RNLI 2 stroke engine better than four stroke?

[jb100]

I was just wondering why the RNLI continue to use 2 stroke over 4 stroke on their inshore lifeboats - 50hp , 30hp and 15hp (I think) have all remained as 2 stroke.

Having recently bought a 4 stroke 20hp I was impressed with the weight at 51kg which is very similar to my old 20hp 2 stroke. However having to pull the four stroke 2-3 times before it fires up due to battery less fuel injected system is slightly annoying . The 2 stroke pretty much always fired on the first pull which was very reassuring when launching from a beach. It seemed to have more life to it if that makes sense!

Is this one of the reasons for keeping the 2 strokes going within the rnli? What are the others?

cheers

[chipko]

To be honest think it’s the simplicity of the motors as they are able to restart a submerged motor after righting the capsized boat, and wipping the plugs out! Mariner do make some mods to their RNLI spec motors to help with this. The larger Atlantic Ribs seem to run twin Yamaha four strokes though.

Is your efi four stroke a Mercury/Mariner per chance? Ours also takes a concerted effort to start hot or cold, pretty annoying really. In contrast our little two strokes, when warm, start with only a whiff of a pull.

PS Welcome to the forum.

[Steve509926]

Originally Posted by chipko

Is your efi four stroke a Mercury/Mariner per chance? Ours also takes a concerted effort to start hot or cold, pretty annoying really.

Hi and welcome.

+1 for the 20hp Merc efi being a PITA to start, at least 3 or 4 good pulls. Not noticed when it's hot though, normally starts 2st or 2nd mid pull.

[User name]

I don't know specifically why the RNLI favour them, but 2 strokes make more power, are much simpler, lighter, easier to rebuild/service and they'll generally start even as they wear and lose some compression. They don't rely on an oil sump for lubrication, where 4 strokes do and can run the oil into the exhaust/inlet if inverted and it'll be a nightmare to start afterwards.

You can quickly drain a 2 stroke engine after being fully submerged, drop a bit of oil into the bore, turn it over manually and then it'll start back up without much fuss. Do that with a 4 stroke and the oil will be contaminated and will need changing before attempting to start.

It's not all positives with 2 stroke though. They wear faster than 4 stroke as they're higher revving and not as well lubricated. The 4 stroke oil helps cool as well as lubricate too. They aren't as economical or as friendly to the environment either. The RNLI, much like most gov organisations are likely servicing them to a schedule rather than an hour count so they're probably still immaculate by the time they're being serviced again. Your average Joe wouldn't look after them as well.

[jb100]

Thanks for the replies

My Tohatsu is a 20hp 2020 Fuel Injected 4 stroke - It always starts on the 3rd pull reliably and I have been told this is due to battery-less fuel injection needing priming.
I also run a Tohatsu 25hp 2 stroke from 1997 and in contrast , first pull, there is always firing and then choke in 2nd pull and its running. Considering this engine is 30 years older its slightly frustrating that the 4 stroke is behind in this regard.

The new Tohatsu 20hp 2023 model is 43kg so I think its actually lighter than most new 2 stroke 20hp outboards so weight can no longer be a factor for RNLI

The theories on the submergence recovery and easier servicing are probably correct. I am very tempted to try and find a late 2 stroke to replace the 4 stroke. Whilst I like the fuel efficiency and smoothness there is something nice about rapid starting and also 2 stroke servicing easiness. Its also very nice having access to a manual choke which gives much more control over starting / flooding etc

[Pikey Dave]

Originally Posted by User name

I don't know specifically why the RNLI favour them, but 2 strokes make more power, are much simpler, lighter, easier to rebuild/service and they'll generally start even as they wear and lose some compression. They don't rely on an oil sump for lubrication, where 4 strokes do and can run the oil into the exhaust/inlet if inverted and it'll be a nightmare to start afterwards.



You can quickly drain a 2 stroke engine after being fully submerged, drop a bit of oil into the bore, turn it over manually and then it'll start back up without much fuss. Do that with a 4 stroke and the oil will be contaminated and will need changing before attempting to start.



It's not all positives with 2 stroke though. They wear faster than 4 stroke as they're higher revving and not as well lubricated. The 4 stroke oil helps cool as well as lubricate too. They aren't as economical or as friendly to the environment either. The RNLI, much like most gov organisations are likely servicing them to a schedule rather than an hour count so they're probably still immaculate by the time they're being serviced again. Your average Joe wouldn't look after them as well.

Agreed, if I was an overfunded organisation with virtually un-limited resources, that had full time in house mechanics looking after 2-3 boats, and someone else was paying for the fuel, then 2 stroke is the way to go. 2 stroke tech is inherently suited to the marine environment imho.

[chipko]

OK, I’ll blame Tohatsu then as all Merc/Mariners up to 30hp are made by Tohatsu, only the hoods and tillers on some models are different.

