mosh

I was just wondering what people thought about putting trim tabs on tunnel hull? I got the boat from a friend wich already has a winder a guess you would call it a fin on the lower unit to help stabilize it. any sugestions?

Ron Olson

My Feedback: (1)

Generally, trim tabs are put on a tunnel hull that was poorly designed in the first place. Usually weight is added to the bow to compensate to water conditions. They can also be used to lengthen the hull to help move the CG forward if done right.
I call it a skeg, I've never heard the term "winder".

ob nut

My Feedback: (1)

In my years of running tunnels, never seen one with trim tabs on it. This "winder" you mention, is this like a "whale tail" used on full size boats? Whale Tail = extended/oversized cavitation plate. As Ron points out, if the tunnel needs trim tabs, the design is bad.

Any pics?

Ron Olson

My Feedback: (1)

Mark, the trick of using the trim tabs to "lengthen" the boat to move the CG forward was one that I picked up from Gary Preusse. I guess if you're the type of person that is always looking for an edge and want to add a couple of grams to the rear instead of ounces to the bow, it would work. The other trick is to use the proper length of tabs, the harder part.

ob nut

My Feedback: (1)

Guess one could state that my tunnels do use trim tabs, so to speak then.. They are actually just 1/8" to 3/16" extentions of the sponson bottom sheet.

Look at the bottom left of the pic and you'll see what I'm talking about.


If Gary P. uses them, then I'll shut up

Ron Olson

My Feedback: (1)

Gary and I have disagreed on a few things but I haven't held a ton of records either so I just shut up, listen and learn. I don't tell him that I disagree either, not a good idea from someone that I buy my parts from and gives me great deals.
He didn't believe me that the Rossi .21 that I bought from him would push a Prather 220 then later he tells me that the fast .21 racers in the Chicago area were running the Octura M-445, an almost identical prop to the 220 in pitch and diameter!
If he or anyone else comes up with a unique idea, I want to know why and how they did it and their thinking behind their theory. If you ever want to hear some highly technical off-the-wall thinking, I don't know if you met Ric Carpenter at the Fun Run, he was hanging around with Dave Homer and George Dalecki, but that guys theories are really over the top but with some logic behind them.

mosh

I realy apreachate all the info and the corect name for the whale tail. The sad things is I knew the name I just couldn't type it. I had a brain fart. I don't think the boat is a poor design, I'm just learning about tunnels and trying to fine tune it for more speed and stibility. I've got another question for you guys. What is a good size prop? I'm using a Octura 440 right now I was just wondering if there was something better.

piper_chuck

My Feedback: (12)

The 440 is ok. A Prather 215 could be too. As could an Octura 437 3 blade. The only real way to know exactly which is best for your engine, boat, fuel, and lake conditions is to experiment. Try several, the best way is if you can borrow some from another boater, and see what works best. The bad thing is next weekend, or even later in the day, what was working great may no longer be right. I tend to be a bit lazy. I play with the props until I find the right one and then I just stick with it. I know others who will go through a half dozen props during open water to decide what's working best that weekend. I'll probably have to change when I get my outrigger running.

mosh

What prop would you recomend under calm condtition and using 40-50% Nitro. I'm looking for speed and big rooster tail.

mosh

I for got I'm running the newer K&B 3.5 with the 13mm.

ob nut

My Feedback: (1)

Speed - get 60% or higher nitro. I'm running a x440 prop on my tunnel and like the speed / handleing. I've tried a cut down X442, don't like it. Put a Grimracer prep'd X1440 on for a run, that was put back on my SS motor. As Piper stated, try many props for that ultimate speed you are looking for. If you want a big roostertail, sorry to say, a 3.5 tunnel won't be the one.

qweedqwag

My Feedback: (18)

Octura 1440 is a great prop, backcut the trailing edge .010 at a time from the prop hub out to the trailing edge tip, this will help the prop get the boat on plane, once established it will really turn some serious RPM. Make sure you balance it after cutting the traling edge.

Mike