|
Post by davegatt on Apr 9, 2021 20:25:48 GMT
Hello All,
I am new to this forum. My name is David and I come from Malta. I recently bought a 2nd hand Jeanneau so 379 (2015). She is equipped with a 29HP Yanmar 3YM 30 engine and sail Drive SD25 with a gear ratio of 2.64.
Since the day i bought the boat, i always felt that the boat is underpropped. She cruises at 6.5 knots at 3200 Revs. Now that she is on the hard, i have decided to remove the prop and take it to an engineer to get it sized ( since prop had no size on it)
I am being told the the current prop is 16 x 11.
Can other Jeanneau 379 owners provide advice as to what prop is the ideal prop for these boats? The engineer recommended 17x 13 however before i proceed in buying one, it would be good if i can receive feedback from other owners.
Thank you
|
|
|
Post by jdl01 on Apr 9, 2021 20:56:22 GMT
My view, after 10 seasons, is that this model is underpowered - she sails far better than she motors. While we can power at 7 knots in a calm sea at 29oo rpm, the moment we hit a chop or a headwind, the speed drops to 6 knots. A 40 horse yanmar would have been far better with relatively little increase in weight. We use a 16 inch, three blade flex o fold prop which came with the boat as part of the performance package. The drag reduction when sailing makes a big difference in attainable speed - approx 1 knot. Jeanneau can give you the specific details on the prop number. We feel it is a worth while investment.
|
|
|
Post by rene460 on Apr 10, 2021 2:51:53 GMT
Hi David, welcome to the forum and congratulations on the new acquisition.
I feel there are actually two different issues in the problem with boat speed as you have described it. Essentially there are two matching processes required in powering a boat. The engine power must be sufficient to drive the boat at the required speed, and the propellor must be matched to the engine to obtain the maximum thrust with the available engine power.
The original purchaser probably had the option of two engine sizes, and chose the smaller one. Jd’s response suggests that the boat may have been offered with the larger engine as an option. The original owner may have wanted to save weight for racing, or just save a bit of money. I agree that it’s not much weight difference for a boat that is normally cruising, but on racing boats they cut the handles off toothbrushes, so they would definitely grasp a lighter engine. With the smaller engine, no propellor selection will match the performance of the larger one, and might just overpower the engine, even if it is the right size for the larger engine. Mind you, if the mechanic says he usually sees that larger size on that engine, then the current propellor may have been an emergency replacement at some earlier time.
With the given engine size, the propellor has to provide the maximum thrust from the available power. If the propellor is too big, the engine will not be able to drive it at the rpm necessary to develop maximum engine power, and this is generally referred to as over propped, and not good for the engine. The practical test is to run the engine at wide open throttle. At this throttle setting, the engine rpm should be at the specified maximum rpm or perhaps a little over. And the boat speed will be what you get. Worth recording when the hull is all clean and freshly antifouled as a base line for monitoring fouling resistance as time goes on. Similarly, a drop in the wide open throttle engine rpm is a good indicator of propellor cleanliness. You can find the maximum specified rpm in your engine manual.
My Yanmar mechanic recommends about 10% over at wide open throttle, but others are happy with just achieving the maximum, which I personally prefer. But you need the boat in the water for that test, and I would suggest that you wait before ordering a new propellor. If the current propellor is the one originally supplied with the boat, it will not be far out for your engine. But Sitara’s response shows that it does happen. Just not the first port of call so to speak.
While you are out of the water, it is useful to check what size you have, and also check the clearance between the blade tips and the hull. In principle, a larger propellor is mor efficient, but it is usually recommended that the tips should clear the hull by about 10% of the propellor diameter to avoid vibrations, so it is helpful to know the dimensions and clearances that you have.
If you are thinking about changing the propellor, it’s worth thinking about the type of boating you do and whether you would prefer a folding or feathering type for less drag when sailing.