Annoyingly the Suzuki 15/20hp, the first of the battery less efi’s, suffer no such problems and start first pull with considerably less effort.

[jb100]

Would you say then that a 2 stroke requires more servicing than 4 stroke?

[Pikey Dave]

Originally Posted by jb100

Would you say then that a 2 stroke requires more servicing than 4 stroke?

I’d say the opposite if the 2 stroke is regularly used. Assuming that we’re talking about carbed 2 strokes v EFI 4 strokes, then as long as the 2 stroke is well used & the correct oiling is used, then the 2 stroke will require less maintenance, in that there’s no engine oil/filter to change, no valves to adjust etc.

[chipko]

Originally Posted by jb100

Would you say then that a 2 stroke requires more servicing than 4 stroke?

Definitely not, we’ll certainly not the ones we’ve had or even run now.

The good thing about the new fangled portable efi four strokes is no pesky carburettor/fuel issues to worry about with the infrequent use outboards get.

[User name]

Defo less maintenance, but ultimately a shorter lifespan on the piston, bores etc on a 2T. Much of a muchness though, as a top end rebuild on a 2T is so much cheaper and easier to do than on a 4T.

[chipko]

Can’t argue with that, but wish I had the time to actually wear out my two strokes. I’d hazard most leisure motors die due to lack of use. [emoji51]

[jb100]

So 2 strokes:
require less maintenance
easier to work on
faster/quicker acceleration
start more easily
can be recovered if submerged

The only disadvantage is length of service - worn out more quickly? Ive got 2 strokes that are 20+ years old with very similar compression/ PSI to when new - they start rapidly. Ive had 4 strokes that are 10 years old that are virtually impossible to start due to a lack of choke.

I can definately now see why RNLI continue with 2 strokes !

[beamishken]

Small two strokes make far more sense than modern efi engines, folk think there not going to have fuel or carb issues with efi when actually the opposite is true, small outboards tend to work in relatively wet environments where water ingress into fuel or the engines themselves is highly likely. With a car two stroke you pump the water out of the cylinders, drain the carb & off you go hence why the rnli use them. You wont be draining an efi quite so easily. The usual two stroke problem is when its stood for a long time the fuel leaves jelly like residue in the float bowl which then blocks the jets. Again its not a huge issue with the simple 2 stroke carbs, a strip down & ultrasonic clean & off they go. Efi engines are a total different animal, water residue sat in vst tanks or in injectors will soon ruin them & end up with expensive repair bills you cant just strip & clean an injector & they cost big money to replace. Very few folk manage to wear out small outboards, they thrive on use but I'd wager in a few years time as small efis get older many will be scrapped due to fuel system faults, almost certainly wont last as long as some old 2 strokes. Once over 40-50hp the 4 strokes start to win, larger drier boats mean extra filtration & better fuel storage make it easier to manage fuel quality & the extra fuel efficiency & range is a big bonus. Hence why larger rnli boats have 4 strokes

[Steve509926]

A side question to improve my knowledge.

Why do some call 2 stroke & 4 stroke, 2T & 4T. Where does the "T" fit in?

[Spongie]

Originally Posted by jb100

I was just wondering why the RNLI continue to use 2 stroke over 4 stroke on their inshore lifeboats - 50hp , 30hp and 15hp (I think) have all remained as 2 stroke.

Having recently bought a 4 stroke 20hp I was impressed with the weight at 51kg which is very similar to my old 20hp 2 stroke. However having to pull the four stroke 2-3 times before it fires up due to battery less fuel injected system is slightly annoying . The 2 stroke pretty much always fired on the first pull which was very reassuring when launching from a beach. It seemed to have more life to it if that makes sense!

Is this one of the reasons for keeping the 2 strokes going within the rnli? What are the others?

cheers

The RNLI are now using 30hp Four Stroke Tohatsu's on boarding boats. the 15s and 50s still remain Mariner (but really Tohatsu) two Strokes

[beamishken]

Originally Posted by Spongie

The RNLI are now using 30hp Four Stroke Tohatsu's on boarding boats. the 15s and 50s still remain Mariner (but really Tohatsu) two Strokes

Presumably as an organisation they need to be as green as possible & managing fuel quality on a boarding boat is probably easier than an actual rescue boat inversion protection probably very difficult on a 4 stroke though so presumably they will continue with the two strokes as long as practical

[Pikey Dave]

Originally Posted by Steve509926

A side question to improve my knowledge.

Why do some call 2 stroke & 4 stroke, 2T & 4T. Where does the "T" fit in?

I think it’s a French/continental thing “Temps” = time

[willk]

Originally Posted by Pikey Dave

I think it’s a French/continental thing “Temps” = time

Passive Aggressive Remainer dog whistles I say...

[Steve509926]

Originally Posted by Pikey Dave

I think it’s a French/continental thing “Temps” = time

Sorry, am I being thick? still don't get it.

Originally Posted by willk

Passive Aggressive Remainer dog whistles I say...

quoi?