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[tonyH]

Hello all!
 
Project J is being planned and the optimum propulsion would be a pair of vertical twins attached to the two props. Hull length is about 3ft6inches with a projected displacement of about 29lbs.
A mate, being a retired machinist, has offered to make them for me, either from bar stock or from castings.
 
Anyone any ideas for suitable units.
 
One minor hiccup is that they will be in an enclosed hull so steam loss is a factor.
 
Thanks
 
Tony

[boatmadman]

How about a pair of these:


http://www.machinistblog.com/bogstandards-paddleduck-engine-plans/


I have made a pair, they are from barstock and turn out very nicely.


Ian

[tonyH]

Thanks Ian,
 
They look the sort of thing but if the height is the 4 1/2 inches in the preamble, they may be about 1/2 inch too high.
The cross section I have to work with is as below, with the maximum beam being about 9 inches, so the tumblehome limits a lot.
 
Tony

[malcolmbeak]

Tony
You might try the MB22. This is a slide valve twin of 3/8" bore and stroke. Height is just under 3". If you are a Paddleducks member, you can download the drawings and a building guide from the downloads section. The engine is non reversing, but I use a fwd/neutral/rev gearbox.
The photo shows the engine fitted with a pump, by-pass valve, displacement lubricator and a regulator.
Malcolm

[SailorGreg]

Does it have to be twin engines?  3'6" and 29 lbs are within the capabilities of just about any small vertical twin, and I'm sure you could arrange for it to drive twin props rather than one.  However, if there are other reasons for going with two engines, crack on - and do post a build log, we'll all be waiting with baited breath.

Greg

[Circlip]

There was a description of a cross coupled Vee twin in Muddle Boats, if you go to the home page, the article may still be there.
 
  Regards  Ian.
 
  http://www.modelboats.co.uk/news/article/queen-alexandra/14470   look at photo 15.

[tonyH]

Hi all and thanks for the ideas
 
The size is spot on Malcolm but I'd be worried about having no simple reverse control since the vessel is going to be a bu**er to drive at the best of times
 
Same reason for two engines Greg. I used a single Hemmens set-up on a previous model (3ft/19lbs) with a Saito gearbox to the two contra-rotating props and while the power was OK the control was limited. Plus, I think that I need more than adequatepower with all the top-hamper that she carries.
 
I've a feeling I saw QE at Woodbridge last year Ian? Mechanically it's a belter but it's still a single setup
 
Part of the overall problem is the access because the intention is to split the hull at or near the waterline as discussed in other threads, so all the works are in the lower half and the fiddly bits are all on a lift-off unit up top (See pic) so small verticals are the target, especially since it would be so rude not to accept the offer from the builder
 
Regards to all
 
Tony
 
 

[Circlip]

I've a feeling I saw QE at Woodbridge last year Ian? Mechanically it's a belter but it's still a single setup

  It drives two propshafts?
 
  Regards  Ian.

[tonyH]

Aye but not independently. If I read the text correctly, the two crankshafts are connected to give contra rotation to the two shafts but at the same speed.
 
Or is it me...............?
 
Probably
 
Tony
 
 

[Circlip]

Aye but not independently

 
       Yer didn't tell us that!
 
    Yer move the goalposts more times than Bernie Fricklstone.
 
  Regards  Ian. 

[tonyH]

An I'm about 3ft taller than 'im as well!!!!