Motorcycle powered hydro

You can get 99% of what you want if you put a nose cone and low water pickup on a stock motor. The merc racing outboards are really just the fishing powerhead on a racing lower unit. The racing gear foot doesn't have forward/neutral/reverse, it's just a direct drive, pull the rope and go. Not what you really want or need if you aren't racing.

A nose cone is a common mod for outboards, you can bond it on with epoxy and add a water pickup that will let you put the drive shaft level with the back of the hull and run the prop as a surfacing prop. Racing rules make you put the shaft a specific distance (for runabouts it is 3/4 of an inch) below the planing surface. For that reason a very slim gearfoot is important. If you aren't racing to set of rules you can just run a stock unit higher and get the same effect for a lot less money. The limit as to how high you can run a production outboard is generally when they stop pumping water. If you put a hose and small scoop on the transom of the hull and rig it to feed the water pump, you can run the motor higher and you don't need the racing gearfoot.

Much cheaper and every bit as effective. Keep your eyes out for a proper motor and then go from there.

 

Get a tail , a long tail to be sure !!!

A while back some one on scream and fly had done there own thing and cut and tucked there own units ! Can tremember but i have a feeling they were doing gear cases and racing lower units to .
For a mod project i have my finger on at work changing a sterndrive to a step back out board a 2 stroke 90 hp 3 cylinder yamaha is 119 kgs and the merc 90 3 cylinder was 170 kgs so looking theres some big variations to be had weight wise .
For what you want a single shaft inboard made up as a whole complete unit including the rudder with hydralic height adjustment would be a great invention .Like a long tail set up but mounted partly inside the boat and sporting a rudder !! Forget about all the other gizmos this is far simpler and a fraction of the weight !!.

 

Your motorcycle engine is chain drive - rig a chain and prop-shaft rig to twin props - one in each pontoon. Do it right and you can have them counter-rotate.

With a couple of chain tensioners, or even better, a couple of conjoined sprockets to allow simple change of direction, you should be able to get a decent length without too much throw.

Chain and sprocket is remarkably efficient and you already know the 520 chain can handle the power. you would also be able to play around with the engine's gearbox and sprocket sizing to get the ideal shaft speed for your props.

 

I like the idea but if I were to go two props I would just do two motors. Then we're talking a bigger boat. That kinda gets out of the thought of my project of a smaller cruising boat that I can pull behind my Cabin Cruiser (when I get one) to play around with when we're out on the river.
Also I don't think I would want that much chain flopping around the boat.. Too much room for things to go wrong then.
I think for this project I will just be building a tunnel and slap a 50 horse Merc on the back and see what I can get. I'm sure I would be plenty happy with the performance I would get with a stock Merc.

 

Have you checked out the longtail drive ?? its really simple and the motor could be inside the boat and the drive down under the tunnel with the prop where it should be about a foot infront of the transom and attach a rudder and make it one complete assembly . the whole shaft and prop could slide up and down to give trim and proper depth control . Get the propeller deep to start and get going and raise slightly for that extra speed and a roosters tail like the big boys get !! no gear boxs and chains and crap to go wrong and waste power . a 1000 cc motor would be a beast and take some holding onto . But there is a throttle so dont have to use all those lively wee pony's

 

Haha, this cracked me up..
http://www.youtube.com/watch?v=eHCKLwXq0e0
I think I'm just going to go with an outboard for this project. If I make a cat hull the direct drive just isn't really reasonable because the shaft angle would end up like 15-20 degrees down. I figure I could dump $1000 on an outboard and I would be plenty happy. Maybe then I could just make my boat a 4 person cruiser

 

quick sketch i drew this morning when i was bored at work. thinkin my boat would loo like this.

 

Do you think 1000cc might be too much power?

Power is not the problem engine life is.

While a Mcy or car may have a fantastic HP , that output is for a very minor time.

1/4 mile , or up a big hill,not hours as a boat or aircraft requires.

To get some concept of long term durability go to the EAA site and learn of the many attempts to get a motorcycle engine reliable at modest HP.

 

Being a car driver and motorcyclist of more than 40 years, I don't understand your reasoning.

I recently returned from a 10 hour drive - my engine was averaging 2500-3000rpm for most of that time. I am sure I culd do the same tomorrow, and the day after that... in fact, for as often as I would wish, assuming regular maintenance.

I raced motorcycles for most of 17 years, including 8-hour endurance races. I have ridden across Europe and Australia - only stopping for gas. Upon strip-down of the 8-hour bikes, there was negligible wear - in fact the bikes were production items, not specialist race bikes. They went on to be used for regular commuting, and further racing, as needs dictated.

