diy surface drive?

Please post some more photos of your setup. I congratulate you on your ingenuity!

Have you tired a lower pitch or smaller prop to get your RPMs and speed up?
Your boat also looks kind of bow-down there. Can any weight be shifted aft as a test to see if you can get more out of the water?

 

I suppose I should start at the beginning... This will take a few posts. I was given the boat by a neighbour who dragged it over with a tractor without the benefit of a trailer - in summer. Thankfully it was 1000 feet. Much earlier, I had been given the motor for a jet boat project. I made manifolds with a hand grinder & stick welder. The motor was bad so it cost me $700 for another and mains & rings. I added a cam from Pet Boy's. - probably 140HP. (these engines cannot take more than 5000 RPM. I shattered the jet drive (alignment problem) so I had a motor. I started with an article and DOS program for estimating the shaft line details from Paul Kamen. He has the stuff here: http://www.well.com/~pk/fishmeal.html. While I tried to get my brain around the theories and limitations of Paul's program, I went ahead with the build. The cogged belt I found would require a pre-load of about 1000 lbs. That is a lot of side thrust so I used a trailer hub for a thrust bearing. The tapered rollers would take the pre-load too. The belt and cogs came from T.B. Woods. Then came a plummer block and finally a stern tube with seal and cutlass bearing. You can see the care I took (not!) in jigging up the stern bearing. The final photo is of the drive running. Below the flexplate (no flywheel - these engines are internally balanced so you can get away without one) you can see the end of the trailer hub, then the belt. The cross member with the two bolts is for the support bearing (plummer block) then comes the water feed to the stern tube. I know I haven't answered all your questions by a long shot but I felt it necessary to give you some background. More later today...

 

This picture, from a video shows the internals of my surface drive running.

 

diy surface drive.

There is the option to have a Transom mounted Trim able jet drive to try to eliminate some of the water jet failings.Poor priming in shallow draught hulls,poor sea keeping in following seas. Better thrust at low RPM going slow.
Easy clearing of weeds and other rubbish.

Looks less threatening than an open prop.

 

I did mention in my previous post that I tried the motor in a jet. Well it was a 14 ft runabout hull that came with a 35 HP OMC. I pulled the drive out of an 18 ft Dowty. Dowty built the Hamilton drive under license in about 1960. It the USA it was sold as a Buehler. These were an axial flow pump with 2 (some had 3) impellers. The Hamilton is an axial flow while Berkley, Jacuzzi etc. were mixed flow. I originally used a Wankel (Mazda 13B) but my neighbours ruined the motor so they gave me the V6. We got more out of the V6 than with the original 292 Ford because I ran one on the river . I did replace the reverse gate with a nozzle and that made the real difference. 2 things bother me about jets. When you calculate the gross weight of the boat you have to add the weight of the water in the pump and that is significant. Also the designers limit the pressure generated and the volume of water pumped. Pumps cavitate when over-revd and you need lots of mass to push the boat Example: The Jacuzzi 12YJ will only go 55 MPH no matter how big the motor.
Besides using a jet would have defeated my original objective: to build a surface drive. I am now looking at a stern drive for the Glasspar because I love the boat. I have tried an airboat, outboard, V-drive, jet boat and now surface drive. Next will probably be a hydrofoil. IMP-sh had some questions so I will answer those tomorrow.

 

Thank`s for the good all-round experience and photos you are passing on. I am not a fan for surface propulsion myself jets,tunnels,pods, pockets whatever you choose to call them I prefer to have the prop in dense water in the middle of the transom and the prop at least two inches below the bottom of the hull to make use of every rev you add to the motor and for good sea keeping qualities.
If you traverse shallow waters it is great to have the ability to lift your drive (not tilt it) and protect it from damage and still have thrust and steerage.

 

I am sure you have heard about the fellow at a boat show who asked about the fuel economy of a 30 ft cruiser. Salesman's response: "If you worry about fuel economy, you can't afford one". Where I live (Ottawa river) There are no marinas near and all fuel has to be carried 400 ft through weeds and sharp clams because the environmentalists frown on 4 wheelers in the water. So fuel consumption is important to me but not for financial reasons. While jets are great in shallow water, they are nearly 20% less efficient than a stern drive because of the drag of the pick-up grate, the tube wall, the slip because of impeller clearance and the impeller hub and shaft in the water flow. A surface drive beats them all. The only things in the water are prop blades and rudder - even the hub is out of the water. Another observation: my 3 jets that I owned held a plane at 3500 RPM. My wife's 16 ft Hurricane with Suzuki 115 - 4 stroke requires only 2100 to maintain a plane. I also had a 430 HP V-drive that would plane at 1800 RPM. I am not badmouthing jets - I had 3. I am still considering one for the Glasspar as my second choice.

