My 1988 mercury 150 Blk Max

[nickantanies]

Hello, I need some help, my motor is running at 6000 rps to reach a top speed of 37 mph. My boat is a 18.3 ft center console with a 21 pitch prop. I went up to a 25 pitch stainless and the boat didn't move. What should my top speed be with this motor. and what pitch should I have on the prop. Many people told me many different things to try. Can you help me. Greatly appreciated. The motor and boat are in great shape. I mostly use for fishing and an occasional cruise.<br />Thank you,<br />Nick A

 

[LubeDude]

Re: My 1988 mercury 150 Blk Max

I am asuming that your boat is an 18.3 foot, not 8.3 (Typo)! First of all you went too far too fast with the prop pitch! Id think a 22-23 pitch would be more in the ball park! Speed seems slow to me though! right now, (when it was running right) My 18' Bass Boat with a 150 Merc runs just under 60MPH at 6,000! Im going to re prop this next summer to get the RPMs down some, just got the boat this fall! I know that the hull design is probably different on the two boats, but thats a lot of difference! Are you trimming the engine any for that speed? Is this a glass boat or an aluminum??<br /><br />LubeDude

 

[mellowyellow]

Re: My 1988 mercury 150 Blk Max

is posted speed read from GPS? speedos ain't so<br />accuate sometimes. what does hull weigh also?<br />p.s. 6000 is a bit high. what are rpm's with new<br />prop?

 

[KCLOST]

Re: My 1988 mercury 150 Blk Max

Your speed does seem a bit low....<br /><br />I'm pushing an 18 ft Ranger with a Black Max 175hp... I have a 24P-4 Blade prop and can reach 60-62 mph... But my top rpms are only about 5300. I just bought a 23 pitch prop to help with that or to use as a spare....<br /><br />If you are reaching 6000rpms, I bet you are going a little faster than 37 mph, you could be going over 50 easily... Are you sure that your speedometer is working correctly? Check to see that the water pick-up hole in the skeg is not plugged with debri....<br />On another note, go to a 22-23 pitch and your rpms will be in the proper operating range a full throttle, and you will gain more speed. <br />Are you trimming up? (like LubeDude asked)

 

[LubeDude]

Re: My 1988 mercury 150 Blk Max

KCLOST:<br /><br />If you ever get to Oregon Well go Bassin!!<br /><br />Ya, we have Bass here, But they got hair one em to keep them warm!! Darn evolution!<br /><br />LubeDude

 

[jsr21]

Re: My 1988 mercury 150 Blk Max

double check that prop...hard to believe a 21 pitch could pull 6000 rpm....is it really a 21?

 

[mnmfors]

Re: My 1988 mercury 150 Blk Max

Just a shot in the dark, maybe the hub is starting to slip. Easy thing to check, just mark the hub and prop, take it for a spin and see if marks you made still line up.

 

[nickantanies]

Re: My 1988 mercury 150 Blk Max

Thank you for all the great help.. I have already winterized the boat. I will check the water pick-up hole on the skeg in Febuary. Also I am installing my gps in feb, so that might give me a more accurate speed reading. Also I am trimming the motor up to get to that 6,000 rpms. I ordered a 22 pitch prop. I guess I have to wait until Feb to try it again. Also I checked the numbers on the prop and it is definitly a 21 pitch. and the boat is fiberglass. Again I really appreciate all your help. One mor thing, should I have the compression checked? thank you NICK ANTANIES!!!

 

[LubeDude]

Re: My 1988 mercury 150 Blk Max

Its never a bad I dea to check your compression once in awhile, Lets you know how things are doing inside!<br /><br />LubeDude

 

[KCLOST]

Re: My 1988 mercury 150 Blk Max

John D.<br /><br />I'm not surprised about the 6000 rpms with a 21P prop...<br />His 150 merc. should really run at 5700-5800 max... Normally a 23P is standard on a 150 merc. on a standard 18 ft bass boat. A change in pitch of 1, results in a 200 rpm change...<br />Hence, my 24P gets 5300 vs his 21 Pitch at 6000. (pretty close)....<br /><br />I'm surprised Nick has had problems with the 25 pitch... It should at least get out of the hole...????????

 

[nickantanies]

Re: My 1988 mercury 150 Blk Max

Thanks KCLOST, I have been trying to find out what the standard prop size for this motor is. I bought the service manuel and it doesn't really say. With the 25p prop the boat bearly got out of its own way... My new 23 pitch prop has arrived, but I already winterized the motor. I have to wait until Feb. Also its not a bass boat, it's more like a bay boat and its also fiberglass. I guess the weight makes a big difference. Thanks again!! Also does anyone know anything about those hydrafoil that you can mount on you motors lower unit. Has anyone used one??? I was thinking of trying that to get up on plain faster.<br />thanks

 

[jsr21]

Re: My 1988 mercury 150 Blk Max

The more I read the more I tend to think the guy that said your hub may be slipping is right. You can compression test it if you want, but if you are turning 6000 rpm with a 21 pitch prop going 37 mph, sumthin is wrong and it isn't compression. If you have trouble coming out of the hole and have poor top speed with the motor screaming, I'll bet it is your prop slipping....My 150 Merc (soon to be 225) has a 17 pitch prop(for skiing) and I can get about 43-44mph @ 5800 rpm.

 

[nickantanies]

Re: My 1988 mercury 150 Blk Max

Its been a while, and I have spoke to many experienced boaters and try to explain this prop problem to them. I noticed that the lower unit on this motor is not the stock lower unit. The intake for the impeller is on the point of the lower unit. Which means th water gets forced into the motor. Hs anyone ever seen this. Most people I talk to had no idea what I was talking about. I called the man I bought the boat from and he said the original owner installed this for better performance and i guess more horse-power. Anyone have any idea or ever heard of this??

 

[Hooty]

Re: My 1988 mercury 150 Blk Max

Does it look kinda like this? If so, it's a low water pickup and the engine is probably pretty high up on the transom. Where's the cav (ventilation) plate in relation to the keel or bottom of the boat?<br /><br />

<br /><br />c/6<br />Hooty

 

[nickantanies]

Re: My 1988 mercury 150 Blk Max

Yes Hooty, it does look like that. I think the cav plat is even with the bottom of the boat. Also what do you use to flush the motor.<br />thank you very much<br />nick