Building an inboard...

I am planning to build my first inboard - a variation of Atkin's Shoals Runner in aluminum. http://www.boat-links.com/Atkinco/Utilities/ShoalsRunner.html

But I have been unable to find any sources of practical information on inboard installation. I expect to use a salvaged Datsun diesel, with the truck transmission and drive shaft (yes, I understand that this is not considered a "best practice" ;-) connecting via u-joint or CV to a stainless prop shaft.



Bearings? Do I really need "marine" bearings here? What sources are available for industrial stainless shaft and thrust bearings?

Seal? The shaft is only an inch or two below the waterline, and I've been advised an agricultural/industrial shaft seal should work fine.

Motor mounts? I'd like to have the softest practical mounts, as I suspect this diesel will vibrate a bit.

Yes, I know I will need professional advice at some point, but I'd like to do my homework first! Are there any decent books on inboard installations? Other advice?

Thanks, Sal's Dad

 

For the stern bearing and shaft seal it is hard to beat the standard rubber stearn bearing and the good old standard packing gland. For your aluminum boat you would want a stern bearing with a composite shell to prevent corrosion. If your stern tube is the right diameter you will not have to ream the end of it to get it to fit. As for the packing gland, get one made of the same alloy as the rest of the boat and weld it on the tube. After installing the packing, do not tighten it to any great extent. When the boat is in the water gradually tighten it till it just barely drips and as you use the boat tighten it ever so slowly till the drip stops and then do not tighten it any more than that or the packing may score the shaft.
You will need to have some way for water to enter the shaft tube to lubricate the stern bearing. A couple of holes a little ways ahead of the forward end of the bearing will do.
I will let someone else comment on the other features you would like to have.

 

For the information you are seeking you could do no better than log on the Glen-l site ,and all will be explained ,also the Hartley site in N.Z have a small book with similiar setups .you will need a self aligning bearing and housing to suit ,these are readily available from bearing supply houses.the jackshaft must be the sliding joint type and have universals at each end.this setup will work and last for years.re truck transmission ,I would not go down that path that is a recipe for trouble,,buy beg borrow a hydraulic marine gear and mount it to the truck engine ,and despite what people will tell you this is quite simply done ,best of luck......cheers.

 

Same Ideas

Hey,

I would really like to get in contact with you about how your boat turned out. I am doing pretty much the same thing with mine. Only dif is i am using a gas 302 with the factory 3 speed and the driveshaft going back to a prop shaft via u-joint. It is a 21 foot fibreglass and i am doing a mid mount engine. I have been having a heck of a time finding resourses out there that can point me in the right direction with this experimental build and might help having another head taking a crack at it too. I have been getting told it cant be done but i want to find out for myself.

Ryan

 

also if anyone else has tips i would love to hear them but please no "your a *****, give up!!" thanks

 

Hey Ryan,

It can be done. (It can always be done, the question is, should it be!)

Firstly, may I suggest you edit post #4 to remove your email address. We can reply on the board, or send you a personal email via the link on your public profile. But the forum is heavily optimized to attract search engines, and some 3rd-party bot will most certainly find your address and spam it if it's out in the open.

Now, I think what you're probably going to want for this engine setup is actually fairly straightforward. Shaft, cutless bearing, packing gland- all conventional, all just as they've been done for years. Now, for an experimental setup, I really like the idea of putting a big, hefty thrust bearing on the propshaft a few feet up from the stuffing box, bracing said thrust bearing very heavily to the hull structure, and putting the driveshaft fitting of your choice where the forward end of the shaft exits that bearing.

Now you can twist that shaft with whatever you like, mounted however you like, and the shaft is supported by that big thrust bearing. Put a CV driveshaft between that and whatever engine you're running at the time and you can pull and swap engines easily- and put them on nice, soft mounts- without having to go through that whole tedious process of aligning the couplings to 0.002" or whatever each time you change something. You just need to get it within the tolerance of the CV joints.

Now, using the car 3-speed in the boat... that may or may not work. Some car transmissions really don't like running full power / full torque for hours on end, as a boat engine tends to do- but a car very rarely does. You might end up with a hot gearbox that's tearing itself apart from the inside. (Especially if it's punked from an old Dodge Caravan.... but that's another story.) A marine gear is generally designed, built and if necessary cooled to handle continuous full power (witness the difference in ratings for anything by ZF or Borg-Warner when you compare their intermittent against continuous ratings for the same gearbox.)

 

Glenn-L's book is the only comprehensive one there is, but it was written half a century ago, so you will find only 'classic' solutions in it.

You can use agricultural seals and bearings instead of marine ones and that way save a lot of $$$. A tapered roller bearing can take enormous axial loads, a dual-lipped simmer ring is as good or better than most commercially available shaft seal systems. But both need oil or grease to be present under all circumstances.

You can use engine supports that were designed for other purposes, like large electric motors or generators. They are much softer than the ones for boat engines because these are always expected to handle axial loads.

