different options for Dukw prop

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fahtal
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different options for Dukw prop

Post by fahtal » Thu Apr 15, 2021 12:37 am

Hi

Did any of you guys ever experimented with different props?

We have an ski boat and you can make a big difference with props on performance. I was wondering if any of you tried that.

Or if any have the specs of the original prop.


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Re: different options for Dukw prop

Post by motto » Thu Apr 15, 2021 4:08 pm

Original DUKW prop is 25" Diameter 13.5" (early) or 14" (late) Pitch.
Unlike most marine propellers pitch is R/H due to the reverse in DOR caused by the water propeller transfer case.
Early props were malleable cast iron, standard props were manganese bronze.

David

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Re: different options for Dukw prop

Post by fahtal » Thu Apr 15, 2021 10:35 pm

great! thank you

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Re: different options for Dukw prop

Post by fahtal » Thu Apr 15, 2021 10:47 pm

motto wrote:
Thu Apr 15, 2021 4:08 pm
Original DUKW prop is 25" Diameter 13.5" (early) or 14" (late) Pitch.
Unlike most marine propellers pitch is R/H due to the reverse in DOR caused by the water propeller transfer case.
Early props were malleable cast iron, standard props were manganese bronze.

David
Do you also know the rpm the prop makes? I think we always swim with prop lever in fwd in second gear at around 1200 enginge rpm, maximum will be around 2200- 2500 rmp and minimal rpm to still be able to stear is 500.

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Re: different options for Dukw prop

Post by motto » Fri Apr 16, 2021 1:17 am

Transmission 2nd speed is 3.50 to 1
Water propeller transfer case in fwd position is 1.3448 to 1
Prop rpm can be worked out for any engine rpm using these figures for these lever positions only

David

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Re: different options for Dukw prop

Post by jeffl » Sat Apr 17, 2021 4:33 am

I found out that after I had my prop welded small chips, straightened and polished that the chart on the firewall was very accurate to gps speeds on water. We typically run fwd and 2nd and 2000 to 2200 rpm and it performs nicely and vibrations to a "minimum". Also I have a modern tach and it shows the original is about 500 rpm lower which could greatly impact any measurements.

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Re: different options for Dukw prop

Post by fahtal » Sat Apr 17, 2021 10:36 pm

motto wrote:
Fri Apr 16, 2021 1:17 am
Transmission 2nd speed is 3.50 to 1
Water propeller transfer case in fwd position is 1.3448 to 1
Prop rpm can be worked out for any engine rpm using these figures for these lever positions only

David
Is the fwd gear ratio correct? I always thought the reverse was 1.3 and fwd more something like 1 to 1 ?

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Re: different options for Dukw prop

Post by fahtal » Mon Apr 19, 2021 12:19 am

Image

Image

So what i found:

2nd gear is 3.5:1

marnie drive is either 1.3448 :1 (as Motto wrote) or 0.743:1 i think both numbers are correct but i don`t know wich one is fwd.

But if the engine rpm is 1000 the 2nd gear output shaft rpm is 1000/3.5= 285.7 rpm then the marine drive output is Either 285.7/ 1.3448= 212.46 or 285.7/0.743= 384,522 rpm

edit: Making sense out of the numbers: when in reverse you want toe make the same rpm as in 2nd gear so the marinedrive rev is 0.743 because the reverse gear is 6:1 which means :

1000 rpm in 2nd and fwd is 212 prop rpm
1000 rpm in R and rev is 224 prop rpm

sounds about right.

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Re: different options for Dukw prop

Post by W. Winget » Mon Apr 19, 2021 6:52 am

Just have to say, for what it's worth, the amount of "effort" and time spent on redesigning a propeller which was accomplished on a Slide Rules by some significant maritime engineers/sailors (1).

Then the expense of possibly locating/machining a prop.

All to make a brick go 6 knots VS 5.5 maybe :?:

You would be better off replicating the Hydrofoil ("Flying DUKW") with modern components, then you could hit upwards of 75 on the water. :D

Change the prop however you want, It's still going to have the same amount of drag with the axles hanging down and wheel wells acting like large paddles dragging in the water.

Just sitting on my mind how much redesign you have to do to mod the DUKW. You think :idea: maybe they would have worked it out by say the Super DUKW prop, or say a LARC? checking into one of those prop designs might be easy enough, but it's still a floating brick :oops: .

Just saying.
V/R W. Winget

1 dead DUKW
1 DUKW cut in half for parts
Too many other projects



(1)Designers of the DUKW: "Rod Stephens Jr. of Sparkman & Stephens, Inc. yacht designers, Dennis Puleston, a British deep-water sailor resident in the U.S., and Frank W. Speir from the Massachusetts Institute of Technology."
Looking for 1918 Standard B 'Liberty' truck parts

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Re: different options for Dukw prop

Post by fahtal » Mon Apr 19, 2021 11:13 am

i totally agree with you. But that is what a hobby is about;)

As i said i was inspired bij the prop of our ski boat. the difference in design and technique. i thougt well 80 years on maybe the experts would look at it at a different angle.

A friend of mine has an boston ducks 4 blade prop. it runs more smooth he says. it is more balanced.

hier is a comparison between the old ski prop and the new one. the new one is from ACME marine. and they cnc all their props.

the old one is 14" pitch and the new one 11,5"

Image
Image


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