Cruisers Forum
 


Join CruisersForum Today

Reply
 
Thread Tools Rate Thread Display Modes
Old 01-02-2016, 02:38   #1
Registered User

Join Date: Dec 2015
Location: Japan
Boat: Sparkman & Stephens 30'
Posts: 22
Prop Strut Bent or Intentionally Offset?

Hi everyone, I've recently purchased an S&S 30. The previous owner is unavailable to answer my various questions and I know little about it's history. It appears to have a bent prop shaft strut, but before I pull it out to straighten I'd like to double check that it's actually bent through misuse and not intentionally offset so that the shaft will clear the skeg for easy removal.

Can anyone familiar with this hull design comment? Should be the same setup on all S&S 30 based hulls including the Yankee 30, Tartan 30, Aqua 30, Pearson Johnson 30, SHE D 30 etc.

You can see pics and a video on my blog here: Bent Prop Shaft Strut Sparkman & Stephens 30' Restoration

Any help would be much appreciated, thank you!
__________________

__________________
Evan Burkosky is offline   Reply With Quote
Old 01-02-2016, 04:24   #2
Bailing as fast as I can.
 
GILow's Avatar

Join Date: Sep 2008
Location: Adelaide, South Australia
Boat: Swanson 42
Posts: 3,585
Prop Strut Bent or Intentionally Offset?

I am 99% sure someone asked exactly the same question a while back. I can't remember the outcome but a bit of searching might find it for you (unless you are using the CF app in which case a LOT of searching will maybe find it for you). If it was the same question the it does suggest it was by design.

I wish I had read the whole thread.


Sent from my iPad using Cruisers Sailing Forum
__________________

__________________
Very funny Scotty, now beam down my clothes.
http://www.swansonsailor.id.au
GILow is offline   Reply With Quote
Old 01-02-2016, 04:28   #3
Registered User

Join Date: Dec 2015
Location: Japan
Boat: Sparkman & Stephens 30'
Posts: 22
Re: Prop Strut Bent or Intentionally Offset?

GILow,

Thanks for the tip! I didn't find that thread with an initial search, but I'll have another go. Good to know someone else had the same question.
__________________
Evan Burkosky is offline   Reply With Quote
Old 01-02-2016, 04:41   #4
Moderator
 
Pete7's Avatar

Cruisers Forum Supporter

Join Date: Aug 2009
Location: Solent, England
Boat: Moody 31
Posts: 8,562
Images: 14
Re: Prop Strut Bent or Intentionally Offset?

I think you will find that it's not bent but slightly offset so the shaft can be removed past the rudder. Mine is also like that. This and a propellor turning in one direction porbably adds up to the prop wash experienced which can be really useful sometimes.

Pete
__________________
Moody 31 - April Lass
Pete7 is offline   Reply With Quote
Old 01-02-2016, 04:52   #5
Registered User

Join Date: Dec 2015
Location: Japan
Boat: Sparkman & Stephens 30'
Posts: 22
Re: Prop Strut Bent or Intentionally Offset?

Hi Pete7, thanks for the reply. Is your boat also one of the S&S designs with the same rudder skeg? It makes sense that it would be offset a bit to get past the skeg. Sounds like you're also saying it's offset to counter prop walk?

That would make sense. It's bent about a half inch to starboard. Would that be the correct side to offset it to to counter prop walk?
__________________
Evan Burkosky is offline   Reply With Quote
Old 01-02-2016, 06:06   #6
Moderator Emeritus
 
GordMay's Avatar

Join Date: Mar 2003
Location: Thunder Bay, Ontario - 48-29N x 89-20W
Boat: (Cruiser Living On Dirt)
Posts: 31,583
Images: 240
Re: Prop Strut Bent or Intentionally Offset?

See also ➥ Right Rotating Prop with Propeller Shaft Offset to Starboard

From Eric W. Sponberg, Naval Architect:
... A port moment (shaft line to port) will cause a turning moment to starboard. Therefore, a clockwise propeller should be offset to port, and a counter-clockwise propeller should be offset to starboard.
__________________
Gord May
"If you didn't have the time or money to do it right in the first place, when will you get the time/$ to fix it?"



