Prop Strut Bent or Intentionally Offset?

[Evan Burkosky]

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!

[GILow]

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

[Evan Burkosky]

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.

[Pete7]

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

[Evan Burkosky]

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?

[GordMay]

See also ➥ http://www.cruisersforum.com/forums/...ard-60965.html

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.”

[Evan Burkosky]

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:

[GordMay]

Originally Posted by Evan Burkosky

... 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.

[nigel1]

As Gordon suggests, that is almost certainly damage and not design.
Looks like the P bracket has been knocked over to the starboard.

[Evan Burkosky]

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!

[keepondancin]

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.

[Minggat]

Originally Posted by Pete7

....... 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.

[GordMay]

BTW: Sparkman & Stephens designed a number of 30 footers. Do you know which make/model you have?
➥ Sailboat Designs of Â*Sparkman & Stephens by LOA

[Chuck Hawley]

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

[fstbttms]

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