Better performance - 18x42 or 18x48 tunnel hull?
 

What would perform better, 1842 or 1848 tunnel hull? I'm running a Mercury 40 3 cylinder?
Anyone have any experience with a 1848?

I have a Nissan 40TLDI on an 17x44 and like it, it gets up shallow and runs well (30ish loaded).....

1842 will run better due to the lighter weight....1848 weighs a good bit more. My podna runs a 1842 southfork tunnel with a 60 merc 2 stroke,thing is awesome in the the mud.

Wider boat will probably run better

Wider will carry a load better. If u ever plan to switch to a surface drive I would not get a tunnel hull.

wider also has more drag in the water

Longer and skinner will be faster with a light load. The wider boat will be slower but can carry more weight with less draft.

What are you going to use the boat for? Do you carry light or heavy loads?

Heavy loads, wider boat.

Is stability a concern? If so, wider boat.

The tunnel hull is nice when on plane, but it was squat more on take-off and draft more at rest.

Boat will always run loaded. 2 batteries, lots of gas, fat boys, dogs, hunting and fishing gear and used to haul alligators too. Like the idea of better stability with wider but don't want to lose a lot of speed or hole shot?

Incorrect. The wider the boat is the higher it will sit out the water which means less drag.


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I have 18x42 weld built tunnel with a 3 cylinder 2 stroke mariner on it that runs 36 with just me and a gas tank or with me and mcnabbs chunky *** his dog and our huntin gear it runs 36 no matter what with a 15 pitch slightly cupped 3 blade prop and a vented tunnel

I agree

I run a 2000 1842 tunnel with stock Merc 3cyl 60HP & 4 blade prop. I run 32.5 loaded down with 10 year old, Brownings, 2 dogs, a limit of ducks, and my big boned hunting partner. I don't know if his weight or wind resistance causes me more loss of performance. :confused: I have had 28 alligators and my BBHP and still got up on plane but had to run the bilge pump the entire way back.
All I know is the longer you go past 40 years of age, stability of the boat becomes more of a concern.
I could probably cut back on CFM sandwiches, that may help a bit also.

You can always have the tunnel closed in later if you decide to go surface drive.

1844 with a manual jackplate.

For what you want the boat for, if it was me, I would go with the 48. It should carry more easier

If it was me and I had the money I'd go with the 48 also it's gonna be quite a bit more but a much more stable and handling boat I wouldn't worry with speed so much if your gettin a tunnel ur not gonna be racing so speed is a lagniappe

I have a 18' x 42" Southfork Tunnel with a 2 Stroke 60 Merc and a 15 pitch 4 Blade Power Tech on it. I am still in the process of getting the bugs worked out of it but I can only get 31 mph out of it. I need to get my power trim working and it feels like the 15 pitch is to much for it. My question is how are these guys with the same hull and less HP running 40 & 43 mph? I would like to see at least 40 mph am I asking to much are these tunnels that slow?

I think it's your prop but I bet if you PM cajunchistian he can talk you through it I have a 13 pitch 4 blade that pushes mine 36 by myself but if I put any load on it dies

Has alot to do with the motor height as well....if your motor is too low it will cause alot of drag.

I'd like to see a 18' tunnel running 43 mph with a 40 merc. No way!!!
35 mph loaded would be great.

hey bad boy if you want to run 43 mph loaded up ill trade you your 1842 tunel for my 1548 semi vee

Tunnels aren't made to be fast if you set everything up right, if you wanna go faster buy a bigger motor

Not interested in trading I am pleased with the way it gets up and runs in the shallow. But the whole reason I bought this thing is to be much faster than my Prodrive at this point I'm not doing much better. I'm going to keep playing with setup and prop but if that don't do it I guess I will have to put a 90 HP on it. :work:

CajunChristian could help you with your prop and setup. You should probably get more out of it than what you're getting. I would take with a grain of salt anyone saying they are running 40-43 on a tunnel with a stock 40.

