Why dont Inboards use U joints?

[springer59]

Can anybody tell me why inboards don't use U joints to get a better motor incline to hull postion? I am currently restoring a 69 Luhrs sport fisher,318,Velvet Drive 71-C trans.The angle of the engine/trans to the "waterline" is about 20 degrees,that makes the front of the motor sit very high at the top front of motor.What's to keep them from adding a U joint or a constant velocity joint to keep the motor to hull angle a little better.As I hope you can see in the photo,the front of the motor could be lowered about 2".It would sure beat trying to find a 15 degree drop reduction gear to bolt on the rear of the trans as it is a straight drive with the shaft to crankshaft in a "straight" line.It really requires a 15 degree wedge spacer on the carb to keep it fairly level with the rest of the world.

 

[Ned L]

Re: Why dont Inboards use U joints?

The simple answer is that universal joints are not designed for thrust. (keep in mind that a boat is very different than a car in that every bit of thrust and power required to move the boat forward is transfered throught the prop shaft & engine to the engine mounts, so in reality is is the engine & its mounts that are 'pulling' the boat through the water. Yes, a thrust bearing can be added before the univeresal joint to change that scenario, but that combination adds complication to the system and those components don't like a wet salty envirenment. --Also typical spicer type universal joints do not provide for constant velocity through a complete revolution, so 'CV' joints would be needed to reduce vibration. As you have mentioned 'Z' drives are available for situations where something really needs to be done.
---- Boats have been put together with nothing but a spicer u-joint & thrust bearing & it does work (I have pics of such a setup in an early '60's Ulrichsen skiff that was custom built for commercial fishing). -- Just like lots of small commercial boats over the years have used engines & transmissions pulled right out of cars, dry stack exhaust, slam it in 2nd gear & off you go (reverse is painfully slow though).

 

[Fishin Magician]

Re: Why dont Inboards use U joints?

Excellent answer Ned.....spot on..

u joints = loss of HP..

 

[springer59]

Re: Why dont Inboards use U joints?

thanks Ned L that was the kind of answer i was looking for, could you send me the pictures in case i decide tp do something really stupid, i would appreciate it, thanks, springer

 

[QC]

Re: Why dont Inboards use U joints?

universal joints are not designed for thrust.

Awesome answer as others have said. Thanks!

 

[Ned L]

Re: Why dont Inboards use U joints?

Here are the pair of early 1960's Ulrichsen skiffs that were custom built for two Greek fishermen brothers. They were in Belford N.J. In the second photo youcan see the thrust bearing and spicer universal joint.

 

[springer59]

Re: Why dont Inboards use U joints?

Thanks,just shows why I joined the great iboats site.

 

[Jlawsen]

Re: Why dont Inboards use U joints?

Great response Ned L!

 

[hottoddie]

Re: Why dont Inboards use U joints?

Some boats with remote mounted Walter V-Drives use a double u joint and a short shaft between the transmission and the V-Drive. In that case the V-Drive is bolted to the stringer system and takes that thrust loads and all the engine and trans take is the torque loads. Great system, had it in my 32 ft Stafire express. Made for easy access to the stuffing box as well. Some Carver Santego models use the same system.

 

[Ned L]

Re: Why dont Inboards use U joints?

Yep, that would work fine, and the double universal joints take care of & solve the changing velocity problem of the Spicer type U-joint (they each cancel out the other's changing velocity). That also gets the U-joints up out of the bilge.