Tunnel Hulll ?

[wyodeputy]

Can anyone here elaborate on the benefits of a tunnel hull for a Outboard Jet. I've started a mod (16x48 w/ 35 HP jet). The hull is beat up pretty bad and I'm really having to work on it removing and covering dents. So this would be a good point to stop and fabricate a tunnel but I've never run a jet with a tunnel hull so can anybody mention the pros / cons? Don't wanna waste the time, effort and materials in fabrication if the difference is negligible. Thanks in advance !

 

[crazymanme2]

It gives your jet cleaner water.With a tunnel the water doesn't get pushed down in that area & the motor can be run higher on the transom.That is the differences that I noticed when I made a tunnel out of mine.

 

[semojetman]

I am also interested in making mine into a tunnel hull.

Would like to hear some before and after stories

 

[optaylor823]

I would say that if it does not cost to much money to add the tunnel then do it. It may save your jet foot one day. With the jet foot sitting higher than the bottom of the boat it helps to protect the foot and we all know a jet foot is not cheap. I run a tunnel on my boat and I think I can ran a little shallower then some of the boat that I had before with out a tunnel. The boats were not the same brand.

 

[JMR]

Sometimes, the difference between skimming cleanly over ledges and rock, or smashing the intake into a underwater wall of stone ...is inches.
A tunnel gives you about 3 extra inches of clearance....which I have really wished I had before.

 

[semojetman]

I really like the tunnel idea, unfortuantely my boat is a flat bottom, and outboard jets do not recomend a tunnel on a flat bottom. I'm still looking into to it though.

 

[Lil' Blue Rude]

Tunnel hull + jet= cavitation! A jet intake can only be raised so much before it will begin to suck air. It's not the same thing as a prop. Even if the jet doesn't cavitate it will be hurting the performance of your boat because the nozzle off the jet will be 3 inches higher so it won't be pushing against as much water. it will be shooting alot more of the jet of water into the air. It will be the same as over triming your motor on a boat that won't bounce, once the jet gets trimmed so high you start losing speed because you don't have the opposing force from the water to push off of. . If there was something to a tunnel hull and outboard jets I think Blazer jet boat company would have had a tunnel hull model in production by now. That's just my 2 cents from years of outboard jet experience.

 

[crazymanme2]

A tunnel hull will let you run your motor a little higher than a normal flat bottom boat.The boat pushes the water down,that's why you have a wake.With a tunnel hull there is no bottom in the center to push the water down which lets you run your motor higher & in clean water.That's why some boat manufactures have a partial tunnel on the back of their boat.
A tunnel hull raises the jet foot above the bottom of the boat, protecting it from damage.

Here's a link to a tunnel boat:

https://www.akmining.com/boat/lor1655.htm

 

[reedjj]

Tunnel hull + jet= cavitation! A jet intake can only be raised so much before it will begin to suck air. It's not the same thing as a prop. Even if the jet doesn't cavitate it will be hurting the performance of your boat because the nozzle off the jet will be 3 inches higher so it won't be pushing against as much water. it will be shooting alot more of the jet of water into the air. It will be the same as over triming your motor on a boat that won't bounce, once the jet gets trimmed so high you start losing speed because you don't have the opposing force from the water to push off of. . If there was something to a tunnel hull and outboard jets I think Blazer jet boat company would have had a tunnel hull model in production by now. That's just my 2 cents from years of outboard jet experience.

So your saying that a jet motor and a tunnell hull don't mix? I thought that was the whole pt behind a tunnell hull. A lot of the manufacturers offer models in a Jet Tunnel... Lowe, G3, SeaArk, on and on.

Do you reccommend a regular flat bottom over a tunnell hull for a Jet outboard Application? I know lots of guys do it but I thought the tunnell with a jet was the best way to go for shallow running.

