Building a new boat {OK dreaming about it!!]

[farmerden]

I think it's time to start another topic that we can get eleven opinions from ten people! The new hull I have acquired will need to have the engine placed in it. Standard practise would be to place the engine low to get the center of gravity as low as possible. This also allows the prop to run parallel to the keel and push the boat ahead and not the stern up.How am I doing so far? Alright the problem I have in the "Steam Queen" is the engine sits down where I can't work on it. And when tied up at the dock in shows everyone wants to watch the engine slowly turn over all day long Soo with the engine buried in the bilge the people can't see as easy as they could if the engine was elevated. So here's the plan-- Under the engine I will place a shallow fresh water tank.That's takes care of the center of gravity,also the Semple 354 only weighs about 175 lb. Now I've got the engine up and visable. Hmmm! but the driveshaft is way down low! I'll have to use some sprockets and a chain to hook then up. And guess what? now I can fool around with spocket sizes and dial in the boat to the propeller rather than chase round trying to find an over-square prop.I've got a couple but they're hard to find,expensive,and in the end an educated guess at best.So all that's needed is a thrust bearing on the drive-shaft and still alline the driveshaft to the engine and Bob's your uncle--Whaddya think?[/img] by up I mean 6-8in higher!

[Wearyman]

Well, I'm not a steam mechanic (yet!) but based on my amateur general mechanical experience I would say that it should work. You will likely have to have a clamp with an internal hub on the engine end to keep the "sprocket" end tight and prevent it flailing about.

I'd actually recommend two of those. One on the engine end of the shaft, and another just aft of the shaft sprocket. This should reduce shaft flex to a minimum and allow the most efficient transfer of power from the engine to the prop. Bear in mind that you will lose a very small amount of power, but if you build it right the power loss will be so negligible it won't be even measurable. Also bear in mind that extra mechanics means extra lubing and maintenance. You will want to ensure you keep either a dry bilge, or build a grease box around the gears and fill it with light silicon grease to keep moisture from rusting your gears.

But that sounds very doable. Interesting idea about using water ballast. I wonder if it would be appropriate to even put your hot well down there? That would clear some deck space, and possibly make the well more efficient by using the insulating properties of the wooden boat sides to keep the water warm. It's a thought anyway.

[87gn@tahoe]

Sounds sorta like what my father did on his "George H. Sandin".

He used a heavy duty roller chain and sprockets to drive the prop at a 2:1 ratio down to a shaft mounted in a pillow block bearing, running to a u-joint and the prop shaft propper.He did it not for appearence or C-o-G purposes though... The boiler is a bit too small for the engine, so he figured having it run at a lower RPM would make steam consumption more manageable. he also likes having the engine level, as the prop shaft is at quite an angle.

He originally had it set up with a '70's Ford V8 timing chain... He went to the heavy duty roller chain after the timing chain snapped while at full throttle... It's amazing how smothly that engine ran for the few seconds it was at somewhere around 1000-RPM "Bart" from the forum here ended up towing us back to the marina with the "Otter"

[steamboatjack]

Good idea, I use a similar system on Grayling but with a tooth belt instead of a chain, this is quieter. you maybe surprised how much load the HTD (high torque drive) can take, you would be advised to fit a plummer block on the tank top near the drive pulley and this can incorporate the propeller thrust bearing as well as supporting the belt pull.
I drive from the forward end of my engine as there is more room here due to the prop shaft angle, the bigger the pulley diameters the less heavy belt/chain required. The shafts should of course be kept parallel.
The only down side I had was when reducing speed the prop tends to drive the engine causing belt slap, I ended up fitting a jockey wheel on the slack side but if you make provision to finely tension the belt this can be avoided (same goes for a chain no doubt).
Other brit boats I know are Valhalla (chain) Mudlark (tooth belt).
regards Jack.

[Wearyman]

...The only down side I had was when reducing speed the prop tends to drive the engine causing belt slap, I ended up fitting a jockey wheel on the slack side but if you make provision to finely tension the belt this can be avoided (same goes for a chain no doubt)....

I'm not familiar with what a "Jockey Wheel" is, but it sounds rather like a belt/chain interlink system probably ought to have some kind of clutch mechanism to prevent prop inertia from causing problems or damage. Some kind of throw lever with a locking pull that will take it "off gear" and allow the prop to spin down on it's own. I don't know how feasible something like that is though.

