What size rigger for a CMB 35 Gas Engine

[Troy Glass]

I have a CMB RS35 Gas engine I want to make A rigger for and I was thinking of using the JAE .91/1.01 plans and scaling it up, but how big do you think it would need to be? would 50 inch's be long enough with maybe 3 inch's wide sponsons? what are your thoughts.

 

[RaceMechaniX]

Troy,

It's a very tricky motor to put in a rigger. First, it's got to be a 5" minimum tub to use the CMB motor mounts which I highly recommend. The tub has to be pretty high to pick up the forward motor mounts, so figure about 4" there. To handle the power and torque of the 35 yuo are going to want to make it at least 48". You'll also want to have heavy duty boom tubes and sponsons to take the abuse. Its hard to build a rigger this big and still be light. You will also need a very strong pipe mount in the rear. The CMB pipe and muffler weigh quite a bit and exert some big side loads in hard turns.

You can see pics of mine in my gallery: Eagle SGX GX-2 Rigger with CMB 35RS

Tyler

 

[lohring]

If you want to go a little faster in a straight line.

http://www.modelgasboats.com/Magazine_Content/Tech_Articles/CMB_35_Record_Engine/#

Lohring Miller

 

[Marty Davis]

If you want to go a little faster in a straight line.

http://www.modelgasboats.com/Magazine_Content/Tech_Articles/CMB_35_Record_Engine/#

Lohring Miller

Lohring:

It is neat to see how detailed your testing is. The results of your testing speak for themselves. I just sent a link to this testing data to Brian Callahan. I am positive that he will enjoy the detail.

Note: In typical short Brian Callahan reply: : "Very Impressive"

 

[Troy Glass]

Thanks for that Tyler what size prop are you running?

Troy,

It's a very tricky motor to put in a rigger. First, it's got to be a 5" minimum tub to use the CMB motor mounts which I highly recommend. The tub has to be pretty high to pick up the forward motor mounts, so figure about 4" there. To handle the power and torque of the 35 yuo are going to want to make it at least 48". You'll also want to have heavy duty boom tubes and sponsons to take the abuse. Its hard to build a rigger this big and still be light. You will also need a very strong pipe mount in the rear. The CMB pipe and muffler weigh quite a bit and exert some big side loads in hard turns.

You can see pics of mine in my gallery: Eagle SGX GX-2 Rigger with CMB 35RS

Tyler

 

[RaceMechaniX]

Troy,

My motor ended up liking small props and spinning lots of revs after I raised the timing, shortened the pipe and increased the intake timing. Its favorite props were ABC 2718, ABC 2818, ABC 2916 and Octura 1475 pitched up.

I tried several larger props like a 3317 and the boat would not get off the beach.

Tyler

 

[lohring]

Marty

Thanks, your inertia dyno articles at rcboat.com were the inspiration. Over the years we've done tons of boat testing as well. As electronics got better, we learned more. One of my favorite onboard videos is

showing what a prop looks like lifting out. Videos of different sponson designs were instructive as well.
Troy

We ran both a 2170 and a 2175. The smaller prop was best for top speed, but our engine was setup for maximum rpm since no props have enough pitch. With a setup like Tyler's the best power (nearly 12 hp) will be around 18,000 to 19,000 rpm. The engine is a monster with huge torque. It lifted our test boat, an Aeromarine Cyclone, completely out of the water when we hit the throttle the first time.

lohring Miller