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Author Topic:   Speed
fishhawk posted 04-02-2002 04:20 PM ET (US)   Profile for fishhawk   Send Email to fishhawk  
I have a 13' BW w/ 3cyl. 40hp mariner, power trim & tilt,mounted on a hyd. jackplate w/ 5" setback, turning a 3 blade 10"dia. x 16" pitch alum prop. Last summer BEFORE i mounted the jackplate top speed at wot was 33-34mph (gps)@ 5200rpm. w/ 2 people 18gal. fuel aboard. Known factors are,
1) eng. wgt.----------------- 204lbs.
2) oper. rpm.-----------------5000-5600
3) wgt. of people ------------300lbs
4) wgt of batt.---------------65lbs
5) wgt of fuel & tank --------170lbs
6) wgt of jackplate-----------24lbs
7) wgt of hull----------------350lbs
8) misc. (anchor etc.)--------25lbs
total wgt --------------------1138 lbs
Can anyone give me an approx. idea of what top speed should be, and recommend what prop i should start with. I realize that to reach 5600rpm im going to have to drop about 4" of pitch. Does anyone have any experence w/ a jackplate on a 13' ? thanks, jay
Bigshot posted 04-04-2002 01:19 PM ET (US)     Profile for Bigshot  Send Email to Bigshot     
Bigshot posted 04-04-2002 01:21 PM ET (US)     Profile for Bigshot  Send Email to Bigshot     

I would either drop to a 15" alum or a 14" Stainless. that should get you around 5400 with 2 people, a bit higher solo.

EasyE posted 04-04-2002 02:51 PM ET (US)     Profile for EasyE  Send Email to EasyE     
Need the gear ratio of lower unit to figure what prop to use...EasyE
fishhawk posted 04-05-2002 02:31 PM ET (US)     Profile for fishhawk  Send Email to fishhawk     
EasyE, its 1.83:1 --------- fishhawk
Bigshot posted 04-05-2002 02:41 PM ET (US)     Profile for Bigshot  Send Email to Bigshot     
Gear ratios are fine to start with and guess but he already has a prop and hard numbers. I think my sizes will be real close to what he is looking for. Call prop shop like hill or geberal and relay the data to them, they'll tell ya too.

I am pretty picky with dialing in props and this 70 Zuki is the fiorst to stump me. If I would have went with the stock prop...I would have missed out. I have 5 props I am messing with of all different diameter and pitch and materials. Some borrowed, some from the Bigshot archives. No matter how close I think I am, the prop shop always does the final assesment and is always right.

Bigshot posted 04-05-2002 02:43 PM ET (US)     Profile for Bigshot  Send Email to Bigshot     
PS Hawk: 2" of pitch will give you 400 RPM's. You drop to a 12 and that thing will wiz right passed 6k.
NEVER SCARED posted 04-05-2002 03:20 PM ET (US)     Profile for NEVER SCARED    
English or Metric units?
EasyE posted 04-05-2002 09:08 PM ET (US)     Profile for EasyE  Send Email to EasyE     
Fishhawk, if you go to:

Find your engine catagory and check out the 10 3/8 x 14 SCB prop...that will give you the speed you deserve out of that engine.

Just as a comparision...a 30hp Johnson clamped on the back 13' will give you 32mph with no jacks or tilts. Your engine, IF it is still pumpin out 40hp and being that its jacked up, setback, and tilted with a 14P cupped speed prop should dish out about 38-42mph. 15P would be a waste of money because it would be too tall and you would have to be drivin solo~~~EasyE

fishhawk posted 04-06-2002 02:58 AM ET (US)     Profile for fishhawk  Send Email to fishhawk     
My thanks to all, as soon as the ice is out i'll run it w/ several different props. once i get it dialed in right i'll post the results here. Jay

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