Philippines Banca 100 Islands

Any thoughts on this Thrust bearing CV, from python we are about to order. They are telling us we need a flexible unit because we are not running through a transmission. However the engine will be on Unisorb mounts, and this 2 cylinder type engine does not vibrate a whole lot. Please see comments from Python Drive on this rigid type CV.. Flexible type is double the cost and for this project just not feasible.


Python-Drive P30-145 mm.
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For our Python-Drive CV is It's not possible to make a straight connection between the CV joint (adaptor) and the flywheel adaptor, if you have a straight connection you need a flexible shaft coupling to make sure you don't transfer any (torsional) vibrations into the drive shaft. If you want to install our CV joint without a flexible shaft coupling, the installation is at your own risk and we cannot grant any warranty on this installation.

 

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here's a youtube video of a sample Python Drive unit working. At about 18 seconds in, you'll see both parts of the Python Dive

http://www.youtube.com/watch?v=nE2ZK181dE0



can you show us a pic ( or model number ) of a non-flexible type that you'd like to use?




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3/4" dia is for single piston 16 to 18 Hp. Gas engine. We used 1" dia for twin piston (Kohler or Briggs, can't recall), 1 1/4" is the recommended size according to calculations from Hurth transmission. It is traditional to use bronze tube for bushings (tubo busina) for 3/4" but you won't find any bonze bushing for 1" or larger. Best would be to use G.I. pipe, with guyakan (hardwood) for water lubricated bearing on the prop side and bronze castings with packing glands on the engine side.

Why the need for 30 Hp? 18 Hp can do the job. We used the 30 Hp gas on the 45-48 footer and a 12" prop. With 30 Hp, there is a lot of choice of diesel inline twins or triples from Yanmar (used) and even the hand tractor (kubota). Might be too heavy for a 36 footer though.

 

There is a lot of flex type joint manufactured locally made from welded tubings and flat bars and bolted though a flexible material cut from a belt drive, sometimes from a discarded truck tires. Quality of product varies but there are some good ones in Binondo, Manila. Should not be a problem as traditional banca making is a cottage industry and parts are almost found locally.

Dont use CV joint or universal joints. Use it only if your shaft is not aligned with the engine. If straight, the joints will wear only on one point. Not good.

If the marine engine you are using can take the the thrust of the prop, then you DON'T need a thrust bearing. Converted automotive engines with transmissions cannot take the prop thrust so it is standard practice to use thrust bearing.

 

Going into Week 2

 

Thanks for your reply, we appreciate it. As for Thrust bearing. Kohler specs say that there is a PTO bearing (power take off) that can handle some thrust. However they said its not recommended for longer running times it was designed to handle some thrust during the change over of the PTO gear. Its not a marine engine, its a commercial use engine used in Bobcats, and stump grinders, its bullproof reliable however not so much designed to take direct thrust we think. We opted to go for the python drive which is in transit, yes we will level out the shaft a bit coming from the engine to help with efficiency.

As for use of the 30HP, we often carry many dive tanks, a portable 12v compressor and lots of water and supplies during trips. We find that the 16hp briggs is laboring too hard and must run at a higher RPM constantly, which caused alot of vibration. Single cylinder tends to vibrate alot more than a Twin. Also the weight of this Kohler 30hp is almost same (105lbs) vs Briggs 16 (90lbs) almost 2x hp with out 15 lbs increase in weight. We calculated that the engine RPM would be much less and therefore provide better fuel economy and smoother running overall. This all remains to be seen we will keep updating as the build progresses. Thanks again for your input!

 

You are on the right track then. PM me if you need to find some equipments in Manila. I assume you are in Hundred Islands.

 

yes Sir, 100 Islands North Western Pangasinan. Thanks again!

 

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Pics look awesome!

I envy you guys living in paradise




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Are you sure you will use 0.75" prop shaft and cutless bearing? Command Pro have 1.4" (36 mm.) shaft and with max 30 Hp, 3600 RPM.

A quick check with ABYC, ABS, Dave Gerr, all indicates a MINIMUM of 0.80-0.86" diameter prop shaft at around 26 Hp, 3100 shaft RPM (cruising) and using austhenitic stainless steel grade 304.

You have a thrust bearing, so the 0.75" dia. prop shaft will still narrow down due to a taper/necking after the thrust bearing side.

P.S.
Is the Hundred Island still as pristine as it used to be?

 

Yes its 1-1/8" this command kohler pro we have here in the box, there are options on shaft sizes for these engines. 1-1/8" in standard around here on the engine side.

About the 3/4" well we already have the dripless stuffing box. As i know the next step up from 3/4" 316 stainless would be 1" 316 stainless, and that would be already for very large engines. Our other bancas here are all using 5/8" shaft, even some of the ferrys are running fully loaded 18HP with 5/8".

I didnt know of the ABS check perhaps we are a little out of spec here (is 304 softer than 316?), unless we chance the coupling spec on the python and get a new dripless not sure if going to 1" change is a good idea. Dripless was only 150$ so no big loss on that and we have a few days to change our minds on the Python coupling. Thoughts? Thanks again.

 

Also note that our Prop is from a LONG Tail boat 3/4" was hooked up to a 34HP Kohler previously with a 3/4" x 12 foot shaft direct drive. Pushing a boat load of people at about 30 knots in thailand. The specs from ABS might be very conservative or "Best Scenario" for vibration. However we do have some very nice VIBRASORB mounts that will be used mounting the engine. This should absorb any extra vibration. We also will be using 2 pillow blocks, 3/4" made by Browning. Perhaps we should make it 3 just to be safe.

 

The rule of thumb for shaft sizing is 1/14 of the prop diameter. Originally, you stated you were going to use 10" diameter prop. This is where probably the error is coming in. Assuming the prop is correctly sized. 10"/14=0.71". I have noted that the you patterned the specs from racing boats. At about 3500 rpm and 30 Hp, Dave Gerr chart shows 0.75" will work. The higher the RPM, the smaller the shaft diameter as the chart shows. But yours is a workboat. You will be cruising at a much lower RPM. 80% of power perhaps. The 3 bladed Bp chart also shows the 10" prop dia is inefficient.

The rules I have stated uses the yield point of the material for the propeller shaft with a safety factor of around 3 for leisure craft. Another factor that could affect the shaft diameter is the bearing spacing which follows the rule of between 20X to 40X shaft diameter.

I have an idea of what a long tail is but haven't built one. Can you post a sketch of your propulsion arrangement?

 

Yes I have seen the practice of using 5/8" SS for prop shaft with 16-18 Hp. but the fisherman baby their engine. Also note that traditional bancas have the prop shaft sheated in bronze bushing with about mil and a half clearance. The bronze bushing covers about 90% of the shaft and relies on water lubrication. The bronze tube lacks the P bracket but retains a skeg to reinforce the tube.

This has the effect of increasing the section modulus of the shaft and prevents vibration. It is similar to an enclosed tube shaft in ships (which allows for a reduction in diameter).

 

As requested - attached are the propulsion sketches. (Rough for reference only)

Im looking for exact specs on the prop however looks to be a 2 Blade with rather shallow pitch, will update with exact specs later.

Looking forward to comments. Thanks!