Folding prop

[Isola]

Hello,
I'm totally new on this forum and wonder if any of you members have fitted a folding prop on a Bavaria Ocean 40? I'm planning to buy one but everyone I ask give me different figures ... I believe the hull on my boat (from 2002) is the same as the aft cockpit model. Engine is a MD22 59hp.

Thanks in advance!

[IslandAlchemy]

You have opened Pandora's box.

There are many options, folding or feathering, 2, 3, or 4 blade, bronze, stainless, composite, etc.

I guess the first question is....what do you want from it?  Are you looking for just better sailing performance?

Theortically, the most efficient prop is a 2-blade folding with the biggest diameter you can fit in the gap.  More blades give you more grip.  Feathering gives you less forward drive but better close-quarters handing and better response in reverse.

The choice (as they say), is yours......

[Symphony]

Welcome to the forum

Nothing difficult about fitting either a folding or feathering prop to your boat - except there is a wide choice of both types and brands so you need to do a bit of research first before buying. Broadly there are 3 different types - folding, of which perhaps FlexOfold are the best known (although Volvo have their own type as well), feathering where the blades mechanically switch from forwards to reverse or float when sailing, MaxProp and Featherstream are good examples, or variable pitch such as Bruntons Autoprop. Each of these have their own selling points - folding is simplest, cheapest and probably lowest drag, feathering, more expensive and in some cases more flexible - for example with some you can reset the pitch or have different pitches in forward and reverse. The Autoprop adjusts pitch automatically according to load and speed which makes it popular for those who spend a lot of time motoring or motor sailing.

All types reduce drag when sailing giving some improvement in speed under sail, particularly in light airs. Which you choose depends on what your objectives are. Most give at least as good motoring performance as the standard fixed props, but some folders are not so good in reverse. Feathering props can give improved motoring performance if the boat has marginal power - not a problem for you and whichever you choose you are unlikely to be disappointed. However if I was choosing a prop for your boat (which is heavier than the aft cockpit version) and was going long term cruising, particularly in the Med I would favour either a feathering prop such as the Featherstream, or an Autoprop if I expected high motoring hours.

I have had a FlexOfold 2 blade on 2 Bavarias - a 2001 37 with an MD 2030 and now on a B33 with a D1 30. Performance is virtually the same as the standard prop and I like the simplicity and low maintenance. I have also had a Featherstream on another boat which was underpowered and motoring performance was better than the original fixed prop.

The important thing is to first make your decision on type and brand and then fit the size recommended by the maker or dealer. Because designs vary some props are more efficient than others and sizes (pitch and diameter) can vary. For example my B33 had a factory fit fixed prop of 16*13, but the folder is a 16*11. Your supplier will have experience of what works with its design. If you are in the UK then Darglow Marine are worth talking to as they have more than 30 years experience with Max Prop, FlexOfold and now make the Featherstream.

Hope this helps.

[Bavaria 34]

You have opened Pandora's box.

There are many options, folding or feathering, 2, 3, or 4 blade, bronze, stainless, composite, etc.

I guess the first question is....what do you want from it?  Are you looking for just better sailing performance?

Theortically, the most efficient prop is a 2-blade folding with the biggest diameter you can fit in the gap.  More blades give you more grip.  Feathering gives you less forward drive but better close-quarters handing and better response in reverse.

The choice (as they say), is yours......

Bob, are you getting my pm's?

[Salty]

Hello,
I'm totally new on this forum and wonder if any of you members have fitted a folding prop on a Bavaria Ocean 40? I'm planning to buy one but everyone I ask give me different figures ... I believe the hull on my boat (from 2002) is the same as the aft cockpit model. Engine is a MD22 59hp.

Thanks in advance!

I bought a Volvo two blade folding prop that was advertised on eBay a number of years ago, it was the same diameter and pitch as the aluminium fixed blade prop originally fitted to my B36(2002), and despite that it was a obviously a much more expensive prop to manufacture, it only cost me about £100. It was a direct, straightforward and easy replacement for the original prop, and works a treat in both ahead and astern. I can’t say that I’ve noticed any difference in performance without wondering if there might be some degree of wishful thinking involved, but I don’t think there is any less performance than before the change. With just an MD2020 engine of only 19hp it will drive the boat at around 7 knots on a clean hull.

