Tiny power boat

Have a look in DIY mainising at "Thai longtail with 6.5hp Lifan/Honda"
easy to turn into an inboard has the clutch and chain drive.

I have an old 10ft Jetski now fitted with a 15 hp outboard....rocket ship ...

Be sure to have a lanyard to cut the engine if you get thrown out ......

 

Mudman I'd sure like to see some photos of your boats. I am seriously considering a new Jon boat. C'mon back with several showing how your boat works.
Years ago I rented a skiff with a 5 Hp B&S and a reversable prop.

Messingabout has the oil system worked out.
In Lawn mowers and Tillers, if you put too much oil in those lttle 5 Hp B&S with the Pulsa jet Carbs you sometimes get enough oil up in the Valve area to cause a smoky exhaust and realy balky starting.

To little oil, and the splasher dont carry enough oil to the Cam and lifters.
That's when the over heating starts, and shorty after the overheating, the Metal to metal contact between the Rod and crank, and a hemorrage is about to suprise you.

I watched a race of those little guys on lake. The lake was churning, those kids were flying, dipping, skidding....having just plain too much fun.
That's when your engine with the normal B&S engine will run out of oil.

 

I have see the go devil. I wanted to make one of those at one point, but decided against it.

Only time will tell if this project will turn out as I hope. I have a cruise and carry outboard, it works great despite many peoples beliefs. On the test floating of the boat I will use that outboard and see what kind of speed I get, if its enough for me I might not put the briggs in the boat, but I think that I will do it just for fun.

I havent got the boat built yet, just some frame pieces assembled today. Next week I will start building up the frame. Hopefully.

 

Not to jack the thread, but this is basicly what we do. There is no modification to the B&S engine. 3600 rpm. We are running across ponds and shallows, so there is no wave action. Some guys go nuts though and jump beaver dams levees, etc. Those fellas usually break their engines. Probably from oil loss and over revving.

These guys provide a kit, but it is simple enough to fabricate one on your own. We change shaft lengths, transom heights, boat widths, boat lengths, hp, props, etc. Everyone has their own preference and everyone has a different configuration. Some guys with the larger engines play with cams and stuff, but most of us leave the engines alone. If it ain't broke......

http://www.boghogmudmotors.com/longtail.php

Thudpucker, Here is a link to my boat. I'll try and get the other guys boat pics.
http://www.boatdesign.net/forums/surface-drives/mudboat-surface-drive-prototype-25060.html

Ranger
Just to give you an idea of smaller boats and Hp. My brother has a 6.5 hp longtail on a 12x36 that runs at 12 mph. Great little boat. One guy I hunt with has a traditional mudboat which is a pirogue with a 5 hp B&S. Straight inboard pirogue. He probably runs at 12 mph, maybe a little better, which is fast in a priogue.

10 hp on a 9 foot boat, I guess a little better than 20 mph, maybe 25 because the mud props are not as fast as a conventional prop. 20 to 25 mph on a skateboard, very fast indeed. Hmmmmmm, I am a speed demon myself, but safety is first. Better wear a helmet. I'd probably put a hot foot also to keep both hands on the wheel. Throw in an engine cut off switch to a lanyard, and wear that life jacket for sure while underway. I got in a bass boat once and the driver handed me a motorcycle helmet!!!!!!!:!:

Do you have the drive unit for the vertical shaft Briggs? Are you planning on ataching the Briggs as shown in the diagrams? I really want to see this set up. (Vertical shaft Briggs are also good for hovercraft))

 

Hi Mudman,

The reason I'm using the 10 hp briggs is for speed The plans say that it will go 25 mph with a real outboard motor, and the boat is only 6 foot 6 in the plans aswell. Like you I'm crusing around in a smooth bayou, bay or lake. If he water is not calm then I dont go out.

As for the lower unit, I dont have one yet. My dad wants to see the boat built and floating before spending any serious money on theis project. I will probably couple it to the engine via some sort of shaft coupler (duh) Like shown here http://www.mcmaster.com/#catalog/115/1154/=1nrdmv

With a Mercury 9.9 4 stroke lower unit I will have a 2:1 gear ratio so that will give me some extra speed. I like speed.

Thanks for you advice and support, Ranger

 

Check him out looking in Mcmaster Carr. I buy a lot of stuff from them. I imagine that the lower unit will have a splined shaft not keyed. Not only that, but the outboard style lower unit is designed for the horizontal fin to ride at the waters surface, or even with the bottom of the boat.

