Prop Fell Off! Help!

[Alan Wheeler]

Just lost my port prop on 10 year old FP Bahia

Yanmar did not appear very concerned.Still trying to get some form of compensation.

What?!?, on a 10yr old vessel??

[josef]

Sure. Why not?

[Alan Wheeler]

Because no one on earth (in their right mind)would give a warranty or be expected to cover a failure with SST, in saltwater, in a high stress use situation. This fault has nothing to do with a product failure due to poor design, maybe lack of maintenance on behalf of the owner. But mostly, that is the risk you take with using SST shaft in the hard working environment you use it in.
How often do you inspect your prop shaft?? I bet never. Have you had the other shaft inspected seeing as you have already had one failure?? Your shaft and drive system should be visually inspected with every annual haul out. At the point of severe wear on the bearing, the shaft should be replaced, not sleeved as I know of the odd few that have. Of course, that is my opinion of SST. Some do sleeve and get away with it. But I feel it is way too mission critical for that. But anyway, your failure is afact of life using SST. Sadly we don't have a lot of alternatives, and as long as you are using the correct grade, which would have bee done, there is little more that can be done, economically at least.

[Tropic1]

I've read through this post and find it amazing that props just fall off. Having the SD20's and folding props ($$) on my boat and I'm quite worried about loosing one (or both). You would think that the method of attaching a prop should be foolproof and not requireing locktite, etc so a bolt won't back out. The interesting thing to me is I've never heard of props falling off outboards (or any other type of drive for that matter) and those are basically the same as a saildrive, what am I missing here? They (outboards) must have a better way of attaching them. I know on my straight-shaft speedboat, the tapered shaft with key and castle nut with a cotterpin is very secure. Until this post I've never heard of this issue with the SD20, but based on the replys it's not that uncommon. Did the prop manufacturers pay off Yanmar?

[Therapy]

Originally Posted by Tropic1

I've read through this post and find it amazing that props just fall off. Having the SD20's and folding props ($$) on my boat and I'm quite worried about loosing one (or both). You would think that the method of attaching a prop should be foolproof and not requireing locktite, etc so a bolt won't back out. The interesting thing to me is I've never heard of props falling off outboards (or any other type of drive for that matter) and those are basically the same as a saildrive, what am I missing here? They (outboards) must have a better way of attaching them. I know on my straight-shaft speedboat, the tapered shaft with key and castle nut with a cotterpin is very secure. Until this post I've never heard of this issue with the SD20, but based on the replys it's not that uncommon. Did the prop manufacturers pay off Yanmar?

Ditto!
Another thing to remember during the survey.
Do the surveyors remember all this stuff??

[Ex-Calif]

I am following this thread with interest as I have a Volvo saildrive and am a bit perplexed about mechanical locking vs various "compounds" on the Yanmar drive. It seems crazy that any prop would depend on some sort of adhesive for it not to fall off - sorry if I am misinterpreting the Yanmar install - please correct my ignorance.

In looking at the pictures, it appears that the cone is threaded and then a long bolt threads into the shaft. This sets up a locking feature due to the two threads acting upon each other in tension. Then the long bolt needs to be locked because if it backs off the cone can back off. This should also be a mechanical lock independent of adhesives.

Our Vovlo uses something very similar. With the original prop the prop goes on (however it is splined) then the prop nut goes on with an external thread on the shaft. The nut is then keyed to the shaft with a shear pin which cannot come out due to a cover that is installed.

When we switched to the MaxProp the same prop nut is used but a threaded bolt is added that threads into internal threads on the shaft. This is how the drive spline is attached. Then the MaxProp itself is in two halves like a clamshell. When the clamshells are assembled around the drive spline they encapsuate the locking bolt. The halves of the prop are secured with 6 allen head bolts and cotter pins.

With the importance of having the engine option and the cost and criticality of losing a prop (or two) I will definitely put this on my list of criteria for a boat purchase.

BTW - It is also excellent advice to pull the prop yearly, inspect the shaft thoroughly for any cracking or corrosoin, paying particular attention to the threaded areas. We've had our prop off 3 times this year (don't ask - LOL)

[Jacana]

Would have to be and is a design fault.I know exactly where and when I lost a prop on my sd20 saildrive and if it wasnt for over 100ft of water between me and the prop I would not have had to pay $300 for new prop $120 for new cone $50 for nylon washer and $4 for allen keyed bolt.Apart from which at the time you do not know your prop or props have gone awol and as you can imagine if you needed to alter course stop start or reverse to avoid a marine "incident" you would be stuffed.Could someone post diagram of locking nut set up they now use instead of cone set up.I was thinking of drilling through shaft to accomodate a split pin although it will no doubt weaken shaft.Regardless of how you screw ,attach,tighten,loctite the current set up whenever you are in reverse your prop can drop off ,if that aint a design fault then santas not real.