[Isola]

Thank you for all replies! In this case it's not about choosing what kind of propeller and then go ahead and buy it ... I wouldn't pay full price for a folding or feathering propeller, but have found a three bladed Volvo Penta folding prop for half of what it would cost new. And it's almost new and cooperized (if that's what you call it).
The original fixed prop is according to this forum 17x15 and the folding prop that I'm interested in is 18x13. I have asked a prop specialist here in Sweden and they recommend a three bladed 17x11 Penta folding, witch sounds small to me. Variprop in Germany recommend a three bladed 19 with adjustable pitch.

I have just bought the boat and never sailed it. To me it appears like a 59 hp engine in a 8300 kg boat is a bit overpowered, and I would be surprised if I should rev it to more than 2000 to get 6-6,5 knots out of it. I know that the MD22 is a high revving overhead-cam engine (at least compared to for example a D2-55) but I'm not very keen on listening to it at 2800 revs at cruising speed – so a slightly bigger prop make sense to me.

Anyone out there with experience from this?

[JEN-et-ROSS]

Hi. We have a 29 year old Volvo Penta 3 bladed folding prop on a B38.
About 5 years ago we sent it to be tested and refurbished by Darglow. It was returned to us effectively 'Zero Timed' (3 new oversized pins and no sign of 'de-zincing') so should be good for another few decades.
So if you can get hold of an almost new one that is of suitable size and pitch I would recommend that approach.
The only thing to bear in mind is that the anodes require regular replacement, depending on your area 6-12 months........Bill

[Symphony]

As I suggested earlier, direct comparison of size between different types of prop is problematic. The Volvo prop has a unique design of blade and appropriate sizes are rarely the same as for a fixed prop (or indeed another design of folder/featherer as you have found with the Variprop recommendation). Hence my suggestion that you follow the manufacturers recommendation.

This does not help if you are buying a second hand prop of course but it might help if you knew what boat and engine/box combination it came off. The best you can do is compare it with the prop currently fitted. You think it is 17*15 (it would be sensible to check the actual prop fitted - it will be stamped on the boss) and the folder is not that different in size. A rule of thumb is that 1" of diameter is equal to 11/2"-2" inches of pitch, so an 18*13 will be roughly the same as your 17*15. In general diameter is preferred to pitch, but on your engine/drive the largest available diameter fixed is 17", so moving to a finer pitch larger diameter is positive.

Not sure what you mean by "cooperized". Volvo props are bronze with stainless pivot pins and fastenings. There is no standard finish, although many people use an antifoul such as Trilux or paint at least the blades with Velox. They have a reputation for heavy anode erosion and wear of pin bearing surfaces and gears. So it is worth inspecting closely and if you do buy, check the anodes regularly and replace promptly. Painting does reduce anode erosion because it reduces the area of bronze exposed to seawater.

Not sure you will find the boat overpowered. The main market for the Ocean range was long term cruisers and liveaboards (like some on this forum) so real life payloads of 2 tons or more are common, plus there is a lot of windage, particularly if fitted with such things as sprayhoods, biminis, radar arches and solar panels! One appreciates the power when you want to motor against the wind and headseas. The aft cockpit versions were a bit lighter and aimed at the charter and coastal cruising market where the standard MD 2040 was perfectly adequate. You will find boats like the HR 36 and similar size Malos as well as Moodys and smaller Oysters of the same era used the same engine.

[Isola]

Again, thanks for the answers!
Unfortunately the original prop is in a bad condition and the stamp is gone, but other Bavaria Ocean 40 owners with the same engine/saildrive claims they have a 17x15. Cooperized is just what it sounds like – a cooper plated prop. It's starting to get common in Sweden and it works like a miracle, no growth at all! See attached picture.

