Shafts 'n engines

[Guest]

Shafts \'n engines

Anyone reengined a Moonraker? Anyone had any experience with Monal shafts?

Specifically, what is the biggest engine I can cram in without having to change shaft size, P brackets etc. Perkins do a 240hp unit that would fit in the same footprint as the existing ones. Would I have to upgrade the shaft size? I have tried looking for data re tensile strengths of Monal shafts, but all I found was a French site advocating drinking a solution of magnesium alloy called "Monal" which didn't really help.

 

[Guest]

Re: Shafts \'n engines

IMHO yerl be fine with smaller dia shafts so long as there's a suitiable propellor. The key thing (crap pun intended) is the resistance to getting it started, and with a propellor in water able to slip by, there's not much resistance to startup torque anywhere near likely to shear the shaft, unlike massive truck. Shafts in boats get hurt by hitting things, not by splooshing thru water.

 

[jfm]

Re: Some dodgy maths, make bridges out of tinfoil

Generally there is massive "over capacity" in the spec of a shaft so upgrading from your present (175hp?) engines should be fine.

If you want a bit of basic maths it might go like this, using deliberately conservative numbers at every stage....
1. Tensile strength say 40 tons per square inch
2. outside dia of your shafts 2 inches
3. max torque of your new motors = say 750 Nm
4. Gearbox = 2:1 so shaft torque = 1500Nm
5. 1600Nm = 1100 ft/lbs (because despite being a very youthful poster on this BB I like imperial)
6. The rotational force exerted at a radius of 1 inch (your shaft's outer surface) by a torque of 1100 ft/lbs is 13200lbs (just multiply by 12)
7. 13200lbs is 5.9 tons
8. Therefore you need cross sectional area area of 0.15 inches
9. A tube with 2 inch outside dia needs a wall thickness of only .025inches (= .55millimetre) in order to have a cross section area of 0.15 inches
10. Therefore the rest of your shaft, the 1.9+ inches diameter of core metal is redundant and can be removed without the shaft busting.

Now, this is all a bit theoretical, it's nice to have a bit of extra metal in there to give safety margin, fatigue resistance (very important as the shaft will fail thru fatigue rather than excess stress, generally) and stiffness, and I dont really advocate making shafts out of tinfoil wrapped over old bog roll centres. But it demonstrates that the HP upgrade you have in mind is sweet FA in the scheme of things!

E&OE, as Fairline would say


JFM

 

[Guest]

Re: hmm.

Wow, proper calculations. Now, any idea where we can get an magnesium-aluminium cocktail? Do they taste like chromium-steel? (aka Screwdriver)

 

[jfm]

Re: Happy hour

Proper is a very generous description. Anyway, no idea about screwdriver but I believe Col's boat has a long sloe screw

JFM

 

[Guest]

Re: Some dodgy maths, make bridges out of tinfoil

We have got 145hp Perkins at the moment, although with the intercoolers being the way they (probably) are it is probably putting out about 100hp if we are lucky. New turbo's are about £800 each and we hopefully can repair the intercoolers. So I am trying to work out if it is worth reengining. The shafts are about 1 1/4 inch (quite narrow) and there are 17x13 props on there at the moment, although the originals were 17x14s. There used to be some sort of propeller calculating programme on the Net but I can't find it any more. I was wondering if something like four-bladed 18x14s would be enough with the original shafts with 240hp Perkins to give about 20 knots cruising? I like 20 knots - makes the maths easy!

Oh yeah. The French site is http://www.biam2.org/www/Spe15237.html that refers to Monal. On closer inspection, it is actually quite a well-know medication. D'oh! Me being a med student and all you would have thought that I would have noticed. Whoops.

 

[jfm]

Re: need more data

Cor blimey I never had a motor yacht when I was a student - can you get them on student loans? Maybe I should enroll with OU and get a student loan to buy a nice Ferretti or something.

On props the most significant variable is pitch, not diameter. I wd think intuitively that 2x240 on a moonie36 should give 20kts comfortably. Now, to work out prop pitch you need to get the engine rpm at which 245hp is developed by the engine (from the manufacturer) and the step down ratio of the gearbox. Once you have that you can work out the pitch but without that data you are all at sea. Do you have this info?

I dont understand why you think your intercoolers are responsible for the low power output of your current engines. Intercoolers really can't go wrong provided the heat transfer surfaces are kept clean. And what boost pressure are your turbos giving? if that's up to scratch then the turbos are not causing the low power either. If there are no boost gauges why not fit a pressure uage to the exhaust manifolds, any pressure gauge covering say 0-2 bar will be fine

JFM

 

[Guest]

Re: Shafts \'n engines

Doug,,try giving Johnathan Norris a ring at T.W.Norris 020 8560 3453 they are prop/shaft company, I feel sure they could answer your questions

 

[Guest]

Re: need more data

Nah - Dad owns the boat. I drive/fit it out/play with electronics/tell him what to buy etc. It is a good relationship! Good luck with a student loan - they are not even free anymore. They charge you a rate of interest above inflation levels, and you can get as good a loan anywhere else, to be honest. No grants for me, and thanks to Gordon "smile please" Brown I now have to pay 1000 quid a year. There was talk of medical students paying overseas rates as well because it costs so much to train them. That would be around 30 grand a year! No boating for me if that comes in...

I spoke to one bloke who reckoned that anything below 26" diameter props would be a waste of time and that we would notice no difference between our speed now. 26" is massive! The P brackets would be so huge that the props would be pointing almost vertical! So I don't think that is right.

