Scratch-built aluminum inboard v-drive boat

[zollis]

For the past 18 months or so I have been reading through the various vehicle build logs and came to realize that there is many similarities ( and of cause differences ) when building my boat.

The similarities.

It is taking a long time , longer than anticipated, about 5 years up to now. The motivation started very high but fades away especially over winter. In summer the urge to get it on the water returns and building progress again, only as fast as the budget allows.

Secondly the drive train. Automotive engine with drive shaft, gearbox and prop shaft. The engine systems ; water, fuel, oil, exhaust are similar to a vehicle except that there is no wind flow to take heat away.

Instrumentation with all the wiring issues are similar.


Main differences.


Most important there is far less moving parts. The 4 corners of the suspension are not there. Monocoque construction that needs to be water tight with a smooth bottom to skim on top of the water.



Start of the build.


The aluminum sheet that determines the shape of the boat must be cut to such a form / outline that the sheet develop into a pipe or cone or combination of them . Compounded curves are not feasible. Why don't u use Cad or an existing plywood boat to get the patterns from ? You might ask .

First I had no access to Cad and the shape of boat I dreamed of I could not find. I had a specific shape in mind that looks like the SK boats of the late 50's early 60's.

More with pics to follow.










Z.C.

[Jack]

XC,
There are a few boaters around this forum. I had, at one time, 142 USA builders that I did design and international compliance consulting with. Wood/FRP/Steel/Alum.

How big is this boat? I'm guessing around 20 feet? Build upside down and let gravity help you with the plating.
Any issues, just ask away.

[zollis]

Molleur, thank you for the offer. For now the lenght is kept as a little surprise. I have uploaded some pics in my members list. Can someone please help to attatch them on my post.


Before I started building I made a list of goals for the boat.

1.) The launch and retrieve must be easy .

2.) The boat must be capable to pull a skier.

3.) Ground handeling , pushing the boat while on the trailer must be easy. Preferably by myself.

4.) A normal car must be able to tow the boat.

5.) The lenght of the boat was dictated by the build site.

All the above pointed to aluminum for minimum weight.

Why inboard? I had enough of outboards blowing up.


Where to begin ?

I wanted to understand how this sheet metal development story works for a boat . I found an informative chapter in an old boat book called "MoTor BoaTing Ideal series" where it explained the ins and outs of development specifically for plywood construction boats.

I also found plans for a plywood boat called "Skeeto". This was close to what I envisioned but not quite. At least it was a starting point.

From this I build to scale a wire frame boat. Layed on ali sheet to see what happens. In the pics you can see there is about 3 different boats in the wire frame.

Also a wooden boat was build to scale. In that pic where the hull is up-side-down there is straight lines drawn with pen . Now folks those lines , they are one of the secrets to develop a sheet ali boat. In that position a straight ruler on its edge have a full touch across the sheet .

From all this a full size wooden frame work was build. The ali sheets can wrap around the frame to take its shape plus the advantage that there is plenty of space for G-clamps to clamp.

Building this full size frame work was a mission. The laminations around the sheer (deck to sides joint) took time. A lot of time was also spend on fairing (smoothing out) the wood.

Next time plating the hull . With pics.






Z.C.

[Randy V]

For you...

[Jack]

Z.C. Looking good!

[zollis]

Today I had the boat on the water for the very first time. The list of last tasks kept on expanding . Eventually some tasks , mainly cosmetic just have to wait for later because summer is getting shorter .

With which size propeller to start with? I chose a 12 inch diameter by 12 inch pitch.

All the systems are working good. Engine cooling, exhaust cooling, v-drive box and shafts, clutch , all working fine. No water leaks or oil leaks . Engine and v-drive box temperatures seems good. Only made 4 short runs. The boat goes onto the plane quite easy.

The tachometer is working erratic.

