Volkswagen Jetta 1.6 - how many HP - prop calc

[sailingmonica]

Hi to all, new to this forum.

We built our own 42 ft sailboat and marinized a VW Jetta Diesel 1.6 (non turbo, with hydraulic lifters) from a car. It workes great, have already been down South through the ICW and had no problems. Except we cannot seem to be able to figure out the right prop size.

I have subscribed to boatdiesel.com, but in order to get the calc I have to input Hp and RPM. Except I do not know what to enter, because the engine is rated 53 Hp at 4,000 RPM on a car, where there is little resistance. My boat is 42 ft LOL, 31 ft LOW, full keel, propeller in aperture, 30,000 lbs displacement (unloaded), shaft length 70 inches, shaft diameter 1.25 inches, ZF transmission with 2.6:1 ratio in forward, using an Aquadrive system (thrust bearing/CV joint combo). Calculated hull speed 7.3 knots.

Currently I have a 3 blade RH 16X10 propeller. I have good control while docking (very important to me), but pick up speed very slowly and can only get up to maybe 6 knots, if that. And that is at about 3,000 - 3,200 RPM. I can never achieve full rated RPM, but I don't really expect that. All I want to know is how many marine HP can I get from a 53 HP car engine. Has anyone done this before? Any suggestions are welcome and appreciated.

Monica

Welcome Monica,

the power of your engine does´nt change, no matter which application it is used in. But of course, at the given rpm you will not have the full "rated" hp available. There either the prop diameter is too large, or the pitch to high to achieve the rated rpm.
We have some members here pretty familiar with the VW Golf engines (yours is one), and others skilled on prop settings. And one on both.
Wait they will chime in. CDK..Baeckmo..!!..???

Regards
Richard

[marshmat]

Hi Monica, welcome aboard the forum.

Your engine has no way of knowing whether it's in a boat or a car- given the same RPM and the same shaft torque, it'll put out the same power. (Of course, there are a few different ways of measuring horsepower, ie. it'll be a bigger number if you measure it at the crankshaft- "BHP"- instead of the propeller shaft, "SHP".) If you got 53 hp at 4000 rpm in the car, and haven't made any modifications to the engine, it'll still make 53 hp at 4000 rpm in the boat. If it's too heavily loaded to reach full RPM, then obviously it won't reach full power either. Of course, sometimes when an engine is marinized, the cam might be changed, injector timing tweaked, etc. all of which will change the ratings.

Generally speaking, a prop is usually chosen so that the engine is fully loaded at full RPM. Since you can only reach about 3200 rpm on an engine that is meant to rev up to 4000, your prop is probably a bit too big. Or it might just be a mass of weedy barnacles- worth checking. Being unable to reach full RPM means that the engine is, somehow, overloaded- which can greatly reduce its lifespan.

A 16" dia. by 10" pitch 3-blade prop sounds to be in the right ballpark for the specs you've provided. (A very rough calculation suggests 17x10 as a starting point.) Thus, I am suspicious that either your prop is not what it appears to be, or your engine has been detuned to a fair bit below its rated 53 hp. The former problem calls for an inspection and possibly repair/replacement of the prop; the latter problem would call for engine repair (if faulty) or a smaller diameter, lower pitch prop (if the engine has in fact been detuned).

Finally, your relatively heavy, 31' LWL full-keel yacht is not going to do any better than 7 knots under power, tops, and roughly 50 hp should be in the right ballpark for a hull of this weight.

Somehow I did know it will be one I did not mention!
Sorry Matt..........

[baeckmo]

Oops, didn't observe the challenge, ya know how to tease me Richard!! Lady in distress and all.........

In addition to Matt's advice, let's check your existing setup; there is something weird somewhere. A preliminary calc shows that a 16x10 prop, running ~1190 rpm as yours does, will only use about 15 hp, and supply some 1630 Newtons of thrust at 6 knots, provided it is not completely fouled by seaweed or totally hidden behind a thick, square lump of keel structure.

With this prop your engine should be running full rpms, ie at the governor limited speed (~4100-4200 rpm) if it is what it says. My first guess is that the prop is not clean.

But this screw is not correct anyway, I would rather see a 17*11, giving ~3900 rpm at ~7 knots (thrust 4000 N), provided the engine is not de-tuned or suffers from high exhaust back pressure or faulty fuel system (check how the fuel return from injection pump is installed).

So, first get wet and check what you have down below!

[Angélique]

Originally Posted by baeckmo

... or totally hidden behind a thick, square lump of keel structure.

Take a look: pic. ‘‘Monica’’ from behind

See also this thread: Hello from Toronto

Nice story Monica and a beautiful boat !!

Regards, Angel

[marshmat]

Looks clean enough to me.... and Toronto isn't exactly prime territory for fouling organisms.

So we're more likely looking at an engine not making its supposed rated power- maybe it was detuned a bit during marinizing, maybe there's a back pressure problem, maybe the reduction gear isn't as steep as it says..... even so, baeckmo's calcs suggest that you shouldn't need full power anyway, so what else could be going on..... hmmm..... this isn't one of those computerized motors, is it?

[Angélique]

Were the bottom and propeller just as clean as the picture shows when the problems occurred? In a one year cruise ‘‘Monica’’ could have been in prime territory for fouling organisms and cleaned afterwards. If it is a current picture, in what state came the boat out of the water?

Regards, Angel

[CDK]

Originally Posted by apex1

Welcome Monica,

the power of your engine does´nt change, no matter which application it is used in. But of course, at the given rpm you will not have the full "rated" hp available. There either the prop diameter is too large, or the pitch to high to achieve the rated rpm.
We have some members here pretty familiar with the VW Golf engines (yours is one), and others skilled on prop settings. And one on both.
Wait they will chime in. CDK..Baeckmo..!!..???

