By all means test it with your old prop. Too many RPMs is not harmful, going the other way is for diesels. A good prop shop will be able to suggest the next thing to try once you have the RPM info in hand. In general a slower turning prop that is bigger/more pitch is a more pleasant experience and more efficient too as long as you can still hit the max rated RPM. Limiting engine speed with a big prop instead of the governor is hard on diesels. Joe Coquina
From: CnC-List <cnc-list-boun...@cnc-list.com> On Behalf Of Olivier Chatot via CnC-List Sent: Thursday, January 2, 2020 9:32 AM To: cnc-list@cnc-list.com Cc: Olivier Chatot <ocha...@gmail.com> Subject: [EXTERNAL] Re: Stus-List Fitting transmission with different gear ratio Thank you for the comments! I see that my understanding was basically correct. The shaft RPM will be lower than before, and using a larger prop or a prop with greater pitch would counter this difference. I'll update you later if I end up using the transmission with a different gear ratio. I won't get a new propeller right away to get a chance to test the new transmission with the old prop. I think there's a chance the gear ratios are close enough that I'll get the same speeds at still reasonable engine RPMs. What I'm thinking is that lower prop RPM also means that the prop slip will be lower, so even though the prop RPM would be 19% lower, the boat speed is likely to decrease by less than 19%. Thank you, Olivier Chatot C&C 38-3 On Wed, Jan 1, 2020, 18:39 Joe Della Barba via CnC-List <cnc-list@cnc-list.com<mailto:cnc-list@cnc-list.com>> wrote: Different gear ratio = different prop, so factor that expense in unless you want to be like driving a car stuck in 2nd gear. Also make sure you CAN fit the correct prop for that ratio. Joe Coquina On 1/1/2020 4:43 PM, Olivier Chatot via CnC-List wrote: Hi all, I have an interesting situation with my transmission. I would like to share it with you and get some opinions. I have a Yanmar 3HM35F engine with a Kanzaki KBW10 transmission. I need to replace this transmission because it's been malfunctioning. Someone near me has a new Kanzaki KM3P for sale. I believe the mounting flange is the same shape and size, so physically mounting this transmision would be possible. However, this transmission has a different gear ratio than my old transmission. My old transmission has a gear ratio of 2.14 (2.50 in reverse) and the new transmission has a gear ratio of 2.61 (3.16 in reverse). Since the gear ratio of the new transmission is higher, the prop would turn more slowly. But I believe it would be safe. Do you agree that it would be safe to use a transmission with a higher gear ratio? Or, do you see something important I'm missing? Other specs of the two transmissions are identical. Notably, the rotation direction of the two transmissions are the same. Any comment is greatly appreciated. Olivier Chatot C&C 38-3 _______________________________________________ Thanks everyone for supporting this list with your contributions. Each and every one is greatly appreciated. If you want to support the list - use PayPal to send contribution -- https://www.paypal.me/stumurray _______________________________________________ Thanks everyone for supporting this list with your contributions. Each and every one is greatly appreciated. If you want to support the list - use PayPal to send contribution -- https://www.paypal.me/stumurray
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