Tiny power boat

Discussion in 'Boat Design' started by Rangerspeedboat, Apr 13, 2009.

  1. messabout
    Joined: Jan 2006
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    Location: Lakeland Fl USA

    messabout Senior Member

    Ranger; I think that you will find the 10HP engine to be too heavy for practical use on an eight foot boat. In the end, it is likely that a 4 or 5 HP converntional outboard will go faster with less fuss and bother. The cost of a suitable engine is, of course, a factor. Perhaps you could earn some cash while working, instead of spending a lot of time on the beastly lawn mower thing. Ask me how I know these things.....I was an ambitious boat fiend kid a long time ago. I managed to graft a good sized chain saw engine onto a lower unit. I had the advantage of my fathers machine shop to make whatever parts were needed. It worked but not as well as an ordinary outboard. I too had problems figuring out what prop to use on the hybrid. In the end, I abandoned the project and got a nice little outboard. Shoulda done that in the first place.

    I encourage you to pursue your project no matter what kind of engine you use.
     
  2. Rangerspeedboat
    Joined: Apr 2009
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    Location: Texas

    Rangerspeedboat Senior Member

    I too wonder about the weight of the engine. Only time will thell though.

    I have a backup engine that I can use if this one is too heavy.

    I'm a light guy (a 110lb freshman), I turn side ways and dont cast a shadow :D

    So add another 50lb engine lawn mower battery and 3 gallons of fuel then you get up arond 200 lbs.

    I have 3 out of 4 frame pieces cut and ready to assemble. This is turning out to be a smaller boat than I thought, but I still think it will work nicely.

    Now I'm trying to figure out a way to launch it from a bayou. The lower unit is giving me problems.
     
  3. rasorinc
    Joined: Nov 2007
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    rasorinc Senior Member

    Glad to hear you are making headway. Remember we all love pictures. How about a set of light weight transom wheels and you pick up the bow and guide it where you want. Google transom wheels for fishing boats to get some ideas as there are many styles. They should be pull out or removeable so you can put them in the boat.
     
  4. Rangerspeedboat
    Joined: Apr 2009
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    Location: Texas

    Rangerspeedboat Senior Member

    I will se if I can bring a camera to school and get some pics.

    As for transom wheels, thats a great idea. Maybe put some in the front on the sides and have a boat car.

    My problem is that I'm launching the boat into a the muddy, shallow, Taylor bayou in Texas. It has no real launching point where I live so I have to use what I got.

    If you want to see the bayou and bay, google Shoreacres TX. Then just look around for a bayou (to the left)

    Transom wheels are a good idea, but I would need some in the front so I could get it up on land.

    Thanks, Ranger
     
  5. rasorinc
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    Location: OREGON

    rasorinc Senior Member

    they have bow wheels for boats that are removeable. REMEMBER---WEIGHT ps If it is not to late can you make the length around 10'? Always nice to bring a friend. Are your plans showing bottom and side frames????
     
  6. Rangerspeedboat
    Joined: Apr 2009
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    Rangerspeedboat Senior Member

    Here are alot of pictures of the plans. I made them as close as I could for you to see.

    The plans do have bottom and side frames. The lines paper pics I drew myself, those are the side frames. I have 1,2 and 3 done.

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    These plans are old, but give a me a good idea of what I need. As you can see I modified them to fit my needs and the materials that I have.

    Rasorinc, I hope this helps

    Thanks, Ranger
     
  7. Rangerspeedboat
    Joined: Apr 2009
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    Location: Texas

    Rangerspeedboat Senior Member

    Fuel pump

    I got my fuel pump on thursday and played with it a bit. This morning I hooked it up to the engine.

    Here are some pics of the pump

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    Here is where the vacuum line connects, a piece of 1/4" copper tubing sodered onto the crankcase vent works good. I plugged up the old vent hole with a metal plug

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    Here you can see where I drilled a small 1/8" hole to prevent over pressurizing of the crankcase.
     
  8. messabout
    Joined: Jan 2006
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    Location: Lakeland Fl USA

    messabout Senior Member

    Ranger: You are one helluva kid. I salute you for your ambition and obvious commitment to your project.

    I would never have thought of using a fuel pump of that type (Walbro maybe) on a 4 cycle engine. It's worth a try. One of the several problems that you may encounter is oil in the pressure line. If the rings and valve guides in the engine are tired, you may have more pressure than you can use profitably. You can regulate the pressure that gets to the pump by experimenting with various sizes of crank case venting. If the input to the pump is a vacuum design it will not work at all. There is almost always a positive pressure in the crankcase.

    Once again, I do admire your resolve and certainly wish you well.

    P.S. Rasorinc is right about stretching the length to ten feet.
     
  9. thudpucker
    Joined: Jul 2007
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    Location: Al.

    thudpucker Senior Member

    You might (I repeat Might) have a problem with B&S engine on a boat for two reasons.
    One, it dont hold enough oil for use in a bouncing jostling carriage like a boat will be.
    Two, the B&S carbs dont do well in a bouncing environment. In fact B&S put some Foam in the fuel tanks of their Roto-tiller engines so the fuel wouldnt bounce so bad. It would turn to froth, the engine would run out of gas and quit. But it would always re-start.

