Exhaust joints

[Simonp]

Sorry I couldn't come up with a more interesting title! Its an important subject nonetheless.

I have the Simmonds with the Daimler V8 and have nearly always suffered with exhaust joints that fail and then flood the boat. There are two flexible joints on the straight part of the exhaust pipes ( and 2 pipes). On these joints I have tried various radiator hoses - but these have either torn or burn't through - then tried a higher temperature hose but that was too stiff and tore as well.

Think I may have a combination of problems - firstly the engine is moving about too much side to side and for and aft with the thrust. Currently has a two blade prop which gives much greater performance/acceleration/bite but the engine is trying to join me in the cockpit! - now has new engine mounts. With this prop the engine is running at 5000 rpm at full speed and I guess of course the exhaust (water cooled and the flow seems ok) is getting much hotter - engine temp is fine.

Am planning to revert to 3 blade prop which is much smoother - gives less acceleration but still quite good speed at 3500 rpm max (cooler exhaust). Should I use convoluted hose which has more give in it or is there a standard marine application that has passed me!

Any help and thoughts appreciated. I really would like to get the boat back on the water but it will be doing the rounds of the Daimler SP 250 50th anniversary car rallies this year and will also be appearing on the Daimler stand at the Classic Car Show in November.

SimonP

[puddleduck]

Hi Simon,
Normally in large powerboats and motoryachts there is a metal exhaust bellows, ie some kind of flexible aragement to overcome the exact problem you are describing, then a rubber hose connection somewhere between the through-hull fitting and the fixed part of the exhaust. Marine exhaust hose is high temperature stuff and usually has a wire vulcanized inside the 'laminate' of the hose construction, but as you say this makes it very stiff.

Is there any way you can move the rubber hose connection further away from the heat source? Offshore raceboats employ jacketed exhausts, so that the ehaust is cooled without upsetting back pressure by pumping loads of water in, but it's a very expensive option.

Can you straight after the manifold extend the metal part of the exhaust so that it has a chance to cool down a bit before it attaches to the rubber hose? As the water injected into the exhaust is already hot, having been around the engine, try fitting a supplementary bypass hose just after the hull water intake and inject cold water directly into the exhaust - there is usually ample amounts coming up through the intake due to the ram effect.

cheers, Chris H.

[Simonp]

Thanks Chris - I can't believe I hadn't picked up that marine exhaust hose is a running line and can be bought most places. Anyway we are now fitting this and hopefully it will solve the problem permanently. I don't want to have a boat full of sooty water again - the mess is unbelievable!

SimonP