bertram31.com

Good Morning

I have a marine engineering company in the UK and one of my customers has a Bertram 31 and has carried out an extensive refit, we have installed a pair of Yanmar 4LHA’s fort him and have used your site for tips along the way which has been really useful!!

The owner installed Tides Marine stern seals which are a lip seal type propeller shaft seal. we are having problems with these leaking at high rpm, it appears the shaft have a small amount of whip at high rpm which is causing the lip seal it shake and leak, we have installed the shaft material as per your recommendation. I see that you fit the deep sea seal to yours.

My question is - to prevent the shafts from whipping we would recommend a forward shaft bearing but from what I can see on your website you never do this??

would you suggest we just fit the deep sea seals? do you experience a small amount of shaft whip at high rpm?

I really appreciate your help

Many thanks

Regards

Mike

If you have a whip you need to find out why instead of masking the problem.

Shaft needs to be straight and true from end to end .005" TIR (.13mm TIR) or better.

Coupling face needs to be dead on true as in .001 TIR (.025mm) or better.

Engine needs to be aligned to the face of the Prop coupling, shaft needs to be centered in log and straight through cutless bearing within .003" (.08mm). Should be done/checked in water as on land hull flexs. While your at it, check condition of cutless bearing...new has a clearance of .007 (.018mm). When you get to about .015 clearance (.04mm) think about changing.

Props need to be in good condition, verify its seated properly and not riding the key or a bur. If wheels out it will create imbalance causing whip, vibration leading to a leaky seal.

With everything as it is supposed to be the shaft should run without whipping,wobbling, vibrating...aside from just getting on plane when boat and engine start moving around under high load. When all is good...then consider an intermediate strut for additional support. They are not meant to fix problems, at least not on shorter shafts like most of the 31's.

I said most as with a reduction gear the shafts are not very long for there diameter. The exception is the older boats that had 10deg struts and 1:1 gears. Turning faster the shaft diameter was a slender 1-1/4" (31.75mm), the lack of reduction gears meant shafts were longer at 94" (2387.6mm). Together a long, slender shaft turning faster (3000rpm at cruise) would vibrate like crazy unless the shaft was held even closer to .003 TIR (.076mm) and the wheels needed to be right on. Some of the 10deg boats had intermediate bearing...mine didn't. I thought about it but when all was right boat ran great.

Anyway, if all is right, shafts should not whip.

https://www.proboat.com/2010/11/running-gear-alignment/

http://www.yachtsurvey.com/alignment.htm

David

Carl is 100% correct. He better be since that is part of his business. Make sure the props are balanced. Even new out of the box, they can be out enough to cause the shaft to wobble. Make sure the coupling is on the shaft properly. If is cocked it will cause a wobble.

Check the shaft to make sure it is true. You will probably need to pull it from the boat to double check that part.

As carls said. you have to get that shaft to run straight.

I am running the same seals on my 31. Not a drip even at hight speeds. I will say this, my shaft has a slight wobble at idle but once at speed it is straight as an arrow.

Tony Meola wrote: Make sure the props are balanced. Even new out of the box, they can be out enough to cause the shaft to wobble.

I am pretty much out of that end of the business now, but last I heard "out of the box" wheels, the factory allowed them to be 10% off.
To someone who knows what a boats running gear should feel like, 10% off is huge, especially on smaller faster turning wheels.
We used to tell customers we would like to have their new incoming wheels checked before we give them to you...they may be out and if they are out, we will recommend "reconditioning" and that will be at an additional cost.

Tough sell for sure and many shops just handed over the wheels...many people didn't know better, didn't run boat or lived with a vibration.

The exception was the machined wheels like Acme.

Tony Meola wrote: I will say this, my shaft has a slight wobble at idle but once at speed it is straight as an arrow.

Shaft or alignment may be out a bit.
As shaft spins faster it can find its own center, plus the force of the water will steady it some.

The alignment we try to hold real tight...but also need to realize the motor sits on flexible mounts and the boat is pretty much a plastic heap flexing. Alignment can be perfect at rest, but all that changes when you put in gear.


Which brings me to another point...Also need to check condition of mounts, they should allow some movement and then return. Broken, worn or loose mounts can be the cause of a whip too.

Carl

Mounts are good. Might be out of alignment slightly, will have to check it one day.

Tony-

I like the shafts to run steady at all speeds, but if it has a little movement at low trolling speed then steadies as you gain...that's something I can live with.

But not a bad idea to check alignment. If alignment is out shaft is being fatigued with every rotation and you get that bending a wire hanger back and forth effect were after several bends the wire just breaks in two. A few thou out I would not worry about, it can run a ton of years that way. But if really out, shafts do break right at the rear of the coupling. Its the 2nd most common places to have a shaft snap, the #1 place is at the rear hub of the prop. If shaft turns freely by hand and only a little motion at low speeds...when you get to checking it you get to checking.

I mentioned mounts in regards to the original post from David...just another thing to check.

Carl

Shaft is turns easily with the boat in the water. On land, depends on bow she is chocked up. They can take a hell of a twist sometimes if the ground is not completely flat. Luckily, believe it or not I have been put in the same spot for the last 20 years. Ground is hard sand but pretty level. Not perfect but what are you going to do, Nature is nature.

Tony Meola wrote:Carl

Shaft is turns easily with the boat in the water.

Tony - Unless your in the habit of running your boat on land, I would not worry to much about it.





Maiden Voyage...

Carl

That is a familiar sight. We are about a half mile from the mouth of Forked River on Barnagat Bay. On weekends the speed boat crowd hits sone of the dockside bars on the river. On their runs home at night, they have a tendency to put their boats up in the marsh. One guy managed to put a 40 foot cruiser a good 25 yards up into the marsh. You should have seen the path he made in the mud.

Took two weeks for them to figure out how to drag him back out without destroying everything.