Timber or steel for engine mounts

[banjoship]

Originally Posted by GILow

Steel angles with timber infills. Engine is sitting in position, waiting for a friend to make the coupling adapter.

Attachment 211056

Matt,

It is hard to tell from the photo, but it appears that your new engine is situated low in the bilge. Low is good, of course, however it can have implications for the exhaust.

Trying to judge from my own S42, I would guess that the top of your engine/exhaust manifold will be about 300+mm below the waterline??? If I have got that right, that implies a big riser from the manifold, before injection of raw water.

I am sure you have thought this through. And it is very difficult to judge positions from the photo. In my case when I repowered, the manifold was about 100mm below waterline, and I made up a 450mm riser, top neck about 300mm above waterline. (The Ford that I replaced was a taller engine, with manifold above the waterline).

As a side point, my syphon breaker on the raw water injection hose is a hose to the very top of the cockpit drain below the engine instrument panel, when I start the engine there is a visible flow of water into the cockpit drain. I have the flow set that there is a sputter of water into the cockpit sole at cruising revs. great telltale. This arrangement is good for high centre cockpits.

Best
Lee

[GILow]

Originally Posted by banjoship

Matt,



It is hard to tell from the photo, but it appears that your new engine is situated low in the bilge. Low is good, of course, however it can have implications for the exhaust.



Trying to judge from my own S42, I would guess that the top of your engine/exhaust manifold will be about 300+mm below the waterline??? If I have got that right, that implies a big riser from the manifold, before injection of raw water.



I am sure you have thought this through. And it is very difficult to judge positions from the photo. In my case when I repowered, the manifold was about 100mm below waterline, and I made up a 450mm riser, top neck about 300mm above waterline. (The Ford that I replaced was a taller engine, with manifold above the waterline).



As a side point, my syphon breaker on the raw water injection hose is a hose to the very top of the cockpit drain below the engine instrument panel, when I start the engine there is a visible flow of water into the cockpit drain. I have the flow set that there is a sputter of water into the cockpit sole at cruising revs. great telltale. This arrangement is good for high centre cockpits.



Best

Lee

Lee, you know your swannies well and you are completely correct with your height perception.

Actually, if you look carefully in the background you can just make out the raw water strainer which I had installed so that it was just fractionally above the waterline when you opened the lid to clean it. However, the waterline is now 220 mm lower than that line as I’ve removed so much weight from the boat.

Anyway, I’ve got some time up my sleeve thanks to Covid-19 so I will get a chance to weld up a nice big exhaust riser if I want to go that path. It was certainly the preferred option from Beta Marine though they were also happy with a syphon breaker between the engine and injection elbow.

If I go with the riser it will prevent me from reclaiming that space for storage, so maybe I will stick with a syphon breaker and use your clever tell-tale idea instead.

[jimbunyard]

Unless you're sailing in dead flat conditions all the time, having an engine with the exhaust manifold outlet 100mm below the waterline without an at least 200mm riser would scare the bejesus out of me.

Though few want to believe it, see https://www.cruisersforum.com/forums...re-231189.html

[GILow]

Originally Posted by jimbunyard

Unless you're sailing in dead flat conditions all the time, having an engine with the exhaust manifold outlet 100mm below the waterline without an at least 200mm riser would scare the bejesus out of me.



Though few want to believe it, see https://www.cruisersforum.com/forums...re-231189.html

I’ve waded through a bit of that thread but I really cannot find the connection? Can you point me to the relevant bit?

[jimbunyard]

Some might say none of it is relevant, but I think it all is.

The overall point is that a poorly designed exhaust system can cause a catastrophic failure; in Hunterdog's case (from the information we can see) it appears that (maybe) an improperly fastened rod bolt fell off, an oversized exhaust system (thus not developing sufficient exhaust velocity/volume), with no riser (see post #120), allowed water to enter the ex manifold and subsequently the forward cylinder when the boat surfed down a large wave, destroying the engine. (others disagree)

Impossible to say if a riser or a properly dimensioned exhaust diameter or a better overall exhaust system design would have prevented the Beneteau fiasco, but for your application, given the control you have over the design, I can't imagine an installation where seawater could conceivably have unimpeded access to the exhaust valves, which, without a riser and with a below-the-waterline exhaust manifold outlet, it at some point will certainly have.

In an excess of caution on my boat that never goes offshore, I have a siphon break in the raw water line between the r/w pump outlet and the heat ex inlet, a ten inch exhaust riser, and an exhaust riser where the exhaust exits the hull. But perhaps I've seen too many boats sunk or almost sunk by poor design, maintenance and neglect...or just unfortunate concatenations.

[GILow]

Oh... right...

My boat is totally different and I can easily make my exhaust safe for the engine.