Worth changing propeller

[Sparkylarks]

Back in 2017, I installed a new 2-blade folding propeller, on the original Volvo Penta 2003engine which worked seamlessly until I got a new engine last year. The new engine is a Volvo D1-30, and performs smoothly up until about 1500 RPM, achieving a boat speed of 6 knots, very quickly. However, any throttle increase beyond this point causes a significant rise in noise and vibration. When the engine reaches 2200 RPM, despite the speed only slightly increasing to about 6.5 or 7 knots, the noise and vibration levels become intense. I can go up to 3000rpm in neutral( rated RPM is 3200)These vibrations have been so pronounced that I've had to repeatedly retighten the gearbox bolts, with some even working their way loose.Given these symptoms, I suspect that the current propeller may be too large or the pitch too high, creating excessive drag. Flexofold has suggested switching from a 17"x12" to a 16"x12" propeller. Do you think this reduction of one inch in diameter would make a material difference?To add to the complexity, the engine required some realignment during its last service. I'm trying to discern if the misalignment was causing the vibrations or if it's a consequence of the propeller not being quite right.Really it boils down to, do I get the realignment done, and put the boat back in the water and see how it goes, or get the realignment done and replace the propeller blades now.

 

[Refueler]

I am probably wrong ... I hope so - but I cannot help but feel your problem is deeper than just prop. Unless prop is seriously damaged.

If engine alignment / mounting and setup is correct - too big a prop would just mean engine not reaching high revs / optimal loads. The engine would labour just like driving your car in top gear too low a speed ...

To me - the give away factors are the loose bolts etc. Something with that setup is not right. If the boat is out of water - I would have a decent engine guy have a serious look and measure it all up ...

 

[B27]

What length is the boat?

Normally, if the prop is wrongly sized, I would not expect that to directly cause harsh vibration.
Is it perhaps aggravating a problem with engine mounts, flexible coupling or something?

Or perhaps there is a fault with the engine, one cylinder playing up somehow, becoming more noticeable under load.

I would suggest checking the prop sizing against all the online calculators and also against Dave Gerr's book.
You'll need to be sure of the gearbox ratios.

 

[Tranona]

Back in 2017, I installed a new 2-blade folding propeller, on the original Volvo Penta 2003engine which worked seamlessly until I got a new engine last year. The new engine is a Volvo D1-30, and performs smoothly up until about 1500 RPM, achieving a boat speed of 6 knots, very quickly. However, any throttle increase beyond this point causes a significant rise in noise and vibration. When the engine reaches 2200 RPM, despite the speed only slightly increasing to about 6.5 or 7 knots, the noise and vibration levels become intense. I can go up to 3000rpm in neutral( rated RPM is 3200)These vibrations have been so pronounced that I've had to repeatedly retighten the gearbox bolts, with some even working their way loose.Given these symptoms, I suspect that the current propeller may be too large or the pitch too high, creating excessive drag. Flexofold has suggested switching from a 17"x12" to a 16"x12" propeller. Do you think this reduction of one inch in diameter would make a material difference?To add to the complexity, the engine required some realignment during its last service. I'm trying to discern if the misalignment was causing the vibrations or if it's a consequence of the propeller not being quite right.Really it boils down to, do I get the realignment done, and put the boat back in the water and see how it goes, or get the realignment done and replace the propeller blades now.

Welcome.

What you are describing is typical "overpropping" and should not have been accepted at commissioning the new engine. The 2003 runs to 3600 but had a different gearbox ratio and that changes with the new engine and the existing prop is too big. Depending on the boat, a 16*12 or11 is normal for a D1 30. I had one on a saildrive and a 16*11 Flexofold 2 blade. The reduction in diameter will up engine speed by around 300rpm. You should be able to achieve 3200 in neutral - this needs checking if it does not and 3000 in flat water somewhere +/- 7 knots. Are you dealing with Flexofold direct or with Darglow Engineering? The latter have a huge amount of experience with Flexofold and Their recommendation will be sound.

