Reply
 
Thread Tools Search this Thread Display Modes
 
Old 10-15-2016, 04:34 PM   #1
Veteran Member
 
scott2640's Avatar
 
City: Rochester, NY
Join Date: Sep 2016
Posts: 46
Stretch my prop shaft

I've been keeping an eye online for various components for my build. I came across a prop shaft about 12" shorter than ideally need.

It could work but I would have to slide the engine back almost right to the bulkhead. It would make it tight in that area if something needed maintenance.

I'm talking about a couple grand in savings for this shaft which is in excellent condition so I would love to make it work.

Anybody have any ideas about how to gain some length to the shaft or am I out of luck?
__________________
A ship is safe in the harbor, but that is not what ships are for.

www.seadreamerproject.com
www.youtube.com/c/SixPointsWoodWorks
scott2640 is offline   Reply With Quote
Old 10-15-2016, 05:03 PM   #2
Ted
Guru
 
Ted's Avatar
 
City: Campbell River
Vessel Name: Okisollo
Join Date: Apr 2012
Posts: 783
Use a "muff coupling", as it's in the engine room you
should be able to use steel shafting for the needed extension.

Ted
Ted is online now   Reply With Quote
Old 10-15-2016, 05:41 PM   #3
Guru
 
Nomad Willy's Avatar
 
City: Concrete Washington State
Vessel Name: Willy
Vessel Model: Willard Nomad 30'
Join Date: Oct 2007
Posts: 18,743
Ted is that the kind that has two halves that are screwed together like a clamp w opposing socket head cap screws?
__________________
Eric

North Western Washington State USA
Nomad Willy is offline   Reply With Quote
Old 10-15-2016, 07:23 PM   #4
Ted
Guru
 
Ted's Avatar
 
City: Campbell River
Vessel Name: Okisollo
Join Date: Apr 2012
Posts: 783
Quote:
Originally Posted by Nomad Willy View Post
Ted is that the kind that has two halves that are screwed together like a clamp w opposing socket head cap screws?
Yes, and keyed as well, although I have used one that wasn't keyed

Ted
Ted is online now   Reply With Quote
Old 10-15-2016, 10:04 PM   #5
Senior Member
 
cool beans's Avatar
 
City: Norfolk, VA
Vessel Model: Bayliner 3870
Join Date: Jul 2015
Posts: 308
What about something like an Aqua drive CV shaft?
cool beans is offline   Reply With Quote
Old 10-15-2016, 10:16 PM   #6
Ted
Guru
 
Ted's Avatar
 
City: Campbell River
Vessel Name: Okisollo
Join Date: Apr 2012
Posts: 783
Quote:
Originally Posted by cool beans View Post
What about something like an Aqua drive CV shaft?
To use that you will need a thrust bearing mounted in the boat to take the load
(push) from the prop. I don't think it would be an easy refit. I installed an Aqua-Drive once.

Ted
Ted is online now   Reply With Quote
Old 10-16-2016, 07:46 AM   #7
Veteran Member
 
scott2640's Avatar
 
City: Rochester, NY
Join Date: Sep 2016
Posts: 46
It a brand new build so I can put anything anywhere, blank canvass so to speak.

The muff coupling may be perfect. What does the aqua drive do?
__________________
A ship is safe in the harbor, but that is not what ships are for.

www.seadreamerproject.com
www.youtube.com/c/SixPointsWoodWorks
scott2640 is offline   Reply With Quote
Old 10-16-2016, 08:17 AM   #8
Guru
 
TDunn's Avatar
 
City: Maine Coast
Vessel Name: Tortuga
Vessel Model: Nunes Brothers Raised Deck Cruiser
Join Date: Feb 2015
Posts: 889
The problems with a coupler as I see them are.

1. You have to get the short shaft segment properly aligned to the rest of the shaft. That should be done in a lathe.

2. Cost. I don't know how much couplers cost but I do know that ideally you will have to get the short shaft segment made up with a broached slot in it which will cost a few bucks.

3. Long term stability. You have to be certain that the coupler fits both the existing shaft and the short piece tightly and can be adequately tightened. Otherwise it will loosen up over time (lots of vibration in a prop shaft) and your alignment will go.

4. Is the shaft you have long enough to clear the packing and have room for the coupler?

I would look into having an extension welded onto the shaft. A good welder can make the extended shaft as strong the original. If you go this route do have the welded shaft inspected to make sure the welds are full penetration with no voids.
TDunn is offline   Reply With Quote
Old 10-16-2016, 09:24 AM   #9
Guru
 
foggysail's Avatar
 
City: Ashland, MA
Vessel Model: 1990 Silverton 40 aftcabin
Join Date: Jul 2016
Posts: 1,208
I would be concerned with the dynamic balance after adding any type of splicing device
foggysail is offline   Reply With Quote
Old 10-16-2016, 10:09 AM   #10
Technical Guru
 
Ski in NC's Avatar
 
City: Wilmington, NC
Vessel Name: Louisa
Vessel Model: Custom Built 38
Join Date: Jan 2014
Posts: 6,194
I would do none of the splices, extensions, welds, etc. You have lots of time left before you need a shaft. Just keep your eyes open for one that a little longer than what you think you need. One will pop up somewhere.

