Top Speed Of Our Boat?

[LuvBoating]

RPM's at 28mph only if the that's the highest tach reading achievable. This is about the tach reading, not the speedo or speed.

The fact the throttle will go further at this point is a pretty good hint there's either a big issue with the current prop size (way off), the motor isn't running as well as it should (possibly a carb issue), or there's an issue with the throttle cable being improperly adjusted.......

The throttle will go a little bit further. But, to check the RPM's, it will have to be at 28 mph, because, right now, that's the highest mph we can get before the engine starts bogging down. The prop is a 19 pitch, and when I asked the marine parts person at local marine service, she told me that a 19 pitch prop should be ok on local lakes here. But, this is the same prop we used on the St John's River in Jacksonville, FL.. Jacksonville is 15 ft. above sea-level and here it's 4,495 ft. above.

Will have to just find out what the RPM's are at our current top speed (28) and find out from the marine service if we really do have the correct prop here.

 

[ahicks]

great plan

 

[tpenfield]

When you were in Florida, how fast did this boat go at WOT? Do you remember what RPM you were getting then?

A 20 foot boat w/ a 5.7L should move right along . . .

 

[Scott Danforth]

a 20' boat with a dry weight about 3300# with a 250-260hp 5.7 and Alpha 1 G2 spinning a 3 blade 19P prop should be able to hit 44-45mph at about 4400 RPM at sea level without much trouble

your celebrity is listed as a dry weight of 3300#

the fact that you are only getting 28mph means that you are significantly down on power.

The causes of said lack of power have been covered. your fuel is past its use-by date, your over-propped for the altitude, or you have other issues with your boat.

the bogging you are probably experiencing is the stale fuel and the need to re-jet for altitude.

from manual 15 (for your 1992 Mercruiser)

the maintenance schedule: http://boatinfo.no/lib/mercruiser/manuals/mercruiser15.html#/14

here is some reading on altitude: http://boatinfo.no/lib/mercruiser/manuals/mercruiser15.html#/12

Here is some reading on the rochester carbs: http://boatinfo.no/lib/mercruiser/manuals/mercruiser15.html#/436

Here is some reading on the webber carbs: http://boatinfo.no/lib/mercruiser/manuals/mercruiser15.html#/468

 

[JimS123]

Personally, I think that getting the rpms at 28 mph will be a complete and total waste of time. Furthermore, if that data is used to select a prop you will most assuredly end up buying the wrong one.

Prop selection is done at wide open throttle on an engine that is fully broken in and is running in tip-top condition. If your engine bogs down at wide open throttle, you have a serious engine running problem.

Whether its carb, gas, altitude or cables, your boat is not running very well. You asked the original question because your suspicion was that the boat should be going faster. You were right. The speed you are losing correlates to the bogging down and thus you are losing rpm as well.

In retrospect, the discussion about props was bad advice right from the beginning. But, it was based on what was known at the time.

I feel sorry for you in that you don't have a reputable mechanic / dealer. Your mechanic's continual bad advice just shows that he won't do what's necessary because he doesn't understand how to fix it. I'm sure if you give him a laptop he could fix a current MPI just fine.

Just drain the water out of the block and find some good indoor storage. In the interim, find a local auto mechanic that works on old card. If you say to him "points, condensor, accelerator pump" and he doesn't give you a glazed stare, you know you got your man.

 

[tpenfield]

Is the issue here that the OP contends that the boat *should* perform equally well as it did before despite running on old gas and at high altitude?

 

[LuvBoating]

When you were in Florida, how fast did this boat go at WOT? Do you remember what RPM you were getting then?

A 20 foot boat w/ a 5.7L should move right along . . .

We never had the boat at WOT in Florida. There was no reason to have it WOT. When the boat was up on plane, we were at 23 mph and that was fast enough for us. Even though the boat wasn't at WOT, 23 mph was fast enough for us.

