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Old 23-04-2017, 09:15   #1
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Backup propeller questions

I have read that it can be useful to have a backup propeller as spare equipment.

I assume the basic scenario here is that I would be in distant harbor, which is not my home harbor, and I have a prop strike. Then I guess, I would have the boat towed to an anchorage where I can immediately install the spare prop, without worrying about the problem of having to source a prop locally. I guess this would be more of a concern if I were in a foreign country with limited mechanical resources.

My questions are:

(1) Is a spare prop not really necessary in US ports, because it is easy to get them, or will getting a replacement prop going to be a huge hassle? For example, let's say I had a prop strike in Camden, a smallish port in Maine. Will I be able to get going again quickly, or will I be marooned in Camden for 2 weeks waiting for a "delivery"?

(2) Can a prop be installed while the boat is in the water, or does it need to be taken to a yard? Assume a 40' with twin inboard engines and fixed pitch prop.

(3) If a prop can be replaced while the boat is in the water, is this something I could accomplish myself with dive gear, or is it more a job for a professional? Would I be just screwing the new prop on, or is it more complicated than that?
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Old 23-04-2017, 10:04   #2
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Re: Backup propeller questions

Most boat props can come UPS as fast as you an get on the telephone with credit card in hand. It would help to research sources ahead of time, and do write down the particulars of your props. BUT, you're not likely to know enough about the damage until the boat is pulled - You hit something, one side vibrates badly, but is there shaft, strut, rudder, or other damage down there? You might be able to determine that it's only a prop with a diver, but the cost of that, and the delay getting the dive done needs to be balanced against the cost of an immediate pull and thorough inspection.

I designed my rudder (size of a small door, behind the prop) so that I could change the prop underwater. Since then, I've discovered is that what I really did was make it possible for me to replace the prop or even pull the shaft and Cutless bearings by myself without professional help when the boat is on chocks.






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Old 23-04-2017, 18:06   #3
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Re: Backup propeller questions

Running twins, the question remains: Which spare prop ? Port or Starboard in a counter-rotating configuration.

More than likely you will have a keyway with pin, the prop nut, and finally the propeller onto a tapered shaft.

There are tools specific to the task. And then the block of wood, wrench and hammer approach. Swinging a hammer in the water ?
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Old 23-04-2017, 18:10   #4
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Re: Backup propeller questions

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Running twins, the question remains: Which spare prop ? Port or Starboard in a counter-rotating configuration.

...
Right, I would need two.
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Old 23-04-2017, 18:33   #5
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Re: Backup propeller questions

Having just pulled my 15" max prop off to replace my cutlass bearing, it's not a job I would want to do underwater. I have above average mechanical abilities and access to big boy tools. I used a very large gear puller from work, about 3' tall, to pull the hub off. I had the puller about maxed out with an 1.5" box wrench on the nut. Ended up getting out the MAPP torch to get a little thermal expansion going in my favor.

Came off with a bang.

I'm sure if I were marooned some where I'd figure out a way to get it off with a hammer but man would that be a job.

Some marinas would allow you to do a short haul in the slings over lunch break for a reduced rate. I bet if you had all the tools right there and were ready to go.

I think having a spare is a good idea if you are a long way from civilization but almost anywhere is a machine shop. Props can be made to fit with a machinist and cash.
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Old 23-04-2017, 20:08   #6
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Re: Backup propeller questions

Yeah you would need both a lefty and a righty. So twice what a single screw would have to pay for prop backup. I have a spare prop but I have a single screw and both props were given to me. If I had a twin, I would not keep spares.

Even on a 1" shaft, a prop that has been on the shaft for 20 or 30 or 40 years is not coming off without a fight. I just re-propped last year so I am sure that now I could anchor in chest deep water and change props myself. When I took off the original folding prop, it nearly took an act of congress to get the hub off. No way a diver with ANY tools could have done it in the water. So if you want to be able to do that, every time you haul out you should pull the prop, clean and never-seeze the threads, and use a new shaft key and cotter pin to re secure it. Otherwise in a few years it will be stuck on there like white on rice.
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Old 24-04-2017, 06:02   #7
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Re: Backup propeller questions

I think we all agree that the underwater prop change is an attractive idea (it was for me) that runs into reality, even when talking about smaller props on twins. But, there may be some marginal value to carrying spares. It could save you time/money in a remote place, particularly if you go to remote places where prop damage frequent and your props are unprotected. My prop is big and very well protected, I've had bunches of soft groundings in Florida, have gotten off by myself all but one time, and never done any prop damage. I could get a spare overnight, so I'll spend the $900 on some more likely breakdown, such as a spare raw water pump.
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Old 24-04-2017, 06:51   #8
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Re: Backup propeller questions

Some of the spare prop thing is simple practicality as noted. That being, it's easier to service your boat if you already have spares on hand which you KNOW fit. Be it a prop, an alternator, or winch bearing. That way you lose little enough time effecting the fix. Especially if you're trying to get ahead of a weather system, or season in location X.

