What size propeller shaft for a crackerbox?

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Harald1966
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What size propeller shaft for a crackerbox?

Post by Harald1966 »

Hi.
What diameter size do you recommend for a 15' crackerbox with mercruiser 350?
Is one inch (25mm) OK?

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Roberta
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Re: What size propeller shaft for a crackerbox?

Post by Roberta »

1" shaft with 1/1 gear ratio transmission. Any gear reduction might require a bigger shaft and more pitch and diameter prop. Big motor for a Cracker Box.

Roberta
Roberta "Queen of the Boat Builders"
Built Zip "Oliver IV", Super Spartan "Jimmy 70", and Torpedo "The Glen L".

Harald1966
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Re: What size propeller shaft for a crackerbox?

Post by Harald1966 »

I have a Borg Warner Velvet drive ratio 2,1:1
Direct drive not possible...

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Roberta
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Re: What size propeller shaft for a crackerbox?

Post by Roberta »

A 1-1/8" shaft would be better because you will have to use a bigger, more pitchy prop to handle that power and ratio.

Roberta
Roberta "Queen of the Boat Builders"
Built Zip "Oliver IV", Super Spartan "Jimmy 70", and Torpedo "The Glen L".

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kens
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Re: What size propeller shaft for a crackerbox?

Post by kens »

Roberta wrote:
Tue Jan 12, 2021 9:11 am
A 1-1/8" shaft would be better because you will have to use a bigger, more pitchy prop to handle that power and ratio.

Roberta
NO !!
You do not put a V-8 in something as light as a crackerbox and then put a reduction gear on it.
Much less a 2.1 : 1 VelvetDrive.
Oak is over rated, everything about it takes extra time; then it warps, splits or checks !!! :roll:

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kens
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Re: What size propeller shaft for a crackerbox?

Post by kens »

Harald1966 wrote:
Tue Jan 12, 2021 8:42 am
I have a Borg Warner Velvet drive ratio 2,1:1
Direct drive not possible...
For something as light as a Crackerbox, a 1:1 gear MUST be possible.

for something like a 350 V8 + 2.1:1 gear a shaft of 1 3/8" with a prop 20"dia. is possible,,,,but NOT in a crackerbox
Oak is over rated, everything about it takes extra time; then it warps, splits or checks !!! :roll:

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Roberta
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Re: What size propeller shaft for a crackerbox?

Post by Roberta »

I totally agree with Ken on this. A really small aluminum V8 or V6 is appropriate for a Crackerbox.

Roberta
Roberta "Queen of the Boat Builders"
Built Zip "Oliver IV", Super Spartan "Jimmy 70", and Torpedo "The Glen L".

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kens
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Re: What size propeller shaft for a crackerbox?

Post by kens »

Roberta wrote:
Tue Jan 12, 2021 4:49 pm
I totally agree with Ken on this. A really small aluminum V8 or V6 is appropriate for a Crackerbox.

Roberta
No, the Crackerbox was designed around the ubiquitous SBC, the 350.
it will accept all the cam, heads, carbs, hot rod parts, et. al.,,,,
BUT, It was NOT designed around a reduction gear.
Oak is over rated, everything about it takes extra time; then it warps, splits or checks !!! :roll:

TAB
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Re: What size propeller shaft for a crackerbox?

Post by TAB »

All of the cracker box guys i know, ( granted they race them) run a direct drive. They want to use the prop as a brake into slow down. They don't even use a free wheel or throw out barring. I would recommend for a pleasure boat you do.

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Bill Edmundson
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Re: What size propeller shaft for a crackerbox?

Post by Bill Edmundson »

Harrold

What HP and max RPM are you planning to run. Also, would like the total weight of the boat, including you and fuel.

Bill
Mini -Tug, KH Tahoe 19 & Bartender 24 - There can be no miracle recoveries without first screwing up.
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