Regards
Richard

I won't take the bait this time Richard. As long as I didn't solve my own problem I don't feel qualified....

[liki]

Would the engine in question be 1.6D JP or ME or similar, 40kW@4800rpm and 100Nm at 2300rpm. Torque peak translates into a little over 24kW.

If it can provide still 90Nm at 3200 rpm, it should mean power output (maximum) of about 30kW. 90Nm@3200 rpm is a pure guess.

Cornelis you´re too humble!

Liki, you should translate JP or ME, except for CDK and Baeckmo (and me), there will hardly anyone else understand what you are referring to.

Nice boat Monica!

[liki]

you should translate JP or ME

Yes, these are VAG motor type codes, telling the exact type of the engine. Otherwise meaningless, but the correct engine rating can be found out if the type is known - It should be marked somewhere in the engine block or head.

[Angélique]

Originally Posted by sailingmonica

... the engine is rated 53 Hp at 4,000 RPM on a car

The engine is most likely rated 54.8 Hp (40.3 kW) @ 4,800 rpm (engine #1) or 50.7 Hp (37.3 kW) @ 5,000 rpm (engine #2). See engine spec's below.

... pick up speed very slowly and can only get up to maybe 6 knots, if that. And that is at about 3,000 - 3,200 RPM. I can never achieve full rated RPM

Looking at the data that Matt, baeckmo and liki have provided the prop should be a piece of cake for the engine.

What is the max rpm with the transmission in its neutral position? If there is no engine problem, and its not detuned, it sould be easy to reach 4,800 rpm for engine #1 and 5,000 rpm for engine #2.

Matt / baeckmo / liki / CDK, till what rpm and for how long (short) can she safely test it while running unloaded?

If you can't reach the 'max-power' rpm while running unloaded then its maybe a governor problem. Or just the screw on the fuelpump -that limits the full throttle position of the leverage wich is connected to the throttle handle- is to far out. Dirt in the fuel system can also be the problem.

From your information I gather that you have the first of the two engines below. If not then I guess its the second.

1983+ Volkswagen Golf 1.6 Diesel (engine #1)

http://www.carfolio.com/specificatio...car/?car=38577

- Bore × stroke: 76.50 mm × 86.40 mm, 3.01 in × 3.4 in
- Cylinders: Straight 4
- Displacement: 1.6 litre, 1588 cc, (96.906 cu in)
- Type: Single OverHead Camshaft, 2 valves per cylinder, 8 valves in total
- Compression ratio: 23.00:1
- Fuel system: Bosch diesel inj.
- Maximum power: (DIN) 54.8 HP/PS/PK/CV/... (54.0 bhp) (40.3 kW) @ 4800 rpm
- Specific output: 34 bhp/litre, 0.56 bhp/cu in
- Maximum torque: (DIN) 100.0 Nm (74 ft·lb) (10.2 kgm) @ 2300 rpm
- bmep = Brake Mean Effective Pressure: 791.3 kPa (114.8 psi)
- Specific torque: 62.97 Nm/litre
- Maximum rpm: ????
- Main bearings: 5
- Coolant: Water
- Bore/stroke ratio: 0.89
- Unitary capacity: 397 cc/cylinder
- Aspiration: Normal D. (atmospheric pressure)
- Compressor: None
- Intercooler: None
- Catalytic converter: None

1978+ Volkswagen Golf L Diesel (engine #2)

http://www.carfolio.com/specificatio...car/?car=43032

- Bore × stroke: 76.50 mm × 80.00 mm, 3.01 in × 3.15 in
- Cylinders: Straight 4
- Displacement: 1.5 litre, 1471 cc, (89.766 cu in)
- Type: Single OverHead Camshaft, 2 valves per cylinder, 8 valves in total
- Compression ratio: 23.50:1
- Fuel system: Bosch diesel inj.
- Maximum power: (DIN) 50.7 HP/PS/PK/CV/... (50.0 bhp) (37.3 kW) @ 5000 rpm
- Specific output: 34 bhp/litre, 0.56 bhp/cu in
- Maximum torque: (DIN) 80.0 Nm (59 ft·lb) (8.2 kgm) @ 3000 rpm
- bmep = Brake Mean Effective Pressure: 683.4 kPa (99.1 psi)
- Specific torque: 54.38 Nm/litre
- Maximum rpm: ????
- Main bearings: 5
- Coolant: Water
- Bore/stroke ratio: 0.96
- Unitary capacity: 367.75 cc/cylinder
- Aspiration: Normal D. (atmospheric pressure)
- Compressor: None
- Intercooler: None
- Catalytic converter: None

When was the last distribution belt replacement? It has nothing to do with this problem but to avoid serious problems in the future its best to replace it on time.

Regards,

Angel

P.S.
Jeff / Monica, I see four posts of Monica in two threads, but Monica's post number is still at one. Is there a problem?

[Jeff]

P.S. Jeff / Monica, I see four posts of Monica in two threads, but Monica's post number is still at one. Is there a problem?

Posts in the Open Discussion and Forum Questions & Suggestions forums do not increment a user's post count since they're considered more friendly conversation rather than the rest of the forums which are more closely on-topic and/or technical in nature.

[Angélique]

The possiblity of too much back pressure -and much more- has already been mentioned (baeckmo & Matt) but how is the air intake? Is it sufficient? Engine #1 has to take in -without to much resistance- 1,588 L / 4 stroke x 4,800 rpm = 1,906 L/min = nearly 2 m³ air per minute. Matt / baeckmo / liki / CDK, how big a hole do you need for that also taking into account the resistance of the air filter? Monica, does your air intake match with that figure (hope it comes) And... is the air filter clean ?

Regards,
Angel

P.S. Thanx for the info Jeff !!