The prop has been replaced twice, since we bought the boat in Florida in 2009. We don't know what the pitch was of the prop that was on the boat when we bought it and don't know the pitch of the prop that came extra with the boat. Both the extra (new prop) and another new prop was put on the boat since we've owned it. The original was damaged and replaced with the extra (new) one and when the extra (new) was damaged by a marine mechanic, the owner of the marina put a new one on. We gave him the old-damaged one. So, what the pitch on the original and the extra, we don't know. What we do know is, the one we have now, installed in 2011 in Florida, is a 19P.

I'm being told, by a marine mechanic, that we should have either a 17 or a 15 on it now.

 

[LuvBoating]

Is the issue here that the OP contends that the boat *should* perform equally well as it did before despite running on old gas and at high altitude?

We didn't know about the altitude/prop pitch, but did know about the old gas. There is no way for us to drain out the gas and no marine service here that has a storage tank for used/old gas (I've called around). So, we simply had to run around local lake to use up some of it, of which we used up 1/2 tank of it. It is now too late in the boating season to use up the entire other 1/2 tank. We are going to take the boat out one more time, before putting new gas in along with a bottle of ethanol treatment. Then the boat will go to marine service for winterization.

 

[LuvBoating]

Personally, I think that getting the rpms at 28 mph will be a complete and total waste of time. Furthermore, if that data is used to select a prop you will most assuredly end up buying the wrong one.

Prop selection is done at wide open throttle on an engine that is fully broken in and is running in tip-top condition. If your engine bogs down at wide open throttle, you have a serious engine running problem.

Whether its carb, gas, altitude or cables, your boat is not running very well. You asked the original question because your suspicion was that the boat should be going faster. You were right. The speed you are losing correlates to the bogging down and thus you are losing rpm as well.

In retrospect, the discussion about props was bad advice right from the beginning. But, it was based on what was known at the time.

I feel sorry for you in that you don't have a reputable mechanic / dealer. Your mechanic's continual bad advice just shows that he won't do what's necessary because he doesn't understand how to fix it. I'm sure if you give him a laptop he could fix a current MPI just fine.

Just drain the water out of the block and find some good indoor storage. In the interim, find a local auto mechanic that works on old card. If you say to him "points, condensor, accelerator pump" and he doesn't give you a glazed stare, you know you got your man.

Well, if you were to be on the boat, going 28 mph on plane, you surely wouldn't say "the boat isn't running well". I'll guarantee that!

 

[JASinIL2006]

My boat is just a shade smaller (19') and about the same weight, maybe a tad lighter, and it has a 350 Mag (essentially a 5.7L) in front of a Alpha One, Gen 2 drive.

Correctly propped, with a four-blade stainless steel prop, I can hit 50 mph (GPS) on calm waters. With a three-blade prop (and a slight tailwind) I can almost hit 60.

It seems to me that you should be able to top out at better than 28 mph. We have a cabin on a lake up in Canada. If we have leftover gas, I leave it up there, after using Stabil. I can always tell when we have year-old gas in the tank. If more than a quarter (or maybe a third) is old gas, I don't get up on plane as quickly, and it takes more throttle to pull tubes and skiers than is required normally.

Seems like three things keep getting mentioned: you have suspect gasoline in the boat; your carb needs adjustment; and, your prop may be wrong for the boat. It's hard to imagine you can ever fix the latter two if you don't first take care of the bad gas. You can add a half tank of good gas, but then you just a full tank that, if not used completely the following season, will be even more likely to be bad. Clearly the old gas has lost some of its ability to produce energy when burned. Adding fresh gas, or some magical additive, won't regain that gas' ability to produce energy.

You can buy ten new props and have the carb rebuilt/adjusted a dozen times, but until you're running good gas, all the money spend on props and repairs could be a waste.

