Autoprop experiences? Flexible shaft couplings?

We just hauled our IP35 for the winter and are getting organized for winter projects. The boat (new to us this year) came with a 3-blade fixed prop installed, but is over propped (engine will only reach 2500 rpm). It also had a fixed 2-blade and a 3-blade Autoprop in lockers. The Autoprop is in need of servicing.

My decision is whether to cut down the fixed 3-blade prop at a local prop shop, or send the Autoprop out for servicing. I'm looking for any experiences others have had with an Autoprop. The reviews I have found online are mixed. If anyone has used an Autoprop on an IP35 and been happy with it, I'd love to get the size of the prop (I'm a little wary since the installed prop is the wrong size).

In addition, I'm deciding whether to install a flexible shaft coupling (need to replace the cutless bearing anyway, so the shaft will already be out). Any experiences with these and recommendations re: brands or styles would also be appreciated.

The boat will be heading out for a 1-year coastal cruise next summer, mostly on the ICW--so will be motoring a fair bit.

Thanks in advance,

Hite
IP35 #17
Sea Monkey

Hite,

Like you my boat came with a fixed prop and had an autoprop in a locker. The boat was under proped (2800 rpm gave me 5.5 kts) so i looked into the auto prop. Read the information on line and it looked promising. Paid $650 to have to have the prop reconditioned. Was initially very pleased with the performance. Boat backed straight and I got 7.2 kts under power. However after only 70 hours I started getting a vibration. Thought it was marine growth and dove on it several times. Thought it my be the shaft zinc and checked that out but the vibration kept getting worse. Checked with AB Marine (U.S. Distributor of Auto Prop) several times and they were convinced it could only be a problem with my boat. One day while setting the anchor a terrible clanging occurred while shifthing into reverse. Transmission shifter became jammed and boat stayed in forward. Shut down the engine and dove down expecting to find a crab pot line fouled around the prop. What i found was that all the bearings had fallen out of two of the blades. AB Marine was terrible to work with refusing to acknowledge any responsibility for early failure. Said it was due to a failure of a part not normally replaced in overhaul. Wanted me to pay for suspect part plus all parts lost when auto prop failed. After six months of negotiating finally paid and additional $300 and they returned the prop. Rattling started after only a month and prop failed at 70 hours. So after almost a $1,000 not to mention a diver and short haul, another $600 i went back to a properly fixed pitch prop. Bottom line the auto prop is a good idea but it is not reliable and AB marine is terrible to work with.

Bob and Hayden,

Thank you for your comments. I was already a bit leery of the autoprop since I'm usually a KISS fan. Your comments helped confirm that.

I'm happy with my standard shaft seal; the coupling I was referring to goes between the shaft and the transmission. They are made to dampen vibrations and act as a safety to protect the engine and tranny in case the prop strikes something hard and stops suddenly. With the keel design of the IP I think the prop strike scenario is unlikely, but the vibration dampening could increase motoring comfort--and since we'll be doing a lot of motoring on the ICW, I'm still considering it. Any comments from those with experience would be appreciated.

Another factor is that my shaft is a bit long (by an inch or two), which also contributes to vibrations and can cause excessive wear on the cutless bearing. I already have to pull the shaft this winter to replace the cutless, so I'm going to cut the shaft to the right length. Most of the flexible couplings add a bit to the overall shaft length, so I might as well adjust for that at the same time. I suppose I could cut the shaft to fit a low-clearance zinc at the prop, the if I add the coupling I can fit a standard zinc. Any thoughts?

Another issue: since my fixed three-blade prop is the wrong size, I'm now faced with the decision of having it cut down or getting a new one. Mine appears to be a standard Michigan Wheel or similar; an estimate on having it cut down is close to the price of a new one. The Campbell Sailer fixed three-blade prop gets great reviews; anyone have experience with one on an IP? Reviews suggest they increase they increase thrust, cut down on drag, and reduce vibrations--sounds too good to be true.