 

[Lil' Blue Rude]

When I said that none of the leading manufactures don't make a tunnel hull model I was talking about companies like Blazer, Legend, LegendCraft, Alweld, Weldbuilt. Here in SE Mo. Outboard jets are mostly what people are running and these are the main companies that tailor build boat for the outboard jet enthuisist. I've never considered Lowe, G3, SeaArk a leading manufacture for outboardjets because for ever jet you will see two with props. 99% of the boat that are made by the manufcturers I listed have jets on them.

If your raising the motor up 3 inches out of the water that would just mean that your are puttin 3 inches of your boat that wasn't tunnelled into the water so you boat hits instead of you motor. " A jet tunnel doesn’t work well with a flat bottom boat due to air ingestion." That is staight from the outboardjets site. It might work on a semi v brecause the jet foot would have to sit lower in the water then it would on a flat bottom boat.

When I said leading manufatcure I should have also said that they are leaders in flat bottoms. If you want to run shallow get a light set up and make sure you've got the power to push it. The black lines in the pic show where a semi v bottom would be and the red line shows where the foot would need to be. If you have a flat bottom and you want to mod the bottom you can flatten out the center rib from the back to around 12" forward. Most manufactures have started to do this anyway. I do recomend a flat bottom over a tunnel hull for a jet. If you don't load your boat down way to much and keep it in atleast 3 inches of water you'll be ok for running skinny. They can run shallower but your probably gonna bump.

 

[JMR]

Based on where I've seen different hull types around the country, it seems that most of the non-tunnel jet outboard hulls (like Blazer Boats, which is located in Missouri) are in areas like Missouri and the mid-west where the shallow rivers don't have very much rock to deal with...and non-tunnel hulls run just fine.
And in areas like Virginia and Penn, the shallow rivers have a lot rock to deal with, and that's where the tunnel hulls (like James River Jets in VA, and RockProof Boats in PA) start showing up, because they are an advantage in those conditions.

You can get a Blazer hull that's as thin as .080, because it works just fine if rocks and ledges are not involved, and the lighter weight is more a performance advantage than the durability of a heavier hull gauge.
Going the other direction, you can get a hull from James River Jets with a .190 bottom, and if rocks are still a problem, have that bottom covered with UHMW.

Just my opinion, ...I'm guessing mostly.

 

[georgiaken]

Up here in PA, it's a mixed bag and a matter of preference/budget. When buying used, you often have to compromise to what is available on the market and at what price.

Lots of guys run tunnels, but they also complain about cavitation.

The guys with tunnels and UHMW can usually get into slightly skinnier water than the guys with just a tunnel (no UHMW) or no tunnel at all.

By slightly, I mean an inch to three or so inches skinnier for the guys with tunnels. The UHMW gives you some confidence running areas that people without UHMW would avoid...it's slippery enough to slide over some areas when running fast, but it does add weight.

I am by no means an expert, but I have not seen the same enthusiasm up here for racing jets etc. It's more a means to get to fish than anything.

In the end, it's a matter of choice I suppose, but in PA, people seem to really go for the tunnel boats.

You'll see tunnels on many, if not most of the custom boats up here...you'll also see side fins, splash guards and sometimes jack plates as well.

Our rivers can be treacherous...

 

[Lil' Blue Rude]

Based on where I've seen different hull types around the country, it seems that most of the non-tunnel jet outboard hulls (like Blazer Boats, which is located in Missouri) are in areas like Missouri and the mid-west where the shallow rivers don't have very much rock to deal with...and non-tunnel hulls run just fine.
And in areas like Virginia and Penn, the shallow rivers have a lot rock to deal with, and that's where the tunnel hulls (like James River Jets in VA, and RockProof Boats in PA) start showing up, because they are an advantage in those conditions.

You can get a Blazer hull that's as thin as .080, because it works just fine if rocks and ledges are not involved, and the lighter weight is more a performance advantage than the durability of a heavier hull gauge.
Going the other direction, you can get a hull from James River Jets with a .190 bottom, and if rocks are still a problem, have that bottom covered with UHMW.

