How to mock up an exhaust riser ?

[genkinyc]

Hi All,

I need to have a 1 5/8" stainless steel exhaust riser made for my sailboat's new engine install.

This piece will need to rise about 7-8" and then gooseneck down, with a shift to the left

How could I mock this up, for something to bring the welder?

I am looking for some kind of cheap plastic pipe that would hold it's shape, something like that. PVC pipe is no good, I have compound curves, that need me to be able to shape the piece.

A metal coat hanger would trace the shape, but not the 1 5/8" volume of the tube.

I thought of a metal coat hanger threaded inside some shopvac tubing..

Any ideas ?

 

[OccupantRJ]

Flexible exhaust tubing.

 

[rburke65]

I was going to suggest the same thing.

 

[genkinyc]

Thanks guys - I will check out flexible exhaust tubing.

 

[The Cobbler]

1-1/2 pump discharge hose filled with plaster of paris , molded into shape before the plaster sets

 

[dogdog]

Not sure, I have seen those Ice Engine works things for exhaust fab works.... for cars anyways... it is plastic, but not cheap....so....not sure if that is what you are looking for.

https://www.icengineworks.com/

https://www.trick-tools.com/Icengineworks-Exhaust-Header-Modeling-Systems-864

 

[joe_padavano]

Use a coat hanger or heavy wire with a series of cardboard disks spaced along it.

 

[anythingyoucanimagine]

Is this something you can remove from the boat in one piece?

Just use the cheapest exhaust flex hose you can find. Put it into place then fill it up with spray foam (like insulation great stuff foam cans). Water makes Great Stuff foam set quicker and acetone will clean it up before it hardens.

You could also use PVC (schedule 40 or DWV) and glue the couplings. You can heat and bend PVC pipe with a torch.

Best possible solution, make a full size scale model of the transom in the area where you need the exhaust pipe made. Bring the model into the welder and tell him "make something fit for that". Giving the welder a model of the part is one thing, letting the fabrication shop test fit the parts/welds as they build the part will get you better results.

Is it wet or dry exhaust? If you can swing it, breaking up compound curves in places by using flex couplings can make it a lot cheaper (and also give you more points of failure/stuff to monitor/maintain).