Now I have to check every part and bolt from bow (nose) to transom (tail) before I take it out on the water again. This will take a bit of time as I made most of the components from scratch eg. heat exchanger, drive shaft and prop shaft, rudder, fin, propeller strut, water cooled exhaust manifold, bell housing, v-drive box, seats and more.



Soon I will have the time to post the complete build process in a logical manner.


I can tell you this: tonight I am going to sleep with great relief / alleviation in my hart.






Z.C.

[zollis]

After the full size frame / jig was build another project interrupted the build process. The best place to store it in the mean time was " levitating" it from the roof rafters.






Z.C.

[zollis]

Then when I had more space and time the aluminum was clamped to the jig , and tack welded. In hindsight I should have taken more pics.











Z.C.

[zollis]

After many pounds of welding wire and untold amount of hours I had my hull. Notice how the bottom has a 100 % flat section now. Compared to the previous pics which shows a slight V shape.

The center section at the bottom was cut out after the hull was tack welded into its shape. A 4mm thick plate pressed into U shape (about 550 mm wide by 2100 mm long) was then welded in . The engine, the rudder, the skeg and the V-drive box all mounts onto this stronger piece. The rest of the hull is 2.5 mm 5052 right thru.

One pic shows the redundant off-cut or rather out-cut.













Z.C.

[zollis]

For the v-drive box I started with a VW Kombi trans-axle, pre 1968. At each wheel there is a reduction box. What I did was to cut off the side shaft and then rotated the gear so it faces in the same direction as the brake drum. A new seat was machined for a new oil seal. The hole were the side shaft used to be was then blanked off.

The brake drum was machined much smaller and is retained as the output flange.

This box gives a reduction of about 30 %. The prop turns about 2800 rpm when the engine is doing 4000 rpm.

Mounting this box was a bit of a mission. The first attempt was not satisfactory. A better improved method of mounting is used now.

The "Better Idea" was to use a standard C.V. shaft as the input shaft,-- OR so I thought.

Can any one guess what the out come of this C.V. shaft was???

Just to show what I started off with, I took 2 pics today of a similar transaxle.







Z.C.

[Ian Anderson]

That looks like a VW type 2 drive shaft. So I am interested as that is what I use on the Dax GT40

Ian

[Jim Cowden]

Nice zollis.

You did a good job on the deck.
A weld down the centre or did you over lock, its hard to tell.

Jim

[Randy V]

I learned something here today.. I had no idea that the VW Kombi had gear reduction units on their rear axle assemblies!

You are doing some marvelous work there!

[zollis]

Ian, no it might look similar but this CV shaft is not VW .

Jim, to get that deck without ripples took some special welding techniques. Each side has a double fold down the center line with bolts holding them together. Makes it strong enough to walk on ,--- as long as you step on the joint.

Jim and Randy, thank you for the compliments.

The main underwater stuff.

The rudder. The shape I scaled up from a sketch I saw in a book. It has a leading edge extension on the top side . This helps to balance the water forces as u go thru a turn and therefore makes the steering effort more easy . To help prevent the propeller scraping the bottom of the shore when the boat is beached the rudder is made a little longer . Fabricated from 4 mm 5083 double skinned with a wedge profile. About 3/4 inch wide at the trailing end.

The propeller shaft strut. Fabricated from 3/8 stainless. All edges tapered to about 2 mm thick. The corners is cropped / rounded to help prevent cracks starting in the alloy . The depth is such that there is about 2 inch clearance between the propeller blade tip and the bottom of the hull.

The fin. Fabricated from 4 mm stainless. The function of the fin is quite important on a flat bottom boat. It is the pivot around which the boat turns. It also helps to keep the boat going in a straight line. In the inside of the hull there is an extra brace bracket to take the forces to structural members.

As you can see from the pics the hull bottom is FLAT. No Vee, no hook, no rocker.



















Z.C.

[Cliff Beer]

Zollis, the underside of your boat, including the flat bottom, skeg, rudder and prop shaft configuration looks almost identical to my 1989 Malibu Skier. I think you've got a good combination there. Are you trying to build an old skool ski boat?

