Exhaust Hard lagging vs. soft jackets

[EricatNordic]

On dry stack and dry portions of wet exhaust for inboard engines, what are the advantages /disadvantages of using hard lagging (fiberglass insulation or foam wound with frp tape)rather then sewn insulation blankets bound to the enxhaust pipe with safety wire?

Is one method better then the other?

Does anyone have experience with them in terms of longevity?

 

[pauljohn]

Pros on soft lagging - can be removed and replaced at will, looks better (IMO).
Cons - expensive, takes up more space, has those annoying hooks and wire.

Pros on hard lagging - cheap, more compact, I think it works better as an insulator but that could be due to the installer who does the job.
Cons - can not be removed without replacing with new, messy to put on.
If you ever think you might need to remove it to inspect welds, pipes etc. I would pay the extra and go for the soft.
I think the hard type lasts longer.
Almost all the big boats I have dealt with go with the soft, but of course money is not an issue.

 

[pauljohn]

Sorry, also meant to say I am most familiar with the plaster that is used for hard insulation not frp. The plaster is very messy and has to be cut off.

 

[EricatNordic]

Thanks,

When you say the hard type last longer, do you mean the hard lagging does something to preserve the metal exhaust stack to make it last longer, or the covering itself last longer then a jacket.

The samples I saw look like the material they make modern orthepedic cast from. Some sort of reneforced tape and resin. Probably not really FRP now that I think of it. Maybe it is plaster.

 

[MikeHalloran]

No lagging makes the metal last longer. Lagging reduces heat input to the engine room and reduces the probability of severe burns to personnel from accidental contact with hot surfaces.

The soft lagging, or "blankets" can usually be removed and replaced ... once. After the engines have been run hard for a few hours, the binders that hold the glass and ceramic fibers together as batting, yarn, or cloth, have burned off, and the blankets become friable.

If the hemmed ends of the blankets are installed right up against a hot flange, or over it, as many owners do, the heat resistant (but not fireproof) fabric cover will no longer be able to retain the wire inside, and you won't even get to reinstall the blanket once; it will just fall apart when you untwist the wire.

Usual practice of boatbuilders wrt to soft lagging is to install it a little loose for construction and development, and tuck in the hems and tighten the wires after sea trial.

There are at least three variants of hard lagging. The kind that looks like a plaster cast is durable enough, but easily stained and impossible to clean. It can be applied in situ, but it is messy.

Hard lagging with a glossy finish can be done with boat resin, but the resin burns away at the flanges, and is not itself fireproof. It can also be applied in situ, and is messy. It can be done in a variety of colors. It resists staining and is easy to clean.

Hard lagging with a glossy finish that _is_ fireproof is available from several marine exhaust vendors, only in black. It resists staining and is easy to clean. It chars at really hot flanges, but does not burn. It is extremely messy to apply, and must be oven- cured, so it can't be done in situ.



Mike Halloran
Pembroke Pines, FL, USA

 

[EricatNordic]

Thanks again.