You will not know actual length until hull is done and engine set. And you won't know actual engine location accurately until you layout the whole engine room. Sometimes it helps to scoot engine a little fore or aft for various reasons, you want to retain that flexibility.

What dia and what length are we talking about?

You don't want to do a new build and have obvious cobbled together bits on something as critical as the shaft line, even if it is harmless. Kind of like a zit on the nose of a pretty girl.
Ski in NC is offline   Reply With Quote
Old 10-16-2016, 10:32 AM   #11
Guru
 
GoneFarrell's Avatar
 
City: Columbia City, OR & Mulege, BCS
Vessel Name: Imagine
Vessel Model: Farrell 34
Join Date: Oct 2015
Posts: 849
scott,
Search McMaster Carr for shaft couplings. You will see that a 2" dia 2-piece coupling in steel is around $250 and is good for around 1000 ft-lbs of torque. Stainless ones are 2X the $$ and about 1/2 the load capacity because of lower yield point in SST.

There is a lot of torque-ripple on a propshaft, meaning you should have a safety factor of at least 4 vs. "normal" running torque, whatever that is on your boat, because this part is a mission-critical part like a propeller or the joint to the transmission.

Keep shopping for a single-piece and maybe put out a "wanted/bids" ad if you know the specs for the shaft. Have fun!
GoneFarrell is offline   Reply With Quote
Old 10-16-2016, 11:04 AM   #12
Guru
 
foggysail's Avatar
 
City: Ashland, MA
Vessel Model: 1990 Silverton 40 aftcabin
Join Date: Jul 2016
Posts: 1,208
Quote:
Originally Posted by Ski in NC View Post
I would do none of the splices, extensions, welds, etc. You have lots of time left before you need a shaft. Just keep your eyes open for one that a little longer than what you think you need. One will pop up somewhere.

You will not know actual length until hull is done and engine set. And you won't know actual engine location accurately until you layout the whole engine room. Sometimes it helps to scoot engine a little fore or aft for various reasons, you want to retain that flexibility.

What dia and what length are we talking about?

You don't want to do a new build and have obvious cobbled together bits on something as critical as the shaft line, even if it is harmless. Kind of like a zit on the nose of a pretty girl.

RIGHT ON!!

A 1 1/2" X 10' new shaft can be had for about $1K from Deep Blue Yacht Supply. A 2" shaft is twice that amount. All shaft machining are guaranteed to be true to within 0.0005."

I still remember an old Ford I owned whose driveshaft had a tiny, tiny bend in it. The car could not go over 40mph due to vibration. What will the OP do if he goes ahead with a shaft extension only to find vibration that will kill the cutless bearing?
foggysail is offline   Reply With Quote
Old 10-16-2016, 11:26 AM   #13
Guru
 
foggysail's Avatar
 
City: Ashland, MA
Vessel Model: 1990 Silverton 40 aftcabin
Join Date: Jul 2016
Posts: 1,208
There is an assortment of shafts over on Ebay for less than $1K
foggysail is offline   Reply With Quote
Old 10-16-2016, 12:04 PM   #14
Guru
 
psneeld's Avatar
 
City: Ft Pierce
Vessel Name: Sold
Vessel Model: Was an Albin/PSN 40
Join Date: Oct 2011
Posts: 28,149
Out of all the professional advice I have had relayed to me or have read....this one is my favorite.....

"For heaven' sake ... why do these guys keep overcomplicating stuff so friggin much?

Have a machine shop make up a 12" intermediate shaft with flanges to match the existing items. It just bolts in place between the gearbox and the existing shaft flange."
psneeld is online now   Reply With Quote
Old 10-16-2016, 02:07 PM   #15
Guru
 
Join Date: Oct 2007
Posts: 1,121
What am I missing? In order to save $1K on the correct length shaft, you would consider spending $1K to add a reasonable extension per suggestions.
Chrisjs is offline   Reply With Quote
Old 10-16-2016, 02:15 PM   #16
Technical Guru
 
Ski in NC's Avatar
 
City: Wilmington, NC
Vessel Name: Louisa
Vessel Model: Custom Built 38
Join Date: Jan 2014
Posts: 6,194
Quote:
Originally Posted by psneeld View Post
Out of all the professional advice I have had relayed to me or have read....this one is my favorite.....

"For heaven' sake ... why do these guys keep overcomplicating stuff so friggin much?

