.12 rigger weight distribution

[Don Templeton]

Well, I just had to go out and get a digital postal scale to go with

the new camera and have been trying to gather some information

on my new rigger. Other than the fact that it's about a half pound

heaver than I would like, I came up with some interesting figures.

Any comments would be appreciated. I've got all winter to fix it!

Length of tub: 23-1/4" +another 15/16" to tip of prop

Trailing edge of sponsons from nose: 8-7/8"

CG of boat from nose: 11-1/8"

Weight of boat (less fuel): 48.2 oz. ( 3Lbs/0.2 oz.)

Weight on prop tip when sitting level on trailing edge of sponsons: 8.5 oz.

I also noticed that I could reduce the weight on the prop to 7.6 oz.

by adding 1/4" to the rear of the sponsons.

How do those figures sound to all of you with 12s?

Don ???

 

[Don Templeton]

Hey Mike P,

After I posted this I read your reply to Propjockey on where to stick it.

Everything thing seems to be in order according to that formula with

even to collet in the right place.

I guess I better read first before I post from now on!

Don

P.S. It would be nice to know the weight on the prop of

some other boats.

 

[TomMoorehouse]

ok don lets compare notes....

the length of the ff tub is about 23"

the key dimension to me is the distance from the trailing edge of the front sopnson to the trailing edge of the rear sponson. for that i have about 15.5 inches.

using the cg measurement from mike p's post i'm a little more toward the back.... about 1/2" closer to the rear..... it might be slightly more cause i dont have the reciever, prop, and switch on the boat yet..... but im close to that.

the LOA from tip of the front sponson to the end of my flex shaft im at about 27"

cant do weights :-

 

[Propjockey]

'Hydro-therapy'

Tub length--22"

T.E. of front sponson to T.E. of rear--13.5"

(rear sponsons were moved rearward 1" from plans)

Drive dog to balance point--10.3" (right on the money according to Mike's formula)

 

[Don Templeton]

"OK" I re-measured the trailing edge of sponsons to the front of the

drive dog. 14.75" (My drive dog is only 1/4"behind the transom.)

The CG from the drive dog. 12.00"*

Using Mike's formula-( 12.00* devided by 14.75" = .814 ) or 81.4%

*Changed 12/11/02

Sure would like to here from some more 12 guys,especially the

fast ones I keep hearing about. You need to ask Santa for a

digital scale. I picked up a real nice 10# (Sunbeam) at Office

supply for 59.95. It runs on 9 volt or AC. They also have 5#

units for less but wouldn't work for larger boats.

This is great fun!

Don

 

[MikeP]

That's pretty cool you call it Mike's formula, but remember I was just the copy and paste guy.

-MikeP

 

[Don Templeton]

Tom,

Just for the fun of it I'm going to take a wild guess on the final

weight of your Firefighter.

2Lbs/4oz ( 2-1/4Lbs ) "OK" That's Better

How about you Propjockey? Take a guess. I wouldn't even take

a guess on your's. ;D

 

[Don Templeton]

MIke,

You might be a copy and paste guy but you'r one hell of a boat builder!

 

[MikeP]

Thanks Don.

I will guess Toms FF .12 boat is 2.5lbs.

-MikeP

 

[Don Templeton]

I messed up on my weight guess!

Ment to say 2Lbs/4oz-( 2.25Lbs) :-[ I'll go back and change it. ;D

 

[Hammerhead]

Hey Don! Good references! Thanks. One more question, before I go to far with my own project. What is the angle of attack of the rear sponsons in relation to the bottom of the hull.

I plan on packing mine completely under the hull, this is one of the characteristics unique to my boats. I usually run my big riggers between 2.5-3degrees. Yours look a little steeper than that. I plan on starting out with a V937. They are notorious for lift. Don't want to do any diving. I designed my front sponsons with 4.5 degrees.

Hammer

 

[Don Templeton]

Hammer,

You are right about my rears. I was hopeing no one would notice.

They are at 6 degrees (way to much) and I am planning to change

that to about 2 degrees. They are attached with machine screws

so I'll take them off and work on the bottoms. My fronts are at

approx. 4 degrees+. The bottom of the strut is level with the

front sponsons and at about 2 degrees up in front. The rear

sponsons are set at 1/8" above the bottom of the strut.