Alternately you could use a direct gear system. Just build in a vertical gearbox connected to the shaft end that uses large-tooth sprockets tightly held together to drive the prop shaft. As long as you aren't in the habit of throwing it into full reverse while running at full forward it would work almost as though it was directly connected to the engine. Of course, you are again looking at adding weight and complexity.

My last thought is that you could add a double universal to the prop shaft and keep the direct drive functionality. Basically, one universal right off the engine, attached to a shaft running at an angle down into the bilge. A second Universal joint at the bottom of the bilge/level your prop is at attached between the diagonal and the horizontal sections of the shaft, and then out to the prop. I have no idea how well that would work though, perhaps some of the guys with more mechanical experience could chime in on that one.

[Edward]

A jockey wheel is a freewheeling wheel pushing against a belt or chain to keep it tensioned .
Edward

[87gn@tahoe]

We've also experienced "slap" while reducing speed and while going "dead slow" as the engine isn't timed quite right, nor does the U-joint provide a consistent velocity.

We had a teflon tensioner that was sacrificial (VERY) but instead worked on shiming the pillow block bearing to a close tolerence so the "slap" is minimal.

We've been looking into adapting an automotive CV joint to replace the current u-joint.

[Edward]

Although automotive CV joints work I don't think they would last very long .
I've been told that this is because , smoothly as we like to think our engines run , they are not as smooth as a high revving (in comparison ) IC engine . A single cylinder steam engine isn't producing much thrust through the prop when it's at tdc and bdc and it's the prop being driven by the water which helps carry the engine over these points . So used in conjunction with a single the stress on the joint would be reversed twice each revolution , with a twin four times . Even though the hp isn't very high a surprising amount of torque is involved and cv joints don't like dealing with this highly fluctuating load .
I suppose a nice big flywheel might help , but this is a retrograde step . I think Steamboatjacks idea of a belt drive is better , it has a bit of flex/stretch built in and is definitely quieter than chain drive or a gearbox which would also gobble up power .

Regards Edward .

[mcandrew1894]

On the matter of CV joints or U joints.

If sized for the torque....and not necessarily the Horsepower, they should work fine.

IC engines make their torque at high RPM, comparitively, to a low speed steam engine. At 2 hp, @ 600 rpm the torque of a launch steam engine is 10 times what a 2hp outboard puts out at 6000 rpm.


The pertinent formula is the following

Power = 2 x pi x (Revolutions / time) x Torque

Horsepower (HP)= (2 x pi x N x T)/33,000 with units of revolutions per minute and torque unit of pound-feet.

Re-arranging, we can solve for torque

T (torque) = HP x 33000/(2 x pi x N) Keep the units straight!

Now when you look at the spec sheet for a CV or U joint, they usually give a capacity in terms of HP @ some RPM. Knowing that you can determine how much torque the joint is rated for.

How much torque can a 5 hp steam engine put out at 300 rpm?

OK The power output is 5 HP, and N = 300 rpm
( OK...this only applies if you REALLY have 5 HP ....Measuring is another post)

T= 5 x 33000 / (2 x pi x 300) = 87 pound-feet

Now lets look at a catalog of cv/u joints.. typically they are rated at 1750 or 3600 rpm,....and I am being hyperthetical here

Lets look at what HP would be required at torque level of 87 pound feet and 1750 RPM

HP = (2 x pi x 87 x 1750)/33000
HP = 29 Horsepower @ 1750 rpm

To summerize....it takes a U joint ( or CV joint) that is rated at 29 HP @ 1750 rpm to handle the torque of a 5 HP steam engine at 300 rpm.

Amazing what some brute torque can do huh!

This will be a fairly substantial joint.....and it will by its very nature act as a flywheel and smooth out the rotation of the whole system.

Don't forget...you always need 2 U joints .....never one.

Here's a picture of mine for a 2-3 HP compound...works great!

Dave

[farmerden]

Dave That's an interesting set-up for the sight glass and the three drains in the boiler. Do you have a better photo of it? I've always wanted to have something like that up front so I wouldn't be stuck back with the engine all the time.I think something like the might do the trick. Do you think the captain might even let the engineer steer the boat? Den