Wednesday, 23 January 2008

Props, gearboxes and final drive ratios

I'm nearly there as far as a decision about gearboxes etc.

Crowthers got back to me:
Have now carried out calculations for you and have the following recommendation:-
Based on a direct drive gearbox 1:1 the propeller would be 21" diameter.
1:5:1 the correct propeller would be 28" diameter but we note you would be unable to swing this and therefore put forward one of our compensated range of propellers which would be 24" but with a larger blade area ratio to give the equivalent of the 28" required.
Obviously it would not be possible for you to have 2:1 reduction as even with our compensated range you would not be able to accommodate a big enough diameter.

That leaves me with two options for a prm gearbox:
A prm 500 or prm 750 with 1.5:1 reduction throwing a 24" compensated prop
A prm 750 with a 1:1 reduction throwing a 21" standard prop

Both gearboxes are an expensive choice! About par for the course

I now hunt for a gearbox. There's not much call for the bigger prm units on the inland waterways. I'll have trawl the marine breakers on the coast.

The positive side is that the mounting dimensions for both the 500 & the 750 are identical, which means that I can make a mounting plate up ready for the gearbox to connect to the engine.

If any of you have a 500 or 750 at the back of the garage - let me know!

Monday, 21 January 2008

A Three Pot National

For those of you who have missed Sarah's comment on the last post - Here is Warriors National 3DM in glorious sound and vision.

Are there any more three pot units out there?

Sunday, 20 January 2008

Nationals in Action

Progress on the engine is currently consisting of cleaning, wire brushing, cleaning, wire brushing and more cleaning. A slow and laborious task that has to be done before any real painting and restoration work can take place. Not very exciting and certainly not good blog reading. Still, it has to be done.

During those times that I've not been cleaning, wire........etc etc, various searches for info and connections for National engines have thrown up a few video clips. If you've got a few minutes spare have a look (and listen):
The first three are of the Stewarts & Lloyds Tug No3 'Vesta' (2DM)
The next two are MB Swallow and her 2DM
and finishing off with the small woolwich Alcor with her 2DM

I don't think I'm contravening any copyright by publishing the links as they're all out in the public domain. If anyone has any objections or would like some recognition for them, let me know.


Friday, 18 January 2008

Thoughts on gearboxes etc

Its been a funny week, this week.
My parents have been over from 'Europe' (they live on a Dutch Barge - of no fixed abode) so I have been entertaining and talking boats/engines etc.

Mini and Vix - you'll be glad to know that this entry is not about rushing in with hammer and spanner, but thinking about engineering solutions for the future.

Long discussions took place about how to connect the engine to a gearbox/prop.

It sounds simple enough, but, as the 3D is an industrial engine the non flywheel end of the engine had the hand start dog fitted to it. A large triple vee belt pulley was bolted to the flywheel which was the power end of the engine.

Obviously, a genuine marine engine (see Warriors 3DM) had a different configuration at the non flywheel end of the crankshaft to allow the coupling of a gear box. So what to do?

The first decision has to be which way round to face the engine. The most common configuration for 'traditional' marine engines is to have the flywheel at the bow end and the gearbox connected to the non flywheel end. That said, as the years progressed and the basic engine block for both marine/automotive and stationary use became common, the flywheel often found its way to the gearbox end of the engine (often found on Gardners). In modern engines this is almost now the standard configuration.

Many marinised 'stationary' vintage engines have the gearbox at the flywheel end as this is usually the easiest engineering solution. It also protects the engine should the prop suddenly strike an object and stop suddenly. Something has to 'give' to absorb the stored energy in the flywheel. Better a bent prop blade/stripped gear/bent shaft rather than snapping the crank in your prized vintage engine!

The other decision has to be gearbox/prop shaft arrangements.
  1. A close coupled prm type gearbox
  2. A remote gearbox with double propshafts (as fitted to NB 'Hadar').
  3. Pure hydraulic drive system (hyd' pump bolted to the engine - hyd' motor down by the stern gland)

Above are NB Hadar's 'remote gearbox, using two shorter shafts reduces shaft torque 'wind up' and vibration

I'm fairly sure that current DM2 RN's use a prm 150 gearbox (not sure of the reduction ratio). I contacted prm and they advised that a prm 260 should be used due to the additional power/torque of the 3 cylinder engine.

