Mariner outboard

olsluggo

Cadet
Joined
Jul 28, 2005
Messages
13
Not being familiar with outboard motors I have a silly question.I have a 92 ,115 mariner outboard that I bought used.With my 19 ft.boat I have to turn 4000 rpms to level out.My question is ,when I am cruising how many RPMs can I run and not overwork the engine?I have always had a Mercruiser I/O 140 hp in my other boat and always ran 3000 rpms.With this boat I have to run 3500 to keep on the level.
 

studlymandingo

Commander
Joined
Mar 22, 2006
Messages
2,716
Re: Mariner outboard

Are you trimming the motor when you are running? A set of smart tabs would really help in keeping the boat on plane at lower rpms. Bear in mind that outboards are meant to be run at much higher RPM than I/O. However, 4000 is a bit much just to stay on plane. How fast are you traveling at that RPM? There may be other issues with the boat that need to be addressed such as wet foam. Post some more information on the boat and motor and you will get some ideas on where to go. Do a search on "Smart Tabs".<br /><br />Welcome to iboats!
 

05GlastronSX

Chief Petty Officer
Joined
May 29, 2005
Messages
437
Re: Mariner outboard

you can run practically any RPM (within the max RPM limit for that engine of course)and not hurt your engine. Outboards are designed to be run at WOT(wide open throttle). A well maintained outboard will run WOT all day if you give it gas and oil. 4,000 RPM is a little much though just to get it on plane. It's probably either a prop problem or your boat is very underpowered.
 

olsluggo

Cadet
Joined
Jul 28, 2005
Messages
13
Re: Mariner outboard

My boatis a 1992 Kencraft,18.5 feet in length,garage kept and well maintained.I trailer it to the bay so it doesn't stay in the water.The original owner is deceased so I cannot ask him any questions.When I get on plane I throttled back to 3500 RPMs and the speed indicator shows 25mph.I don't trim the motor I leave it all the way down.
 

studlymandingo

Commander
Joined
Mar 22, 2006
Messages
2,716
Re: Mariner outboard

A couple of things: First, you stated that you don't trim your motor, you leave it all the way down. By having the motor trimmed all the way down, you are plowing the front end. The motor trim is to properly adjust the attitude of the boat. Once you are on plane, you want to trim the motor out so the bow raises up thereby reducing drag on the hull, you will increase speed, improve handling, and increase your fuel mileage by doing so. Do a search on trim/tilt and read more about it. Secondly, you will want to check the weight of the boat, without knowing the way the boat was kept before you owned it, there could be some saturated foam inside which could be adding some weight. The Kencraft company makes the Sea King and Bayrider now, is it one of these boats? I would do some research (get on the NADA website) and find the weight of the boat. Go to a set of scales and weigh-in, see if you are carrying some weight. <br /><br />My guess is you will see a vast improvement by trimming up when you get on plane!!!<br /><br />Keep us posted as to how you come out. The great thing about these forums is that everyone can read as to what works and what doesn't, a great resource for everyone!
 
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