Hard mount vs soft mount

[Kez]

Is there any advantage in hard mounting the engine?

The vibration mounts on the market (except for the Octura Humdinger, which has a cradle to support the engine) all have two seperate mounting pads. Would it put a lot of stress on the crankcase?

I would like to hear from boaters who hard mount their engine. How do you minimize vibration?

Thanks,

Kez

 

[MikeP]

I have done both, I can't answer your first question but, using the rubber mounts or the grouments to build a motor mount with alows me to make cheap lightweight mounts without alot of tools. The mount I made for a .21 was mounted solid, I had to use a mill to make it and it was custom fit for the hull.

As a rule from what I have heard bigger motors need rubber motor mounts of some kind.

I always take precautions to protect the radio gear either way.

I like the mounts that CMD uses on the Eagle SG. I can build those myself cheap and light, they fit any size hullmotor.

-MikeP

 

[Kez]

Thanks Mike.

When you hard mount your .21, how bad is the vibation?

I have an OS .45 hard mounted in a hydro. It shakes so bad that on the starting stand, I can see the rudder resonate and vibrate like a tuning fork! Since I have the maple block epoxied and bolted to the frame, it would be impossible to retrofit a soft mount. Is this kind of vibration acceptable to a sport 40?

Kez

 

[Hammerhead]

I don't know that much about noise restrictions in the states during races, but if you use solid mounts on even a .21, you will be getting in trouble unless you have a full cowl over your engine room.

Still toying around with the idea of having a solid mount in my .12. I think I might be able to get away with it. I have heard a lot of people say that having a solid mount directs more torque to the prop. Having that extra torque will always be nice in a smaller rigger.

As for a sport .40. I'm sure you have a beautiful boat. If it is vibrating that much, I would figure out some way to put rubber mounts in it. That much vibration could only cause radio problems. This ultimately could lead to the distruction of your boat. Take all precautions.

Hammer

 

[MikeP]

I had a OS .46 mounted solid in a prather hydro. I had alot of problems with vibration breaking control linkages and causing things to come loose. I also got alot of wear on my cowling mounts. The fuel would foam up to bad to run on the second tank when it got down to about half empty.

I have solid mounts in my .21 and don't have any problems.

-MikeP

 

[Kez]

Thanks Hammerhead, Mike.

I have also heard the argument that a solid mount will transfer more power to the prop. In my .21 boats, I am using a 3/16 aluminum plate (much like the Dumas mount) and then glue it to the boat with silicon. It works very well and the silicon will last several seasons. However, I do not trust the silicon to harness a .45. The commercial units all have two seperate pads attached to rubber shock mounts. I could be wrong but I think this could stress and distort the engine mounting lugs and crankcase etc.

Mike, your experience with solid mounting the OS45 is exactly what I have. In my case, I have noticed about 0.002" wobble in my cable nut and I am wondering how much this is transfering to vibration. Not all nuts are machined the same. I bought 3 Prather cable nuts and 1 is almost perfect but the other two do not run true.

Hammerhead, I am new to this forum but I noticed that you live in Japan. Do you know if KNK has a website? I am looking for a KNK Jupiter. I have built one in my youth and want to build another one again ...to be used as a retrival boat.

Thanks,

Kez