    I can see you want to keep the cost's down and you are in the inventive spirit. Go for it. But see if you can come up with a Marine, two cycle powerplant. Trade that Snapper for an outboard!
     
  10. Rangerspeedboat
    Joined: Apr 2009
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    Location: Texas

    Rangerspeedboat Senior Member

    The water where I will be using the boat in is always smooth water, if its not smooth, then I dont go out. Yes there will still be some bouncing and moving about, but I think that the fuel pump will take care of giving me enough fuel. The pump I got off of ebay and it came off of a 17hp industrial engine, and it works fine for my needs. I have been starting the engine and running it every day, and have nad no problems. The pump is a vacuum style, (oh no it wont work) but it still does, there is a slight vacuum from the crankcase. As for the fuel tank, I will probably be using a marine 6 gallon fuel tank filled only half way, I have some 6 gallon tanks just not any 3 gallon.

    I just had an idea for the lubrication, drill a small hole in the crankcase that is lined up with the connecting rod and crank and thread in a brass fitting, then run a hose to a small oil pump. From there you run the pickup line to the oil drain, this should pump oil and shoot it onto the moving parts. The pump can either be hand pump or driven off the engine somehow.

    I admit, if 6,7,8, or 9.9 power head came my way and was cheap I would use it instead. Unfortunately "cheap" is not really a term when you get into any good hobby, improvise is though ;)



    Thanks for the support, Ranger
     
  11. thudpucker
    Joined: Jul 2007
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    Location: Al.

    thudpucker Senior Member

    Go to your local lawn mower shop and tell him of your Re-circulating Oiling Idea.
    He'll show you a block or two where the Rod has failed from Lube, and also what will happen if you get too much oil in the crank case.

    Keep looking for a 9.5 and up Jon/Rude as they are light and I have heard of people turning the 9's into 15's.
     
  12. Rangerspeedboat
    Joined: Apr 2009
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    Location: Texas

    Rangerspeedboat Senior Member

    Why would a rod fail? Too much oil? Not enough?

    Please explain.

    Thanks, Ranger
     
  13. mudman
    Joined: Mar 2007
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    Location: Madisonville, LA

    mudman Junior Member

    I've been running B&S on small boats for 20 years. We use 5 hp horizontal shaft engines for the mud motors, and run them on 12 foot flat boats. I have never had a problem with a rod failing. Some guys do have carb trouble, primarily because the small engine carbs are extremely cheap and clog with dirt very easily.

    I think that 10 hp is a bit much for a 9 foot boat. 10 hp is great for a 14 footer. I ran a 25 tiller on 12 foot boat and I gotta say that it was scary.

    I have wondered how to get a vertical shaft to work on a boat without a right angle gearbox, and I have thought of using a lower unit. I do believe that a used 5 or 6 hp O/B will better serve you than a frankenstien deal. I don't want to discourage you, but I just made a monster and it took nearly 2 years to get it right. (It's also a much bigger monster than you a creating) I also have lathes, mills, and welding machines at my disposal. It's alot of trial and error to get it right.

    I wish you the best of luck with your project, but put a little more length on that hull for 10 hp. The engine should not require any mods to run as a marine engine. Doesn't it have a splash type lubrication? I wouldn't change any of that. Use the engine as is. There is no need to modify a running small air cooled engine for marine purposes. Why would you drill a hole in the crankcase?!!!??!?! Just put oil in the cap that says "OIL GOES HERE".

    These engines don't use much fuel either. We run 1 gallon gravity feed on the 5 hp B&S. You'd be suprised how far you will go on 1 gallon.
     
  14. messabout
    Joined: Jan 2006
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    Location: Lakeland Fl USA

    messabout Senior Member

    I will not quibble about the design of your fuel pump. If it works dont fix it. I am a professional race engine builder. Having placed a manometer on about a zillion engines, I swear that I have never seen a standard 4 cyle that produced a negative crankcase pressure. At low speed, a single cylinder engine may or may not produce an oscillating pressure (positive to negative to positive....an so on). As rotational speed is increased the oscillations will diminish and eventually revert to all positive. That is why the engine has a crankcase vent that is placed well above the oil level.

    Certain all out (spell scandlously expensive) race engines use a dry sump system. They have a bank of several pumps that evacuate the crank case to deposit the oil in a remote holding vessel. The pressure pumps deliver the oil back to the appropriate places whill the scavenge pumps pick up the oil and returns it to the tank. The scavenge pumps always have a larger pumping capacity than the pressure pumps. That can create a small negative pressure in the crank case. You do not have a dry sump system on the B&S unless there are some Grand Prix Briggs engines out there that I have yet to encounter. None the less if your system works then go for it.

    Hang in there dude!
     

  15. Rangerspeedboat
    Joined: Apr 2009
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    Location: Texas

    Rangerspeedboat Senior Member

    The system works well Messabout, (not to offend) But if the crankcase reverts all to positive pressure then how is it getting the air to push out all the time? There has to be negative pressure somewhere. This engine does have oscillating pressure.

    Well some people do say that it wont work, or not well. Here is a little video that I found using the same idea as mine.

    http://www.youtube.com/watch?v=lXpzxcE_wdE
     
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