Using a CS 6/1 in a boat

[millman56]

Plenty of 2:1 reversing marine gearboxes here in the UK, they must be available  anywhere there are small boats,  the problem is that they are normally close coupled to the propulsion engine via a rigid adapter housing and a drive plate,   not a  practical option with a CS...    A rigid steel frame holding the engine and g-box would be an option although the commonly used gearboxes don`t have much in the way of remote mounting arrangements other than the housing flange bolt-holes and a couple of lugs at the rear,    a little ingenuity and fabrication would overcome this.
Another option that would  keep the drive-line low would be to retain the initial belt drive reduction plan and mount a 1:1 reversing box somewhere along the final drive-line.     PRM,  ZF Hurth and Borg Warner are a few manufacturers who spring to mind, if you live near the sea, sourcing a used box should be no problem.

Is a kitchen rudder a scoop that is lowered behind the screw ?

Mark.

[millman56]

Just read the previous posts and some of my input`s already been covered.
One thing thats already been discussed is the vibration of the engine, all well and good balancing an engine at a fixed speed and power output but these engines really want to jump about when they are lugging down, just imagine the situation if you were running a current dragging you towards the rocks or being chased by South China Sea pirates at full power

Mark.

[Pedro_at_Sea]

millman56,
2:1 gearboxes are all over the place, all of your mentioned companies does not produce 1:1 gearboxes ...
Rocks are bad companions for boats, that's for sure 
Pirates, I will not run from them, I will run against them 
I cracked my head for a long time to fix the drive problem and think the belt drive system would be the best solution.
Gearbox can be mounted on a plate and just bolted down, have done that in my dinghy, which had a small 4 HP diesel in 
You can see pictures from building my dinghy here: http://petermican.com/index.php/gallery/my-dinghy

[richardhula]

Richard,
An just reversing gearbox would be great, so far I could not find any.
So I have to use Pulleys to speed up a standard 2:1 gearbox  
What prop size would you suggest for my 6/1 baby ?
Have a great day
Pedro

Marine Lister's used Blackstone gearbox's (2G, 3G etc.). They were generally available with or without reduction gears (2:1, 3:1). I admit they may be hard to find and spares rarer still. Using a modern PRM hydraulic box may be the answer given its no hardship to provide overall 1:1 ratio with your intended transmission system.

I met a guy with a Pelapone twin (vintage industrial diesel) that used almost the same system with engine in forward engine room and belt drive from front of engine to long shaft running underneath and close to floor of flat-bottomed narrowboat, then up to PRM gearbox at stern. This gave him more headroom in back cabin as floor could be lower than normal traditional narrowboat arrangement.

I would aim for a larger diameter prop in the range that your calculations suggest with smaller pitch to match. This will give better stopping power and acceleration. It depends on what clearance you have though.

[Pedro_at_Sea]

Hi Richard,
thank you very much for your suggestions.

I have a mechanical PRM 80 or PRM 120 in mind, very reasonable and simple, no need for cooling this gearbox. (hydr. gearboxes need cooling)

What prop size and pitch would you suggest for my 3 ton boat ?
Clearance in no problem as the boat is still in the design stage, I can realize almost any prop size and clearance 

Thanks again and have a great day
Pedro

[richardhula]

Sorry can't help with specific prop sizes. Your 18" x 16" prop sounds about right although you don't mention number of blades. Remember pitch dictates speed with no slip (i.e. prop turning through semi solid such as cheese  ) Diameter dictates the amount of push to get to and maintain this speed hopefully with minimal slip. In water you will have slip but a larger diameter prop will reduce this but load the engine more, that's why I suggested largest practical diameter.

FWIW I have a 24 x 22" three blade prop on 2:1 gearing via PRM240 from JP2M - basically an 18/2 although it revs to 1200 rpm. This seems spot on rivers especially as I can't swing a larger diameter. Most of the time its dragging the boat close to the bottom of our shallow (poorly dredged) canals though with revs little more than 650 rpm.

[Pedro_at_Sea]

Richard,
thank you very much for this info's.
At least I can orientate on something now 
I worry always that mt 6 HP engine cannot handle this big diameter prop.
My last boat could not turn fully a 20" 3 blade prop with 30 HP and an 2:1 gearbox.
This engine should run at max 2000 rpm, but I never got her above 1500 rpm.
Must say boat had 25 tons too.

So now a 6 HP should turn an 18" prop
There is only one way, to try it 
I will try first a 2 blade one which I can get very cheap here locally, made of aluminum, which is good enough for testing.

Thanks again and have a great day
Pedro

[richardhula]

Well they always say its torque that turns the prop not horsepower.

[Pedro_at_Sea]

Richard,

"Torque" I should have enough 

Just run your engine specs trough my software:

Result: prop 23"x18" ...... 651 pounds of pull

So this is very close to reality and shows me that my software is more on the conservative side.

Results for my "baby":  3 blade prop 18"x18"   ..... 269 pounds of pull
                                2 blade prop 19"x18"
                                For 6 knots only 4 HP required with this set up

So I am confident now that my engine can handle this big wheel :-)
Let's me sleep better now ...

To my knowledge, a 2 blade prop is more efficient than a three blade one, is that correct ?
If so, I will go for a 2 blade prop ...

Thanks and have a great day
Pedro

[millman56]

Pedro,  I like your Yanmar instalation in the dinghy, thats a neat way round the gearbox adaptation problem.     PRM do a  1:1 gearbox  in your power range but its  hydraulically operated. 

Mark.

[Pedro_at_Sea]

Hi Mark,
yeah, that was an very easy way to run a non-usual diesel engine in a dinghy.
Simple and cheap too 
This dinghy was perfect, will build the same again ...

Thanks for the PRM tip.
I asked PRM a few weeks ago and they returned: NO 1:1 at all

I prefer a manual gearbox anyway, less can go wrong and I can fix it myself, no need for cooling too ...

Have a great day
Pedro