Diesel for Llittle Boats

[chop duster]

Myles,
Unfortunately the 18-1900rpm is just off planning speed.
15 knots cruise @ around 2100rpm has been looking the best.
You appear to know a bit about diesels so what are your thoughts on:
Have a couple of Cummins 6BTA 370hp's sitting in the shed with only 700 hrs on them.
Fuel Curves etc.. attached.
What are you thoughts around the actual fuel consumption figures one could expect from the cummins as opposed to the volvo figures I have given above.? Im'm thinking the HP/gram ratio will be similar.
P.S - I have my head around the need for tweaking props etc...

[Midnight]

G'day Chop
The 6BTA's are a great engine, and it is what I will repower my Berty with when the time comes.

The big advantage is the nice flat torque curve of the Cummins. It makes more torque at 1600rpm than your current 70 series Volvo makes at peak torque.

At your cruise revs, assuming you can use the existing gear boxes (I know MG506 is ok at 320hp, the 370 Cummins might be touch and go), you will make over 100ft/lbs more torque with the Cummins and significantly more HP. You will be able to swing a lot more pitch, as long as your existing shaft size can handle it.

You are currently using about 500hp to do 15kts, that really won't change a lot, but instead of using 500 of 540 available HP and running at around 93% load, you can run 500 of 740 available HP, at a load factor of 68% for the same performance. A much better scenario for long engine life.
You will probably do even better, as the Cummins will be a bit lighter.

Fuel burn will be directly related to the HP extracted, so if you stick to 15kts, you can expect pretty much the same burn you have now.

The problem with the burns at certain RPM's on the charts they publish, is it depends on the load they use in the "propeller curve". If you use the 19L/100hp you won't be far off.

What type of hull do you have? What speed is the hull really happy at?

I know my Bertram hates dragging its bum at the 18kts I get around at, once I gets over 21kts it really comes alive. The wake flattens out, the ride is miles better and it is generally just a nicer boat to be in. My problem is I don't have the HP to cruise there.

Basically, if you have the Cummins there and the extra coin to do the repower (may need a change in gears, shafts and definitely props), I would do it for sure.
The difference in spare parts price alone would have me do it haha Volvo make nice engines, but they are rapists when it comes to buying spares.

Decisions decisions

Cheers,
Myles

[The Woo]

Interesting reading. We're currently undergoing what you guys are talling about. Upgrading the old girl from a pair of 210hp 6BT's to 370hp 6BTA's. It'll be very interesting to see the burn difference. I suspect she'll be a much "nicer" boat with some horsepower under her skirt, as the hull is one that likes to run "fast".
We did briefly consider Yanmar's 6LY3, 5.8 litre engine @ 380hp, but despite it being low, it's longer than the Cummins. That, compounded by the boat's layout being more suitable to Cummins servicability, led us to buy a pair of "remans" from the factory. As you guys would likely know the "remans" are actually new, but the fuel pumps are removed/replaced after the engines are manufacturer and fitted with a "remanufactured" plate. A nice way of getting around emmission laws etc for those of us who want to avoid electronic engines for as long as we can.

Back to smaller, tralierable boats..... Anyone have any experience with the new 4cylinder or V6 Hyundai marine diesels? They're SUV based products, and the specs are quite interesting for their weight. I would have thought they'd be a nice little setup (they're really quite compact!) for a 6-7 metre trailerboat with a pocket shaft and bow thruster. Not having to fish around outboards is so nice!

[Midnight]

Yep, the factory "remans" are the go! Good luck with it Woo, I'm sure it will be like a new boat! What hull, if I may ask?

The Hyundais look good. The hang on parts are all pretty easy to get at, and the base engine is an absolute class leader. Time will tell how good the marinization is.
They are offering very good value for money over their competitors at the moment, and their commitment to making it work seems pretty keen. I would give one a go if I was in the market.

Cheers

[ScottB]

Hi Midnight,

Putting 2 and two together, I would suggest that you check here http://www.thehulltruth.com/boating-...oat-refit.html for The Woo's project. I would say it is going to be mighty impressive when finished!

BTW Just wanted to say to all that this is great thread. Very informative!

Scott

[The Woo]

Far out, you nailed me to the wall in one foul swoop! Nice work Scott, and thank you sir!

And yes, Midnight, I had a really good chat with the fellas from Hyundai running the stand at last year's show, mainly asking if they had any larger high speed stuff forthcoming (due dilligence prior to committing to Cummins). As you say, the packaging looks good, the performance sure seems to be there, the weightr isn't, and yep, time will tell to see how well the alloys last etc. I really do wish them well, good competition is needed in that end of the market!

Oh, you asked what hull we have. 33' O'Brien flybridge.

[Midnight]

Thanks for the link Scott, I will have to sit down and read all 5 pages at some point!

Good luck with the project Ben, as you said, well worth the effort, and she will be a dream at 23-24kt cruise

I plan to do a similar "mega refit" to my B33 someday. It is a great hull and the layout suits me well as a compromise between fishing boat and family cruiser.