 

[Refueler]

I went back a number of times and reread first post ...

"the noise and vibration levels become intense. I can go up to 3000rpm in neutral( rated RPM is 3200)These vibrations have been so pronounced that I've had to repeatedly retighten the gearbox bolts, with some even working their way loose"

in NEUTRAL ?????

Sorry but I still think there's more going on here ...

 

[Sparkylarks]

I went back a number of times and reread first post ...

"the noise and vibration levels become intense. I can go up to 3000rpm in neutral( rated RPM is 3200)These vibrations have been so pronounced that I've had to repeatedly retighten the gearbox bolts, with some even working their way loose"

in NEUTRAL ?????

Sorry but I still think there's more going on here ...

to be clear, in neutral, the engine sounds very sweet, and as i push the throttle the revs go up in proportion topping out around the 3000, and no vibration or harsh sound at alll

 

[Sparkylarks]

I am probably wrong ... I hope so - but I cannot help but feel your problem is deeper than just prop. Unless prop is seriously damaged.

If engine alignment / mounting and setup is correct - too big a prop would just mean engine not reaching high revs / optimal loads. The engine would labour just like driving your car in top gear too low a speed ...

To me - the give away factors are the loose bolts etc. Something with that setup is not right. If the boat is out of water - I would have a decent engine guy have a serious look and measure it all up ...

The guy who installed the engine, and works for the Volvo Dealer, I know him well personally and he knows his stuff, came back after 50 run hours and diagnosed the misalignment.
the boat is laid up now and he will look at the alignment again.

 

[Sparkylarks]

Welcome.

What you are describing is typical "overpropping" and should not have been accepted at commissioning the new engine. The 2003 runs to 3600 but had a different gearbox ratio and that changes with the new engine and the existing prop is too big. Depending on the boat, a 16*12 or11 is normal for a D1 30. I had one on a saildrive and a 16*11 Flexofold 2 blade. The reduction in diameter will up engine speed by around 300rpm. You should be able to achieve 3200 in neutral - this needs checking if it does not and 3000 in flat water somewhere +/- 7 knots. Are you dealing with Flexofold direct or with Darglow Engineering? The latter have a huge amount of experience with Flexofold and Their recommendation will be sound.

the boat is on the hard at the moment, but I am pretty confident in saying that in neutral she reaches 3000+ rpm, Probably the 3200.
It is when I go into forward she seams over propped.

I did not really notice it for the first few months. I was getting more speed with less revs out of my new engine, I was happy.
I tend to just use the engine for getting out to races, and don;t really push it, I get 6 knts I'm happy.

Over the summer, I started to notice the noise and when doing a cruise had big fuel bug problems.
Then with a few of the guys on the cruise they were really of the opinion that the vibration was too high and I started to look at it more, and then reallystarted looking at it in more detail and realised that it might be over propped.

So I contacted Flexofold directly, They supplioed that last prop.
I suspected overpropping, and Flexofold have recommended reducing from 17x12 to 16x12.
I am sort of wondering if that makes enough of a difference.

when I look at the online calculators, i am seeing maybe 16x10 recommended,but I think I need consider

the vibration and noise is probably from mounting misalignment, so get it realigned and I can monitor that.

the Over propping is better to be considered an unrelated issue, and reducing the prop diameter is going to be needed as well as getting the alignment fixed
, and I should investigate more to see if I reduce to a 16x12 or a 16xT

 

[Sparkylarks]

What length is the boat?

Normally, if the prop is wrongly sized, I would not expect that to directly cause harsh vibration.
Is it perhaps aggravating a problem with engine mounts, flexible coupling or something?

Or perhaps there is a fault with the engine, one cylinder playing up somehow, becoming more noticeable under load.