Have a machine shop make up a 12" intermediate shaft with flanges to match the existing items. It just bolts in place between the gearbox and the existing shaft flange."
I've made those in my shop. I doubt I would do it for under $1k. The accuracy on flange face concentricity and parallelism has to be dead nuts or you will get a shake. Not a trivial fab job.
Ski in NC is offline   Reply With Quote
Old 10-16-2016, 02:33 PM   #17
Guru
 
Nomad Willy's Avatar
 
City: Concrete Washington State
Vessel Name: Willy
Vessel Model: Willard Nomad 30'
Join Date: Oct 2007
Posts: 18,743
Scott,
To expand on what Ski wrote ..
Go to places where they make up prop shafts like boat shops and machine shops that regularly make up boat shafts. Soon you will probably find someone w a shaft a bit longer than you want that can be made to fit your boat easily. They will probably take your shaft in trade. Some shafts are made out of better, more expensive metal.

The Aqua Drive is the best way to drive a boat IMO. Look it up w a web search.

But a good coupling is excellent. And be aware that there is no such thing as a straight shaft. If you have several new shafts all can be tested for varying degrees of straightness. But none will ever be perfectly straight. .002" is considered straight .. as I recall. And a different degree of "straightness" will be required for various applications, lengths and dia of shaft ect.

Like Ted I installed an Aqua Drive and consider it a challanging undertaking. One needs to install a sort-of bulkhead to mount the AD to and this needs to be done very accurately. Not easy but often shims or washers can be used to fix mistakes. I know about that.
__________________
Eric

North Western Washington State USA
Nomad Willy is offline   Reply With Quote
Old 10-16-2016, 02:55 PM   #18
Guru
 
Nomad Willy's Avatar
 
City: Concrete Washington State
Vessel Name: Willy
Vessel Model: Willard Nomad 30'
Join Date: Oct 2007
Posts: 18,743
Scott,
The Aqua Drive is a thrust bearing. The installer builds a bearing holder, mounting platform or whatever you want to call it but it needs to take the thrust of the engine w gear and prop. Also it meeds to hold the shaft in place laterally and vertically. The AD bearing needs to be mounted so as not to transfer much shaft vibration to the hull of the boat or the much of reasons for installing the AD would be compromised.
The shaft aft of the AD bearing will be permantly mounted in the boat and perfectly aligned to the cutlass bearing. Unless the hull gets tweeked, bent or otherwise deformed the prop shaft will never need to be aligned again. In theory anyway.
Then ahead of the AD thrust bearing and between the gear output flange and the input flange of the AD bearing the AD provides a CV joint. Just like on the front end of your car. This allows the engine to be able to move (within limits) any way it wants from vibration. Also all the thrust of the prop is taken by the AD thrust bearing so this relives the trans thrust bearing from that duty. Not that it matters but aft trans seals could last linger ??

Since the engine is no longer shaking the prop shaft the prop shaft no longer shakes the boat. And more importantly the engine can (and usually is) mounted on much softer engine mounts. And the engine mounts no longer need to absorb the thrust of the prop. So they can be designed to move in ways regular engine mounts are extremely limited.

More money but clearly a better way to go ... IMO ..
__________________
Eric

North Western Washington State USA
Nomad Willy is offline   Reply With Quote
Old 10-16-2016, 02:59 PM   #19
Guru
 
psneeld's Avatar
 
City: Ft Pierce
Vessel Name: Sold
Vessel Model: Was an Albin/PSN 40
Join Date: Oct 2011
Posts: 28,149
Quote:
Originally Posted by Ski in NC View Post
I've made those in my shop. I doubt I would do it for under $1k. The accuracy on flange face concentricity and parallelism has to be dead nuts or you will get a shake. Not a trivial fab job.
Good to know, thanks Ski...but like a lot of projects...

What is handy...materials or professional services, etc....and what can it be done for.....

In the end...to me at least...what is the most practical, cheapest, easiest way for me to accomplish a project. Those 3 become a balancing act.

If the short shaft and flanges are that much...it probably would bump me into the right sized shaft depending on all costs of course.

Then again...like they say....friends in low places ....who might make one up for a deal.....just throwing out an idea that was passed along for the typical DIYer.
psneeld is online now   Reply With Quote
Old 10-16-2016, 03:30 PM   #20
TF Site Team
 
Larry M's Avatar
 
City: Jacksonville
Join Date: Nov 2008
Posts: 11,682
Quote:
Originally Posted by Nomad Willy View Post
...The Aqua Drive is the best way to drive a boat IMO. Look it up w a web search...
Sounds impressive but the price..? Your right more money. From their web site it looks like $1500 to $2300 plus the installation costs for Hobo. As far as increasing transmission life. We're rebuilding ours now but only for PM at 8400 hours. Call me old fashion and one who likes simple but I'll pass.
Larry M is offline   Reply With Quote
Reply

Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


» Trawler Port Captains
Port Captains are TF volunteers who can serve as local guides or assist with local arrangements and information. Search below to locate Port Captains near your destination. To learn more about this program read here: TF Port Captain Program





All times are GMT -5. The time now is 08:41 PM.


Powered by vBulletin® Version 3.8.8 Beta 4
Copyright ©2000 - 2024, vBulletin Solutions, Inc.
Search Engine Optimization by vBSEO 3.6.0
Copyright 2006 - 2012