Where to put motor

[Michael Hopkins]

I am building a rigger from scratch and was wondering how do you figure out were to put the motor (location) to get the proper cg

What I was going to do is finish the boat install hardware and radio gear fuel tank and the motor last but I need to know to find were to install the motor so the boat will have the proper cg .

Thanks for any help

 

[Terry Keeley]

Look down a couple posts...

 

[Michael Hopkins]

Look down a couple posts...

So the motor should go about 70% of the afterplane is this right

 

[Terry Keeley]

Look down a couple posts...

So the motor should go about 70% of the afterplane is this right

No, if you balance the boat at about 70% you should have something to work with...

 

[Joe Warren]

Have you already determined where the Trailing edge of the front sponsons will be?

 

[Michael Hopkins]

Have you already determined where the Trailing edge of the front sponsons will be?

Joe I have 29" from the trailing edge of the front sponson to the transom my balance point on the boat is at 21'' from the transom with everything in the boat ready to run less fuel and I have the turn fin's trailing edge at 21'' from the transom .

Am I close ???

 

[Neil LaGarry]

This is the only place for free set ups and builds. http://ne-stuff.blogspot.com/2008/12/japanese-style-rc-hydro-boats.html

 

[Joe Warren]

You never mentioned what size you were bulding. Or if it is gas or nitro & if you plan to run a ski under the boat?

 

[Joe Warren]

My Guess based on the 29 inch after plane would be a .45

I would matter greatly if he plans to run a ski over the strut too

 

[Michael Hopkins]

You never mentioned what size you were bulding. Or if it is gas or nitro & if you plan to run a ski under the boat?

Joe it's a gas rigger with a rear ex. motor and it does have a center ski under the rear covering the flex tube

 

[Joe Warren]

I agree with What Greg said. Very short to support a gas engine.

 

[Terry Keeley]

Assuming the drive dog was another 3" aft of the transom, your balance point would be 21"/32" or about 66% of the after plane, definitely in the ballpark.

 

[Michael Hopkins]

Assuming the drive dog was another 3" aft of the transom, your balance point would be 21"/32" or about 66% of the after plane, definitely in the ballpark.

Terry the hull is 40'' / with the front sponsons overall length is 42'' and from front sponson tip to end of strut with no cable it's 45'' yes the strut is extended version

 

[moparbarn]

Assuming the drive dog was another 3" aft of the transom, your balance point would be 21"/32" or about 66% of the after plane, definitely in the ballpark.

Terry the hull is 40'' / with the front sponsons overall length is 42'' and from front sponson tip to end of strut with no cable it's 45'' yes the strut is extended version

doesn't sound too short for a gasser. my hurricane gas rigger is within 1/2" + or - of all those measurements.

 

[Michael Hopkins]

Terry can you post how you find your 66% (mathematical method)

Are you taking the overall and finding 66% of that

 

[Terry Keeley]

Terry can you post how you find your 66% (mathematical method)

Are you taking the overall and finding 66% of that

You're just working with the "footprint", so the distance from the TE of the front sponsons to the drive dog.

You said the TE of the fronts to the transom was 29" so i added another 3" to get to the d. dog.

To find the balance point as a percentage of that footprint divide the balance point distance fwd of the d. dog by the afterplane or distance from the fronts to the d. dog.

I made a mistake, it should be 24" / 32" = 0.75 x 100 = 75%

Think the JAE's shift the weight a little further back to compensate for the lift from the ski.

 

[Michael Hopkins]

Thank you Terry