Selecting a propeller - your help would be appeciated

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cmedsailor

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I know there are lots of discussions about this subject and I got completely lost reading some of them, but I will try to be as specific as possible on what my requirements are.
I currently have a 2 bladed fixed propeller on my Beneteau Oceanis 361 boat (VP md2030d, 29hp). I do race occasionally for fun and get competitive at times, but I am quite happy with its drag while sailing. Most of the time I use the boat for cruising with my family which means motor sailing or “relaxed sailing” (meaning “do everything myselfsailing” with my autopilot friend). Big disadvantage of the propeller is its ability to push the boat against anything but calm conditions. SOG drops below 5 knots. This must be improved as I am planning next year to make a 300+ miles trip and chances of meeting waves and wind are close to 100%!!
So, my requirements is to have a propeller that produces maximum drag equivalent to the 2 bladed fixed (as I said I am quite happy with it) but be able to push the boat when motor (sailing) against rough waters.
One of my thoughts is to buy a 3 blade fixed propeller and use it only when needed (during big cruising trips) as long as it is possible to change a propeller while the boat is in the water. Unfortunately I have never tried this, not even out if the water, because I bought the boat only a year ago. I like the simplicity of the fixed propellers, lack of vibrations but I would not like to carry a “3 blade bucket” all the time (only occasionally).
Another though is of course to buy a folding or feathering propeller and this is where things get confusing. Money is always an issue nevertheless I wouldn’t buy the cheapest and throw it away after some time in order to buy something better and therefore paying twice. There are lots of selections like autoprop, max-porp, kiwis etc, etc.
I would appreciate your comments.
 
I fitted a maxprop this year which is excellent but expensive, I would look at the Featherstream from Darglow Engineering which received excellent reviews. I would have bought one however a suitably sized Maxprop was available at the time without a delay on delivery, if price is an issue look at the Kiwi prop. I prefer feathering to folding.
 
I would suspect if assuming your present prop transmits all the available engine power to the water then changing the prop alone will not change your situation, only increasing the avaiable power will
 
Your engine would seem on the face of it to be quite powerful enough to push the boat along at better than 5 knots in calm conditions. You don't say what diameter and pitch the prop is though and I would tend to think this is where your problem lies. A 3 blader will be marginally better than 2 but again only if you get the pitch and diameter right. Also as you say the drag when sailing will be higher which is not ideal. I am a great fan of the Brunton Autoprop myself. There are 4 reasons why I think this might be the way for you to go.
1. In calm conditions it will adopt a course pitch and drive you faster than a fixed blade prop probably would.
2. When into wind and tide it adjusts pitch to give you the optimum drive without overloading.
3. When sailing it feathers and will produce much less drag than you currently have with the 2 blader.
4. When motor sailing at low revs it will again adopt course pitch and give you more drive than a conventional prop.

Most other folding or feathering props are less efficient than a fixed blader. The Autoprop is almost as good as a fixed pitch prop under ideal conditions but considerably better over the range of conditions you will meet when cruising. There is only one disadvantage. They are expensive. But I don't know anyone who has fitted one who ever regretted it.
 
You have almost answered your own question!
To improve your motoring performance you need a 3 bladed prop.
If you want to have lower drag than a fixed blade you need a folder , a feathering or an Auto prop.
Your choice then is largely dictated by the depth of your pocket. Nothing is less than £1k and can be over £2k. The fact that so many alternatives exist suggests that there is no one "best" choice. All achieve the same objective to a greater or lesser extent, and as you are a regular on the forum you will see that there are supporters of every type - only last week there was a thread on the subject.
So, back to being a good consumer. Do your homework, collect material from all the suppliers, seek their advice, compare the pros and cons and make your decision. Nobody else can do it for you!
I can understand you not wanting to commit such a large sum of money when you are wary of the outcome. A compromise might be to buy a fixed 3 blade prop of the correct size and try it to see if you get the motoring performance you want. You may also find that the penalty when sailing is not as great as you think. You will at least have a benchmark for comparison. If this is the case you have saved a lot of dosh. If you like the motoring performance, but not the drag, buy your chosen folder/featherer and sell the fixed prop.
 
My engine and 2 blade fixed propeller pushes the boat at a SOG lower than 5 knots in ROUGH conditions. In a calm sea I get around 6,2 knots and 2500 rpm.
 
Have a look at Steel Developments and in particular their feathering props.
One advantage is they are user pitchable both ahead and astern (individually) so no more guessing at the best pitch for your setup
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You still don't say what pitch and diameter the prop is, but when you are labouring agaings headwinds and tide does the engine RPM fall? Do you tend to get black smoke at full RPM? Are you in fact using maximum RPM or like many reluctant to go beyond 3/4 throttle?
 
