Laminating Stainless Steel with GRP. Is it feasible? Making a Muffler for my Detroits

[Bertramdriver]

OK I'll own up, sometimes on long runs the Detroits exhaust noise gives me a head ache. To tame the beasts I've been experimenting with mufflers to redirect the exhaust gas into the seawater slip stream rather than broadcast the exhaust note behind the boat in the open air. The prototype mufflers are in fact doctored stainless steel 10" diameter cooking pots with one half of the sidewalls cut away.
Surprisingly, and after shifting the escape angle around a couple of times, they have been quite effective at redirecting the exhaust fumes away from the helm, so no fumes. Also they have reduced broadcast noise by a significant factor. (I keep forgetting to take my sound meter out with me so I can't quote numbers) The downside is the "hammer" effect of the exhaust pulse smacking into the flat bottom of the pot before escaping from the side, transmitting vibration and attenuated noise into the helm area via the transom wall.
So, I'm confident enough in the principle to move to the next phase which is to replace the cooking pots with a 60* curved pipe. This should smooth the gas flow and eliminate the hammer, allow me to direct the exhaust down into the slipstream, whilst retaining the benefits of quieter fume free motoring
Look at this on eBay:

http://pages.ebay.com/link/?nav=item.view&alt=web&id=400787537329

45 degree bend, single skin stainless steel, flue pipe systems, ducting

My quandary is whether or not the stainless steel (almost certainly 304 rather than 316) will be strong enough to withstand the pressures and the longer term effects of corrosion in salt water. My thought is to laminate the steel externally with glass mat and high temperature resin, but I'm wondering if covering the steel with a strong material like GRP, having a low coefficient of expansion isn't going to cause warping, cracking and other nasties. The internal surfaces will rapidly acquire a water resistant finish once the Detroits start blowing through.
Does anyone have any experiance or thoughts on this mix of materials?

 

[DownWest]

Can't see your e-bay as blocked over here. But, looked after a biggish ketch with two DD 140hp. And had to replace one of the mufflers, as it rotted through.
On the assumption the mufflers are downstream of the water injection system, then temperature is not a problem. Vetus use plastic watertraps and mufflers ( I am currently fitting one to a Swan. Even better is GRP, using polyester resin. You could build one from GRP sheet and tube, taping it all together, then apply some extra layers. Look at the Vetus site for ideas;

They do roar a bit though ))

 

[pcatterall]

Can't see your e-bay as blocked over here. But, looked after a biggish ketch with two DD 140hp. And had to replace one of the mufflers, as it rotted through.
On the assumption the mufflers are downstream of the water injection system, then temperature is not a problem. Vetus use plastic watertraps and mufflers ( I am currently fitting one to a Swan. Even better is GRP, using polyester resin. You could build one from GRP sheet and tube, taping it all together, then apply some extra layers. Look at the Vetus site for ideas;

They do roar a bit though ))

My initial thought..... heat should not be an issue?

 

[DownWest]

My initial thought..... heat should not be an issue?

Nope, unless the raw water pump fails, then a GRP one will last longer than a moulded plastic ( Vetus) one. Mate with a daytrip sardine boat had that happen and his Vetus muffler melted, before he realised what was happening. Same reason I would use polyester rather than époxy resin for the OPs build. Polyester withstands higher temps if a problem occures.

On the noise issue: I fitted a new genset to the same ketch. The Vetus kit that arrived with it for both the exhaust and intake (Single cylinder diesel in a special box) cut the noise to the water splashing out of the side exit. Standing next to it, one could converse without any raising of voice.

 

[lw395]

Polyester won't bond well to stainless.
So the resin would need to completely encapsulate the stainless.
GRP has a fairly low modulus, so will probably stretch to accommodate the expansion of the stainless?
It sounds do-able for the wet part of the exhaust.
I can't see it working well for any dry exhaust.
Stainless is a very poor conductor of heat, so local heating of the resin will be an issue.