I would suggest checking the prop sizing against all the online calculators and also against Dave Gerr's book.
You'll need to be sure of the gearbox ratios.

the boat is Beneteau 35s5

LOA:	35.42 ft / 10.80 m
LWL:	29.36 ft / 8.95 m
S.A. (reported):	556.00 ft² / 51.65 m²
Beam:	11.83 ft / 3.61 m
Displacement:	11,460.00 lb / 5,198 kg
Ballast:	4,190.00 lb / 1,901 kg
Max Draft:	6.00 ft / 1.83 m

I used the vicprop calculateor and it came up with the below, I had to estimate a few of the values i.e. beam at water line and the drauft excludign the keal, but I use conservative values and tried a few modifications and came still always come up with a 16x10

Propeller Size​ ​
Number of blades​	Diameter (inches)​		Pitch (inches)​
2 Blade​	16.1​	X​	9.7​
3 Blade​	15.3​	X​	9.6​
4 Blade​	14.4​	X​	9.4​

I can post the full calculations if you want.

 

[Tranona]

I also used Vicprop to check but that is based on a fixed blade prop. Flexofold are invariably a bit different which is why I suggested you go to Darglow. Chris has an enormous database of boats and engine combinations plus a bit more sophisticated programme. He has supplied or made 4 propellers for me and spot on.

The noise and vibration you are getting is overloading the engine and can do serious damage long term Volvo commissioning rules won't accept less than 2900rpm. I went through this with my new Bavaria 33 with the D1 30 because I supplied the propeller (from Chris) and was present at commissioning. Relieved that it achieved 3100rpm - right in the middle of the range. Change of an inch of diameter or pitch will change rpm by 250-300rpm.

The misalignment is maybe a bit of a red herring and probably exaggerated by the overloading of the engine but of course needs checking.

The key dimensions of your boat are virtually identical to my Bavaria - same LWL and beam, slightly heavier at 5400kgs, 2.17 rather than 2.14 reduction. 7.3 knots at 3100 rpm, cruising 5.5knots at 2200rpm. 16*11 propeller.

 

[B27]

I've been on boats which are 'over propped', made worse by a serious coating of weed.
The outcome was failure to rev, slow progress and a bit of black smoke.
Not big vibration.

Fact is, lots of people take liberties over propping boats and so long as they don't have a tiny engine, then let the weed grow, then try punching into a gale and chop, they tend to live happily ever after.

IMHO, the question is 'What is the vibration all about?'

That could be fouling on the prop, damage to the prop, bent shaft, knackered cutless bearing. I don't know what else!


Dave Gerr's take on props is based on:
1) you need enough blade area to support the thrust you're extracting, at a sustainable pressure.
2) generally props will 'slip' about 30% if the blade area is sensible.

So calculate the 'forward threading' of the prop, ie pitch x prop rpm gives you a number in inches per minute, take 70% of that and convert it into knots.

Obviously this is a precis of a condensed version with the detail left out, but I think it's a good sanity check.
I'd suggest borrowing or buying the book if you feel you're getting mixed messages from 'calculators'.

But this doesn't sound like a pitch and diameter problem to me!

 

[chris-s]

Our 32’ Beneteau (4500kgs) powered by the same engine with a 2.37:1 gearbox spins a 16x12 three bladed prop, tho we have now swapped it out for a featherstream.

 

[Sparkylarks]

Thanks everyone for the help, I think my plan is
1) get the mechanic down, to check and fix alignment, that is already booked
2) once launched in the spring, take the aligned engine out for a spin with the mechanic
3) if the vibration is sorted I can reassess the over propping. TBH, if the vibration gets sorted, I don't mind the fact that I max out at 2400rpm or so.

If I feel I need to change, I can

I'll reach out to Darglow, but I am based in Ireland, and so the new trading arrangements, post Brexit probably makes purchasing a non runner.

