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Old 06-16-2008, 10:02 AM   #1
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Greetings,

We just got a call from the new owner of our small sloop Velella. He loves the boat and has taken it down the Whitsundays. He called to tell us that when he took it out of the water an engineer informed him that the Gori 2 blade folding prop we purchased from Yanmar along with the 10gm saildrive had the wrong pitch for the engine. He didn't seem too concerned and is now getting a new prop that will deliver a more appropriate thrust for the engine. Sailing Velella around the top of Australia to Cairns we just assumed the lack of power was due to the small engine.

You live and learn eh?

Now with a 33' Alajuela cutter we are preparing for some blue water extended cruising in the new year, our experience with Velalla has got me thinking about props.

Mico has a displacement of 6.14 tonnes and is powered by an Iveco 39 hp diesel driving a bronze, fixed, 2 blade prop with a 420 mm diameter via a 25mm stainless shaft - I don't know its pitch.

We are taking Mico out of the water next month for the first time (for us) to do a few modifications in preparation for next year. I have dived on the hull a number of times and the current prop looks ok although a bit on the 'thin' side.

The biggest job we will be doing will be remounting the engine (80hrs) on some proper mounts. The previous owner installed the new engine without mounts - simply coach bolting it to the engine bearers. The engine runs fine but the thought of a year at sea with the constant vibration we experience is too much to contemplate

It's not going to be a cheap exercise but a local marine engineering company has given us a price and will be remounting the engine.

So my question/s - should we also look at getting a folding prop and keep the current one as a spare? Do all you world cruisers carry a spare prop? What prop should we be looking at? Fixed, folding or feathered?

Mico has done one circumnavigation so we are confident she will do another - but being cautious yachties - we are more inclined to over engineer and be over prepared (if there is such a thing).

We'd love to hear of your experience.

Many thanks,

Robin & Shaun
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Old 06-17-2008, 04:10 AM   #2
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Hi,

There are companies who deal with propellors, including the matter of the correct pitch for your boat. They take into account things like the horsepower of the engine, the reduction on the gearbox, the weight of the boat and the type of propellor. In general, a two-blade propellor will give you a slightly rougher ride and less push than a three-blade prop. Apparently that's because at one point in the rotation is will be in line with the skeg (or similar) and not pushing much water. A fixed three-blade gives you a better ride than a fixed two-blade, but it has more drag, particularly if you have a mark on the shaft inside the boat which enables you to line up the two-blader with the skeg when you're sailing. I've had both. I prefer the three-blader because it's got more grunt and accept the additional drag. I would, however, prefer to have a three-blade feathering propellor, which has the advantage of good propulsion but no drag when sailing. But you need expert advice on these things. It's a bit formulaic, and so an expert is required.....Tel.
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Old 06-17-2008, 04:44 AM   #3
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Cliff Friesen in his :-

Considerations On Choosing A Sailboat Propeller

Has some excellent observations on props for our kind of boats :-PROPS

Also have a look at this site for calculating the critical prop measurements :CALC

Once you get your boat on the hard you should be able to measure the pitch quite easily.

Richard
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Old 06-17-2008, 08:06 AM   #4
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Hi,

Thanks for both responses - very much appreciated! I take the point about the fixed 2 blade Tel - and it certainly seems to be carried through in your link Richard. The harmonic set up has me now re-thinking the vibration issue. Things are never simple are they?

With the engine currently bolted direct to the bearers without any flexible mounts, everything hums on mico. How much of this has to do with the lack of mounts or the 2 blade prop will be interesting to find out. All I know is that I am getting tired of people saying 'oh you have an Iveco - they are so quiet you hardly hear them running' Not on mico it aint.

Seating the engine on flexible mounts is not going to be an easy job. I did think we could get away with simply machining new brackets that attach to the sides of the motor with the top arms sitting over the new engine mounts (reverse to what they currently are). This way we could keep the same shaft angle. Unfortunately the rear brackets are cast unlike the front which are removable.

The engineering company have come up with the solution of fabricating a stainless steel bar that will sit on rear mounts on the bearers, with a drop down section to carry another two engine mounts on which the rear of the motor will then sit. The front will be tackled as previously stated. We have plenty of room under the engine but no room above. Basically we are looking at 6 engine mounts all up.

At $5000 for the engine work, I'd hate to discover that the vibration is all down to a 2 blade prop! Stay tuned.

Kind regards,

Robin & Shaun
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Old 06-17-2008, 08:57 AM   #5
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Quote:
Originally Posted by mico View Post
At $5000 for the engine work, I'd hate to discover that the vibration is all down to a 2 blade prop! Stay tuned.
Folks I recently re-engined a steel ketch designed and built in Holland in the 70s - the old engine had to be taken out in small pieces - the new one had to be installed without its Oil Pan (sump) without its Heat Exchanger. New Riser blocks had to made to go on the engine bearers - new engine mounts - 2 new brackets had to be fabricated - ALL so that the new engine could fit, giving some space between the top of the engine and the headlining. The Engine was put together and marinised by a first class engineering company in Brisbane - Australia . It was installed in Langkawi - Malaysia. ( It purrs!)

You mention $5000 for engine work - what will that provide?

Send me a PM with your Email Address and I will put you in touch with some solutions.

Richard
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