If I use a prm 260 it would be a 2:1 reduction ratio. That would mean prop speeds of 125 to 500 rpm, which in turn will need a large diameter/pitch prop. If I went up to a prm 500, I could get it in 1.5:1 reduction. This would mean prop speeds of 167 to 667 rpm, thereby needing a smaller diameter/pitch prop.

A prm 260 is £1,200, a prm 500 is £1,800. Cheaper gearbox - bigger prop/shaft etc. More expensive gearbox - smaller prop etc.

I've emailed Crowthers with my dilemma, to see what they can advise regarding ratios, props, shafts and stern gear. No response yet, I'll give it a week and then follow it up with a phone call.

Why am I worrying about this now you may ask? Well, I have a plan that may see a close coupled gearbox on the non-flywheel end of the engine (trad' configuration), but it will need the non flywheel end of the crankshaft machining and an output flange fitting. If I adopt this plan, the work needs to be done when the crank is sent away for its regrind.

Of course - If one uses the pure hydraulic drive system all of the above is solved. Basic systems start from around £2,500 though. I'm not sure about the efficiency of the hydraulic drive system as well.

I am now going to sit back and await detailed comments from you blogger's with regard to the best solution........ Please?

Saturday, 12 January 2008


You know.... there are some times when you can be such a plank. In fairness, I've been a 'plank' so often I could probably board out a house!

I've just found out that I've been a plank again.

'Mini' left a comment on the last posting...."you seem to know what you are doing"......

It was of course the kiss of 'plank-dome'.

As you will know, I struggled like hell to get the liners out. In the end though, out they came.

Swallow has a magnificent National 2DM. The web site also illustrates the manual and some other documentation. The last two pages show the RN liner puller. What's the first operation that you should do:
1. (at the bottom of the liner) Unscrew nuts & remove gland.

What gland? What nuts? It was all hidden under oil sludge. I though there would be 'O' rings at the bottom - not a stuffing box!

I wonder how much blood, sweat and tears would been necessary if I had..."unscrewed nuts & removed glands".

Guess what the next job is?....

....Unscrewing nuts and removing glands... At least it will be easy to remove the packing material. Lets hope I haven't cracked any of the collars in my session of brute force and ignorance!
Mini - do you want to put in a revised post?

Friday, 4 January 2008

Bottom end rebuild starts!

Not a lot to report due to having to return to work. However, a bit of a milestone I suppose - I've actually started putting some bits back together. After attacking various bits with the steam cleaner, I wanted to put a bit of paint on some bits. More to protect the 'de-greased' castings from further oil and grease than anything else.

Working on the principal of re-assembling from the bottom upwards, The legs, crankcase and sump got a couple of coats of etcher primer/undercoat.

Once painted, I couldn't resist putting a couple of bits back together. So without further ado, the legs went back on the the crankcase (they'll probably have to come off at some time in the future, but for now - who cares!).

Tuesday, 1 January 2008

A New Year!

A happy new year to one and all. I hope everything you wish for comes your way.

Will 2008 see National 3D 56214 running? Will the boat be built? Will my family ever understand me? Only the last one I can say for sure - the answers a big resounding NO. Here's a little tale which probably sum it up:

How did you spend New Years Eve? I went to Tesco's car park in Banbury and met a very pretty young woman by the recycling bins. Why? Engine bits of course!

I get an email from Lionel (the engines previous custodian). "In the process of garage sort-out have found the National balance weights, can you ring me ASAP".

Phone call duly ensues. His daughter is going to party the night away in Banbury and, to save a trip up to the Welsh/Shropshire borders, she could meet me and hand over the missing items. Arrangements are made and, when the rest of my household are getting ready to go out for the evening, I'm heading for Banbury.

The meeting takes place and the goods transferred from one boot to another. I wish her a happy new year and get that knowing smile back. Its the one my daughter often gives me....'Dad, your sad'....

Thank you Catherine, for meeting a strange man in Tesco's car park.

As it turns out, I get back in plenty of time to get showered, put the glad rags on and join in the festivities!

A win-win situation all round. They still don't understand me though!

Have a good 2008