Diesel for Llittle Boats

[Smithy]

Had some mates fish that jack shafted platey at Port Stephens at the start of the year and they didn't like it. One of those bangy plateys.

You're onto something with those diesel cats. There are certainly a couple of them working out of here used by the spanner crab boys. When you look in the fuel book at the diesel dock where we are getting our diesel they are all only using 60-70 litres a day. I'd say the shear weight of those old Shark cat hulls will help them immensely. The other option is something like a 7.2KC with twin Yanmar diesels or similar. There are a couple running around. Very worthwhile on the 2nd hand market but would be exxy to build new from scratch. Probably over the $200K mark. There is a 7.2m in our club called Reel Capture. It came up in a previous thread. Jeffo mentioned it had more a displacement boat feel about it. Maybe the big cats work well like that and it is only us Aussies who want to power them up with big outboard horsepower and go fast on the top. Roger B on here ran a semi displacement cat charter boat in England that was very successful with moderate horsepower Perkins diesels. There is Craig Pollermounter the Canterbury Bulldogs footballer's Kevlacat that pops up from time to time on Boatpoint which is a sistership to Reel Capture. Reel Capture was Fred Temminck the old Kevlacat owners personal boat so you know it was built well and pretty much to survey standard. There was an 8m KC with a lock up cab for sale recently with twin Yanmars which was on a trailer in NQ that was sub $100K.

[myusernam]

i rememner a guy on here claiming he had a 7m noosa cat long cabin with twin 4cyl vovlo diesels that gruised at 22 - 24knots with the same fuel burn combined. If so pretty good but sounds a bit too good to be true..

[PB]

The biggest problem with boat manufacturers changing engine configurations is they don't change anything else and 9 times out of 10 one configuration wont work as good as the other and sometimes its the opposite but this only means the hull wasn't designed right in the first place. where starting from scratch for our new mid mount inboard as we believe its the only way it should be done. yes it would be a hell of alot cheaper to just modify out current outboard version but the calculations just don't add up.

[dugggy]

jackshaf.jpgv50.jpgboat 012.JPG
These are pics of the setup I inherited.The Cummins sits very low and the jackshaft leaves the transom clear.Hopefully the shear weight of it so low will help with stability at rest too.Gladly swap the old Cummins for a new V6 Hyundai diesel though,600kg lighter and 50% more HP.
Doug

[Smithy]

I agree. At the end of the day there is only so much calarific value of energy in each litre of whatever fuel and if it has to push X weight at Y speed, there is only so much that can be done for the mechanical efficiency of the motor and the slipperyness of the hull through the water to give you the fuel burn. Some figures you see seem to defy the laws of physics. Unless you start with a full tank and finish with a full tank or have floscan or similar you are really just guessing. I have been told by the skipper of the new charter boat at Noosa he gets his 20l/h for his 20knots on a

9.9m ally boat out of Noosaville at the moment its got a 330 Volvo with a duoprop it burns 20per hour at 27rpm at 21knots with 14pob we do sunshine out to massounds out to chardons back sunshine home 23lt of diesel for the day

. I'd like to be getting that with my 3.5T, 25' boat with a 230hp let alone a 30' boat with a 330hp.

[cormorant]

Must be a buyers market out there as there is a fair few reasonablly maintained boats out there for sale. Lots cheaper to buy them than build em.


Just did a search for Diesel shaft cat . There is a has been built few sailfish ones made, markam and devilcats but you are getting away from anything you can trailer easily. Here is a couple with underfloor set outs .

http://www.boatpoint.com.au/boats-fo...spx?R=12113944

http://www.boatpoint.com.au/boats-fo...spx?R=12301305

http://www.boatpoint.com.au/boats-fo...spx?R=12184812

http://www.boatpoint.com.au/boats-fo...spx?R=12113934

Never heard of these- leg

http://www.boatpoint.com.au/boats-fo...spx?R=11301850

Guess they didn't pay the storage bill? Bargain or trouble?
http://www.boatpoint.com.au/boats-fo...spx?R=12074558


Not a diesel but crap this seems cheap

http://www.boatpoint.com.au/boats-fo...spx?R=12654755

[Midnight]

I agree Smithy, some of the figures you see quoted shows that the owner has no idea how much fuel their boat really burns. Basically, you can't get around 20L/hr per 100hp used.

