Lost Propeller!

[foreverunderway]

You can't just put any old prop on, even if it fits the shaft, taper and is the correct diameter. Most props can only be tweaked a couple of degrees either way and the pitch on a prop must be correct for your engine, transmission and reduction gear.
Caution is the watch word here as an over pitched prop can do serious damage to your engine and an under pitched prop won't give you the thrust you need..

 

[Bill Blatchford]

I understand all that. That is why I have set of props. If someone with a 42 GB classic with JD 135 hp six cylinder engines is looking I can help. One would have to take them to a prop shop for tweaking and fitting. Still it would be a cost saving for the right person. We repowered with JD 4045 160 hp and we now have 28x34 4 blades.

 

[rclarke246]

The diver saw no damage but I’ll have him double check.
My insurance agent says the deductible is greater than the loss so I’d be better off not filing a claim.
Was lucky to find a new set of props from a local guy who had the same boat. Currently making sure they’re balanced and getting Propspeed coated. Thanks

 

[foreverunderway]

I understand all that. That is why I have set of props. If someone with a 42 GB classic with JD 135 hp six cylinder engines is looking I can help. One would have to take them to a prop shop for tweaking and fitting. Still it would be a cost saving for the right person. We repowered with JD 4045 160 hp and we now have 28x34 4 blades.

I wasn't directing my post to you. Perhaps the OP hasn't the experience to know these things. A lot of folks operating pleasure craft may not have your knowledge and experience.

 

[Olebird]

Did you hit the MOB button??

 

[Vinny]

Probability lost in the muck where a fish finder or sonar would never see it.

I was with a diver a few days ago looking for a rudder almost the size of a sheet of plywood that broke off a tug/tow boat.

Even knowing about where it was lost in 18’ of water in Indiana Harbor we never found it using a towed sonar array.

Sorry to say, I would save the diver money and put it towards a replacement prop.

 

[Nickair]

Insurance deductible screws taking care of the loss. That is unfortunate.

This does bring up an issue of marking prop loss location, at time of happening, with a marked MOB.

The prop isn’t going anywhere unless the diver gets out there to recover it, as free salvage. Not likely he can find it without knowing right where to look. Even then.

Another point is to have back up prop/s and shaft/s, onboard for underway, other than local opts. Mine were buried and would have taken half a day to get them available. Lol.

 

[slowgoesit]

The diver saw no damage but I’ll have him double check.
My insurance agent says the deductible is greater than the loss so I’d be better off not filing a claim.
Was lucky to find a new set of props from a local guy who had the same boat. Currently making sure they’re balanced and getting Propspeed coated. Thanks

Hopefully by another boatyard than the one who caused the problem in the first place!

 

[Njlarry]

Agreed completely, and if it is installed incorrectly, or has loose nuts, or reversed nuts, your case with the yard will be stronger.

Prop installation info... https://stevedmarineconsulting.com/propeller-installation/

Prop nut install details... http://stevedmarineconsulting.com/wp-content/uploads/2015/03/Prop-Nuts-Letters.pdf

Great information well written.
I've read different opinions. Should both nuts be torqued the same and are there accepted bronze nut to stainless shaft torque value tables based on shaft diameter?
Thanks for your contribution to this forum.

 

[Arc]

If this is a wide channel the dive is easy. Anchor boat , yes just do it. Drop second anchor under boat. Diver uses it for marker and does search pattern. That’s all assuming you had a good reference when lost. Here in NY if we have 0 visibility , that’s a good day.

 

[Baker]

When it gets down to buying a new one, I highly suggest you check these people out first....especially since the reside in your home state!!

Marine Connection Liquidators - Propellers

 

[Steve DAntonio]

Great information well written.
I've read different opinions. Should both nuts be torqued the same and are there accepted bronze nut to stainless shaft torque value tables based on shaft diameter?
Thanks for your contribution to this forum.

While it would be the right way to install any critical fastener, I can't recall the last time I saw a yard use a torque wrench on a prop nut, so it may be a non issue. Bronze nuts (these are typically manganese bronze, so really brass) are self-lubricating (they won't gall). You can look up the torque value of a given diameter, and I'd use bronze/brass as the material, but again, in most cases the yard is using a large wrench (hopefully smooth jaw), and a big guy to heave on it.

