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Old 08-27-2009, 07:46 PM   #1
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30 Horspower Saab Diesel with a variable pitch prop

I am looking into replacing the diesel engine in my 25 foot trawler, I would like to know if any one has any advice regarding the Sabb Diesel 30 horse Power with a variable prop. I
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Old 08-27-2009, 10:20 PM   #2
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RE: 30 Horspower Saab Diesel with a variable pitch prop

Robert,
Why on earth would you want an old Sabb engine w a heavy, complicated and perhaps troublesome vari-pitch prop. In theory the way to go is w vari-pitch prop but in the real world a nice modern engine and gear box** ..* well why would you not want that? Is your 25' trawler an Albin? I had one and can give you lots of opnions there,

Eric Henning
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Old 08-28-2009, 04:39 AM   #3
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RE: 30 Horspower Saab Diesel with a variable pitch prop

The problem with the old Sabbs may be parts locating.

A heavy duty slow running engine with CPP is a good choice IF you run enough hours a year to need such efficency and reliability.

Yes there heavy , but it adds to the reliability that a 3200rpm flea like a Yanmar or Kubota could only dream of.

That said either Y or K are fine modern high speed diesels , with a proper selection and gear box they can do yachtie duty for a long time.Couple of hundred hours a year at cruise.

For replacement selection we use working "swept volume" to decide on the replacement size and cruise RPM.

Take the cubic inches of the old engine and multiply by the usual cruise RPM

Divide that number by the cubic inches of the replacement and you have the new required RPM at cruise.

Look in the makers site and see if you can run there cont, and if its at least 300rpm below the rated top rpm.

If it isn't , look at the next larger size.

3 Cyl will usually be smoother than 4 , as well as lighter.

Have you considered your own marinization (saves 1/2 to 2/3 of cost?)

Smaller engine cruise loaded to 80% is most desirable from a engine service life , but may not be enough to punch thru F 7 at normal cruise speeds.

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Old 08-28-2009, 11:31 AM   #4
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30 Horspower Saab Diesel with a variable pitch prop

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nomadwilly wrote:Why on earth would you want an old Sabb engine w a heavy, complicated and perhaps troublesome vari-pitch prop.
I would echo Eric's question.* If one was talking about a cruise ship or a tug or a ferry a variable pitch prop would probably be the most efficient way to go.* But we're talking about a 25' boat here.* If there's anything that warrants the KISS principle it's this.*

I don't know enough to suggest what sort of engines are ideal or available for this type of boat, but I agree with Eric that a nice, simple, reliable diesel mated to a basic marine gear, propshaft, and prop*would be the far more cost-effective and reliable way to go.* Given the size of the boat, whatever efficiency*might be realized from the use a variable-pitch prop will pobably be measured by very small*fractions of a gallon per hour, and this minimal savings*will probably be more than wiped out by the maintenance and potential problems generated by the drive train.*

The more moving parts you have, the more you increase the chances for a failure or problem.* This is why jet engines are WAY more reliable than piston engines.* You have two or three primary*moving parts depending on the engine type, versus--- well, I don't know how many if you include pistons, valves, camshafts, rocker arms, etc.*

-- Edited by Marin on Friday 28th of August 2009 11:32:35 AM
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Old 08-28-2009, 12:09 PM   #5
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RE: 30 Horspower Saab Diesel with a variable pitch prop

One thought that may make some of the folks that never lived with a gas engine may have a hissy fit ,

But why diesel?? If the boat does under 200-250 hours a year.

Gas has all the advantages , cost , quiet , cheap to service , easy to service in the size engine this boat needs.

My guess would be 10 hp ,under 1/2 gph in diesel or 5/6 gph in gasoline.

An electric start Honda with factory gear reduction would be under $2k.

The fuel could be kept in outboard 12g tanks , and emptied into the owners car at the end of any cruising.

Just a thought.
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Old 08-28-2009, 02:25 PM   #6
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RE: 30 Horspower Saab Diesel with a variable pitch prop

Ten horsepower on a 26 foot boat? I dunno.... Not everyone want to cruise at a glacial pace. On the other hand, I consider everything under 15 knots to be a glacial pace.......
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Old 08-29-2009, 04:18 AM   #7
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30 Horspower Saab Diesel with a variable pitch prop

"Ten horsepower on a 26 foot boat?"

Well it is assumed its a displacement boat , so huge additions of power only make waves and heat the ocean

A 26 ft boat woulds be hard pressed to get a 25 ft LWL so 5K , 6mph is the economical cruise .

I assume the boat would weigh under 12,000lbs , @ 2240 per ton , under 5 tons.

