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Thread: first jet boat questions

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    Default first jet boat questions

    i recently purchased an older 20' smokercraft 20' flat bottom boat with a 78 mercury 115hp prop and just bought a jet unit for it. havent got it installed yet but i am in the planning stage right now. I have the equipment to weld aluminum and have welded alot of steel just need to learn aluminum before getting started. my plan so far is to fill the boat and any rivets or joints that leak i plan on welding them up hopefully to eventually end up with a fully welded boat.

    as for the transom i am reinforcing it and going to set the hieght required to get the jet foot in the right place but i am debating between just haveing the foot below the boat or building a tunnel. i have heard both ways on putting a tunnel on a flat bottom boat, some say it works great and some say it gets too much airiation and cavitates badly. what are your ideas?

    any help would be greatly appreciated.


    Ryan

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    Be carefull rivited boats are tricky to weld the material is thinner and will burn through easy. My rivited boat has rubber gasket like stuff in between some seems makes it real hard to weld. I like the tunnel concept but be carefull to get the tunnel right if its wrong you will be worse off than if you did not have a tunnel. Thas my 2 cents I am far from a pro so take my advice lightly.

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    You could always just start with the jet below the bottom of the boat and then move into a tunnel in the future. and 999 is right, the riveted aluminum is thinner than welded boats, so definately be careful.. especially on bottom welding.

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    yeah i noticed the skin was pretty thin and i anticipate going slow to prevent burning throgh. i will deffinately start with the jet below, because if my measurements are correct, the transom is just the right height to put the top of the foot about 1/4" below the bottom of the boat as it sits now so i will try that for a base line and then go from there. i plan on just running it the way it is this summer then over winter making any changes i feel i need after boating in it a season.

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    Member dkwarthog's Avatar
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    I'm not an expert by any means on boats and tunnels, but if you havent done much aluminum welding, I would recommend doing ALOT of practice before tackling the rivet welding. Welding thin aluminum is a real skill and burning holes in your hull would be a bummer and make it harder to fix.

    Typically, you weld faster on aluminum to avoid burn throughs...at least that is my experience. Hot and fast with alot of rod....oh and ALOT CLEANER surface required than welding steel...any contamination will foul up an aluminum bead...

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    Member thewhop2000's Avatar
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    Default You might want to take some wooden shims

    Depending on where your engine sits in relation to the water, you might need to shim once or twice if you are sitting too low. Just slip the shim under the engine mounts on your transom. This raises the engine and how it runs , lets you know, when you have got it right. Your rooster tail should not be too high nor too low. Just watch other boats and see what kind of spray they put out. I know when I converted a short shaft 50 to a jet, it took me a month to get my engine to water level just right.
    If a dipnetter dips a fish and there is no one around to see/hear it, Did he really dip?

  7. #7

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    Quote Originally Posted by dkwarthog View Post
    I'm not an expert by any means on boats and tunnels, but if you havent done much aluminum welding, I would recommend doing ALOT of practice before tackling the rivet welding. Welding thin aluminum is a real skill and burning holes in your hull would be a bummer and make it harder to fix.

    Typically, you weld faster on aluminum to avoid burn throughs...at least that is my experience. Hot and fast with alot of rod....oh and ALOT CLEANER surface required than welding steel...any contamination will foul up an aluminum bead...

    sorry for the confusion, i was not meaning welding slower i meant take my time and not rush and prep more.

    i would really like to make the bottom of the hull thicker and more robust, been contemplating skinning it with a thicker aluminum and then basically plug welding from the inside from the existing floor to the new sheets in a periodic spacing to tie the two together.

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    I am in the same boat with you! lol. I am putting ALOT of time in a boat alot of others would say just get a different boat. But if I did that I would have never learned this much. Take your time do as much research as possible and have fun. Here is a look at my project and I am not even half done. It has taken me 10 times longer then I thought it would. I am going to do float pods, a full uhmw bottom, rewire the whole boat and alot of other stuff. When I am done I will have 1975 boat that I will not be able to sell for half of what I have put into it. It will be cool though. My fist Alum welding was 30mins practice on a couple pieces. Then the transome on my boat it is real ugly but I know it is not going to come apart. I am real new on this site but the guys here are very helpfull. Some forums suck. This one seems like it has some great people that know alot and are willing to put in there 2 cents. Good luck!

    http://www.youtube.com/watch?v=YLGm1tRC134

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    Member HKYDDY's Avatar
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    Default welding aluminum

    I have welded literally tons of steel and a little aluminum. You can fudge a little when prepping steel, but none at all when prepping aluminum to weld. It is relatively easy to weld once you get the hang of it. The quality of your weld will definitely be proportional to how clean and well prepped the aluminum is. I would definitely practice on some thinner material than you are going to be welding if possible. It is always easier to weld thicker metals than thinner. Once you are good at welding the thinner material, then thicker will be a breeze. I wish I still had access to a machine with a spool gun. Fast and hot is the name of the game. Like women.

