Better performance - 18x42 or 18x48 tunnel hull?

[redfish150]

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

[j.e.hagen]

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

[Bad Boy]

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.

[scott craft]

Originally Posted by Bad Boy

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?

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.

[CajunChristian]

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.
D

[CajunChristian]

Originally Posted by redfish150

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

Exactly how much would you pay to see one?
D

[Bad Boy]

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.

[CajunChristian]

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,

[Bad Boy]

Help me out what would be better?

[CajunChristian]

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.
D

[redfish150]

Originally Posted by CajunChristian

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.
D

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

[Ray]

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.

[Bad Boy]

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?

[dp*]

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

[toodeep]

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

[Bad Boy]

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

[Bad Boy]

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.

[toodeep]

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.

[Bad Boy]

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.

[Bad Boy]

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?