A few years back I bought a Sailfish 25'. The boat had been modified by the previous owner. He removed the outboard bracket and the rear fuel tank, installed a 315HP Yanmar Diesel with a Bravo 3 outdrive. The boat runs great, at 22 kts I'm only burning 6 or 7 GPH. The problem I'm having is that I have difficulty getting on step, the engine is putting out a lot of black smoke until I plane off. Also at 30 kts I overheat rapidly, and I'm can only get about 3400RPM when I should be able to get 3600. I suspect that I have a prop problem, the boat came with SS 26 props. I think 26 is too much pitch, my question is…..what would be the correct pitch for my boat.
Grady White Performance
- Thread starter kodiak
- Start date
Since you have such an unusual set up, I don't think any of us would have an answer. As far as overheating, there could be several culprits...water pump, manifold, raw water pickup etc. Diesel engines will blow smoke when under load but there are fuel additives that can help with that.
I would post this question over on boatdiesel.com.
Another good resource might be Carolina Classic 25 owners. Find them and ask what props they are running with their 315s.
Another good resource might be Carolina Classic 25 owners. Find them and ask what props they are running with their 315s.
From experience with my diesel truck the black smoke is caused when it is under load. If it seems to be more than should be expected you may have an air restriction issue where the motor is starving for air when it's working hard. I knows it's kinda apples to oranges but the only time my truck blows black is under a heavy towing load merging onto the highway or if I haven't put the pedal to the metal in awhile. Since it is an unusual setup you may want to investigate that the motor it getting enough air.
Sounds like a cool setup, I love the low GPH!
Sounds like a cool setup, I love the low GPH!
Check your turbo system. Black smoke means unburned fuel, and you can have unburned fuel because there's not enough air getting into the cylinders and there can be not enough air getting into the cylinders because there's either an issue with the turbo itself (less likely) or there is an issue with the wastegate. Not enough fuel being burned = why you don't have the 'get up and go'.
I'm not sure if your engine uses a vacuum controlled wastegate or possibly a mechanical wastegate, but that's a good place to check. Another easy thing to check is the inlet air passageways, starting at the filter (need to be cleaned?)... do you have an intercooler (aftercooler)?
When's the last time you checked the raw water impeller?
As far as the two props are concerned, it's possible that you're pitched to high. BUT, you won't know this until you get the other problem figured out. Don't do anything with the props until you get the engine running properly. What's the bottom condition of the boat like? How about the prop(s) condition? Do you carry a lot of extra weight?
You mentioned you've had the boat for a couple years? Has the engine ALWAYS performed this way, or is this relatively new?
Unrelated, but are you staying up with your anodes? Is there also an electrical anode system on the drive or the hull? In Mercruiser terms, it would be called Mercathode.
Edit... got bumped off... are you getting full down/in trim? Do you know which position the celery stick is in? Injectors could come into play, but let's hold off on that till the easy things are checked. What about fuel condition (additives) and fuel filter condition?
I'm not sure if your engine uses a vacuum controlled wastegate or possibly a mechanical wastegate, but that's a good place to check. Another easy thing to check is the inlet air passageways, starting at the filter (need to be cleaned?)... do you have an intercooler (aftercooler)?
When's the last time you checked the raw water impeller?
As far as the two props are concerned, it's possible that you're pitched to high. BUT, you won't know this until you get the other problem figured out. Don't do anything with the props until you get the engine running properly. What's the bottom condition of the boat like? How about the prop(s) condition? Do you carry a lot of extra weight?
You mentioned you've had the boat for a couple years? Has the engine ALWAYS performed this way, or is this relatively new?
Unrelated, but are you staying up with your anodes? Is there also an electrical anode system on the drive or the hull? In Mercruiser terms, it would be called Mercathode.
Edit... got bumped off... are you getting full down/in trim? Do you know which position the celery stick is in? Injectors could come into play, but let's hold off on that till the easy things are checked. What about fuel condition (additives) and fuel filter condition?
1998sailfish
Well-Known Member
3600 rpm's from a Yanmar (or any) diesel for that matter ???? Are you sure you don't mean 2600 rpm's ?? Cheezzzz, my 478 ci Isuzu truck diesel is turbo charged and reaches peak hp at 2400 rpm as well as torque near that range. Yeow......... isn't this motor over revving big time? sounds like the prop pitch or size is way off. Over rev = overheat
I'm not sure exactly which model/year Yan he has, but I looked on Yanmar's website at one that had similar HP and it was in the 3,800-range. My GM 6.5TD is about 3,600. That max RPM that he quoted might be right - but it would good to know the exact model.