My previous boat was a Sirius 42 (British 17 ton steel boat) witch my wife and I lived on in the Med for 6 years. We had a new D2-55 in it and and motored in storms and very tough conditions many times without any problems. So 4 more hp in a half the weight boat is plenty to me! I think I will buy the prop and try it – if it doesn't work like expected I can always sell it again. I'll report as soon as I've tried it!

[Symphony]

OK I understand now. There was an article in the last issue of Practical Boat Owner about copper plating props. Written by a chap called Vyv Cox who is a metallurgist and who writes regularly on issues to do with corrosion and corrosion protection. He reported success after 2 years in the water with a copper plated fixed blade bronze prop. He has also carried out long term tests on Velox on a Bruntons Autoprop with success. I did my prop last year with Velox and look forward to seeing how it has fared when I haul out in 2 months' time.

[sy_Anniina]

Not quite the B40 Ocean, but we have similar body design B40, vintage 2001, engine MD22L-B, saildrive 120S-E, 2.20 printed on label so i guess this is the gear ratio.

We have a Volvo folding propeller. Not 100% sure on the dimensions, but the blade has stamping P/N 3581227. Based on Google it looks like the propeller is 17x12 LH, Calling Volvo with P/N should clarify this. Our cruising RPM is around 2000 with flat water speed around 6.7kn, so not really revving. Based on this 18x13 sounds big - if your saildrive has the same gear ratio.

This copper plating sounds like an interesting idea. Having a faint recollection of electrochemical copper plating in school makes me think about trying it out as a DIY project.

Hope this helps.

Tommi
S/y Anniina

[IslandAlchemy]

Your comment comparing a D2-55 to an MD-22 is misleading when you assume that because the MD-22 is rated at 59hp, it is more powerful than the D2-55.  The D2-55 is the more powerful engine except at maximum revs.

The D2-55 rates its 53hp at about full open throttle, whereas the MD-22 rates at 49hp at full open throttle.  At 2000rpm, a D2-55 is giving you 38hp, whereas the MD-22 will only be giving you 35hp.

Look at the power curves and you will see what I mean.

Also, the MD-22 has less torque than the D2-55 (135 vs 123 at 2,000rpm), so putting a bigger prop on than you had on a D2 will kill an MD-22.

[Isola]

Interesting information– thank you!
Your boat has a different keel, is lighter but has the same hull as the Ocean. And your saildrive is the same, the engine is basically the same – the extra 9 hp in my comes from the fact that it revs higher. And who wants to rev above 3000 anyway?

6,7 kn at 2000 revs is impressing – witch makes me wonder if your prop is really a 17x12? I can find one private ad on google saying 3581227 is 17x12 but it could be a 18x15 prop instead ... Old Volvo parts numbers are difficult to find but I came across this one (see attached file). Of course 3581227 is mysteriously gone on it but if you read the pale red column it sounds like your prop is bigger. The prop I'm interested in is stamped 3581225 witch according to this is 18x13, so it seems too be accurate. Can you rev your engine fully?

I definitely think you should try copper plating your prop. If you read Swedish there was an interesting article about it in Kryssarklubben a while ago: https://www.sxk.se/system/files/blekingekretsen/forkoppring_av_propeller.pdf

Island Alchemy – you are absolutely right! But I'm not putting a bigger prop on the MD22 then I had on my D2-55, and that was on a totally different boat. So it can't be compared.

[sy_Anniina]

Thanks Isola for the copperplating info link!

I'd have to measure the prop dimensions, but your estimate and datasheet really suggest our prop may well be 18x15. BTW, our keel is 2.1m deep cast-lead version.

Haven't experimented if I can reach max revs while motoring - can do this but you need to wait until May as the boat is at hard now.

BR

Tommi
s/y Anniina

[sy_Anniina]

Just measured using templates and did the calculations with app from https://sites.google.com/site/thepropellerhub/simple-pitch-measuring

Drums.... Our propeller was indeed 18x15. The measurement and calculations resulted on pitch of 14.977 so 15 is quite propable number for the pitch.

Luckily our propeller was back home waiting for polishing...

