Cape Cruiser 23 Re-power with Mercury

[S&C]

Hi Everyone,

I am looking for some help choosing between a Mercury 150 4-stroke (regular recreational engine) and a Mercury 150 Sea Pro (commercially tuned version) for my 23.

I have decided already that I don't want the other version of the 150 (Pro XS) or a different brand, or a different horsepower.

The most important feature to me is reliability. I do not need a high top-speed, but I would like a normal cruise around 20kn and a fast cruise (not wide open) around 25kn. Assuming the 150 Sea Pro is more reliable, which is the manufacturer's sales pitch, the only thing causing hesitation is the risk that the lower rpm range 4800 - 5300 of the Sea Pro (vs. 5000-5800 on the 4-stroke) will mean that I don't get a "fast" cruise.

Does anybody have a 150 Sea Pro on a 23?
What do you all think?

Thanks,

S&C

[jennykatz]

We have the 23 venture CC 23 with a Mercury 115 CT. which has the same lower unit as the 150 mercury So the only thing we are missing is top speed At 4000 rpm we are doing 20 mph
4500 rpm 25mph 5500 rpm 34mph Since we had the cape cruiser she is rated at 120 Hp the newer ones went to 150 Hp I saved about $4000 buying the smaller 2.1 L vs 3.0 L Good luck Jim W

[S&C]

Hi Folks,

Thanks for the reply and DMs. I've decided to go ahead with the regular Mercury 150 4 stroke rather than the Sea Pro. Once it is on I will post some performance data.

In case anyone else is doing some reading before making a decision, here is what I found for 2021 engines:

In the 150hp class the main differences are:
- SP has stiffer upper engine mounts
- SP has cylinder-firing mapped differently by the computer to reduce max RPM substantially and alter where max torque and horsepower are provided relative to RPM.
- SP has lower unit oil drain on the bullet, 4S has it behind the prop
- SP may have "heavier duty" lower unit, (same gear ratio though), I haven't been able to confirm
- Dealers told me that the SP is best for: (1) pushing heavy boats at high RPM, example given was heavily loaded crab and oyster boats (2) boats with multiple operators that may not be invested in running the engine in the most longevity-focused style
- Dealers told me that a SP and 4S both maintained in a similar fashion will probably have the same lifetime, unless they are pushing heavy boats or being driven like they are stolen, in which case the SP will last longer.

A fellow C-Brat who was very generous with his time provided this chart of RPM and torque for the 2020 SP and 4S that is from the manufacturer. I couldn't find it online and my local dealers couldn't give me anything similar, so no link.

HORSEPOWER
Sea Pro
max hp is 140.8 and occurs at 5,250 RPM
4S
max hp is 160.9 and occurs at 5,400 RPM

TORQUE
Sea Pro
max torque is 160.7 ft. lb and occurs at 4,250 RPM
4S
max torque is 180 ft. lb and occurs at 3,000 RPM


Thanks everyone.

[S&C]

The generous C-Brat passed along this helpful info for people looking for torque curves and horsepower curves:

So there is a thing called CARB (California Air Resources Board IIRC) and they require this kind of data to be submitted for SIME (Spark Ignition Marine Engines) in addition to other types of things.

Note that the mfgrs provide this info, and I believe it's tested in a tank or some other non-realistic way. OTOH, they apparently test all the motors the same way so it should still be a good comparative tool. And it doesn't seem like they are cheating since some will report their 90 hp, say, at 89 hp or whatever.

Here is the link and you can then drill down to whichever motor. First select mfgr name , then hit "browse," and go from there.

https://www.arb.ca.gov/msprog/offroad/cert/cert.php?eng_id=SIME&year=

Note that while for some mfgrs the motor model fairly obvious, others use slightly more obscure model numbers. (Merc for example) I was able to decode these by a combination of figuring out the hp, plus googling those numbers. I also converted kw to hp and nm to ft lbs for our discussion.