Hite, Sea Monkey
I have an IP35 with a fixed 3 blade prop, and I am plelased with it.
You didn't mention the size of your existing 3 blade fixed prop, it should be stamped on the hub.
My boat is out of the water, I can check the size of you want. But I think it is a 17 " x 8" checked. Today its 17x14 x 1 1/4" its identical to the one in Hayden's photo a Michigan wheel, but my HM 35 engine only makes 30 hp vs. Hayden's 39hp
I don 't know what the transmission turn down ratio is...yet.
I get a maximum of 2700 rpm and make 6.3 knots at full throttle
No prop vibration.but the rudder and wheel vibrate a little, its intermittant.
I am not convinced your prop is too big, and running your engine at 2500 is not hurting it.
What engine do you have ? The HM 35F or the newer series Yanmar making 39 hp ?
You dont have to run your engine at the max 3400 rpm.
Actually running your engine at a lower speed will save considerable fuel
Refer to the graphs on the Yanmar Marine website for your engine , fuel vs. rpm
and rpm vs. torque. Lower rpms are much more energy efficient.
And I think the commonly held opinion that you need to run near
the max WOT... is bogus.
Since you asked, Here are my suggestions/ comments
Yes replace that cutlass bearing if it is sloppy, but if it has a short life, say less than 4 years, then its short life is probably caused by shaft vibration the underlying problem....
If you have the shaft off , then you can cut an inch or two off it. It cant hurt, provided you leave enough room to get the zinc anode on the shaft. But I don't think 1 or 2 inches is causing your vibration problem....
And I would certainly leave enough shaft to mount the regular anode.
Up here the professional fishermen leave an extra inch or two on the length of the shaft when new, so they have enough extra length to machine it a second time, if it ever becomes necessary...
I don't think I would use that transmission/ drive shaft coupler.... if you have to use it to reduce vibration , then it means there is some other underlying problem with your drive shaft or engine alignment.
When you pull the shaft then have a machine shop check that the shaft is not bent, and check that the existing coupling is mounted squarely on the shaft, if the coupling and shaft are even a little out of alignment, then vibration will be the result.


Lastly ( or first of all) check the engine motor mounts for alignment between the shaft coupling and the transmission coupling , You could do this just as you take the drive shaft clear of the transmission, but before you pull the shaft, actually that could be your whole problem right there, and you should do that first, preferrably with the boat in the water. check motor/ shaft alignment
Its basic , get back to fundamentals...Personnally I'd check the engine alignment first, then consider the other stuff.
There is lots of info on the internet, and the book " Mechanical and. Electrical boat maintenence "by Nigel Calder
Or you could get any compedent marine diesel mechanic to check it for you...
Do that first
Regards
Ed
IP 35
Finnback

Ed,

Thank you for your informative reply. I bought the boat last June, and was told by the surveyor during the sea trial that the boat was over-propped, and I never really questioned that. The engine is a Yanmar 3HM35F, and it reaches 3800 rpms WOT in neutral, but only 2500 (that's being generous) in gear. I haven't cleaned the old prop yet to check the size. The old autoprop is in poor shape and I have decided not to get it refurbished. My choice now is to stick with the existing Michigan Wheel (possibly having it cut down), or go with a new fixed three-blade prop.

I will definitely check shaft alignment when I pull the shaft. Too late to check in the water now that the boat is on the hard, but I'll check again after launching in the spring. Vibrations are not unusually high, but I would like to minimize noise and vibration when motoring, both for wear & tear, and also since we will probably be doing a lot of motoring on the ICW next year. The shaft length was also noted by the surveyor--that's what brought up that issue. I generally motor at 1800 rps for fuel consumption, but would like to make sure I have the right prop size. Not sure about speed at 1800 rpms--some where in the 5-knot range. Both my tach and log were intermittent last summer. I finally got the tach sorted out and the log went belly up (another winter project). My speed readings were SOG from GPS, but we do have some current around here and I never bothered to run any laps to figure it out.

The cutless bearing is worn (has play in it), so it needs to be replaced. I don't know how old it is--I'll go dig through the PO's logs to see what I can learn.

In summary, my thoughts about prop, shaft, and coupling were driven by the surveyor's comments more than my own experiences with the boat (which admittedly are few since I've had it less than six months). I'll re-confirm everything before making any drastic moves.

Hite

Sea. Monkey
I have the same engine. HM 35
I'll check the prop size, on the way home from work.
I re read my comments this morning.
Keep the fixed prop, toss the autoprop,
Replace the cutless, check engine shaft alighnment...
Still seems reasonable - the day after....

