Mercury 150 planes out but at high RPM??

[capevt]

Greetings - just joined the site today.

I have a 2001 Key Largo 206 with a 2001 Mercruy 150 carb'd engine. The engine is in very good condition - great compression (125 psi), cleaned out carb's, new plugs, Thermostats, water pump, filters,etc...

The boat (full tank of gas, 1 person, no gear) won't plane off until about 4200 rpm and will come off plane under 4000. WOT I'm getting around 5400 rpm. It has a 15x17P prop which is original and was standard equipment when the boat was sold new. The boat just seems to be working hard for the performance it is delivering. Should I not be expecting so much?

Is this a prop issue?? Any insight would help, really scratching my head on this one :facepalm:

Thanks,

 

[SparkieBoat]

Re: Mercury 150 planes out but at high RPM??

you need to try raising your motor, sounds like your motor may be too low. a set of trim tabs will make a huge difference. you are propped about right. a 20' boat with a 150 is NOT over powered, but can do better than what you are describing. If it was my boat it would have a 200 or a 225 on it.

 

[capevt]

Re: Mercury 150 planes out but at high RPM??

I agree - max HP is listed at 200 and i think that would really make the difference - It's a fairly deep vee hull.
By raising the engine, I assume you are referring to trimming it up? I'll give that a go and see what happens.

I appreciate the feedback.

 

[SparkieBoat]

Re: Mercury 150 planes out but at high RPM??

no I am not talking about the trim, I am talking about the bolts that hold it to the transom, the motor has 4 holes it the top set and a long slot for the bottom holes, remove the top bolts, (put a block(s) of wood under the motor), then loosen the bottom bolts, raise the jack on front of trailer until bottom holes line up with the bolts, rebolt the motor, use some silicone caulking around the bolt holes on the transom before rebolting. if the prop ventilates (RPMs spike with no increase in speed) then lower 1 hole until it quits ventilating. a picture of the motor in relationship to the bottom of the boat would be helpful. sell the 150 and get a 200, you will be much happier, trim tabs will make a huge difference as well, you will not regret getting them.

 

[Mag535]

Re: Mercury 150 planes out but at high RPM??

What top speed do you get? How heavy is the boat in test condition? Have it performed better before? How long have you had it? Are you sure there is no water trapped in the bottom etc? Clean hull?
If everything els is Ok I would try smaller diameter and higher pitch prop.

I have a Maxum 19 with same engine running a 14,25 x 21 prop and getting 53 mph top. Runs great, gets on plane fast and carries the weight well, but will ad trimtabs anyway as it has a huge impact on both getting on plane and cruising at low speed. Mag

 

[split71]

Re: Mercury 150 planes out but at high RPM??

Just a point of reference...I have a 16' Key Largo with a fresh Evinrude 88 which originally had a 13x19 prop. Two people, full of fuel and I could get on plane at around 3k RPM but would max out at 4,200 RPM which is to low.
I had a spare 13x15 and now I get on plane around 4,000 and max out at 5,100...I will say it jumps up on plane pretty quick compared to the 19 pitch prop.

 

[SparkieBoat]

Re: Mercury 150 planes out but at high RPM??

split..i would be willing to bet you could raise that motor a couple of inches and see dramatic preformance increase...

 

[Texasmark]

Re: Mercury 150 planes out but at high RPM??

Respecting the great advice you have already received, I'd say that you just have a lot of boat and the numbers don't look that bad. Your top end rpm's are right where you want them (per the book) and that speaks volumes to me. Installing trim tabs would help a lot in getting the transom up earlier and keeping it up longer.

I don't know where your anti-vent plate is, but if you do a lot of big water fishing/running, you don't want it too high or you will have ventilation issues under rough water conditions (high rpms and loss of thrust).

My 2c,

Mark

 

[split71]

Re: Mercury 150 planes out but at high RPM??

Sparkie, I'll give it a shot...and thanks for the advise!!