Hi Tony and thanks for your reply. We, too ran vehicles with the mix as you describe, made up of DERV (red diesel) and recycled chip fat. I didn't do the hard work myself, recycling the used cooking oil, as my mileage was just a bit high. If HVO takes off, then our diesel engines should be safe for a while. The sanity of "Food Crops for Fuel" is not a discussion for this forum, luckily.

On the electric motor thing, I am undecided although, having had the idea of a generator aboard (we only ever anchor unless we have no choice, which means shore power is unknown to us) I am interested to see Arne's comment that it has been done. We are about to renew efforts in selling our (now gaff rigged) Cornish Crabber ANNIE and part of a sale could be the very little used Nanni diesel we have in CONSTANCE, as ANNIE's Volvo is possibly older than she is - 38 years! It goes well and has never let us down but.... So this would leave us with a clean sheet on deciding how to propel CONSTANCE if in a hurry or a calm. Ideally we would K.I.S.S, and just make the change to HVO for CONSTANCE.

Thanks again for all interest and comments on this thread.

Pol

Very many thanks, Arme, Graeme and Tony

Apologies that I wasn't clearer about the "fumes" problem. It really is just exhaust fumes that are objected to. Especially motoring with a light following wind. We don't get a lot of engine smell of any type below. The installation is in quite a tight-fitting but ventilated box, so, as Arne has pointed out, it is mostly self-ventilating. And the motor is pretty unused, so it hasn't got the little weeps and seeps yet. The breather is led back to the crank case. 

Arne mentioned the possibility of leading the exhaust under water. In fact, with her narrow stern, she squats down by  several inches under power so the exhaust is virtually under water. I'd be happier burning veg oil with this going on, as I imagine the exhaust gases are a little less harmful than those from red diesel/DERV.

The discovery of HVO (hydrogen-treated veg oil) as an alternative to diesel is of interest because using that will eliminate all but the takeaway-shop smell, which I know from burning a percentage of veg-oil in an ancient Isuzu Trooper makes a big difference to those who are especially averse to the smell of diesel exhaust fumes! I am told by the internet that HVO is safe to use in all diesel engines, and that there are a few truck fleets using it now. The price is a little higher than road diesel in the UK, but we use so little in a season on the boat that the benefit will far outweigh the extra cost.

I only discovered HVO when looking into using veg oil in my Yanmar diesel-powered mobile sawmill. For commercial vehicles/plant the rules changed recently and I am no longer allowed to use red diesel/DERV for this. 

Thanks again. Pol.

Hi Tony, not intending to be argumentative. The speech marks were merely to emphasise that various types of "fume" have arisen in the course of  the discussion. I think you have now clarified the question perfectly.

It is not clear exactly what Pol means by "diesel fumes". I am not sure that he literally means the smell of diesel fuel, but if he does, then your suggestion of the tank breather or a fuel leak might well be right on the money.

I think everyone is trying to be helpful. The problem is, we can't smell it via the internet, so we are all, to some extent, guessing. Its fortunate that Pol has found someone qualified, with whom he can discuss the problem further, if he wants to. The rest of us can now listen and learn.

The crank case breather emits not only "oil fumes" but also any blow-by which gets past the rings, which is why an old or well-worn engine smells fumey when it runs. As already stated, it is usual to direct those fumes from the breather back to the engine air intake.

Tony wrote: but that would vent oil fumes and not diesel fumes...  "diesel fumes"? If its the smell of diesel fuel then it won't be the engine. There would have to be a fuel leak somewhere between the tank filler cap and the injector pump. 

Can Pol be a little more specific about the term "diesel fumes"? Is it the smell of diesel fuel?  Is it the smell of exhaust?  I would have thought that an exhaust leak or a fuel leak would have been diagnosed easily enough by someone as experienced as Pol. My guess is its probably just the smell of a tired engine with the odd oil leak, which gets smelly when hot, possibly exacerbated by fumes from the crank case - and perhaps a crew particularly sensitive to those sorts of smell.

It might sound obvious but you need to consider if the exhaust is drifting back into the boat too. Pleasure boats all seem to have an exhaust pipe which bubbles away at about the waterline down about the transom somewhere. Its probably the worst place for it - I don't know - all the longline boats in our local fleet had dry exhausts which vented upwards, overhead, for exactly that reason, and exhaust fumes were never a problem. The little pleasure boat I am living in now is no longer running, but the last trip I did with it and its tired old Bukh - it had a crude fixed shelter over the cockpit - and it dragged exhaust fumes up from the transom something awful.

I happen to like diesel engines very much, and the engine smell doesn't bother me at all - but for reasons which are not entirely rational, I plan eventually to go entirely away from fossil fuels this time, and I too will be following Paul's electric conversion with great interest. 

I'd like to try and do without a generator though. I am rather more inspired by Kurt (Mehitabel) and learning to live within the limits of solar, in the same way as we learn to work within the limits of wind and tide and get our satisfaction from that. The prototype will be a Yamaha 9.9 and if that does the job, then step 2 will be (hopefully) to swap it out for an electric equivalent, to be used stringently. Lucky for me though, I'm retired and won't have to be under pressure of time or work requirements - I realize not everyone is so lucky.

A diesel engine has a "breather". (In fact probably any 4-stroke engine will have one). If I recall correctly, it is actually a breather for the crank case. In the case of a Ford diesel, it is a simple vent, about 1/2" diameter, located on the rocker cover. There's usually a bit of fume coming from there, especially with an older motor, and its usual to run a hose from the breather back into the intake manifold (via the air filter, if I recall correctly) so that any fumes from the breather get consumed by the engine itself. (My diesel mechanic friend used to have a joke: "the more stuffed the engine is, the better it will run!")

Have a look for the engine breather and make sure it is not venting directly into the engine compartment. This may help somewhat.