Newbie Question!! - How long can I run WOT?

[danpar]

Forgive me for asking a dumb question, but I am new to having a boat. I have bought myself a 1988 Cajun fish & ski 17ft with a 3.0l OMC I/O
It runs WOT 31mph @ 4800 rpm 17 pitch SS prop.
I have been running it at about 4000 rpm simply because I wouldn't run my car flat out! I notice on here people talking a lot about WOT.
So, how long are people running at WOT? - I don't want to blow my engine haha!

Any advice?

 

[Howard Sterndrive]

Re: Newbie Question!! - How long can I run WOT?

It runs WOT 31mph @ 4800 rpm 17 pitch SS prop.

you want a 19P if you're going to run WOT even briefly, because your engine should not be run any faster than 4600 rpm

Once you prop it right, you can run WOT indefinitely but obviously it is putting maximum stress on the drive and engine and will burn a lot more fuel than at a nice cruising rpm like 3600 rpm

I have outrun a storm at WOT for about an hour with a 3.0.

Your fuel tank is probably only holds enough gas for 2 hours of WOT

 

[Brewman61]

Re: Newbie Question!! - How long can I run WOT?

I very seldom run at WOT for any length of time. It makes the gas go "bye bye" at a very rapid rate. Pulling up a skiier I may hit it all the way for a few seconds, then ease back once I get on plane and dial back to the speed the skiier wants. For normal cruising, I normally go just fast enough to stay on plane, maybe a tick more. At $4/gallon I like to make my gas last.

 

[jtmarten]

Re: Newbie Question!! - How long can I run WOT?

'Til the gas gauge is on E.
4800 isn't too bad, re-propping with a 19p will drop you 2-400 and gain a little top speed.

 

[danpar]

Re: Newbie Question!! - How long can I run WOT?

Does 31 mph sound about right or should it be running faster? I don't know how accurate my speedo is though.

 

[Howard Sterndrive]

Re: Newbie Question!! - How long can I run WOT?

31 is brutal
and unless your prop is really chewed, 31 is not really even possible if your tach is accurate and the engine is doing 4800 and you have a 17P.

with typical SS prop efficiency, should be going around 42mph at 4800

borrow someone's GPS

 

[UNSUREBOATGUY]

Re: Newbie Question!! - How long can I run WOT?

I have a 16" Four Winns Freedom (1987) with the 3.0. I finally got around to taking a GPS and ran the boat with a shop tach hooked up. My two boys (6 and 2 1/2) and I were tooling around on the lake yesterday and were getting around 34 mph at about 4400-4600. The water was pretty choppy so I'm not exactly sure what the performance would be on smooth water, but with that light load and a 14 x 19p aluminum prop, we still had a fair amount of throttle left. If I put it all the way down, I would have been over-revving for sure. We usually carry quite a bit more weight, but I'm saving up for a higher pitch prop to try myself.

I know my tach was very far off (I adjusted it so it is much closer now) and the speedo isn't very accurate either. I would strongly suggest taking a GPS and a shop tach out on the water to do real testing before coming to too many conclusions.

I'm no expert, but I would make sure your tach and speedo are accurate (tach especially). I would guess a higher pitch prop would be a good idea unless you boat with a lot of extra weight. Once you get your true WOT tach and speed readings, there are some very helpful folks in the prop forum that I am sure might be able to help out. Good luck and happy boating.