2 Hp per ton is a reasonable cruise with 3HP ton* (50% more fuel burn )would only get to near hull speed , another 1K

To go fast , in this boat would require a SL of over 3 , pure plaining , so were looking for a* hundredHP not ten.

3 times the speed , with a displacement hull shape , probably 10X the fuel burn, just means someone bought the wrong boat.





-- Edited by FF on Saturday 29th of August 2009 04:20:20 AM
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Old 08-29-2009, 07:33 AM   #8
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30 Horspower Saab Diesel with a variable pitch prop

Thank you for your input. After reading the suggestions and comments I will abandon the old saab diesel and investigate a more tradional power train for the boat. I will look at yanmar, kubota, and volvo diesel engines ranging in horsepower from 18 to 30 driving a one inch stainless steel shaft with a prop in the range of 12/14 or a if possible a 12/16, hull speed is said to be 10k that I cannot confirm at this time. The vessel is a Hercules trawler designed by Glen-L the boat measures between 24 and 25 feet and weighs approximately 5500 lbs loaded with water and fuel. I would like to attain a cruise speed between 8 and 10 knots at 2800 rpm any slower and it limits my travel. I am running out of Lake Ontario from Hamilton Harbour which is on the south west tip of Lake Ontario. I travel from Hamilton to Niagara on the lake, and Toronto island, to cover this distance it takes 4 to 5 hours at 5 to 5.5 knots I am desperately looking for a little more speed, 8 to 10 knots would make me happy.

-- Edited by Knotinahurry on Saturday 29th of August 2009 07:35:30 AM
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Old 08-29-2009, 11:32 AM   #9
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RE: 30 Horspower Saab Diesel with a variable pitch prop

"Take the cubic inches of the old engine and multiply by the usual cruise RPM ..."

If memory serves,*the term for that kind of calculation is aruspicy.
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Old 08-29-2009, 01:37 PM   #10
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RE: 30 Horspower Saab Diesel with a variable pitch prop

Aruspicy:
Also haruspicy. The ancient Druidic, Etruscan and Roman practice of examining the entrails, mainly the liver (hepatoscopy), of sacrificial animals for purposes of divination; frequent part of augury performed by a specialised priest, the Aruspex. Mention of it also occurs in the Old Testament (Ezekiel 21:21) in regard to practices of non-Hebrew tribes, including the Egyptians.

The practice ceased with the establishment of Christianity as the state religion of Rome but until then it was popular with people who could afford to sacrifice (the animal was naturally eaten afterwards) and given great heed by emperors and generals. It may have lasted longer in north-western Europe which wasn't christianised until much later. In modern times, there's limited use of this practice in association with voodoo.

Some practitioners used human entrails and this widely illegal practice of (anthropomancy) is recorded as late as the fourth century CE but may have been part of the black arts in later times.
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Old 08-29-2009, 02:35 PM   #11
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RE: 30 Horspower Saab Diesel with a variable pitch prop

"The ancient Druidic, Etruscan and Roman practice of examining the entrails ..."

Yeah, that's it, that's what I meant to say.
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Old 08-29-2009, 06:40 PM   #12
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30 Horspower Saab Diesel with a variable pitch prop

Robert,
I did some research on your behalf. I had a 25' Albin for a number of years and have seen about 30 of them in a club. The Albin 25 is about exactly the same size and displacement as the GL Hercules. I looked at their website and they show no hull lines so I'm not shure but I suspect It's too much of a displacement hull to get you very close to 10 knots cruise. The Albins had a power range of 22 to 44hp. My own Albin had a 34hp Yanmar w 1 1/8" shaft and 15" propeller. I could get a bit over 10 knots WOT. When I first owned the boat I ran it at 8.5 knots most all the time (2750 rpm on a 3450 rpm max). Later I ran the boat to Alaska and back at 2425 rpm and 7.3 knots. We looked at a Glen L 28' Jolly Rodger that had a 4-107 Perkins. The Willard we bought had a Perkins 4-107 also. I took out the Perkins and installed a 37 hp Mitsubishi. The same engine is availible in a 33 hp version (destroked). The 33 hp Mitsu is the smallest 4 cyl engine availible. Other engines you may consider or that I have considered are, 33 or 42 hp Vetus, 32 hp Isusu, 27 hp Yanmar, 44 hp Westerbeke and perhaps Volvo. The engine you need is within a very narrow power range** .. very close to 35 hp. The Westerbeke 44, the Vetus 42 and the Klassen 37 hp engines are all the exact same engine** ..* Mitsu 4 cyl w 107 cu in 78x92 mm bore/stroke. Volvo engines are very good and very popular in Europe but parts prices may be high in the US. Universal did have a 42 hp Kabota but no more. Beta (England) offers Kabota engines marinized. There are lots of engines just below 30 hp and lots just above 40 hp but very few about 35 hp. That was my delema. If you use a 3 cyl eng in a light boat you may want to consider an Aqua Drive and very soft mounts.
What is your highest concern reguarding the engine, cost, weight, power, smoothness, fuel burn or what? Since you already have the boat you may need to consider the shaft offset.