Also, do have a bit of a browse through the archives, there are lots of posts on this topic there, among the wealth of priceless and timeless information on all things Jeanneau.
rene460
|
|
|
Post by zaphod on Apr 10, 2021 6:58:22 GMT
I would guess that Jeanneau knows what they are doing when it comes to matching the correct prop to the engine.
If you are thinking about a new prop you should seriously consider a low drag prop. I switched from a 17" 3 blade ZF fixed prop to a 3 blade Flexofold and it made a huge difference. Not only was I much faster under sail, I was slightly faster under power, and have a lot less propwalk as well. My 39i is a bit longer that yours, and has the 40 hp engine so I cruise at 7.5kts @2500rpm and hit over 8.5kts@ 3000rpm.
Whatever prop you choose you should let the prop manufacturer calculate the correct prop for your boat. They will want to know boat model, engine model, transmission model and gear ratios and shaft size.
I ordered my prop direct from Flexofold in Denmark, and they shipped it to my door in a few days!
|
|
|
Post by davegatt on Apr 11, 2021 11:32:04 GMT
Thank you all for the precious information provided.
Surely i need to do more homework before moving to buy a new prop to avoid getting it wrong.
Thanks again David
|
|
|
Post by dbostrom on May 8, 2021 21:22:22 GMT
I would guess that Jeanneau knows what they are doing when it comes to matching the correct prop to the engine. If you are thinking about a new prop you should seriously consider a low drag prop. I switched from a 17" 3 blade ZF fixed prop to a 3 blade Flexofold and it made a huge difference. Not only was I much faster under sail, I was slightly faster under power, and have a lot less propwalk as well. My 39i is a bit longer that yours, and has the 40 hp engine so I cruise at 7.5kts @2500rpm and hit over 8.5kts@ 3000rpm. Whatever prop you choose you should let the prop manufacturer calculate the correct prop for your boat. They will want to know boat model, engine model, transmission model and gear ratios and shaft size. I ordered my prop direct from Flexofold in Denmark, and they shipped it to my door in a few days! Strongly second the Flexofold. It's fantastically simple, extremely robust. Admirable design. Ours is 11 years old and the only service beyond annual disassembly/reassembly to avoid seizure of the three (and only three) fasteners holding it together has been to replace the 3 little nylon buffers that arrest the blades when they've unfolded. Propwalk is so little that reversing has to be very prolonged at very slow speed to even notice it.
|
|
|
Post by vasko on May 9, 2021 4:33:30 GMT
My engine is VP - 28hp and I changed the prop to 17x13 2B folding Eliche-Radice - the prop is defiantly overoropped - but in my case U deliberately want it to be as I cruise on lower rpm (1500) and want to achieve better speed at it ...
If you want a well balanced prop I would not suggest to go over 16x12
|
|
|
Post by hoppy on May 9, 2021 11:10:28 GMT
I would guess that Jeanneau knows what they are doing when it comes to matching the correct prop to the engine. If you are thinking about a new prop you should seriously consider a low drag prop. I switched from a 17" 3 blade ZF fixed prop to a 3 blade Flexofold and it made a huge difference. Not only was I much faster under sail, I was slightly faster under power, and have a lot less propwalk as well. My 39i is a bit longer that yours, and has the 40 hp engine so I cruise at 7.5kts @2500rpm and hit over 8.5kts@ 3000rpm. Whatever prop you choose you should let the prop manufacturer calculate the correct prop for your boat. They will want to know boat model, engine model, transmission model and gear ratios and shaft size. I ordered my prop direct from Flexofold in Denmark, and they shipped it to my door in a few days! Strongly second the Flexofold. It's fantastically simple, extremely robust. Admirable design. Ours is 11 years old and the only service beyond annual disassembly/reassembly to avoid seizure of the three (and only three) fasteners holding it together has been to replace the 3 little nylon buffers that arrest the blades when they've unfolded. Propwalk is so little that reversing has to be very prolonged at very slow speed to even notice it. I agree, the 3 blade Flexofold was great on my SO40
|
|