# Question about jets and tunnels



## Ring King

Figured I'd get more experience here than in the boats and blinds category. I'm looking to buy a new boat for up here. I've found several that I like. Some of them are jet outboards on flat bottom boats and some are jet outboards on tunnel hulls. My question is how bad are the tunnel hull boats with jet outboards when running in chop. I know they'll blow out and cavitate in rough water, but how rough is rough? Is it manageable by going slower in the rough water to keep the bow up and transom down? I want a boat that will run shallow, but I may have to get across some choppy water to get there. How much shallow water navigation is given up by going with a flat bottom with jet over a tunnel hull with jet?

I was originally looking at a mudmotor for my needs, but I've been talking to a lot of the locals here in Cordova and they say that the jet is the way to go.


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## Jake Windemere

I have a 1648 riveted jon with a flat bottom and a 40 hp Evinrude jet (28 hp at the jet).

It works perfectly. The foot will bump the bottom at times but that seems to be of no consequence in sand or silt. Once the boat gets that shallow the difference between a tunnel and no tunnel is not much.

Even in choppy water I never notice any cavitating. I can't speak for what a tunnel would do.

The advantage I can see with a tunnel is that you'd probably never hit the foot. on the bottom. The disadvantage is that you may sit a little deeper in the water at rest.


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## Waterproof

Tunnel with an outboard.
No Tunnel with a jet.

The whole reason for a tunnel is so that you can run regular outboard set a little higher then usual and get a water stream across the prop at speed to shoot through shallow areas. With a jet you want smooth stream of water flow across the pickup foot to avoid cavitation and power loss. The more chop in the water and the worse a tunnel is with a jet.


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## Jake Windemere

Rip and Ann Bliss, who run a remote lodge on Alexander Creek (Pirenna Lodge) both changed from flat bottom jons to tunnel jons.

They report that they really like the tunnels. If I understand correctly it is because they suck less sand with the foot up higher.


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## ak_powder_monkey

A flat bottom will actually draw less water on step than a tunnel hull, a flat bottom will be lighter thus requiring less power to go faster and allowing for better handling, A flat bottom will draw less off step as well but your jet foot will hang down pretty far.

the only advantage to a tunnel hull that you won't hit your jet foot if/when you screw up so you might suck a few less rocks, and that you don't have to worry about grounding your jet when you come into shallow beaches. 

All and all a 18 foot flat bottom with a 40hp jet and a tiller will let you run stuff you'd never think you can run in a boat, I will say its good its never my motor on the boats I drive  

Oh and if you plan on using your jet for duck hunting realize that jets and water vegitation don't mix... don't ask how I know..


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## Ring King

Vegetation isn't a problem where I'm at. We have none!!

I've run tunnel hulls with regular outboards and they work great as long as the tunnel is vented. They'll run pretty much the same territory as a mud motor minus the most extreme no water situations. You'd probably be amazed at where some of the Louisiana boys will go with an outboard on a tunnel. I know I was shocked when I saw it and I was running a surface drive mud motor!

Tunnels and jets must be a fairly good combination as I see tons of them around Alaska. I wouldn't think a flat bottom with jet would run any higher in the water than a tunnel hull. I may be wrong though. I do understand that they will sit deeper in the water at rest due to the lack of floation area in the rear caused by the tunnel itself.

I'm going to be using this rig to run the rivers around Cordova and I'd like to be able to use it on the bay here to hunt the mud flats. What I'm worrying about is getting home if I leave on a calm day and then the weather turns sour. What size chop does it take to render the boat useless with a tunnel and jet outboard. Are we talking 1ft or are we talking 3-5ft. I wouldn't want to be out in open water with a flat bottom (tunnel or not) in much over 1.5ft waves anyway. You'll beat yourself silly at anything over an idle regardless of what kinda power you're using!!


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## Waterproof

The answer to that question would be proportional to your speed and how much porpoising your rig was doing going over the chop and rollers.

There truly is no purpose to run a jet with a tunnel as it isn't going to gain you anything anyway. If the jet is setup correctly your pick up foot is going to be level with or up to 1/2" below hull line on the back and at most you would gain a couple of inches of clearance by having a tunnel and raising the pick up foot a little more. The drawback to that is you now have more chances for cavitation due to all the turbulence created when the water is forced into the tunnel and out.

