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  • #21660

    james
    Participant

    Engines are 1994 cummins 6cta 8.3’s rated 400 hp with denso pumps.

    Work completed in the last 1.5 years: Two new aftercoolers, Rebuild of seawater pumps, replace serpantine belts, new injector tips, Valve lash adjusted, two new turbo chargers, descaling of HX exchangers, addition of Fresh water flushing (used all the time since new coolers put on).

    This weekend while boating, when we put the boat on plane, 2150 rpm, 20 PSI boost, 19.5 KTS, with very clean props, moderately fouled bottom. Temps started to creap above 180, at which point I brought the boat off plane. Transition on to plane had zero black smoke going over the hump. Water temps in tampa area are in the high 80’s.

    Question, given my environment, would I be better served using 165 degree thrermostats??

Viewing 12 replies - 1 through 12 (of 12 total)
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  • #55495

    james
    Participant

    update from a survey

    We have our boat in contract, and thus doing sea trial and survey. As part of the Survey, we did a 1 minute WOT run, RPM’s on both engines stabilized at 2675, we were pretty well loaded up with people, fuel and water. Thought I’d give the community an update on this old thread. The mechanic who was aboard was very pleased with the RPM, he said most setup’s he see’s struggle to get past 2550. I attribute that to boat manufacturers propping over optimistically, and owners not paying attention to their boats.

    Temperatures stayed in the 165 range, but we are in relatively cool water in gulf of mexico now.

    #28392

    james
    Participant

    Performance Update

    We completed engine service including taking Air Coolers off and cleaning them, going through the heat exchangers, installing new SBMAR pumps and hoses.

    I did a sea trial last week after filling fuel. So for us the boat was heavy. Boat came onto a plane with very little or no smoke. I finally did a full WOT throttle test and got 2650 on both engines. I would have rather gotten 2700, and might drop pitch another 1/2 inch next time the boat comes out for bottom work. In the mean while, we tend to run the boat a lot of the time at 900 rpm trawler type speed, and planing cruise is 2200 or so. Also, at WOT the temps stayed around 175, I attribute that to: Cooler water temps, better pumps, and cleaned cooling system.

    Next steps, install new exhaust elbow and install wolverine heaters.

    #26255

    Rob Schepis
    Forum Moderator
    Vessel Name: Tenacious
    Engines: 6BTA 5.9 330's - "Seaboard Style"
    Location: Long Island, NY
    Country: USA

    James, I don’t disagree. Thanks for keeping this thread updated. Safe travels.

    These should depict why I won’t be boating on New Years Eve…. Tenacious got wrapped earlier this week… and here’s a few shots from this morning.

    #26243

    james
    Participant

    Boost asynch

    Rob – sorry you don’t get the trip! I think the prop’s were causing asymetric boost on the engines and greater fuel consumption on STBD side. When I ran her today, the boost readings were identical at 2,200 rpm, both at 20 PSI. In the past starboard would go to 22 at that RPM, so it was asking for more fuel to hit the RPM’s.

    I attribute a good bit of it to the paint, but I think the props were adding there own set of issues. I could see the combination of the two leaving me 50 rpm short of desired.

    #26242

    Rob Schepis
    Forum Moderator
    Vessel Name: Tenacious
    Engines: 6BTA 5.9 330's - "Seaboard Style"
    Location: Long Island, NY
    Country: USA

    So you did the bottom clean & paint at the same time as the prop recon. If so, then you really can’t say the small pitch correction was that much of a player compared to the fresh bottom job?…… either way all good steps in the right direction. New Year’s Trip & Boating… unfortunately those two don’t go together for me 🙁

    #26238

    james
    Participant

    Update

    I’ve finally gotten the boat back with fresh bottom paint. We also sent the props out to be reconditioned and had to do the cutlas bearings and engine alignment. Some interesting stuff. The props had picked up more pitch, most likely through a grounding and shifted from 24 to 24.5 or so. The starboard had more than the port.

    On the run back today, I put the boat up on a plane, synching the engines and watching the boost gauges. At 2200 rpms, we had 20 psi of boost on both engines, and were running a solid 21 kts. This differed from prior, at 2200 rpms, the starboard would have 22 psi boost and port 19 to 20. We also were using more fuel on the STBD side than port side. That tells me that the small difference in pitch was causing the stbd engine to work harder to produce RPM’s.

    I didn’t go full WOT as it was bumpy and I was checking a lot of stuff out. Having said that, when I put it on a plane, I did zero trim tabs, and the boat popped up with zero smoke from the engines. The also never had temps go above 175.

    Learning for me, even a small difference in pitch matters, and the boat/engines are running pretty darned good now. After our new years trip, I’ll be pulling the aftercoolers off for service it will be exactly two years, and I expect/hope to have them slide right apart.

