Wrong Shaft Drive Install.

From the very first install of power boat shaft drives they have never been installed mechanically correct but just for tradition and appearances.
Centre line motor crank and prop shaft drive is incorrect.
Using twin u/v`s install the motor should be off set in relation to the u?v`s and off set in relation to the shaft down angle for longer service and less maintenance and vibration.

The prop shaft should be off set of the centre line that side determined by the prop rotation.
Rudders should be also off set from the centre line of the shaft for optimum steering and control of torque and better steering.

Would you sacrifice symmetry, tradition, appearance for longer reliable service with less maintenance, less vibration and a more balance control?
It`s all about good boat design.

 

Why the sudden outburst Tom?
I don't question your insight, but what caused you to start such a thread other than booze or a bad nights sleep?

And what is "symentary" ?

 

How could there be a tradition on day one? Traditions take a long time to get established. What is the reason to install a UV joint anyway? A soft coupling does the job fine without the expense or complication.

 

We get a lot ot people telling us that something will not be efficient yet are happy to tolerate the simple incorrect basics of mechanics which are easy to perform and you do not need to throw big bucks to get the best results. The tradition of centre line building certainly has been around a long time and is likely to stay that way for the less adventerous happy with mediocre design.

 

I have fixed the spelling mistake as it does not seem obvious. I seem to have rattled a cage or two perhaps there may be some thinking done before replying. I am used to dealing with politicians so I can not be insulted with assumptions of my character. I had better get my spell check working.

 

Can you explain, even in political terms, how can a tradition pre-exist? That is, the tradition is already in place before the shafts existed.

 

I have re-worded that post so it may be easier to understand.

 

Heck, even I can answer that one.

The tradition of symmetry existed long before power ever showed up: masts, centerboards, rudders, keels, etc. Power components just fell right in line with that existing tradition.

I'll let the rest of you duke it out over whether that's a good thing or a bad thing....

 

I think the "tradition" is just that. There's no reasonable rational behind the schooner rig either, but some still have them built. Most good designers do incorporate shaft and rudder offset. How about curved shafts?

I do think you're over stating the "incorrect" install, as I've seen an awful lot of offset designs. I do believe there are more straight down the centerline installations, but likely from those that don't know better or preferred the simplicity of the arrangement. One argument in their favor might be the difficultly to drill an angled and offset shaft hole. Though this is less an issue now, certainly could have contributed to the tradition taking root, in the deadwood of those late 19th century craft.

 

The use of twin u/v's between gearbox and prop shaft certainly gets my vote. Not only does it reduce noise and vibration, it also makes alignment less critical and avoids wear due to misalignment.
I guess somewhere in the past a rowing boat was motorized with primitive means and the same basic setup is still copied.

About the asymmetrical engine placement I am not so sure because the rotational effect depends on engine power. Boats are often offered with several engine options; it would require different offset values and still the optimal value would be valid for a very narrow speed range.

 

One of our (NZ) research organizations have recently done research for a majour propulsion producer
on vibration and wear for shaft drives and it showed that C/V`s U/V`s must be of set for best performance. Meaning not runnung lined up along a centre line. Three to five degrees is good.

 

Universal joints and CV joints should not run for extended periods at near-zero angle difference between the input and output. The reason for this has nothing to do with efficiency. Rather it is because excess wear can occur if the joints run at zero or near-zero angle difference.

 

Two joint prop-shafts between the engine and shaft log are becoming common on boats. While more expensive than a one-piece shaft they eliminate the need for precise alignment of the engine. Also, "soft" engine mounts can be used which can reduce vibration transmission from the engine to the hull structure.

 

Single universal joint with thrust bearing !!!

I have always used a single universal joint on any and all propellor shafts i have done and soft mounted the motor on rubber mounts .
Just one differance i always mount a thrust brearing for the propellor shaft to take all the push and pull on to ,never the motor or the universal joints or rubber engine mounts !! . I have always done this since the first boat i ever made while i was still in short pants at school in 1959 !! Have never changed this method on other inboard board boats i have made over the years untill i started using outboards !!.

 

One universal joint would be a good way to create vibration
One CV yes but one uni ( hookes joint) no