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Post by fish on Mar 16, 2022 20:11:18 GMT 12
we run at 70 litres an hour at 18knots. Seems a lot, but can get to Te Kouma in a couple of hours from Westhaven, no wet weather gear etc. Life is short. Used to sail, four hours min to the end of Waiheke. Still love sailing, but love getting somewhere anchoring up and relaxing that is further than Issy bay on a friday evening. On the bigger Rivs etc, if you are spending $2m+ and worrying about the fuel, you bought the wrong boat! The fuel numbers may look alarming, but I'd love to know what the depreciation per hour is worth on some of those big recreational engines. It is one thing having a low revving high torque commercial rated diesel in a workboat, but some of these modern high revving, turbo'ed, electronic injection engines sound like they are rated to squeeze the last ounce of power out of them. I don't know what they cost, but it must add up. (said while ignoring the cost of my sail wardrobe). |
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Post by ComfortZone on Mar 16, 2022 22:06:24 GMT 12
we run at 70 litres an hour at 18knots. Seems a lot, but can get to Te Kouma in a couple of hours from Westhaven, no wet weather gear etc. Life is short. Used to sail, four hours min to the end of Waiheke. Still love sailing, but love getting somewhere anchoring up and relaxing that is further than Issy bay on a friday evening. On the bigger Rivs etc, if you are spending $2m+ and worrying about the fuel, you bought the wrong boat! The fuel numbers may look alarming, but I'd love to know what the depreciation per hour is worth on some of those big recreational engines. It is one thing having a low revving high torque commercial rated diesel in a workboat, but some of these modern high revving, turbo'ed, electronic injection engines sound like they are rated to squeeze the last ounce of power out of them. I don't know what they cost, but it must add up. (said while ignoring the cost of my sail wardrobe). there are not really any big recreational engines. There are a few engines around 4.0 litres eg Volvos and MTU's (VM from Italy) where they have squeezed alot of power out of them, over 300hp in some cases. Not alot of feedback yet as to whether these are handgrenades, revving up to 4000 rpm Another notable example is the Yanmar 6LP, the "landcruiser" straight 6 which is rated at 315hp and have been around for a couple of decades with a good rep. All the bigger engines (2500 - 3000rpm) are marinised truck/industrial blocks eg Cats, Cummins, Iveco, John Deere, Volvo, MAN, Scania etc If you look at a catalogue you will see the same basic block with a whole range of ratings and different power outputs. The "hand grenade" pleasure boat version might be rated for 200hrs use per annum and 15 minutes in 4 hrs at full throttle. Further down the scale will be a Patrol Boat rating whilst the lowest output engine will be rated for 24hr continuous duty at full throttle. It mostly comes down to the capacity of the cooling system to remove heat, but obviously more power = more stress=less life Engine makers have always pushed their engines and eventually find their limits, the 3208 cat started off as an NA motor in the early 70s with 210hp, added turbo's and intercoolers and initially plateaued at 375hp which was still regarded as a good engine, pushed it further to 425/435hp, this was too much and they had a lot of problems. Everyone has heir favorites, I like the big Scania's and next step down Cummins followed by Cats. Don't like Volvo's - 'green grenades" Preventative maintenance is a must, especially the Intercoolers, if these fail you get salt water straight into the cylinders with catastrophic results. There are plenty of planing launches around with 30+ year old motors running well, no doubt not quite achieving their nameplate outputs |
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Post by dutyfree on Mar 17, 2022 7:28:07 GMT 12
we run twin Cummins 6BTA engines. 5.9l and I understand one of the longest and largest run of diesel engines ever (since early 80s I think). Used in many applications, trucks, buses boats etc. Ours are the 330 so rated for something like 1 hour of max revs (2800rpm) per 10 hours of operation. Almost never go there so run at 70% to 75% of max, plus the time spent at 8 knots. Like every type of boat and as noted by Comfort Zone, their longevity is all about maintenance. Across 4 boats (ignoring my first tinny) the engines have had a max of 3400 hours on a 35 year old volvo, (and about 2000 hours on a yacht based volvo, almost 20 years old when we sold her) to 1000 hours on a 10 year old volvo (370hp) and 1200 hours on 20 year old cummins. As noted by CZ, intercoolers, aftercoolers, oil coolers all need maintenance and some owners ignore them. So nice owners like me come along and get them maintained  . Oil changes at least annually, filters etc. all help them last. I need new turbos and exhaust elbows soon. Not because there are problems, but they are getting on in years and hours. Good stuff about engines like Cummins is that they have been around so long there are a huge number of resources that can show you common problems, improvements etc. For example on the exhaust elbows I will probably swap from the standard cummins to a set out of a USA crowd that are designed to minimise any "splash back" of salt water towards the turbo. |
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Post by ComfortZone on Mar 17, 2022 9:20:15 GMT 12
Jeez 😳 no wonder they’re all idling around at 7-8kts … even the increment to 10kts is a trebling of burn. It's not actually good for any diesel, even our little yacht engines, to run at low loads for extended periods of time. A diesel likes to be run most of its life around 70-80% load by fuel burn. The turbo on a bigger diesel, say DF's Cummins starts working around 2000 rpm (the Cummins should cruise around 2200-2400 rpm), on Fogg's little Yanmar around 2400rpm. These turbo engines need to run above these revs a fair amount of their hours. As an aside this is why I do not like turbo's for yachts, they never get run hard enough and just clog up the turbine blades and exhaust elbows. In the case of your Yanmar Fogg, if you are running it around 2000rpm most of the time, every 5 hours give it a hard run, up to 3200rpm for 30 minutes or so to keep everything clean inside |
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Fuel costs
Mar 17, 2022 10:06:21 GMT 12
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Post by Deleted on Mar 17, 2022 10:06:21 GMT 12
I've often wondered why they don't run diesel electrics like the big ships do. you have a small diesel engine running a couple of big electric motors... very efficient?
