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Jack runs a Spear tunnel, right? Tohatsu 50? How is his set up?
Yes, Tohatsu 50, 3 blade prop and what looks like a huge Shaw-wing plate. And I'm sure he runs his own modified intake scoops on the motor.
 

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Shaw Wing made a big difference on @K3anderson 's non-tunnel Guide...especially in handling.
 

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Discussion Starter #103
Yes, Tohatsu 50, 3 blade prop and what looks like a huge Shaw-wing plate. And I'm sure he runs his own modified intake scoops on the motor.
I have his custom intake screens on my Tohatsu 50, if you scroll thru this thread earlier I installed them. My Heron has done great for a Non-Tunnel Skiff of course it will always be limited even with the upgrades I have made. But it changed night and day running a cav plate, and heavy cupped prop. The screens Jack makes allow for more water flow lowering your chance of overheating. I personally installed the Trans cavplate because I feel it offer's a better design as a half pipe, keeps water around the prop better.
 

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I'm not saying I won't use a cav plate on my build, but I will try it first without one.

Look at Sabine Skiffs. Brian Little is as "mad at shallow water" as anyone and I've never seen a cav plate on any of his skiffs, tunnel or not.
 

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While we are sharing cav plates. Here is a fiberglass one I just finished building but haven't installed. My "wing tips" may be a little long but I figured they could be trimmed after some testing.
CavPlate.jpg
 

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While we are sharing cav plates. Here is a fiberglass one I just finished building but haven't installed. My "wing tips" may be a little long but I figured they could be trimmed after some testing. View attachment 127418
I don't know how common it is, but they "say" that if you kick up shell with something like that, there's a chance that instead of throwing the shell clear, it bounces off the plate and back into the prop. Kind of like a disposal lol.
 

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Soooo.....What would I gain or lose on a small skiff by choosing tunnel or no tunnel if each of them takes advantage of all this magic?
 

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Discussion Starter #110
Soooo.....What would I gain or lose on a small skiff by choosing tunnel or no tunnel if each of them takes advantage of all this magic?
A tunnel skiff will always run skinnier, I have been on Eric Glass Chittum (Laguna Madre edition) and you get scared how skinny it can go almost seems like its a fan boat.
 

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All else equal on a small skiff I gain ? inches with a tunnel but give up ? speed? Approximate of course.
 

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I don’t think it would be “inches” and most are relatively slow anyhow. A huge consideration is whether the skiff is properly set up to take advantage of the tunnel. Most FL style skiffs are not...at least from the factory they aren’t.
 

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Hoping for some experts to tell me what I'm giving up with a properly set up small tunnel skiff vs no tunnel properly set up in terms of inches and or speed in terms of best guess numbers.
 

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Hoping for some experts to tell me what I'm giving up with a properly set up small tunnel skiff vs no tunnel properly set up in terms of inches and or speed in terms of best guess numbers.
Have had both. My first poling skiff was a 2007 Beavertail tiller, no tunnel but did have a fixed jack plate. That skiff would run in about 9” but took about 15” to get up. I ran that skiff for 9 years. My next skiff was a Spear Glades X tunnel tiller with a 30 etec and micro jacker jack plate. That skiff would run super skinny, 6 inches or less. But even with a good prop it had trouble spinning up on plane with the 30 horse. That skiff would have come alive with a 50.

It all depends on the skiff but I’d guess, in general, you’ll give up 1/2” to 3/4” of poling draft with a tunnel and up to 10% on top speed. My main reason for not going with another tunnel is the 90% rule. Buy a skiff that fits the areas you fish 90% of the time. For the areas I fish most often, I simply don’t need a tunnel. I found when I moved to the tunnel skiff I missed being able to trim the motor down and just go. With a tunnel and jack plate there’s always a degree of finessing and constant adjustments etc. Also , my BT would carve up a windy creek like nobody’s business. My tunnel skiff not so much. Also running in a chop , my tunnel would always cavitate some and if you lowered the motor enough to cut that out, the cavitation plate would throw water up on the back deck.
 