I would like to hear your opinion on that set up.

Don

( Took a better measurment on the front sponson

angle and they are right on 5 degrees )

12/12/02

 

[Propjockey]

Don,

How about 3 lbs, 2 oz. I can lose 6.5 oz by dumping the electric start and clutch and replacing with a grooved flywheel. I want to see how it runs first though.

 

[TomMoorehouse]

Well I just could not take the suspense any more! Feeling pretty silly I went to the post office with my boat to determine its weight. The clerk says with a big smile 2lbs 8.9oz. I did have a couple items missing from the boat. Missing was the reciever, Radio switch, and about 4" of 1/16" pushrod. I figure they are good for maybe 2 more ounces? So if anybody asks me I will simply say it weighs a little over 2 1/2 lbs.

Could have I made the boat lighter.... sure:

I used .150 flex shaft, could have been .125. I figure that extra weight was worth the extra chance I have not losing a prop.

I used 1/16" plywood for the tub bottom. I could have used 1/32" I prefered the extra strength of the 1/16"

I used .414 black epoxy tubes. I could have used smaller Carbon fiber tubes. This is my prototype for the kit boat. I have a bunch of reasons for choosing these tubes.... low cost, easy of use (you can put a screw through them), readily available.

I used speedmaster .21 size hardware. I could have used lighter electric based stuff. I did a TON of research on hardware. I really don't know of any that really suits this application well. I could have used lighter electric stuff but they all had aspects i did not like.... like the rudders did not have a kick up feature and the struts looked too weak.

I could have used more balsa. I used 1/8 light ply and 5 ply.... again I wanted the extra strength.

I could have the tub skinnier. It would have been no problem to make the tub at about 2 inches but I went with 3.25. This is my kit prototype boat. I wanted the people that buy them to have the option to use an octura 3-30

mount and that is the width you need for it. Why the octura 3-30 mount? Well It will work with pull start engines. It can be made pretty light and will strenghten the boat.

So what did I do to keep weight down?

I opted for the Dave Brown Airplane motor mount.... it is super light! I used good quality 1/8" light ply in a lot of places. The front sponsons use a plywood/balsa/foam hybrid construction. I spent a TON of time determining

this construction method. I tried several other construction methods as well. I determined this one to have the best low weight to ease of construction ratio. I used a www.grimracer.com fuel cell.

I believe that this setup will provide the people that get the kit the best boat, at the lowest cost, that will last for years. That was my goal.

 

[Don Templeton]

"Gee" Tom, Too bad! I'm really soory! What a shame!

You goofed up and built the perfect rigger for 99% of us. While it

may be easy to build for the beginner, this is not a beginner or

first boat by any means. This is a complete, competitive racing machine with lots of adjustability built in for oval or SAW and

built to take the punishment of all out competition, which

is considerable.

"Too Bad" Tom :'(

Don

 

[Don Templeton]

Propjockey,

If that boat will start and come up from a dead stop, it will be

one of the most fun boats you could ever own.

If not, Back to the drawing board, which is where I spend most of my time anyway. And where I like to be.

Don

 

[Hammerhead]

Hey Don! When I make riggers, I always start with the strut level with the bottom of the hull. Then, I will run it, see how it sticks to the water, and lower it a little bit at a time. I usually never exceed the angle of the rear sponsons.(2.5 to 3 degrees) As far as the depth, I usually run with the bottom of the strut barrel 1/16" above the running surface of the rear sponsons for starters. I never go below.

6Degrees? You haven't run your boat yet, have you? Gee whiz. If they are really shallow it will run, I guess. You should talk to MikeP about that. I think he originally set the rear sponsons of his CF .21 at 6 degrees, and now they are at 1.8 or 2.

Hammer

 

[Propjockey]

Thanks Don!

BTW--if it doesn't come out of the water with the .15, I have a backup plan ;D

 

[Don Templeton]

Hammer,I agree with you on the rear sponsons. that was a

mess up in mounting. I will for sure get them to no more than

2 degrees. However, I am surprised that you would set

them deeper or even level with the strut bottom. I don't want the boat to rely on them unless it needs to.

Thanks for the input. I guess I'll find out when it comes spring.

Thanks,

Don