Mercedes engine in LM27

[achterliek]

We came across a LM27 recently, which we bought after short discussion. It has a OM636 Mercedes Diesel engine (45hp) fitted. This appears to be somehow uncommon. Anyone with a similar setup ? Which kind of propeller would be needed ?
I think this was a retrofit and I am not sure, if the previous owner also took care of the propeller dimensions.

[Sula]

Congratulations on your acquisition of an LM27.

I am sure this engine will have been a retrofit, and I think it is a poor choice of engine for the LM27 because it is grossly over-powered for the boat.

I can only imagine that the OM636 was used because it was available cheaply second-hand at the time an owner urgently needed to replace the original engine. Given such circumstances I would not be surprised if the propellor had never been changed, or a random one fitted just because it was available and cheap.

I very much doubt you would be able to fit a propellor large enough to convert the full 45hp to drive to an LM27, and even the nearest you could get to that would mean the boat would be going rather fast at engine tickover for easy manoeuvring. Note that it is generally considered that diesel engines are better running highly loaded at least part of the time, rather than continuous

You would never want to use the full 45hp, even if you could fit a propellor to transmit it. You would simply be burning a lot of fuel to get a rather small increase in speed over the standard 20hp LM27s were usually fitted with. More likely in practice the engine will reach maximum revs without needing anywhere near that amount of power.

I don't know what the availability of spares for this engine are like, and I would suggest you investigate the availability and sources for spares before you need them.

Wishing you lots of happy adventures in your new boat.

[Sula]

Having done a quick search on the YBW 'Practical BoatOwner' forums, it seems that many people speak highly of the OM636 as a boat engine, and that spares are readily available (or at lest were until relatively recently).

Link - www.google.com/search?q=ybw+om636+site:forums.ybw.com&client=safari&rls=en&sxsrf=AOaemvJRAfGswhzUIMJ2m9jjeCm-m_-lZw:1630146566683&sa=X&ved=2ahUKEwiCpqeYwdPyAhWShVwKHWb6CFcQrQIoBHoECAYQBQ&biw=1300&bih=731

[jandane]

It is correct, that the OM636 had a fine reputation for reliability but as Sula says, it has the double amount of power needed. If you contact a propeller firm you can have them to calculate the size and pitch of a new one. The diesels runs best at rews close to maximum torque. Example: in my LM 28 I have a BUKH DV24. Max torque is 2250 r/m. My propeller is designe to give the best cruising speed there. That is 6 knots. If going for full throttle it can run 7,9knots. Find the maximum torque revs on your engine. If your LM27 runs 5,5 knots there, be happy. Open the throttle fully and if you can get 6,8 knots it is good. On the attached photo you can see recommended sizes and if yours is close to the size of the ne recommended for Bukh DV36 you are on the right track

[achterliek]

Thanks for your infos. The LM27 is being serviced by the vendor right now. I won't drive it this year, so I cannot tell anything about speed. I will get information about the propeller size that is currently installed later.
The engine is very common and parts are available, as it has been used for 45 years in trucks, cabs and construction machines. It delivers 45hp at 3500rpm. Torque is nearly flat at 96-100Nm at any rpm above idle. I do not have any information about my transmission yet. The previous owner hardly used it - 800hours on the counter.

What is the maximum propeller size that I can fit into the LM27 ? Is a four blade propeller an option ?

[Alejandro]

Aug 28, 2021 2:08:21 GMT Sula said:

Congratulations on your acquisition of an LM27.

I am sure this engine will have been a retrofit, and I think it is a poor choice of engine for the LM27 because it is grossly over-powered for the boat.

I can only imagine that the OM636 was used because it was available cheaply second-hand at the time an owner urgently needed to replace the original engine. Given such circumstances I would not be surprised if the propellor had never been changed, or a random one fitted just because it was available and cheap.

I very much doubt you would be able to fit a propellor large enough to convert the full 45hp to drive to an LM27, and even the nearest you could get to that would mean the boat would be going rather fast at engine tickover for easy manoeuvring. Note that it is generally considered that diesel engines are better running highly loaded at least part of the time, rather than continuous

You would never want to use the full 45hp, even if you could fit a propellor to transmit it. You would simply be burning a lot of fuel to get a rather small increase in speed over the standard 20hp LM27s were usually fitted with. More likely in practice the engine will reach maximum revs without needing anywhere near that amount of power.

I don't know what the availability of spares for this engine are like, and I would suggest you investigate the availability and sources for spares before you need them.

Wishing you lots of happy adventures in your new boat.

[Alejandro]

Hola, tengo dos Mercedes OM636 con caja Borg Warner V-Drive 1.51/1 montados en un antiguo catamaran SOLARIS 23”. Quisiera saber si alguien tiene datos de las helices correctas para este equipo.
Muchas gracias

[Alejandro]

Hello, I have two Mercedes OM636 with Borg Warner V-Drive 1.51/1 box mounted on an old SOLARIS 23” catamaran. I would like to know if anyone has data on the correct propellers for this equipment.
Thank you so much

[Sula]

Apr 12, 2024 16:21:41 GMT Alejandro said:

Hello, I have two Mercedes OM636 with Borg Warner V-Drive 1.51/1 box mounted on an old SOLARIS 23” catamaran. I would like to know if anyone has data on the correct propellers for this equipment.
Thank you so much

Any company that sells propellors should be able to advise you of an appropriate propellor sizing for your combination of engine(s) and hull(s).    You will need to check the clearance between the propellor and the hull, as that may limit the size you can fit.

You can find free propellor size calculators on the internet - for example www.vicprop.com/free-propeller-sizing-calculators , others available, but I don;'t know if they have an option for catamarans, and in any case it would be wise to get the advice of a specialist before spending money on new propellors. 


-----------------------------------------


Cualquier empresa que venda hélices debería poder aconsejarle un tamaño de hélice adecuado para su combinación de motor(es) y casco(s). Deberá comprobar el espacio libre entre la hélice y el casco, ya que puede limitar el tamaño que puede instalar.

En Internet se pueden encontrar calculadoras gratuitas del tamaño de las hélices, por ejemplo www.vicprop.com/free-propeller-sizing-calculators , hay otras disponibles, pero no sé si tienen una opción para catamaranes y, en cualquier caso, sería aconsejable contar con el asesoramiento de un especialista antes de gastar dinero en hélices nuevas.