My Bertram 25 with a 200hp Volvo Turbo diesel was 30L/hr at 18kts (3.5 tonnes deep v). I know that because I ran the boat from Scarborough to Mackay at 18kts the whole way, and went from full tank to full tank at each refuel. I used to average around 15L/hr start up to shut down for a 15hr day, out to the shelf and back.
30L/hr is close enough to 150hp being used to push that boat to 18kts.

My Bertram 33 is 80L/hr at 18kts On the Floscans (11tonnes, deep v). 40L/hr or 200hp being used from each engine. For the season last year, I did just under 300hrs for an average "block hour" fuel burn of just under 22L/hr. but I do a lot of trolling and putting around the Hawkesbury at 7kts when we go family boating.

There are very few mechanical diesel engines that will make more than 100hp/19-20L burnt, and it all has to do with the calorific value as Smithy mentioned earlier. We used the same formula for water pumps and tractors on the farm, always works.



Cheers,
Myles

[Smithy]

Cormorant,

some good links there. The two KCs and the Broadbill are certainly good buying for the right person. Even the Shark Cats if you don't want to go too fast.

[wirlybird]

i have seen an ex waterways Broadbill with 225 hondas sell for 26 grand i dont think its well priced as far as the market is conserned. but its tough out there ATM

[chop duster]

bit off OP subject but:

While researching our TAMD70D's the best info I come accross regarding fuel consumption was the attached graphs denoting grams of fuel used/horsepower @ a given RPM, giving you the most fuel efficient points in the RPM range...

Calc's below:

1 litre of fuel is 850 grams.

@ 1600rpm the engine uses 162grams of fuel per horse power.
@1600rpm puts out about 195hp
Therefore, 195 x 162 = 31590grams of fuel.
31590 divided by 850 = 37 litres / h

@ 1825rpm the engine uses 157grams of fuel per horse power.
@1825rpm puts out about 235hp
Therefore, 235 x 157 = 36895grams of fuel.
36895 divided by 850 = 43 litres / h

@ 1900rpm the engine uses 157grams of fuel per horse power.
@1900rpm puts out about 240hp
Therefore, 240 x 157 = 337680grams of fuel.
37680 divided by 850 = 44.3 litres / h

@ 2000rpm the engine uses 160grams of fuel per horse power.
@ 2000rpm puts out about 245hp
Therefore, 245 x 160 = 39200grams of fuel.
3920 divided by 850 = 46 litres / h

@ 2100rpm the engine uses 162grams of fuel per horse power.
@ 2100rpm puts out about 251hp
Therefore, 251 x 162 = 40662grams of fuel.
40662 divided by 850 = 47.8 litres / h

@ 2500rpm the engine uses 170grams of fuel per horse power.
@ 2500rpm puts out about 270hp
Therefore, 270 x 170 = 45900grams of fuel.
45900 divided by 850= 54litres / h

The least amount of grams required to make a horsepower is the most efficient rpm.
Boat planning speeds etc.. obviously throw these calc's ut of wack in the real world, although apart from a flowscan these are the next best thing....

[cormorant]

Please don't upset our shark cat owners - they are just uninspiring at those speeds but as a workboat and with the diesel rebate etc they worked out OK.

Chop Duster it is so good with diesels that you can get the full curve and know you are running them correctly loaded as you get a good life. You can see exactly where your ecconomy and designed longevity is especially with the commercial derated versions. Just have to buy the right size and style at the beginning for the performance your hull requires and you can use in 80% of conditions. Yep I've run outboards and 40kn plus plus performance and had a few wonderfull days a year when it is glassed out but 90% of the time they are underutilised. Had the same with underpowered and wrung the neck ot of smaller ones as well and got away with it on 2 strokes as they eat it but not with a new 4stroke. Non of the bullcrap outboard advertising with the commercial rated diesels..

