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tr_guy79
#1 Posted : Saturday, May 07, 2011 8:46:28 PM(UTC)
tr_guy79

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Had the boat out again today, for a little cruise. As per GPS and original tachs, I am getting 19 mph @ 2800 rpm. I did the math on it, and with 11" pitch props, that is a hell of a lot of slip. Does that sound right? my tabs are not working so the running angle is not the best, and may be contributing some slip, but by my math (11x2800x60 / 63360), I should be up around 23 (assuming 20% slip). The 20% slip seemed about right, since this would put me at a calculated top speed of 36 mph @ 4400 rpm.

-Shane
"McKenna Renee"
1972 '32 FB Express. Twin 318 / Edelbrock 1409s
Chesapeake City Md (Upper Bay / C&D Canal)
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cap'n Brent
#2 Posted : Sunday, May 08, 2011 7:21:01 AM(UTC)
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Sounds about right to me mine turns 24.5 @3k but less weight. By about 400lbs my tabs inop as well. My boat is a fisherman that may differ. I slip next to a 74 sedan and looking at the boats together his looks heavier than mine with more glass and super structure. If you can squeeze 30mph out of a 32 cabin I think you are doing something. Another neighbor of mine has a 32 carved aft cabin, took him for a ride with about 700 lbs of passengers the old girl jumped up on plane. He about made a mess in the back of his shorts. Wow he said this gets right on top and quick. Proudly I said yes it dose, yours dosnt?
HP Chadwick bay Sunset Bay lake Erie NY boat name Sunrise 32' f/b fisherman chry 318 twin blue bastards,28'express singel 318
"It would be a labor of love, if I loved to labor" cpt Brent
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dougrose
#3 Posted : Sunday, May 08, 2011 8:24:49 AM(UTC)
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With 11" pitch and 2800 rpm you are getting 29 smph slipstream speed. Accounting for shaft angle, it is a little over 28 smph. Since you are moving at 19 smph, then your apparent slip is 9/28 or 32%. This is not so bad for small props, and will improve when you have your tabs working properly. The larger, slower props used with gear reduction will do a bit better.

I don't know if any Marinettes ever have gone 36 smph, since it says 35 in the brochures and normally they are somewhat fanciful. I don't know that you will ever see 36 unless you can find some downhill water....


1975 32' Flybridge Sedan, twin Perkins 6-354 diesels, 1:1.53 velvetdrives, 16 X 19 props. Merritt Island, Florida
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Docsnow
#4 Posted : Sunday, May 08, 2011 9:00:46 AM(UTC)
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Originally Posted by: dougrose Go to Quoted Post

since it says 35 in the brochures and normally they are somewhat fanciful. I don't know that you will ever see 36 unless you can find some downhill water....


The BigM Boucher is sort of like the EPA gas ratings on the new car stickers. As in both glamorizations Shhh it has to be under ideal situations or as for cars on a dyno Whistle

Norm,

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http://www.picturetrail.com/gid23690601 Try it now there's music to listen to while U view the Big M's

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 You'll have bad times, but they'll just wake you up to the good times you weren't paying attention to

Some people try to turn back their odometers.Not me, I want people to know "why" I look this way.I've traveled a long way and some of the roads weren't paved.
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cap'n Brent
#5 Posted : Sunday, May 08, 2011 11:27:37 PM(UTC)
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Originally Posted by: Docsnow Go to Quoted Post
Originally Posted by: dougrose Go to Quoted Post

since it says 35 in the brochures and normally they are somewhat fanciful. I don't know that you will ever see 36 unless you can find some downhill water....


The BigM Boucher is sort of like the EPA gas ratings on the new car stickers. As in both glamorizations Shhh it has to be under ideal situations or as for cars on a dyno Whistle

Norm,

Big BigMs Live On Applause

You must not have seen my vid hat flies off at 57 mph.. he he
HP Chadwick bay Sunset Bay lake Erie NY boat name Sunrise 32' f/b fisherman chry 318 twin blue bastards,28'express singel 318
"It would be a labor of love, if I loved to labor" cpt Brent
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tr_guy79
#6 Posted : Monday, May 09, 2011 9:17:45 AM(UTC)
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Had her out again yesterday and got 24.4 at 3k, so I guess that seems about right... Now to figure out why 3k is 1/2 throttle on the port, and full throttle on the stbd (already have another post going about that)...

-Shane
"McKenna Renee"
1972 '32 FB Express. Twin 318 / Edelbrock 1409s
Chesapeake City Md (Upper Bay / C&D Canal)
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fastjeff
#7 Posted : Monday, May 09, 2011 1:32:37 PM(UTC)
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Full throttle! Not good. I suspect the distributor is sticking on you.

Jeff
"...reality is not nearly as lovely as the world of Liberal Land. No wonder so many people want to go there." - Tom Sowell
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Jack Marchand
#8 Posted : Tuesday, May 10, 2011 2:22:59 PM(UTC)
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Mine does 30 mph by GPS, that was with too big of props. Have better ones now and should get closer to rated RPM...Will know in about a week, That's when I go back to the boat.
75 FB express, "Big Enough II" twin 318s, 950hrs, raw water cooling, 1 to 1 transmisions, Beautiful Lake Charlevoix, MI
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