Prop shaft alignment on the hard vs on water

[kito]

Well, time for my next question I sure have appreciated all the good info I have gotten here. Anyway, my buddy and I spend most of last saturday afternoon trying to get the new strut, shaft log and prop shaft aligned with not much success. This boat has been on the hard for at least the last 10 years. Am I just spinning my wheels trying to align while still on the hard? I heard that the hull would have to settle while on the water to accurately do the alignment. Can I at least align the shaft log, prop and skeg on the hard? I can align the engine to the coupling when it's on the water for a few weeks. Right now, when we had the log, prop shaft and skeg aligned dead nuts, the engine would not align height wise on the aft end.......too tall even with the adjustment screw all the way down. Seems to me the hull would relax after getting the weight off the keel and line up right. I am off about 1/4" .....does this sound about right?

 

[Don S/V ILLusion]

Don't waste your time trying toget it right on a boat which has been out that long. Even if you get it right now, it's likely to drastically change after its floating a while.

 

[kito]

Don't waste your time trying toget it right on a boat which has been out that long. Even if you get it right now, it's likely to drastically change after its floating a while.

I was just hoping the cutless bearing and shaft log could be aligned on the hard so I would not need a haul out after a few weeks to align those items. May be no way around it though.

 

[kloudie1]

The check to complete before launch is to make sure that when the shaft is centered in the log, it is not binding in the Cutless. once in the water, you can do the engine alignment to the shaft while the shaft is blocked to the center of the log.

 

[Anonymous 121765]

Kito,

Take heed what Don & Kloudie recommend. Boats on stands will flex.

The shaft can be in place (check to see if it is straight), just don't connect the flanges until in the water. Hopefully, the engine has not been moved. If unsure, find a marine mechanic for alignment.

CR

 

[Maine Sail]

1/4" is HUGE.. I would suspect something is not right with the new strut, like it is perhaps longer?

I have aligned hundreds of boats, replaced a pile of shafts and couplings & replaced struts. I always get the alignment as close as I can on the hard. In hundreds of vessels the worst change I have seen from on land to on the hard was approx 0.012" (a late 80's Hunter).. I still wait two weeks, under full rig tension, for the final minor adjustment. Even then I often see a 0.001 - 0.005" difference between on the hard and in the water. Many boats are less than a 0.001" change. You are talking .25", not .003", which is HUGE!!

Doing the heavy lifting should not be done in the water or you can easily lose sight of the cutlass and stern tube clearances (you can't see them). Get it as good as you can on land and make final small adjustments after the rig has taken a set. Boat builders do this every day and the dealer only makes final tweaks... If your vessel moves 1/4", at the coupling, then something is not right..

Many boats don't move at all..... The Cherubini has a thick hull so something is not right..

 

[kito]

MS, I may have mis-spoke about the 1/4". I had to lift up the prop shaft about a 1/4" to align with the engine coupling. Problem is the aft mounts are down all the way already. With the shaft mated I see compression on the cutless bearing top front and bottom rear. Which means it needs to rotate a bit. We first aligned the log with the strut using a cutless bearing that fit good inside the log. We tweeked the strut until the shaft was centered to the skeg and the shaft spun without resistance. I figured the engine could be adjusted to mate but didn't think I would run out of height adjustment. Looks like I need to rotate the strut up to add more angle to the shaft and raise my shaft log. It's a Vee shaped strut and is up as far as it will go. Looks like rotation is my only option. A days work needs to be redone....oh well. At least I learned something.

 

[jibes138]

MS, I may have mis-spoke about the 1/4". I had to lift up the prop shaft about a 1/4" to align with the engine coupling. Problem is the aft mounts are down all the way already. With the shaft mated I see compression on the cutless bearing top front and bottom rear. Which means it needs to rotate a bit. We first aligned the log with the strut using a cutless bearing that fit good inside the log. We tweeked the strut until the shaft was centered to the skeg and the shaft spun without resistance. I figured the engine could be adjusted to mate but didn't think I would run out of height adjustment. Looks like I need to rotate the strut up to add more angle to the shaft and raise my shaft log. It's a Vee shaped strut and is up as far as it will go. Looks like rotation is my only option. A days work needs to be redone....oh well. At least I learned something.

didnt you replace your motor mounts recently and comment the flanges were much thinner? Maybe that is where you lost height? Perhaps shims under the mounts will fix it?

 

[kito]

Yes, I installed new motor mounts and the feet are thinner but the stud heights are the same. I believe it's the strut angle thats off. I modeled a quick assembly of the shaft and strut on my Pro/e CAD system at work and a 1/2 degree rotation on the shaft will raise the coupling end about 3/8". I am thinking rotating the strut 1 degree will do the trick and will leave me some down adjustment too.

 

[rardiH36]

Kito:

I decided to participate in this thread because I recently had to replace my cutlass bearing ... and we have same vintage (although different models) of Cherubini Hunters. Post #10 of the below thread has a detailed description of my strut replacement.

http://forums.hunter.sailboatowners.com/showthread.php?p=1123679&highlight=cutlass

In my case, when I first fitted my new "exact replacement" strut through the shaft, and then dry pressed it up to the mating surface of my boat's hull, the binding was so severe that shaft wouldn't rotate by hand. So modification for the final fitting was needed as I describe in my linked post. While your V-shaped strut mounting might not be so extremely off as mine initially was, my first impression when reading your accounts is that your most probable cause is that your new strut is not of compatible size for a direct replacement fit, or it has been positioned wrong. The recount of my experience in the linked thread might give you an idea or two to follow-up on.

Not sure about your boat, but I am confused about the shaft log being part of the adjustment process. On my boat, the shaft log is a piece of special-purpose hose which is clamped to the stern tube fitting on the aft end and into which the stuffing box is clamped on the forward end. If the shaft/coupling isn't supported between the stuffing box and the coupling, maybe the shaft will droop down a bit because the log hose does flex, but the log on my boat is not really "adjustable" in respect of the alignment procedure. Primarily your new strut has to be the right height and correct angle in all directions so the shaft goes through the center of the stern tube (hence also through the very center of the log hose and stuffing box), and then the coupling must match up exactly to the engine's transmission plate. The shaft should rotate freely with no binding and the shaft should pass evenly through the cutlass bearing with no obvious pressure on any side.

I would think if you don't achieve this before launching, it's probably too out of whack to expect that another engine alignment after launch will fix.

I would get all perfectly aligned before launching. Then again after launching before you use the engine too much.

 

[tommays]

Having started with a really bad original job going back to the 1970 build there was NO WAY the strut and shaft log were EVER RIGHT which kind off explained the badly worn cutlass bearings

That being said it did work for 40 years and it was not super obvious until i tried to put in new parts and it was NOT possible



In simple terms .090 at the rear base of the strut changes the height of a motor with a 4' prop shaft about 1" so the the mistake does not have to be big to make a big problem



all is well these days but without a lot of work it would have never been right





i cant speak for other boat but the Cal 29 is crazy (more than 1" solid glass) thick in that area and does NOT flex

 

[kito]

Thanks for the link Rardi. I will read through it. My strut has vee shaped tangs and not a flat flange like yours. Makes it hard to do any shimming. Maybe I named it wrong but I call the shaft log the metal fitting that goes through the hull and is attached to the stuffing box hose. It is a part of my alignment because I installed a new one. I want the shaft to have equal clearance though it. My strut is oem made by Damher. I believe my only option to raise the height at the coupling is to rotate the strut up a tiny bit. The log will have to be shimmed under to top flange to match the angle the shaft is coming through so to have equal clearance.