The only reason you would have less sand pulled into the jet with a tunnel is if you ran cleaner water. The water gets stirred and silted just as much with a tunnel as without when it comes to the sand and sediment factor.


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## semperfi

Ring King said:



> Vegetation isn't a problem where I'm at. We have none!!
> 
> I've run tunnel hulls with regular outboards and they work great as long as the tunnel is vented. They'll run pretty much the same territory as a mud motor minus the most extreme no water situations. You'd probably be amazed at where some of the Louisiana boys will go with an outboard on a tunnel. I know I was shocked when I saw it and I was running a surface drive mud motor!
> 
> Tunnels and jets must be a fairly good combination as I see tons of them around Alaska. I wouldn't think a flat bottom with jet would run any higher in the water than a tunnel hull. I may be wrong though. I do understand that they will sit deeper in the water at rest due to the lack of floation area in the rear caused by the tunnel itself.
> 
> I'm going to be using this rig to run the rivers around Cordova and I'd like to be able to use it on the bay here to hunt the mud flats. What I'm worrying about is getting home if I leave on a calm day and then the weather turns sour. What size chop does it take to render the boat useless with a tunnel and jet outboard. Are we talking 1ft or are we talking 3-5ft. I wouldn't want to be out in open water with a flat bottom (tunnel or not) in much over 1.5ft waves anyway. You'll beat yourself silly at anything over an idle regardless of what kinda power you're using!!




What does "vented" mean on a tunnel?


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## Waterproof

Vented on a tunnel is a line that runs from the front part of the tunnel to the back of the boat. It's purpose is to prevent a vacuum from happening in the tunnel and creating more drag.


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## skydonkey

If you had a tunnel with a jack plate intalled could you lower it down in rough water and get any better perfomance out of the jet?

SKYDONKEY


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## Jake Windemere

Speculation here but I think that lowering the jet would only cause problems with drag and water spraying off of the foot.


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## Waterproof

skydonkey said:


> If you had a tunnel with a jack plate intalled could you lower it down in rough water and get any better perfomance out of the jet?
> 
> SKYDONKEY





No you couldn't. The way jets work is that they are designed for minimal drag in the water with their pick-up shoe and the more you stick down in the water the more drag you create to the detriment of the jet. 

Optimal placement for a pick-up shoe on a jet is even to 1/2" below the hull line of your boat.


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## Ring King

Alright, so I've decided against the tunnel hull. I'm going to try and talk the guy down a little on his asking price for the 1752 Crestliner center console jon boat. It's a 1996 boat and trailer with a 2003 60hp 4 stroke Mercury jet on it.

Is there anything crazy that I need to look for when evaluating the jet before buying it. I'm quite familiar with outboards, but this will be my first one with a jet foot. I know to check the intake grates for damage and make sure the reverse will engage without hanging up due to bent parts, but is there anything else to look for. It's got a new impellor and liner in it. I don't think the impellor is stainless though. That may be an upgrade I need to make.


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## Waterproof

I would at the very least take the 8 nuts off the impeller housing and check out the impeller and liner sleeve. I would look for scoring on the liner which would indicate how much sand the jet has been run through. Also check the spacer washers on the impeller shaft. You should see a stack of washers on the shaft that sit above and below the impeller. Those are the shims that move your impeller up and down in regards to spacing of it with the liner. If the majority of the shims (washers) are above the impeller you are going to be needing a new liner sleeve in the immediate future. If they are below then your liner is fairly new still and has a lot of adjusment/erosion left. Also see how much play the impeller has on the shaft with regards to spin and the brass catch key.

As far as prop goes yes I would invest the money in a Stainless prop and with a 60HP it would be your call as to whether you get a 4 blade versus a 3 blade. I personally run and like the 4 blades but I also have a 115hp motor. The 4 blades will get you a much better hole shot and up on plane faster. If you go any smaller then a 60hp though you won't see a noticable difference in performance and of course the 4 blade costs more.


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## 1CRAZY1

Matt, clean out box!


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