Eric Henning

-- Edited by nomadwilly on Saturday 29th of August 2009 06:45:32 PM
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Old 08-30-2009, 05:42 AM   #13
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30 Horspower Saab Diesel with a variable pitch prop

"Take the cubic inches of the old engine and multiply by the usual cruise RPM ..."

"If memory serves, the term for that kind of calculation is aruspicy."

Actually its a measure of WORK ,the swept volume (displacement) of the engine times the RPM.

A thought that has not yet put forward is to keep the usually efficient and trouble free CPP and just stick in a replacement motor.

A bellhousing adapter might be needed to be Mfg , but that's hardly a problem.

At only 5500lbs the boat is nice and light , only about 2 1/2 tons or so.

With 10hp to 15hp per ton the wake drag will probably be really high but well above displacement speed may be possible.

The usual problem is the stern will sink further and further , although Herrishof used a retrofitted mounted set of horizontal fins to counter this on his canoe sterned , overpowered boats.

Might work for your boat?

3 cyl are* balanced by their design ,
to get a 4 cyl smooth usually takes a special counter shaft and operation with certain speeds restricted.

So an Aquadrive and soft mounts are a needed* addition to a 4 banger ,

but hardly needed on a smoother 3.

We installed Volvo MD3B is various boats and the soft mounts were no smoother (but they were* quieter) than the workboat style bolted down.


-- Edited by FF on Sunday 30th of August 2009 05:47:40 AM
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Old 09-25-2009, 08:10 PM   #14
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RE: 30 Horspower Saab Diesel with a variable pitch prop

If you are abandoning the Sabb, what is to become of it?** These are monuments to Cast Iron, and last forever.* Slow turning is the way to go, and why not have something to fiddle with.* And don't forget, if you like the concept of the adjustable pitch but have been talked out of the Sabb, you can fit it to a newer diesel.

Who would seriously put a gas engine in a boat anyway?
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Old 09-26-2009, 05:47 AM   #15
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RE: 30 Horspower Saab Diesel with a variable pitch prop

"Who would seriously put a gas engine in a boat anyway?"


Anyone that wanted to lower the yearly cost of operation that runs the usual yacht 100 -200 hours of operation.

The engine cost is a fraction of most diesels ('cept used diesels).

The oil is std , not more expensive , there is NO underloading hassles from light loads , parts are usually 1/10 the cost of diesel , and anyone can fix them with the usual tool box.

The ease of proper winter storage (drain the carb vs insert preserving fuel into the injection system) and many other low cost procedures make gas the first choice for a limited time coastal cruiser. The great lakes is gas boat heaven .(3 or 4 month season)

The usual downfall of gas is the limited Hp for folks that really need say 250hp+.

Not many trawler guys cruising at that power level.

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Old 09-27-2009, 05:03 PM   #16
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RE: 30 Horspower Saab Diesel with a variable pitch prop

Hi FF,

Just checking to see who is out there.**

Unfortunately you are right, not many are doing much cruising, mostly sitting at the marina at best.

Most probably are so overpowered that is all they can afford to do.

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Old 09-27-2009, 10:11 PM   #17
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RE: 30 Horspower Saab Diesel with a variable pitch prop

Very good Fred,
I'm buyin this 100%. Would like to add two really big reasons to go gas. smoothness and quietness. These are huge issues on a yacht and the reasons I would have for converting to gas if I did. Another big item w the women is smell.

Eric Henning
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Old 09-28-2009, 05:12 AM   #18
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RE: 30 Horspower Saab Diesel with a variable pitch prop

The biggest downside on a gas boat is the Gov mandated gas with alcohol added.

The storage life is so short movable (6 or 12) gal tanks , and draining into the car is the only solution.
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Old 09-28-2009, 06:48 PM   #19
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RE: 30 Horspower Saab Diesel with a variable pitch prop

Do women like the smell of gas?
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Old 09-28-2009, 08:18 PM   #20
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RE: 30 Horspower Saab Diesel with a variable pitch prop

My wife doesn't....that's why we keep a good supply of "Gas X" on the boat.
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