GordMay is offline   Reply With Quote
Old 01-02-2016, 07:14   #7
Registered User

Join Date: Dec 2015
Location: Japan
Boat: Sparkman & Stephens 30'
Posts: 22
Re: Prop Strut Bent or Intentionally Offset?

GordMay, thank you for the info on offset in regards to prop rotation. This boat actually has a RH (clockwise) rotating prop, so it seems the offset should be to port, not starboard as it is now. The engine and transmission were changed several years ago by the PO, so perhaps the prop rotation was also changed at that time?

At any rate, even if the strut is supposed to be offset, should it be offset via a gentle curve the length of the strut? Wouldn't the strut normally be straight but the bracket where it joins the hull slightly offset? Furthermore, shouldn't the propshaft be centred in the shaft log? Currently the shaft is offset so far to starboard that it appears to rub slightly on the inside starboard wall of the shaft log.

I've attached a couple of pics that show the curve of the strut and offset of shaft through shaft log:



__________________
Evan Burkosky is offline   Reply With Quote
Old 01-02-2016, 07:18   #8
Moderator Emeritus
 
GordMay's Avatar

Join Date: Mar 2003
Location: Thunder Bay, Ontario - 48-29N x 89-20W
Boat: (Cruiser Living On Dirt)
Posts: 31,583
Images: 240
Re: Prop Strut Bent or Intentionally Offset?

Quote:
Originally Posted by Evan Burkosky View Post
... Wouldn't the strut normally be straight but the bracket where it joins the hull slightly offset? Furthermore, shouldn't the propshaft be centred in the shaft log? Currently the shaft is offset so far to starboard that it appears to rub slightly on the inside starboard wall of the shaft log...
I agree with your observations, suggesting your example is damage, not design.
__________________
Gord May
"If you didn't have the time or money to do it right in the first place, when will you get the time/$ to fix it?"



GordMay is offline   Reply With Quote
Old 01-02-2016, 07:32   #9
Moderator
 
nigel1's Avatar

Cruisers Forum Supporter

Join Date: Oct 2009
Location: Manchester, UK
Boat: Beneteau 473
Posts: 5,193
Re: Prop Strut Bent or Intentionally Offset?

As Gordon suggests, that is almost certainly damage and not design.
Looks like the P bracket has been knocked over to the starboard.
__________________
Nigel
Beneteau 473
Manchester, UK
nigel1 is offline   Reply With Quote
Old 01-02-2016, 07:33   #10
Registered User

Join Date: Dec 2015
Location: Japan
Boat: Sparkman & Stephens 30'
Posts: 22
Re: Prop Strut Bent or Intentionally Offset?

Thanks GordMay, good to have confirmation of my gut feeling. Further reinforcing the evidence that this is damage, the marina workers tell me she had to be towed to the marina yard as there was a rope wrapped round the prop shaft and she couldn't move under her own power.

GILow, I searched the forums again but couldn't find the other thread you mentioned. If anyone else has a link to the thread in question could you please post it? Thanks!
__________________
Evan Burkosky is offline   Reply With Quote
Old 01-02-2016, 08:33   #11
Registered User

Join Date: Nov 2005
Location: 5 Mile River
Boat: Bristol 41.1 Keep on Dancin'
Posts: 539
Re: Prop Strut Bent or Intentionally Offset?

When I did the survey on my Bristol, there was a similar situation. On close examination, there was a small crack in the strut which necessitated a new strut. Rope will do that, good thing bronze will bend, better than yanking out the bottom of the boat.
__________________
keepondancin is offline   Reply With Quote
Old 01-02-2016, 09:18   #12
Senior Cruiser
 
Minggat's Avatar

Cruisers Forum Supporter

Join Date: Apr 2008
Location: Hawaii, South Pacific bound
Boat: Islander 36
Posts: 1,221
Re: Prop Strut Bent or Intentionally Offset?