Following the installation procedures is key, no pun intended, make sure there is no key binding, perform the lapping procedure, lightly oil the shaft taper and key, block the prop to the hull, install the large nut first, then remove it, then install the half nut, and then large nut. Get all that right and you are likely to never have a prop loss issue.

Now, if you are intent on torquing the nuts, here's the drill...

"Firstly, on a propeller taper, the propeller hub has to be pressed onto the taper using more force than the thrust generated by the propeller itself.
This ensures that it will not move further up the taper under normal thrust loads thereby loosening the propeller nut.

(using 3” diameter shaft as illustration)

In tons, the clamping force required is:
Nominal diameter of shaft x condition factor.
(Factor 2.875 is dry taper ; 2.6 is for oiled taper)
3 x 2.875 = 8.625 TonsF.
Convert to Lbs.:
2.875 x 2240 Lbs. = 19,320 LbsF.

Torque required on nut to deliver clamping force of 19,320 Lbs:
(Nom Diameter of thread (2.25) x Factor x LbsF) / 12).
(Factor is 0.2 for dry thread ; 0.15 for oiled thread)
2.25 x 0.2 x 19,320 = 8,694 Inch/Lbs.
Divided by 12 = 724 Ft/Lbs.

The above can be adjusted by experiment as some boats do not generate as much thrust as is possible on some high speed boats, the variable is the factor."

Next, find a torque wrench that can measure 724 Ft/lbs...

 

[OldDan1943]

In my mind.... the boat should be hauled and the propeller end of the shaft threads need to be check and the taper pass the bluing test. Finally, new nuts torqued to specs. Check the 'trueness' of the shaft and the condition of the strut bearing.
While it is out of the water, remove the other prop and do the same.
As pointed out, after addressing the problem with the yard... ask what they are going to offer in the way of compensation.
Think about it.... if you use the same yard, they will do everything possible to make sure it doesn't happen again. No yard wants a bad reputation.
I think the prop on my AT34 is in the neighborhood of $2000, Labor extra, any machining extra, painting extra.
While it is out of the water, might consider pressure wash and more bottom paint.

 

[cdsailor]

...block the prop to the hull...

I’m guessing there must be better and worse places to block against the prop to avoid potentially damaging the prop? What’s the appropriate way?

Thanks.

 

[Comodave]

I’m guessing there must be better and worse places to block against the prop. What’s the appropriate way?

Thanks.

You usually block the prop to the hull so the prop can’t turn. Where else would you block it?

 

[cdsailor]

You usually block the prop to the hull so the prop can’t turn. Where else would you block it?

I think that much is obvious. I suppose you could block the prop near the hub or at the end of a blade, couldn't you? I'd like to hear from Steve the best practice for block placement, particularly since I was under the impression that blocking against the prop was, perhaps, not the best practice, but I'm not a marine professional. I've appreciated Steve's input so far. Curious to get a bit more from him.

Thanks.

 

[High Wire]

You usually block the prop to the hull so the prop can’t turn. Where else would you block it?

A block on the ground under the prop works. There usually 12X12's around the yard of sufficient length.

 

[Comodave]

Blocking to the hull or to the ground puts the same stress on the prop either way and I thought that was the concern when he mentioned blocking at the hub versus the prop blade.

 

[Steve DAntonio]

I think that much is obvious. I suppose you could block the prop near the hub or at the end of a blade, couldn't you? I'd like to hear from Steve the best practice for block placement, particularly since I was under the impression that blocking against the prop was, perhaps, not the best practice, but I'm not a marine professional. I've appreciated Steve's input so far. Curious to get a bit more from him.

Thanks.

The attached photo, from Dave Gerr's excellent book, "The Nature of Boats" illustrates the blocking procedure.

I've never damaged a prop using this approach, however, I agree, it seems counter intuitive, the tip of the blade is thinnest.

 

[rclarke246]

I did get the new set of props from a local guy, former ST44 owner. Had my mechanic test for proper balance as well as "Prop Speed" application.

Total out-of-pocket was about $6,000.
Negotiated with the yard who paid me about 50%, but I now have a spare prop for the port shaft, so, not too shabby, I'd say.

May find a diver, one day, who'd be willing to retrieve my lost prop for a handsome finders-fee.