Mahe 36: Sail Drives and Props

[MKB53]

Hi All

I recently had a problem with the inlet on the port leg getting blocked (inside, not the outer holes). Not the first time but as a result I was spending a lot of time checking water flow etc.

On the last few days of our recent trip we had some quick downwind sailing with a good bit of surfing. Half way through the one day I started the motor to boost the battery a bit (no sun) and there was no water flow at all. I got into the engine room and primed it and all was fine. Next day the same thing happened so I left it. When we got into calmer water and slowed down I got ready to do the job again but this time when I started the motor I could see it was sucking water and after a bit the flow got through the whole system.

All that I can think is that when you are surfing (speeds above 10-12 kts) it is generating some sort of airlock.

Has anyone had any similar experiences?

Cheers
Martin

[kitingcakes]

Originally Posted by Scott730

All I could get out of the Volvo rep was it was non standard and they only would support the standard configuration. Typical BS from a rep that didn't want to do any leg work or think outside the box. Since only one of my props needed replacement, I didn't push the issue. Think I paid around $200 US for the replacement. Volvo Part number 850342.
Scott

Hi Scott,
How did these props work for you? We purchased a used Mahe and both props need replacing. The numbers are too corroded to read and I'm not near the boat, and the yard isn't able to provide additional value either without pulling and sourcing "in person". I am hoping to confirm the correct size and part so I can order and drop ship. We have D1-20 engines with 130S-B sail drives. Pic attached.
Thanks for the help!
-Anne

[Seastream]

All:

Anybody experience more vibration with the Volvo three blade folding props vs two blade fixed? After just having the above swapout done, that is my experience. It can be minimized by some throttle adjustment (syncing the engines?) but is still more vibration than I had with the two blade fixed. I just want to ensure I'm not going to break anything. One prop is new, the other reconditioned (looks new!) by H&H propeller.

Bob

[Jef & Marin, Netherlands]

I have had vibrations on the starboard prop. This happened from one day to the other. When we put our boat on a sandbank, we found a 10 cm long line wedged between the propeller hub and the saildrive.
After removing this, the vibrations stayed, and did not get better in the following months.
When the boat went out later that year, we found that the propeller hub was out of center. We had to replace the hub, costing 500 euro.
The core of the hub and the bronze outside are coupled by plastic or rubber, which electrically isolates the prop from the saildrive, and probably should also have anti-vibrational properties. In our case this coupling must have been damaged or distorted by the piece of line.
My advice to you would be to take the boat out of the water and measure excentricity of the propeller hub, using a caliper or a dial gauge mounted to a support. I would measure both at the front and the rear of the hub. In my case the hub had an opposite excentricity on the fore and aft. of the hub. The excentricity was only one or 2 mm.
Also I would notify the supplier of the propeller in writing that you have this problem. It should be straightforward to determine which prop is causiing this, and I hope you can figure out whether the problem is with the new or the 2nd hand propeller.

To prevent damage to the saildrive bearings by the vibrations, we have used that engine only for harbour manouvring. For long distance motoring we have used only the other engine.

It would be nice for you if your problem is not the same as I had, since it is quite some hassle; both technically, and in relation to your propeller supplier.

[Edmund]

Two engines not synced do tend to create vibrations, yes. I have had two sets of 3-blade folding on my boat, and vibrations when engines is not synced has been there always, on both prop sets. My current 18x13 props also seems to be a little bit worse than the original 17x12. In general, as long as you manage to more or less eliminate the vibrations with trottle adjustment I think there is no reason to worry.
I have never tried fixed props though, so I would not know if they vibrate less than the folding.

[Sail IC]

I bought an Orana 2 months ago and the fixed propellers are driving me crazy. Not only the whining, but between 6-8 knots I also get significant vibrations especially in following seas when the boat is changing speed. Looking in the wake there is a lot of bubbles so I think (or hope) the vibrations come from the propellers cavitating.

I planning to put on folding props, more or less decided on flexofold, but this is brand independent. What inspired me is what Edmund did, so I'm looking for his opinion and if good it might be useful for other Mahe owners.

Folding props are pricy, on cats you need two, and a 3-blade is 50% more expensive that 2-blade. The benefit of a 3-blade is better thrust due its larger blade area so it maneuvers better around the marina. For everything else, a 2-blade is better, ie motor efficiency, drag when sailing, and price.

The Orana comes standard with 17" props, and that is what flexofold are recommending. But there are a lot of space between the propeller tip and hull (130mm, 5") so it could easily house a bigger prop. In addition, a folding prop move the blades aft by 135mm (flexofold), and given the slope of the hull the space increases further.

So rather than using a 17" 3-blade, go with a 18" 2-blade. With its better bite over a 17" 2-blade it might maneuver closer to a 17" 3-blade, and maintain the other benefits.

