Tunnel Hulls?

[fishndirk]

Anyone with experience with tunnel hulls? I know the concept is to raise the prop higher up in the water, thus allowing a shallower draft and better back woods running. Does anyone have experience weather this takes away from top end performance or performance in high speed turns? What are the pro's and cons?

 

[pootnic]

Re: Tunnel Hulls?

Are you talking a true tunnel hull(bow to stern)or the little jet/prop tunnels you see on alot of jon boats?
A true tunnel would give you better preformance,theres nothing to disturb the water from the prop.
On them smaller tunnels,you will lose some top end(3-5mph) and if not set up right it will cavitate in turns but that can be said with regular hulls as well.
From what I've read it has something to do with the disturbed water flow to the prop.Some people say it (tunnel) sucks the boat down,it can be helped a bit by venting.

 

[mr 88]

Re: Tunnel Hulls?

You will have to be more specfic as to tunnel hull.The ventilation plate on any hull should be about flush with hulls bottom so whatever concept your talking about is incorrect in most applications,[ racing is a whole new ballgame.] If your talking about a Catamaran,they are very stable due to there beam and hull design.They turn extremely well and are a faster hull due to less wetted surface.They are a little more fuel efficient and do draw less water The cons are they do not cut the water as well as a deep v in heavy seas.Unless there is a "step pad" in the middle you probably should run two engines if outboard driven.Check Mfgs' recommendations on that specfic issue.The water feeding the single engine on a Cat can be a little sketchy with out the hull flattening out/compressing the water before it hits the drive.What is the make and model boat you are talking about?

 

[metriccrescentwrench]

Re: Tunnel Hulls?

The only "tunnel hulls" I'm familiar with are meant to go fast, the aerodynamic design of the boat lifts the entire hull until there is very little boat still making contact with the water, resulting in reduced drag and higher speeds. And it takes a good bit of speed before these hulls really start to work. I'm suspecting you're talking about something else entirely though, so I'm hoping to learn something from this thread.

.The ventilation plate on any hull should be about flush with hulls bottom so whatever concept your talking about is incorrect in most applications

That's definitely not true for all boats. My Checkmate runs very nicely with the centerline of the prop only 2.5" below the hull, that puts the AV plate well above the bottom of the hull (NOTE - don't try this without a water pressure gauge !!!)

 

[cr2k]

Re: Tunnel Hulls?

When you run your prop at that setting you will need to get a lower unit that has a water pick up in the bullet or make some other arrangements for sea water pick up.

 

[fishndirk]

Re: Tunnel Hulls?

Yeah the one im refering to in specific is the G3 mod v tunnel hull boats. Or any type like that. The hull has extended step plates off the back with a cut out in the middle back of the boat. Seems to me like the step extensions would add to plaining but the short tunnel cutout would decrease performance while manuvering. Just cureous if anyone has had experience with these...

 

[Bamaman1]

Re: Tunnel Hulls?

I have tunnel hull pleasure boat experience dating back to 1970. Most real tunnels you currently see are not pleasure boats--they're fly weight racing boats. I had a # of friends running 18' Flying Dutchmen boats with the largest Merc's of the day--125 & 135 hp straight 6's. One of my buddies had a tunnel hull with two Merc factory blueprint motors.

In those days, the fastest boats were Allison Craft 17's, which were running the low 70's. This was prior to the Merc Black Max motors.

The pros are floating on a blanket of air with maybe 1' of the boat in the water. When you trim the motor down and go into a turn, you feel like you're going to be slung over the side--high g's. You might be running side by side with a V bottom boat and go out into the big lake full of white caps. You'll actually increase speed maybe 5 mph in big waves--leaving the V bottom boats being pounded by the waves while you don't even feel the waves. Fuel mileage is absolutely incredible with such efficiency.

The cons are that 18' tunnel hulls must be relatively light--maybe 800-1200 pounds for a pleasure boat. They're also not good with heavy passenger loads. If you put a modern direct injected 2 stroke 250 hp motor on one, you'd be looking at 100+ mph with the right prop. At those speeds, a good gust of wind would cause you to go airborne. There again, any boat running over 75 mph can instantaneously go past the point of no control.

I can tell you I'd like to have an outboard tunnel hull with a 150 hp motor. As long as you didn't go too fast on a gusty day, they'd give you a thrill like you've never experienced.

 

[fishndirk]

Re: Tunnel Hulls?

Thanks, but im just thinking...I do a lot of fishing, my main thing (river and backwater) but I also duck hunt. I want a boat that can handle 4 to 5 people and harldy loose any pefrormance. Not really into racing, I just dont want the boat to cavitate the hell out of itsefll when im comming around a turn all fast.

 

[Bamaman1]

Re: Tunnel Hulls?

Tunnel hulls don't cavitatea when you go into a corner, as you've got the power trim and hopefully a hydraulic jack plate to tailor the motor height.

If you're wanting to duck hunt, you need an aluminum jon boat with the widest transom you can find. Fiberglass boats are not for backwater use, as they scratch easily. Sounds as if you need two boats if you want to carry 4-5 people.

