New Lifeboat Hull Conversion Building

[bkueber]

Got the deck caulked this weekend, also got the Epiphanes teak oil sealer on. Then it was on to the prop shaft cover. It was built up from 3/4 by 1/4 western red cedar strip planking over a series of plywood ribs. It was really fragrant working with the cedar!

[farmerden]

Hi Bret Boy She's sure looking fine! I was looking at the construction pics and noticed [this time] that there was only one U-joint between two steady bearings.Isn't this going to create a flat spot [vibration] as the driveshaft turns? Sorry to take so long to notice it. Den

[bkueber]

Hi Bret Boy She's sure looking fine! I was looking at the construction pics and noticed [this time] that there was only one U-joint between two steady bearings.Isn't this going to create a flat spot [vibration] as the driveshaft turns? Sorry to take so long to notice it. Den

Den,

I don't know? Could you explain the premise? I am not that familiar with power transmission, so I am not sure .

Thanks, Bret

[farmerden]

Hi Bret This goes back to my youth when I was building hot-rods and race-cars so I'm really digging in my memory archives! But it goes something like this- A single universal joint operating at an angle will transmit inconsistant velocity at the output end. Two universal joints that are in phase and the imput and output shafts are on the same plane,create constant velocity.This means that the output velocity will be identical to the imput velocity.This same plane detail really manifested itself when dealing with heavy truck drivelines weighing in excess of 500 lbs. All this being said you may never feel a vibration at the rpm's you are running. Indeed a Model A hotrod I had got a driveline vibration at approx. 85 MPH .So I drove slightly less than that speed and felt no vibration!! I would run your set-up as is and if you have no problem leave it.If there is a problem switch to a constant velocity joint-I think that would work.If anybody else with more info wants to jump in -now's the time!! Den

[fredrosse]

farmerden is correct that a single universal joint will cause oscillations in the RPM between the driving and driven shafts.

The magnitude of these oscillations depends on the angle between the shafts, and is non-existent if the shafts are parallel. With the arrangement you have here both the engine and propeller will experience constant small acceleration and deceleration twice on every revolution due to the universal joint. The vibrations caused by this condition may indeed be insignificant due to the low RPM of a steamboat engine, and the low rotating mass of the propeller and engine crankshaft. Note that a single cylinder double acting steam engine will also produce oscillations in its RPM due to the non-constant torque inherent with a piston & connecting rod arrangement.

A “CV” (meaning “Constant Velocity”) joint from an automobile front wheel drive system will eliminate the oscillations. These must be used on automobile drive trains to eliminate the universal joint problem farmerden mentions.

A torsionally flexible coupling can eliminate this problem. The only one I know of that is satisfactory for this service (and costs a reasonable amount of money) is the Lovejoy S-Flex type. The jaw type couplings (with a star shaped rubber bushing) would not function well to absorb these vibrations.

I think I notice a hard coupling between the engine and drive shaft on your setup. I would recommend this be replaced with a torsionally flexible coupling, which will absorb shock if the propeller strikes a submerged object, as well as damping the vibrations mentioned above.. The only practical place I can see to put this is where the hard coupling is presently mounted, the engine output shaft.

The two shafts must be aligned axially. The conventional method is to have another pillow block on the other side of the coupling to maintain alignment of the shafts. Another method is to have the driven shaft enter the hub of the engine side coupling hub, with a sliding fit. The sketch below shows this setup, which is probably the better option for your boat.

[farmerden]

Hey Bret It is interesting that your older "twin" the"Coberg Queen" runs a CV joint! Den [/img]

[bkueber]

Den,

I may need to change that out, we will see if it pounds when running. I did download and print the Lovejoy coupling catalog. On other news, I got the boiler lagged and banded this weekend, and finished the flexible trim. I got a start on the piping as well. I used white oak for the lagging, with a layer of aviation firewall liner underneath, good to 1000 degrees. The white oak was already cut into strips and glued to a fabric backing, as it was made to use on roll-top desks. I just cemented it to the liner and used a variety of hole saws and a jigsaw to cut the openings.

[farmerden]

Bret- The flexable trim tidies it up very nicely. Who in the world markets roll-top desk material like you used? You are really good at finding and adapting stuff to suit your needs. But aircraft insulation?Just how fast is this boat going to go?? Looks great! Den

[bkueber]

Bret- The flexable trim tidies it up very nicely. Who in the world markets roll-top desk material like you used? You are really good at finding and adapting stuff to suit your needs. But aircraft insulation?Just how fast is this boat going to go?? Looks great! Den

Den,

The roll top desk stuff - Google Tambor you want the solid wood stuff

You can pick your material oak, hickiry,cherry, maple ect.

Aircraft Insulation from www.aircraftspruce.com

I used it due to its thinness (little over 1/8) and its binder (silicone) Which allows it to be used as a template to transfer the holes from boiler to wood.

[fredrosse]

Boat is looking great. The oak lagging seems like a perfect choice, congrats on making use of your inventive thinking to apply an available product from another application.

When do you plan to get into the water?

From the pictures I could not tell how far down the boiler shell goes, and where the ashpan (not water cooled) begins. This area can, on some installations, tend to burn wood lagging.

If the ashpan sides are close to the aircraft insulation/oak lagging, then the temperatures there may get a bit too hot. One method to reduce this temperature is to put several layers of crumpled up aluminum foil around the inside of the ashpan. About one inch thick, just on the outer perimeter. That provides additional insulation, and keeps the ashpan walls cooler.

On a wood hull, some insulation is also needed to isolate heat from the bottom of the ashpan, but with a metal hull, very well already "water cooled", I would think this unnecessary for your boat.