Just my opinion, ...I'm guessing mostly.

:mrgreen: I don't know what part of Missouri you where in but we got plenty of rocks and gravel. :mrgreen: You just have to watch what your doin and be quick enoughto get out of trouble.(or have good insurance) My biggest thing is if there was something to a flat bottomm tunnel, Blazer would be making or have made something considering they where dezined around outboard jets.

 

[semojetman]

I have checked with Outboard Jets Co. and they agree with the fact that tunnels are not good on flat bottoms. I see the advantage and the disadvantage on a semi-V.

From what I've seen, read, and heard, I believe for me, i'm just gonna run my flat bottom and be happy.

I've ran a flat bottom 1752 thru 3 inches, so I dont have any business in anything skinnier than that anyways

 

[Scottinva]

On the East Coast, where we are not just dealing with gravel and rocks, but razor sharp ledges, pretty much all of the custom builders put tunnels on their boats - Snyder, JRJ, Rockproof, etc. If they are properly setup, they are a non issue for cavitation. Most are also going from building flat bottom boats to a slight semi V. I have a custom Snyder with a tunnel and 6" hydraulic jackplate - a big no no. I have cavitated 4 times in 3 years (over 40 trips a year) and every time was running through 1-2 footers. I am very happy with my setup and wouldn't trade it for anything.

Scott

 

[Lil' Blue Rude]

1-2 footers?? We don't have ledges but we to have some bad showels with rocks as big around as a 55 gallon drum. They'll split a boat wide open.

 

[Scottinva]

I think the big difference is our boats are built to run into big boulders and take the impact. They are not speed demons by any stretch of the imagination - mid to upper 30s max! and any loss in speed due to the tunnel is not an issue. Our boats have 3/16 to 1/4 in bottoms with 3/8 to 3/4 UHMW screwed to the bottom of that. I have hit boulders running 30 mph so hard that the we went completely airborn. The only damage to the boat was a small gouge in the UHMW. Just a different type of boat for a different area. Out here we run tunnels. There may be a loss of speed, but I would rather have the protection the tunnel provides. Just something different. I love the big boats with the 250 outboard jets, but they really aren't that practical around here unless it is built like aa absolute tank.

Scott

 

[reedjj]

Its very interesting... All the different points of view from members from different parts of the country.

I was gonna do a jet on my boat but all the Fl guys I talked to said DO NOT do it. Apparently here in Fl the impellers suck up so much sand that they wear aout so fast the benefit of a Jet outboard does not outweigh the cost. I was told if I wanna run really shallow swampy land to get a mud motor.

 

[Lil' Blue Rude]

Is it really that bad of a river that you can't dodge the rocks? Please don't think I'm meaning that as a smart blank comment I'm just curious why you guys need such beefy boats. We don't run big 250hp motors where I run. I personaly own a 40/28 Evinrude and love it. I run the Current River here in SE Mo and there are alot of places that are 3 inches deep and around 30 feet wide. What are boats lack in durabilty the more then make up for in speed and manuverability. I can go from about 40mph down river to a dead stop pointing back up river with the crack of the throttle.(Scare the crap out of you too :shock: ) Did once, don't want to do it again unless I have to.

 

[Seth]

Is it really that bad of a river that you can't dodge the rocks? Please don't think I'm meaning that as a smart blank comment I'm just curious why you guys need such beefy boats. We don't run big 250hp motors where I run. I personaly own a 40/28 Evinrude and love it. I run the Current River here in SE Mo and there are alot of places that are 3 inches deep and around 30 feet wide. What are boats lack in durabilty the more then make up for in speed and manuverability. I can go from about 40mph down river to a dead stop pointing back up river with the crack of the throttle.(Scare the crap out of you too :shock: ) Did once, don't want to do it again unless I have to.

180's in a flat bottom are fun. It's good for scaring and soaking your passengers too. :lol: