Refiting the shaft system HANSE 531
After many trials I have determined that I would like to make a complete refit on my HANSE 531 shaft system and skeg.
The reasons are multiple. This is the scope of the work
I can not use the AUTOPROP due to hard vibrations, as the skeg causes flow disturbance. The skeg has a hard deadwood end that has not fairing at all.
i have broght a GORI prop but after my calculations i discovered they basically sell undersized propellers as they dont like your engine burned by unexpertise sailors while motoring in overdrive mode, Overdrive mode addds pitch and speed at the expense of some extra vibration. As a result the efficency is low and I can barely get 8 knots a top crusing rpm ( 3200 rpm) while in standard mode.
The AUTOPROP trials ate my cutlass bearings in one week so I looked for elastomere THORDON bearings as they claim to be the best.
We have several problems
First we discovered the water flow in the shaft line was minimal because the HANSE 531 has no pump, nor the line was derived from the colling water. we discoverd the system has poor engineering as the shaft exit is below the water intake and there must be some back pressure that makes the water flowing imoposible.
So before installing the THORDON elastomere bearings we install a Johnson pump rated at 20 liter minute.
Despite those mods I am not happy with the elastomere bearings the shaft whips in overdrive mode with the gori, transmitting some vibrations to the hull, it didnt resolve but actually worsen the vibrations with the AUTOPROP, and the elastomere seems to be too hard for this job.
So we will replace the THORDON bearings for the standard nitrile/brass
3- SHAFT LENGHT AND OVERHANGING
We also figured out we need to enlage the shaft . the purpose is duofold. First we need to put the propeller as far as possible to the deadwood skeg to minimize water disturbance. Second we need the extra space to allow more tip clearance and thus select the the right size prop without design tradeoffs.
But we can not overhang more than 2 shaft diameters so we are considering a strut bearing housing made in SS and bolt the the hull,
For good performances we need to laminate a strong backplate and apply antivibration compound to the hull inside.
4.- SKEG SHAPE FAIRING
We will cut the skeg and glass a faired shape to minimize water flow disturbance forward to the propeller. That seems the easiest part of the work.
Unfortunatelly we still have some questions
A) BEARING SPACING DISTANCE
The HANSE 531 includes a AQUADRIVE look a like CV bearing at the end of the shaft, one 70 mm long cutlass bearing in the gland and a 140 mm long cutlass bearing in the skeg. If I place an extra cutlas bearing in the new strut I have to eliminate at least one of the existing bearings
B) USING A SKF BEARING INSIDE AFTER THE GLAND
I have found some references in the forums about using SKF ball bearings inside the boat . The ideal type looks to be self aligning, interference mounting and capable of absorbing the propeller thrust. It seems some vehicle bearings have those specs.
But as the aquadrive has a bearing in their CV I dont know if the installation of an extra bearing will pose aligment problems due to the close bearing spacing.
Following the ABYC recommendations the bearing spacing should be 20 to 40 shaft diameters ( 35 mm) but Im confused with the aquadrive as I think this must be considered a bearing itself.
So in that case I have to eliminate the old cutlass bearings (gland and skeg) and leave the shaft supported only by the aquadrive in one end and the new strut bearing in the other end.
C) TYPE OF STRUT (I or V)
I read that some sailboats with a I strut do transmit vibration to the hull so Im considering to fit a V strut at the expense of some dragging I expect the dragging to be nminimised by a good desing ( good alignment of the strut blades to the hull line).
As a summary my target is to achieve 9 knots speed at a decent rpm with a standard pitch with minimal vibration.
The HANSE 531 features a hull speed of aprox 9,4 knots the horse power is a 100 HP yanmar and the top rpm is 3800 with a 2,62 gear ratio.
As you can see I have a lot of work forward and I would like to hear from informed cruisers opinions concerning the mentioned issues.
Thanks in advance
Please post a picture of the undewater gear. Also, what is the length of the prop shaft from prop to motor flange?
Jose, what was the original drive on the Hanse 531? What was unsatisfactory or wrong about it?
I am slightly confused with all the "why's" that are brought to mind by what you are doing. I think you are making something that should be simple, much more complex and must be extrememly expensive.
I certainly do not agree with the "overdrive" mode you run in. There is no such thing as overdirve. If you do not run the engine at the correct RPM with correct prop, you will never reach proper hull speed and the boat will be sluggish and hard to control.
:confused: I can't help but wonder why the autoprop would be less bothered by the physical structure than the Gori? With all the modifications you're talking about it would seem you would eliminate or greatly reduce all the problems that lead you to dump the autoprop......or am I missing something here?
Pics are always nice to help us understand too!
I've asked for more details in the other thread. I think there is something else going on here. Can we move the topic?
Thank you for your post to my message.
Yes I didnt explain why I think I should modify the shaft,bearings and prop.
As you know reaching (near) hull speed is an easy target if the prop engine and shaft are designed properly.
Unfortunatelly I discovered the following design problems.
1.= The shaft in the Yanmar 100 Hp that comes with my HANSE turns at 1450 rpms which corresponds to 3800 rpms with a 2,62 gear ratio.
I can understand why they put shafts to turn at those speeds 1450 rpm is simply too much.
I discovered that for optimum performance my shaft should turn at 800 rpm, So I'm running too fast.
With a lower shaft speed you can select a larger prop which in turn has a better efficiency.
With lower shaft speed the prop can turn vibration free and below the cavitation limit
So Im researching if I can change the YANMAR 2,62 tratio ransmision for a 3,00 that is also offered in the Yanmar 100 HP model catalog as an option. That is only another possibility
That will put the shaft at 1260 rpm at top . Not ideal but closer to ideal.
2 -We fitted the GORI prop in July. It works without vibration in normal mode and with barely noticieable vibration in overdrive mode over 2000 rpm. I think that slight vibration is becuse the THORDON elastomere bearings
As you know the Gori prop has two modes normal and overdrive, In overdrive the pitch is increased to allow motorsailing at lower rpm.
That works quite fine and we read 8,6 knots at 2 200 rpm when helped by the main or when we had following currents.( we dont use the overdrive mode in other conditions or over 2 200 rpm)
But in normal pitch mode the top speed reaches only 8,4 knots at 3300 rpm that is the high cruising rpm we use to set. Dissapointing.....
This speed is well under hull speed.
Our target is 9 knots at 3300, That is the peak thrust and power as per the Yanmar specs.
The HANSE 531 features a flat bottom and low displacement (18 tons), The water lenght is almost the size of the boat because the plumb bow, The bottom was fresh painted, So I can see why we canot reach near hull speed with GORI...but there is an explanation.
When I ordered the Gori prop I e mailed the factory before ordering because I didnt like the size of the prop recommended by the Spanish Reps of Gori. They confirmed I shall use the size I have been told by the rep.
My test confirmed that the prop is too small to have good efficincy so it didnt reach near hull speed in normal mode.
The answer is simple, Gori didnt like to overcharge the engine if the skipper revs up too much in overdrive mode.
So in my opinion they recommend props two inches smaller than the optimal calculations.
I think this trade off is unaceptable
I was finally ofered a refund in the AUTOPROP. When I checked the Gori performace I didnt ship back the AUTOPROP as I considered the performance of the GORI is far below the AUTOPROP. The AUTOPROP is some inches larger than the GORI, so is more efficient the blade area is also larger.
So the question was if with some mods I can still fit the AUTOPROP back.
That involves changing the shaft concept entirely.
a) Longer shaft
b) More tip clearance
c) More skeg clearance
d) Fairing the skeg
e) Suporting the shaft right at the prop hub with a strong strut and a soft bearing
If the aforementioned solves the vibration we can maybe give another chance to the AUTOPROP.
Remember that with the AUTOPROP we have only the vibration in forward and NOT in reverse we hit 8 knots in reverse at 2800 rpm which impressed us so much. Also not prop walk in reverse wich makes med mooring a breeze.
Yes the AUTOPROP operates without vibration whith the clean undisturbed waterflow going aft to.
Well I hope you have a much better idea of what I have in mind.