The other part of this is that a lot of boats come with fixed props originally. And along the way one owner or another will switch to a folding or feathering prop, for better performance under sail, under power, or both (in theory). And the original fixed prop is kept on hand since it fits, & also that selling it might yield all of $100.

Also, if you normally run a folding prop, which isn't so great in terms of efficiency when motoring. And you have a long, uphill stretch under power ahead of you, then it can make a lot of sense to switch back to the fixed prop for that passage, due to it's improved performance over a folder.

EDIT: In rare circumstances, a boat may lose their propeller. So having a spare right there can be a big headache preventative. Ditto if you maim the prop on your shaft; mechanically, through being in an electrically hot harbor, etc.
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Old 24-04-2017, 07:10   #9
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Re: Backup propeller questions

Quite agree, took us some time but eventually we found the exact sized prop on e bay for £25, (£250 new). So we now have a spare in case one is damaged. Actually what we now plan to do is prep one with undercoat then antifoul paint during the winter so its a simple fit during the Spring.

The spare is currently in my shed being cleaned up.

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Old 24-04-2017, 07:45   #10
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Re: Backup propeller questions

Quote:
Originally Posted by jsc7 View Post
Can a prop be installed while the boat is in the water, or does it need to be taken to a yard? Assume a 40' with twin inboard engines and fixed pitch prop.
Yes, the props can be pulled underwater.

Quote:
Originally Posted by jsc7 View Post
If a prop can be replaced while the boat is in the water, is this something I could accomplish myself with dive gear, or is it more a job for a professional? Would I be just screwing the new prop on, or is it more complicated than that?
Shaft mounted props will require a puller. On land, some laymen use a gear puller. This is not practical underwater and the correct tool for the job in any case is a prop puller. Saildrive props do not require a puller of any sort. Prop R&R is not rocket science and anybody with a modicum of mechanical ability and the right tools can do it.

Quote:
Originally Posted by Three Sisters View Post
Swinging a hammer in the water ?
Not an issue.

Quote:
Originally Posted by GrowleyMonster View Post
No way a diver with ANY tools could have done it in the water.
If it can be done in the yard, it can be done underwater. I have pulled over a hundred props and have a 100% success rate. They key is having the right tools.

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Old 24-04-2017, 07:52   #11
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Re: Backup propeller questions

When I bought my boat, a Morgan 462 center-cockpit ketch, I found a "spare" prop in a locker. Turns out that the previous owner had replaced a worn Max Prop 3-blade feathering propeller with a fixed-blade Michigan Wheel. I had the Max Prop reconditioned, and it's as good as new, and will be reinstalling it when I haul the boat in June for routine maintenance (bottom paint, check the shaft and rudder bearings, check through-hulls, etc). The fixed-blade prop will go into a locker as the new spare. I'm planning on doing some extended cruising from from home, perhaps even circumnavigating, so having a spare prop that fits my shaft, and matches my engine and transmission, seems like a pretty good idea.

Replacing the prop underwater is possible, but probably a last-resort type thing.

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Old 24-04-2017, 08:15   #12
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Re: Backup propeller questions

Because I had max props, I often had the original prop buried away as a spare. But I doubt I would have a spare if that were not the case. Completely damaging a prop beyond use on a slow displacement boat doesn't seem that likely to me. A bent blade can be bent back temporarily. Removing under water is possible but not easy at all. Most often you are going to need a puller and a scuba tank.Finally, it's a sailboat after all, you can use a bent prop to get into harbor at low rpm if necessary.
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Old 24-04-2017, 08:24   #13
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Re: Backup propeller questions

We moved to a feathering prop and kept our newish fixed prop as a spare. Our props have been changed underwater by an experienced diver.

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Old 24-04-2017, 16:36   #14
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Re: Backup propeller questions

Quote:
Also, if you normally run a folding prop, which isn't so great in terms of efficiency when motoring. And you have a long, uphill stretch under power ahead of you, then it can make a lot of sense to switch back to the fixed prop for that passage, due to it's improved performance over a folder.
Aww, come on, Unciv! You gotta stop thinking about folding props as all being like the tiny two bladers that race boats tend to fit. If you look at the test results, good three blade folding props (like Flex-O-fold in particular) are in fact MORE efficient than typical fixed props. So, avast with the advice to change back!!!

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Old 24-04-2017, 16:48   #15
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Re: Backup propeller questions

Based on other posts I think the OP is likely to end up with a power vessel. So, no folding/feathering props.

I pull mine (Kiwi Props) for extended in water storage to eliminate fouling and for maintenance. Pull them when dry storaging too so they dont walk off. Easy job, but bigger wheels on a power vessel could be a bigger chore.
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