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Fuel costs
Mar 17, 2022 10:24:16 GMT 12
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Post by Fogg on Mar 17, 2022 10:24:16 GMT 12
Yes I’d prefer a bigger engine with no turbo but I inherited it so I regularly run it around 2600-2800rpm for that reason.
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Post by ComfortZone on Mar 17, 2022 11:03:29 GMT 12
I've often wondered why they don't run diesel electrics like the big ships do. you have a small diesel engine running a couple of big electric motors... very efficient? Nigel Calder obtained a 2M Euro grant for his HYMAR project a few years ago to investigate this concept for small boats. Had to conclude that a direct coupled shaft to the diesel engine was still the most efficient. Too many power losses going diesel-electric. It was tried with a Nordhavn 75 trawler some years ago, in the finish all the electric drives and generators were replaced with conventional drive, same with some Lagoon catamarans. if you have a day sailor or a race boat where you just want to get to/from the start line and can plug into power at night then battery/electric drive looks a better option Diesel-electric works for the big cruise ships because their "hotel" electrical load at peak far exceeds propulsion demands. So they typically have their electric pod drives and a whole bunch of generators which are run according to load demand. |
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Fuel costs
Mar 17, 2022 11:57:30 GMT 12
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Post by Fogg on Mar 17, 2022 11:57:30 GMT 12
That’s a really good explanation (if I’m understanding it correctly) 😊
In other words, if your main energy demand is ‘small city’ style electricity (like a cruise ship) then use big diesel engines to generate electricity to do everything including consumer supply and propulsion. But if your primary energy need is propulsion (like a private vessel) then use a diesel engine to drive you along whilst generating smaller amounts of electricity on the side for your relatively small ‘house’ needs.
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Post by ComfortZone on Mar 17, 2022 12:24:30 GMT 12
That’s a really good explanation (if I’m understanding it correctly) 😊 In other words, if your main energy demand is ‘small city’ style electricity (like a cruise ship) then use big diesel engines to generate electricity to do everything including consumer supply and propulsion. But if your primary energy need is propulsion (like a private vessel) then use a diesel engine to drive you along whilst generating smaller amounts of electricity on the side for your relatively small ‘house’ needs. Where propulsion is the main energy demand, same philosophy for big ships. All the mega container ships have one thumping great diesel engine, 2 stroke, about the size of a five story apartment building generating ~100,000hp at ~80-120 rpm eg en.wikipedia.org/wiki/W%C3%A4rtsil%C3%A4-Sulzer_RTA96-C |
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Post by Deleted on Mar 17, 2022 15:32:38 GMT 12
Want to kill a small diesel(regardless of brand or turbo non turbo)run it at low revs,in out of bays or marinas for 20/30 minutes.They have not had a chance to warm up.They need up wards of of an hour at 3/4 throttle,no long periods of idle,like some do to charge battery or fridge.
Why do you think trucks get close to a million kms??Yes they will have injectors done and top tune but pulling hard and hot most of the time,the new engines you dont idle just start and go,no cool down,turn straight off turbo and non(most are turbo)
Yachts can lay long periods unused and the moisture/acids will never burn off even though warm/hot. Regular use.
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Fuel costs
Mar 17, 2022 15:43:52 GMT 12
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Post by Fogg on Mar 17, 2022 15:43:52 GMT 12
I’m not understanding your middle paragraph - are saying switch off a hot engine immediately is better?
I guess we do it in cars all the time but I’ve heard some turbo models have some kind of cool-down function which continues running for a couple of mins?
After a long hot run on the boat engine I’ve always let it idle in neutral for about 2-3 mins before shutting down to give it a chance to cool itself a bit from peak working temp - before it loses all water flow. I’ve understood that otherwise the remaining water can boil away letting the engine get too hot immediately after shutdown unless you do this. Are you saying that’s wrong?
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Post by Deleted on Mar 17, 2022 16:32:09 GMT 12
I’m not understanding your middle paragraph - are saying switch off a hot engine immediately is better? I guess we do it in cars all the time but I’ve heard some turbo models have some kind of cool-down function which continues running for a couple of mins? After a long hot run on the boat engine I’ve always let it idle in neutral for about 2-3 mins before shutting down to give it a chance to cool itself a bit from peak working temp - before it loses all water flow. I’ve understood that otherwise the remaining water can boil away letting the engine get too hot immediately after shutdown unless you do this. Are you saying that’s wrong? Normally a turbo timer fitted,shuts off auto after 2 minutes.The new Scanias idle for 30seconds,by the time you have walked 40 ft to open trailer doors,shut off,bugger hooking up trailers.And NO scania will not increase timer. |
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Fuel costs
Mar 17, 2022 16:42:18 GMT 12
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Post by Fogg on Mar 17, 2022 16:42:18 GMT 12
Ok so this sounds like turbo cool-down period is a good idea if the trucks have an automated system.
But given Fogg doesn’t have an automated system it sounds like I should continue with my current practise ie to give it 2-3 mins idling before shutting down.
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Post by dutyfree on Mar 17, 2022 19:09:41 GMT 12
Cummins specify effective cool down times for my engines. It is quite a few minutes, so the 5knots into the marina will normally satisfy. I try never to idle the engines in the marina with no load.
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Post by jim on Mar 17, 2022 20:23:16 GMT 12
Turbos are quite neat - using otherwise lost energy in the exhaust gases, and they are quite simple too, but if not given a cool down the bearings in them can turn oil into carbon and tar which then leads to trouble... i understand the ceramic turbos are moderately immune to this problem but the safe bet would be to give them a cool down period.
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. Oil changes at least annually, filters etc. all help them last.
