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Old 03-04-2013, 09:36 AM   #81
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Good morning Daddyo,
Print off my post and show it to a good prop guy. See if he agrees and see if he can/will interpret the dia that will work and if it's too big for your 2.5-1 gear. What you really need is a 3-1 gear.

FD yup .. very close. So close that in some conversations she could be called FD. But technically not. Some FD Seaton designs have some emersed transom to but it's smaller than yours and the buttock line is much steeper.

You could fair in the trailing edge of that keel by adding on to make a tear drop TE.
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Old 03-04-2013, 09:47 AM   #82
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Greetings,

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Old 03-04-2013, 10:11 AM   #83
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^^^^
That's it! Add an engine and run four and three blades
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Old 03-04-2013, 10:15 AM   #84
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Greetings,
THAT would certainly be a Titanic undertaking....
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Old 03-04-2013, 10:56 AM   #85
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Daddyo,
More thoughts. My gear is 2.57-1 so almost the same as yours but my present and original prop is 18" dia. There is much more room for a bigger prop on Willy but the builder/designer installed an 18" wheel. Similar to you w room for a bigger prop but your situation may have something to do w the fact that they were planning on single engines too.

One might be inclined to say Willard and DeFever didn't know what they were doing but I'm quite sure they did. I think it has to do w low levels of power and both of our boats may have nearly the perfect prop. But it looks like both could benefit from deeper gears and bigger props.

RT yes I've said before that three screws may be a very good arrangement.

More later.
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Old 03-04-2013, 11:40 AM   #86
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I'd love to have a 5-1 turning a 30+ wheel but knock on wood, the trannys are good although I hear BWVDs are on barrowed time up at my hours (4700).
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Old 03-04-2013, 12:37 PM   #87
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Here are some numbers from Gerr's Prop - diameter/power/rpm chart/calculator. The numbers are based on a "standard three blade 50% disc area ratio prop". I used 1400 rpm simply as a reference to take a look at operating implications for these relatively large engines at 2.5 and 3:1 gear ratios. With some engine charts and a transmission spec sheet, you can also use Gerr's chart to get a sense as to where to set the new red line and confirm adequate transmission torque margins in an over prop scenario.

2.5:1 ratio

24" prop - 15 Hp
26" 23
28 32
30 43
32 60


3:1 Ratio

24" 8 HP
26 12
28 18
30 25
32 33
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