Flex coupler for inboard

Designs for inboard or outboard power

Moderator: BruceDow

cusoak
Posts: 928
Joined: Sat Dec 26, 2009 8:49 am
Location: Senecaville Ohio

Flex coupler for inboard

Postby cusoak » Tue Aug 23, 2016 4:49 am

I am looking into putting in a flex coupler in my 1966 Cenruty Resorter 17ft mahogany boat with a 318 Chrysler.
I had a shaft break in the coupling.
I think that I have read here that some of the people building inboards have used them.
Would like to get some imput on what you have used and cost.
Thanks Jeff

Hooked
Posts: 22
Joined: Thu Jan 29, 2015 12:33 pm
Location: Lafayette, La.

Re: Flex coupler for inboard

Postby Hooked » Tue Aug 23, 2016 5:09 am

Hi cusoak,

I installed an R & D flex coupling from PYI, Inc. on a 40' sailboat that we sailed from Los Angeles to New Orleans. Never had any problems and the folks at PYI were very helpful. They have models for power boats also. Just pick the model of your gearbox and it will tell you which one to buy.
Also reduced zinc consumption, if your boat stays in the water. Google "R & D Flex Couplings".
Good luck,
Kelvin
Building a modified Ski King

User avatar
Roberta
Posts: 5946
Joined: Tue Jul 31, 2007 5:23 pm
Location: East Troy, Wisconsin

Re: Flex coupler for inboard

Postby Roberta » Tue Aug 23, 2016 5:27 am

I'm using the Globe Drivesaver. It installs easy as the counter bored bolts attach to the transmission flange and then the prop shaft hub gets bolted to the drive saver. Very smooth operating so for after about 25 hrs.

Roberta
Attachments
Prop shaft in 001.JPG
Roberta "Queen of the Boat Builders"
Built Zip "Oliver IV", Super Spartan "Jimmy 70", and Torpedo "The Glen L".

User avatar
kens
Posts: 4445
Joined: Wed Nov 12, 2003 5:25 pm
Location: Coastal Georgia

Re: Flex coupler for inboard

Postby kens » Tue Aug 23, 2016 7:20 am

I have a Globe drivesaver.
Oak is over rated, everything about it takes extra time; then it warps, splits or checks !!! :roll:

User avatar
Bill Edmundson
Posts: 10446
Joined: Wed Nov 23, 2005 6:45 am
Location: Birmingham, AL, USA
Contact:

Re: Flex coupler for inboard

Postby Bill Edmundson » Tue Aug 23, 2016 7:34 am

My Tahoe is hard coupled. Getting the alignment that close was a pain. You do need to check it from time to time. No problems in a little over 100 hours.

Bill
Mini -Tug, KH Tahoe 19 & Bartender 24 - There can be no miracle recoveries without first screwing up.
Tahoe 19 Build

User avatar
Roberta
Posts: 5946
Joined: Tue Jul 31, 2007 5:23 pm
Location: East Troy, Wisconsin

Re: Flex coupler for inboard

Postby Roberta » Tue Aug 23, 2016 7:46 am

Bill is right about the alignment being a pain. It is very important to get the alignment as close as possible to reduce vibration and subsequent wear. The Globe has some tolerance, but can fail if the fit is out of tolerance. I set mine up at about 0.002" when metal to metal. I did all the adjusting before the bolt holes were drilled in the motor mount pads. Then the drivesaver was installed after everything was aligned and bolted down. So far so good.

Roberta :D
Roberta "Queen of the Boat Builders"
Built Zip "Oliver IV", Super Spartan "Jimmy 70", and Torpedo "The Glen L".

Brian
Posts: 171
Joined: Mon Feb 18, 2013 10:06 pm
Location: Hawaii

Re: Flex coupler for inboard

Postby Brian » Mon Oct 03, 2016 10:38 am

I've been wondering about these myself, hoping to get a little relief from the metal-to-metal aligning process. Maybe not? In any case the Globe Drivesaver looks pretty thick. Did you cut your prop shaft at the coupler end to allow for that width, or did you size the shaft length for the Drivesaver when you first ordered the shaft? I've gotten some advice on these that they're mainly for commercial boats that might hit logs, etc., as a breakaway, and not really to make up for slight misalignment or to reduce vibration. I'm probably ordering my shaft this week (Monte Carlo with an Ilmor 430), so it's very timely.

User avatar
Roberta
Posts: 5946
Joined: Tue Jul 31, 2007 5:23 pm
Location: East Troy, Wisconsin

Re: Flex coupler for inboard

Postby Roberta » Mon Oct 03, 2016 11:21 am

Not sure if the Drive Saver is solely for commercial use. Many of us builders are using them, or something similar. What I like about it is that it is bolted to the output flange on the transmission first, using nuts, washers, and bolts. Then the prop shaft flange is bolted to it using only the bolts and lock washers. This makes the installation very easy not having to use two wrenches. The unit is only about 1" thick.