    #22206

    Rob Schepis
    Forum Moderator
    Vessel Name: Tenacious
    Engines: 6BTA 5.9 330's - "Seaboard Style"
    Location: Long Island, NY
    Country: USA

    Sounds good James. Please do keep this thread updated as full circle threads with closure are of much greater value than ones left open-ended……..

    #22109

    james
    Participant

    Rob – I agree, I’m going to get the bottom done before I work the props at all. Looking at old posts I had on boat diesel, I had a higher cruise speed and less boost around 6 months ago. We had a soft grounding a while back, and lost all the paint on the prop’s and on the small keel the boat has. It’s been a struggle to keep it clean since then. Pushing 3 years in the gulf of mexico is a long time.

    #22108

    Rob Schepis
    Forum Moderator
    Vessel Name: Tenacious
    Engines: 6BTA 5.9 330's - "Seaboard Style"
    Location: Long Island, NY
    Country: USA

    Words like “very good” , “ok” , “pretty clean” leave a lot to interpretation. Probably best to record rpms and speed now “as-is” and then do a short haul and get everything CLEAN and do another sea trail and compare. Then you’ll have two sets of numbers – clean and not-clean and you’ll know how a fouling bottom effects the rpms. Really want to get all else up to snuff before playing with the props. One of the key benefits to under-propping engine(s) is so that when things get less than perfect as to bottom / running gear condition you are still able to exceed rated rpm and do it easily and don’t end up in over loaded condition as you are now.

    #22064

    james
    Participant

    Aetna's installed and temp issue id'd

    While doing generator maintenance work, I noticed that we had a saltwater leak on the hose from the gear oil cooler to the aftercooler. We fixed that leak, and temps are back where they belong.

    Now to the more important issue. I finally got the Aetna Tachometers installed, and was not thrilled with what I saw. I did a brief full WOT test, and only got up to around 2550 with 31 PSI boost per engine. I backed off pretty quickly as I knew I was throwing a lot of fuel into those engines.

    Here is the 64,000 question. My bottom paint is approaching 3 years old in hot gulf of mexico water. It is a struggle to keep it clean. Prior to my last run, I had the props perfect, the rudders very good, the struts ok, trim tabs ok. Hull pretty clean. Does it seem feasible that my bottom condition is costing me 150 rpm’s or so?

    Props are 24x24x3 pushing a 33,000 pound Tiara 4000 Loaded for bear. I’m open to dropping the pitch again, but would hate to do it just because of failing bottom paint. Intent is to have these engines be the C series types that go to 10,000+ hrs. We run 75% of our time at 1,200 rpm displacement mode with no boost and engine heat in the low 170’s even with 180 stats.

    #21678

    james
    Participant

    Thanks Tony

    Tony – We do have the factory instruments with the PCB board. I’ll talk to my mechanic about what it would take to put in higher quality alarms, something I’ve been thinking about for a while.

    We are switching to Aetna digital tach’s in the next week or so, my VDO’s are all over the place and not trustworthy. We did do a photo tach test on the engines at the dock all the way up to 2600 indicated, and built a cross reference table. That table shows me getting 2704 RPM on port and 2645 on STBD. STBD numbers are very suspect, at very high RPM’s the needles start jumping all over the place.

    We did proactively take an inch off the prop’s at least a year ago, dropping from 24X25X3 to 24X24X3. I noticed a drop in cruise speed, but not a real uplift in peak RPM (with questionable measurement).

    I just dove my boat again yesterday. Found some good sized barnacle patches which I had missed on the friday dive. So, the combination of 3/4 fuel load, full water and all of our standard gear, with a fouled bottom, we were asking a lot of the engines. Being a cautious soul, as soon as I saw the heat creep, I dropped off a plane and ran as a displacement craft, which is 1,000 rpm, zero boost and engines purring. I’ll post an update after we get the Aetna’s in and calibrated.

    #21677

    Tony Athens
    Moderator
    Vessel Name: Local Banks
    Engines: QSB 6.7 550 HP
    Location: Oxnard, CA
    Country: USA

    If you can control your temps at 190F or less, there is no issue at all.. If fact the engine is more efficient at these high temp….So if you stabilize at 185-ish, ZERO issues
    ………….But there is a BIG BUT..

    You need to be 100% sure you have a good working coolant alarm that tells goes off between 195 and 205F.. Cummins default is 205, but we prefer a tad lower with 180 Stats.. With 160-165F stats we like the set point closer to 195-ish…………………….

    Another thing to look at is your propping–The earlier 400’s like you have really need to see an honest 2700 or more loaded as you use the boat.. If you are at 20 PSI of boost at 2150, I am thinking you may not even be making the minimum rated of 2600? Tachs checked for accuracy? Easy to do at the dock in neutral at 2400 RPM-ish.

    Factory instruments/alarms with the PCB board?

    Tony

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