Unequal size exhaust hose and thru hull connection

After a repower the new wet exhaust hose has an ID of 2". The existing bronze exhaust thru-hull which is fiberglassed into the transom has a barb OD of 1.75".

Want to avoid replacing the quality bronze thru-hull. Anyone know a secure method to connect the two? Or a supplier of bronze or composite reducers in these diameters?

 

Hi Jason, maybe you could use a shortish length of the original hose on the barb first, with the inside diameter cut to a taper so as not to cause excessive turbulence at the diameter restriction, and then fit the larger hose over it, and clamp at the barb / tail as usual. If the smaller pipe fits inside the larger pipe, that may be an easy solution.

 

Make sure that you are not creating unacceptable levels of back pressure.
The motor’s specifications should spell that out clearly.

 

The exhaust should never reduce towards the outlet. Also, a 2 inch pipe has 31% more section area than a 1.75 in pipe.

 

The manifold outlet has some thickness, so again a maybe, run the inner hose all the way up the outer, to but up against the manifold outlet, so no appreciable diameter discrepancy during flow. Could be difficult if a tight fit between pipes.

 

The previous hose was of small diamteter. The fitting on the stern and the manifold will have the same ratio difference. 31% reduction in flow is unaceptable.

 

Could you use the old bronze outlet for a bilge pump outlet, with a high loop to reduce chances of water ingress, and fit a new bigger exhaust outlet in a convenient place ? Then you don't need to plug or remove the original, and it's still useful.