Outboard vs Diesel Inboard

[Swift]

Just saw this. I hope the NSW Rural Fire service did a proper risk assessment before they took delivery of that boat with twin outboards! The fools!
https://www.flashover.com.au/how-worono ... nsw-fires/

While I'm logged on I thought I'd add some thoughts to the debate I was initially excited to open the link about the boat fire but then disappointed because the boat that exploded was an inboard not an outboard. This was a little different because Inboards tend to be those older cabin cruisers that explode every so often. The ones without the modern benefits of Sealed Carbys or fuel injection, bilge blowers electronic ignition Not to say that all old cruisers are time bombs, there's a beautiful well cared for 50 ft Halvorsen cruiser built in 1947 still going strong. (Ray White Marine) A great example, 73 years has got to count for something

Now on the other hand small outboards are engines that tend not to go boom. Not that I could find anyway. Not acording to an outboard mecahnic I know. I found some cases where the engines had small fires due to electrical problems, fires that were quickly put out with a fire extinguishers There was one guy who was on a RIB with no extinguisher so he chucked the motor overboard. I guess we will never know the cause of that fire!. Some of these fires didn’t even involve petrol at all, The motors were largely undamaged. Small outboards have tiny carbys with small float bowls, they don't have high pressure fuel pumps and they have fuel lines that are self sealing when disconnected. I’m not saying more serious fires don't happen, I'm sure that out there amongst the millions of outboards, particularly the older ones that some bad things have happened. (you would think). It will just take someone with more interest and patience than me to find them.

I should just explain that I keep referring to small outboards, that's because apart from driving other peoples boats I have little experience with large outboards. Except maybe the big 180hp Honda outboard, the one with the same motor as the Honda Euro I used to own. I know that motor and I bet that the outboard is every bit as dangerous as that car!


Yeah but ain't that there petrol tank gunna blow one day and kill yer all? I think Michael has more than adequately answered that one. Only a fool would put electrical devices or wires in the same locker as the petrol tanks. Oh! and diesel has a 60c + flash point? Really? That one almost slid by me. Measuring flash point is highly complicated, how the liquid is heated how far above the the sample cup the ignition source is, the altitude etc. Results are variable. That’s why industry relies on standardised testing like as detailed in the publication Sea Transport of Petroleum, more details : https://en.wikipedia.org/wiki/Flash_point. (Transport by sea! get it! ) Flash Point Petrol 43c Diesel 52. Now 9c difference is is still significant but much less than some would have you believe. Can an overheated engine room get up to 52 C ? I don't know….maybe?

For anyone that remains unconvinced I expect that after their next sail that feeling you get of having had a great sail the right way, the safe way suddenly turns into terror as they contemplate driving home sitting trapped between a hot motor and 70 or more litres of the devils petrol.

Cheers Keith

[steve]

Keith,

You provided a link to a website which lists some flashpoints. The website states that the flashpoint of petrol is minus 43C, rather than plus 43C as you imply. Therefore the flashpoint of petrol is 95 degC lower than that of diesel. Petrol and diesel are very different.

There are significant differences between the dangers presented by outboards and those presented by cars. One difference is due to the temporary pipes between outboards and their tanks. Another is the way outboard tanks are refilled.

As an owner of an outboard I am always conscious of the danger the petrol presents but I consider the danger acceptable. Most diesel inboard owners carry petrol for the outboards on their tenders so they also need to be conscious of the dangers.

Steve

[Miker]

Mike;

I must respectfully disagree with your comment about the relative flammability of petrol and diesel. Petrol has a much lower flashpoint (around -40C) meaning that at ambient temperature it readily evaporates, causing vapours that can easily ignite from even a tiny arc such as in a 12VDC switch. Explosions on petrol-fuelled boats are far from unknown (https://transportsafety.vic.gov.au/mari ... refuelling).

Diesel has a flashpoint of about +60C, so at ambient the quantity of vapour is miniscule and not ignitable. The biggest risk is from an aerosol spray from a minute high pressure leak contacting a very hot (exhaust) surface.

Cheers, Graeme

I don't disagree with the relative flammability between diesel and petrol, but they're both flammable and petrol obviously more so. My point was that if you understand the dangers, then you theoretically should have no problems. I water ski raced behind plenty of inboards, they were time bombs if not cared for properly and blowers used correctly every time. Any enclosed fuel that has the potential to ignite is a problem. It just needs to be looked after and respected, and yes petrol has it's obvious concerns if not handled correctly.

The biggest risk is from the person handling the equipment not understanding the dangers and mitigating them.