I read that the predominant wind in the med sea is the one that comes from the bow. jokes apart, That is proven and true. We use to motor or motorsail 50% of the time in summer.
The boat is sailing very well, The have now a CODE O with furler in adtion to the self tacking jib and the big asymetrical we had last year. We are making good speeds averaging 8 knots easily in 30 to 40 hours crossings between islands, So we are overall very happy with the HANSE 531 except for the motoring performance.
Waiting your comments
First question Yes I can asnwer, because in the AUTOPROP the blades are hanging freely to allow self pitching.
Second question, Exactely You read my mind. My intention is give another chance to the AUTOPROP( please read my last post)
I will be sailing again next week and I will measure the shaft I think I should make a drawing so you can read what we have.
Quite honestly. I think you have the wrong Autoprop. What is the current tip clearance? and pitch angle? Can you more describe the vibration?
Theres no reason to run a 3.14 gear on a full displacement hull. The 2.62 is an excelent choice.
1450 is not too much at all. It is quite a good speed for your boat. I know of shafts turning much faster than that. In fact, I know of a haft turning at 9500RPM. Yep 9500, that ain't a mistake. Sure it is in a race boat, but it is a very long shaft, 1.5" diameter and has some 4-5ft between bearings and a 2000Hp engien on the end. It spins with no vibration at all. In fact the slightest vibration would tear the boat apart. I know, because it did when one blade let go on the two blade prop.
But be aware that Cavitation is not your problem. Cavitation is a very different beast compleatly. You issue is most likely tip compression noise. This is where the water between the tip of the blade is trying to be squeezed between the hull and the tip. But because water does not compress, the blade hammers the hull. I have said this before. If the gap is too small, something has to give. If the hull doesn't, the blade does. It can cause a dramatic vibration. I honestly think you have too big a diameter prop. Especially if you are reaching hull speed with low engine RPM. Thats too much pitch. The engine MUST rev to max. I can not stress that enough.
I have some questions that answers to may help one of us give more detailed advice.
So I assume the Hanse 531 is 53ft, is that correct??
What is the exact Water line length???
What diameter prop do you have??
What pitch do you have???
What is the clearance between blade tip and bottom of hull???
AS a simple Engineer I've got to put my farthing's worth in.
The Prop sets itself to the most efficient drive angle. A fixed prop can't.
At low speed low power it sets itself to it's most efficient angle.
At High speed low power it sets itself to it's most efficient angle.
and all the other variations.
Now, power required at speed is to the square.
2 knots = 4 gallumphs times the factor for your boat.
8 knots = 16 gallumphs times the factor for your boat.
Get close to the water line speed and you need three times as much power to get a planing boat onto the plane then with that same power you'll go three times as fast as your waterline speed. (That's why racing mono looked like roadkill hedgehogs).
(Cruising mono's don't plane very well so the number's bigger).
Now, 10hp gives say 4 knots. That's 4x4/10 = 1.6. So 1.6 is the boat factor.
Therefore THEORY says v x v / hp = bf,
So v x v = bf x hp is 20(hp)x1.6(bf) = kts x kts
That will give us 1.6 x 20 = kts x kts = 32. Square root of 32 is about 5.65. Not the 8 you expected.
So you how many horses to do close to 8 knots, your waterline speed.
v x v = bf x hp therefore hp = v x v / bf. Thats 8x8/1.6=40hp and add 50% to that for head winds in a storm and thats 50 to 55 hp.
Forget the prop. If it's self pitching it will do the very best it can with whatever horse power you throw at it and that's why they are so good.
With a fixed pitch prop the have to be matched to engine and boat speed, like a car with one gear. You give up some speed to get enough power low down. From a start on full throttle you'll churn up the water and not get a lot of thrust because the blades are stalled. As speed picks up to hald the design speed they'll start to work betteras they begin to unstall on parts of the blade. At three quarters design speed they are working properly at last and at their most efficient (fuel burn to miles covered) and at top speed they don't have enough bite so the blades are spinning too fast and churning water around rather than pushing it backwards. Your self pitching prop works at it's best angle all the time whatever the speed so you don't need such a big engine but that's only about ten percent IN THEORY.