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There’s not really an exact rule of thumb for lost draft due to a tunnel. It’s different with each hull and tunnel design because it’s lost displacement. Somewhere, I remember seeing Morejohn post the volume of his tunnel design for the Whipray. It was just a few gallons.

Let’s call it 5 gallons for simplicity. If the volume of a tunnel is 5 gallons, then you’ll lose enough draft to displace that 5 gallons (.67 cubic feet). Across an average skiff hull, I would think that is easily less than 1/2” lost draft. You have to have a model of the hull or Chris Morejohn’s expertise to tell exactly what the tunnel translates to in displacement.

The other way to look at tunnel impacts to displacement is buoyancy. Sticking with our 5-gallon figure for tunnel volume, you would have about the same draft as a non-tunnel skiff if you can lighten your boat by 42 pounds (the weight of 5 gallons of water). Not accounting for distribution of weight and other factors. So a 800lb non-tunnel skiff will draft about the same as a 758lb tunnel skiff with a 5gal tunnel.
 

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For what it is worth, on my non tunnel Conchfish build I may go with no cav plate, a low water pickup and a custom prop. On a non tunnel I really don't think a plate is doing much when you are running with the jack plate up. It is probably out of the water and not directing anything towards your prop or intakes.
I would disagree with this. I have 3 buddies that put cav plates on their skiffs (EVOx -Shaw wing, Fury - Perma-trim, Fury- Simmons custom rigging plate) and all three said it greatly improved the overall handling and performance. All can run their motors jacked all the way up, all day no overheat issues. All of them said that they have to use very little trim tab as well. I'm putting a Perma-trim on my new EVOx for that very reason, along with a Foreman prop and Foreman intakes.

I do agree that you should run it first without to get a baseline performance. You will likely be able to raise the motor mounting after installing the cav plate if you decide to install one.
 

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I'm not saying I won't use a cav plate on my build, but I will try it first without one.

Look at Sabine Skiffs. Brian Little is as "mad at shallow water" as anyone and I've never seen a cav plate on any of his skiffs, tunnel or not.
I have run and fished on a Sabine Versatile with tunnel quite a bit. Definitely would improve the performance of the boat if it had a cav plate. The tabs don't push the bow down enough when it is choppy and for a flat bottom boat, you need to get the bow down smooth out the ride. Also, even with a super cupped shallow water angry 4 blade prop on it, it still blows out in tight turns at high jack settings. I get it, it is a flat bottom boat at high jack settings, so we slow down going into turns but that boat would get a huge benefit from a cav plate. They are really cool skiffs.
Besides, when Brian is really mad at shallow water, he's running a jet...
 

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There’s not really an exact rule of thumb for lost draft due to a tunnel. It’s different with each hull and tunnel design because it’s lost displacement. Somewhere, I remember seeing Morejohn post the volume of his tunnel design for the Whipray. It was just a few gallons.

Let’s call it 5 gallons for simplicity. If the volume of a tunnel is 5 gallons, then you’ll lose enough draft to displace that 5 gallons (.67 cubic feet). Across an average skiff hull, I would think that is easily less than 1/2” lost draft. You have to have a model of the hull or Chris Morejohn’s expertise to tell exactly what the tunnel translates to in displacement.

The other way to look at tunnel impacts to displacement is buoyancy. Sticking with our 5-gallon figure for tunnel volume, you would have about the same draft as a non-tunnel skiff if you can lighten your boat by 42 pounds (the weight of 5 gallons of water). Not accounting for distribution of weight and other factors. So a 800lb non-tunnel skiff will draft about the same as a 758lb tunnel skiff with a 5gal tunnel.

Seems like in one of Chris's tunnel drawings, he says they buoyancy loss is around 43 pounds, so I think your number is spot on.
 
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