[PinotNoir]

Great discussion here guys.

I've just bought a Top Hat, REB, in Avalon. She has an inboard Diesel but I also wanted to mount an outboard on a swing mount on the transom, like Michael mentioned in this post.

Was there anything special you had to do? Who did that for you? Can you send me some photos, or post them?

REB needs a bit of work, mostly on the rigging and to her running gear, she has some oil in the bilge and water in the engine bay, but her bones are great.

Cheers,
Andrew

[Phillip]

Just one question Andrew,

What's wrong with your diesel engine?????

What mark is REB?

[PinotNoir]

Hi Phillip,
It runs, but will not throttle up, it is pressurising into the crank case, which could indicate that the rings are gone?
I would consider a rebuild but the cost of removal and reinstalling is quite high and a bit of a barrier. I would like to rebuild it one day but right now an outboard mounted on the transom seems like a good option, given all of the other works required to get her back into the wind.
I've sourced a transom mount and a long shaft 15hp outboard from the 90's that has very few hours on it. It, like my OB on the tender is 2 stroke.
Do you have any experience on the Solé Mini 2 diesel?

Also, I think she is a Mk III, I have a plan and a sail plan but no text outlining the details. She has a relatively vertical transom and is flat above the companion way. Are there any critical dimensions or characteristics that I could use to determine what she is? She was sold to us as a Mk III.
Cheers

[Phillip]

Andrew,
Look at the post "Top Hat History"

There you will find a diagram that will help you to determine what mark she is.

[Miker]

Hi Phillip,
It runs, but will not throttle up, it is pressurising into the crank case, which could indicate that the rings are gone?
I would consider a rebuild but the cost of removal and reinstalling is quite high and a bit of a barrier. I would like to rebuild it one day but right now an outboard mounted on the transom seems like a good option, given all of the other works required to get her back into the wind.
I've sourced a transom mount and a long shaft 15hp outboard from the 90's that has very few hours on it. It, like my OB on the tender is 2 stroke.
Do you have any experience on the Solé Mini 2 diesel?

Also, I think she is a Mk III, I have a plan and a sail plan but no text outlining the details. She has a relatively vertical transom and is flat above the companion way. Are there any critical dimensions or characteristics that I could use to determine what she is? She was sold to us as a Mk III.
Cheers

Hey Andrew, pressurising the crank case may not necessarily be rings. If the engine hasn't been started for a long time, there may be a problem with the crank case breather system. That's the first place I'd look. I'd also do a compression check, just to see whether the compression is indeed low or not. I know, it's fiddly, but may save you a few bucks if you don't really need to pull the engine out/down.

On the transom hung outboard, a 15hp may be too much, not necessarily in power, but in weight. Remember, you'll add 20 odd kgs to the transom and under power you may bury her bum too much. You'll also need to make sure you put a backing board inside the transom, as they weren't built to take more than a boarding ladder. With mine, before I installed the backing board, I could see the transom flexing under rough conditions, to the point where there are fine cracks in the gelcoat. I used approx 20mm marine ply, epoxy coated and glued in place from the inside, then bolted through the transom to the bracket. It needs to be at least three times the size of the bracket mount.

I'm in Careel Bay and have seen REB in Clareville a few times, I just looked up an ad from DBY sales and she's definitely a MkIII. Looks like a nice fit out as well.

That makes two new owners in my area, REB and Horizon. Welcome!

[Phillip]

Michael is spot on about the work required to hang an outboard on.
The Mark 1's have a transom that's over 10mm thick but sadly Formit skimped on resin to increase profits.

May pay to have a diesel mechanic, not a marine one as they cost more for the marine bit, inspect your diesel engine onboard.
As Michael said it maybe a minor thing easily fixed.

[Shaun]

Welcome Andrew,
I would investigate the inboard, and try to get it to working well, before going along the outboard road.
I prefer the outboard in the well, the only drawbacks in the we'll are , possibly more exhaust fumes, and not being able to lift prop clear of the water, without some sort of lifting system while sailing.
You'll find an "ultra long" shaft better on the transom, it will allow you to mount it slightly higher, which decreases the chance of it being dunced underwater.
If you can try to make the inside reinforcements of the transom all the way to each side, even if it's in a couple of pieces, fibreglassed in, with an additional layer centred where your mounting the bracket. Otherwise an inside pad as big as Miker said will be fine, I did an inside pad about 3 times the size of the bracket, it was fine in all conditions, I just noticed a few hairline gel coat cracks around the bracket, as it flexed.