P.s. cutlass bearing looks good, but I'll have another check.
No damage to the blades,
Weed unlikely it was launched in June 2022m I had a diver down in October, and October was when I found the first loose bolts.
Diver again in May 2023

I'll double check the shaft is straight,

 

[Tranona]

Propping down to 2400rpm is not good for the engine - as I said Volvo require min 2900 to approve the installation on a new boat. Your pattern of usage is not good either. Short runs at low load results in early coking up of the exhaust (well known issue, not just with Volvo but perhaps worse with both the 20X0 and D1 series because of the cast iron elbow) which will be also affected by the overfuelling that comes from overpropping. Small diesels require periods of running at higher rpm to burn off fuel and carbon deposits. Sorry if it sounds doom and gloom, but it is reality. Propped to achieve 2900+ and periods of cruising at 2200-2400 with occasional bursts to maximum will greatly extend the life of the engine, particularly the exhaust elbow.

Darglow do a lot of business with EU customers but of course you may find it easier to deal direct with Flexofold. I think you can buy a pair of blades rather than a new propeller.

 

[Daydream believer]

My 35hp Beta had serious vibration issues when I bought the boat in Burnham. It had been badly installed by a local company before I purchased the launch. First thing was to deal with shaft whip. It has a plumer block mid length that needed renewing & re aligning. The engine was not in line with the cutlass bearing so that was dealt with. Finally the rubber mountings were not as recommended by Beta. That last item was surprisingly effective in reducing vibration.
I am told that 3 bladed props are less prone to vibration, My launch has a 3 blade & my yacht a 2 blade Brunton on a saildrive. The Brunton does not give any noticeable vibration

 

[B27]

My 35hp Beta had serious vibration issues when I bought the boat in Burnham. It had been badly installed by a local company before I purchased the launch. First thing was to deal with shaft whip. It has a plumer block mid length that needed renewing & re aligning. The engine was not in line with the cutlass bearing so that was dealt with. Finally the rubber mountings were not as recommended by Beta. That last item was surprisingly effective in reducing vibration.
I am told that 3 bladed props are less prone to vibration, My launch has a 3 blade & my yacht a 2 blade Brunton on a saildrive. The Brunton does not give any noticeable vibration

Good points.
As well as 'mechanical' vibration' caused by the engine moving about, or something being out of balance, there is 'vibration' caused by the prop blades inter-acting with something like a keel or skeg.
If the prop is close to the hull, the wash coming off the tip of a blade hits the hull.
If the hull has a skeg or something for that wash to hit, you will feel vibration in the boat.
If the hull is smooth with no fin or skeg in prop wash, less so.
A round bottom may be better than a Vee bottom.
More blades and less diameter will be smoother, generally.

This kind of thing will get more noticeable the harder you drive the boat.

I get this to a mild extent (IMHO) if I use a lot of engine power.
Because I have a big two blade prop which would ideally be further from the hull surface and there's a kind of keel strake in the hull moulding where the prop is.
I don't believe it's harmful, it's not like the engine orbiting its mountings 1GM-style, but it's not 'turbine smooth'.

 

[Daydream believer]

Bruntons did warn me that in only very few isolated cases the Ambasador rope cutter had caused turbulence in front of the prop, which caused additional vibration. I did not notice this.
Perhaps the presence of an anode or cutter on a shaft could cause issues although the OP says his prop is very near the deadwood so presumably no such items.

 

[kacecar]

I've been reading this thread with some interest as I too have a folding prop and experience significant vibration at higher revs - in both forward and reverse. I suspect the reasons for the vibration on my boat could include all of the possible sources already discussed in this thread but I still have a specific question about the differences between the original and the replacement props and the possible effect on vibration at higher revs.

I had to replace the original prop because is shed its blades (don't ask!) but prior to that had no problem with vibration that I would put down to the prop itself. The replacement item, from a different manufacturer (the old one isn't made any more) is smaller in diameter, features noticeably broader blades and a deeper pitch. My question is: could the broader blades and deeper pitch on the replacement prop be the cause of, or even just aggravate, the vibration experienced at the higher revs?

Apologies if this constitutes thread drift.