Independant fuel tanks - port engine consumes more fuel

[BruceK]

No black smoke. Smokes for about 1 minute on a cold start but even then not really noticeable. More grey and diesel smelling. The odour being more noticeable. Gone within a minute as said.

I'll check the pipes again. Pretty sure no balancer though and returns are correct however the tanks and piping are pretty damn inaccessible. I'll have to use my endoscope. God forbid the tanks ever have to come out. It will be a power saw job.

Btw. I have averaged a seasonal fuel burn of roughly 2.7 litre per mile on a 70/30 plane/hull speed split. 7 ton lwl 34ft. If this isn't 30% more than expected then it may well be a fuel routing issue

 

[A_8]

No black smoke. Smokes for about 1 minute on a cold start but even then not really noticeable. More grey and diesel smelling. The odour being more noticeable. Gone within a minute as said.

I'll check the pipes again. Pretty sure no balancer though and returns are correct however the tanks and piping are pretty damn inaccessible. I'll have to use my endoscope. God forbid the tanks ever have to come out. It will be a power saw job.

Btw. I have averaged a seasonal fuel burn of roughly 2.7 litre per mile on a 70/30 plane/hull speed split. 7 ton lwl 34ft. If this isn't 30% more than expected then it may well be a fuel routing issue

2.7 ltr per mile is pretty much what I get, varies between 2.6 and 2.9 depending on how big the waves are and currents of course. Boat is measured at 6.5-7.5 tons, depending on fuel plus water, KAD43 with DPE 1:78 and C4's top speed when new 35 knots and 3950 rpm's now 33.8 and maybe 3800 rpm. It will however pull itself on the plane without the supechargers even if it takes them a bit of time getting there.

 

[benjenbav]

Hi Tico. I haven't checked that but I seriously doubt it. If both tanks were full that'd leave a trail of diesel down the estuary from the overflow.

Surely the return would have to be greater than 50% of the intake volume for that to be a problem unless you run only on the engine which is draining the opposite tank ...or you have fusion power so that the more you burn the more you generate

Return should be well below 50% unless injectors are shot, I would have expected.

 

[BruceK]

Now you have me scratching my head. What you say makes sence and then my apologies to Tico. However in my defence I thought the return would far exceed the intake.

 

[BruceK]

OK I took the RNLI mechanic out today, he's been doing some jobs on the boat, to see if we could find shut off valves, balancer pipes and balancer shutoff valves etc. After an hour of turning the boat inside out, niks, nada zilch. We caught a brief glimps of the port tank but nothing of the starboard other than the hoses that lead to it. This perplexed him endlessly and his efforts to locate the valves or a balance pipe took on a bit of a frenzied determination. Eventually he just said "It's a good un" and capitulated. So some more head scratching and I realised I always fill the port tank first. If there was a balance pipe this would go a long way in explaining why starboard takes on less fuel at fillup. However that does not adequately explain then why port side is consumed quicker as is borne out by the list as the tanks empty and the rate at which the guages drop. If the boat wasn't listing a few degrees to starboard as the tanks approach empty I'd pin in on the variance of the guages.

So the next question, is there any sort of aftermarket fuel consumption meter that can be readily fitted and will not break the bank?

 

[vas]

OK I took the RNLI mechanic out today, he's been doing some jobs on the boat, to see if we could find shut off valves, balancer pipes and balancer shutoff valves etc. After an hour of turning the boat inside out, niks, nada zilch. We caught a brief glimps of the port tank but nothing of the starboard other than the hoses that lead to it. This perplexed him endlessly and his efforts to locate the valves or a balance pipe took on a bit of a frenzied determination. Eventually he just said "It's a good un" and capitulated. So some more head scratching and I realised I always fill the port tank first. If there was a balance pipe this would go a long way in explaining why starboard takes on less fuel at fillup. However that does not adequately explain then why port side is consumed quicker as is borne out by the list as the tanks empty and the rate at which the guages drop. If the boat wasn't listing a few degrees to starboard as the tanks approach empty I'd pin in on the variance of the guages.

not much then... have you tried asking other boat owners of their experience (with same boat that is!)

So the next question, is there any sort of aftermarket fuel consumption meter that can be readily fitted and will not break the bank?

ah, that's an easy question to answer: NOPE
you need 4 meters one for each line going and returning from each engine so 2X2=4. You wont get away with less than 2K for senders and display, for something worth having that is.
If you do come across something around the 500euro mark and especially a NMEA2K I'm interested
Much better rigging two 20lt tanks for each engine, starting off them and see how much you'll progress until running out of diesel.

cheers

V.

 

[n.herring]

I had a new boat in 1998 where one engine used over 20% more fuel, 2x250 hp. Everything ran perfect except for fuel burn, turned out to be timing wrong on one engine, worth looking at, Neil

 

[Seastoke]

bruce it could be a plus one engine is saving you 30%

 

[BruceK]

bruce it could be a plus one engine is saving you 30%

I hope you are taking part in the Trafalgar day celebrations out in the bay next weekend. I'll make sure you get 30% wetter. I have a bigger crew than you. 50% bigger, and my boy is deadly with the supersoaker.

