Go Back  Offshoreonly.com > General Discussion > General Boating Discussion
What prop to get on plane on one engine? >

What prop to get on plane on one engine?

Notices

What prop to get on plane on one engine?

Old 12-22-2021, 08:09 AM
  #11  
Registered
 
Join Date: Oct 2005
Location: Plainville/Old Lyme, CT Boca Raton, FL
Posts: 6,017
Received 102 Likes on 60 Posts
Default

Play with the prop slip calculator on the Mercury site. Just for haha’s I put in these parameters:

1.5 ratio
20% slip
Wanting to achieve 25mph at 3500rpm gives you a 14P prop.
302Sport is offline  
Old 12-22-2021, 08:25 AM
  #12  
Were doomed!
Charter Member
iTrader: (1)
 
Wally's Avatar
 
Join Date: Oct 2000
Location: Chicago, IL
Posts: 6,206
Received 475 Likes on 241 Posts
Default

I think it more depends on the boat and its setup. Ive been on and witnessed first had a 2000 38' powerquest with twin 500efi's get up on plane on one engine! Blew me away! But me trying to get my old 1984 30' scarab II with twin mildly built 454's there was no way it would do it! I eve tried to test it while running....ran the boat up to about 30/35mph...trimmed one side up till it was blowing out then killed that engine and kept trimming up to try and get the drive as high as possible....boat instantly started dragging and i'd say in under 30sec it fell off plane...even with giving it more and more power it was either too heavy or the drag of the drive being offset tot he side (TRS) was too much...
__________________
-Wally

Money can't buy happiness, but it can buy horsepower. And I've never seen a sad person hauling a$$!
Wally is offline  
Old 12-22-2021, 08:50 AM
  #13  
Registered
 
Join Date: Jan 2007
Location: Mansfield, TX
Posts: 6,187
Received 167 Likes on 92 Posts
Default

Originally Posted by Sydwayz View Post
Yep, I've done it several time in different 37ATs.
I ran stock 28 Bravo1 4 blades on my boat, and I know Pat has done it with 30s. You would be better off with a meaty 5 blade for this task, but a 4 blade has worked.

Bury the tabs, and ease the boat up. You may have to waddle the steering wheel a bit back and forth for it to surf it's way up. I've been on plane as slow as 17mph in the 37AT hull with the tabs buried.
I've run as fast as 30mph with only a single screw, WITH the second downed side prop on. Realize, you are putting TREMENDOUS stress on the drive that IS working.

If you "have anything left" with the downed side, it would be beneficial to reduce the torque/weight stress on the good drive to get on plane. The last thing you want to do is break the good side.
I did this once with a drive that was knocking really bad. I used as little as possible to pop the boat up on plane.
I got everything moving and set with the good engine/drive, and started the engine with the knocking drive; engaged forward for a few seconds, just long enough to pop it up on plane. Then killed that motor and trimmed it out.

Taking the downed side prop off is a tremendous drag reduction. But I've never had to do it.
Dang, that's impressive. Ever try to surf behind one at 17mph?
TexomaPowerboater is offline  
Old 12-22-2021, 09:52 AM
  #14  
Forum Regulator
VIP Member
iTrader: (1)
 
Sydwayz's Avatar
 
Join Date: May 2001
Location: Worldwide
Posts: 23,510
Received 765 Likes on 334 Posts
Default

Originally Posted by TexomaPowerboater View Post
Dang, that's impressive. Ever try to surf behind one at 17mph?
Never thought to. But we have tubed behind a 37AT.
Sydwayz is offline  
Old 12-22-2021, 10:20 AM
  #15  
Registered
 
Join Date: Oct 2000
Location: Rotonda West, Florida
Posts: 2,484
Received 112 Likes on 52 Posts
Default

I had a drive failure on a Sunday boating in New Jersey on the way back to the ramp. This was our 27' Magnum Sport "the Hairy Canary", with twin 454 cu.in BBCs, TRS drives (raised X-dimension), with 27" Mirage props with added cup and thinned leading edges/labbed props. I thought a transmission on the starboard side failed. At first, with the port drive tucked down all the way and the starboard drive elevated a bit I could not get the boat on plane.

My weight at this time was 200 lbs., and my friend who was 200 lbs., I figured bow weight would make the boat plane, and it did. I had my father put the throttle down on with me and my friend on the bow, the Magnum did as expected, came on plane and we were on our way; the 400 lbs/. of added bow weight allowed the boat to plane and stay on plane as we crawled back to cockpit while the Magnum was underway on plane.