[Ex-Calif]

Originally Posted by Jacana

Could someone post diagram of locking nut set up they now use instead of cone set up.

You may be asking about the specifics for the Yanmar but here is a picture of the MaxProp guts.

You can see on the left side, that when the shaft nut goes on, then the locking bolt, then the pinion gear, there is no way the prop nut will back off unless perhaps the lockbolt shears.

The blades ride in the journals at the bottom effectively holding the pinion gear in place.

[Jacana]

Thanks mate ,yeah ,would like to see sd20 saildrive prop set up with lock nut instead of cone.Regards Geoff.

[Alan Wheeler]

I've read through this post and find it amazing that props just fall off. Having the SD20's and folding props ($$) on my boat and I'm quite worried about loosing one (or both). You would think that the method of attaching a prop should be foolproof and not requireing locktite,

Hold on guy's, this is all chicken little stuff. The sky isn't falling. Your prop won't just fall off. There are millions of these installations all over the world that work flawlessly. Now to be very clear here, I am talking about the technique of a morse tapered fit, with backing nut with either a lock nut or a locking set screw to stop the whole lot from coming loose. Some even have a pin that goes through a Castle Nut or right through the backing nut and on through the shaft and out the otherside. And then many have a keyway as well. What ever system, they are all very safe and solid systems. To have a prop fall off, there will always be a reason, other than "just fall off". Main reason number one will be incorrectly fitted in the first place.

[Ex-Calif]

I was specifically referring to the Yanmar Saildrive.

I still don't see how it "locks" together.

[SeaKing]

Here is the photo I found that made me aware of the standard nut instead of the cone. This was on a boat we first looked at buying. I was going thru photos last year when I lost my prop and saw that. I called the previous owner that we talked to and asked him about the nut. He told me a lot of the charter operators use that due to the problems with the cone type.

I feel the cone give more surface area for the prop to contact with to help it to "spin" off or loosen the nut when a grounding/mudding occurs. Or in my case when the transmission is engaged accidentally when the prop is spinning quickly while under sail. I think that is what happen to me, my nephew was at the helm that day when my reverse gave out on one engine and the prop came off the other.

The small hex screw from Yanmar comes with a dot of a hard thread lock on it. I installed the nut and hex screw underwater with a good 1/2 in drive pull bar and socket on the nut for torque and feel I got the hex screw tight enough.

I am currently out of the water and will change the other to the nut style.

I am changing the oil seals and will add reservoirs for the gear lube to add a positive pressure to the gearcase. The thinking in this is if the seals are compromised the pressure will not allow the water intrusion. Another Voyage owner has done this and told me he has had no problems with water intrusion.

On my one cone that stayed on, it has a different set up than the cone that "fell off" It has a hex bolt through the cone and the washer under the hex bolt has an edge folded against the edge of the hex bolt holding it from spinning loose. If I can find a photo of that I will post it

[Ex-Calif]

That looks exactly like the Volvo setup.

The threaded area and the prop nut on the Volvo are drilled for a pin for one locking option.

I agree a tab washer that bends one tab over the prop nut and one tab against the locking polt would be the way to go here.

I would also remove all the paint from the zinc.

[Jacana]

Thats the problem.Currently you cannot lock off whether you use a nut or cone as there is no way to put a split pin through without drilling and possibly weakening the drive shaft.I have toyed with the idea of putting a length of cable through the cone then onto prop though worried about unbalancing the prop.P.S you have to dry dock your boat to change oil in sd20 leg,thats if you want to do it properly.I regulary sit mine on sandbank and wait for low tide to do mine and always check props and always take off and put on with boat out of water and yes I loctite the allen bolt.For those lucky souls who havent dropped a prop well done however when you put sails down make sure you run both motors in gear before you get into a tight spot.

[Jacana]

Would like a pic of that setup.The bolt on mine goes inside the cone and you cannot see it.Dont understand how you can get or see a washer that can bend inside same.How do you know the prop you lost was put on differently than the one you have still got? Regards Geoff.