Heavy on the tiller - oversized engine, prop pitch?

Hi

I am in the process of buying a old 32 foot sailboat. It has a 30 hp engine in it and a two blade folding prop.

When under motor it was increadibly heavy on the steering to keep her straight. It felt as if the tiller would break. It would be unmanageable for a few hours and I don't think a tiller pilot could handle it.

I'm happy with the rest of the boat.I also noticed the stern was really sucked down into the water or there was a large wake which meant the exhaust was under water. Also a lot of vibration.At full throttle the engine only got up to 2000 rpm (at 6knts). I have the same, but smaller, engine on my boat and run it more around 2800rpm.
One hypothesis was that the prop is just dirty. But having a look from the dock it didn't appear to be. My thought was that by going to the two blade prop they had significantly increased the pitch of the blades which then put a lot more water on the rudder.

I could then change the prop but I would have to buy the boat first. I would hate to be stuck with a boat that was impossible to motor.

Thanks, Jack

30hp is a lot for a 32 footer. Large wake and the stern sucked down indicates way too much power and speed. Lots of vibration could be caused by several things, engine alignment, shell on the folding prop, blades not opened fully etc. Heavy steering could be not enough prebalance on the rudder or simply trying to go too fast.
We are going to need details. Make of boat and engine. If it's a one off the keel/rudder configuration and whether the propeller is on a skeg or mounted in a cut out in the back of the keel.

At low speed it still had a lot of force on the tiller. More than I would expect.

The walking effect of the prop will cause the tiller to feel heavy. The walk will cause the boat to go in circles and you compensate for this with rudder, you feel the side thrust from the walk. As you get up to hull speed and the boat doesn't want to move forward faster, the
energy or effort to make the boat move forward is wasted but the energy put to prop walk is basically not effected so the tiller will get heavier.,,,, Cut power and the tiller will go instantly light. There are also some other things happening like prop wash, torque and gyroscopic forces that can also have a small effect.

An over powered boat with a big pitch prop will cause more prop walk

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jbarnes85 said..

Jolene said..
The walking effect of the prop will cause the tiller to feel heavy. The walk will cause the boat to go in circles and you compensate for this with rudder, you feel the side thrust from the walk. As you get up to hull speed and the boat doesn't want to move forward faster, the
energy or effort to make the boat move forward is wasted but the energy put to prop walk is basically not effected so the tiller will get heavier.,,,, Cut power and the tiller will go instantly light. There are also some other things happening like prop wash, torque and gyroscopic forces that can also have a small effect.

An over powered boat with a big pitch prop will cause more prop walk

That makes sense. Once hull speed is reached that energy has to go somewhere and some will go to the rudder increasing the required force on the tiller to keep it straight I do believe we got to hull speed with a lot less than 2000 rpm and I tried to increase the revs.

Surely it cannot be good for the engine to run as such low revs all the time Could this be recitified by changing to a prop with a less pitch? Say a three blade prop?

If I recall, and maybe I need to take it for another spin, even at low revs the tiller was increadibly heavy.... compared to my compass 28 with a 15hp Yanmar and three blade prop. On mine I motor along at 2800 rpm or so but I couldn't even get this above 2000 rpm.

yes not many Cav32s with tiller. It's one thing that appeals to me about the boat.

Does the tiller have a heavy feel when the boat is stationary? or is this problem only under power.
I ask because my boat developed very heavy steering, to the extent that it was difficult to maintain a course, slipped the boat and spent nearly two days removing rudder and shaft, honing the rudder bearing, greasing and reinstalling. No more problem.

Looks like another inspection of the boat might be best once you've had another think and run some additional tests to be sure.

As uncle Bob mentioned, check the rudder when stationary. Then feel how the tiller responds at all speeds.

When the prop is overpitched, it will have more walk as mentioned. With an overpitched / oversize prop, as soon as you reach max rpm that the engine settles at, back the throttle off a whisker and cruise there. Any additional throttle past that point will cause over fuelling as the governor tries to reach a higher commanded engine speed/rpm. That's not going to be good on the engine. But the engine won't mind being run at 2000 rpm as long as you use it right.

The vibrations, you'll find that they'll come and go through out the rev range. Run the engine in neutral and feel where the engine has a tendency to vibrate. For instance on my 3 cylinder, around 1300rpm, there is inherent vibration in the engine. I deliberately avoid running near this rpm in gear. Check what the engine does between cruise speed and hull speed in neutral. Avoid running the engine in these trouble spots to avoid unnecessary wear and tear. Any vibrations that appear when in gear which wasn't there in neutral is then likely to be caused by prop/shaft/gearing etc.