With that combination I would guess you'll end up with quite a flat/minimal wake, a modest amount of soft water behind the boat, very good tracking, and excellent ability to turn. One thing to watch out for (if not already considered) - you want your boat to lean into the turn. This is accomplished with a number of contributing factors, but the caster on the rudder post is one. Zero caster works if everything else is set up right, but you may need a couple of degrees to help get her to lean into the turn.

One other thought, your skeg looks good, but you may need a bit more surface area to turn really well - you might consider adding a second skeg of the same size/dimension right in front or behind it. My Malibu has three skegs in very tight formation right in the middle of the boat underneath the engine. Tracking at the front is provided by the steep V bow (which flattens out quickly)

Good luck!

[zollis]

Cliff , yes an OLD skool ski boat that is used in fresh protected water only. The flatter and smoother the water the better, perhaps with a touch of light ripple. Definitely no salt water and big waves.

To get the boat to lean into the turn there is slight ( about 2 inch ) relieve on the bottom on the outer edges. In the second pic from post# 9 it is visible. The rudder post is mounted square to the bottom.

The way I reason regarding the skeg is that to be able to turn quite tightly while at idle there can only be one pivot. A second skeg might induce drag.


Cooling systems.

The engine environment in a boat can become pretty hot if the heat is not taken away by dedicated methods. Reason; there is minimal airflow, if any, around the exhaust pipe , sump etc.

Having an aluminum head and a cast iron block I decided to go with a dual water cooling system. Two water pumps are used. The normal one to circulate antifreeze coolant thru the engine and heat exchanger in a closed loop. The second pump to suck water out the river then thru the heat exchanger and out thru the exhaust as a total loss.

The heat exchanger was made from stainless steel. The river water circulating thru the tubes while the clean engine coolant circulates around the tubes. Two removable end plates provide access to clean the inside of the tubes.

On the engine side the standard thermostat was retained with a standard radiator cap to pressurize the system. An expansion tank was also fitted.

[zollis]

On the second cooling system ( the raw / river water side) a second pump was used. This pump needs to turn quite slower than engine revs. To install a small v-belt pulley onto the main crankshaft pulley took some time and machining. Fabricating the mounting brackets for the pump was a challenge, because the space required was just not enough to make it easy.

Once the raw water exits the heat exchanger it enters a distribution block where individual runners take the water to each exhaust primary, there it is injected as close to the cylinder head as possible. For excess water there is an extra pipe that routes the water into the stainless silencer/muffler.

The exhaust note is rather dampened.

The exhaust primary pipe was made from mild steel and then galvanized.

One alteration that was required was the internal bracing for the under water propeller shaft strut had to move as it was now in the way of the v-pulley. A short torque arm with a small relocation of a cross brace did the trick. See last pic.

[zollis]

A few xtra pics to show the small v-pulley and the mounting of the second pump.

[zollis]

The steering and it's components "A"

The steering wheel mounts directly onto the steering helm ( steering box) which in turn mounts directly onto the dash board.

Before drilling the mounting holes , careful measurements was made to ensure there is enough space behind and under the deck for the helm to fit. As it turned out a 6 mm spacer was required to clear the bottom flange of of the dash. Pic a30.

Borrowing a WW2 bomber seat from my mate gave me the first realistic feel how the driving position would be.

The helm provides the motion for the cable which is inside the casing. This combination needs a large radius to change direction. Pic a40.

[zollis]

The steering and it's components "B"

At the transom the cable and casing are fixed solid. The reason being so that there is no movement of the outer casing as it winds thru the hull.

The linkage components between the rudder post and the cable are in the pics. Notice how the shanks of the screwed ends are a tight fit into the hex bar before they were welded. Pics b20 and b30.

A bigger , thicker tiller arm was also made. Pic b 40. Perhaps a little elaborate procedure where a band saw and belt sander could have sufficed.