The gearbox will do what is expected of it in your boat, but you must remove excess heat by adding an oil cooler or cool it externally with an air duct and a fan. And did you already decide on engine and exhaust cooling?

However.... The classical constructions are still around in great numbers because anybody can install and service them. Only if you have more than basic knowledge of mechanical engineering and the skills to turn ideas into reality you can go your own way without getting into troubles.

 

Thanks alot for the replies, they are extremely helpful. For engine cooling I was thinking of using a closed system with a high performance rad and electric fan mounted in front of the engine with direct cold air supplied by a scoop. I wasn't too sure if that would be enough to cool the motor but it is my first try. If not i am going to do fresh water pick up from the rear.

With the trans, i have a large oil cooler that I plan to mount with my rad. I am also going to prop the boat to my 2nd gear so when i get to a cruising speed, 3rd will drop the rpms a little bit. Im not trying to build a record speed boat, just want to satisfy my curiosity if it will work. If it does, hey maybe ill try a supercharger on my little 5.0 lol

The exhast cooling I wasn't too concerned with. My original plan was to put on a set of flowmaster mufflers and drop them through trumpets on the side. Are water cooled headers a must? if so why?

The engine right now is mounted on steel frame i welded up using the original motor and trans mounts out of my donor car. It is a really solid set up for that and when it runs there is near zero vibration felt in the boat which was another concern.

Thanks again,

Ryan

 

Hi Ryan,

Going air-cooled with a big car radiator might work. I'm not an expert on this, so I can't offer much advice on how to do it.

I'm not sure that choosing a prop based on your rig's 2nd gear will work, though. A car only needs full power when accelerating; at steady speed, it has no way to absorb that power, hence why dropping the engine RPM (upshifting) once you reach steady speed works in a car. A planing boat requires more power the faster you go; there is no drop in power demand once you reach steady speed. Propping for 2nd gear, then shifting to 3rd once at speed, would be like trying to run your car in 5th gear at 30 mph with the pedal to the floor- the engine won't like it. I'd say, choose your prop based on the ratio your box gives you in 3rd. Then you'd use 2nd for climbing to plane, and 1st for idling around the dock.

 

I've set up automotive rigs like this when I was a kid and you're not going to be able to use a clutch to shift gears. We always used the three speed out of GM trucks and only used 3rd gear. We did use the clutch to change from forward to reverse. You can use a race setup to shift gears, but this is a pretty high dollar way to go and it's typically an automatic, because you can't flat shift fast enough before the prop freezes at flow speed.

I've tried self contained (closed loop) cooling, using automotive radiator, etc. but you need a lot of inlet and exhaust vent area to make this work. On a small block Chevy, you'll need at least 4 sq. ft. of cooling inlet opening and a little more for the exhaust of this air. That's some big *** holes in the boat. The only way I've seen this work without melting down the engine is to have the engine wide open without any enclosure at all. It's the only way to get the heat out reasonably efficiently. On a car you have a lot of air passing over and around the engine, sucking the heat out and under the car. Even at idle, the fan can dump huge volumes of air under the car. In a boat's compartment you need the same surface area for venting.

You can use dry exhaust, but again it has to be out in the open, not contained in a compartment, under a floor, etc. The typical set up is headers mounted upside down, so they point up and over the stern of the boat or a tractor pull setup, where they go straight up. If you plan on going through any portion of the boat, they exhaust needs to be water cooled. The reason is quite simple, you'll literally melt down all the wiring, the hull, plastic and soft metal parts in just a few hours operation. Even if you triple wrapped the headers, the heat is just so high it'll even cook the hair out of my ex-wife's nose (I can dream, can't I). Inside a compartment, the temperatures need to be below 250 degrees (which is hot for a boat) or you'll cook stuff. Exhaust port temperatures is about 1,600 degrees and no amount of header wrapping will lower this enough. This is why it's water cooled.

I've tried air cooled engines too, and had similar issues with venting heated air, which of course was a bigger issue.

When looking to go fast, you should be careful about the hull you've selected to toss major HP at. Some hulls are designed to max out at a certain S/L (Speed/Length ratio) and if pushed further, they get unstable. What do you mean "unstable", well like high speed barrel rolls and/or the stern wanting to switch ends with the bow kind of stuff. I've done both and it's not fun, I broke my arm in a tripped chine incident years ago and it can easily kill you. At 60 MPH, the water is like concrete, which isn't any BS. So, be sure you have a design capable of the speeds you're likely to ask of it.

 

PAR already explained in vivid details what can and will go wrong.
For this experiment to end successfully, you have to create an environment for your engine that closely resembles the car it was in. Lots of free space around the engine and air speeds in proportion to the amount of horsepower you require.

I assumed you were going to use an automatic gearbox, otherwise I would have mentioned the need for a clutch...

 

thanks alot. Looks like I'm heading in the right direction. I have lots of airflow going through the rad and over the engine, and I am using an automatic. I am not sure what this boat was rated at for HP, but I think if i could hit 40 MPH that would put a huge grin on my face. All i need is to beat my father in law's Lund. lol