 

[BruceK]

not much then... have you tried asking other boat owners of their experience (with same boat that is!)


ah, that's an easy question to answer: NOPE
you need 4 meters one for each line going and returning from each engine so 2X2=4. You wont get away with less than 2K for senders and display, for something worth having that is.
If you do come across something around the 500euro mark and especially a NMEA2K I'm interested
Much better rigging two 20lt tanks for each engine, starting off them and see how much you'll progress until running out of diesel.

cheers

V.

I asked the factory. They said tip the starboard seating and all will be revealed. Unfortunately the boat never came with starboard seating, ever. And Port side seating reveals nothing. In fact this boat never had starboard seating until 2006. I think my boat was propably built before the lad I asked was born. I've been to a owners forum (American). I think I'm the only one there with a 1992 boat.

1992 Formula 34 PC

 

[vas]

I asked the factory. They said tip the starboard seating and all will be revealed. Unfortunately the boat never came with starboard seating, ever. And Port side seating reveals nothing. In fact this boat never had starboard seating until 2006. I think my boat was propably built before the lad I asked was born. I've been to a owners forum (American). I think I'm the only one there with a 1992 boat.

1992 Formula 34 PC

easy!
check where the stbrd seating is on newer boats, and jigsaw a hole there, you'll find what you want then
you'll also have a problem covering the hole, but that's minor issue.

Serious, timing seems like a plausible cause.

V.

 

[epervier]

On my Weymouth I had four tanks, two belly tanks of 50 gallons each in the bilges inbetween the donks, fwd one feed the stb donk the stern one feed the port donk, then in the stern I had port and stb tanks of 100 gallons each with fillers at deck level, they gravity fed to the two belly tanks, but both engine fuel returns went back to the port stern tank, a very similar problem to yours, easliy remedied by opening the balance pipe between the two stern tanks,

may of course not be your problem, but I'd thought I'd chuck in my tupence worth.

 

[Deleted User YDKXO]

OK I took the RNLI mechanic out today, he's been doing some jobs on the boat

I know you mentioned this but did the RNLI mechanic confirm that each engine returned fuel to its own tank? After you've solved this mystery I would think that fitting a balance pipe, if you haven't got one, would be a good idea anyway

 

[Bandit]

You have outdrives are the ratios the same?

Other possibilities:
Obviously Engines return to wrong other tanks?
One duoprop is slipping on the bush
Injectors hosing
Fuel pump or wrongly set

 

[BruceK]

OK. The plot thickens. I received a mini library of build, plumbing and electrical drawings from TAG Formula (enough to rebuild the boat!). Excellent service from the TAG department there, what a difference :encouragement:

There is no balance pipe, return feeds are to original source tank, but starboard tank is significantly bigger to offset the genny, which is no longer present. So this would explain why the starboard fuel guage does indeed drop slower than port and why without having full tanks the boat takes on a list to starboard if I dont have my water ballast bag over the port tank. It still doesn't explain why the starboard motor consumes +30% extra fuel.
I will check to ensure no post factory install balance system has been put in place (maybe using the now defunct genny feed?) but I doubt this to be the case. It's unlikely to be prop slip. The props have recently been repaired (by a very reputable engineer works) and rehubbed and this trend was present before then. Not gearbox tightness. Both were nice and easy to rotate while in neutral spinning the propshaft (without props on) by hand. Would a difference in gearbox reduction not be painfully obvious / very noticeable?

Could I have faulty injectors 4 years since replacement? And could they account for so much extra burn yet both engines sound exactly the same and healthy?

(I'm beginning to wonder if doing a night school in diesel mechanics may just be a good financial strategy )

 

[Freebee]

what sort of level gauges do you have in the tanks, does tank dipping support your gauge readouts?

 

[BruceK]

what sort of level gauges do you have in the tanks, does tank dipping support your gauge readouts?

I am basing this on how much fuel I put into each tank on refill

 

[n.herring]

As said previously check the timing, I had 2 new engines one as per spec the other set up for a different variant of the same block, made about 25% difference on fuel. Neil

 

[A_8]

As said previously check the timing, I had 2 new engines one as per spec the other set up for a different variant of the same block, made about 25% difference on fuel. Neil

Was there any other signs the timing was off like temperature, vibrations, power, smoke etc?

 

[BruceK]

No. I haven't had timing checked this season, the engines were serviced at the end of last season and will be serviced now in Nov again. What I can say is the engines sound and feel very good. Oil pressure, temp etc are bang on on starboard and slightly cool on port which has the calorifier but both engines pull extremely well. (remember I am also slightly underpropped) I popped in a video at the beginning of this thread where the engines can be heard as well. I really have no idea which is why I've come to the forum with it. But in the last fill after having the boat on the hard port tank too 320 litres, starboard 250. Pretty much the ratio of all of this season's fillups. PO also said he always put about 80 litres more in starboard so this issue has been around a long time. I'm even once wondered if someone was nicking the fuel. (Boat out on the Conwy River with pontoon docking on starboard side) But if so, they seem to be nicking in precise quantities relative to my engine hours so that's not it.