Once you reach hull speed, all she's going to do is dig the stern deeper into the water with any additional thrust from the prop. This boat will have plenty of reserve with a 30hp engine past the hull speed. Typically on a boat that size, 15hp of efficient thrust is plenty to reach hull speed. So pay attention not to overpower the hull when testing. All of the wasted/additional thrust is going past your rudder, and the side effects are likely to be felt on the tiller, which may be less noticeable on a wheel with greater mechanical advantage.

2 blade props typically have larger diameter/pitch and effects such as propwalk etc may be more noticeable compared to conventional 3 blade. This is not a hard rule, there are of course many exceptions. Just things you might want to consider.

Cheers,
Evan

Hi Jack

Interesting one again.
We are looking at a heavy tiller. vibration and inability to reach peak RPM.

When under motor it was increadibly heavy on the steering to keep her straight. It felt as if the tiller would break.

If it was due to prop walk I would expect the tiller to be easy on one side (swing?) and heavy on the other side.
The reason that I suggest this is that on one swing the boat would be going with the flow and on the other against the flow. so you would have something like weather helm.

under motor
By this I take it that the tiller feel is normal or light under sail. This would eliminate growth or tight bearings as the cause.

I don't think a tiller pilot could handle it.
Did the previous owner use an auto pilot? I ask this because it is a rare boat nowadays that doesn't have one.
What does the P.O have to say about this?

I also noticed the stern was really sucked down into the water or there was a large wake which meant the exhaust was under water.
This would indicate that you are you have the throttle open too far. A boat trying to go faster than theoretical hull speed can do all sorts of things.

Also a lot of vibration
This can be easily checked.
Is there vibration at high revs in neutral?
Yes = engine mounts or some other engine imbalance
No = The problem is in gearbox (unlikely), coupling missing a bolt or with deteriorated anti-vibration rubber if
fitted, bent propshaft, extremely worn cutlass bearing or prop.

Is there vibration at high revs in forward or reverse?
Yes. =The problem is in gearbox (unlikely), coupling missing bolt or with deteriorated anti-vibration rubber if fitted, bent propshaft, extremely worn cutlass bearing or prop.

At full throttle the engine only got up to 2000 rpm (at 6knts). I have the same, but smaller, engine on my boat and run it more around 2800rpm.
Again test in neutral. What does it rev up to?
Is the tacho accurate?
Is the throttle cable restricted in its travel?
One positive thing is, If you are getting 6 knots at 2000 rpm you are saving on fuel.


I do believe we got to hull speed with a lot less than 2000 rpm and I tried to increase the revs. Surely it cannot be good for the engine to run as such low revs all the time
What RPM are we talking about? Very low speeds, like idle at around 800 rpm can create problems in the long run.
However speeds of around 1500 rpm underload would not bother me at all.

looking forward to see your solution

All the best
Gary

How does it run in reverse?
How does the tiller react in reverse?
Did you try and do an emergency stop to halt the boats forward movement using high revs?

Thanks All.

Lets see if I can answer some of the notes above:
- Yes it definitely swings to one side only, as described by Gary.
- The tiller is not heavy when sailing. She steers well when under sail.
- Unfortunately I dont recall what it was like in reverse. Didn't try an emergency stop.
- I dont remember clearly but I think there was no vibration when in neutral.
- Good to know 1500 rpm is OK for the boat. I was definitely pushing it too high. Gosh I wish they put a 20hp engine in it instead of the 30hp. Looks like lots of Cavalier 32 owners have put 30hp Yanmars in their boats, I found two that sold recently with them in there and with lots of hours (albeit they had the prop between the skeg and rudder).

I got a diver to have a look at the bottom before I took it out. On reflection he did mention that when he opened the prop there was some give/movement in the blades. This could create the vibration.

I have attached some photos I took with my Go Pro at the berth. I notice that the prop is half closed. I kind of thought it would stay open since there is no moving water to push it closed at the berth. Maybe the prop isn't opening fully but then I dont think we would have been motoring to speed at low revs if that's the case.

The other thing I notice is that most Cavalier 32s have the prop between the skeg and the rudder. This one, and some other older ones have the shaft coming out in front of the skeg. I suspect these ones were made in NZ and the others made in Australia or they just changed the design later. I also see a couple Cavalier 32s in New Zealand for sale that have a tiller (which is rare in Australia).

Ill try and line up another test run and try going at lower rpm.

I suspect the folding prop has issues and Ill look at replacing with a three blade fixed prop (or maybe a kiwi prop depending on cost differences). Not sure what changing the prop costs. Asked the diver if he could do it and he said a big maybe. $700 to get her in a sling. Thanks Sam I will reach out to DH Porter.

Thanks for all the tips. Ill work up a plan of tests to do under motor. I suspect I wont get to the bottom of it before I buy it.