Quote:
Originally Posted by Pete7 View Post
....... This and a propellor turning in one direction porbably adds up to the prop wash experienced which can be really useful sometimes.

Pete
I believe you mean prop WALK.

A critical thing to be looking at is the engine alignment. I cannot emphasize that enough.

My prop strut is also an offset design. But the prop strut was not aligned with the shaft log. And the shaft log is the point that not the engine and the prop strut must align to.

To correct mine, removing and resetting the prop strut was a herendous job. I finally chopped off the strut right above the hub, then encased the remaining stub in fiberglass when I built a little mini keel. No more prop strut. Corrected a 43 year old manufacturing defect. And now my engine can actually be aligned correctly.

This means engine noise was radically reduced.
__________________
Minggat is offline   Reply With Quote
Old 01-02-2016, 09:22   #13
Moderator Emeritus
 
GordMay's Avatar

Join Date: Mar 2003
Location: Thunder Bay, Ontario - 48-29N x 89-20W
Boat: (Cruiser Living On Dirt)
Posts: 31,583
Images: 240
Re: Prop Strut Bent or Intentionally Offset?

BTW: Sparkman & Stephens designed a number of 30 footers. Do you know which make/model you have?
Sailboat Designs of *Sparkman & Stephens by LOA
__________________
Gord May
"If you didn't have the time or money to do it right in the first place, when will you get the time/$ to fix it?"



GordMay is offline   Reply With Quote
Old 01-02-2016, 09:40   #14
Marine Service Provider

Join Date: Sep 2011
Location: California
Boat: Alerion Express 38 Yawl
Posts: 269
Re: Prop Strut Bent or Intentionally Offset?

I'll throw in, here.

1. I would think you'd see that your engine was installed slightly "offset" if the shaft were in fact intended to be offset.

2. The fact that the shaft appears to be offset where it exits the hull is concerning. I think that supports the "bend" not "intentional" theory. Generally, you'd expect the shaft to be right down the center.

3. If a bent strut, and not intentional, it makes me wonder how they expected to pull the shaft without pulling the engine. I think the SKYE 51 has a similar issue.

4. I suspect that if you broke free the shaft coupling bolts, the two flanges would spring apart and the misalignment would be instantly obvious.

5. Cool little boats. I almost bought a Yankee 30 in the late 70s for my father.

Chuck
__________________
Chuck Hawley is offline   Reply With Quote
Old 01-02-2016, 10:09   #15
Marine Service Provider
 
fstbttms's Avatar

Cruisers Forum Supporter

Join Date: Oct 2006
Location: Under a boat, in a marina, in the San Francisco Bay
Posts: 3,594
Re: Prop Strut Bent or Intentionally Offset?

The strut on boats with offset shafts are not mounted on the centerline. Your strut is bent.
__________________

__________________
fstbttms is offline   Reply With Quote
Reply

Thread Tools
Display Modes Rate This Thread
Rate This Thread:

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


Similar Threads
Thread Thread Starter Forum Replies Last Post
Right Rotating Prop with Propeller Shaft Offset to Starboard Bets Engines and Propulsion Systems 9 17-05-2015 11:11
Prop strut movement Romanr9999 Propellers & Drive Systems 2 08-02-2014 23:00
Help with intentionally over-propping a sailboat for fuel efficency? calderp Propellers & Drive Systems 21 30-05-2013 15:36
Bent strut Wakuu Propellers & Drive Systems 0 03-01-2013 11:31
Have you ever intentionally NOT used GPS on extended offshore passage? sneuman Navigation 15 17-06-2011 12:45



Copyright 2002- Social Knowledge, LLC All Rights Reserved.

All times are GMT -7. The time now is 00:36.


Google+
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2017, vBulletin Solutions, Inc.
Social Knowledge Networks
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2017, vBulletin Solutions, Inc.

ShowCase vBulletin Plugins by Drive Thru Online, Inc.