Diesel outboards

The fact that the BSS has "onerous" requirements regarding propane on board has nothing to do with the engines. Those requirements will apply even if you buy a dedicated LPG outboard like a Lehr or Tohatsu.

I have no cristal ball but I can see what is happening today. Electric is still only viable in fringe applications and expensive. But, a lot of people discover their normal use patterns can be met with electric vehicles, so it gains market share. This will continue, and prices will go down (Dacia is going electric for example).
Commercial traffic remains diesel, and electric has a hard time gaining market there (some public transport applications).
Private use has seen a slight increase in gasoline engine sales, owning to several factors. LPG remains about the same overall, maybe a slight increase EU wide but with strong regional variation. CNG same thing, popular where the infrastructure already exists, but otherwise stagnating. Hydrogen is still in its infancy.

For boats, anything except diesel and gasoline is a fringe application right now. Gasoline rules outboards because of the power/weight ratio, and diesel, inboards because of range and percieved safety. I don't expect this to change in the near future, even if lighter weight diesel engines are possible (Schrick had one developed for drones, but those got bigger and now use turbopros).

 

It's the permanent propane installations for cooking & heating that cause grief. An outboard with a couple of 14 Kg cylinders in a locker vented to the outside of the vessel is practicable & easy to maintain in a safe condition. The Tohatsu unit is 5 hp only. The Outboard Expert: Tohatsu Propane Outboard Engine - boats.com https://www.boats.com/on-the-water/the-outboard-expert-tohatsu-propane-outboard-engine/
A 25 hp would suit my purposes. LEHR 25 hp 4-Stroke Outboard Engine – LEHR https://golehr.com/lehr-25-hp-4-stroke-outboard-engine/

As for hydrogen, it's fraught with complications & expensive to obtain. IIRC, Bill Gates built a plant or plants in order to fuel his latest motor yacht. Yes, he's incredibly rich & has no need to concern himself with the lousy economics, but why bother? Does he think he's going to live forever? OTOH, commercial fishermen are concerned with fuel costs & watching the multi engines sport fishers that use a gallon every 400 metres at Haulover Inlet suggest there's a huge market for 300 hp Cox Marine outboards on those transoms.

It's tough to make predictions, especially about the future.

 

Details matter my friend. A 25hp engine can not use household propane cylinders, it uses dedicated liquid draw tanks (and Lehr mentions it, but without explaining). This means no swapping cylinders, you have to carry your tanks (wich can look like normal cylinders if you want) to the refill factory, or refill them illegally at the next LPG petrol station.

A 300HP yamaha outboard weighs 250kg. The weight of the naked diesel engine they are planning to use is 340kg and the driveleg will easily be another 60kg. That is 150kg weight increase per engine, maybe tolerable for a single engine installation, but for a boat such as you show with 3 engines it would mean 450kg excess weight right on the transom, plus the associated reduction in speed or payload. The best part will be the price, they have chosen a boutique engine manufacturer and I can guarantee the price will leave you stunned. I am sure they will find some customers, but it will not become mainstream.

 

I mentioned the price earlier; £35,000 plus VAT each, but a 25% increase in range is worth considering. OTOH, smaller fuel loads would reduce payloads. Safety is important as well. Diesel is safer than ethanol petrol. In addition, servicing intervals are apparently longer, according to the website. That's a cost saving consideration.

Like all things, there are judgments to be made. IIRC, Mercedes Benz diesels had most of the taxi business in Germany, Whether that is still the case, I don't know, but there were clearly good financial reasons for the choice. Until totalitarianism triumphs, the free market will decide.

http://c7tmt1feswm1z4gtt3clxm81-wpengine.netdna-ssl.com/wp-content/uploads/2015/01/tank_options1.png

 

So it costs £42,000, wich is double what the similar power petrol outboard costs. I am sure they will have customers, but as you say, the market will decide how many.

I am not sure what you mean with the picture from the Lehr website. The info page for the 25HP engine clearly states one has to use liquid pickup tanks.

 

Just above "22 & 31 lb Liquid Draw Composite Tanks" is "Fuel Tank Type: (Optional)". The equivalent 20lb 5 Gallon Standard Tank of Propane is B. https://www.boconline.co.uk/shop/en/uk/gas-a-z/propane/propane-cylinder

 

The only "optional" is the size of the tank not the liquid draw part. A 25hp engine can not run full power on a standard household propane cylinder simply because such cylinders are to small to sustain the needed evaporation. Basicly the cylinder will freeze over and the supply of gaseous propane will stop. The only way to use one would be to invert the cylinder (so you draw liquid), wich is considered unsafe. Otherwise you must use a much bigger propane tank that can sustain the needed evaporation rate. Engine heated evaporators were invented to circumvent this exact problem.
Anyway, a 14kg cylinder will give you about the same range as a 20-25l petrol tank (varies with exact gas composition and engine optimisation) and filling at an Autogas station is common enough even if illegal. If you want to be legal you fix the tanks in the boat and trailer it to the gas station. If that suits your needs it is a good solution.

 

I guess you could water bath the tanks in a boat.

 

There are no piston aircraft engines with transmissions. They are all direct drive. Well, perhaps a few experimentals, but 'transmissions' is not a thing to have problems in aviation.

 

I spoke with BMC Best UK Price Buy Inflatable Boat Rib Outboard Motor Yamaha Mercury Zodiac Package - LEHR ~ Propane Motors https://www.ribs.co.uk/outboard-motors-yamaha-mercury-mariner-suzuki-tohatsu-lehr/lehr-propane-motors/
They confirmed to me that the standard Propane cylinders that are used for BBQs etc., are suitable for Lehr outboards. Icing is not a problem; the only problem is that a 25 hp would have to be a special order with a 6 months wait.
Find a Stockist - Propane & Butane Gas Stockist Finder https://www.camping-gas.com/find-a-stockist/#container_top

 

Well if they say so, we must believe them, after all they have the technical data on hand. But I sure want to see it.
What's up with the lead time? Is Parsun backlogged? Or do you actually have to wait until Lehr reorganizes (as I said the rumor is they are down, the US site certainly is).

 

Parsun backlogged? About Us – LEHR https://golehr.com/about-us/

 

You think Lehr has it's own factory in the US?

 

Thielert was never an experimental engine. Nor was its replacement the Austro engines. Lycomings 120CI diesel also has a reduction drive, as well as a timing belt and common rail injection. And I guess you want to dismiss all the certified Rotax 912 and 914 engines ever produced. More than likely more of those been sold in new airplanes than everything else combined in the last 15 years...

I should also mention that all variants of the Allison V 1710 and Merlin engines had a propellor reduction drive (they had to so that they could drive those huge props) but the torque pulses of a high compression diesel engine are particularly difficult to deal with.

 

Lehr has it's own factory in the US? No idea. You just mentioned the US site was down. The link works for me. If Parsun is the manufacturer for Lehr, should we expect an OEM propane range of outboards from them as well?

Just found this. Lehr suggests a fork lift truck tank for the 15 hp. That would help in sourcing the appropriate agencies for refilling the tanks.
http://golehr.com/downloads/LEHR_15hp_Operators_Manual.pdf