 

This hull was very advanced in 1958. While other boats had round chines and flat bottoms, the Glasspar had 12 degreed of deadrise. It was the forerunner to the modern deep V with 20 degrees of deadrise. The G3 did 54 MPH with a 70 HP direct reversing Mercury. To do this the motor had to be trimmed way out and it headed for the sky when the throttle was opened. It was the first commercial design that rode on its stern and produced a healthy rooster tail.
My surface drive points down 6 degrees and this buries the bow. Then it broaches to the left. I even tried twin rudders and a down angled hydrofoil on the stern but to no avail.
My first prop was a 3 blade 12"X 19. It would not stop ventilating. Then I understood what was required. At 5000 RPM I wasn't moving enough mass to plane the boat. The second prop was a 16" X 19 4 blade. The bigger prop hooked up at about 4000 RPM and tore your head off with acceleration. I could also have changed the gear reduction on the bigger prop for more power. This is cheaper than buying another prop.
The advantage of the Arneson drive is that you can lower the prop for grip to plane and raise it for speed to get maximum RPM. The ideal boat for this type of drive is the tunnel hull. The entrapped air lifts the bow and you go!
I worked as (civilian)for the Canadian Navy as technical authority for props, shafting and transmissions for our ships before I retired. I had a Naval Architect tell me that my Rube Goldberg junk would never work. It was gratifying to give her the ride of her life in a junk pile.

 

Here's some pics of my surface drive design. The boat is a 3 point shovel nose cab over. This is a mock up in wood to get a better eye on the degree of shaft angle. It will be braced by heim joints and bars.
The aluminum peices are cut and ready for welding.
There's enough clearance for an 8 inch prop if needed.
The rudder will be steered via conventional cables and pulleys.

 

I think you should beef it up a bit... those bits of timber look a bit flimsy...

 

Perhaps you might wish to review why you are doing this. Hydros are called 3 point hydros for a reason. They ride on 2 sponsons and the prop. Below a plane, the prop is sealed in the water by the bottom of the boat and ventilation of the blades can't occur. There is a slight chance that the prop will cavitate but usually the hydro is moving fast enough for easy transition to "prop riding". That is just another name for surfacing the prop. A prop running on the surface does not drag the strut or the hub through the water. Only the blades are immersed - and you can get away with a 2 blade on a hydro. A surface drive hanging off the stern will require at least 4 to 6 blades to overcome ventilation. My own boat only required an 8 in. dia. prop to plane with an outboard. My surface prop was 16 in. in diameter. Albert Hickman, inventor/designer of the Sea Sled and surfacing drive never considered the hydro shape. The stern of which is probably too narrow to plane easily. A catamaran or tunnel hull has the width to offer an easy to plane hull with the air entrapment advantage to lift the bow when at speed.

 

By my mesurements, my prop should be at the same point at the waters surface as a outboard on the same boat. An outboard when starting has it's prop well below the surface before it achieves full speed. The only thing different with my design (I think ) is that the engine has moved forward and the prop has moved to the rear 24 inches.
The real test comes in the spring.

 

This may be true but the outboard has the benefit of what is called the cavitation plate which is actually an anti-ventilation plate just above the prop. You do not have this benefit. Further the outboard prop shaft is parallel to the water surface and draws its inflow from under the boat. The surfacing prop is at a serious down angle and will attempt to draw a prodigious amount water from between the prop and the surface. The required volume won't be available and will be replaced by air. If you are contemplating some sort of a U-joint for flexibility you will need a thrust bearing between the prop and the U-joint. This is discussed elsewhere in this thread. Remember that in designing performance boats the position of the machinery weight in the hull is very important. Further the weight of the propulsion equipment has to be kept as light as possible. A thrust beating, shaft, shaft log, strut and prop is all you need in a hydro. You will be carrying all this plus a U-joint, stern supports and a mechanism to raise and lower the prop. Note that as soon as you run a shaft out of alignment with the primary shaft (as in lowering the prop) you will get considerable side thrust and that means loss of power.

 

I'm useing the old theroy of K.I.S.S. I don't have a trimmable shaft tube (which has tapered bearing for thrust). The engine and drive will weigh approx. as much as an outboard of simular HP. This is a cab over style hydro that will have "moveable ballast" ME If the bow is light underway, I move my butt forward, and if it's too bow down, I'll slide to the rear of the cockpit. It's a kneeling position boat.

 

The style of boat won't be an issue at speed. As soon as it planes you are on the sponsons. My own boat weighed less than 400, the motor close to 300 and me and the rest - about 1000 lbs. I had about 150 HP to play with. So 15 HP per 100 lbs.
The prop is a different story. The first prop I tried was a 12 X 19 pitch. It could fling a V-drive flat bottom across the water at nearly 90 MPH or pull half a dozen skiers. The boat weighed 2000 lbs and was over 6 ft wide with 430 HP. This same prop could not plane a 1000 lb boat 6 ft wide. It could not grab enough water to plane the boat. My second prop was 16 X 19. Note the pitch stayed the same but had about 1.3 times more surface area. Elsewhere in this thread there is a picture of a boat called Manta. Compare the size of the props to the width of the boat. They are very big.
A further consideration is the rudder. I doubled my rudders and still had trouble with with the stern walking sideways.