[JP Dalik]

I don't see why you couldn't.

The one advantage the polyester had for us was that if "kicked" faster than the epoxy. After holding the tube in place with a few claw glass fillets I cut small pieces of chop and started moving around the tube. Then took a strand or 3 of heavy roving and put that around and over the chop. I worked this until I felt there was enough meat to support any loading the piece might get during the tubing installation. I did this to both sides of each tube.

When I tried a similar technique with the expoxy I found that it would run out of the fiberglass leaving it dry on top and saturated on the bottom before it "kicked" You may have an advantage in the Texas sun and not have to worry at all, but that was the issue I had.

Is there a reason you need epoxy? or is just cause you got some left? Big tube little tube?

[scot]

Thanks JP,

I believe I read (on this site) once that epoxy should not be used in the exhaust system because it starts melting at 250 degrees.

Epoxy is all I use on repair/rebuild work. Most of the transom on my boat has been rebuilt / modified with the 1/2 pocket and all of the work is in epoxy. I have always heard that you "can put epoxy onto polyester...but you can't put polyester on epoxy"

So, if I cannot use the epoxy to bond in the exhuast fitting, I will be forced to use a bronze thru-hull.

I buy it in the 5 gal pals and basically use it for everything. I would mix an epoxy+milled fiber+ cabosil putty to install the pipe, "if" epoxy is OK here. I would completely pack the gap and use a generous fillet on the inside and outside.

[JohnD]

Scot,

My exhaust was done in the same maner as JP described and was first tack'd in place using plexis adheasive.

I know enough about the chemistry to be dangerous but I too have heard the warnings about not trying to bond polyester to existing epoxy FG.

br,
JohnD

[CaptPatrick]

Scot,

Here's how I do it...

Cut the hole for the exhaust tube and scarf the exterior at 12:1. Fit the pipe to be a snug fit in the hole.

Build a flange onto the pipe with Coosa Board, or similar product, and corresponding to the transom angle. With the pipe in place, tack the flange to the pipe. Thickened polyester is fine. Remove the assembly and glass the flange to the pipe with polyester and chopped strand mat.

Now, install the finished flanged pipe and bed with thickened epoxy. No additional glass work reqiuired...

Rebuild the exterior joint with polyester and glass, epoxy fair, and you're ready for paint.

[scot]

Capt Patrick,

My B25 transom is already epoxy, I had to fill (2) I/O holes and have built a shallow pocket, cored and cloth inside, all epoxy. So, what ever I do it will be tying into an epoxy base material.

Based on your comment;

Now, install the finished flanged pipe and bed with thickened epoxy

It is OK to bed and secure the fitting with epoxy, why would you scarf and rebuild with polyester outboard rather than finishing with epoxy?

Also, I see the need for the flange plate on a bare glass transom (it's thin), but I don't think I would need the plate on a 2" thick cored transom would I? ...it's only cored in the 25's "bubble" area, but that's where the fitting will be located.

The image shows the design of the installation;

The thru-hull is going throught the cored area.

Thanks

[CaptPatrick]

Scot,

I do the flange just to exclude the need to get down and glass in the tight area. Remember, this is a B31, out board, under the deck ledger, and real close to the hull underneith and outboard.

You may have more working room in your rig... If your exit hole is solid epoxy, then stick with epoxy. Use a medium fast setting epoxy, mixed primarily with cabosil, and do the job early in the morning when the temperature is still in the 70's. It'll be set before the hot afternoon temps get there. Once the construction joint has been made you can go to a less thixothropic mix for fairing. I'd still do some undercutting and go for a fileted joint between the pipe and transom.

[scot]

Gracias Amigo, that's the answer I was hoping for. And yes, there is a bunch of room during this phase...everything is opened up.

[Bob H.]

Capt Pat, That oval exhaust looks sweet...once again a picture is worth a thousand words...did you run the generator exhust through the pt side? BH