Prop sizing (diameter, pitch) for Bavaria 41 (2004) saildrive vs. engine speed (RPM) and boat speed

Feb 17, 2021
13
Bavaria 41 Olympia
My Volvo Penta 2004 D-2 55 pushes my Bavaria 41 at 7 knts at 1800 RPM with existing 3 bladed Aluminum prop. I can push RPMs to 2200 and get 8 knts. Above that either hub or clutch begins to slip. The 55 specs suggest it should be maxing out at 3500 RPM, so I am not close. Even before slipping appeared, I could only get 2400 RPM max. The reason for the slipping is one question I would like to know. Prop re hubbed does not solve slipping problem. Boat runs fine if I don't push RPMs so I could leave it alone and run at 1800-2000 RPM with great fuel usage at 7 knts. I want to know if I need a lesser pitched prop to allow engine RPMs to increase. What is the 3 bladed propeller match (diameter and pitch) for this boat and engine sizing?? Anyone with experience on this question, both the prop match and slippage, which may be the transmission clutch. Any help?
 
Feb 21, 2013
4,638
Hunter 46 Point Richmond, CA
..........My Volvo Penta 2004 D-2 55 pushes my Bavaria 41 at 7 knts at 1800 RPM with existing 3 bladed Aluminum prop. I can push RPMs to 2200 and get 8 knts...........
Hull speed for your sailboat is √35.25 x 1.34 = 8.0 knots based on the 35.35' LWL from SailboatData.com - BAVARIA 41 Sailboat so you are already doing that at 2200 rpm. That propeller should also give you good low speed thrust. If you want to replace it suggest taking to a propeller shop like Volvo Penta Duo Propellers at Propeller Depot OR Volvo Penta stern drive boat propellers (deepblueyachtsupply.com) OR consult with Volvo Penta.
 
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Jul 19, 2013
384
Pearson 31-2 Boston
I thought the target for prop sizing is to reach hull speed as cruising RPM, normally 80% of max RPM. SSo you should be running at 2800 when you hit eight knots. I think the problem that comes up from being over propped - cruising at 2200 versus 2800, is a diesel engine needs cruising RPMs to burn out the moisture and pollutants that develop inside, and an engine that doesn't regularly run at cruising RPM will not have a long and happy life.
 
Feb 21, 2013
4,638
Hunter 46 Point Richmond, CA
80% of 3000 rpm = 2400 rpm my14_d2-55.pdf (coastalmarineengine.com). As a comparison, my 40 hp Yanmar 3JH4E achieved hull speed at 80% of max 3000 rpm and my current 75 hp Yanmar 4JH3-TE achieves hull speed at 70% of max 3800 rpm.....maybe the later is not optimized?
1633136943135.png
 
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Feb 17, 2021
13
Bavaria 41 Olympia
I am working with Seattle Vovlo Penta dealer who has concluded lowering pitch 2 inches will increase RPMs 400. Responses are great. Thanks. Any comment on slippage of cone clutch appreciated. Decreased pitch will possibly result in less slippage. Clutch needs replacement? Fine if I run it below threshold. My boat at 8 knts throws massive wake so I have assumed hull speed is more like 7 or 7.4.
 
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Nov 19, 2017
17
Bavaria Bavaria 40 North Hero, VT
I have a Bavaria 40 with a D2-55 Volvo-Penta and a MS25S saildrive. The calculated hull speed is 8.1 kts. I still have the original prop, not on the boat, which is a 17x14 L, which translates to a 17" diameter x 14 pitch, left hand rotation. I have a Max-Prop 3 blade classic feathering prop on the boat. From PYI Inc., maker of the Max-Prop, the blades I have are 18" diameter and has about a 14" pitch. The blade setting angle is set to 22 degrees, yielding a pitch of about 13.6 inches. I routinely run the engine at 2000 rpm, getting a boat speed of about 7.1 - 7.2 kts in smooth water with little headwind. If I push the rpm to 2200, I get about 7.6 kts of boat speed. When I run at 2000 rpm, I burn about 0.79 gal/hr., with the burn rate going up for higher rpms. So I'm content to run at 2000 rpm and push it to 2200 rpm for short bursts of needed power or higher speed. If I really needed to go faster, I'd probably trade in the sailboat for a powerboat! :)
 
Oct 22, 2014
20,995
CAL 35 Cruiser #21 moored EVERETT WA
My boat at 8 knts throws massive wake so I have assumed hull speed is more like 7 or 7.4.
Not necessarily.
Wake can be caused by your over pitched prop inefficiently digging into the water and dropping your stern down causing a wake in the same way a wake boat filled with water in the stern creates a wake. Low stern big power boat is out of balance.

If your prop is correct you should be able to turn all that prop blade dig into direct thrust at 80% WOT. This will level your boat and improve efficiency/performance.

I've posted these images before but they really show two different prop designs. The designs reflect difference in performance.
WestbyNorth prop Campbell Sailor
2922CDBE-C1D8-486B-9CB7-A30D78BF72B0.jpeg
Lots of thrust no stern droop.

Michigan Wheel
C01D7F6F-743C-44A9-81B7-EE8489770367.jpeg
Stern drooped nearly a foot. Engine smoked. Bad performance.
Original Prop on Boat.