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Thread: alumacraft tunnel hull help

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    Default alumacraft tunnel hull help


    Hey guys i just picked up a 165 alumacraft cc tunnel hull with a 50hp 2 stroke yamaha and was wondering if i need to get a jack plate for it? It currently has a 4blade prop and is seems kinda slow. Will a 3 blade and jack plate make it faster? The boat gets on plane really easy but the top end seems too low.

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    I forgot to mention that im running around 25-28mph depending on my load.

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    PawPaw Gene is offline Crappie.com 2012 Man of the Year * Crappie.com Supporter
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    Juan, what is your RPM's at wide open throttle. If you're not able to turn 5500 then you're over propped and lugging the motor. If you're turning over 5500 you're over revving the motor and loosing speed maybe. I have a 50 yamma on a light weight glass bass hull that at 5500 my speed is 30 to 32. The best thing to do is to go talk to a prop mechanic, they can do wonders for you sometimes.
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    I have a 16ft G-3 with a 40 yamaha and top out at 30mph. Could be a prop issue or rpm like the other guy says

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    Default Re: alumacraft tunnel hull help

    The tunnel will have a slower top end then a non tunnel but you can run in some shallow water. I would put a jack plate on it so you can use the tunnel. Top end sounds about right to me. Yes I would get rid of the 4 blade prop and go with a 3 blade prop. It will give you a little more top end but slower hole shot. Better yet put a jet on it and use the boat for what it was built for. Running in shallow water.

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    Thanks guys for the info. Imma talk to my local shop and hopefully get a jack plate too. When i baught the boat the last owner said the boat needed to run with a 4blade prop. But idk.

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    Default Re: alumacraft tunnel hull help

    Quote Originally Posted by juanbenz View Post
    Thanks guys for the info. Imma talk to my local shop and hopefully get a jack plate too. When i baught the boat the last owner said the boat needed to run with a 4blade prop. But idk.

    In my humble opinion. 4 blade props are for big hp motors. They do a pretty good job on a pontoon to.

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    To get your question answered you need to get your rpm's at wide open and a know if your prop is running in the water of the tunnel. If running in the water from the tunnel you need a 4 blade tunnel prop with lots of cup for grip. The tunnel water is poor quality compared to the water under the boat. The jack plate will help you some as you can adjust your motor up or down depending on the situation. If you get a jack plate you should put on a water pressure gauge. With the 4 blade tunnel prop you can run very high and loose pressure. I can run with about 1/4 or my prop out of the water without loosing pressure.

    You can also look into venting your tunnel. I did that to mine and it broke the suction of the tunnel to the water. The tunnel in your boat is like an upside down airplane wing sucking you to the water.

    The best place to get you question answered that I know of is Boats, Blinds, & Gadgets Forum - Refuge Forums the guys on this forum know tunnels and how to set them up right.

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    Yeah imma take the rig to the shop and find out what my rpm is at wot. The boat didnt come with a rpm guage. How do you vent the tunnel? And what will that do? Sounds like i have to get a pressure gauge too. What kind of set up do you have?

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    Default alumacraft tunnel hull help

    You may be money ahead getting a digital tach so you can always know your rpm. The better ones are around $50-60 several places make them just make sure they work for an outboard. Once you start playing with your jack plate and props you will need one.

    The tunnel in your boat acts like a upside down airplane wing so instead of it lifting you up it pulls the back of your boat down while at highest speeds. By venting basically drilling a hole in the front of the tunnel and welding a pipe that goes up and over the back transom. Or like i did welding a pipe at the back of the tunnel going to the front so i don't have a pipe on the floor of the boat. The vent breaks the suction of the water witch makes the boat squat. Vented tunnels will ride higher with less drag and go a little faster.

    I have a 20/60 plate boat with a 4" tunnel. I have had it about 9 years now and it is still not set-up correctly. Too much money time and know how that I lack. It was a used boat with no motor and setup for a heavy 90 Johnson. I put a 70 Yamaha on it and I could never get the right rpm with the lowest tunnel pitch prop I could find. The boat would always plow the front down once on plane. I figured out that the hull had been hooked causing the front to plow. With the larger bigger motor it prob worked great. I had some plate welded over the hook and it helped some but not enough. So I vented the tunnel and that helped a lot and was able to get to right rpm but with the rear not sucked to the water it porpoises once you get past 25 mph so I need some pods or trim tabs now for it to run right.
    Long story short it may not be worth the money and effort to gain 2 or 3 mph.
    The main thing is to make sure your motor is running in the correct rpm range at wot. Name:  ImageUploadedByTapatalk1360201676.379020.jpg
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