‘05 420DA Props

MojoHaiku

New Member
May 27, 2012
24
Anderson, SC
Boat Info
2005 Sea Ray 420 Sundancer
Meli’s Gringo
Engines
Mercruiser 8.1 HO
Just bought an ‘05 420 Sundancer. Engines are 8.1 HO Mercs. Boat should be delivered in a couple of weeks - trucking down to South Carolina from Minnesota. Surveyor report mentions “vessel reaches WOT RPM 5100 port, 5000 starboard - at 32.9 mph”
Engine red line RPM’s is 4400 - 4600. Surveyor says engines are not “straining” at the 5100. Seller says that when he bought the boat, a MarineMax dealer suggested a prop change because the boat wouldn’t reach 4600. Props are four blade, 22” Dia, 21” pitch. Sea Trial was NOT fully loaded... Does it sound like there is anything I should be worried about? Or should I just relax and drive the boat? I’m not a speed demon. Just cruise on a quiet inland South Carolina lake...
 
These are the props that would be on her from the factory.

Props.JPG
 
Are you positive about that RPM range? I thought the HO version of the 496 was rated to a higher RPM. Also, there's something amiss with the range you wrote - there's a always a 400 number range, not 200. The base 496 might be 4400-4800?

Even so, I'd rather see a little higher RPM than lower. Being as you're going to start putting a lot of stuff in it, filling the fuel tanks, water tanks, etc, it's better to start higher. Besides, you can always control your RPM with the throttle.
 
Last edited:
I just happen to have this link handy as I posted this the other day for someone.
https://marine.needmanual.com/2001-...-service-manual-number-30.html?page_number=27
I agree with Dennis, my opinion is on a boat that size, your fine. If you fill your fuel tanks and put some guests on board along with everything else that will be on it once you own it, I'll bet you will be right in the ball park. Enjoy the new boat.
 
Last edited:
Are you positive about that RPM range? I thought the HO version of the 496 was rated to a higher RPM. Also, there's something amiss with the range you wrote - there's a always a 400 number range, not 200. The base 496 might be 4400-4800?

Even so, I'd rather see a little higher RPM than lower. Being as you're going to start putting a lot of stuff in it, filling the fuel tanks, water tanks, etc, it's better to start higher. Besides, you can always control your RPM with the throttle.
Thank you, LD.. Those are the numbers the surveyor gave me... Have not researched to verify... Maybe he was thinking of the non-HO.. I think I’m going to just take it easy and run it and if i’m not happy for some reason, pay the $ and swap at next haul out... Was a little concerned about higher fuel consumption...
 
RPM range on the 8.1 is 4200-4600 for the "S" and 4400-4800 for the "HO". I would get the boat home, get your stuff on it and then evaluate the RPM range. Like others have said, I would rather see an engine that could turn above the RPM range than below it. Easier to back off the throttle than to damage an engine lugging trying to turn too much prop. Plus, how often are you going to run WOT in a 420? My guess is by the time you add your stuff, fuel and water you will be in good shape RPM wise.

One propeller is a different pitch because that is the counter rotating propeller - port side transmission actually runs in reverse to turn that propeller in the opposite direction, the pitch difference is to compensate for that. Looking at the stern prop rotation is - STBD=Clockwise, Port=CounterClockwise

Anderson SC, guess that is Lake Hartwell?
 
Last edited:
My allotted stupid question of the day, but here goes... Why is one a half inch larger than the other?
Gearing of the trans. and rotation. SR does that on many models, new boats as well. Also both props are the exact same diameter. the .5 is the difference in pitch.
 
RPM range on the 8.1 is 4200-4600 for the "S" and 4400-4800 for the "HO". I would get the boat home, get your stuff on it and then evaluate the RPM range. Like others have said, I would rather see an engine that could turn above the RPM range than below it. Easier to back off the throttle than to damage an engine lugging trying to turn too much prop. Plus, how often are you going to run WOT in a 420? My guess is by the time you add your stuff, fuel and water you will be in good shape RPM wise.

One propeller is a different pitch because that is the counter rotating propeller - port side transmission actually runs in reverse to turn that propeller in the opposite direction, the pitch difference is to compensate for that.

Anderson SC, guess that is Lake Hartwell?
Yep, Lake Hartwell... Was just on Norman a few weeks back. Beautiful...
 
Gearing of the trans. and rotation. SR does that on many models, new boats as well. Also both props are the exact same diameter. the .5 is the difference in pitch.
Ahhh thanks for correcting me on the pitch... : )
 
Just turning one prop in reverse and one forward isn't the reason for the pitch difference.

The transmission Sea Ray used with the 8.1's has a slightly final drive ratio difference in the reverse or "B" position than in forward or "A" position. The difference is minute, but on high torque high reving gas engines it is noticable so Sea Ray specs a .5" differential in the prop pitch.
 

Forum statistics

Threads
112,944
Messages
1,422,711
Members
60,927
Latest member
Jaguar65
Back
Top