Jae 21 GT done

[Ron Zaker Jr]

Hey Butch, nice boat!

I hope you can bring it to the cities to race with us.

I just finished converting my JAE 21 G2 to a GT by building a new tub for it. I would say Joe has made major improvements in the kit. You almost can't build it crooked with the interlocking tub sides and bottom. Interesting also that they are now running some toe-in on the fin sponson. Mine came in at 4.32 lbs. I am using 3 metal gear servos, which are pretty heavy I think. I also decided to build it with the S-bend in the stuff tube, which I had stopped doing.

very very nice

 

[BobBonahoom]

Thank you Ron!

I have this boat set up to run with either a regular drive set up or a square drive. I can interchange them at the pond to see which is faster. My theory is that using a square drive, the S-bend in the stuff tube is lower friction than with an end loaded shaft running in the S-bend. We will see if there is any difference in speed when I test it.

 

[shoboat]

Bob,

I do not think the speed will be much of a factor?

Bearing life will be the advantage.

I will be curious to see how your test results turn out?

Some have found between 2 to 5 more MPH documented

of course. I think Mark Grim found extra MPH on his gas

boats also?

Thanks,

Mark Sholund

 

[Richard Dahlheimer]

Bob, your new JAE looks great. Nice workmanship. I hope I can see it at the Eagan pond.

Richard

 

[BobBonahoom]

Bob,

I do not think the speed will be much of a factor?

Bearing life will be the advantage.

I will be curious to see how your test results turn out?

Thanks,

Mark Sholund

Mark,

We actually had a fire in a 21 boat when the heat generated at the S-Bend burned the inside of the radio box. This was a regular drive not a square drive. I think this was from the end load force on the flex shaft pushing against the S-Bend. It had to be robbing power to make that much heat.

I did some tests about 10 years ago using electric motors and motor-generators that showed an S-Bend (with no end load) was a lower friction set up than a gradual bend. Rod Geraghty did the same tests and found the same thing. So with no end load by using a square drive, we should get less friction/heat and more power to the prop. Of course the other benefit is not loading the engine bearings as you mentioned.

 

[shoboat]

Bob,

I heard you and your son did some testing last week?

How did the propellers work and the square drive set up?

Greg said your boat pulled more propeller?

Curious,

Mark Sholund

 

[BobBonahoom]

Mark,

My JAE "Lite" boat (old shorter tub that weighs 3.8 libs) ran well with an 1819 prop. This boat has a CMB Beta Evo engine and a Bouchie pipe at 8-1/4". It is not a square drive and uses ball bearings in the strut tube. It has no strut, instead the brass tube with the bearings is just glued to the ski. It ran 69 mph on 60% with 18% oil (6% castor) using a medium plug. Turbo head button with 0.005" clearance. Had to run it rich or it would not get back on the pipe after slowing down. I was happy with it for the first time out.

 

[shoboat]

Bob,

Starting to put together a new JAE-21-GT for propeller testing purposes.

It will be nice to see what I can get to work on it with a few different motor

and pipe combinations. The boat is built already thanks to Mike Walker

and Joe Petro from Zipp Kits. The ABC1800 series and 1900 series should be

plenty to get this boat into the 80's in oval trim. 78 MPH with a reduced cupped

1919-19-38% so far. I still think a little too much cup is holding some of the new

propellers back a little bit in performance.

Thanks For The Report Bob,

Mark Sholund

 

[user 10522]

Good boat

Skickat från min iPad med Tapatalk