That is not true with A4 direct drive boats. The redline RPM of an A4 is 3600 RPMs. Outside of a few planing powerboats or perhaps the reduction gear A4s, none of them get near that. Many direct drive A4 boats are massively over propped and hit maybe 2000 RPM. The 10x7 Indigo 3 blade will get you 2400-2500 RPMs. For a 2 blade A4, 12x6 is a good starting point. Gasoline engines do not carbon themselves to death the way RPM restricted diesels do. Joe Coquina
From: CnC-List [mailto:cnc-list-boun...@cnc-list.com] On Behalf Of ALAN BERGEN via CnC-List Sent: Tuesday, October 30, 2018 11:04 AM To: C&C <cnc-list@cnc-list.com> Cc: ALAN BERGEN <trya...@alumni.usc.edu> Subject: [EXTERNAL] Re: Stus-List Propeller Sizing The prop diameter should be as large as possible while still clearing the hull by a couple of inches. When you run the engine at full throttle, you should be able to reach rated rpm. If the engine runs more than 5% over rated rpm, the pitch is too low. If the engine cannot reach rated rpm, the pitch is too high. Alan Bergen 35 Mk III Thirsty Rose City YC Portland, OR On Tue, Oct 30, 2018 at 7:04 AM, David Morris via CnC-List <cnc-list@cnc-list.com<mailto:cnc-list@cnc-list.com>> wrote: I determined at haulout this weekend our newly-acquired 1975 C&C 30 MKI, Atomic 4, direct drive is equipped with a Gori two-blade folding prop, measuring approx. 11.5”. I have neither the experience or expertise to know if this is a great prop for the boat, a lousy one, or, more likely, somewhere in between. After a major tune-up on the engine, we seemed to be able to run at around 6.2 knots in relatively calm water. Any advice, suggestions, observations anyone would care to offer on prop selection would be much appreciated. David J. Morris, MBA President, D.J. Morris & Associates Ltd. 427 Division Street, Kingston, ON Canada K7K 4A8 Tel. 613-531-4429 email: djmor...@djma-ltd.com<mailto:djmor...@djma-ltd.com> Member: Professional Writers Association of Canada Blogging at: http://davidmorrisjourneys.wordpress.com/ [https://ipmcdn.avast.com/images/icons/icon-envelope-tick-round-orange-animated-no-repeat-v1.gif]<https://urldefense.proofpoint.com/v2/url?u=https-3A__www.avast.com_sig-2Demail-3Futm-5Fmedium-3Demail-26utm-5Fsource-3Dlink-26utm-5Fcampaign-3Dsig-2Demail-26utm-5Fcontent-3Demailclient&d=DwMFAg&c=clK7kQUTWtAVEOVIgvi0NU5BOUHhpN0H8p7CSfnc_gI&r=9w3G7Cf8YfQnrjmtuNxwDJYr3JMv9f1pAfgAJ9xXYQQ&m=eY7MGZm-ox1o3m9zLLDvZme6VW26veqjMcA4EWFuCRM&s=BZ5buLpUfDgb6LKWORSPk7sER1T7Vr7VsE9i1eFb1F4&e=> Virus-free. www.avast.com<https://urldefense.proofpoint.com/v2/url?u=https-3A__www.avast.com_sig-2Demail-3Futm-5Fmedium-3Demail-26utm-5Fsource-3Dlink-26utm-5Fcampaign-3Dsig-2Demail-26utm-5Fcontent-3Demailclient&d=DwMFAg&c=clK7kQUTWtAVEOVIgvi0NU5BOUHhpN0H8p7CSfnc_gI&r=9w3G7Cf8YfQnrjmtuNxwDJYr3JMv9f1pAfgAJ9xXYQQ&m=eY7MGZm-ox1o3m9zLLDvZme6VW26veqjMcA4EWFuCRM&s=BZ5buLpUfDgb6LKWORSPk7sER1T7Vr7VsE9i1eFb1F4&e=> _______________________________________________ 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://urldefense.proofpoint.com/v2/url?u=https-3A__www.paypal.me_stumurray&d=DwICAg&c=clK7kQUTWtAVEOVIgvi0NU5BOUHhpN0H8p7CSfnc_gI&r=9w3G7Cf8YfQnrjmtuNxwDJYr3JMv9f1pAfgAJ9xXYQQ&m=eY7MGZm-ox1o3m9zLLDvZme6VW26veqjMcA4EWFuCRM&s=ulGCOUuuNxaQ5FW1FGoY8_AnSxRGTq2wQangEahYpRs&e=
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