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

Feb 17, 2021
7
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
3,774
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
317
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.
 
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Feb 21, 2013
3,774
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?
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Feb 17, 2021
7
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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