18' sea ray with 3.0 speed questions

[mwe-maxxowner]

A friend of mine recently bought an 88(I think) Seville sea ray 18' with the 3.0 mercruiser I/o. We have a few questions. Runs pretty well and has a nice wake. Idles like a champ and purrs like a kitten. We believe he made a good buy.

My question is this: with a 19? prop we got about 32 mph on a calm day. Two adult males on board and no other weight. Besides a few life jackets and a kneeboard. It has a decent holeshot, but we also like to cruise the lake sometimes in addition to boarding. Is that about all the speed we can hope for, or do we need to make sure its running up to par and investigate a prop change?

What plugs do we need?

I don't know if we reached Max wot rpm because the tach is inoperative. It seems once the throttle is halfway up, pushing further makes no change in speed or rpms.

That motor is rated at 140 horse, so we expected it to be similar to my black Max merc 150,but this isn't the case.

 

[fat fanny]

Re: 18' sea ray with 3.0 speed questions

Work with your trim after plaining out it will increase your speed and smooth out your ride as well. Also it is advisable to get that tach working you do not want to over rev that engine.

 

[airshot]

Re: 18' sea ray with 3.0 speed questions

There is no absolute answer to your speed question. First things first....get the engine properly tuned or check to be sure it is properly
tuned, make sure throttle is opening up completely and by all means as recomended in the previous post, get that tach fixed!!!! Only then can you make proper adjustments to prop pitch. Once all that is done then when you reach the max WOT with a prop that allows you to reach WOT will you know what your max speed wil be. By the way, you need a GPS to get the most accurate speed reading.
Actually the first thing you really need is a Mercruiser service manual for your engine, you will find the answers to most all your questions there.
Airshot

 

[Bondo]

Re: 18' sea ray with 3.0 speed questions

Work with your trim after plaining out it will increase your speed and smooth out your ride as well. Also it is advisable to get that tach working you do not want to over rev that engine.

There is no absolute answer to your speed question. First things first....get the engine properly tuned or check to be sure it is properly
tuned, make sure throttle is opening up completely and by all means as recomended in the previous post, get that tach fixed!!!! Only then can you make proper adjustments to prop pitch. Once all that is done then when you reach the max WOT with a prop that allows you to reach WOT will you know what your max speed wil be. By the way, you need a GPS to get the most accurate speed reading.
Actually the first thing you really need is a Mercruiser service manual for your engine, you will find the answers to most all your questions there.
Airshot

Ayuh,.... What they said,.... a tune up, 'n compression test for a baseline...

 

[r.j.dawg]

Re: 18' sea ray with 3.0 speed questions

First things first..... get that tach working or replace it. Without knowing the RPM range you are working in there is no way you can get that engine tuned properly.

 

[mwe-maxxowner]

Re: 18' sea ray with 3.0 speed questions

Thanks guys. New plugs and tune up are up soon. Then compression and spark tests for sure. I have no idea what's up with the tach, and speed is Droid and iPhone verified. The speedo on the boat doesn't work either. The motor gives a nice holeshot and pulls me right up on a kneeboard, so I think we're okay on power. I just think either we're expecting too much, or throttle isn't opening all the way. Or perhaps we have room to go up a few degrees on the prop. It certainly doesn't sound to be over revving.

We did play some with the trim. Full down was about 30. As we trimmed up IR climbed to about 32, 33, when it started to porpoise and slow back down.

 

[Scott Danforth]

Re: 18' sea ray with 3.0 speed questions

you can not compare the 150hp outboard to a 140hp 3.0 no more than you can compare a 200hp Hyabusa motorcycle to a 200hp honda civic. That being stated, not bad numbers so far. get the tuneup done. make sure you have good fuel and the carb is top notch. you should be able to hit about 36ish +/- trimmed properly on the right conditions.

 

[fishrdan]

Re: 18' sea ray with 3.0 speed questions

140HP I/O VS 150HP outboard isn't going to be apples to apples, 10HP less and and extra 300# of engine weight with the 140.

I agree with the others about getting the tach working to see if the engine is turning within it's WOT RPM range, 4200-4600RPM. I think your boat is underperforming as I'm running 35-36MPH in my 18'er with a Mercruiser 140, and I'm hauling around a lOT of fishing gear, extra 400-500#.