Looks like a Gori so should be fine.
Hard to tell with the prop half folded but I would be having a close look at whether the prop is opening fully or the blades are too close to the deadwood when spinning.
shorten the blades and put in more pitch.

Great advice above, but if you don't want to change props and gearboxes, back off your revs till it feels comfortable. If that speed is too slow, talk to the experts as above.

Mine is a similar setup, although not tiller and is a 3GM20. It has been over propped in an earlier life with the folding prop. We don't normally get above 2300 rpm, which gives 7.3 knots (about hull speed). At 1800 rpm we get 6 knots with a clean bum and approx 1.25 litres per hour. I don't have any vibration, but did previously and was fixed by a slight realignment of engine mounts (by a professional).

It tracks beautifully under sail, but not on motor. The autopilot works hard to keep it on track. It is a bitch in reverse, always wanting to walk to port.

Being over propped wont cause vibrations.

I would also shift that shaft anode down close to the skeg, needs to be as close to the propeller as possible.

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Yara said..

Ramona said..
Being over propped wont cause vibrations.

I would also shift that shaft anode down close to the skeg, needs to be as close to the propeller as possible.

Being over-propped will certainly limit the revs. Large swirling masses of water hitting the skeg is going to exaggerate the "prop walk" phenomena. There are some good articles out there that explain that "prop walk" is caused by the swirling flow hitting vertical hull surfaces, which is why long keelers have such a difficult time going astern. Nothing to do with water density differences, even though that theory makes it easy to work out which way the effect is going to happen.

Great thanks.

Spoke to Austral Propellers this morning. They agreed that perhaps the prop is over sized which would limit the revs. They also mentioned that if the revs are limited you might see some black smoke in the exhaust which I did see a very tiny amount of.

They sent me to get the diameter of the current prop and a few other things and they will tell me if the current one is over sized.

Interesting to discover that buying a new prop is not straight forward. He said that we really need to have accurate measurements of the shaft taper before they make a new prop. This is because in the past many standards were used. This could be done by sending them the current one (which probably wont come off under water) or by taking it out of the water and taking the prop off to measure the dimensions of the shaft taper. They can be all ready to make it so that if I am getting it antifouled they can be ready with the casting molds so that when I send the dimensions they can make it in a couple of days and get it back on before it goes back in the water.

Anyway ill keep you updated as I work through the issue.

Jack
I agree with yara on this one.
Your comment
"might see some black smoke in the exhaust which I did see a very tiny amount of."
has me wondering if you might be over thinking this one.

Diesel engines exhaust small amount of black smoke as a matter of course.

gary

If you're looking for a rule of thumb, I recently replaced my Cav28 old 2-blade flappy folder prop with a 2-blade geared folding prop for about $3200, including parts, labour and a new prop shaft, new cutlass bearing and bits and bobs. The new prop works very nicely. I've posted further details on my blog, here

theboattinkerer.blogspot.com/2020/06/episode-26-wobbly-prop.html

Incidentally, the previous photo shows both blades in a half-open position, which looks wrong. If it is a flappy-folder, one blade will be down and the other horizontal (see photo on my blog). If it is a geared prop, the blades will be in the same position, but they should be either open or closed, not half open, as shown in your photo. You should find out if the blades are jammed, but you might need a bit of a swim to find out.

When I was exploring options, I was advised that a rebuild would cost the same as a new prop, so I got the new prop, and I'm glad I did. However, I still have the old prop and prop shaft advertised on Gumtree for the price of the scrap bronze. PM me if interested

Yes, agree this is a difficult one and you may be overthinking it. From my experience getting the right prop/engine combination is very much trial and error, part science and part art. An experienced shipwright at my marina said that it can be an iterative process, so as advised above wait (and experiment) until your next slipping. You definitely don't want to change engines without thinking through the alternatives first!

In my case (a piddly Yanmar 1GM10) the prop manufacturer (JBC) adjusted the angle of the two feathering blades and it was a great success for me, with higher revs leading to better engine cooling and (I suspect) lower load on the engine and gear box. The JBC guy said it was definitely overpropped. The first step is to check the engine manufacturer's recommendation (RTFM) on revs for your engine. There should be a recommended range for idling (easy to adjust yourself while the boat's in the water, but don't idle too long as it's not good for the cylinders), maximum revs under no load ("racing" the engine- for me 3,600rpm), and a sweet spot for cruising well for the right combination of speed and fuel efficiency. For me that's about 75-80% of max revs. These revs are assuming flat water, clean hull, minimal headwind etc. (Plan some time trials and perhaps calibrate your log while at it.) Above that it gets noticeably noisier, more vibration, and fuel efficiency goes down markedly.

It's good to know you have that 15-20% in reserve for emergencies though. Although people sailed without engines for thousands of years, I see mine as my most important piece of safety equipment.