diy surface drive?

Sorry every single long tail SD in Thailand and Malaysia uses a 2 blade alluminium prop made by AAAand so cheap you would not beleive me.

I mean a small 8inch dia drilled machined tapered for 3 dollar

 

We don't have barnacles (fresh water) and I am 6 years retired from propulsion tech authority for Canadian navy and live on the Ottawa river. We do get stuff growing on the hulls thanks to sewage that takes toilet bowl cleaner to get off. My buddy has a 32 foot fire breather that he cleans with a very high pressure sprayer. So he loans it to a neighbour to use on his spanking new van. He would not listen ando now he has a black bumper on his red van.

 

Frosty,
An 8 inch prop doesn't exactly transmit, say, 800 HP to the water. The larger the prop, harder the tip hits the water. I had a new 4 blade 17 inch dia & 19 pitch at 4400 RPM shaft speed and it transmitted a surprising amount vibration. I expected it to be completely smooth. It would also be extremely difficult to plane a 2 blade unless you could trim the drive and those far east egg beaters do trim.

 

8 Inch is the smallest and was used to represent the price.

I dont think you fully understand the Thai longtail principle but yes they vibrate but wether they vibrate more than the single yanmar deisel is unkown.

The largest AAA SD prop I have seen would be 24 inch dia.

I don't think many participants on this thread are thinking 800HP.

I have a made SD with Seafury props. The prop holder does nothing but place it in its position, its the prop that does the work. I was amazed at the smoothness of my 4 foot shafted 4 bladed 24-24 cleavers with 500Hp total

 

Frosty,
I don't think that a smooth drive (single diesel) is really on the mind of the operator. I also note that your boat has 4 bladed props. That means that you always have at least one blade dipped. I remember when Mercury speed props were brass and had 2 blades in the 50s and 60s. Try to buy a 2 blade from mercury today. I have used 2 blades on V-drive performance flat bottoms but they were only good for racing. Too much vibration at lower speeds. I admit you make a valid point for 2 blades - inexpensive.

 

The tiny bit of twisted metal in the image 2 absorbs about 2000 Hp Aero Engine Hydro. Take your pick. Have a big or small prop for SP work. You can use almost anything for SP.

 

Tom,
I note also that the Hydro used a 3:1 overdrive which translated to a small diameter 12,000 RPM prop With a very small mass, If low speed 2 blade props were good they would use them on ships. Have you ever watched a light plane with a two blade at an idle? They shake themselves apart. The three blades do not. Believe it or not, if you could balance a one blade, it would be more efficient than a 2 blade which is more efficient than three...

 

Right Grumpyrelic, I am not sure about 2 blade props shaking a plane apart there have been plenty of them that have not. Some old steam boats got along at about 25 MPH nearly 1 MPH for each RPM with 2 blade props.. You can balance a single blade prop and they are being used. Hey SP props are a mystery for most of us and I think an expert may do quite well installing them on boats,if you can find one locally. Is it really necessary for our slow recreation boats. I don`t think so. But it is a lot of fun.Just make sure that your expensive SP drive can be changed to subsurface drive in case you get sick of the hassles. a trimmable drive should be able to be changed to subsurface drive and can be free of many damage potentials.

 

Tom,
I had a 2 cycle 4 cylinder drone engine (67 lbs - 72 HP) on a 12 ft rowboat. No flywheel - just the prop. Shook like it had tremors at idle. but did 60 MPH for 40 minutes very smoothly until it self destructed. I still have the prop 40 years later.
To complete the circle, my surface drive is being replaced this year with a mercruiser. I really want to be able to go astern and trim the drive.
Sometimes performance isn't about speed and manoeuvrability. My wife's deck boat will do 36 knots but in the hot summer it putts along at 2 knots very nicely and the stereo sounds great. In boats the journey is more important than the destination.

 

AAA props for sale along with new long tail kits. The 3 bigger long tails are under the Bridge on the river Kwai

 

A few more long tail stuff.

Relick a flywheel is very important did you not know it would break without a flywheel.

Ever heard of harmonic vibration.

 

You have had some fun then no doubt you will find a use for the prop.I had an old outboard motor about 5 HP the model had a World record speed of 60 MPH .
You are luck to be able to have these choices.My choice was to have a lot of camping and exploring the quiet places and there has been a lot of interesting experiences (like meeting escaped prisoners in the wilds) and it cost almost nothing.I am pretty tight.

 

1. The drone engine (they were also used in the Bensen Gyrocopter) was a prop start 4 cylinder horizontally opposed engine was built by McCulloch. It never had a a flywheel and didn't need one. It turned 4500 RPM on a single speed carb. I put a chev 6 carb on mine so I could throttle it. It melted two pistons and did not blow up.
2. My flat bottom had a v-drive on a 390 Cu. In. Ford. no flywheel - just a flex plate for the starter. I have photos. No harmonic balancer - just a light pulley.
It had 428 cobra-jet rods, heads cam, valves, 3 two barrels and took 16 quarts of oil. At 7000 RPM my prop turned 8100 with 16% overdrive gearbox. 3 blade 14' pitch Equipoise. I ran it 5 years and sold it.
3. My Surface Drive engine is a 90 degree 3.8 V6 with an offset crank. It is internally balanced with a flexplate and no harmonic balancer. Limited to 5000 RPM
I did have a balancer and flywheel on my 1969 350 Chevelle 300 HP standard 4 speedcar. It depends on the requirement. Boats don't stall when you "pop" the clutch and these boats all started in gear - no neutral or reverse.

 

To calculate my SD system, I used a DOS program from Paul Kamen, a naval architect who worked for Arneson. He wrote an interesting article available here:

http://www.simplicity-marine.com/surfprop.htm

Absolutely worth the read.

 

Like this. These guys are resting in the shade of the Bridge on the River Kwai. The one that was bombed and built by slaves of war in Thailand on the Burma railway.