[Santelia]

Hi everybody,
I'm considering to buy a boat with twin Cummins V8 natural aspired 320hp (903 model?). Has anyone any experience with those old boys? General reliability? Useful lifetime? The boat is a 49' full displacement, so she cruises on 10-11kn and has max at 15kn. Any opinion on fuel consumption with such engines at hull speed?

[Capt J]

I have no experience with the Cummins 903's, but have always heard that they were good motors and lasted a long time.

[Santelia]

Hi Capt J,
thank you for your opinion.
Any idea on how much smokey are the Cummins 903s?
And typical lifecycle for such a use?

[Freespool]

All the good 903 mechanics are to old to get in the engine room anymore.

Good engines. A little smokey at cold start up. They like to run a lot. The more they run the less trouble they give you.

[Santelia]

Thank you Freespool,
so, would I have to hire some whitehaired paleo-mechanic to make any extensive servicing?

[Freespool]

Originally Posted by Santelia

Thank you Freespool,
so, would I have to hire some whitehaired paleo-mechanic to make any extensive servicing?

I think they quit making them in 1984 or so for civilian use. I built many of them years ago. The last one I worked on was probably 7 to 10 years ago.

[dennismc]

I would question the 15 kts wot on a full displacement hull with that HP.

[Santelia]

Ok Freespool, so you could be a precious source of first-hand information.

@ dennismc, do you mean that 2x320hp are not enough or that a 49' full displacement has a structural limit at a slower speed?

[Capt J]

Originally Posted by Santelia

Ok Freespool, so you could be a precious source of first-hand information.

@ dennismc, do you mean that 2x320hp are not enough or that a 49' full displacement has a structural limit at a slower speed?

A full displacement does not have the length to do 15 knots or be capable of doing that, a full displacements hull speed at 49' probably would not do 11 knots either. It sounds like the boat you're looking at is a semi-displacement hull, that's ok too.

I'd hate to guess how much fuel those engines burn, but guessing with 320hp, they probably burn around 20-25gph for both at cruise rpm. I've always heard very good things about 903's and know of a boat that had 6500 hours on them without any rebuild or anything (a charter SF) and was running fine. I just have no experience with them.

[Santelia]

Me too was wondering if 15 knots were actually possible at FD hull speed.
The boat has a bow deep V and rounded lines in the aft half of the hull, while ending in a usual transom at stern.

As far as fuel consumption is concerned, boat specs say fuel tanks are 660 gal (2,498 l) and cruise range is 700 nm. I thought that maybe, to reach that range, speed was intended to be not more than 7 knots. So it gave a fuel consumption of around 24.5 l/h, that's 6.4 gal/h.

Where am I wrong?
If I figure out how to do it, I'll put a hull picture to better talk about the matter.

[rcrapps]

If you’re considering a purchase, you really should have an ole white-haired surveyor on line (not sales person). He can help you figure the real hull design and fuel / speed.
His brother or in-law may be the ole white-haired mechanic you’re going to need.

Let your fingers do some walking (in the phone book) and call up some Cummins shops. They may give you some idea if they would / could work on those old beasts. Ask about for part availability in your future.

I’ve just done light work on those 555s and 903s. So far, parts (hang on) have not been an issue.
I like them, but then, I’m still running our old Detroit’s and like old simple engines.

Good luck and keep in touch with us all.

[Jimbo1959]

Very large, heavy engines. Parts are going to be hard to find. Smoke alot and probably leak quite abit. could be a can of worms. Get a good engine tech, take oil samples and maybe even a compression test.

[Santelia]

Thanks. So it seems that I have to expect difficulties in find spare parts. And someone says they are very solid and long runner, while someone else says they are smokey and leaky. Should I consider to change them, what engine would you suggest for a twin set to run a 49' fd boat, around 20t displacement, at hull speed for long trips? High torque at low rpm, long lifetime, easy and very light maintenance needs, low fuel consumption are the goals to reach. I would add a low sensibility for less than perfect fuel...

[rcrapps]

I hope you have not purchased this boat yet. Re-powering this old girl could be expensive. Not just the cost of the engines, the gears, maybe shafts, controls, fuel lines and new water lines. Then the labor for r&r. And then, the fabrication of the engine beds for new mounting points. Hill time, Lift charges, ,,,

Those old Cummins may look tall, but maybe not as tall as the new straight 6 cylinder engines that usually would replace it. Your going need a good local guy to offer what can fit before you fall in love with any engine brand yet. Or down angle clutch brand yet also.

Rethink your purchase. Maybe easier (cheaper) to pick up a newer boat, with ready to go engines.

Probably think about how long you’re going to keep this ship vs. money in/out.

Or,, spend the bux on the Cummins. Parts are still out there. Maybe expensive. Maybe real expensive. May have to make or repair what you have. Get tight with a good machine shop.
This could be cheaper in the long run than a repower.

Keep in touch,

[SeaEric]

If you like the boat, get it and the engines checked out thoroughly. If it's healthy, buy it. Run it and enjoy until the engine(s) quit. At that point, there will be many options. Repair, rebuild, replace. The point is liking the boat itself. There are plenty of old Cummins engines around to provide economical RTO replacement or parts supply. If and when the time comes, perhaps you will decide that it makes sense to re-power her with modern iron.