I am still waiting on the turbo diesel outboards ( apart from the avgas etecs) and the podded diesel V- drives to get in the market as they priced right will be so good since there is so many pleasure boats in the USA now designed for very heavy twin and triple set ups and I would love a diesel version. Won't go as fast but won't burn the bum out of my wallet in running costs. I just hate sticking my head in the bilge maintaining a diesel.
http://www.megoutboards.com/

Here is one you'll like Smithy. Need a mini me version and not sure propping it for lighter weight would get huge performance improvement. Probably a bit off track as a small boat but I used to be surprised just how good these were loaded up in average weather and bouncing them off a dock won't hurt em. Windage on he cabin so far forward for drifting etc is a issue. With all these new marine parks and costs of fishing there will be a lot of great old hulls about in teh next few years. I see the upgrading of teh VMR fleets and standardisation of vessels is allowing some very well appointed boats on the market as well.

http://www.gumtree.com.au/s-ad/sorel...tres/100412669

Now this would be good to run around in for a while - comes with spares and what a great delivery home trip!!!! Nearly worth tossing in with 4 guys and having the adventure of a lifetime bringing her home. If she was a shaft drive I'd be tempted.

http://www.boatpoint.com.au/boats-fo...spx?R=12898300

Smithy

Here is a bloke local to you QLD rs- your kicker motor instead of a troll valve!! Never seen one of these

http://www.klaxondieseloutboards.com/

[myusernam]

$54000 rebuild...WTF?! surely a new motor is cheaper?

[chop duster]

Bit of food for thought --
The 2 TAMD70D volvos (2x270hp) combined chew 108 L/H to produce 540hp.
The 250 Merc Verado on our center console chews 110 L/H to produce 250hp. But it is exactly 1/3 the weight and pushing a bit over a ton to 45 knots...

[cormorant]

$54000 rebuild...WTF?! surely a new motor is cheaper?

And their lies the reason there isn't commercial diesel motors in small boats - it is bloody unaffordable to justify the costs unless you spread them over a lot of hours of commercial use with capital cost tax deductions and fuel rebates.

It used to be a old govt department strategy to repower vessels just before sale as they could bulk buy without tax etc new motors and fit them up and sell them at a profit retail attached to a boat and some charity not for profits did the same as they had a double bonus if the engine supplier alowed the "donation"of the difference between wholesale and retail and the supplier got a tax deduction. Most of these loopholes have been stopped. Some of the supply contracts had "uptime" clauses so if a replacement block or it's repair wasn't avaliable etc etc there are large daily penalty's for a vessel not being avaliable and in service within a few days. A 2 week delay and paying a suitable standby vessel charge of thousands a day often meant vessels were kept in very very good nick and manufacturers left spare motors / powerheads ready to go as it was cheaper than the penalty clauses.

Probably pulled out to rebuild and they decided to repower and rebuilt the other one afterwards. Problem with twins is that you need them both the same so if you upgrade one you do both in teh exact model and spec.

Simply the updated motors with lower fuel use , lower downtime, lower maintainance and fresh legs may have made it ecconomic to repower.

No idea what the story up there is but by the time you have sold off the motors you have a very capable boat at a prety good price.

So how much is a new one delivered Darwin I hear you ask??? I don't know but someone here will.

[Midnight]

Chop Duster,
Your best hp/gram or fuel burnt there probably coincides with the peak torque RPM.

I have always worked on the theory of operating at the peak torque rpm, or just above it, for the cruise speed, to gain the greatest efficiency and have the engine operating at its most comfortable load and rpm.

If you can spec the engines so that this occurs in a new build or repower case, or you are happy with the cruise speed for the hull at the peak torque revs, in an existing set up, then you are absolutely onto a winner.

Thanks for the numbers too, they don't lie. And in all cases there, except WOT which is normally slightly less efficient, you are running pretty well 19L/hr per 100hp.

Cheers,
Myles