BR

Tommi
s/y Anniina

[Isola]

Woaw! I'm for ever thankful to you Tommi!
This makes me confident that 18x13 won't be too big for our boat. When I opened this Pandora's box I heard from resellers that a prop should never be bigger than you can rev the engine fully with it, and others saying the perfect size is a prop that can make you rev 90% ... Some say this will wear out the engine faster and some say it won't. The biggest reseller in Sweden think I should go for a 17x11, but to me that sounds wrong. This engine produce maximum torque at 2200 revs and I can't see why I should go above this for let's say 6,5 knots. Fuel consumption is of course also a big issue.

I will give it a try and return telling you my impression in May when we've put our new boat in the water.

[Symphony]

You are correct. The prop should enable the engine to reach its maximum rated revs, or within 150 rpm or so. Difficult to get exactly right because pitch/diameters tend to go in 1" increments and each increment is equivalent to 250-300 rpm. When an engine is commissioned properly according to Volvo requirements this is one of the key tests. The engineer that commissioned my new 33 in 2015 was very particular about this because it was fitted by me with a non standard size prop. The D1 30 is rated at 3200 rpm and my engine consistently achieves 3100 rpm - I do it periodically as it helps reduce the build up of deposits in the exhaust elbow.

It is almost impossible to wear a modern engine out in private yacht use. Typically the "weekend" sailor will do 150 hours a year and the expected life of the engine is 8000, or over 50 years. Such engines tend to die from lack of use, or rather intermittent short duration use followed by long periods of non use. Other contributory factors to shorter life are long periods of light load running such as for battery charging or motorsailing at low rpm or running for short periods such as just leaving a mooring then shutting down before reaching working temperature.

Boats used commercially tend not to suffer these sorts of problems. My last boat I had on charter for 7 seasons in the Ionian where motoring is more common than sailing. It did around 3500 hours in that time and the engine gave absolutely no problems with oil and filter changes 3 times a year and coolant changes every other year. In particular there were no signs of build up of deposits in the exhaust elbow. It is not uncommon for some charter boats to run over 10000 hours on the original engine.

The propellers fitted by Bavaria are sized to meet the Volvo requirements for each model of boat/engine and any non standard prop should aim to achieve the same load - that is achieve the same maximum rpm. This will allow comfortable cruising at 65-75% power (in the range 2-2500rpm, also the range of maximum torque) as well as achieve at least hull speed at maximum rpm. There is no danger of overrevving (that is with too small a prop) because the engine is governed, but in that case cruising revs will be higher and maximum speed reduced. Too big a prop results in overloading the engine and not achieving either full revs or maximum speed. This is most obvious if the boat is marginally powered because you need to use the higher revs (and therefore power) range to achieve a decent speed.

Not sure fuel consumption is really an issue. That is virtually a direct function of power demanded by the prop to achieve the speed and for a given speed that is the same irrespective of the revs. The power curve shows what the engine can produce at each rpm, but it only does it in response to the load placed on it. Fixed propellers only place maximum load at maximum rpm. The principle behind the Autoprop is that the pitch is infinitely variable and will always fully load the engine to achieve the desired speed. So if the speed your require needs 30 hp it will adjust the pitch so the engine produces that at the lowest rpm.

Another way of illustrating this is to consider boats where there are 2 engine options, such as the 33 I have. The standard is 20hp and the option 30. To achieve a cruising speed of say 5.5 knots the 20 hp will require 2400 rpm and the 30, 2100 rpm with standard propellers. The horsepower required is exactly the same, as is the fuel consumption. The temptation of course with the larger engine is to use the extra power potential and cruise at 6 knots, which is roughly 2400 rpm using more fuel. On the other hand you can cruise as I do at the same speed and have the benefit of lower engine noise.

Anyway, it seems that your 18*13 should load the engine correctly but you will only know when you get the boat afloat. Worth doing some runs in flat water (and preferably no wind or tide) plotting speed against revs at 200 rpm increments from, say 1800 rpm up to maximum. I think your estimate of 6.5 knots at 2200 rpm should be achievable. It is interesting that sy_Anniina reports 6.7 at 2000rpm with his 18*15 - that sounds about right, but I suspect the 2" extra pitch will limit maximum rpm to below the recommended level.