Engine replacement advice

[DIJ]

Hi

I have a 1992 Southerly 115 and it’s Yanmar 3HM35 motor needs replacing. I am advised by local engineers that rebuild is not a great option as too much needs replacing and parts are not plentiful. I have no personal preference for make (happy to take advice) but have been offered a 30hp Yanmar replacement but am not sure it will be powerful enough as the 3HM35 was 35hp and the boat is 7+ metric tonnes. There don’t seem to be any 35hp motors but a few at 38-40 but it seems they may be a little large for my engine compartment.

If anyone can offer advice, especially anyone who has experience of engine replacement in a Southerly 115, I would be most grateful.

[Cheechako]

I suppose it depends a bit how you use the boat, and maybe location. But Yanmar 30 HP is a bit on the low side for a ~36 foot boat probably. It will work though. Yanmar's tend to be a bit over rated in their HP in my opinion being rated at high rpm. But that's just me. If it's a used 3GM30 I would not go there. They had some issues with that engine although many are out there.
If buying new I would look into a Beta (Kubota)
Can't help with your specific boat though.
In general, I look at rated HP at 3200 rpms or so and consider that the HP to use to compare engines.

[Kokanee]

No experience with a Southerly 115, but I've replaced a few engines.

The 30 hp engine should be enough power in most conditions. The general rule of thumb is 4 hp per ton is required to reach hull speed. Powering into a strong wind may be the only time you may need a bit more horsepower.

If you feel you do want the extra power, check the sizes of the Vetus or Nanni engines carefully. My new 42hp Vetus (Mitsubishi based) is much shorter, narrower and lighter than than the original 36hp Volvo.

https://www.vetus.com/media/magentom...03122140_0.pdf

I had a quick look at your Yanmar dimensions. The 42 hp Vetus is smaller in length and height but the engine mounts are 25mm wider. Would that work?

[DIJ]

[QUOTE=Kokanee;3509652]No experience with a Southerly 115, but I've replaced a few engines.

The 30 hp engine should be enough power in most conditions. The general rule of thumb is 4 hp per ton is required to reach hull speed. Powering into a strong wind may be the only time you may need a bit more horsepower.

If you feel you do want the extra power, check the sizes of the Vetus or Nanni engines carefully. My new 42hp Vetus (Mitsubishi based) is much shorter, narrower and lighter than than the original 36hp Volvo.

https://www.vetus.com/media/magentom...03122140_0.pdf

I had a quick look at your Yanmar dimensions. The 42 hp Vetus is smaller in length and height but the engine mounts are 25mm wider. Would that work?[/QUOTE

I am told the 42hp Vetus is 4cylinder and too long! So worth another look.

[DIJ]

Originally Posted by Cheechako

I suppose it depends a bit how you use the boat, and maybe location. But Yanmar 30 HP is a bit on the low side for a ~36 foot boat probably. It will work though. Yanmar's tend to be a bit over rated in their HP in my opinion being rated at high rpm. But that's just me. If it's a used 3GM30 I would not go there. They had some issues with that engine although many are out there.
If buying new I would look into a Beta (Kubota)
Can't help with your specific boat though.
In general, I look at rated HP at 3200 rpms or so and consider that the HP to use to compare engines.

No, I’m looking at new engines, thanks for the input.