Regards
Ed

Ed,

Thank you. I'll try to get out to the boat this afternoon to check my prop size. If I have enough time I might even disconnect the shaft at the coupling to see if there are any obvious alignment issues.

Do I need to drop the rudder all the way to pull the shaft, or is there enough play to drop it partially and move it to the side? Dropping it all the way out will require lifting the boat again.

Hite

Hite,
I checked the boat this morning on the way to work ( do you think I'm obsessed with boating!)
And my prop is a 17"x 15 x 1 1/4". Michigan Wheel.
I'm happy to know you will check your alignment , thats' the methodical place to start.

Re the shaft, Yes I think you could wiggle the shaft out thru the cutlass without removing the rudder, but I cant say for sure because I have never tried it.
Actuallly I did take the drive shaft off my previous boat, a C&C 35 but I could not get the coupling off the drive shaft, even with using a three jaw puller... If memory serves me correctly I think you have to get that coupling off the shaft and it is not easy, because it tends to be rusted on Solid!! So, instead I pulled the engine out of the boat, and pulled the drive shaft forward. Now that probably sounds drastic, but its easy really...
I had to use a puller to remove the prop, then pulled the drive shaft in to the boat and removed it that way, leaving the rudder untouched...
Again removing the engine is easier then you might think, it just sounds big!
Disconnect all the hoses and cables, you could take a few pics with your phone, just in case u cant remember how they go back together... Apart from the usual tools , sockets combination wrenches and screwdrivers, you will need some wooden blocking and a part sheet of plywood.
Use your boom vang as a pulley, hoist up the engine, slide blocks under it,and then slide it forward out of the way., right out of the engine compartment completely Leave the 4 motor mounts attached to the engine and use them - for skates....
Then pull the driveshaft.
If you can change the tire on your car, and get the hose clamps off a thru hull fitting, then I think you could pull the engine, its low tech...

But I think all this may be unnecessary, check your drive shaft alignment first, actually that takes more skill and experience then pulling the engine, and its importance is underrated.
Hope this helps...

Ed
IP 35
Finnback

Ed,

Thanks for checking the measurements. I assume you also have a 2.83:1 transmission?

I made it to the boat this afternoon and spent a few minutes chipping barnacles off the prop and trying to clean it up enough to see the size stamped on the hub. I didn't get it clean enough to read before I had to leave, though. I couldn't even see where it is stamped. If I make it out again tomorrow I'll just measure it myself--the diameter is pretty straightforward, and the pitch should be three times the fore-aft measurement of one blade, right?

On removing the shaft, I had actually thought of moving the engine instead--but then dismissed the idea as too hard. I get the mechanics of moving it, but I don't have overhead access to the engine for lifting. I'll take a closer look at it, though--I like the idea of sliding it out on blocks/runners. I'll also give the coupling a shot with the puller, using heat and cold if necessary to help break it free. Any chance of replacing the cutless bearing with the shaft in place--I.e. sliding the old bearing off, and sliding the new bearing over the shaft? Dropping the rudder or moving the engine will be a hassle either way--seems like an awful lot of work just to change a bearing.

My big time window for boat work is coming up in a couple of weeks. I'm keeping my fingers crossed for decent weather.

Hite

Hayden,

Great photos, thank you. Did the stern tube come off without dropping the rudder? I'm wondering about the clearance at the aft end of the shaft. I'll try the screw trick to get the cutless bearing out.

It looks like you have more shaft exposed with the fixed prop than with the old Prowell prop. It looks similar to mine with my fixed-blade prop in place (I really need to get some photos). I had not thought of the difference in clearance with a different prop--yet another reason to leave the shaft length alone, in case I want to change props in the future.

I'll get the prop off and do some clean-up in the garage on a cold, snowy day this winter to confirm my current prop size--the cutless bearing is the first order of business. Once I get that done, I can decide whether to keep the existing prop, re-pitch it, or go with a different prop. I started exploring prop options based on the survey comment that I was over-propped, which in turn was based on only being able to reach 65% of WOT when in gear. I am intrigued by your comment that other IP owners have re-pitched to 13.5"--it sounds like it's not unusual to be a bit over-pitched. I am still interested in comments on the Campbell Sailer prop, which has airfoil-shaped blades with a thick chord for better efficiency (the design appeals to my engineering side, I can't help it). They're a little pricey, but might be worth it if I would otherwise be re-pitching my existing prop anyway. Do you know anyone who has one of these?

