Bavaria 38 Ocean Prop Survey

[Jeffatoms]

Dear Ocean Series 38 owners.  We have a dilemma.  We recently upgraded from a Volvo 120 SE saildrive to a 130 on our MD22L engine.  We believe our 17x12 LH fixed three blade Volvo prop is mis-sized for our boat.  It appears to cavitate at 2300 RPMs wherein the power essentially stops and thr boat slows down.  If we back off on the throttle to 1000 and then back up to 2200 RPMs we cruise at approx 5.5 knots but we cant go any faster.  We have never felt the prop was properly sized and we are wondering what other owners have in fixed 3 blade prop dims that works well without cavitating?

Thanks much for your input!

[symphony2]

Surprised if it is cavitation as it sounds like classic symptoms of over propping which restricts the ability of the engine to achieve its rated maximum - 3000rpm from memory on and MD22. The diameter is right but the pitch needs reducing by at least 1" which will raise the revs  by approx 250-300, so at the lower limit of the recommended rev range at full throttle. You should be able to achieve just under 8 knots at around 2800-3000 and cruise at 6 knots at 2200 rpm.

Will be interesting to hear how that compares with other Ocean owners.

[Yngmar]

Fixed 3-blade aluminium alloy, Volvo (dia x pitch) 17 x 15 L Part No 21381279

This is for the MD22L-B (50 HP) with the 120S-E Saildrive on our Bavaria 40 Ocean.

You also need to know the gear ratio, which is stamped on the type label on top of the gearbox, just after the type. Ours says "120SE 220" (there may have been a period there once), so it's a 120S-E with gear ratio 2.20:1. Apparently there are different gear ratios for some of the 120/130 models, so this is important - check your type label.

At 1500 rpm we get 5.5 knots with a clean hull, with full throttle 8.0 knots (hull speed) and the propeller seems appropriately sized for the setup, has excellent stopping power and gets the 50 HP pushing the boat in tougher conditions, which we did make use of once.

If you have a 12 pitch propeller with the same engine and gear ratio, I can see this being problematically underpitched.

[symphony2]

The 130 is 2.17 - virtually the same as the 120se. Initially I thought 17*12 was underpropped but symptoms suggest the opposite. Just run the stats through Vicprop and it gives 18*12, so roughly the same as 17*13.

[Yngmar]

There's two gear ratios available for the 130 saildrive, 2.19:1 and 2.47:1. He really needs to check the label to find out which one he's got.

[symphony2]

That is true, but it is only one variation and I am not sure why anyone would choose that for use with a an MD22. I assume the 2.47 was offered because it is the same as the 120 for use with the 20X0 and 200X series small engines which rev to 3600 compared with the D series and MD 22 which max at 3-3200rpm.

When I replaced my 120 on a 2030 with a 130 drive we used the standard 2.17 and changed the prop. Volvo have always aimed at shaft speeds of just under 1500 rpm with their standard offerings, although with shaft drive they have also offered a greater reduction to cover applications, typically commercial where a larger slower turning prop is better.

[Jeffatoms]

Thanks much for the response.  Just checked and it is 2.19.