Best prop for TT outboard?

[jstew0903]

I have a older dumas hull that is 27"x14" I have a thunder tiger .21 outboard and wanted to know what prop would do best on it. I also am running Redmax 40% in it. This is my wifes boat and she is getting a little downhearted that my boat is alot faster than hers. I have prather 220 stainles steel on it. It was on there when I bought it. The guy also gave me a octura x637 prop with the deal. Also is there any type of maintenance(lube) that I need to do on the gear drive on this outboard. If anyone wants I can post a pic of the boat. Thanks agin for the help.

Jason

 

[Jerry Dunlap]

Jason,

The Prather 220 is too much prop for the TT. When I was running a TT, I had success with both the X440 and X640.

A X442 will also work. It can swing more than the X637. Any type of light weight gear lube will work fine. The gears are very well matched.

Of the three motors, O.S. Max 21, TT, and K&B 3.5ss, the TT was not as fast. However, it's a beautiful motor and quiet.

Jerry Dunlap

 

[Propjockey]

Jason,

I've never run this engine, but it comes new with a Prather stainless 215. I'm with Jerry--the 220 is too much.

 

[Kris Flynn]

you boath could be right...i havnt done anything with this engine either, but TimD is the man to talk to about it...he changed the gears so he could spin a 220 and also added a pipe (and a few other mods) and was able to achieve 50MPH+

 

[TimD]

JAson,

If you have a stock standard TT then a Prather 220 is too big. With a few minor changes to the TT the Prather 215 will work very well. If you can get your hands on a gear reduction set for it then the motor will be able to pull the Prather 220 or an Octura X642.

The biggest thing with a TT is you have to let them rev. in other words don't over prop the thing. When I first started out with the TT I went to using the Octura X437/3 with no mods at all and it went a lot better. Once I started doing some mods the motor's characteristics changed and I ended up back on the Prather 215 or an X440 / 2.

If you want any advice to get it going - just drop me an email.

Tim.

P.S My friend's TT ran 47MPH with no pipe and a GPS in the boat - not to shabby!

 

[jstew0903]

Thanks for the help guys, I thought it was to much prop, it just doesnt rev up very well, and it seems to drink the fuel pretty bad. Can I use this prop on my K&B that has a pipe and a red carb on it? I think I will have to cut the diameter down to get it to fit though. I have a x440 on it now. I think the x440 has just been sharpened and polished. My tunnell want to spin out in the corners. If I round the tips will it keep the rear of the boat more in the water? I heard someone say if you round the tips it produces less lift. I think I need a turn fin It seems like it spins and rolls over in a hard turn. Will the fin keep it from rolling over? If my boat is 29" long where should the CG be. It is a Hyro Sports Marine whistler 2.5 hull.

 

[Propjockey]

You might also try raising the engine to unload the prop a little and pick up more RPMs.

 

[Jerry Dunlap]

Jason,

There's a couple of things you might try to improve the cornering.

1. A turn fin on the CG(which should be about 9" from the transom).

2. Front stumble blocks to assist in keeping the sponsons from grabbing and spinning out the boat. If you don't know what stumble block are, e-mail me and I'll send you a photo.

The boat you describe is an old model and many improvement have been made to model tunnel boats.

Jerry Dunlap

 

[hg-md]

TimD,

Is there more than 1 version of the TT? Where can one aquire the different gears that you speak of? What is this ratio you recommend and what is the original ratio? I do not have a TT but I do find the gear drive in it interesting to the point that I may get one. I think this could present itself as very beneficial... :

Is the drive for this unit very reliable?

 

[TimD]

The earlier versions of the TT had a 12mm crank and the later ones had a 13mm crank.

The standard gear ratio is 1.04 to 1. The different gear ratio set's were available from TT. I think the ratio I was using was around 1.28 to 1 (not exactly sure tho.)

The gear drive is ultra reliable - never ever had an issue with them. The earlier flex shafts were too short and used to round the ends off the shaft but the later ones were much better.

The gear drive design is the main reason for my liking the TT. They transform a pretty ordinary motor into a moster as the gear reduction multiplies the torque of the motor. If you don't change the prop tho you will not see much difference between ratio's.

The other thing that is cool about it is that the motor runs in the normal direction (K@B, O.S run backwards)

Normally not an issue unless you run other boats and forget to change the starter direction :