When I thought the transmission had failed I was incorrect, it was a broken prop shaft. When I raised the drive when to see if in fact it was the transmission that had I failed, I would look at the prop stay stationary while my father put the drive in gear, forward and reverse, and there was no propellor movement, and the prop was there at that time - clearly visible before we put the boat on plane. So, the assumption was transmission failure, due to the fact we raced the **** out that boat every weekend.

When we arrived at the ramp and pulled the boat out of the water, the propeller was gone, and half of the prop shaft was gone. The water pressure, force of water while on plane extracted the blue-printed Mirage prop I bought, with the shaft, that was a something I will never forget.

The 34' Phantom with Bravos drives and 34" labbed Bravo props would not plane on one engine (540 cu. in EFI motors), no matter what I tried, no way could we get the boat on plane (water hose burst that day while boating on the Elk River, in Maryland/upper Chesapeake Bay), that was a long idle home to New Jersey that day!
Smarty is offline  
Old 12-22-2021, 01:25 PM
  #16  
Platinum Member
Platinum Member
 
Twin O/B Sonic's Avatar
 
Join Date: Mar 2002
Location: Cardington Ohio
Posts: 3,613
Received 980 Likes on 397 Posts
Default

I thought of this before for same reason.
Never did it though.

My guess is:
Way down on pitch, as much diameter as will fit, and as much cup as they can hammer into the blades.

On the way down on pitch part, Iíve seen bent valves from too much load while trying to do same.

As in, WFO nets 20 mph @ 3k RPM, you probably ainít making it back to dock under your own power anyhow.
Twin O/B Sonic is offline  
Old 12-23-2021, 09:10 AM
  #17  
Registered
 
Join Date: Oct 2010
Location: Hemlock, MI
Posts: 896
Received 95 Likes on 60 Posts
Default

One tidbit for thought......is your boat setup with dual (actively plumbed) power steering pumps or the typical Merc setup where one motor pressurizes steering system and the other's pump is just looped to return line and useless? That is how my boat was setup, and both times I have needed to come home on 1 engine, the dang power steering motor died. Without the power steering (and dual external add-on rams) forget about trying to get on plane when your arms aren't strong enough to keep the wheel straight at anything above 2200 rpm (8.2 mph on mine).
Gimme Fuel is offline  
The following users liked this post:
Twin O/B Sonic (12-23-2021)
Old 12-23-2021, 05:24 PM
  #18  
Registered
 
Join Date: Jan 2021
Posts: 268
Received 134 Likes on 73 Posts
Default

Originally Posted by Gimme Fuel View Post
One tidbit for thought......is your boat setup with dual (actively plumbed) power steering pumps or the typical Merc setup where one motor pressurizes steering system and the other's pump is just looped to return line and useless? That is how my boat was setup, and both times I have needed to come home on 1 engine, the dang power steering motor died. Without the power steering (and dual external add-on rams) forget about trying to get on plane when your arms aren't strong enough to keep the wheel straight at anything above 2200 rpm (8.2 mph on mine).
just a thought, the steering went out on my boat and I thought if I just had a ratchet strap I could have pointed the boat in the right direction and locked the steering down and gotten myself closer to the dock. Now I've got a ratchet strap in my small tool box.
carnutsx2 is offline  
Old 01-03-2022, 10:53 AM
  #19  
Registered
 
Join Date: Oct 2010
Location: Hemlock, MI
Posts: 896
Received 95 Likes on 60 Posts
Default

Originally Posted by carnutsx2 View Post
just a thought, the steering went out on my boat and I thought if I just had a ratchet strap I could have pointed the boat in the right direction and locked the steering down and gotten myself closer to the dock. Now I've got a ratchet strap in my small tool box.
I wouldn't trust the steering cable/wheel to hold that much force. Would save your arm if you are still easy with the sticks.
Gimme Fuel is offline  
Old 01-03-2022, 12:22 PM
  #20  
Registered
 
Join Date: Jan 2021
Posts: 268
Received 134 Likes on 73 Posts
Default

Originally Posted by Gimme Fuel View Post
I wouldn't trust the steering cable/wheel to hold that much force. Would save your arm if you are still easy with the sticks.
the power steering system still worked, I stripped the cable at the helm.
carnutsx2 is offline  

Contact Us - Archive - Advertising - Cookie Policy - Privacy Statement - Terms of Service - Do Not Sell My Personal Information -

Copyright © 2021 MH Sub I, LLC dba Internet Brands. All rights reserved. Use of this site indicates your consent to the Terms of Use.