I suppose that you could drill some holes in the fin and bolt it directly to the bottom of the hull with plenty of silicone. Scary having a hole in the boat though, plus the bolts create drag. Construct some engine mounts and mount the engine in line with the shaft. (you will need dials to get it true).

I've seen guys use a thick flexible hose with pipe clamps for a shaft coupling. I do not advise it. They tend to break. You will need to search for a proper shaft coupling to go from splined to keyed. You may even need a lovejoy so that you don't wear out your lower unit gears.

The lower unit will have to be mounted straight with the hull. A little off and you will loose speed due to rudder compensation.

I'd probably look into a right angled gearbox and go true inboard. Sorry for my ignorance, but are the dog gears in the lower unit? Just wondering about FNR capabilities.

 

From my research all the gears and shifting happens in the lower unit, so FNR is a go. The cavitation plate will be my mounting plate to the boat. As for splined shaft, your forgetting that I have to cut about 10 inches so I dont have a big way up in the air, so there will be no splines. Even if it had splines after I cut it, Mcmaster Carr has couplings for splined shafts. Probably use carriage bolts to reduce drag as much as possible, or maybe recess the bolts somehow. I'm not sure how I'm going to line it up to make it straight, probably just do a ton of measuring from side to side.

Hope this helps mudman, Ranger

 

Well I made a mistake.

I went to gluing and screwing the engine mount to the transom frame piece. I didnt cut the engine mount at a 15 degree angle. So now the transom is at a 90 degree angle, no good for a small outboard.

I'm going to "test" a outboard on the boat before installing the inboard. Plus I dont have the parts for the inboard.

Well now I have to wait till tuesday to do any work on the boat. By then the glue will be nice and hard as a rock. All I had to do is just cut the motor mount piece at a 15 degree angle on the table saw. Oh well.

 

The 90 deg transom may not be a problem ..yes it means you carnt tuck the outboard under to push you up onto the plane quite as easily....the main thing to check is that the leg of the outboard does not touch the transom when pushed forwards as this will affect the steering ( been there done that ) You may need rather than to cut some 15 deg blocks just to have some square blocks on the outside of the transom as thick as the motor clamps will allow to push the motor back ...that will keep it away from the the transom.....fine for a test run ...good luck

 

Ok, that saves alot of time and effort.

All I want to do with the outboard is to see if the boat floats and see what it will do. However if I like the boat with the outboard, can I use the blocks permantly?

The outboard might be a temporary permanant solution, I might never use it, or use it forever. It all depends if I get up on a plane and go fast enough for my liking.

I think I will still go with taking it apart and fixing it the right way. I would rather do that now than later.

 

If you go with 15 deg angle blocks then they need to start at the bottom of the transom which means that they might be too thick at the top for the outbord clamps.....I once built a canoe and had he transom vertical and had to cut it out and re glass at 15 deg because the outboard hit the transom...how big is your outboard ?? ..I have a 9ft long 3 ft wide ex-jetski wth a 15 hp Johnson ....that goes about 25 kts....fast enough for me !!

If you have an inboard you carnt lift the prop if it gets shallow ..so think outboard ....or even a thai longtail /mudmotor That would be different !!!

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My reps bad because I speak the truth ..some dont like it ....

 

I dont have a big outboard. It's just a cruise and carry 2.7 outboard, it doesnt do much, but it will move a 12 sears fibreglass boat at a good speed.

I'm thinking that with an 8' boat the little outboard will get the boat on a plane and go pretty fast. However I dont think it will be fast enough for me. Thats why I'm designing the boat as an inboard.

If a 2.7 wont go fast enough for me, a 10 hp inboard will surely do what I want.

 

the easy way to get your speed (on the plane) is for every one inch of pitch and every 1000rpm you will get 1 mile per hour ......so a 10 in pitch at 3000rpm is about 30 mph ..got it

remember that an inboard takes up space inside the boat right where you wan to be .. got any photos yet ..we all love photos

 

If you read to post, I'm building the boat. I cant get picture because I'm building it in school. Pictures will come, probably around the first of June.

 

Pictures

Finally, I got the boat from school and to my dads shop. So far I got the frame mostly put together.


Me and the boat frame




Stern, the plywood is for the engine to mount on.


This is where I will sit, its 3 foot long. I thought that would be enough, and its working out ok.


Next section forward, not sure what to call it.


Bow, I have a problem though.



I need to connect the chines (right term?) to the stem (right term?). Me and my dad are working on it, but I bet that one of you guys can tell me what to do and it will work perfectly.

If you want some more pics of the bow, just ask.