 

[mr 88]

Re: Tunnel Hulls?

"incorrect in MOST applications"'Racing is a whole new ballgame" Which is why I wrote that down because somone was going to have a different answer for a very specific application. Where is the waterpickup on your motor vs the standard recreational boaters? You even say" don't try this without a water pressure gauge" Not quite what the average boater worrys about.Yes you could throw a jackplate on it with a low water pickup and have the prop catching air,again not what the OP is looking for,he wants it for fishing,unlike your setup.I do own a few boats,6, and among them is a 1966 Power Cat 15T [three sponsons] and a 1962 Custom Craft Manta Ray with a 5 pt bottom,not oblivious to the go fast crowd.

That's definitely not true for all boats. My Checkmate runs very nicely with the centerline of the prop only 2.5" below the hull, that puts the AV plate well above the bottom of the hull (NOTE - don't try this without a water pressure gauge !!!)[/QUOTE]

 

[metriccrescentwrench]

Re: Tunnel Hulls?

Yeah the one im refering to in specific is the G3 mod v tunnel hull boats.

OK, I looked at the G3 website. It's basically a big jon boat with a "tunnel" built into the hull. Their "tunnel" looks like it's maybe 8 inches wide and 6 inches deep, and they've added flotation pods on the rear. That's a totally different concept than what has traditionally been called a tunnel hull.

When you run your prop at that setting you will need to get a lower unit that has a water pick up in the bullet or make some other arrangements for sea water pick up.

Actually my engine and lower unit is totally stock and I've got over 20 psi of water pressure at speed. Other guys who go even higher do run low-water pickups though.

 

[pootnic]

Re: Tunnel Hulls?

Most posts here aren't talking about the boat your looking at.
In a jon boat like that,there are 2 types of small tunnels;1 for props and 1 for jets.
The prop one will be alittle deeper(approx 8") then the jet one(approx 3").
Your going to lose some top end,3-5 mph,like said earlier won't cavitate any more then a regular jon if set up right.
The votes still out on a jack plate,some like it,others raise there transom to fit the bill.If it's factory won't have to worry about modding.
If your looking at 1 with those pods as well,I can see them creating drag when running,probably hurting top end as well but will give you added floatation/bouyancy,especially if your looking to carry 5 people.The stern wouldn't squat as much when taking off,with those pods....that would be a big jon,big motor with all the gear that goes into duck hunting.
I'm thinking a reg. jon should carry more weight then a tunnel,just because theres more boat on the water.

I run a C1652V,mod V;jet tunnel.It's rated for 5 people(685lbs) 1100 total lbs but you would want bigger if duck hunting with 4/5 people.I run a prop on the jet tunnel now,allows me to raise the prop abit higher.I can still hit the prop though,with a prop tunnel it would be better.

 

[sschefer]

Re: Tunnel Hulls?

pootnic you've got it. There are a couple of midwest companies that make vented tunnel style boats. Most are in a traditional flats boat configuration. It's a tricky hull combination to get right but can be great boats.

 

[fishndirk]

Re: Tunnel Hulls?

Thanks to all for the posts. Thanks to pootnic, thats pretty much the info i was looking for. If I do go with that type of hull I will definately leave it as the stock set up since I dont have any experience with that type of hull.

 

[mommicked]

Re: Tunnel Hulls?

If you plan on heavy loads most of the time and speed also.I would think a hydro jack plate would help w that.You can put the engine lower in deep water and get on plane faster than w it in the tunnel pocket w a load.You can also raise it for the shallows but you'll still have some of the skeg below the boat so you need to be carefull.You could get a jet drive outboard or lower unit that would be higher than the hull but I hear they dont like heavy loads and will be slower w same hp as a prop,also steering is slower than a prop.But im no expert.I would suggest a 4 blade prop if you go w the prop tunnel.I have a 1860G3 w/o tunnel and the 4 blade made a huge difference in performance on my boat.All of this info Ive read or heard,except for my exp. w the 4 blade.

 

[fishndirk]

Re: Tunnel Hulls?

Yeah the 18CC is the one im looking at. Ill look into hydro jack plates. Ive seen them on bass boats and they look awesome, just not sure if all that would be worth it on a boat like what were talking about though.

 

[mommicked]

Re: Tunnel Hulls?

Definately get the lightest, highest hp outboard.Mine has a F90 and its fast but squats alot getting on plane quickly.Id like to add the sponsons to mine,they make great steps to get aboard also!I think the CC is a great shallow water boat.You can stand up and get a better view of the shallows ahead than when seated.I had to settle for a SC.

 

[captsteve25]

Re: Tunnel Hulls?

Dirk, I have the G3, 1860 with tunnel, pods, jackplate, four blade prop and nose cone. Very nice boat for backcountry fishing. This is a pretty heavy, rugged boat-not real fast but sweet for fishing.
Don't expect to run offshore unless you have a good dental plan.