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Old 07-03-2012, 11:08 PM   #1
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Mainship 350 Props

I bought a 97 Mainship 350 last fall. Everything I read about performance said it should plane and do 16-18 knots. My boat will do 13.5. The engines are twin volvo penta 200 hp and the props are 20 x 16 (so I am told) Anyone have a similar boat running different props? Anyone have any comments or suggestions? I dont really want to go that fast but I'm thinking larger or more pitched props may save me fuel? Thanks all.
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Old 07-04-2012, 12:33 PM   #2
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What rpm are you running at max speed?
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Old 07-04-2012, 01:12 PM   #3
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You need to know your engines' WOT RPM....look in manual or call Volvo. The boat should turn up WOT RPM when fully loaded. Otherwise props need to be DE-pitched. Increasing pitch most likely to overload engines and cause serious damage unless you are reaching WOT RPM too easily: that is rare.

Have you added much weight to the boat relative to its as-new state? Is the bottom and running gear clean?
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Old 07-05-2012, 10:54 AM   #4
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Mainship 350 Props

WOT is 3900 and I can get there fairly quick. As for weight, we have a 10' zodiac w 15hp engine, normally carry full water and fuel but not that much other extra weight. ( and 200 feet of anchor chain)
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Old 07-05-2012, 10:55 AM   #5
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Bottom condition is good.
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Old 07-05-2012, 12:16 PM   #6
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Are those engines gas or diesel?That sounds a little high for diesel and a lotta low for gassers.
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Old 07-05-2012, 04:05 PM   #7
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I agree....WOT 3900 doesn't sound right. Also, are the tachos that are telling you that mechanical or electronic....and if the former, have they been checked against teh engine flywheel by a mechanic with a photo-tach? Standard tacho gauges are notoriously inaccurate. Very important to get rpm readings accurate before making any re-prop-ing decisions.
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Old 07-05-2012, 10:52 PM   #8
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I checked the manual and 3900 is the correct WOT. The Tach's however may not be too accurate. I'll have them checked out. Thanks
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Old 07-05-2012, 10:53 PM   #9
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Diesel Volvo Penta's 200 hp
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Old 07-06-2012, 10:00 AM   #10
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I have a 98 350 with twin Yanmar 170 HP 4LH DTE engines. The boat does about 17 to 18 MPH at 3300 to 3400 RPMs. My props are bigger, I am thinking around 22". I will check my papers down at the boat this weekend and get back to you on Monday.
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Old 07-06-2012, 10:26 AM   #11
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Thanks David. Is 3400 your max rpm?
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Old 07-06-2012, 10:26 AM   #12
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Motors sound like TAMD41s and the 3900 is correct. I have TMD41s (150 hp) in my 36' nova sundeck (25K Lb?) with 21 x 14 4 blade props. i can get 12 knt at 3600. I have not checked high idel to see if it is my govenor or the load that is limiting the max RPM. I never cruse above 2800 @ 8knt so i am not risking overloading. If you cannot get to the 3900 RPM then running near your actual maximum RPM can be a dangerous overloading situation

Get all the data on your boat ( HP, waterline length, transmissin gear ratio, estimated weight, prop size, hull type probably semi planing) and go to the Boatdiesel.com and use their prop calculator. Just pay the $20 or whatever is costs to sign up at boat diesel, it is well worth it.

It tells me that i am under propped (recomends 21 x 17), that is why i need to check the max RPM in neutral (high idle) and see if possibly my govenor is holding me back from full RPMs or mabey my boat has added 10K lb over the years.

Got to the seaboard marine site and read Tony Athens article "Propellers move boats engines only turn them" It explaines all the facts and myths about propellers, pitch and engines ratings.
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Old 07-06-2012, 11:02 AM   #13
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Yes, the Yanmars maximum RPMs are 3300 to 3400.
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Old 07-06-2012, 11:46 AM   #14
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I have a 36 foot Nova Sundeck with Volvo TMD40s, (136 HP) and run at 2450 RPMs.(using digital tachs) to get a speed of 8.5 knots. Top RPM under load is 3400 with a speed of 11.6 knots running the measured mile markers.
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