 

[Chris51280]

Besides the fuel and altitude.
Another scenario is, are you having equal compression and are you sure all 8 fire? I was running on 4 cylinders on the 4.3 and only noticed that I could only get up to 3400rpm. I thought I needed a different prop as well. No backfire, No sputtering. Until I started to unplug spark plug boots and noticed that 2 wires were switched.
My take away, make sure you have good even compression and you have spark on all 8

 

[JimS123]

Well, if you were to be on the boat, going 28 mph on plane, you surely wouldn't say "the boat isn't running well". I'll guarantee that!

By your own admission, the motor lugs when you try to run wide open throttle. You didn't say that at the beginning, thus some of the suggestions were a little off. That tells me that the motor's performance is crappier than any boat I have ever been on. If that happened to me it would alert me that the time to fix the blasted thing is not now, it was needed a long time ago.

I'm an old fart as well, thus I never run more than 28 mph either.!!! However, just to be sure that my engine isn't about to die and disappoint me, every year, once and a while, when the water is calm and there are no boats around, I hammer it for 20 or 30 seconds. Oh sure, the wife yells, but so what....LOL.

Your data at 28 mph will surely indicate you need a 15" prop. If your mechanic talks you into spending the money, please DON'T try to go fast ever again. If you do keep an eye out for the BOOM, since you will over-rev for sure.

I'm out for the duration. We keep going over the same things over and over and you don't believe any of us. Post again next Summer and let us know it the boat runs.

 

[PITBoat]

The thread that keeps drawing you back in... And leaving you slightly frustrated every time.

 

[Scott Danforth]

I still cant get over willing to spend $35-$75 a month for storage, about the same per month on insurance, the required $200-$500 a year on maintenance from oil changes to filters to cleaners to impellers, alignment checks, etc

and balking at burning fuel or keeping the fuel system maintained

by your own admission, you went out 3 times since 2018 and burned less than half a tank. you have only put on 25 hours in 8 years

at the rate of usage of the boat it costs you more to own a boat than if you were to simply rent a boat and go out boating once a month between may and september and let the maintenance, storage and fuel be taken care of by the rental company.

 

[LuvBoating]

The thread that keeps drawing you back in... And leaving you slightly frustrated every time.

Why? Because some of you sound more "demanding" than "recommending"? But, that's ok, any forum thread can get that way.

 

[LuvBoating]

I still cant get over willing to spend $35-$75 a month for storage, about the same per month on insurance, the required $200-$500 a year on maintenance from oil changes to filters to cleaners to impellers, alignment checks, etc

and balking at burning fuel or keeping the fuel system maintained

by your own admission, you went out 3 times since 2018 and burned less than half a tank. you have only put on 25 hours in 8 years

at the rate of usage of the boat it costs you more to own a boat than if you were to simply rent a boat and go out boating once a month between may and september and let the maintenance, storage and fuel be taken care of by the rental company.

Well, there are folks that spend their money in many different ways and have different things they no longer use, but keep.

My 1/2 bother has a full-size cabin cruiser at his home in Florida and has never/ever had it on the water. Him and his wife have used the inside for storage. He knows it needs some engine repair, but won't take the time to do it. He has a fully dressed motorcycle, now sitting inside a trailer in PA and only takes it out to start/run it. Other than that, goes nowhere with it. Not any more anyway.

Yes, our boat has definitely cost us money for repairs, but that's just part of owning an older boat. Only certain things I can do to it and engine stuff isn't one of them.

Our boat hasn't gone out, both in Florida and here, nearly as much as it should have. But, we've been told about boats in Dry Storage that only go out once or twice a year. Father's Day and 4th of July.........that's it. We even see boats in our current storage place that haven't been used for years and they look like it. The owners just keep paying the monthly storage fee to keep them there.

When we lived in Florida, repairs, a surgery, wildfire smoke smell, tide table, wind, rain, heat/humidity kept us from taking it out. Very logical reasons.

IOW, there are those that have things, don't use that things much-to-at all, that others wonder "why have it then?"