I used a stainless steel tube, in place of the prop shaft, to fit everything up and get the proper measurements. Then I ordered the shaft a bit longer. Once the proper length was determined, with the Drive Saver in place, I had the shaft sized and fitted to the prop and drive hub. Keys ways and keys were cut and the prop lapped in to the shaft.

Roberta
Roberta "Queen of the Boat Builders"
Built Zip "Oliver IV", Super Spartan "Jimmy 70", and Torpedo "The Glen L".

Brian
Posts: 171
Joined: Mon Feb 18, 2013 10:06 pm
Location: Hawaii

Re: Flex coupler for inboard

Postby Brian » Mon Oct 03, 2016 12:16 pm

So this is a critical moment for me then. To use Drivesaver or not. Are there HP limits? Where did you get yours?
Brian

User avatar
steveh41
Posts: 570
Joined: Mon Jun 14, 2010 7:16 pm
Location: Catheys Valley, CA
Contact:

Re: Flex coupler for inboard

Postby steveh41 » Mon Oct 03, 2016 2:22 pm

Brian,

I have PYI flex couplings on main (250 hp @ 2200 rpm) and aux (40 hp @ 2800 rpm) engines... these were recommended and supplied by the shop that machined the driveshafts and fitted the couplers and props. You can check the PYI website for hp and torque limits and dimensions for the different models. You don't want to depend on the flex to compensate for misalignment though... you should still try to be within a few thousandths of straight on. Using a length of straight tubing to align the drivetrain as Roberta suggests is a great way to minimize shaft sag while you're trying to get everything to line up. Having said that, (I've heard) hard coupling works great when it's set up correctly and there's no significant flex to worry about in a wood hull as compared to FG.

Steve
The longest journey begins with a single step… then repeat as necessary!

bob smith
Posts: 487
Joined: Thu Aug 21, 2008 6:59 am
Location: Chester, SC

Re: Flex coupler for inboard

Postby bob smith » Mon Oct 03, 2016 3:09 pm

I used Globe Drivesavers in the past but not currently. They will not correct misalignment but can suppress some noise and vibration. The really nice thing is they electrically isolate the prop and shaft from the rest of the boat.
Bob Smith
Chester, SC

User avatar
Roberta
Posts: 5946
Joined: Tue Jul 31, 2007 5:23 pm
Location: East Troy, Wisconsin

Re: Flex coupler for inboard

Postby Roberta » Mon Oct 03, 2016 3:20 pm

Not sure on the HP ratings. They list torque ratings in the application guide. I'm running a 330 hp Crusader 5.7 MPI through a Velvet Drive Liberty A 8 deg. down angle transmission with 1:1 ratio. 13x13 four blade OJ prop. I used the blue one which is rated higher than the red one. The red one probably would have been fine. For the life of me, I don't remember where I bought it. At the time I thought the Blue one was the correct one for the size of my motor. Not sure if they changed things in the specs.

Roberta
Roberta "Queen of the Boat Builders"
Built Zip "Oliver IV", Super Spartan "Jimmy 70", and Torpedo "The Glen L".

User avatar
steveh41
Posts: 570
Joined: Mon Jun 14, 2010 7:16 pm
Location: Catheys Valley, CA
Contact:

Re: Flex coupler for inboard

Postby steveh41 » Mon Oct 03, 2016 4:31 pm

The PYI website flexible coupler calculator gives a part number based on the engine hp at rated rpm for a given transmission gear ratio and type... this takes into account the torque to be handled at the prop shaft without me getting confused! :lol:

Steve
The longest journey begins with a single step… then repeat as necessary!

User avatar
Roberta
Posts: 5946
Joined: Tue Jul 31, 2007 5:23 pm
Location: East Troy, Wisconsin

Re: Flex coupler for inboard

Postby Roberta » Mon Oct 03, 2016 5:11 pm

The PYI unit looks to be able to tolerate more dis-alignment, but it would be about 3/4" thicker (1.77" long)than the Globe, which is 1" thick. The Globe needs to be within 0.005" and the PYI says up to 0.010" out. I don't think I would want to run that far out. The PYI will need two wrenches on the bolting when attaching the prop flange, where the Globe needs only one. This would have been an issue for me with the down angle transmission. Both units look good, though.

Roberta :D
Roberta "Queen of the Boat Builders"
Built Zip "Oliver IV", Super Spartan "Jimmy 70", and Torpedo "The Glen L".


Return to “Power Boats”

Who is online

Users browsing this forum: Majestic-12 [Bot] and 12 guests