Looking for w.o.t for 1982 sportcraft 25ft

[SALMONBOY35]

It has,a 5.7 l. 

Just looking top speed also. I can't get above 22 mph. And that is a 5200 rpm

[sherman brown]

the speed and the rpm's don't seem to match. I don't run my 5.7 over 5000 rpm's in my 21' glass boat and run well over 30 mph. maybe your prop hub is slipping. are you plaining off ok? what type speedometer are you going by? if your going by a dash speedometer that is run off water pressure the pitot tube could be blocked.

[SALMONBOY35]

I'm am running off gps... I have just changed my prop. No better result.

 

 

[SALMONBOY35]

Now my fishhawk says I am doing around 31 32 mph.

 

[Fat Trout]

The 25 is a big boat and a 5.7 is 250 hp if i recall correctly. I had a 232 sportcraft with a soft top and a 5.7. top end was 29 or 30 at WOT but only if flat calm. Im not sure if you have a hard top but thats a bigger boat than the 232 and 30+ yrs old it may be carrying more extra weight in water soaked decking /transom or whatever and the engine might not be as strong as it once was.
Also, my current and prior fish hawk top speeds both read high compared to gps.

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[FishingFool34]

fish hawk reads speed off a paddle wheel... it will almost never be right unless you're in flat calm conditions. GPS is measuring speed over ground where a paddle wheel is measuring speed through water. Technically they are two different things. With any kind of waves/currents a paddlewheel will always read different than GPS. If you have GPS I would use that for speed and ignore what the fishhawk says, for this purpose.

Were you only getting 22mph before you changed props? Did you put on a different pitch prop? What does the factory equip that boat with for a prop? Sounds like maybe someone changed props at some point to an incorrect size/pitch and then it became the new "factory" prop (aka you didn't know someone before you changed it and you assumed it was "factory"). I would find out what size/pitch prop came with the boat right off the factory floor and make sure that is what you're using. 

Props are expensive and if a previous owner damaged the factory one he may have just put on whatever he had available at the time and just left it that way and sold the boat. If you're the original owner and never touched the prop before disregard all of this lol. 

Edited May 1, 2019 by FishingFool34

[SALMONBOY35]

Fishing fool

I when I changed the prop ..I called a marine mechanic and told him what I had.. he ordered it.. so he,made,sure it was proper..I just,checked... it is same as the old prop....

Also being an OMC 800.. prob just junk...

It prob a bad forward gear or prop shaft..

After I have been doing research on line

 

Thanks everyone for info... 

[sherman brown]

do you have your gps set on mph or knots? I think a knot is something like 1.3 mph so 22 x 1.3 is a little over 28 mph. check your gps and see which one your using.

[jth21usa]

Isn't the max RPM for that engine around 4500RPM's? If you can get to 5200 you have the wrong prop.

[sherman brown]

2 hours ago, jth21usa said:

Isn't the max RPM for that engine around 4500RPM's? If you can get to 5200 you have the wrong prop.

I think its 4800 to 5000 but I wouldnt want to run that rpm all day. I usually only run about 3500 when cruising.

[L&M]

 

12 hours ago, sherman brown said:

I think its 4800 to 5000 but I wouldn't want to run that rpm all day. I usually only run about 3500 when cruising.

 

What Sherman said, just asking for trouble if your running it that hard consistently. If it's turning that high and everything is in order you are under propped ( to low of pitch ) 

 

WOT early flat tappet cam 5.7L 

 4400 - 4800 RPM's.

[FishingFool34]

16 hours ago, SALMONBOY35 said:

Fishing fool

I when I changed the prop ..I called a marine mechanic and told him what I had.. he ordered it.. so he,made,sure it was proper..I just,checked... it is same as the old prop....

Also being an OMC 800.. prob just junk...

It prob a bad forward gear or prop shaft..

After I have been doing research on line

 

Thanks everyone for info... 

what kind of speeds/rpms were you seeing when it was running right? Did it just randomly start going slower one day or has it progressively been getting slower?

[jth21usa]

I bet the prop is just too small, which is why the rpm’s are off and you are going slow. What size do you have on? I had a 23 cuddly with a 5.7 and I believe it would go high 30’s.

[SALMONBOY35]

thanks for all the help guys. going to try a few things and work out from there.. being that it is an OMC.. I think there is a the  problem .. but I wanna check out for proper prop and then work my way down the list..
 

[SALMONBOY35]

this just started at the end of last year... I thought maybe prop slippage, but it keeps doing it with a new prop..

 

[sherman brown]

you can try going to a bigger prop or go up about 4 degrees in pitch. you should lose about 200 rpm's for every 2 degrees of prop[ pitch.

 

what diameter and pitch prop are you using now?????

 

I have a 14 1/4 diameter prop on my mercruiser 5.7 motor. I had to cut part of the little trim tab/anode so the larger prop would work.

[SALMONBOY35]

I have a14.8x 17r

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[SALMONBOY35]

you can try going to a bigger prop or go up about 4 degrees in pitch. you should lose about 200 rpm's for every 2 degrees of prop[ pitch.
 
what diameter and pitch prop are you using now?????
 
I have a 14 1/4 diameter prop on my mercruiser 5.7 motor. I had to cut part of the little trim tab/anode so the larger prop would work.

I have a 14.8x 17r


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[FishingFool34]

17p is in the ballpark for a prop on a 5.7... you could try a 19p but sounds like it could be something else wrong. 

[SALMONBOY35]

Just to give an update..
Think we found the problem..
Water pump shaft worn down to about nothing..
Omc water pump shaft turns prop shaft.. So replacing it and going from there..



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[sherman brown]

something has got to be wrong. if your turning 4500 to 4800 you are turning the right rpm. does it get up on plane and stay there? what type of speedometer are you going by? if its not a gps then I wouldnt trust it to be right. I am running a 14 1/4x17 pitch on my 21' glass boat and at wot with minimal weight it runs 5000 rpms. I don't run wot that often and don't know what my top speed is. in most cases I run about 3500 on calm water and less when pulling a tube. if your going by the boat speedometer it could be bad. it works off water pressure being forced into the pitot tube and up the hose to the speedometer. they some times get a leak and it doesn't work right.

[SALMONBOY35]

so water pump shaft was replaced. still no change... I am so frustrated...
I am to the point of just going to buy a new boat...
 

[Todd in NY]

Have you checked your RPM's with a different tachometer? I had a tach on a previous boat that was very inconsistent before it quit working.

 

Also, see if your speed or RPM's change as you adjust your trim on your outdrive and/or trim tabs in small increments.

[Gill-T]

Compression test?  Tune-up kit? Timing off? Carb need adjustment?  Are you misfiring? Sounds like it is time to get another set of eyes on it. 

[outwest]

Here is my input You need to verify your actual speed and just find a hand held gps or some newer phones have gps on them . Next is rpm find someone with a hand held meter and check it . Granted you are getting frustrated but you will get it figured out ! Now if you are getting the correct RPM while under load on the water I have to say its from the engine crankshaft back and the first thing is the Engine coupler which is mounted in rubber and they will go bad and slip . After that its outdrive issue or prop issue , but you changed the prop . Try not to over think your problem and if you know some one with a larger prop ask them to borrow there spare for half day . Last thing All pm you my phone no. and you can call me , I am on ohio game and fish and there is a very good boat mechanic on there and im certain he would talk to you .