small tug engine sugestions

[yowiepower]

G’day all from the land down under. Could some one please give me an idea on the sort of engine I should be looking for I am currently in the planning stage of my boat project which is a 21 foot mal low pelikan tug design, I am going to build in steel. What I would like to know is what make/model engine should I look for in the 120-150 hp range? What gearbox would be recommended? My first post so please forgive stupid questions.

[Frosty]

Small tug? Make one,- don't waste money on some thing like crap Yanmar.

I would use a Hino E700 180 HP and bolt up a Borg warner.

Keel cool it with fresh water system and big ole chinese heat exchanger with dry exhaust.

[marshmat]

Hi yowiepower, welcome aboard

Frosty's a little bitter about Yanmar these days (he has a couple of troublesome ones). In any case, most of the Yanmar line seem to be intended either for sailboat auxiliaries or for fast craft that need light, high-revving motors.

What it really comes down to, yowie, is what you can readily get repaired in your area. Everything breaks, eventually. If you buy a Cummins and the nearest Cummins service centre is 1200 miles away, shame on you. On the other hand, if you have a Cummins dealer in the next town over, and he has good mechanics, that could be a big factor in favour of that brand.

For a tug-like boat, you're probably more interested in something that can run quietly and smoothly at 75% throttle for hours on end, than in something that can give you short blasts of insanely high power.

The way to figure out your gearbox needs (and, to some extent, your engine needs) is to start with the propeller calculations. Do the Bp-delta calculation for your hull, with a few different propeller styles, and you'll know how much torque you need at what RPM on the shaft. From there, you can start matching engines to gearboxes.

Welcome here yowie,

the 120 to 150 range is a bit a difficult one because thats exactly the upper end of the 4cyl. and the lower of the six cyl. engines at a heavy duty power rating. (M1 or M2)
The "Vetus Deutz" DT 66 is a six cyl. of about 160 horses shaft rating at 6.6ltr. displacemet, the "JohnDeere 6068" 6 cyl. of 6.8 ltr. displacement is another example in that ballpark. The "John Deere 4045" 4 cyl. of 4.5 ltr. comes at the lower end of your power requirement.
Cummins is worth a closer look too.
Gearboxes to fit these high torque engines are commonly ZF, PRM or Twin Disk . When really heavy duty "Reintjes" is the gear.

If you are out for extended use, or do´nt like to buy a second and third prop due to failed Prop calc.s (a common mistake), you should choose a Controllable Pitch Propeller (no gearbox). That makes your engines happy, economic, and last ´til eternity. (due to the better "load" characteristics achieved by prop setting, which is´nt possible with a fixed prop/gearbox)
Main names in that field are "Sabb", "Hundested", "Helseth", "Westmekan" to name the most common and proven. The complete Scandinavian fishing fleet uses one or the other of the brands named.

Choose the largest wheel you can turn at the lowest rpm and match that with the highest torque engine you can find.
Take care to have a min. tip clearance of 15% (prop dia.) between prop and hull, 20% is better.

Regards
Richard

[CTMD]

Yowiepower where in SW Victoria are you? Port Fairy, Warrnambool? I might have a local contact for you for second hand engines. Would you be interested?

[Frosty]

A variable pitch prop and shaft arrangement will I think be more that the entire boat will cost.

Originally Posted by Frosty

A variable pitch prop and shaft arrangement will I think be more that the entire boat will cost.

Well Frosty, that is a very common belief, nevertheless it is´nt true. If compared with a high quality conventional installation, the price is about the same! When you have to replace a prop due to wrong calc.s or so, you are way above the cost of a CPP system. And I have seen many owners replacing the original prop (some even more than once) pretty soon.

[Frosty]

A freind of mine bought a 90 foot Russian trawler, it was on the beach. I went to see him and found my way down to the engine room where he was fixing a starter motor to start the generator to start the compressor to pump up enough air to start the main and see if the variable pitch prop worked.

He said that if the prop dont work the boat is scrap.