Whirling of shafts. Scary stuff. Any straight rod has a frequency in bending. When the speed is the same as the frequency you get resonance. The shaft is bent in one direction (relative to itself) and that makes it out of balance so it shakes everything. Very high loads on bearings and motor mounts and your nerves. This also happens at half, quarter, double the speed too. It's a serious problem if the shaft designer hasn't got it right. Replacing the rod with a tube of the same weight will incease that speed by a two to four times but then the half speed becomes a problem so the only solution is to tell the shaft designer the length of the shaft, the revs you want to use most of the time (cruise, hurry and storm). He should be able to tell you what speeds to avoid with what you have or with a new shaft to his design. Your prop designer may be able to help witht he calc, length is the crucial factor. Halve the length and you increase the speed by four times (the square factor again).
Trust this helps. It's not straightforward but the answer is in there. Try your local technical college if you can't find any brains on the dock side.
By the way, a good fixed blade prop is matched to you cruise speed so don't expect big improvements in fuel consumption. Personally I'd want self pitching and folding for fixed drive on a cat. Because you sail faster than a mono then prop drag is worse (square of the speed again). I'd prefer a drive leg that comes clear but they are expensive and bulky.
Send me some boat factors so we can build a picture.
Boat type, waterline length, boat speed, engine revs, engine type. Somebody else can do the spreadsheet?
I see from the new posts in the original thread
that the reason for all this work seems to be that you feel the boat is being driven significantly below the hull speed that should be possible for it under power.
Have you considered contacting Hanse to ask them why they chose to power the boat this way? Perhaps there were simple design considerations or compromises that they chose, which you might benefit from hearing from them?
They might have simply chosen gear that was "stock" for different models in their yard, or simply cheaper than optimum gear. That's normal in production building. Or, they might have explored those options and found that given the hull construction and the cost of the different parts, they didn't feel the gain was significantly possible.
Might be related to waterline length and how far the hull squats under power, too. It would certainly seem worth talking to Hanse about this.
The first thing we all need to learn, is that before we do anything to change the propulsion system on a vessel, is to contact the mfr.
What was your original need to change the drive system?
Now that we have two threads going on this subject, it has gotten a little confusing.
Would posters like me to either close this thread and direct all posters to the original? or...seeing as the original is so large and did originaly start with a different situation, close the original and redirect to this one??
Wheels, the main topic seems to have changed from "What's wrong with this boat" (the other thread) to "How shall I rebuild this boat?"
And I'd suggest that's worth keeping the threads apart, perhaps simply going back up a few notes in the old thread and closing it--after the message indicating the new shift in topic would be pursued HERE not there.
If it makes more sense to you to merge them over there and keep it all together...No problem for me, I just agree it needs some bigger road signs to make sure people figure out which way to go.<G>
I have moved the posts in reference to this subject, from the other thread to here. Sorry but it moves in Chronological order, so hence the insertion part way up.
Also please note that the variouse posts are merged together. Partly my stuff up...nah actually all my stuff up. Sorry bout that chief.
After the summer sailing session I have finally found a yard that seems to know what to do with the multiple problems I have experienced.
The list of wrong things the yard have found on my engine shaft assembly is too large and I would say too embarasing to list now, bad engineering and improvisation leaded HANSE by those days. I hope they have improved with experience.
We are refitting the assembly from the Yanmar engine connecting plate ENTIRELY.
And I would give the BRUNTONS AUTOPROP a second chance after the refitting
Im enclosing two pics
The new shaft ( strut bearing not shown still on fabrication phase)
Drawings of the engineering proposal ( Better turn right for better view)
Good year to all sailors
just some pics to illustrate our progress
Vacuum bagged glassing of the V strut
a real aquadrive in place on a fresh recut beam support replaces rusty and misaligned python drive.
Works near completion
preparation of deadwood skeg
deadwood skeg base plate for e glass fairer.
fabrication of SS V strut
I think pics are self explanatory
More pics of the refitting works
Two more pics
Lamination of the V strut base plates
Check of the fairing e glass shape to finer lines and provide non turbulent flow.
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