Even then Cliff you can only adjust for one set of conditions, and you have to be out of the water to do that, where the Brunton Autoprop will automatically adjust to the optimum pitch under all conditions on it's own.
 
At nearly double the price! - Certainly the Vruntons are noce pieces of kit but they are VERY expensive for the use the average "weekend" sailor would get out of them.
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Sounds to me like you might have the wrong 2-blader for your boat/engine. So one alternative would be to try out more fixed 2-bladers to find one that will do what you want. Before the big expense of a folding/feathering job!

Myself I wouldn't try changing the prop underwater. Would rather dry the boat on scrubbing piles for that job.
 
Two points here Cliff.
1. He isn't an average weekend sailor and is looking to do some extensive cruising.
2. I did say originally "you get what you pay for"

On the latter score I am always surprised that a guy will spend £100k or more on a boat and then complain because a vital bit of gear that affects that boats performance costs 3-4% of that.
For those operating on a tight budget however I do recognise that the Autoprop is expensive. The best usually is.
 
I would not go as far to say Bruntons are "the best" - they do have some (one) feature in their favour namely auto pitching however the cost/value/benefit equation does come into it and for value for money/performance the Steel developments prop fits the bill for me. Most leisure sailors are not multi millionares despite what the press say but to those who are (or think / act is if they are) then good luck and go blow 3~4k or more on a prop rather than look at alternatives.
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This performance is quite normal. I have a Bavaria 37 with the same engine (albeit a saildrive) and a standard Volvo 2 bladed prop. I cruise at 5.8 knots at 2400 in flat water (lots of it in the Ionian!). Maximum revs is 3600 which gives about 7.2 knots. Struggles motoring into wind and waves, but doing more than 5 in these conditions is uncomfortable anyway, but one can bash away slightly faster by increasing revs - remember at 2600 you are well below maximum power output. I find motor sailing just off the wind the most effective way of making progress.

Why have I not changed the propeller? Because I can think of better things to spend the money on. I have a feathering propeller on my other boat because it is heavy and underpowered both sail and motor. The prop improves light airs sailing performance, but is marginally inferior when motoring than the previous fixed 3 blade. Still not convinced it was a good buy!

So, you have to decide what is important for you. A 3 blade prop will improve motoring performance. However the difference in price between a fixed and a folder/featherer/Autoprop buys an awful lot of good canvas to improve light airs sailing performance. If it were me, I would go the fixed route, improve the rig and then if I still wanted to spend money for what might be only a small improvement, go for a more sophisticated prop.
 
Indeed it is autopitching that sets them ahead of the rest. I personally don't know of any other prop that gives you this function and feathers as well. It's up to every individual owner to decide if the cost is worth that advantage. You obviously don't believe it is. No problem. Don't buy one! I have one however and I would not swap it for the world.

p.s. I am not a rich fat cat either!
 
[ QUOTE ]
p.s. I am not a rich fat cat either!

[/ QUOTE ]That makes two of us /forums/images/graemlins/grin.gif perhaps we should start a "sailing on a shoe string" club - ooops too many of them already... /forums/images/graemlins/ooo.gif
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Artificial Intelligence is no match for Natural Stupidity
 
Like Tranona, I think that the prop is not your problem. We have a three-balder and an engine of similar power on a slightly smaller boat. The calculated maximum speed is 7 knots, which is achievable of full throttle, but at the expense of 50% higher feul consumption, some black exhaust and a blackened transom, so I prefer to cruise at 5.5 to 6 knots. Last Monday, we were of a mooring in Rotheasy and needed to move over to the harbour against a force 6 easterly. The speed through the water on full power was only 5.5 knots, but the trip was made easier by reducing to cruising power and settling for 4.8 knots until we got into some shelter.
 
I had an autoprop for 7 years. It was excellent but the early ones with water lubricated bearings needed the said bearings changing more frequently than expected . We lost a blade eventually and had to get hauled out to put the original prop on. I have heard similar stories about other complex props with moving parts generally on boats doing big mileage . For that reason I would not risk another but i do miss the performance.
 
I tend to agree with you generally. That's why I asked if his 5 knots was achieved at max revs with black smoke or cruising RPM. Your performance would be fairly normal for a 36 ft boat I think. I still don't know if he can achieve what you get though. If he can't get 5 knots flat out I tend to think he is under-propped. If its 3/4 throttle its fairly normal and if he want's to go faster use more throttle and burn more fuel!
 
Volvo 3 bladed folding propeller

FWIW I am very happy with my Volvo 3 blade folding propeller, no vibrations and it is very good ahead AND astern with minimal drag whan sailing.
My boat is smaller than yours at 33 ft and my engine is the Volvo 2002 (17hp), In flat water I can get 6.8 kts flat out and 6 kts cruising.
For example, last week I motored all the way back from Holland to UK in 15 to 25kt head winds and 2m seas, and averaged 5.5kts.
 
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