Modern motorcycle engines are extremely well-engineered and can produce high horsepower at moderate RPM.

A 1200cc Yamaha touring bike/engine, like the FJ series for example, puts out close to 110BHP at 8500RPM, but it also puts out 80% of that power at only 5500RPM. One of those under-stressed engines is good for 100,000 miles with only oil changes and basic maintenance. Being a shaft-driven engine, it is also well-suited to boats. Light, powerful and simple.

The EAA reference I find unusual - the properties of an aircraft engine are very, very different to those of a vehicle operating at sea level. It is the air pressure and the 3D nature of forces imparted that is the source of issues with aircraft engines. Although, Rotax - one of the worlds leading motorcycle engine manufacturers - is one of the leading (if not THE leading) manufacturers of engines for microlight and ultralight aircraft.

I can't see the correlation between aircraft engine reliability and boat use.

 

Thik and work on the therory that if you have lots horses you dont have to use oll of then all of the time and so lasts way longer . I have a motor twicce what my boat should have and its never ever going to wear out i only ever open it up aboyt once every couple of months and its economical as well 3500 rpms is its best cruising rev's and its hardly working at all . Same would apply to a 1000 cc motor in this little boat . should last for long time !

 

What he ^^^ said!

 

Fast Fred is correct. There is a huge difference in duty cycle between continuous operation at percentages of power greater than 75% and the operation that you see in a ground vehicle even in some of the most difficult racing applications.

For example, internal cooling is one of the critical aspects when continuous high power is required. In a road racing engine the maximum power is required for only as much as 30 seconds at a time. At that point power is backed off and the metal cools. This operation cycle sets up the required cooling flows and metal cross sections.

When operated at high power for a continuous period, as is seen in aircraft and boats, the engine never gets a chance to get a "breathe" so to speak. Higher metal temperatures in and around the cylinder head limit the amount of heat that is transferred from the valves to the valve seat, and therefore valve temperatures are higher.

So you ask yourself, "so what's a few degrees in valve temperature???". Well, the short answer is that at these temperatures, a 25*F increase in valve temperature cuts the life in half. A 50*F increase in valve temperature cuts the life to 1/4, and a 100*F increase in valve temperature cuts the life to 1/16 of what it was normally.

There is no question that continuous high power operation is the most difficult duty cycle for reciprocating engines, and that aircraft and marine engines, as a result of this condition are the most difficult set of conditions to design for.

Some engines that are marinized are hugely oversized, and that allows them to operate at lower percentage power and live for a reasonable time, but auto and motorcycle engines, if used to a high percentage of their rated power on a continuous basis won't live very long.

As Fast Fred noted there is a huge market for lower cost aviation powerplants. In order to fly safely and not have frequent power loss problems, most converted auto and cycle engines are considerably de-rated for aviation applications.

Simply put, there is a huge difference between locking the throttle open in a boat or plane for hours, and the amount of heat generated on the straightaway of a track in thirty seconds.

 

Where did anyone say the engine was operating continuously at more than 75% power?

He stated "the many attempts to get a motorcycle engine reliable at modest HP."

In an 130hp 1000cc motorcycle engine rated for 10,000 RPM, what is modest?

I would say modest is running it at peak torque, or around 5-6000rpm and getting 70% of peak HP. Something like a Yamaha or Suzuki big-block motor should last a heck of a long time so lightly loaded.

I guess it all comes down to nit-picking what is meant by 'modest'.

I also don't know how your analogy works when applied to long-distance autobahn or desert driving - I have literally run at close to 100mph for nearly three hours on cruise control on my BMW1200. I don't recall there being a service warning for such a thing. Constant speed - no variation. Certainly I have never run a boat such as the OP is proposing for nearly three hours at constant high throttle.

I don't doubt your figures at all, but you are talking about an extreme case that is unlikely to be encountered in real-world boat use - it isn't an aeroplane that has to keep a certain airspeed to remain functional.

Specifically, the OP was talking about a fun boat, not a speed boat. He expressly stated that in the original post.

Personally, I think a motorcycle engine is only useful as a slow-speed tractor and wouldn't put one in a boat except if I happened to have one spare - the noise, maintenance and fuel cost is too high to use it as a performance engine, IMO.

 

hey hydro, go to http://miniboatmadness.com got some guys over there that can help ya too. take a look.

Outlaw

 

I would like a boat that runs on a motorcycle engine - with the motorcycle left intact. Run it up on shore, unhook/unload the motorcycle and go for a ride.