To recap and clarify some earlier discussion, I don't know that I have a vibration problem. I'm not sure how old the cutless bearing is (still looking through old logs), and I have no complaints about engine/shaft noise or vibration. I do know that the cutless is worn and needs replacing, though--and I will certainly take any improvements I can get in terms of noise/vibration, cruising speed, and fuel economy. We'll be on the ICW next year and probably motoring a lot (I'd rather sail but I'm being realistic here). My main reason for looking into changing the prop or re-pitching is that (I hear) it's bad for the engine to be fully loaded at low rpms--but I've heard other opinions on that, including from Ed here. I'll check with the local engine gurus and do some more research on that.

So my next steps are:
- remove prop and put in garage for a snowy day cleanup job
- unbolt flange at transmission and check shaft alignment as best I can
- pull stern tube, replace cutless bearing, reinstall stern tube
- align shaft (will do again in water)
- decide what to do about the prop, if anything

I'll also take some photos to post here.

Hite

Hite Hayden, et al.
Good input from everybody.
Here is my perspective
Pull the prop, clean it up at home and have it checked at the local prop shop.
If its balanced then I would keep it as is. Think .KISS and " if its not broken, then don't fix it!" I still have the "17x14" as installed by the factory, second guessing the factory engineering is usually not a real good idea.but if I were to change it, the I would change the pitch by at least one full inch. Changing the pitch by 1/2 inch sounds way to wimpy for an Island Packet owner!
Try to get the cutlass out as Hayden showed, with the drilled hole and screw .Great idea Hayden !! In any event pull the cutlass.
Eyeball the prop shaft as it exits the stern does it look straight, and centred in the stern tube? Perhaps if is grossly off to one side and "wobbles" when it it rotated, then check the engine /shaft alignment.
An excellent resource is on line, search for stuffing box" , Pbase , Compass Marine in Maine USA. They have some excellent 'hands on" articles posted on these type of repairs.
So optimistically, u just need to change the cutlass.
And forget about the WOT thing, you are over thinking it...lower rpms means better fuel economy.
Ed

Ed/Hayden,

Thanks to both of you. I'll do just as Ed suggested in the latest email. I still want to understand why my surveyor felt so strongly that the boat was overpropped, so I'll continue reading up and asking around locally for my own education on that.

BTW, I'm a big fan of the Compass Marine "how-to" articles. The guy who makes those posts on Cruisers Forum as "Maine Sail"--he recommends the Campbell Sailer prop; that's how I found out about it. If I won't do the engine any harm, I'll just leave the prop as is and save the money for the trip next year.

I hope to get out to the boat tomorrow, and will certainly make it this weekend. The shrink wrap went on today.

Hite

Hite
Look at the right hand side of the home page on this website ipyoa
And find one of the top contributers. " Dan Maher"
His photos show very graphically how to remove the stern tube , and cutlass bearing
Looks easy, bring vice grips for the nuts on the backing plate of the stern tube, and tie them on with string , so you don't lose them down in the Bilge
Looks easy

Ed

I had the standard 17X14 fixed blade prop on my 89-35. Had it de-pitched at the prop-shop (Bay Propeller in Portsmouth VA) to a 17X12. Wish I had gone to 17X10, which I will do this winter when I haul. It changed Cruising RPM from 2400 to 2600 and WOT from 2800 to 3000. I believe these engines are designed to run at 3400 WOT. As it came from the factory the engine is overloaded at WOT, mine ran at 180F, should be 160F and there was unburned fuel out the exhaust. Transom is much cleaner, reduced "mustache" with 17X12 wheel, I expect the 17X10 to be cleaner still, and believe I will achieve 7kts. cruise at 2800rpm, with better fuel economy.

Guys
Some IP 35's have the 30 hp engine and others have the 39 hp engine, that's a 30% increase.
This discussion about prop pitch, engine and boat speed, distills down to
- change the prop pitch so that we can obtain close to 3400 rpm - under load
rationale - increase the rpm will increase boat speed, and reduce black smoke.
- but the Yanmar marine on line graphs show that
Fuel economy improves with reduced rpm,
and Torque -a measure of engine output-
is maximum at 2400 rpm and trends downward with increased rpm.

