Prop for MD22L with a Volvo 130 Saildrive on BAV 38 Ocean

[Jeffatoms]

We are replacing a Volvo 120SE saildrive with a 130 on our Bavaria 38 Ocean on Monday.  We have the choice of a 16x11LH three blade or a 17x12LH three blade prop.  Wondering what other boats (19,000 pounds displacement) have with the 130 saildrive and the benefits of either of the two props we have, including RPM and engine load feedback.

Thanks in advance!
Jeff and Sue
SV Zephyrus

[Symphony]

The 130 has the same reduction ratio as the 120SE so the same prop as you had originally will work if you were happy with the performance. Having said that 16*11 is far too small and 17*12 is the size that the Vicprop calculator suggests (actually the optimum is 18*11.2, but this is effectively the same as 17*12).

This assumes a standard Volvo fixed blade propeller. If it is a folding or feathering propeller then you should seek the advice of the manufacturer.

[geoff]

With the same md22 the 40ocean  same displacement has as standard a fixed ali 17x15 . With that prop my boat reached 7ish kt at 2000rpm with plenty more available at huge cost in fuel. Geoff

[Jeffatoms]

Thank you both!  Geoff, do you have the 120 series or 130 series saildrive?

[Symphony]

The drive does not make any difference. The reduction ratio (the key figure) is the same. The 130 was never fitted to the MD22 in production as it did not come out until 2005/6 when the D2-55 engine replaced the MD22. Personally I think a 17*15 is overpropped, as indicated by the relatively high speed at only 2000 rpm. The correct size of prop is one that allows you to get to the maximum rated rpm (3000 in your case) and achieve hull speed which is about 8.4 knots. This allows you to cruise at approx 65-70% maximum revs (+/- 2000 rpm) at a speed between 6-6.5 knots. This leaves you with about 1/3 revs and 50% of potential hp to deal with adverse conditions or if you do want to go at higher speed with the attendant fuel consumption. Fuel consumption is a direct function of the load demanded by the prop to achieve a speed and will be exactly the same whether you overprop to reduce revs or you prop to use the maximum rev range. The only advantage of using lower revs is a potential reduction in noise.

When you get the boat in the water do some timed runs in flat water at 200rpm intervals from 1800rpm up to the maximum revs you can reach, which should be in the range 2800-3000. You will then be able to plot speed against rpm. If you can achieve maximum revs easily but not maximum speed (8.4+) then you might consider going up an inch in pitch, but I am pretty sure you won't need to. This is the process used by Volvo commissioning engineers with new installations using a non standard prop (as they did with my boat when it was new) although Bavaria usually get the prop size spot on so provided the installation achieves maximum rated rpm within the expected range they don't bother with going through the whole process.

Hope this helps and good luck tomorrow.

[geoff]

The reduction ratios for 120 and 130 are not the same . The 120 come in 2 ratios 2.47 [most early units including the early 120se and most of the rest. I only know this because I have just rebuilt a 120sd [2.47] to replace my original 120se [2.18] . I also have another 120se a bit older which is 2.47.  My 40ocean  which I bought new in 2001 had the 120se [2.18] and 3 blade 17x15 prop . I was not overproped in as much as it would rev close to 3000   [2900 if I remember the commissioning] Never tried such revs again as half the transom seemed to be underwater. Geoff

[Symphony]

The 2.47 ratio 120 was fitted to the MD20X0 series of engines which were rated at 3600rpm, hence the greater reduction to bring the shaft speed down to just under 1500 rpm. The lower revving engines like your MD22 use the 2.18 reduction as originally installed in your boat. When the newer D series engines which are rated at 3200 were introduced with the 130 leg the ratio was standardised at 2.2 so giving virtually the same shaft speed as the previous 20x0 engines.

This difference in ratios only creates an issue if you replace a 120 (2.47) on an engine like a 2030 with a 130 drive as I did as it gives you a shaft speed of 1636 instead of 1475. We reduced the pitch by 1" to compensate.

What size propeller are you using with a 2.47:1?

[geoff]

After the rubber hub of the original prop started to go south , about 4 years ago I fitted an 18in Kiwi  with pitch set to about 23deg . That gave me the same speed/ revs as the old. I left it as set for the new leg and find I am about .5kt shy on speed ,so next scrub I will add a tad of pitch. Geoff

[Irmascherkid]

i have 2 brand new volvo penta 3 blade fixed 17 x15" LH props ( part no 21381274 ) with cones that i am about to advertise if you want?

[Jeffatoms]

UPDATE:

After $30,000 spent on auxiliary power we are back in business with a new 130 saildrive on the existing, 2,200 hour MD22 and it's great. We will pursue it legal matter with the fraudulent boat yard on the "canal" in Seattle but for now everything works, the prop was interchangeable and the new saildrive should outlast us.  As an FYI, it powers through the water at 6.5 kts at 2,100 rpms.  Perfect.  No smoke at all.  The engine should be good for a few years too.

BTW, the 130S-C s a vast improvement on the 120SE for lots of reasons but it was $10,000US to get there.