Cheers,
Myles

[Smithy]

On the 370s, I used to fish on a boat with 2x370 electronic Ivecos (the new 370-400 block) that had fuel flow. At a 20knot cruise it was burning 35litres/hr/side. I'd hate to think you were up in the 100/hr range. To me that would be what the mid range 450hp sort of motors would be doing. The 51' Riv I worked on with 2x1,000hp Mtus burnt 125-129litres an hour a side for its 20knots but it would do 230litres an hour a side at WOT.

Woo and Myles,

Jimmy is a Seasal dealer now. Dunno if he has had the opportunity to fit one yet. Certainly a #1 contender if I ever repower.

[The Woo]

Well if Jimmy's a dealer best we put our collective thinking caps on and come up with a boat for him to showcase a nice little V6 with!

[Midnight]

Hull shape makes a huge difference in HP required and in turn fuel burn. The deep v's need big HP to keep em going, especially if they are heavy, but some of the other designs that are flatter in the bum don't quite need the same grunt.

Viking 2(46ft deeeeep v) burns 162L/hr combined at 23kts with the 660hp QSM11's in it. I think from memory the Viking is still at 145L/hr at 20-21kts. Only 14L/hr at 8 kits though

Most of the guys in the USA, running 330 6BTA's in the same hull as mine are burning around 80L/hr at 21kts, however the majority of them run around at 24 and just burn the extra gas.
When they go from the Cats like mine to the Cummins, the boat loses over 500kg in weight! Helps a lot with the deep v getting out of the hole.

Sorry to go so far off the original thread purpose, I will shut up now haha

But yeah, let's design a 7m, deep v platey, with a jack shafted V6 Hyundai in it, to a Bravo 3 duo-prop leg. Will be a cracking trailer boat for dudes who do a lot of trolling.

Cheers,
Myles

[chop duster]

The woo, I was looking for your thread on the hull truth the other day but couldn't find it. Small world huh?...

Myles, the rig is an old 85/86 44 riviera, not many around. Think there was only 14 or so made. 14500kg dry, 4.65m beam, she is a bloody big 44 footer.
Was available for a good price, and having the cummins sitting there we couldn't say no. She tops out at about 17 knots, this speed I feel would be a good and achievable cruise with the cummins. Perfect world we would step up to the c series 450's but we will make do with what we have available.
The cummins have twin disc boxes 2:1 attached so will suit our current props (with a little trimming) and shafts as confirmed by the local prop god 'rosco'.
Your thoughts basically mirror mine. Only thing holding us up is funds and time.

We will more than likely just run the ovlovs for another year or so if they hold out that long, and sell them as parts when the time comes.

[The Woo]

Yep, a jack shafted Bravo drive with a "veranda" cockpit extension out over the drive so you could theoretically drop a line directly from the transom and not touch the drive unit.
A recess under the transom live well would allow full trim up of the Bravo.
Weight low and centred brings naturally good trim and ride, without excessive downward drive trim or tab use.
Great, now I'll be dreaming about trailerable mid mounted diesel boats! haha

[The Woo]

The woo, I was looking for your thread on the hull truth the other day but couldn't find it. Small world huh?...

Myles, the rig is an old 85/86 44 riviera, not many around. Think there was only 14 or so made. 14500kg dry, 4.65m beam, she is a bloody big 44 footer.
Was available for a good price, and having the cummins sitting there we couldn't say no. She tops out at about 17 knots, this speed I feel would be a good and achievable cruise with the cummins. Perfect world we would step up to the c series 450's but we will make do with what we have available.
The cummins have twin disc boxes 2:1 attached so will suit our current props (with a little trimming) and shafts as confirmed by the local prop god 'rosco'.
Your thoughts basically mirror mine. Only thing holding us up is funds and time.

We will more than likely just run the ovlovs for another year or so if they hold out that long, and sell them as parts when the time comes.

Small world indeed, nice to meet you all

The 44's were a rare boat for sure, they fairly quickly bacame the 46, but I'm unsure if there was actually any moulding changed or if BBC realised what a bloody big 44 he'd built and thought, "nah, that's a 46 all day!".

It sounds like you've got yourself an interesting time ahead Chop Duster (love the 24 Mustang avatar, I remember the orioginal advertisement and my mate Noah fished one pretty hard for years).
You might be suprised just how long those 70 series hold on, they actually weren't a bad donk if the coolers etc were services properly.

[Midnight]

Good luck Chop,
Nice to have the Cummins up your sleeve anyway. The Volvos will part out at a good price, as some parts are no longer being held by Volvo, and the ones that are require a second mortgage!
Cheers,
Myles

[chop duster]

Funny you should say that. The aluminium heat exchanger housing is a joke, and apparently a well documented problem. We replaced the port cooler with a retrofitted cooler of the cummins (tube type heat exchanger) a couple of months ago, this works a bloody treat. We are currently in the process of doing the same to the starboard motor. I'm loving the simplicity of the cummins, availability of parts and about 200kg lighter for an extra 100hp...