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    Moderator LuJon's Avatar
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    I would never stand between a man and his project.... But aside from the "fun" factor this boat just doesn't sound like it is even a remotely good candidate for the work you are wanting to do. It is what 30+ years old, so the aluminum is going to be seriously oxidized, I am no welder but the research I have done on it says that you need more heat and power to blow through the layer of oxidization. This seems like a really bad thing when dealing with metal that is on the thin side to begin with.

    Just a thought but wouldn't it be a lot more economical to just replace the broken rivets with new rivets and some sealer? Then use the heck out of the boat in places that it works well and save all that cash to buy a better un-powered welded shell of a boat to to build up. When the new project is ready for water then move your motor and controls over to it. At least that way you will be on the water the whole time and have a boat that will really do what you want in the end.

  11. #11

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    Quote Originally Posted by 999crazy View Post
    I am in the same boat with you! lol. I am putting ALOT of time in a boat alot of others would say just get a different boat. But if I did that I would have never learned this much. Take your time do as much research as possible and have fun. Here is a look at my project and I am not even half done. It has taken me 10 times longer then I thought it would. I am going to do float pods, a full uhmw bottom, rewire the whole boat and alot of other stuff. When I am done I will have 1975 boat that I will not be able to sell for half of what I have put into it. It will be cool though. My fist Alum welding was 30mins practice on a couple pieces. Then the transome on my boat it is real ugly but I know it is not going to come apart. I am real new on this site but the guys here are very helpfull. Some forums suck. This one seems like it has some great people that know alot and are willing to put in there 2 cents. Good luck!

    http://www.youtube.com/watch?v=YLGm1tRC134
    that is a cool project there, i hope mine can come out half as nice as that.

    keep up the good work!

    Quote Originally Posted by HKYDDY View Post
    I have welded literally tons of steel and a little aluminum. You can fudge a little when prepping steel, but none at all when prepping aluminum to weld. It is relatively easy to weld once you get the hang of it. The quality of your weld will definitely be proportional to how clean and well prepped the aluminum is. I would definitely practice on some thinner material than you are going to be welding if possible. It is always easier to weld thicker metals than thinner. Once you are good at welding the thinner material, then thicker will be a breeze. I wish I still had access to a machine with a spool gun. Fast and hot is the name of the game. Like women.
    yeah i have practiced the aluminum a little and i know what you mean about surface prep, i do plan on practicing alot before starting in on the project and i have some thin scrap aluminum to start practicing with once i get time.

    thanks for the tips.

    Quote Originally Posted by LuJon View Post
    I would never stand between a man and his project.... But aside from the "fun" factor this boat just doesn't sound like it is even a remotely good candidate for the work you are wanting to do. It is what 30+ years old, so the aluminum is going to be seriously oxidized, I am no welder but the research I have done on it says that you need more heat and power to blow through the layer of oxidization. This seems like a really bad thing when dealing with metal that is on the thin side to begin with.

    Just a thought but wouldn't it be a lot more economical to just replace the broken rivets with new rivets and some sealer? Then use the heck out of the boat in places that it works well and save all that cash to buy a better un-powered welded shell of a boat to to build up. When the new project is ready for water then move your motor and controls over to it. At least that way you will be on the water the whole time and have a boat that will really do what you want in the end.
    i understand where you are coming from and i am still on the lookout for a better hull to start with i could just not pass up the boat and motor i got for 1000 bucks and 200 for the jet unit for it.

    also this is just planning right now i am kind of dreaming up what i want to do to see if it is doable. for now i am going to install the jet and get her sea worthy and run it this summer and fish the hell out of it then this winter if i decide to still modify it that will be the time. i have also contemplated, if the boat handles like i want, just building a whole new hull with the dimensions of the one i have with the slight modifications i want to do. that will be a big under taking but i got to have something to keep me busy during the winter right?

    trust me all is up in the air right now and this thread is just me trying to get ideas of what can be accomplished with the boat i have cause money is tight right now and no one knows what the future might bring.....maybe a whole different direcdtion once i get it on the water and truely learn what i want in a boat, this is my first boat so it will be a great learning experience for now.

    oh and i finally got out to test the boat and i dont have any major leaks and only about a slosh of water after 4 hours on the water so i am just going to clean it up and run it for now, so no rivits to fix at the current time. i will try and get some pics up of what i am working with once i get the time.

    thanks all for the input and keep uit coming, you guys rock!

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