 

[tpenfield]

It seems that your recommendations so far are:

1) get rid of the old fuel (one way or another)
2) get fresh fuel
3) clean the fuel system, if you want
4) establish what your WOT speed and RPM are (that will give you a true sense of the condition of the engine)
5) evaluate what adjustments may be needed for altitude operation. (carburetor, propeller, etc.)

Are you not accepting of these recommendations?

Are there certain recommendations that you were hoping to hear?

 

[JimS123]

Why? Because some of you sound more "demanding" than "recommending"? But, that's ok, any forum thread can get that way.

YOU started the thread.

You asked for advice.

You got sound recommendations from several sources.

You said you would not follow the advice, not because you couldn't but because you didn't want to (needed to buy gas cans, drive too far, yada, yada)

You enumerated your plan and it made no sense. Likely make things worse.

I'm sorry if repeating the good advice sounds like a demand.

Lack of use is not the issue. The amount of use is what dictates what maintenance is required and I guess that's hard to understand.

If your car balked and stumbled over 30 mph, I'm sure you would fix it. Or just wait for the inevitable and then just call AAA and Uber. Even on little lakes you can't just coast to the side of the road.

This is an awesome forum, mostly because people truly want to help others. Sure, sometimes some people have strange ideas, but in this case everybody was spot on.

As I said before, best wishes for a successful solution.

 

[LuvBoating]

It seems that your recommendations so far are:

1) get rid of the old fuel (one way or another)
2) get fresh fuel
3) clean the fuel system, if you want
4) establish what your WOT speed and RPM are (that will give you a true sense of the condition of the engine)
5) evaluate what adjustments may be needed for altitude operation. (carburetor, propeller, etc.)

Are you not accepting of these recommendations?

Are there certain recommendations that you were hoping to hear?

Simply can't, and I repeat, CAN'T, get rid of the 1/2 tank of old fuel. We definitely can't do it, and when I asked the marine service yesterday if they could drain it, they said "nope. Have no storage tank for used fuel". And, there isn't any other marine service locally that will even do any kind of work on our boat, due to it's age (1992). Now, just how many times do I have to say that in this thread??

We will fill the other 1/2 of tank with fresh fuel before we have the boat winterized. Only thing we can do!

We are going to pour a 1/2 bottle of Quicksilver Engine and Fuel System Treatment into the gas tank before putting the boat on the water for the last time this season. Another, "only think we can do".

Can't get the boat to WOT, only 90% of throttle down........to 28 mph. The RPM's we will check the next time on the water.

If necessary, next Spring, when we have summerization done to the boat (hose clamps and block plugs reinserted) we will have a new, correct pitch, prop put on.

So, that means we can only do 3 out of 5 things. That's it!

 

[LuvBoating]

YOU started the thread.

You asked for advice.

You got sound recommendations from several sources.

You said you would not follow the advice, not because you couldn't but because you didn't want to (needed to buy gas cans, drive too far, yada, yada)

You enumerated your plan and it made no sense. Likely make things worse.

I'm sorry if repeating the good advice sounds like a demand.

Lack of use is not the issue. The amount of use is what dictates what maintenance is required and I guess that's hard to understand.

If your car balked and stumbled over 30 mph, I'm sure you would fix it. Or just wait for the inevitable and then just call AAA and Uber. Even on little lakes you can't just coast to the side of the road.

This is an awesome forum, mostly because people truly want to help others. Sure, sometimes some people have strange ideas, but in this case everybody was spot on.

As I said before, best wishes for a successful solution.

Well, guy, the recommendations were fine, but if some recommendations simply can't be done.........end of story! There are a certain amount of forum members that are much younger, and much "physical" than we are and do their own boat repair work. We just can't and won't. So, since we have to rely on a marine service to do our work, and some of it can't be done (as in re-jetting, emptying a fuel tank or whatever), we have to go with that. The marine service we go to is the only one within miles and miles that will work on a 1992 boat. Certain things a person just has to put up with.

And, we aren't going to empty our own gas tank out when there is nowhere to do that. Now, being somewhat sarcastic here, but.........."just what part of that sentence don't you understand"????