The Work required from the engine - or sails - to push the boat thru the water increases as " the square"of boat speed. There is that whole 1.3x square root of LWL thing.
Therefore reducing pitch, and increasing engine speed - won't necessarily make the boat go faster. But it will burn more fuel.

On a more seat of the pants level,I ask myself -
Would you run the engine in your car for hours, close to WOT and 'redline '
and then expect the engine to run for 30 years?
No I think I'll stick with the present set up,
a 17x 14 prop giving 6.3 knots @ 2500 rpm.

Regards
Ed
Finnback

There's some great discussion here. Thank you to all who are contributing.

Ed and Hayden--I looked through Dan's photo journal; thank you.

Ed--you referred in an earlier post to Nigel Calder; I read his Mechanical & Electrical Manual cover to cover 20 years ago and it quickly became my favorite book, although I don't have a current copy. I do have his Marine Diesel Engines book, though, and he clearly advises there that the prop size and gear reduction ratio must be chosen to allow the engine to operate at full rated rpms at full load in adverse conditions, which matches what my surveyor said and what I have heard elsewhere. Your experience differs with that, and I'm always interested in learning more--I am not a diesel expert by any stretch of the imagination. Here's how I understand what others are saying, and maybe you can point out the flaws in this thinking:

The ability to reach high rpms while motoring does not mean that's the way the boat should be operated; rather, it just is a rule of thumb to make sure the boat, engine, transmission, and prop size are matched appropriately. Cruising rpms will be lower, but then something is left in reserve for punching through wind and chop when needed. I don't fully understand the ill effects to the engine if it is fully loaded at lower rpms, but I keep hearing and reading from various sources (Calder, for one) that this is a bad thing. I have a hard time ignoring this advice that I have received from several sources, so I'm wondering if you can elaborate on this. It sure would be nice to not have to change anything, but I also don't want to cause unnecessary wear and tear on the engine.

As always, I appreciate all the good advice here. Thanks again.

Hite

Hite
Why the lower speed is OK
1 thats the way Island Packet. Engineering designed it
Few would argue that the factory make big mistakes
2. The temperature your engine operated at is acceptable
So there is no fear of damage there
3 . Refer to the fine print of operating speed/ break in time
in the Yanmar manual, the original was probably in Japanese so the english translation is a bit twisted, but upon close inspection it says operate at a maximum of less than 3400 , and exceed that for no more then 5 % of the operating time.
So, normal operating range is less than 3400, and 2500 is
Less than. It doesn't say operate at more the 3400 for 5%of the time...
I just re-read the online version, and that's my honest interpretation.
4. Refer to the three graphs, fuel , torque and Power-hp
They show an operating range of 3600 to 2000 rpm, if it was not OK to operate in this range, then hey! It would be libellous show these curves...
5. Common sense would tell you that running at moderate speeds
Is less strenuous then flat out .
6 reducing the prop size and thus allowing for a greater rpm, just spins the smaller prop faster, if the boat is at hull speed , or the engine is achieving full torque, then
The smaller prop will not drive the boat faster, the higher speed will be lost to "Prop Slip". Hayden and others can get a little more boat speed 7.0 versus 6.3 because they have the newer series Yanmar engine making 39 hp versus our 30 hp. Hm35F vs. the 3Jxxx. series
Thats 30 % more horsepower, for 10% more boat speed....
7. Significant energy as fuel is consumed just making the engine itself rotate,
The faster the rotation, then the more fuel will be consumed
3400 will burn more fuel then 2400, regardless of load.Thats what the Yanmar graphs show , and that has been my experience vis a vie switching out props.
8 The reported improvements of reduced black soot on the transom at higher rpms sound like wishful thinking to me.
Sorry I cant quote textbooks and graphs on Marine propulsion, but I'm sure they must be out there...
I'm sticking with my HM35 17x14. And I dont think second guessing the factory by changing the pitch on the prop will help.
A new feathering prop would help under sail, but not power.
If the side busts out of my 30 hp Yanmar ( very unlikely)
Then I would re-power with the new 39 hp Yanmar, keep the existing prop just as is,
and expect to get 7.0 knots versus 6 now. And expect to burn more fuel.

Gee its Miller time
Regards
Ed