What do you think?
Edmund?

[Edmund]

I would definitely follow your own advise: Go for the 18" 2-blade. I would have done so myself, if I didn't already have the 3-blade hubs. The 50% extra for the 3-blade (is it really that much?) is NOT worth it.
How often do you need full thrust when manouvering in the harbour? Never.
I think the major issues when going for a bigger prop are hull clearance, increased risk of vibrations due to more weight rotating, and the fact that higher prop-weight is an issue regarding gearbox wear. And of course you have to find a dia/pitch combination that will fit your boat and engines.

The more difficult question is to choose the best pitch. That depends on a lot; your engines hp and rpm's, gear ratio, weight, risk of/normal rate of growth on hull&propeller, and what you yourself prefer: Utilizing the engine's torque at lower RPM's, or pushing with high RPM's.

I prefer the first option. Lower RPM gives less noise and less fuel consumtion at same speed, and better thrust on idle. Engine wear is negligible.
My aim was to reach the lower limit of max RPM given by the engine manufacturer, boat empty and clean, no wind.

Also keep in mind that the boatbuilders and engine manufacturers calculations are based on full boat weight combined with the worst possible conditions (hull growth, weather, low quality diesel grades, high air temperatures) when they choose the standard propeller for a boat. As they have to do, of course.

Good luck with your choice

Edmund

[Sail IC]

Thanks for your reply.

I found an interesting site that had a formula to calculate the most efficient propeller diameter for a given boat. It seemed to be a sailboat site as I'm sure an oiltanker uses a different formula:

D = (632.7*SHP^0.2)/RPM^0.6
SHP = Shaft horse power
RPM = shaft RPM, ie after gearbox reduction.

If I plug in my numbers (38 SHP, 1461 shaft RPM) I get to 16,5". Standard prop on the Orana is 17", so maybe it isn't that small after all.

Flexofold is recommending me 17x12 3-blade or 17x13 2-blade. They didn't want to recommend a pitch for an 18" 2-blade, so I wonder if it should be a 18x12 or 18x13.

Should run some tests with my current fixed 2-blades, but I don't know what pitch they have. I'll write FP an email and see if they answer.

Cheers

[Edmund]

Be careful with these calculators.
Did it calculate based on a catamaran, or a monohull?

In my case, I found that FP most lightly use Volvo's monohull calculator to find propellers, as Volvo Norway, when they recalculated based on the 1/2 of my boat (3 tonnes, 11 x 1,1 meter hull, 28 hp). ended up with 18x13, not 17x12.

[ricb64]

Hi Edmund
It has been a while but I thought I should try and check as I am currently going through the same decision as I have a very similar boat in terms of waterline and displacement ( I think ie lightship at 5 ton & loaded at 7 ton )
( Tasman C35 lengthened to 37 )

I am currently upgrading to VP D1-30's from MD2020's and also dont wish to be underpropped. ( VP have suggested 17 / 11's for me )

Has your positive experience continued re changing the prop sizes / ie any negative impact on the engines ? ( I suspect not but thought I should check )

At the time did you consider changing entirely to Flexofold or Varifold or were they prohibitive in cost ?
Sorry I probably missed the boat here timewise but any feedback would be very much appreciated

[Edmund]

Hi Ric.

All well in my cellar
The engines and props are working well, after two seasons and around 150 hours of operation. As mentioned earlier, there is one drawback: the level of vibrations is a little bit higher now with the 18x13 than before with the 17x12.
Also, I feel that the boat is more sensitive to load and growth than before. The cruising speed on 2400 rpm tend to fall down to around 8 knots with heavy loads/much people/full tanks and dinghy, and/or much growth underneath. That was not so much the case before. I think...
I would definately again choose one propsize higher than recommended.

I did not consider other brands than Volvo, as I already had the Volvo hubs, and could change only the blades.

Edmund

[Seastream]

Thinking of returning to fixed props. Can I use 2 or 3 blade fixed or only 2 with the d1-20?

[nepomuk1978]

Originally Posted by RoadRacer

Can anyone confirm that FP supply 16 x13 fixed two-blade props on Mahe's with the D1-30 Volvo? Thanks!

Regards,
Chuck
s/v Normandie

Hi Road Racer,

did you ever get a response on this? I'm trying to figure out the same thing.

Thanks so much!

[nepomuk1978]

Hi everyone,

I'm trying to figure out the size of the original Volvo Penta two-blade props that came with the Mahe with the D1-30 engine and 130 Saildrive. Any help would be appreciated. I need to replace them, also considering going to 3-blades if anyone has an opinion or recommendation on size.

Thanks so much!

Nepomuk

[Rufduck]

I know that this is an old post but...
Where do you relocate the new thru hull? The logical place is just behind the sail drive mounting gasket...yes? No?
Cheers, Rufduck