tunnel hull

[rampage11]

wondering if anyone has any experience running tunnels? i just went and picked up my new 15x46 southforks tunnel and was wondering where the motor should be mounted height wise and where motor should be trimmed to. right now im pushing it with a 25 yam 2 stroke. have motor mounted on 3.5 offset by 3.5 lift jack plate.. cavitation plate running bout and inch or so above top of tunnel right now.. just doesnt seem to want to grab and come out of the hole.. boat has pontoons also

 

[Mr. Demeanor]

Re: tunnel hull

Not sure what you mean by tye boat having pontoons too...? Do you mean its a full tunnel with sponsons? Post a pic.

I run a 13' Biel tunnel with a Yamaha 130. Tunnel can tunnel cab be run very high and will run better the higher you can run it. It will actually plane off faster and flatter the higher you mount the engine as long as the prop can hook up well. The prop will have clean, undisturbed water coming through the tunnel which allows the high heights.
Keep bringing the engine up and water your water pressure. You will probably need to low water pickup of some kind eventually to get the most out of it.

You also might want to ask over at screamandfly.com Someone over there probably has had one of these and may have specific advice for you.

 

[rampage11]

Re: tunnel hull

pontoons sponsoons..whatever..flotation pods on transom.. should i go higher or is 1.5 inches above tunnel top about right

 

[Mr. Demeanor]

Re: tunnel hull

pontoons sponsoons..whatever..flotation pods on transom.. should i go higher or is 1.5 inches above tunnel top about right

Ok, so extra flotation....

Theres no real right or wrong answer to be given over the internet. Prop shaft even with the bottom of the sponsons is a good start for a performance tunnel but you might not have water pressure that high. Just keep going up and watch your water pressure and temperature.

 

[oops!]

Re: tunnel hull

pm scotty.........chine walker

he is crazy.......(running tunnels) lol

the drive height and angle of attack for performance is a real dark art.......minute adjustments make all the difference.
teams keep those secrets close.
if you can run a chopper.......half the prop !


there is also a place called scream and fly.

 

[mrdancer]

Re: tunnel hull

An inch above the tunnel is a good general starting point.

Make sure you have the right prop on there. You need a good tunnel prop with double-cupping (surprised Southfork didn't set it up correctly for you!). Baumann's makes a good tunnel prop, as does Powertech. Give them a call, tell them your WOT rpms, boat specs, etc. and they will set you up correctly. The prop will make a world of difference when it comes to tunnels.

If you don't have a water pressure gauge, get one NOW and use it! A hydraulic jackplate is nice, also - lower it for holeshot, raise it while running. If that Southfork has a vent in the tunnel, close it for holeshot, open for running.

 

[Mr. Demeanor]

Re: tunnel hull

His prop choices with a 25 Yamaha are going to be VERY limited. Generally speaking, tunnels do not need bow lifting props like choppers or props with a lot of cup since the boat creates its own lift. With only 25hp it may not get going fast enough to really create that lift though.
Ron Hill makes some small motor performance props. Cleavers and semi-cleavers generally are the fastest on a tunnel.

When you get your engine up like mine, you will need a water pickup. I was losing pressure at about 75mph with a Bobs nosecone and ended up designing a transom mount pickup. Now I have 20 PSI over 80mph.
http://www.youtube.com/watch?v=WIXvi33I0o8&feature=channel&list=UL

 

[mrdancer]

Re: tunnel hull

... Generally speaking, tunnels do not need bow lifting props like choppers or props with a lot of cup since the boat creates its own lift. ...

I think the boat he is referring to is actually a pocket tunnel jon boat, not a full tunnel like yours. See southforkboats.com for more info.

If Baumann or Powertech can't hook him up with a good prop, his only option is to lower the motor for holeshots (where a hydraulic jackplate or mini-jacker would come in handy).

 

[rampage11]

Re: tunnel hull

I'll try and post pic later.. have it in water right now.. from what I've read I'll have to trim out more the higher I go.. with offset of jack plate I should be able to run inch or so above tunnel .. running a 3 blade double cup 20* rake ss prop

 

[WIMUSKY]

Re: tunnel hull

His prop choices with a 25 Yamaha are going to be VERY limited. Generally speaking, tunnels do not need bow lifting props like choppers or props with a lot of cup since the boat creates its own lift. With only 25hp it may not get going fast enough to really create that lift though.
Ron Hill makes some small motor performance props. Cleavers and semi-cleavers generally are the fastest on a tunnel.

When you get your engine up like mine, you will need a water pickup. I was losing pressure at about 75mph with a Bobs nosecone and ended up designing a transom mount pickup. Now I have 20 PSI over 80mph.
http://www.youtube.com/watch?v=WIXvi33I0o8&feature=channel&list=UL

Nice. I watched a few of your vids. Everytime I hear tunnel hull I think of the style of my boat from a dozen years back...

 

[mrdancer]

Re: tunnel hull

I'll try and post pic later.. have it in water right now.. from what I've read I'll have to trim out more the higher I go.. with offset of jack plate I should be able to run inch or so above tunnel .. running a 3 blade double cup 20* rake ss prop

What brand of prop? If it is a factory prop, a four-blade in the same style would probably give you a better bite.

 

[rampage11]

Re: tunnel hull

powertech.. sra3 i believe.. its brand new they may let me trade it for 4 blade.. the tech at powertech said the sra3 3 blade would work good

 

[rampage11]

Re: tunnel hull

one other question..keep being told tunnels r bad about blowing out in corners..what does that mean?

 

[rampage11]

Re: tunnel hull

anyone have anymore input or advice?

 

[rampage11]

Re: tunnel hull

think i need a SRA 4 from powertech

 

[Tthomp3]

Re: tunnel hull

When you hear about blowing out in corners it means that when you take a sharp turn the tunnel will not be directing water towards the prop and it will feel like its not grabbing. It will take a little getting used to but its not a concern. It just feels like you just went into neutral for a second and then it will bite. I have a buddy with a south fork tunnel. Its a fine boat, and it "blows out" in corners. Kind of a weird feeling at first but once you realize whats happening its no big deal.

 

[rampage11]

Re: tunnel hull

thanx..where r u from thomp? does your buddy like his boat?

 

[NSBCraig]

Re: tunnel hull

installing some transom shims upside down so you can trim down more seems to be the key to some friends tunnels, especially when your trying to get up in a little hole.

 

[mrdancer]

Re: tunnel hull

powertech.. sra3 i believe.. its brand new they may let me trade it for 4 blade.. the tech at powertech said the sra3 3 blade would work good

They should let you trade it if there are no dents/dings in the prop. PowerTech and Baumann's both make good three-blade props that will work with tunnels (much better than factory props), but their four-blades will bite and grab the aerated water a little better, IMHO. The three-blades are better for speed, but the four-blades grab better and give better holeshot. If you need more speed with the four-blade, ask Southfork about venting the tunnel (they are familiar with it).


Call the folks back at PowerTech, tell them what you're experiencing, and they should help resolve your problem.

 

[rampage11]

Re: tunnel hull

It's already vented.. I had to trim motor down to last hole. The tunnel has extra 2 inches stuck out from transom.. gailen at southfork said I could cut it out.. may do that because it seems to me its not letting water rise back up after tunnel for motor.. I've contacted nettles props about switching props ..he suppose to call me back