First thing you need is a tach, can't tell anything without one. If you don't know how many rpm's you are turning, how can you make any adjustments???
I can assure you, a 15 is waaaay to much prop on a tunnel boat for that motor. Once you add enough cup to that 15 to stop cavitation, the average pitch goes to about 17 or 18 pitch, a 60 can't turn that much pitch. My guess is you are turning right around 5000 rpm, if that. That motor makes the most torque at 6000 rpm. Torque moves the load, not horsepower.
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Exactly how much would you pay to see one?
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I have the 4 blade Power Tech with the Heavy Cup and it does not cavitate at all. I am going to have it turned down to a 13 p and I agree without a tach it is hard to say but it sounds like its turning about 4500 or so. Yes you are right the motor is lugging and never making it into the Powerband.

You can't turn that 15 down enough without losing more speed. You would be better off buying the correct pitch. I am no very impressed with PowerTech's SCB4, they make better props for your application,

Help me out what would be better?

One of the best running tunnel boat props I have seen lately is the Yamaha Semi cleaver with cup added, BUT, you need to know how many rpm you are turning that 15 before you spend $300 on a SWAG. PowerTech's SCB props are poor imitations of the Yammie props.
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you find that this semi cleaver works good on a tunnel boat loaded up or empty or both? i have ran a 4 blade on a tunnel and it seemed to work better when the boat was loaded. Thanks

When I hunted ducks and gators, I had a 20 X 36 tunnel hull with a 40 Merc.
It ran good, got on plane good, but my friends dad had an 18 X 42 with the same engine that was just a little faster. We figured it was the extra width that gave him the extra speed.
I got on plane just as good, he just had a higher top end speed.
We both ran Welcrafts bought from the same dealer who put in the same tunnels and the same engine with the same prop.
Only difference was the width and length.

Hey Cajun I am assuming that the Yamaha Semicleaver that you are referring to is a 3 blade correct? Also what pitch would you recommend?

The BadBoy from Charenton... Whats up Seth, how ya been man? Give me a call at the shop and I'll help ya get that thing running right. 337-583-4088

i have the 18 42 with a 40 merc and running around 30 turning a 15 with slight cup turning just over 5100 rpm i have redone the southfork tunnel a little bit changed out the cover plate made a larger air hole in the vent tube. for how my boat is set up i think it truns fine./
Joe

That's me Darrel haven't talked in a while. I will give you a call when get a chance.

TooDeep tell me more about you Tunnel Modification. Post pics if you have some I have a feeling that my vent is not big enough.

i flipped boat over and cut the vent opening longer to let the water out faster on take off. then added the plate to cover the hole back. i am sitting on the transom and i can not trim more than half way and i will not pump.

Making some headway. I cut the Pods off the back like Darrel told me to. I got the motor running right again and it ran 37 mph with me and my son and a full tank of gas. With a little more prop work and setup I might be able to get 40 mph out of it.

Welded some Trim Tabs on the back to stop the Porpoising and got almost 39 mph out of it today. Does anyone else have trouble with the Southfork Tunnels Porpoising?

what all did you do to get that speed out of it.

I called Darrel at Jerry's Marine and he led me in the right direction. First thing I did was cut the Floatation Pods off the back, lowered the motor to where the Cavitation Plate is 1" above the Tunnel. Bought a 13 P Semicleaver Yamaha Prop and welded some Aluminum Trim Tabs on back to stop the Porpoising. I think I can get a little more out of it with somemore setup and Prop work.

are you running a stock 40?

I just bought a 18/44. Ran it yesterday and got 36.8. But that's with my cousin sitting on the bow to keep from porpoising. 14p Yamaha prop but I am going to need a little cup as it was blowing out with little trim.

U gonna have to beat dem trim tabs down a tad too

Did that after u left this eve

Now you're talking to the "Charlie Daniels of the torque wrench" when it comes to Mercury outboards. Darrell has forgotten more than any 5 of us will ever know about Mercury outboards, and more specifically about how to make then fly. Darrell belongs to a unique club, the 80+mph tiller club. Listen to what he tells you and do it! He's my brother by another mother:D
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