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I built my TNT in 2002 and have since been making yearly performance upgrades. The most recent (and by far the best!) addition was a pair of 9" lenco electric trim tabs. With these units, the boats handling and speed potontial increased dramatically. My current set up is as follows:
I am running a 25HP 2-stroke merc with a 14.5 inch pich prop, and I added Boyesen reeds to it a few years back. My best top speed was 37 mph on GPS at a recorded 6200 rpm (i realize this is beyond the manufacturures recomended maximum)
I have experimented with one inch less pitch and my speed lowered. My question is, would my speed likely increase with an extra inch of prop pich (to 15.5")? I know this is a tricky one, but if anybody has any suggestions i would greatly appreciate it. I've gotta beat a guy on my lake with a mini Vo-Doo, he's runnin 39 plus with a 30!

Thanks- Andrew

If you're over reving go to the 15.5. You might pick up 2 mph.

Bill

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Mini -Tug, KH Tahoe 19 & Bartender 24 - There can be no miracle recoveries without first screwing up.
Tahoe 19 Build

Dude, your boat is awesome. I've heard speed coat works quite well. I have not used it myself though. It might put an extra couple of mph on it. Maybe you can catch up to Scott with that. I think its pretty cheap as well but applying it would be harder. Get a custom made prop but that'd probably set you back $100's. Turbo-props has one that can fit 18-70hp engines including yours and mine. They have one called the Hot Shot but Mercury sells the Vengeance prop intended for 25hp+ with more dia. lengths and pitches, but then again Turbo's are cheaper. They are both stainless steel as well. I was going to say get a 2 blade propeller but since your getting 6.2K RPM with your three blade you've got now, never mind.

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Tuffy with '75 Merc 650 SS.

Thanks for the tips guys!, Scott, have you figured out anything with your tuffys porposing issue? I'd love to see that thing doing 40 this year!

The pitch of a prop is how far a point on the prop will advance in one revolution. You ran at the the same rpm, so an increase on 1" of pitch will get you 1" further per rev. This is of course assuming everything is ideal and 100% efficiencies all around. There is a balance point though, if you increase the pitch too much, you motor will not have the torque to turn the prop at the high rpms.

Yes we have..threaded rods to help the dumb smart tabs (don't know why I bought those) stay down. If I had $800 I would buy what you have but for now I'm improvising. I might go for an SS prop once I get everything straightened out with the porpoising. But I'm spending my money on a 1958 Merc Mark 25H racing motor right now to buy it soon. I will get to 40 this summer trust me on that even if its 40.000 on the GPS. But I think in a year or two I'll sell my 40 4 stroke and get a Merc 50 stroke if its still around.

Do you think your TNT would improve speed with an SS over a AL prop?

You have to beat the other Scott though. I haven't seen his boat for a while nor himself actually come to think of it.

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Tuffy with '75 Merc 650 SS.

Scott,
What are you planing on using the mark 25h on?

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Boat building can best be defined as an endless series of
tragedies obscured by the occasional miracle, followed by a good bottle of beer.

Don't Dream Your Life, Live Your Dream

also,Lenco's are only around $400-$450

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Boat building can best be defined as an endless series of
tragedies obscured by the occasional miracle, followed by a good bottle of beer.

Don't Dream Your Life, Live Your Dream

Thats because you live in the Us..in good old Canada here everything is stupid expensive. But thats why I go to Detroit for my fishing stuff from Bass Pro Shops because its so much cheaper there.

But anyways...the Mark 25H..needs some cosmetic work along with some cowl work. I'm going build something for it later on but for now I am just going to and keep it in good condition and do some test runs on my 14' AL tin can with it. I'm hopefully building a Zip soon..then the Squirt after that so I'll probably plop it on the Squirt once I'm done. I'm going to go to OldMercs for parts and stuff though and probably restore it a bit.

Clark Craft alike Glen L boat plans has a plan for a 13' 3" - like TNT. It is a bit different but I was thinking of building that but I really want to do the Zip & Squirt.

Minn Kota also has some pretty weird but alright looking trim tabs..heavy price though too much for me. Something around $900.

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Tuffy with '75 Merc 650 SS.

One more inch of prop will not gain you one more inch of forward motion because there is a second factor working against you, water resistance. So one more inch of prop will not get as many RPM's.

When I reduced pitch on my prop by 2 inches I lost 400 RPM's and gained maybe a mile and a half per hour. That's for a Vee Dory, so I would expect your little speedster to gain much more.

Yeah, higher the pitch lower the RPMs. Lower the pitch higher the RPMs. But I guess same for diameter. Whats nuts is that the Mercury Champ motor has a peak HP rating @ 8600 RPM. And it has P-W ratio of 1.05:1...290:275. Wish they could make motors like that.

I really wish gas would go down to 80cents/L again...so I could find a Mark55H.

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Tuffy with '75 Merc 650 SS.

Scott, have you ever seen my dad's 64' merc 6HP? Its a special silver aniversary edition comlete with silver trim. He's owned it since new and it's still in great shape (sorry, its not for sale!) . One day, when he is finished his car, we will likely restore it. Did I ever mention that Scott's (Voo-doo Scott) father has 2 unrestored hurricane mercs? He claims he wouldn't sell them, but i don't think he would ever do anything with them. Just thought you'd like to know.

GAS WAS ONCE AT 80 CENTS A LITER?!?

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Squirt: http://drewsboatsquirt.zoomshare.com/

Andrew. Thats amazing! When I first saw your boat, I'm assuming it was the first year you put it in the lake, I saw you had a Mercury. I was happy. I have quite the obsession for Mercury. I am going to start my own collection very soon hopefully. And no I have not seen your dads Mercury, maybe this summer I will get a chance too.

I just got back from the Sportsmen show yesterday and saw a nice collection of Mercs, Scott-Atwaters, Evinrude's and...crap I forget but I'll see them today..again.

I saw the 100hp tower of power at the boat show this year. It was mint. I guess you could say..I found a "mini" tower of power 65hp '61 Mercury w/ original controls. I need $700 though. I would like it for..well read my signature. The one I'm hopefully buying now, I really want it to make it run on alcohol not gasoline.

...and yes if you (Drew) are not being sarcastic - the farthest down I've ever seen it was 67cents/L but that was a long time ago. It is going up to $1.50 in Toronto this summer. Probably at least $2.00/L up north. Thank heavens for vacation pay..because thats what mine is going toward.

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Tuffy with '75 Merc 650 SS.

I think I'm just gonna move up north for the summer instead of driving 3 hours back and forth.. I almost sold my car when it went up to $1.50-190 a couple years ago.

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Squirt: http://drewsboatsquirt.zoomshare.com/