The reason that I think that the intercoolers and the turbos have gone is based on a number of things. The engines drink oil at the moment (a two day trip drank 5 litres on each engine) and there is a bit too much smoke. I think that the intercooler cores have become clogged and that insufficient air is getting to the cylinders resulting in a smokey burn and less power. Also, the turbos are only giving about 75% boost. When we got the boat, the turbos were jammed as it had been used only on the river and laid up for the last few years. I had to unjam them manually by spinning the turbines over with my hands, so the bushes are probably shot and oil is leaking into the exhaust. The engines are 30 years old and probably have never been rebuilt, so it isn't really surprising. We have also been recommended that some sort of injection wizard comes along on a trip and sets up the injection properly. Any thoughts on that?

Don't know what the 240hp engines do max, but I would think that it is around the 2700-2800rpm mark. The gearboxes that we have at the moment are Borg Warner 1:1s, although we probably will change those to at least 2:1s if we repower. It depends if they will fit or not!

I think that the prop clearance means that about 18-19" props are the absolute maximum diameter. I have been told that four-bladed props increase cruising speed but not top speed, which is fine by me. Anyone tried this? I notice that Sealines all have four-bladers.

 

[tico]

Re: Shafts \'n engines

BTW it's MONEL as the material. this might help on the search.
Good luck

 

[brianrunyard]

Re: Shafts \'n engines

Have a look at
http://lancingmarine.com
They will be able to advise you.

 

[david_bagshaw]

Re: need more data

Just because the turbos give 75 % boost doesnt mean they are knackered. boost pressure is dependant on engine load, if the props were of the wrong size, or the bottom dirty, enough load at the correct rpm would not be put on the engine , thus not enough exhaust gas would go past the turbo, then low turbo pressure., and the ability to climb to full output.

I can assure you if the turbo seals fail, you would know about it immediately, as there would be so much smoke you would not see your hand, with your arms out!!!

You say the engines drink oil, yes they all did 30 years ago when turbo charging was first introduced. express the oil consumption in litres of oil per 1000 litres of fuel burnt.

Do the engines develop full rpm underload

Do they black smoke at full load, if so look to the intercooler

do they blue smoke at full load, when at running temp.

do thet run evenly at ldle when at working temp

Is there a boost control on the pump & if so is it properly connected/ not blocked

Setting pumps is best done in a workshop, after at least the injectors are serviced


Incidently, we run two turbo charged sabre 150s , never mind the using 35 scanias

david

See my web site www.yachtman.co.uk

 

[Guest]

Re: need more data

thanks for the info.

The engines don't do full revs - about 200rpm down. Also, the port engine doesn't rev as high as the other one. It has been antifouled this spring, so I don't think that would be a problem. Sometimes when the engines are cold(ish) and I knock them astern (e.g. when locking) there is so much smoke that I can't see the river behind!

The port engine smokes a lot at full revs - quite a sooty, blueish smoke. The starboard one is a bit better. I don't think that there is a boost control - there is no mention of one in the manual. Also, when at idle having warmed up the port engine revs at 600rpm, not 500rpm like the starboard.

I am beginning to think that the engines are very sick...

I will ask Lancing Marine about the props. Looks like putting four-bladed 17x14s should do something. Also, the props are pretty ancient so probably not doing wonders for speed either.

 

[Guest]

Re: Shafts \'n engines

Pardon me if I sound a bit picky but I have just had to replace perfectly good shafts on my boat because the rubber gaiters at the top of the shafts were perished and in danger of letting the briny be where it should'nt. Thruppence worth of rubber but the couplings would not uncouple and had to be cut from the shafts hence new shafts.

Anyway, my point is that the whole job cost about £1000 including new couplings and cutlass bearings. If it is not being rude, this is a bit of a drop in the bucket compared to the cost of two new Perkins 240hp so why spoil the ship for a ha'pence of tar so to speak.

Nick

 

[david_bagshaw]

Re: need more data

You say

The engines don't do full revs - about 200rpm down. ... not an excessive amount

Also, the port engine doesn't rev as high as the other one...... not unusual, perhaps less pitch will be needed on this ones prop next time



It has been antifouled this spring, so I don't think that would be a problem. ....depends on wher you keep her, is it a bad fouling area...


Sometimes when the engines are cold(ish) and I knock them astern (e.g. when locking) there is so much smoke that I can't see the river behind!..... with engines of this era this was common, due to the low compression ratio, so white smoke is formed from unburnt fuel



The port engine smokes a lot at full revs - quite a sooty, blueish smoke.,..... soot =overload or defective injectors at the first

The starboard one is a bit better......not loaded quite as heavly as the port

I don't think that there is a boost control...... usually a contracption on the back / top of the pump with a pipe to the inlet manifold to sense the pressure.

Also, when at idle having warmed up the port engine revs at 600rpm, not 500rpm like the starboard..... could be nothing, just the setting of the idle screw or had been raised to this level toavoid syncro vibrations as the engines tickover.

My advice for what it is not worth ... and it might save a lot of money,

Service both engines fully, including tappet clearance etc, especially air filters, have the injectors serviced, expect a bill of about £7-10 per injector. be sure to use the correct viscosity oil, quite hard to get the thicker engine oils these older engines were designed to use. Check the engine crankcase breathers are clear.

Also check the dipsticks were cut to the correct length for the installation angle. dont laugh at this as it is a common problem, leading to over filling of the sump.

consider how much extra equipement has been added since she was new


Then run her again. dont buy new props until this is done as you will just introduce a new variable to the equation, and willnever get to the bottom of it.

David


See my web site www.yachtman.co.uk

 

[Guest]

Re: need more data

Thanks very much. Will do. Considerably cheaper than about 18 grand to reengine when all is said and done!