A conventional installation is a shaft and prop with some shaft bearing supports. A variable needs a hollow shaft to operate the prop which by the way only changes pitch. If the shaft is only slightly bent it wont work the prop pitch mechanism.

A good idea for ocean going deepwater tugs with constant RPM engines but for economical coastal DIY ?

[hartley]

g;day yowiepower,south west victoria eh ,warrnambool my old home town
born in hamilton,a looong time ago.where are you going to use the 21 footer
pretty rough coast along there ,portland maybe.good advice from CTMD ,get a good second hand diesel ,a machine shop will be able to bolt up a borg warner gear,plenty of those about ,and easy to bolt up ,keel cooling and dry
exhaust and there you have it ,maybe CTMD could help you along the way
naval architecs KNOW what they are talking about ......cheers hartley

[yowiepower]

Thanks for the ideas guys and the warm welcome,
I am about 60 k’s north of portland CTMD (seems so logical that I would want to build a boat so far from the coast doesn’t it) and we have a holiday house down at pt fairy so any contacts you have would be great. this variable pitch prop sounds very complex also sounds like it costs a small fortune but spot on in many different conditions.

To make that clear again (we had this senseless discussion more than twenty times now), a CPP does NOT cost more than a good quality conventional installation! And all the suppliers named above produce extremely reliable and top quality CPP installations only. There will nothing bend or fail.
And Frosty, no Scandinavian fishboat has a constant speed engine, but ALL have a CPP! And I know for sure that fishermen do´nt have money to waste either. The opposite is reality, they save a lot of money, due to far better economy on their engines. Fuel savings of about 30% are not the maximum achievable. And lifetime easily doubles.
Of course if second hand equipment is the competition, there is no race to win for a CPP.
To conclude: A CPP is not complex, not more expensive than a gearbox/shaft and has at least the same reliability. When it comes to lifetime cost the CPP is far cheaper than the conventional. When economy is a must, the gearbox arrangement is out of race! And when the boat (as I mentioned above) is really in use, the engine lifetime cost will be worlds above in a conventional arrangement.

So, why do´nt we see more of those CPP´s? Thats due to the stupidly and stubbornly repeated nonsense that such installation costs a fortune. Even some boatbuilders and designers are stupid enough to say so. Fact is that nobody who ever did install it comes to the same conclusion. Quite the opposite!

I install far more conventional systems than CPP´s only for one reason, 90% of my boats are fast powerboats, there a CPP has no advantage, the speed optimized fixed prop is the better choice. In my displacement boats you find Sabb and Hundested only!

Regards
Richard

[Frosty]

Wow Apex your soooo good , how could I be so foolish. Im sorry for annoying you and having said something in your presence.

You tell him what to do, I wont say anything anymore.

I cant be bothered to argue with you, Im sure your right.

Dunno why you take that personal Frosty.

It´s just a fact that when you leave the Baltic and North sea region nealrly nobody knows a bit about CPP installations, but almost all believe they are complicated and expensive.

And it was your friend who made a foolish statement. When the shaft is bent (no matter fixed or variable prop) your propulsion is shot! But when a CPP has a damaged blade it is less than half the cost to fix that as it was to fix a similar damage on a fixed prop (if possible).


But lets hear what a well established US designer has to say about his experience with CPP versus fixed prop:

http://www.kastenmarine.com/CPprops.htm

Regards
Richard

[yowiepower]

cheers guys by the sounds of it a CPP will save u money by not having to keep replacing you prop and like everything if you buy quality you will get a good run out of it. also sorry apex1 for opening up that old wound about the cost of a CPP great articale you gave us

Welcome mate. I do´nt mind to inform a amateur or novice, none of us knows everything. But it is annoying to repeat the same prayer to the same audience everytime again. And having everytime the same stupid and non valid "arguments". If they are too lazy to read a article, they should stay quiet. Nobody can be blamed for ignorance, but combined with a know all attitude it´s a plague.

If you can afford a higher than average (of course they are), investment in your propulsion and if the vessel in question is used more than the average 100hrs per annum go for a CPP system. You otherwise may find out soon: the poor man pays twice.

Regards
Richard